Michelle Houngbé
email: michelle.houngbe@inp-toulouse.fr

Anne-Marie Barthe-Delanoë

Stéphane Négny
email: stephane.negny@ensiacet.fr

Servitization of Biomass Processing for a Virtual Biorefinery: Application to the Lignocellulosic Biomass in a French Local Territory

Keywords: Servitization, Biomass, Collaborative network modeling, Collaborative process, Industry 4.0

Processing biomass requires four major steps (pretreatment, fermentation, separation and purification) achieved by dedicated plants called biorefineries. These highly specialized structures cannot cope with the high variability of the whole biomass supply chain. Thus, providing agility to biorefineries is a key challenge to foster biomass processing. The goal is to design a virtual biorefinery as a collective network supported by the servitization of unit operations and the reuse of existing devices. In this regard, the first step described in this paper aims to gather and organize knowledge about a given local area (stakeholders, services) and the existing transformation process operations (inputs, outputs) through a framework. To this end, two metamodels are proposed: one to collect and structure the required information about the local area; one to organize the knowledge about the transformation processes. Their use is illustrated by a use case provided by a municipalities community located in South-West France.

Introduction

Biomass requires dedicated transformation processes, depending on the biomass type, quality, purity (and even quantity) and also on the targeted bioproduct. These processes operate under high-specialized conditions, where each process step requires specific equipment (specific operating methods and specific unit operations). At the plant level, biorefineries are standalone plants dedicated to a specific biomass transformation process. Thus, biorefineries are not able to face the variabilities regarding supply and demand as well as the biomass variety. The challenge, as underlined in [START_REF]Innovating for Sustainable Growth -A bioeconomy for Europe[END_REF], is to bring agility to the biorefinery system to foster biomass processing.

In this sense, the research works presented in [START_REF] Houngbé | Towards Virtual Biorefineries[END_REF] aim to decentralize the biomass process through a virtual biorefinery. The virtual biorefinery concept lies on the shortterm collaboration of different stakeholders, each one achieving one or several steps of the transformation process. This collaboration enables low coupling among the process steps in order to adapt the biomass processing when a change occurs (supply, demand etc.). Besides, leaning on the reuse of existing equipment and/or plants would avoid investments into physical structures dedicated to a given process. To achieve this goal, a servitization framework is required to help the stakeholders to describe their activities with a product-service strategy. This paper focus on the developed approach to support the servitization of the stakeholders involved into this collaborative biomass processing.

The paper is structured as follows: the next section highlights the state of art of servitization for biorefineries. Section 3 describes our proposal to support the servitization of biomass processing stakeholders (farmers, chemical plants, etc.). Section 4 illustrates the proposed servitization framework with a use case provided by a municipalities community located in South-West France, before addressing the further work to be done and concluding.

State of the Art of Servitization in Biorefineries

The servitization concept emerged in the late 1980's under an uncertain industrial context marked by: a strong competition between companies in the global market place; a raise of product customization to satisfy customers changeable needs; the constant evolution of technologies. Since its first definition as "bundles' consisting of customerfocused combinations of goods, services, support, self-service, and knowledge" [START_REF] Vandermerwe | Servitization of business: Adding value by adding services[END_REF], it has been a growing interest for this topic, for the researchers and the industrials [START_REF] Baines | Servitization: revisiting the state-of-the-art and research priorities[END_REF]. By adding different levels of services such as base (spare parts), intermediate (maintenance, training) and advanced (contract) to an initial physical product, servitization affects the whole industry from the marketing department to the production workshop.

The description of the actors' services is part of a Product-Service System (PSS) strategy. As a servitization specification, the PSS differs by taking into consideration the life cycle of the integrated product and service offering. [START_REF] Tukker | Eight types of product-service system: eight ways to sustainability? Experiences from SusProNet[END_REF] classifies the PSSs into eight categories according to four main dimensions: market value for the user, costs for the provider, capital needs, and ability to sustain value in the future. Based on this classification, the agile biorefinery tends to be close to the result-oriented category of PSSs (within the functional result subcategory). Indeed, this is the capability (the capabilities) (i.e. one or more services) proposed by each actor into the collaboration that is (are) involved to fulfill one (or more) step(s) of the biomass transformation according to the targeted objective. However, the PSS was determined for the manufacturing sector by focusing how the company creates added value. In this approach, the transformation process of the matter with all its constraints is not taken into account. Therefore, it has to be adapted in the context of a biorefinery.

As mentioned earlier, this paper focuses on the servitization to support the collaboration which is the core concept of the virtual biorefinery. Regarding the domain of virtual enterprises, that are defined by [START_REF] Camarinha-Matos | Collaborative networks: a new scientific discipline[END_REF] as "temporary consortium of enterprises that join skills and resources, supported by computer networks, to better respond to a business opportunity", they lean on existing frameworks to implement servitization. [START_REF] Ducq | Principles of Servitization and Definition of an Architecture for Model Driven Service System Engineering[END_REF]'s studies have developed a methodology based on Model Driven Service, which is based on Model Driven Engineering, that contains all the phases of the service life cycle (requirements, design, testing and implementation). This approach aims to support the shift from a production focused on the product towards a production focused on a service-oriented strategy for virtual manufacturing environment. Besides, [START_REF] Chen | Framework for manufacturing servitization in virtual enterprise environment and ecosystem[END_REF] propose a framework organized along three dimensions: extended product, service typology and service innovation organization. Combined together, they help companies to determine their servitization position. This framework was tested in several companies, which want to move towards the service-oriented virtual enterprise: a machine tool manufacturer, a TV manufacturer and a clothing manufacturer. These frameworks apply particularly to manufacturing companies.

Regarding the chemical industry, there are fewer examples of servitization compared to the manufacturing domain. But it is important to note that the ongoing trend in the chemical industry area is to shift from a high volume in mass production towards custom products. This customization trend changes the companies' business models to more innovative ones. [START_REF] Buschak | Chemical industry: Servitization in niches[END_REF] show that three types of business models encourage servitization in chemical industries. Chemical Product Services (CPS) gives priority to the sale/use of chemical product-service bundles. Chemical Management Services (CMS) leans on long-term contract policy between customers and suppliers. For instance, PPG, a company specialized in wastewater treatment, is paid according to the amount of cleaned water. Chemical Leasing makes available chemicals for service and ensure their maintenance instead of selling them. Among these three business models promoting servitization, the most widespread is CMS [START_REF] Buschak | Chemical industry: Servitization in niches[END_REF] .

It is interesting to underline that in the literature related to this business area, servitization is studied from the company strategy point of view (macro scale). There is a lack of framework to support and guide servitization of the transformation process (meso scale), especially for biomass transformation process. The next section presents a proposal of such a framework.

A Framework to Support Servitization of Biomass

Transformation Processes

Collaborative Situation Characterization

The first step is to define the collaborative situation: stakeholders, targeted bioproduct, available biomass, etc. To this end, a meta-model structuring the knowledge is necessary, as detailed in [START_REF] Houngbé | Towards Virtual Biorefineries[END_REF]. This meta-model dedicated to the biorefinery is based on the CORE meta-model [START_REF] Bénaben | A Metamodel for Knowledge Management in Crisis Management[END_REF]. This meta-model is structured around four families of concepts: the context (the environment of the collaboration), the actors (the partners of collaboration), the objectives (the purpose of the collaboration) and the performance (assessment of the collaboration based on Key Performance Indicators). An enhanced version of the concepts of the first version of the virtual biorefinery meta-model is proposed here (Figure 1).

In the context package, the deposit concept is crucial. It complies with a sector logic as wood sector, agricultural sector, etc. It takes into account the biomass which is characterized by its intrinsic physical and biochemical properties, by a seasonality and by a crop rotation. Besides, the geographical area where the deposit is located has a specific pedology, topography and climate where a type of production (intensive, extensive, organic) is realized. Finally, the deposit concept integrates the goods concept that includes the roadways to access to the deposit. Finally, people and institutions concerned by its exploitation are also considered.

In the objective package, the biomass processing is the main goal to reach. It produces bioproducts and have to meet market opportunities. However, impact factors about technology, finance, society or environment can affect positively or negatively the main goal. In the partner package, each stakeholder of the collaboration is called an actor. She/he provides one or several services that requires resources. The whole collaboration is orchestrated by a Mediation Information System (MIS).

The performance package consists on assessing the collaboration, thanks to Key Performance Indicators (KPI). Relevant KPI lean for instance on the sale of use performance for each actor and the overall performance. The services generate externalities, positive or negative for the environment (e.g. pollution, reforestation) and the society (e.g. job creation, economic decline).

Thus, the meta-model contains concepts about the whole collaborative situation. The instantiation of the meta-model into a model is made with data about the stakeholders, the availability of biomass on the studied territory or the targeted bioproduct, etc. All of these data can be gathered either manually or automatically. Indeed, in the area of Agriculture 4.0, the amount of emitted data regarding farms, weather conditions, crops, etc. is exploding. Based on these data, information regarding (for example) the biomass valorization opportunities can be inferred based on weather conditions, etc. to feed the model of the virtual biorefinery.

This gathered knowledge about the collaborative situation is essential to define the collaborative transformation process, that will be performed by the virtual biorefinery. Nevertheless, additional knowledge is required in order to choose the relevant transformation process (from a chemical point of view), given the biomass characteristics and the bioproduct identified through the virtual biorefinery model.

Biomass Processing Knowledge Organization

The second step of this servitization framework aims to structure the knowledge required to identify the chemical process involved into the biomass processing.

Lignocellulosic biomass processing can be seen as a four major step process: (i) pretreatment; (ii) conversion; (iii) separation; (iv) purification. Biomass pre-treatment is crucial for the next process phases. Indeed, in this step the structure of the biomass is modified to make sugar accessible from lignin, cellulose and hemicellulose. The next phase is the biomass conversion into building blocks (C2 to C6 sugars). It can be achieved in different ways: chemical, bio chemical, thermochemical. These building blocks are the bases to design bioproducts, bioenergy and biofuel. Finally, separation and purification refine the output to fit with the customer's requirements. Each major step is composed of sub-process or unit operations which are specified according to the input biomass characteristics and the targeted bioproducts.

Given this background, the minimal required knowledge about the chemical process is, for each major step (respectively each sub-process or unit-operation): input (biomass, intermediate products; output (intermediate product, final product); operating conditions. As there is no knowledge base organizing the knowledge about existing processes for biomass transformation at the required level of abstraction, an additional meta-model is proposed to this end, based on the SADT-IDFE0 diagram notation. SADT-IDEF0 offers a degree of details which is relevant regarding the abovementioned needs. An example of such a model is detailed in Section 4.3.

This knowledge base can also embed additional knowledge regarding the matching between the services proposed by the actors and the required process steps (subprocess, unit operation), as Montarnal et al. [START_REF] Montarnal | Automated deduction of cross-organizational collaborative business processes[END_REF] propose in their research work regarding the manufacturing industries. Each process, sub-process and unit operation is therefore seen as an objective that an actor service (or a set of actors' services) will fulfill. This way, the required knowledge about services is structured and ready to be used to deduce a relevant collaborative transformation process.

Case Study

Case Study Presentation

Two municipalities communities from the French department of the Landes (Communauté de Communes Coeur Haute Lande, and Communauté de Communes de Mimizan) look for solutions to recycle green waste. The lignocellulosic biomass is abundant and diversified within their territory. The characterization of these two local territories using the presented framework will support the identification of the existing stakeholders and of their related services to meet these opportunities to valorize local biomass. Besides, this knowledge will also be used to design the collaborative process treatment, performed by the virtual biorefinery.

Instantiation of the Metamodel for Collaborative Situation

To instantiate the metamodel, stakeholders able to play a role in the biomass processing were identified. Then, semi-directive interviews were organized according to an interview guide. These interviews focused on the following topics: business environment, role in green waste processing, existing or possible partnership with a company inside or outside the territory, positive impact of the activity (for the stakeholder, for the territory). The objective is to understand the environment in which these actors of the biomass area evolve. These interviews also helped to determine the existing constraints.

Instantiation of the Context Package

The instantiation of the context (Figure 2) reveals that on these local territories the green waste deposit involves two parts of green waste: woody and non-woody. Each of them owns a specific density, humidity and seasonality.

About 15,000 tons of green waste are available in these territories. Different institutions (cities, local authorities, consular organizations) are involved in this recycling initiative as well as the citizen association "SAS Energie Citoyenne Haute Lande".

Instantiation of the Partner Package

Different types of actor (public entity, farmer, environment service provider) are able to provide services to perform a step of the transformation process. The instantiation of the partner concept shows that a process activity can be realized by different actors, such as the composting step that can be performed by the Communauté de Communes Coeur Haute Lande, Mimizan, VEOLIA or RTE (Electricity Transmission Network) (Figure 3) or such as the shearing (performed by citizens or the local authority).

Resource used by the actor will differentiate the actor's service. But it will be necessary to define functional and non-functional requirement (price, delay, reputation) to sort services in case of competition.

Instantiation of the Objective Package

Regarding the instantiation of the objective package concepts, Figure 4 highlights that the main objective 'composting biomass' meets different opportunities, which represents sub-objectives. The main objective (i.e. the targeted bioproduct) is "biogas fuel" and "standard compost". In this study case, the identified impact factors have a positive impact on the collaboration objective.

Instantiation of the Performance Package

The performance to be reached by some stakeholders as the SIVOM (Figure 5) and the farmers is determined by contract. These services generate positive externalities as job creation (the creation of a new job for compost quality control), or additional revenues linked to the compost sale.

Knowledge Base for Chemical Process Involved in the Composting Processing

In addition to the model representing the knowledge about the collaborative situation, it is now necessary to collect and organize additional knowledge about the composting process and the matching services. To gather knowledge about the generic composting process, we leaned on dedicated handbooks, such as [12]. The model obtained in the Figure 6 represents both the composting process as (sub-)objectives, and the proposed actors' services matching these (sub-)objectives. Fig. 6. Composting process description using a SADT-IDEF0 inspired meta-model.

Perspectives and Conclusion

Biomass processing is subject to several constraints to the structural level (i.e. biorefinery) and to the process level generating high variability in biomass supply and bioproduct production. This is the reason why it is necessary to bring agility to the entire system in order to improve the biomass transformation process. In this perspective, the "virtual biorefinery" concept enables the collaboration between the stakeholders of the biomass processing. It is based on services provided by the actors to fulfill one or more steps of the process biomass treatment. Thus, this paper presents a servitization framework composed by two meta-models. The first meta-model aims to characterize and structure the knowledge about the collaborative situation according to the environment, the partners, the objective(s) and the performance, with data collected manually or with sensors. It is coupled with a second meta-model to structure the additional knowledge about the biomass transformation processes. As presented in the case study, the instantiation of these two meta-models provides the necessary knowledge to establish a collaborative biomass transformation process. On a short-term perspective, the next step of these works is to choose and implement the algorithm to design the collaborative transformation process. The competition among several services fulfilling the same objective has to be considered: the use of functional and non-functional criteria may provide a way to choose the most relevant option.

Fig. 1 .

 1 Fig. 1. Meta-model of collaborative situation for the virtual biorefinery.

Fig. 2 .

 2 Fig. 2. Instantiation of the context package.

Fig. 3 .

 3 Fig. 3. Instantiation of the partner package: example of the RTE actor.

Fig. 4 .

 4 Fig. 4. Instantiation of the objective package.

Fig. 5 .

 5 Fig. 5. Instantiation of the performance package: example of the SIVOM contract.

Acknowledgments. These research works are funded by the French Research Agency (ANR) regarding the research project ARBRE [Grant number ANR-17-CE10-0006], 2017-2021. The authors would like to thank the project partners for their advice and comments regarding this work.


Catherine Thuriot

Marie-Françoise Valax

M.-F Valax

C N R S 259

Computer aids to work organization in hybrid manufacturing

The need for tools which aid the decider organize decisional latitude was identified in a study of task organization decisions in three different manufacturing workshops.

Hierarchical mechanisms in the decisional process were identified at both an organizational and an individual level. The hierarchy was found to be associated with different levels of detail relating to time, resources and work.

The model proposed is based on the notion of decision centers characterized by a specific type of decision associated with a particular level of detail in the factors relating to work, resources, and time. The decisional latitude or leeway in a lower center is thus governed by decisions made at the next higher level.

In a given center attention must be paid to : (1) coherence with higher level decisions, i.e. remaining within imposed decisional limits; (2) feasibility and decisional durability by allowing enough decisional leeway to the lower center.

The design of ergonomic computer aids can be reformulated as a problem in the presentation of latitudes in resources, time, and work loads designed to help the decider make coherent, feasible and durable decisions about task organization.

A prototype is described which presents latitudes in work load and time in a graphical way to aid task organization in hybrid manufacturing industries.

INTRODUCTION

Gains in productivity are a constant preoccupation in manufacturing industry. In large scale manufacturing (auto plants), high levels of productivity can be obtained due to the consistent nature of the assembled product which enables work stations on the production line to be harmonized thereby eliminating dead time. Further gains in productivity can be obtained by automation of elementary operations.

High productivity is less easily achieved, however, in small or medium scale production (or custom manufacture) due to the diversity of the products. Nevertheless, a more flexible automation suited to this type of manufacturing (numerical control machine tools, robots, etc.) has followed the recent advances in microelectronics and computerization. Flexible, completely automated workshops which can turn out a variety of products simultaneously are on the increase, although they are mainly encountered in the larger firms. Nevertheless, they tend to be rather less flexible than the more conventional, partially automated workshops.

In this situation, productivity can be increased by improving product flow through the workshop, which depends on the organization of:

-technical factors relating to the particular products (range, nomenclature, elementary operating processes, definition of new products); -market factors, relating to orders and shipment schedules; -materials, relating to the supply of raw materials, components and partially assembled products, as well as the control of stock of final products; -work, in the organization of task durations and the appropriate allocation of resources (man, machines, raw materials and components).

Computer-Assisted Decision and Scheduling systems are now increasingly being used to organize the technical, market and material factors. However, with respect to the work-related factors, the design of suitable computer aided systems is based on a representation of their function which may not be realistic. This is reflected by the rather too common mismatch between plans produced by computerized systems and the work effectively carried out. Our study is essentially concerned, therefore, with task organization within a workshop.

Most of the current computer aided task organization systems are based on heuristic rules, or local rules such as those relating to the control of queuing for use of a particular machine. Such systems can be set up without too much difficulty, but since they are based on local criteria they are based on highly restrictive hypotheses and may not fit in with overall objectives.

These systems sometimes contain a simulation function which enables the operator to test the choice of certain heuristic rules. The effectiveness of a given choice is evaluated, and the process is iterated until satisfactory results are obtained. It should be noted that these choices, which are in fact scheduling decisions, are made before or during the simulation. They neglect the possibility that decisions need to be made in real time during manufacture, especially those in response to unforeseen situations. The prescriptive nature of such plans leave little decisional leeway.

In an attempt to design a computer assisted system that was more suited to the real requirements of users, we studied the modes of organization of decisional leeway in workshops from an analysis of decision processes. The results of this study made us reconsider the problem of task organization in an attempt to design a more flexible system.

THE DECISIONAL PROCESS IN TASK ORGANIZATION

Modes of organization of decisional leeway were identified from studies carried out at three different sites. The first two studies characterized the decisional process from the structural point of view, while the third defined it functionally.

The results showed that the decisional process is essentially hierarchical on both an organizational and an individual dimension. On each dimension, decisions require processing of data at different levels of detail. These levels are not absolute and depend on the context, especially on the characteristics of the production process.

Organizational dimension of the process

The organizational dimension of the decisional process was identified in the machine shop of a company manufacturing heavy military equipment [1]. In this firm, we found that decisions on task organization could be distinguished on the basis of the level of detail in factors relating to work, resources and time. This decisional hierarchy also depended on the structure of the organization. As shown in Table 1, a particular level of decision was found to be attributed to a category of worker. It should be noted that this schematizes the actual decision taken. Since the responsibility for a decision is attributed to a particular category of worker, interactions between deciders will have important consequences within the same workshop. For example, in order to carry out an operation at a work station other than that planned, the workshop supervisor has to ask the opinion of the foremen and team leaders.

Examples of types of decision

Regulation of work load and capacity

Allocation of operations to machines and teams Organization of tools, raw materials etc.

Distribution of operations to workers

Definition of the order of operations

Individual dimension of the process

The individual dimension of the decisional process was identified in a study carried out in various machine shops of a company manufacturing jet engines. For a given individual, a decision was reached in several stages represented by sliding horizons. Each stage had a particular level of detail in the factors relating to a specific temporal horizon. For example, to decide on the allocation of operations to machines, the team leader constructed a weekly schedule which was then fine tuned to daily and half daily (team) schedules. The task schedule was continually refined as each task approached. Over a weekly horizon, the operations were classified on a daily basis, and the succession of operations was only defined over a half day horizon [2].

Alterations in decisional structure

A study in progress in various types of workshop (casting, machining, assembly) of a company making small electrical appliances has identified organizational and individual dimensions in decision making for task organization. They tended not to adhere to strict hierarchical levels, and were found to depend to a large extent on constraints of the on-going production process.

On the organization dimension, the relationship between decision levels and category of worker was found to depend on the characteristics of the workshop. In the casting and machine shops, decisions were centralized. The workshop supervisor made all the task organization decisions, while the other workers had a consultative role. In contrast, in the assembly shops, decisions were taken by various categories of worker in collaboration.

This diversity was also observed in the individual dimension. For some decisions, the temporal horizons were shorter at the end of the assembly line than at the start (casting and machining).

Study of the decision making process indicated that leeway in task organization fitted into a multi-dimensional hierarchical decision structure in which each level N (higher center of decision) defines the decisional latitude at level N+1 (lower decision center). The structure was not fixed, but varied in response to production constraints within a particular workshop.

MODEL FOR COMPUTER AIDED TASK ORGANIZATION SYSTEM

To make the system as compatible as possible with the real world decision making process in the workshop, we based our design on the constraints approach (time and resources) developed in the Automation and Systems Laboratory (L.A.A.S.) [3]. This model contains tools for analyzing inference and propagation of sets of time and resource constraints impinging on the decision making process. However, this model implemented in Prolog II [4] does not produce results that have direct application, and so we attempted to design an appropriate user interface.

Principle of constraints approach

In the constraints approach, the relationship between the higher and lower decisions centers can be schematized as follows (Fig. 1):

Decisions taken at the higher center are transmitted in the form of time and resource constraints to be adhered to by the lower center. In other words, the constraints derived from decisions taken at the higher center define the decisional latitude of the lower center. Thus at each level, the decisional leeway depends on the limits (or degrees of flexibility) imposed by the next higher level.

Figure 1. Principle of constraints approach At the lower center, problems of coherence between decisions must be resolved, while at the higher center, the durability of the decision needs to be taken into account. The more durable the decision, the greater the scope for decision at the lower center. A decision taken at the higher center must be feasible. If the constraints (time and resources) imposed are not realistic or are incompatible with specific constraints at the lower center then the system will seize up. In this case, constraints have to be relaxed, which may conflict with decisions taken at the higher center. Although relaxation of constraints may lead to flexibility, it can turn out to be costly when used systematically. In this situation, feasibility is a crucial issue, and the more feasible the decision taken at the higher center, the less risk of error and backtracking.

Since decisions are taken by human operators, the feasibility criterion was incorporated in the user interface, which will be tested in future studies.

Model of interface: updating of decisional leeway

To improve the feasibility of decisions, the decider must be provided with information that is compatible with his cognitive system. This is seen at two levels. Firstly, the decider's internal representation of the data presented must be compatible with the objective, and secondly, the external representation of the data (nature and form) must be compatible with the decider's internal representation. The nature of the problem and the information required to solve it must therefore be carefully defined.

Nature of problem

One of the aims of task organization is to define a temporal sequence of operations.

Current computer aided systems construct a solution, and all decisions are designed to conform to this overall objective. In this case, the objective is known, and all decisions converge towards this goal.

Our design approaches the problem differently. The objective is not predetermined, but is constructed by specification of leeways in response to the on-going situation. The previous retrospective approach (goal to data) now becomes prospective (data to goal). Furthermore, the temporal sequence, a fundamental component of the traditional problem, now becomes a datum in the current problem, or one of the constraints to be considered at only the most detailed planning level in order to avoid backtracking [5].

Thus the problem of task organization, which is normally stated in terms of a schedule or temporal sequence, is now specified in terms of a specification of latitudes (time, resources, work).

Data presentation

Data presentation must help the decider in the higher center construct mental representations that are compatible with latitude specifications for the lower center. This mental representation should enable construction of a feasible decisional framework. The decider must therefore be given aids which enable him:

-to grasp the available latitudes -to anticipate the impact of his decision on the latitudes imposed on the lower center.

The presentation of data must provide relevant information for processing of the organizational and individual dimensions of the task-related decisions. This must take account of interactions between and within decision centers during the different stages of decision making (cf. para. 1).

We paid particular attention to the 'succession of operations' constraint which must be introduced as late as possible. Two types of data presentation were devised, one detailed and the other more general, which were distinguished in terms of the perception of temporal proximity between operations (Appendix 1): a) Detailed presentation represents planned operations (duration, and temporal latitudes).

The temporal proximity between operations is readily perceived, and so this presentation must be compatible with processing at lower levels of the decision making hierarchy.

b) The general presentation represents the amount of work or tasks to accomplish for the operations planned. The detailed temporal latitudes are incorporated in terms of work latitudes. The temporal proximity between operations is not directly perceived, and so the general presentation must be compatible with processing at the higher levels of the decision making hierarchy.

With respect to the decisional horizon for task organization on the individual dimension (within a center), the detailed and general plans are components of a temporal structure made up of time intervals defined by the decider.

CONCLUSION

One of the problems of workshop task organization is the specification of decisional latitude. The dynamic nature of production imposes a certain degree of decisional latitude for each center, and an overall coherence between decisions. A study carried out at different sites showed that a workshop resolved this by a distributed decision process. For certain types of decision, we also identified mechanisms for making hierarchical plans by successive levels of integration. Plans were progressively refined by a process of dynamic factoring.

This approach of prospective planning observed in workshops can be assisted by computer systems employing methods based on propagation of sets of constraints. However, since they only provide decision aids, a user interface is required which helps the decider make feasible decisions.

We devised an interface for displaying the temporal distribution of operations. Two modes of data presentation were used:

-the detailed mode presented the planned operations: for the processing of lower levels of planning, it steers the decider to consideration of temporal latitudes, -the general mode presents levels of work: for the processing of higher levels of planning, its steers the decider toconsideration of work latitudes (or work load latitudes).

The design of this interface raised several questions:

1. We have currently decided to use graphical presentation of data, although it is not clear whether this form is compatible with users' representations. There may be individual differences, and it may be more or less suited to particular problems (reasoning on time, work or resource latitudes).

2. Should the retrospective approach be included in the design of the interface since most of the current computer aided organization systems are based on it ? It may be that current users of such systems have developed habits that are not directly transposable to the prospective approach. The problem of upward compatibility or transfer of user experience will need to be taken into account, and specific instructions or training maybe required for optimum use of the proposed system. (1977).

APPENDICES

Presentation of detailed and general data

An operation is defined by (Fig. 2):

-a time latitude bounded by an earliest date (Ci) and a latest date (Fi):

-a true start date (ti);

-a duration Di

The operations can be adjusted by shifting ti within the time latitude or by reducing this latitude. The same data can also be presented at a more general levels (schematic) which leaves out some of the proximity relationships, but emphasizes the range of amounts of work over the intervals (Fig. 4). Any temporal shift in load will thus impinge on only two adjacent intervals.

  F. Valax ; C. Thuriot ; J.-M. Cellier and J. Erschler : Planification et contrôle de l'exécution des activités dans les systèmes de production : Une analyse des fonctions Planification-Ordonnancement. SISTTEM Axe 2 Rapport n°870004, (1989). 2 B. Ciais : Planification des données temporelles : Etude des plans et de leur utilisation dans la fonction ordonnancement d'un système de production. Mémoire de maîtrise, Université Toulouse-le-Mirail, (1989). 3 J. Erschler ; P.Lopez and C Thuriot : Temporal reasoning under resource constraints : Application to tasks scheduling. 2° International Symposium on "Systems research Informatics and Cybernetics", Baden-Baden, West Germany August 11-16, 1989. 4 P. Esquirol : Règles et processus d'inférence pour l'aide à l'ordonnancement de tâches en présence de contraintes. Thèse de Docteur de l'Université Paul Sabatier de Toulouse. (1987) 5 E.D. Sacerdoti : A structure for plans and behavior. American elsevier publishing company inc,

Figure 2 .

 2 Figure 2. Definition of operations and manipulation of time latitude

Figure 4 :

 4 Figure 4: General level, presentation of max and min amounts of work per interval.

Table 1 :

 1 Level of detail in factors relating to the organizational dimension of decisions on task organization

	Function	Workshop	Foreman	Team leader
		supervisor
	Level of detail of factors
	Product	Operation phase	Operation phase	Operation
	Resource	Work station	Work station and	Machine
			machine
	Time	1 week to 2 months	1 day to 1 week	1 hour to 1 day


Bertrand Moal

Nicolas Bronsard

José G Raya

Jean Marc Vital

Frank Schwab

Wafa Skalli

Spine Virginie Lafage
email: virginie.lafage@gmail.com

Jean Marc

Volume and fat infiltration of spino-pelvic musculature in adults with spinal deformity

Keywords: Spino-pelvic musculature, Adults with spinal deformity, Muscular degeneration, Muscular volume, Fat infiltration, Dixon method

AIM:

To investigate fat infiltration and volume of spino-pelvic muscles in adults spinal deformity (ASD) with magnetic resonance imaging (MRI) and 3D method combining dedicated magnetic resonance imaging acquisition (Dixon method) and 3D reconstructions. The results demonstrated that mechanisms of fat infiltration are not similar among the muscle groups. Degeneration impacted the spinal and hip extensors most, key muscles of the sagittal alignment, highlighting the need for considering muscular factors beyond skeletal parameters.

INTRODUCTION

The muscular system plays an essential role in the maintenance of postural balance, however, there has only been limited investigation into the relationship between the muscular system and structural alignment pathologies.

In adult spinal deformity (ASD), recent research has highlighted the critical role of sagittal spino-pelvic alignment in patient-reported pain and function [START_REF] Lafage | Pelvic tilt and truncal inclination: two key radiographic parameters in the setting of adults with spinal deformity[END_REF][START_REF] Schwab | Sagittal plane considerations and the pelvis in the adult patient[END_REF][START_REF] Schwab | Scoliosis Research Society-Schwab adult spinal deformity classification: COMMENTS a validation study[END_REF][START_REF] Schwab | Radiographical spinopelvic parameters and disability in the setting of adult spinal deformity: a prospective multicenter analysis[END_REF] . Therefore, key muscles involved in pelvic-positioning and lumbar-stabilization are at the forefront of research needs.

Preliminary efforts have been directed towards understanding spine or thigh muscles using histological analyses [START_REF] Kawaguchi | Back muscle injury after posterior lumbar spine surgery. Part 2: Histologic and histochemical analyses in humans[END_REF][START_REF] Kawaguchi | Back muscle injury after posterior lumbar spine surgery. A histologic and enzymatic analysis[END_REF][START_REF] Weber | Posterior surgical approach to the lumbar spine and its effect on the multifidus muscle[END_REF][START_REF] Taylor | The impact of self-retaining retractors on the paraspinal muscles during posterior spinal surgery[END_REF], muscular strength [START_REF] Flicker | Lumbar muscle usage in chronic low back pain. Magnetic resonance image evaluation[END_REF][START_REF] Gejo | Serial changes in trunk muscle performance after posterior lumbar surgery[END_REF][START_REF] Kim | Comparison of multifidus muscle atrophy and trunk extension muscle strength: percutaneous versus open pedicle screw fixation[END_REF][12], electromyographical signals [13][START_REF] Mooney | Relationships between myoelectric activity, strength, and MRI of lumbar extensor muscles in back pain patients and normal subjects[END_REF][START_REF] Mayer | Comparison of CT scan muscle measurements and isokinetic trunk strength in postoperative patients[END_REF], muscle cross-sectional areas [via ultrasound, computed tomography (CT)-scan or magnetic resonance imaging (MRI)] [START_REF] Kim | Comparison of multifidus muscle atrophy and trunk extension muscle strength: percutaneous versus open pedicle screw fixation[END_REF][START_REF] Mayer | Comparison of CT scan muscle measurements and isokinetic trunk strength in postoperative patients[END_REF][START_REF] Danneels | CT imaging of trunk muscles in chronic low back pain patients and healthy control subjects[END_REF][START_REF] Hultman | Body composition, endurance, strength, cross-sectional area, and density of MM erector spinae in men with and without low back pain[END_REF][START_REF] Storheim | The effect of comprehensive group training on cross-sectional area, density, and strength of paraspinal muscles in patients sick-listed for subacute low back pain[END_REF][START_REF] Barker | Changes in the crosssectional area of multifidus and psoas in patients with unilateral back pain: the relationship to pain and disability[END_REF][START_REF] Dangaria | Changes in cross-sectional area of psoas major muscle in unilateral sciatica caused by disc herniation[END_REF][START_REF] Parkkola | Magnetic resonance imaging of the discs and trunk muscles in patients with chronic low back pain and healthy control subjects[END_REF][START_REF] Parkkola | Lumbar disc and back muscle degeneration on MRI: correlation to age and body mass[END_REF][START_REF] Valentin | Age and side-related morphometric MRI evaluation of trunk muscles in people without back pain[END_REF][START_REF] Savage | Lumbar muscularity and its relationship with age, occupation and low back pain[END_REF][START_REF] Peltonen | Back extensor and psoas muscle cross-sectional area, prior physical training, and trunk muscle strength--a longitudinal study in adolescent girls[END_REF][START_REF] Gille | Erector spinae muscle changes on magnetic resonance imaging following lumbar surgery through a posterior approach[END_REF], measurement of muscular density with CTscan [START_REF] Mayer | Comparison of CT scan muscle measurements and isokinetic trunk strength in postoperative patients[END_REF][START_REF] Danneels | CT imaging of trunk muscles in chronic low back pain patients and healthy control subjects[END_REF][START_REF] Hultman | Body composition, endurance, strength, cross-sectional area, and density of MM erector spinae in men with and without low back pain[END_REF][START_REF] Storheim | The effect of comprehensive group training on cross-sectional area, density, and strength of paraspinal muscles in patients sick-listed for subacute low back pain[END_REF][START_REF] Airaksinen | Density of lumbar muscles 4 years after decompressive spinal surgery[END_REF], or muscular intensity with MRI [START_REF] Gejo | Serial changes in trunk muscle performance after posterior lumbar surgery[END_REF][START_REF] Kim | Comparison of multifidus muscle atrophy and trunk extension muscle strength: percutaneous versus open pedicle screw fixation[END_REF][START_REF] Parkkola | Lumbar disc and back muscle degeneration on MRI: correlation to age and body mass[END_REF][START_REF] Valentin | Age and side-related morphometric MRI evaluation of trunk muscles in people without back pain[END_REF][START_REF] Peltonen | Back extensor and psoas muscle cross-sectional area, prior physical training, and trunk muscle strength--a longitudinal study in adolescent girls[END_REF][START_REF] Gille | Erector spinae muscle changes on magnetic resonance imaging following lumbar surgery through a posterior approach[END_REF][START_REF] Elliott | Quantification of cervical spine muscle fat: a comparison between T1-weighted and multi-echo gradient echo imaging using a variable projection algorithm (VARPRO)[END_REF]. However, difficulties arise in representing inter-muscle and intersubject variability [START_REF] Tracy | A more efficient magnetic resonance imaging-based strategy for measuring quadriceps muscle volume[END_REF].

l -

To overcome these limitations, Jolivet et al [START_REF] Jolivet | Modélisation biomécanique de la hanche dans le risque de fracture du fémur proximal[END_REF][START_REF] Jolivet | Skeletal muscle segmentation from MRI dataset using a modelbased approach[END_REF][START_REF] Jolivet | Volumic patient-specific reconstruction of muscular system based on a reduced dataset of medical images[END_REF] developed a method of three-dimensional muscle reconstruction via segmentation of a few axial images (MRI or CT-scan). This method has been successfully implemented with CT scans for analysis of muscles involved in knee motion [33] and hip muscles [START_REF] Moal | Validation of 3D spino-pelvic muscle reconstructions based on dedicated MRI sequences for fat-water quantification[END_REF] . Nevertheless, the radiation exposure from CT scans makes it unacceptable as a tool for studies involving ASD patients, frequently subjected to radiographic examination. Notably, the method has also been performed using MRI sequences [START_REF] Südhoff | 3D-patient-specific geometry of the muscles involved in knee motion from selected MRI images[END_REF] . However, contrary to CT scans, MRI cannot be interpreted in terms of tissue composition, so quantification of fat and muscle requires the use of dedicated MRI pulse sequences.

Dixon et al [35-40] developed a MRI method for fat quantification which exploits the slight difference in the Larmor frequency of fat and water protons (chemical shift). By acquiring the signal at different echo times, reconstructions.

METHODS:

Nineteen female ASD patients (mean age 60 ± 13) were included prospectively and consecutively and had T1-weighted Turbo Spin Echo sequence MRIs with Dixon method from the proximal tibia up to T12 vertebra. The Dixon method permitted to evaluate the proportion of fat inside each muscle (fat-water ratio). In order to investigate the accuracy of the

RESULTS:

Phantom acquisition demonstrated a non linear relation between Dixon fat-water ratio and the real fat-water ratio. In order to correct the Dixon fatwater ratio, the non linear relation was approximated with a polynomial function of degree three using the phantom acquisition. On average, Pfat was 13.3% ± 5.3%. Muscles from the spinal extensor group had a Pfat significantly greater than the other muscles groups, and the largest variability (Pfat = 31.9% ± 13.8%, P < 0.001). Muscles from the hip extensor group ranked 2 nd in terms of Pfat (14% ± 8%), and were significantly greater than those of the knee extensor (P = 0.030). Muscles from the knee extensor group demonstrated the least Pfat (12% ± 8%). They were also the only group with a significant correlation between Vmuscle and Pfat (r = -0.741, P < 0.001), however this correlation was lacking in the other groups. No correlation was found between the Vmuscle total and age or body mass index. Except for the spine flexors, Pfat was correlated with age. Vmuscle and Vfat distributions demonstrated that muscular degeneration impacted the spinal extensors most.

the modulation of the signal intensity can be fitted and the fat and water content can be separated.

Thus, by utilizing Dixon acquisitions and 3D muscular reconstructions, muscular volume and fat infiltration has been obtained and used to investigate the main functional groups of muscles associated with sagittal posture. The hypothesis is that volume loss and fat infiltration, previously demonstrated as factors of skeletal muscle degeneration due to aging [START_REF] Baeyens | Sarcopenia: European consensus on definition and diagnosis: Report of the European Working Group on Sarcopenia in Older People[END_REF][START_REF] Song | Sarcopenia and increased adipose tissue infiltration of muscle in elderly African American women[END_REF] , do not equally affect the different muscles.

MATERIALS AND METHODS

Inclusion/exclusion criteria

This study is a prospective consecutive pilot series of ASD patients, recruited following international review board approval and written informed consent. Inclusion criteria were female patients over 35 years old and at least one of the following radiographic parameters: Thoraco-lumbar or lumbar coronal Cobb angle greater than 30°, sagittal vertical axis (SVA) greater than 4 cm, or pelvic tilt (PT) greater than 20°. Patients with existing instrumentation, history of spine surgery, or presenting contraindication for MRI were excluded.

Radiographic acquisition and measurements

All patients underwent a full-length coronal and lateral X-ray in free standing position [START_REF] Horton | Is there an optimal patient stance for obtaining a lateral 36" radiograph? A critical comparison of three techniques[END_REF] . Radiographs were measured using a validated spine software [START_REF] Champain | Validation of new clinical quantitative analysis software applicable in spine orthopaedic studies[END_REF][START_REF] Rillardon | Validation of a tool to measure pelvic and spinal parameters of sagittal balance[END_REF] (SpineView, Laboratory of Biomechanics ENSAM ParisTech, France), which provided the following spinopelvic parameters: Coronal plane: Cobb angle and apex location, coronal alignment; Sagittal plane: SVA, PT, pelvic incidence (PI), pelvic incidence minus lumbar lordosis (PI-LL), lumbar lordosis (L1S1), thoracic kyphosis (T4T12).

Patients MRI acquisition

MRI was performed on a 3T whole-body scanner (Magnetom Skyra, Siemens Healthcare, Erlangen, Germany) using a 24-channel spine matrix coil and three 16-channel flex coils from the same vendor. The imaging protocol included a T1-weighted Turbo Spin Echo sequence for applying the two point Dixon method Water and fat images were automatically generated by the scanner from in and out of phase images (Figure 1). Imaging volume covered the proximal tibia to the lumbar spine (T12 vertebra) and was acquired in four stages.

Phantom MRI acquisition

In order to investigate the accuracy of the 2 points Dixon method for estimating fat vs water, the same MRI acquisition was performed on phantoms composed of four 10 mL plastic vials. One vial was filled with soybean oil (100% fat) and another full of water (0% fat). The remaining two vials contained an emulsion of 10% and 20% fat obtained from intralipid 20% fat emulsion (Sigma-Aldrich, St. Louis, MO, United States). For the acquisition, the phantoms were submerged in a phosphate buffered saline solution.

3D muscle reconstruction

The 3D reconstruction of individual muscles, listed Table 1, was performed using Muscl'X software (ENSAM, Laboratory of Biomechanics, Paris, France) [START_REF] Gille | Erector spinae muscle changes on magnetic resonance imaging following lumbar surgery through a posterior approach[END_REF][START_REF] Jolivet | Modélisation biomécanique de la hanche dans le risque de fracture du fémur proximal[END_REF][START_REF] Jolivet | Volumic patient-specific reconstruction of muscular system based on a reduced dataset of medical images[END_REF][START_REF] Südhoff | 3D-patient-specific geometry of the muscles involved in knee motion from selected MRI images[END_REF] . The reconstruction technique is based on the deformation of parametric specific objects (DPSO algorithm) as described by Jolivet et al [30-32] and briefly summarized hereafter.

For each muscle, a subset of MRI axial slices (MSS: manually segmented slices) were manually segmented. These contours were then approximated by ellipses, and cubic spline interpolation was used to interpolate ellipses on each intermediate MRI slice. These interpolated ellipses were deformed non-linearly using the manual segmentations of MSS. All segmentations were then verified by the operator.

A B

Some muscles were combined, since the low contrast made an accurate separation of the individual muscles difficult. The lumbar part of the psoas was reconstructed separately, but at a point where the distinction with the iliacus was not possible, it was then integrated into the iliacus. The external obturator, adductor longus, brevis and magnus and pectineus were reconstructed into a single group named "Adductor". The vastus lateralis and intermedius were reconstructed together. The muscle reconstructions were done on the fat images. Figure 2 presents the 3D reconstruction of the left muscles for one patient. The femurs were also reconstructed on the water images, the contrast between the cortical and cancellous bone was greater on water images.

Right and left muscles were grouped according to the joint (spine, hip, and knee) and by mechanical action (extensor/flexor) (Table 1). The entire set of muscles were also grouped and named total muscles.

Real fat water ratio: Correction from fat-water ratio with Dixon method

From the fat and water images, the fat-water ratio by voxel was calculated using equation 1 where SIfat represents the signal intensity of the fat signal and SIwater the signal intensity of the water image:

Dixon Dixon fat-water ratio = 100 × [SIfat/(SIfat + SIwater)] (1)
From the Phantom acquisition, an 8-by-10 region of interest (ROI) was drawn in the center of each vial and the mean and the standard deviation of the Dixon fat-water ratio in each ROI were then calculated. Those results demonstrated a non linear relation between Dixon fat-water ratio and the real fat-water ratio. In order to correct the Dixon fat-water ratio, the non linear relation was approximated with a polynomial function of degree three (F) using the phantom acquisition. Then for each patients, the real fat-water ratio was calculated for each voxel for with equation 2.

Real fat-water ratio = F (Dixon fat-water ratio) = 0.0002 × (Dixon fat-water ratio) 3 -0.0071 × (Dixon fat-water ratio) 2 + 0.5607 × (Dixon fat-water ratio) -0.7714

If F (Dixon fat-water ratio) was less than 0%, real fat-water ratio was evaluated at 0 and if F (Dixon fatwater ratio) was greater than 100, real fat-water ratio was evaluated at 100.

Quantification of fat components and muscle parameters

From the 3D reconstructions, muscular volumes were calculated (Vmuscle). The volume of infiltrated fat inside each muscles (Vfat) was calculated with the real fat-water ratio. The volumes were then normalized based upon the volume of the right femur, in an effort to limit the impact of the patient morphology. For each joint, the ratio of Vmuscle and Vfat between flexors and extensors were calculated. The percentage of fat infiltration (Pfat) was also expressed and was calculated as follow: Pfat = 100 × (Vfat/Vmuscle).

Statistical analysis

Muscular volumes and fat infiltration distribution were characterized as well as Pfat. Paired t-test was used to compare muscular volumes and fat infiltration distribution and Anova t-tests were used to compare muscular groups. For the Anova test, an analysis of the homogeneity of variance was performed, followed by Bonferonni or Games-Howell tests. Pearson's correlation coefficient was used to investigate the relationship between muscle parameters and demographic data. For each statistical analysis, the level of significance was set at 0.05.

RESULTS

Demographics

19 consecutive ASD patients with a mean age of 60 years old (range: 37-80) and a mean body mass index (BMI) of 22.9 kg/m 2 (range 17.4-31.2) were included (Table 2). There was no significant correlation between age and BMI (r = 0.375, P = 0.114).

Radiographic analysis

In the coronal plane, the mean coronal alignment was 23 mm (range: 0-119 mm, 16% of the patients reached a threshold of 40 mm). The mean maximal Cobb angle was 40° (range: 0°-60°, 79% of the patients reached the threshold of 30°). Forty-seven percent of the patients had a double curve, 32% a single curve, and 21% did not exhibit any coronal curve. Thoracic kyphosis ranged between -91° and -8° with average of -51° ± 22°. The mean L1S1 was 54° (range: 15°-75°) for a mean PI of 55° (range: 30°-77°). The analysis of PI-LL (mean = 1°, range = -35°-55°) revealed that 21% of the patients were above the threshold defined by the SRS-Schwab classification [3,46] . SVA ranged from -66 to 118 mm. The analysis of the PT revealed that 38% of the patients reached a threshold of 20° [START_REF] Schwab | Scoliosis Research Society-Schwab adult spinal deformity classification: COMMENTS a validation study[END_REF] .

Phantom analysis and correction of the Dixon fat-water ratio

The Table 3 presented the mean and standard deviation of Dixon fat-water ratio for the phantom with the different concentrations of fat. As previously mentioned, the function F, presented in equation 2, was used to approximated this non linear relation between the Dixon fat-water ratio and the real fat-water ratio (Figure 3).

Muscle analysis

Femoral volume normalization: The average femoral volume was 414 ± 71 cm Muscle and fat infiltration repartition by functional groups: "Hip group" Vmuscle was significantly bigger than the "Knee group" Vmuscle which in turn was significantly bigger than those of the "Spine Group" (Figure 4 and Table 4). The Spine extensor group represented on average 9% ± 2% of the total muscular volume but a greater proportion (21% ± 7%) of the total infiltrated fat volume (P < 0.001). The hip extensor group represents 29% ± 2% of the total muscular volume and 32% ± 5% of the total infiltrated fat volume (P < 0.001). For the Spine extensor group and the knee extensor group, the distribution of muscular volume and infiltrated fat was similar (respectively 7% and 17% with standard deviation less than 2%). For the hip flexor and knee extensor groups the distribution of infiltrated fat was significantly smaller than the distribution of muscular volume (P < 0.001).

Percentage of fat infiltration: Pfat:

The analysis of Pfat (Table 5) within each group of muscles revealed not only a large variability among patients (range: 6.1%-28.8%, Figures 5 and6), but also highlighted the difference of Pfat between muscle groups. Muscles from the spinal extensor group had a Pfat significantly greater than the other muscles groups, and the largest variability (Pfat = 31.9% ± 13.8%, P < 0.001). Muscles from the hip extensor group ranked 2 nd in terms of Pfat (14% ± 8%), and were significantly greater than those of the knee extensor (P = 0.030). Muscles from the knee extensor group demonstrated the least Pfat (12% ± 8%). They were also the only group with a significant correlation between Vmuscle and Pfat (r = -0.741, P < 0.001), however this correlation was lacking in the other groups.

Flexors vs extensor: The comparison of flexor vs extensors revealed a larger flexor contribution with regards to Vmuscle for the hip. For the spine, the ratio flex/ext highlight the greater fat infiltration of the extensor (Table 6).

Age vs muscle parameters (Table 7): No correlation was found between Vmuscle and age except for the knee extensors (Pearson's r = -0.701, P = 0.001).

For Vfat, all groups were significantly and positively correlated with age (Pearson's r between 0.555 and 0.645) except the Spine groups. Except the spine extensor, Pfat was positively and significantly correlated with age. 8): For the Spine groups, no correlation was found between Vmuscle, Vfat or Pfat and BMI. Vmuscle of the hip extensors and the knee flexors was significantly and positively correlated with BMI (respectively, Pearson's r = 0.642, P = 0.003 and Pearson's r = 0.470, P = 0.042). BMI was correlated with Vfat and Pfat in the hip and knee flexor and extensor.

BMI vs muscle parameters (Table

DISCUSSION

While the radiographic presentation of ASD patients commonly demonstrates coronal and sagittal components of malalignment, sagittal spino-pelvic parameters have been identified as the main radiographic drivers of disability [START_REF] Schwab | Sagittal plane considerations and the pelvis in the adult patient[END_REF][START_REF] Blondel | Impact of magnitude and percentage of global sagittal plane correction on health-related quality of life at 2-years follow-up[END_REF][START_REF] Glassman | The impact of positive sagittal balance in adult spinal deformity[END_REF][START_REF] Smith | Change in classification grade by the SRS-Schwab Adult Spinal Deformity Classification predicts impact on health-related quality of life measures: prospective analysis of operative and nonoperative treatment[END_REF] . The objective of the current study was to investigate the volume and fat infiltration of the main functional groups of muscles associated with sagittal posture.

Muscular volume

Relationship with posture

Fat infiltration within muscle groups ranged from 8.7% and 31.9% on average-the least affected being the knee extensors. This suggests that muscular degeneration, evaluated with fat infiltration, does not impact the groups of muscles to the same extent. The lumbar spine extensors had the greatest percentage of fat component (31.9%). This is particularly interesting in regard to the loss of lumbar lordosis present in most ASD patients [4] because lumbar spine extensors are highly involved in the maintain of lumbar lordosis. Furthermore, correlations between fat infiltration and age for the spine were smaller than for the other groups and no correlation was found with the BMI. These results suggest that the greater degeneration of those muscles is probably not solely attributed to age and BMI. However the study cannot conclude whether this observation is a cause or a consequence of the spinal deformity. Moreover, in the ASD population, sagittal malalignment is highly associated with pelvic retroversion, described by PT [1] and the agonist of this retroversion, the hip extensor, has the second greatest percentage of fat infiltration.

Flexor and extensor fat infiltration ratios were found to be smaller for the spine groups. This finding in the ASD population studied may reflect the unfavorable balance of forces leading to sagittal plane deformity across the trunk. Coupled with the findings of hip extensors and loss of contractile component with ageing, components of sagittal spino-pelvic misalignment from a perspective of soft tissue imbalance are emerging.

Fat infiltration, age and BMI

The difference between muscular volume and infiltrated fat volume demonstrated that muscle degeneration is not similar among the different functional groups. Those differences were highlighted by the difference of correlation between age and BMI. Only knee extensor muscular volume loss was correlated with age, however, infiltrated fat was correlated with age for each muscle group (except Spine Flexor P = 0.068), reflecting that age-related muscular degeneration is in general more associated with an increase of fat infiltration than an absolute muscular volume loss.

Greater BMI was associated with a greater percentage of infiltrated fat for hip and knee groups, but also associated for the hip extensor and the knee flexor groups with an increase of the muscular volume.

In light of the wide range of age and BMI values observed in this pilot study, the current findings will have to be confirmed in a larger population.

Fat and contractile component evaluation

The evaluation of the fat infiltration using the two points Dixon method has already been applied to investigate different organs (liver [START_REF] Cassidy | Fatty liver disease: MR imaging techniques for the detection and quantification of liver steatosis[END_REF][START_REF] Kim | Comparative MR study of hepatic fat quantification using single-voxel proton spectroscopy, two-point dixon and three-point IDEAL[END_REF] , bones [39] and muscles [START_REF] Gaeta | Muscle fat-fraction and mapping in Duchenne muscular dystrophy: evaluation of disease distribution and correlation with clinical assessments. Preliminary experience[END_REF][START_REF] Fischer | Quantification of muscle fat in patients with low back pain: comparison of multi-echo MR imaging with single-voxel MR spectroscopy[END_REF] ). The decay in signal intensity between the in-phase and opposed phase images due to T2* was not taken into account [38] . The measurement of T2* would have required additional measurements or the use of sequences (e.g., multi echo gradient echo sequences) that were not available at our scanner. Even more, the limited ability of patients with spinal deformities to hold still in the magnet forced us to reduce the scan time, so we could not measure T2* on these patients. Recent studies have shown that the two point Dixon without T2* has excellent concordance with spectroscopy measured in the spine, bones [39] , liver [START_REF] Kim | Comparative MR study of hepatic fat quantification using single-voxel proton spectroscopy, two-point dixon and three-point IDEAL[END_REF] , or spine muscles [START_REF] Fischer | Quantification of muscle fat in patients with low back pain: comparison of multi-echo MR imaging with single-voxel MR spectroscopy[END_REF] . With the 3 points Dixon method applied onto phantoms filled with different proportions of fat and water, Kovanlikaya et al [51] , demonstrated a linear correlation between the fat-water ratio and the proportion of fat. However in our phantom study, this relationship was not linear, explaining why we corrected the fat water ratio evaluated with the two Dixon method with a polynomial function.

This disagreement observed between the nominal and the measured fat fraction in phantoms can be caused partially because of the T1 weighting of the images. Fat have much shorter T1 values (300 ms) than water in muscle (900 ms) at 3T [START_REF] De Bazelaire | MR imaging relaxation times of abdominal and pelvic tissues measured in vivo at 3.0 T: preliminary results[END_REF] . With a TR of 820 ms the magnetization from fat was almost completely relaxed [TR/T1fat approximately 2.73, (1-e-TR/T1fat) = 0.94, i.e., 94% of the signal available for the next excitation], while the magnetization for water did not have enough time to recover [TR/T1water approximately 0.91, (1-e-TR/T1water) = 0.60, i.e., 60% of the signal available for the next excitation]. Therefore in our measurements the signal from water was underestimated and this resulted in overestimation of the fat fraction. Additional errors with the two-point Dixon included sensitivity to B0 inhomogeneity, which could explain why the differences between the in phase and out of phase in the 100% phantom lead to an underestimation of the fat fraction for large values of the fat fraction.

While investigations of the muscles of the thigh [36] or extensor of the spine [50] exist, they are based on a limited number of MRI slices and none of them report results on the entire muscular volume. To our knowledge, there is no study combining 3D reconstruction of muscles and fat component calculated with the two points Dixon method.

Limitations

Due to our experimental design and the limited sample size, we cannot draw any definitive conclusions correlating ASD and muscular factors. The various deformities presented in this population limited the ability to associate changes in a specific muscle groups with deformation type. Given the fact that the prevalence of adult spinal deformity is greater in female than in male patients, only female subjects were included in this study in an effort to limit confounding factors related to gender's difference in muscular system. Female subjects were considered due to the higher incidence of spinal deformity in the female population [START_REF] Kawaguchi | Back muscle injury after posterior lumbar spine surgery. A histologic and enzymatic analysis[END_REF][START_REF] Dangaria | Changes in cross-sectional area of psoas major muscle in unilateral sciatica caused by disc herniation[END_REF] . Data for a larger gender mixed population and an asymptomatic population are important next steps to evaluate more clearly the contractile component and correlation between muscle groups of the spino-pelvic complex and spino-pelvic alignment.

The applied MRI protocol permits a quantitative and qualitative characterization of the main muscles involved in the spino-pelvic complex. Regarding the differences between distribution of muscular and contractile components only, this study demonstrated the necessity of a complete characterization of the muscular system (including the quantification of the fat infiltration) and stress the limitations of considering only geometric parameters. Muscle degeneration seems more related to fat infiltration than volume loss but muscle degeneration does not affect all the muscles equally. In the studied ASD population, lumbar spine and hip extensor were the groups most affected by muscular degeneration, and muscle volume ratios between flexors and extensors were greatest in the spine group.

ACKNOWLEDGMENTS

Authors thank Dr. Prodromos Parasoglou for help in constructing the fat phantom.

COMMENTS

Background

In adult spinal deformity, recent research has highlighted the critical role of sagittal spino-pelvic alignment in patient-reported pain and function. However these patients are mostly analyzed by skeletal parameters obtained with radiographies, with only a minor consideration on the muscular system which limits the understanding of the pathology.

Research frontiers

Numerous methods have been directed towards analyzing muscular system. However difficulties arise in representing inter-muscle and inter-subject variability as well as obtaining a reliable evaluation of muscular volume and fat infiltration.

Innovations and breakthroughs

Combining Dixon magnetic resonance imaging (MRI) acquisitions and 3D muscular reconstructions, muscular volume and fat infiltration have been obtained for the main functional groups of muscles associated with sagittal posture in the setting of adult spinal deformity. The results have demonstrated that mechanisms of fat infiltration are not similar among the muscle groups for this population. Moreover degeneration mostly impacted the spinal and hip extensors, key muscles in opposition with the anterior sagittal malalignment.

Applications

The results suggest the interest of a complete characterization of the muscular system (including the quantification of the fat infiltration) in the evaluation of patients with spinal deformities.

Terminology

Adult spinal deformity refers to abnormal curvatures of the spine in patients who have completed their growth. Dixon MRI allows the separation of fat and water content and so the calculation of fat infiltration within each muscle.

Peer-review

This manuscript describes an observational study of volume loss and fat infiltration of muscles associated with sagittal posture in patients with adult spinal deformity.

[35- 38 ][

 38 Repetition time (TR)/Echo time = 820/11 ms, acquisition matrix = 448 × 308, phase oversampling = 100%, in plane resolution = 0.94 × 0.94 mm 2 , 4 stages, 40 slices by stage, slice thickness = 5 mm, slice gap = 0 mm, flip angle = 157°, turbo factor = 3, echo trains = 107, parallel imaging acceleration factor (iPat) = 2, iPat references lines = 26, bandwidth = 319 Hz/pixel, echo spacing = 15.7, acquisition time per stage = 5:53 min, Total acquisition time = 25 min].

Figure 1

 1 Figure 1 Example of water (A) and fat (B) images with Dixon methods on a 64-year-old female adult spinal deformity patient.

Figure 2

 2 Figure 2 Medial and frontal view of all the left muscles reconstructed for one patient.

3 .

 3 A larger femoral volume was associated with a larger muscular volume when considering the Total Muscle (Pearson r 2 = 0.837, P-value < 0.001).

Figure 3

 3 Figure 3 Average fat-water ratio for the phantom with different concentration of fat (0%, 10%, 20% and 100%) and the approximated function real fat-water ratio = F (Dixon fat-water ratio).

Figure 5 Figure 6

 56 Figure 5 Magnetic resonance imaging samples (A: Lumbar area; B: Pelvis area; C: Limb area) of a 37-year-old female adult spinal deformity patient with a body mass index of 22 kg/m 2 . This patient presents a sagittal deformity with hyperlordosis of the lumbar spine (pelvic incidence minus lumbar lordosis = -29°) and a thoraco-lumbar kyphosis of 45°. The analysis of the muscle quality revealed an 6.1% of fat infiltration on average.

Spine extensor Spine flexor Hip extensor Hip flexor Knee extensor Knee flexor Total muscle

	Quadratus lumborum	x			x
	Tractus medialis	x			x
	Tractus lateralis	x			x
	Psoas	x	x		x
	Iliacus	x	x		x
	Biceps femoris short	x		x	x
	Biceps femoris long	x		x	x
	Semi-membranosus	x		x	x
	Semi-tendinosus	x		x	x
	Gluteus maximus	x			x
	Rectus femoris		x	x	x
	Gracilis		x	x	x
	Sartorius		x	x	x
	Adductor		x		x
	Tensor fascia lata		x		x
	Vastus lateralis intermedius			x	x
	Vastus medialis			x	x

Table 1 Muscles analyzed in this study, and grouping by function and joint

 1

	Medial view	Frontal view
	Adductor
	Biceps femoris long
	Biceps femoris short
	Gluteus maximus
	Gracilis
	Iliacus
	Psoas
	Quadratus lumborum
	Rectus femoris
	Sartorius
	Semi-membranus
	Semi-tendinus
	Tensor fascia lata
	Tractus lateralis
	Tractus medialis
	Vastus medialis
	Vastus lateralis intermedius

Table 3 Mean and standard deviation of Dixon fat-water ratio for the phantom with the different concentrations of fat

 3

		Min	Max	Mean	SD	95%CI
						Lower	Upper
	Age	37	80	60	13	54	66
	BMI	17.4	31.2	22.9	3.52	21.1	24.6

Table 2 Demographic information

 2

BMI: Body mass index.

Table 4 Muscular Volumes of each muscle group

 4

				Percentage of fat component
		Min	Max	Mean	SD	95%CI
						Lower	Upper
	Spine extensor	12.72	71.15	31.90	13.83	25.24	38.57
	Spine flexor	5.67	20.39	11.92	3.63	10.17	13.66
	Hip extensor	6.39	38.09	14.81	7.01	11.43	18.19
	Hip flexor	6.10	20.22	10.76	3.16	9.24	12.29
	Knee extensor	3.84	20.02	8.66	4.03	6.72	10.60
	Knee flexor	6.93	25.44	12.81	4.20	10.78	14.83
	Total muscles	6.12	28.84	13.34	5.33	10.77	15.91

Reported values are normalized based upon the volume of the right femur of each patient (for example, the mean "Total Muscles" volume = 16.67 femurs volume).

Table 5 Percentage of infiltrated fat expressed by functional groups Figure 4 Distribution of Muscular volume and infiltrated fat volume expressed in percentage of the total muscle muscular volume and of the total infiltrated fat volume respectively

 5 . Vmuscle: Muscular volume; Vfat: Infiltrated fat volume.

	17%

Table 7 Correlation between age and muscular volume, infiltrated fat volume and percentage of fat component

 7 Statistically significant difference with a P-value < 0.05; Statistically significant difference with b P-value < 0.01. Vmuscle: Muscular volume; Vfat: Infiltrated fat volume; Pfat: Percentage of fat component.

			Vmuscle		Vfat		Pfat
			r	P	r	P	r	P
	BMI	Spine extensor	0.127	0.606	0.017	0.944	-0.038	0.876
		Spine flexor	-0.027	0.913	0.443	0.057	0.450	0.053
		Hip extensor	0.642 b	0.003	0.693 b	0.001	0.587 b	0.008
		Kip flexor	0.159	0.515	0.657 b	0.002	0.587 b	0.008
		Knee extensor	-0.236	0.330	0.596 b	0.007	0.518 a	0.023
		Knee flexor	0.470 a	0.042	0.761 b	< 0.001	0.570 a	0.011
		All muscles	0.207	0.394	0.592 b	0.008	0.458 a	0.049

Table 8 Correlation between age and muscular volume, infiltrated fat volume and percentage of fat component

 8

	Statistically significant difference with a P-value < 0.05; Statistically significant difference with b P-value < 0.01.
	Vmuscle: Muscular volume; Vfat: Fat volume; Pfat: Percentage of fat component.

Table 6 Ratio between flexors and extensors for each group of muscles (muscular volume and infiltrated fat volume)

 6

	Vmuscle: Muscular volume; Vfat: Infiltrated fat volume.

Moal B et al . Muscle in adult with spinal deformity

program on subject-specific musculoskeletal modeling, with the support of Proteor, Covea, Société Général, ParisTech and Yves Cotrel Foundation. Institutional review board statement: Institutional review board approval. This study is registered at New York University of Medicine's Institutional Review Board. The registration identification number is 11-01647. Frank J. Schwab is a consultant and received grants for research purpose by Medtronic and Depuy. He is a shareholder of Nemaris. Wafa Skalli has royalties from EOS imaging (Royalties) and received a grant for research purpose by the Fondation ParisTech chair program on subject specific musculoskeletal modelling. Virginie Lafage received a grant for research purpose by SRS and ISSG. She is giving lectures for Globus, Depuy Spine, Medtronic, Nuvasive and MDT.

dataset available from the corresponding author at Virginie. lafage@gmail.com.


Bruno Lemiere
email: b.lemiere@brgm.fr

P Sarala

Gloaguen Anne-Sophie Serrand

Eric Gloaguen

Frédéric Eric Fournier

J Melleton

F Lacquement

pXRF measurements on soil samples in the vicinity of a W deposit and Nb-Ta prospect: example

Keywords: pXRF, tungsten, niobium, tantalum, arsenic, copper, mineral exploration, Echassières kaolin district

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.


Jérémie Melleton

Bruno Lemiere

Maha Chalhoub

Eric Gloaguen

H Marasa

L Bouat

Exploration biogeochemistry in the Western Europe environment, an example from Sb deposits

published or not. The documents may come

Exploration biogeochemistry in the Western Europe environment, an example from Sb deposits.

Melleton, J. 1 , Lemiere, B. 1 , Belbèze S. 1 , Chalhoub, M. 1 , Marasa, H. 1 , Derycke V. 1 , Gloaguen, E. 1 , Bouat, L. 1 , Middleton M. 2 1 French Geological Survey, BRGM, Orleans, France 2 Geological Survey of Finland, GTK, Rovaniemi, Finland j.melleton@brgm.fr In Europe, exploration geochemistry is mainly restricted to classical soils geochemical analyses based on total or near total digestion of samples. Examples of biogeochemistry usage in continental Europe remain anecdotic. However, with the actual detection levels in analytical methods and the knowledge about metals accumulation reached in a large spectrum of plants, biogeochemistry has already been successfully tested in various environments and over distinct deposit types.

Within the UpDeep project (European Institute of Innovation and Technology -Raw Materials) framework that aims to develop the geochemical expertise on deep buried exploration in Europe, a biogeochemical survey has been done on several known Sb deposit of the Vendée District (France).

One of the challenging questions of exploration geochemistry in Western Europe is the long-term anthropogenic contamination related to past mining activities but also agricultural and forestry activities, which can strongly affect the primary geochemical anomalies especially in soil horizons and plants. In the studied area, intensive agriculture is widespread, and forestry has been conducted intensively. In such environment, hedges remain the only area where variety of plant species is important enough to chose a good media, in particular for trees.

Within the scope of testing different plant species, oak bark and bramble leaves were sampled at around 110 sites. After powdering, the samples experienced a HNO 3 digestion followed by ICM-MS analyses.

To identify the geochemical signatures related to Sb mineralizations, classical compositional data analyses have been carried out before response ratios and log ratios applications.