Cornelia Woll

Alvaro Artigas

When trade liberalization turns into regulatory reform: the impact on business-government relations in international trade politics

Business-government relations on trade issues are generally characterized as protectionist lobbying or -less often -lobbying for the liberalization of markets. However, with the evolution of the trading system, negotiations today concern not just market opening, but also the regulatory frameworks that structure international trade. This transformation has important consequences for the ways in which private interests can contribute to trade negotiations. Instead of simply trying to exert pressure, businesses and other private actors now form working relationships with governments based on expertise, learning, and information exchange. This article illustrates these new forms of public-private interactions with examples from the U.S., the E.U., and Brazil.

Introduction 1

International trade negotiations have changed profoundly in the last 50 years.

Since the first rounds of talks under the General Agreement on Tariffs and Trade [GATT], trade negotiations have moved from the reciprocal reduction of tariff barriers to include a wealth of non-tariff barriers, focusing increasingly on domestic issues with an impact on trade. The Uruguay Round led to the creation of the World Trade Organization [WTO] in 1995 and expanded the coverage of the multilateral trading system to services and intellectual property rights. Trade-related domains, such as environment or labor standards, competition or investment policies are also affected by the rules negotiated under the WTO (see [START_REF] Hoekman | The Political Economy of the World Trading System[END_REF][START_REF] Barton | The Evolution of the Trade Regime: Politics, Law, and Economics of the GATT and the WTO[END_REF]. With the expansion of trade issues, new non-governmental groups have tried to take part in trade negotiations in order to off-set the influence of big business [START_REF] Bayne | The New Economic Diplomacy: Decision-Making and Negotiation in International Economic Relations[END_REF]. Indeed, activists and the anti-globalization movements have argued that the WTO is captured by big business, which maintain apparently privileged relationships with trade negotiators (e.g. [START_REF] Wallach | The WTO: Five Years of Reasons to Resist Corporate Globalization[END_REF][START_REF] Wesselius | Behind GATS 2000: Corporate Power at Work[END_REF].

Business-government relations have been central to academic writing on trade policy for a long time. According to the school of economic regulation, which still dominates trade policy studies today, trade decisions are the result of industry lobbying [START_REF] Stigler | The Theory of Economic Regulation[END_REF][START_REF] Posner | Theories of Economic Regulation[END_REF]Buchanan, Tollison, & Tullock, 1980;[START_REF] Krueger | American trade policy: a tragedy in the making[END_REF]. In most trade policy accounts, business is assumed to determine first where its material interests lie: in the protection of home markets or in the access to new markets (Frieden & Martin, 2002: 126). It then tries to influence political decisionmakers, offering votes or financial incentives in exchange for the desired outcome.

Within this framework, understanding the making of trade policy implies understanding when firms would lobby for protectionism and when for liberalization, and sophisticated models have been developed to predicting industry behavior according to factor distribution, sectors or firm strategies [START_REF] Alt | The Political Economy of Trading States: Factor Specificity, Collective Action Problems, and Domestic Political Institutions[END_REF][START_REF] Milner | The Political Economy of International Trade[END_REF][START_REF] Hiscox | International Trade & Political Conflict: Commerce, Coalitions, and Mobility[END_REF]. 2 An empirical study of current business-government interactions, however, reveals a more complex reality. First of all, firms maintain a great variety of relations with governments that go far beyond making general demands for open or closed markets. Depending on the sectors, governments may solicit firm input and even delegate tasks to business actors (Cutler, Haufler, & Porter, 1999). Second, businessgovernment relations often take the form of close working relationships, characterized by the mutually beneficial exchange of information and reciprocal learning [START_REF] Shaffer | Defending Interests: Public-Private Partnerships in WTO Litigation[END_REF][START_REF] Woll | Learning to Act on World Trade: Preference Formation of Large Firms in the Unites States and the European Union[END_REF]. Even though firms sometimes know exactly what they want and then pressure their governments to comply with these interests, business-government relations go further beyond simple pressure lobbying than previously assumed in the international political economy literature on trade.

The central argument of this paper is that traditional business-government models fail to capture an increasingly complex empirical reality, because they are based on an outdated and sometimes inaccurate conception the nature of trade negotiations. Pressure lobbying for protectionism or liberalization, as appropriate as it may be for tariff negotiations (e.g. [START_REF] Kingstone | Crafting Coalitions for Reform: Business Preferences, Political Institutions and Neoliberal Reform in Brazil[END_REF], does not account for strategies related to the new dynamics and complex issues negotiated under the WTO. The liberalization of trade in products has moved the target of business lobbyists from tariffs to process and production methods -and therefore to environment and labor standards -even though subsidies, and lately safeguards remain an important issue (Hoekman & Kostecki, 2001:453;[START_REF] Read | Process and Production Methods and the Regulation of International Trade[END_REF]. 3 Recent trading issues increasingly imply the construction or harmonization of specific regulatory regimes, especially in new areas such as intellectual property or service trade [START_REF] Sauvé | GATS 2000: New Directions in Services Trade Liberalization[END_REF]Mattoo & Sauvé, 2003). This not only applies to multilateral agreements, such as the WTO's Sanitary and Phytosanitary Measures Agreement, the Technical Barriers to Trade Agreement, or elements of the General Agreement on Trade in Services [GATS], it has also been particularly true in the case of bilateral agreements since 2001. 1 In this context, business-government relations resemble the interactions of firms and governments on domestic regulatory issues and not the pressure lobbying on tariff negotiations or safeguards (see [START_REF] Willman | The Evolution of Regulatory Relationships: Regulatory Institutions and Firm Behavior in Privatized Industries[END_REF][START_REF] Coen | Business-Regulatory Relations: Learning to Play Regulatory Games in European Utility Markets[END_REF].

In addition, the judicialization or legalization of trade issues through the dispute settlement system of the WTO increases the role of expertise as a primary resource of business lobbying [START_REF] Shaffer | What's New in EU Trade Dispute Settlement? Judicialization, Public-Private Networks and the WTO Legal Order[END_REF].

While the literature acknowledges the changing nature of trade, few authors have fully acknowledged the profound effect of these transformations for businessgovernment interactions (but see [START_REF] Shaffer | Defending Interests: Public-Private Partnerships in WTO Litigation[END_REF][START_REF] Young | The EU and the New Trade Politics[END_REF]. This article seeks to fill this void. It distinguishes two ideal types of business lobbying -pressure lobbying and interactive business-government relations, the latter which we will refer to as regulatory trade lobbying. It discusses why pressure lobbying is inappropriate in the context of regulatory issues and the increasing legalization of trade. We then illustrate the new business-government relations with case examples from the United States, the European Union, and the emerging trade power Brazil. In particular, we highlight that interactive lobbying happens in a context of uncertainty, that governments actively solicit firm participation, and that they depend quite heavily on the expertise firms can provide.

Our case examples were chosen to demonstrate that business-government relations have been surprisingly similar across different domains: in a country with a long lobbying tradition (the US), an unusual political system that has turned into the second most important trading power and lobbying forum (the EU), and an emerging economy with a growing importance in multilateral trade negotiations (Brazil).

Despite the institutional and historical differences in public-private partnerships, trade policy lobbying in these three cases systematically diverges from the pressure lobbying assumed in the mainstream trade policy literature. 4 Our empirical discussion draws on over 120 qualitative interviews carried out with representatives from firms, business associations or governments between September 2002 and December 2004. 5 We have mainly spoken to firms and business associations that have been particularly active on international trade and that have invested considerable resources to affect negotiations. The uncertainty, constraints, and difficulties mentioned by these business actors can thus be assumed to apply even more decisively to smaller and less active firms.

We proceed in three steps. A first section reviews other recent analyses of the multilateral trading system and explains that international trade policymaking increasingly includes intense consideration of regulatory issues. A second section analyzes how these changes in trade policy affect business-government relations, and in particular it distinguishes pressure lobbying from the interactive businessgovernment relations common in regulatory contexts. A third section illustrates these business-government relations with example from trade policy lobbying in the US, the EU, and Brazil, focusing on the role of uncertainty, government solicitation and mutual dependence. As a research agenda, the final section then uses the empirical discussion to articulate hypotheses about the conditions that determine which business-government interactions we should expect in what context. The conclusion then clarifies the implications of our distinctions for the study of trade policy-making.

Trade negotiations as regulatory reform

As early as 1989, Milner and Yoffie (1989: 239-240) remarked that the study of business lobbying is trapped in a dichotomy between liberalization and protectionism. Following David [START_REF] Ricardo | The Principles of Political Economy and Taxation[END_REF][START_REF] Ricardo | The Principles of Political Economy and Taxation[END_REF]), trade was imagined as the exchange of goods between two countries with competitive markets where production follows from a country's comparative advantage. Under protectionism, a country raises the barriers to entry for foreign goods; under free trade, it abandons these barriers and exposes its firms to foreign competition. Multilateral tariff negotiations, the reason for which the GATT was created, ensure nothing more than the reciprocal reduction of external barriers and consequentially the stakes for the affected firms are quite clear.

This assumption, however, holds true only if all countries have perfectly competitive markets on the inside and if their only decisions are whether to open or close these markets to foreign competition. This is not necessarily the case. In his book, "Beyond Free Trade," David Yoffie (1993) argues the nature of competition is very different if (1) there is a high or a low degree of industry concentration in a particular market and (2) government intervention in a sector is intensive or low. Yoffie (1993:19) summarizes the diverse nature of the international trading system in the following picture.

FIGURE 1 ABOUT HERE

The classic international trade model, according to Yoffie, corresponds to the lower left-hand box. National markets have few imperfections and government has a small role, so that a large number of firms compete based on their comparative advantages once trade barriers are reduced. However, Yoffie also identifies three other forms of international competition: (1) oligopolitistic competition between large firms in liberalized national markets;

(2) political competition between two different systems of government intervention, and (3) regulated competition, where both firm concentration and government intervention is high.

Yoffie's characterization corresponds with [START_REF] Cowhey | Managing the World Economy: The Consequences of Corporate Alliances[END_REF] analysis of global trade. To these authors, trade negotiations previously aimed at obtaining a "free trade regime" based on the free movement of goods and national comparative advantage. Today, this logic has eroded. Investment has become coequal with trade, particularly in emerging countries [START_REF] Sauvé | Trade and investment rules: Latin American Perspectives[END_REF], the boundary between services and goods is vanishing, and consequentially the modes of trading have become more complex. Firms often maintain business operations in foreign countries, but are unable to compete on equal footing with national producers due to product or process restrictions. The central question is no longer whether to allow free trade with a foreign country, but how to ensure market access to a foreign market. Instead of following universally applicable rules, these "market access regimes" have to be negotiated sector by sector since they often involve the internationalization or harmonization of domestic policies applying to a particular product or service market. The transformation of the institutional setting is crucial to understanding this evolution. Changes in the international governance of trade have sensibly modified the setting which also affects the lobbying of economic actors. The "new trade 2 Talking about regulation in the context of trade can sometimes lead to confusion. For certain economists, the term "regulation" refers to all forms of government intervention and is the bipolar opposite of free competition (cf. Jordana & Levi-Faur, 2004: 5). For others, regulation refers to economic steering executed by independent administrative agencies. More generally, regulation implies a set of targeted rules. In this article, we view regulation as "the promulgation of an authorative set of rules, accompanied by some mechanism […] for monitoring and promoting compliance with these rules," (Baldwin, Scott, & Hood, 1998: 3).

themes" and the refinement of trade policy instruments, such as the WTO dispute settlement system and its application on national soil, call for an expertise that was less relevant in previous GATT rounds. While the negotiation of regulatory issues requires technical knowledge, the judicialization of trade implies a greater demand legal expertise. Both cases increase the need for detailed knowledge about market barriers [START_REF] Goldstein | Legalization, Trade Liberalization and Domestic Politics: A Cautionary Note[END_REF][START_REF] De Bièvre | Governance in International Trade: Judicialisation and positive integration in the WTO[END_REF][START_REF] Shaffer | What's New in EU Trade Dispute Settlement? Judicialization, Public-Private Networks and the WTO Legal Order[END_REF].

Business-government relations: between pressure and cooperation

How then should we understand business-government relations over multilateral trade? In the context of tariff negotiations, lobbying previously has been presented as largely dichotomized between protectionism and support for reciprocal trade liberalization. Firms or industry representatives had been understood to exert pressure on politicians in order to capture the outcome of negotiations. Lobbying over trade policy became equated with "rent-seeking" and gave a bad reputation to business involvement in politics and trade policy in general (Buchanan et al., 1980;[START_REF] Magee | Black Hole Tariffs and Endogenous Policy Theory: Political Economy in General Equilibrium[END_REF].

In contrast, research on lobbying strategies in the field of business administration and international business has tended moved away from this dichotomy (e.g. [START_REF] Rugman | Global Corporate Strategy and International Trade Policy[END_REF]Dunning, 1997). According to businesscentered studies, the stakes in international trade negotiations are foreign investment and market access relevant to the strategic positioning of firms. This corresponds with the propositions of Yoffie (1993) and [START_REF] Cowhey | Managing the World Economy: The Consequences of Corporate Alliances[END_REF]. When multilateral trade negotiations are about the formulation of specific targeted rules that define market access and operation, business lobbying changes.

On the one hand, firms have to affect the details of the rules in question, which requires closer cooperation than just pressuring for a general outcome of talks. The transmission of information, and not just the provision of electoral or financial incentives, becomes an important part of trade policy lobbying (see [START_REF] Potters | Modelling Political Pressure as Transmission of Information[END_REF][START_REF] Barney | Firm Resources and Sustained Competitive Advantage[END_REF][START_REF] Kostecki | Information and Influence: Lobbying for Agendas and Votes[END_REF]; see also [START_REF] Bauer | American Business & Public Policy -The Politics of Foreign Trade[END_REF]. On the other hand, governments need to negotiate the internationalization of domestic regulations, which requires knowledge about the constraints weighing on a particular market. Since trade negotiations aim at facilitating the operation of business, firms become privileged sources of information for government delegations [START_REF] Coglianese | Seeking Truth for Power: Informational Strategy and Regulatory Policymaking[END_REF]. Expertise thus proves to be an important resource for lobbyists trying to gain access to international trade talks [START_REF] Radaelli | The Role of Knowledge in the Policy Process[END_REF]. By offering this expertise, firms become part of the epistemic communities that thus structure global business regulation [START_REF] Braithwaite | Global Business Regulation[END_REF].

The transformation of multilateral trade negotiations has important consequences for the political activities of business actors, because it affects their political opportunity structure. 6 The growing importance of regulatory affairs in international trade has profoundly changed the informal procedures and interactions between stakeholders. For simple decisions like tariff reductions, economic interest groups can offer their financial or electoral support in exchange for decisions in their favor. This is no longer the case when regulation becomes a means for governments to tie their hands, as in the case of emerging countries like Brazil or South Africa. Many current and widely used trade policy instruments rely on highly formalized procedures of the WTO; this evolution represents a sharp contrast with previous negotiations on tariffs, where demands could be easily formulated and did not require such elaborate procedures. Anti-dumping investigations can lead to highly codified retaliations, and the providing the expertise necessary for launching such proceedings is therefore increasingly costly for business lobbyists. 7

Faced with regulatory stakes and increasing legalization, the exchange between business and government is therefore based on the exchange of technical expertise and legitimacy inter pares. Governments gain information and political support, while firms gain access to the elaboration of a policy issue. This shift in resources is accompanied by a shift in constraints on lobbying success. Pressure lobbying is constrained political competition: many groups try to influence policymakers and seek to prevail against each other in order to be heard [START_REF] Becker | A Theory of Competition among Pressure Groups for Political Influence[END_REF].

Regulatory trade lobbying rests on government solicitation of expertise, so the criteria for success or failure are different. Firms have to prove to the government that they are valuable partners, which requires credibility, reputation, and constructive cooperation [START_REF] Broscheid | Insider and Outsider Lobbying in the European Commission[END_REF]Coen, 2005: 377). Since government delegations can shop around for business partners, they can privilege those that are perceived to facilitate the consultation process [START_REF] Willman | The Evolution of Regulatory Relationships: Regulatory Institutions and Firm Behavior in Privatized Industries[END_REF].

TABLE 1 ABOUT HERE

Table 1 summarizes the two different types of business-government relations on international trade. Like most classifications, this one highlights two ideal types of business-government relations on trade issues. In many contexts, we will find hybrid forms. This seems to be particularly true in the case of emerging countries, where both types of relations co-exist, partly because of higher stakes in tariffs in not so widely liberalized economies. Some firms and economic actors might even use both means simultaneously, although a reliance on pressure can harm working relations in the long run. The central point we would like to make is simply that the transformation of multilateral trade negotiations that has been observed by many authors also has important consequences for business-government relations. The insights about regulatory lobbying in the political science and management literature thus need to be connected systematically with the changing nature of trade.

Business lobbying on multilateral trade negotiations

For business actors, the new stakes are first and foremost a challenge, because the distributive effects of regulatory reform are not as easily predictable as the effects of opening or closing markets. Both government negotiators and firm representatives need to determine how to transnationalize or harmonize domestic regulation, preferably with the greatest possible benefit to the national economy (for government representatives) or particular firms (for business representatives). Quite often, multiple alternatives and a series of intricate details need to be evaluated, so governments solicit industry input and assistance. Firms, in turn, often need a considerable amount of time in order to learn and evaluate the impact of a given set of negotiations.

Three aspects of interactive business-government relations are particularly important: (1) the greater degree of uncertainty about the stakes for both business and government and the learning process that this uncertainty prompts;

(2) the active solicitation of private actor participation; and (3) the mutual dependence that forms as a result of the interaction. These aspects correspond to the changing mode, constraints, and resources highlighted in Table 1. We illustrate each of these aspects through accounts of business lobbyists and government representatives in the US, the EU, and Brazil.

Uncertainty

The effects of trade policies are often difficult to evaluate due in part to the evolution of corporate strategies of individual firms. 8 Increasing vertical integration and the internationalization of corporate strategies interact with growing complexity of trade negotiations and regulation. Many firms find it difficult to catch up with the WTO's agenda, which explains why lobbying during the early years of a trading issue is rarely effective. This is particularly true in countries that are newcomers to trade liberalization like Brazil. The internationalization of their economies combined traditional and new regulatory issues that demanded extensive learning on the part of economic actors. Government officials recall how long it took part of the agricultural industry to "professionalize" their demands during the 1990. As one government official from Brazil noted:

The first thing they [the producers] did when confronted to the opening of the economy was to ask for subsidies, later they launched a badly-knitten anti-dumping procedure, followed by a serious study on tariffs to finally achieve a decent antidumping procedure. It clearly was a learning process but they are now aware of each one of trade defense instruments. 9

In many way, calling for simple trade protection was a matter of habit, sometimes even detrimental to the interests of given sectors, who only learned slowly that they could also demand anti-dumping procedures against tier-countries. The same Brazilian official recalled:

During the 1990s, the textile sector was confronted [with] a strong pressure of Chinese imports. They [the Brazilian textile branch 10 ] demanded subsidies, but they are now demanding an agreement with the EU. This change did not come overnight; the evolution of this position took two years to emerge. 11

Yet, even though there has been a learning process, the existence of traditional trade issues hinders the effective participation of business interests on new regulatory issues, which depends in turn both on a critical mass of multi-national firms operating on national soil and on efficient branch associations.

Moreover, WTO procedures often remain obscure for firms that do not work on trade issues continuously. This not only applies to firms from newcomer countries.

As a representative from a European telecommunications company remembered:

I have to admit, I only discovered the WTO at the margin. Initially, people considered the WTO to be something quite abstract: "value-added", "basic services" …? In most countries, you did not have a realization that there was a new reality… that you couldn't do anything without paying attention to the WTO. 12 Following trade negotiations was just as difficult, as a leading telecom expert from the US explained:

Nobody knew how to read a schedule of commitments. We even had people think that '-none, -none, -none' meant that none had market access. 13 To resolve these difficulties, business representatives had to get creative. As one US business representative described:

We developed a sort of code to talk to one another while government representatives were in the room. We made sure we would start our phrases by saying 'Just to review a little bit what has been said…' so that everybody understood what was going on. 14 Uncertainty on issues and possible outcomes translated into concrete apprehensions in the early period. From Brazil's textile industry to European telecommunication firms or American airlines, all business representatives, who at one point started following WTO affairs, felt that there was a high risk of being traded-off "against bananas." 15 This fear applied not only to firms affected by the negotiations on new trade issues; it was also a consequence of increasingly complex negotiations on traditional industrial sectors like textile or steel.

Information on all aspects of negotiations is sometimes difficult to obtain, even for government representatives. This is particularly true for emerging countries like Brazil. Previous GATT rounds had been conceived as relatively vague and nonconstraining. For a long time, only a few government officials were in charge of these negotiations and they had little sense of what the real situation was in each sector once they started negotiating under the WTO framework: "We handled little information, and we arrived to the negotiation table with rather impressionistic data." 16 Consequentially, it was not unusual for business sector representatives to travel all the way to Geneva to engage in last-minute lobbying activities, to make up for the government's lack of information, and to make their demands visible.

Solicitation

Firms have not always been the ones who have taken the initiative to follow and enter into contact with government negotiators. Quite often, the government made a concerted effort to reach out to business, inform them of the stakes of particular negotiations, and solicit their help.

Brazil has undergone a significant change in this matter, in part as a result of existing negotiations between the Latin American common market MERCOSUR and the US and the EU that required specific negotiating groups to be established. In recent years, the Brazilian government has developed an extensive information network on trade matters, associated with an increased level of interaction with business representatives. In addition to ad hoc committees that existed during the former Cardoso government, new formal institutions like the National Council for Industrial Development (CNDI) were created to meet on regular basis and encourage the widespread participation of regional and sectoral industrial associations. Nontariff restrictions, higher technological standards, and expertise have all compelled government officials to learn more about production processes, which in turn required closer cooperation with business. In the textile sector, for example, the Brazilian government turned to business representatives in order to understand production processes relevant for trade negotiations. 17

Moreover, governments in many emerging countries have set up information channels to allow at least a minimalist understanding of the functioning of the WTO.

Increased transparency and a reliable commitment to a long-term trade policy have been crucial factors in countries with unstable state structures to convince business representatives to invest time and resources in the negotiation process and to engage in formally accepted lobby practices [START_REF] Diniz | Globalização, Reformas Economicas e Elites Empresariais[END_REF].

The asymmetries of world trade have led the governments of emerging economies to search for more detailed knowledge. Although government officials working on trade matters became more numerous and were better trained (through the creation of a new career path as a specialist in foreign trade), countries consistently needed to integrate business input in order to strengthen the national position in the increasingly complex negotiations. Indeed, during the negotiation of the Free Trade Agreement of the Americas (FTAA) and the MERCOSUR-EU association, the Brazilian government's limited number of ill-prepared representatives confronted solid teams ("an army") of US and EU representatives. To make up for this asymmetry, Brazilian business representatives were henceforth included on Brazil's negotiation teams, a novelty if we take into account the peculiar isolationist culture of foreign trade decisions in this country during the time of MERCOSUR's launching.

Last but not least, the transparency associated with these negotiation processes (FTAA official forums between government and entrepreneurs) transposed a new culture of interaction between government and business on trade matters.

Yet the active solicitation of business input is not only common in emerging economies. [START_REF] Shaffer | Defending Interests: Public-Private Partnerships in WTO Litigation[END_REF] has shown this in great detail for the US and the EU. In particular, he underlines that the European Commission undertakes "reverse lobbying:" it constantly has to contact firms to contact it. Government representatives on both sides of the Atlantic engage in extensive outreach programs. In the US, the government used much of its early contacts with business to "try and inform them about why we thought [a particular negotiation] was a good idea." 18 The US government had to make an effort to get companies interested:

If you want a meeting, you call the companies. We didn't even know who they were, so we started casting the net and bringing them in. 19 For government representatives everywhere, consulting with companies was considered crucial: "All trade negotiations are done on behalf of our companies, so it is important that there is a continuous back and forth between them and the government." 20

Governments therefore solicit consultation with business experts, even though there can be differences between countries. Moving beyond lobbying for individual benefits is advantageous to business because it ensures a good working relationship with the Commission. In the US, the logic is similar. Studying service trade lobbying by large US financial companies, [START_REF] Yoffie | Creating Political Advantage: The Rise of the Corporate Political Entrepreneur[END_REF] suggest that American Express built "political capital" by developing an issue which had broad political appeal and fit into the agendas of key politicians, even though the significance of the issue for American Express' business operations was not certain.

Studying government solicitation is thus important for understanding what is demanded and supplied in a public-private partnership on international trade. Unlike the exchange model assumed in the traditional economic models, firms do not just exchange votes or money in order to lobby against regulation. Rather, they offer expertise and political support in exchange for access to the elaboration of specific stakes (see [START_REF] Bouwen | Corporate Lobbying in the European Union: The Logic of Access[END_REF].

Mutual dependence

The business-government relationships that have formed over time have turned out to be quite stable, at least on certain issues. As a representative from AT&T explained:

When I started [in 1992] it was more formal. We scheduled appointments to go see the government. Now we just talk. There has been less face-to-face and more emailing. 26 A government representative from the telecommunications sector confirmed, "it is a quite close knit telecom community in Washington, so we know who handles which issues." 27 In some cases, business representatives will continue to keep up their political contacts, even though they are not really interested in the current stakes. A European business representative qualified: "I don't really work on WTO affairs; I only participate in [the European association's] working group. We just try to follow what is going on." 28 Business representatives believe that somehow this political activity can pay off, even if their premier interests lie elsewhere. A representative from Spain's Telefónica explained:

In a way, the WTO was a very welcome way to seize this opportunity more fully. But the main initiative was investment, not our political representation. In business, you first try to open up new markets and then you start thinking about politics. For us, the WTO was an opportunity to assure that what we have put in place would continue in the adequate political framework. 29 In other words, political activity of firms in the government-created forums can at times be quite low. A European association representative working on the WTO even described its strategy as "a night train: there was a locomotive, some work cars and many sleeping cars." 30 Still, business-government relations continue to hold because they are mutually beneficial for both sides. Governments have access to technical information needed for multilateral talks and businesses have access to the policy process, which is highly valuable once they find that they need to express their opinion on a topic. A German business representative emphasized: "[W]e always try to be in unison with our government. It is never useful not to be in unison with our government." 31

As these close business-government relationships have become more common, expectations in emerging countries have risen that equally tight cooperation could emerge. But these expectations were sometimes frustrated. As the costs of continued business-government cooperation sometimes outweighs its benefits to governments in emerging countries, firms could not always count on being consulted and informed, like their counterparts in the US and the EU. In Brazil, as in other developing countries, the institutional settings and unbalanced relations between a strong state and a weak entrepreneurial class have created a similar lack of information. 32 Firms therefore followed WTO issues independently, resorting sometimes to extensive networks throughout the world where they can obtain information and pass it on to their local branches.

In many countries, however, business and government started cooperating regularly in order to keep up with the often extensive delegations from such countries as the US or the EU. As Stopford and Strange (1991) have suggested, international trade negotiation often turns into a competition between countries for world market shares. For governments, obtaining such share crucially depends on their continuous cooperation with national firms. The dependence of firms on governments is then matched by a dependence of governments on firms for information and technical expertise.

These examples show, first, that uncertainty is high in business-government relations on trade policy issues that go beyond multilateral tariff negotiations.

Uncertainty, in turn, implies that business representatives depend much more on their government counterparts than one would expect from the traditional literature on pressure groups. Second, government representatives are not simply the object of industry pressure; they actively solicit cooperation with business actors in order to obtain valuable technical expertise needed for the multilateral negotiations. This solicitation, in turn, comes with a new set of selection criteria of business partners.

For example, the success of firms might depend on whether they can signal successfully that there are credible and reliable partners for government consultation.

Third, the mutual dependence of business and government in the context of trade negotiations can lead to stable working relationships that can resemble a symbiosis or a particular form of national cooperation rather than pressure lobbying.

Research agenda

While we refer to the traditional type of business-government interaction as pressure lobbying, and to the newer type as regulatory trade lobbying or interactive relations, we would like to underline that both types are lobbying. That is, both involve the attempt by private actors to influence the decision of political actors in their favor. In the pursuit of their interests, firms nonetheless behave differently under pressure lobbying and regulatory lobbying. In regulatory contexts, firms are highly aware that their access to the decision-makers depends on being selected as a policy partner. They therefore have to signal that they are constructive consultants that can help increase the legitimacy of governmental decisions. This is done most effectively if firms are perceived to be not just self-interested, but if they propose general solutions. As [START_REF] Broscheid | Insider and Outsider Lobbying in the European Commission[END_REF] have argued for the European context, lobbyists therefore have to strike a delicate balance between arguing for their immediate interest and making more general 'public interest' arguments that will gain them access to the policy-process.

These observations help us to specify several hypotheses about when we should expect what kind of behavior in the context of multilateral trade negotiations.

We have seen that an understanding of the stakes and a capacity to evaluate the payoffs of negotiations is crucial to trade policy lobbying, which leads us to the first set of hypotheses:

1. When the stakes are clear, firms are more likely to try to exert pressure on their government representatives. Inversely, when the stakes are difficult to evaluate, firms will prefer to engage in consultation procedures.

Government solicitation furthermore plays an important role and varies depending on whether the issue that is negotiated multilaterally. Our second set of hypotheses therefore points to the way in which the degree of solicitation is connected with the resources business actors can employ for their lobbying efforts:

2. Solicitation is most likely when trade negotiations require technical expertise. When governments do not need to obtain technical expertise from firms, lobbying will rely more heavily on financial and electoral support and possibly public opinion.

The discretion that governments have in selecting private partners depends, in turn, on the institutional setting and the policy process of each country. Since it is generally deemed undesirable that government consults exclusively with business, many countries prescribe specific consultation procedures, which can in turn affect the competition between groups for access. Our third hypothesis connects the constraints in different settings with the most likely lobbying behavior:

3. When the policy process ensures through formal procedures that all stake-holders can participate, competition between groups will lead to more aggressive lobbying styles. Inversely, when access depends on the informal selection of business representatives by their respective governments, firms are more likely to enter into constructive cooperation.

Finally, we refer to recent studies on lobbying to limit this third hypothesis. As [START_REF] Naurin | Dressed For Politics: Why Increasing Transparency in the European Union Will Not Make Lobbyists Behave Any Better Than They Already Do[END_REF] has shown, corporate lobbyists can chose to exert pressure when they feel that their clients or association members are watching them. In cases where lobbying is delegated from firms to a business association (or even from firms to a relatively autonomous in-house lobbying department), lobbyists will be careful not make too many concessions to governments if the principals can monitor their entire work efforts. Under highly transparent procedures, lobbyists will continue to promote their immediate self-interests even if this implies less access in order not to anger the members of the business associations or their superiors (see also [START_REF] Coglianese | Seeking Truth for Power: Informational Strategy and Regulatory Policymaking[END_REF].

4. Accepting a trade-off between lobbying for one's immediate interest and lobbying for a public solution in order to gain access is most likely when transparency is low, however this assumption does not hold true in cases of pervasive rent-seeking relations. Inversely, under high transparency, aggressive self-interested lobbying might occur, even when governments have certain discretion over the selection of their business partners.

These four sets of hypotheses remain to be tested and articulated more systematically.

They are merely suggested here in order to clarify our observations and to move beyond a distinction of two fixed types of lobbying behavior. By specifying four hypotheses about the origins and components of our two types, we hope to indicate that the two might evolve or mix when the basis on which they rest changes.

Conclusion

This paper is motivated by a frustration with theoretical models of businessgovernment relations in the context of multilateral trade negotiations. While empirical studies of corporate political activities acknowledge a variety of lobbying methods and motivations, theoretical accounts of trade policy quite often rely on the simplified models that postulate business pressure for open or closed markets only. These models, however, rely on an outdated conception of the stakes of international trade negotiations. We have therefore attempted to bring together recent insights about the nature of multilateral trade talks with an analysis of business-government relations.

By pointing out that regulatory stakes and the legalization of trade create different kinds of business-government interactions, we caution against hasty conclusions about the power and influence of firms in international trade. When firms are solicited partners of governmental trade delegations, they do not necessarily wield the same influence as they do under successful pressure lobbying. Observing an increase in business participating on trade issues therefore does not necessarily imply that firms control multilateral trade talks (cf. [START_REF] Wallach | The WTO: Five Years of Reasons to Resist Corporate Globalization[END_REF]. On the contrary, the shift towards regulatory negotiations means that businesses have to master greater detail in order to capture a government's decision, and working on so many details at the same time can even be a risk for them. In some cases, firms are uncertain of the real effects of their actions and prefer to engage only moderately in on-going talks, so as "not to give rise to Frankenstein."

All in all, by distinguishing between business-government relations on tariff negotiations and on regulatory or legal issues, we do not want to suggest that the newer issues have entirely replaced pressure lobbying with regulatory lobbying. We simply call for a more nuanced treatment of business-government relations in trade policy analyses that considers the effects of different multilateral stakes on business demands and lobbying behavior. . We would like to thank David Levi-Faur, Nicolas Jabko, the participants of the two panels and two anonymous referees for their helpful comments. 2 Others have furthermore studied which institutional conditions allow industry demands to be more or less successful [START_REF] O'halloran | Politics, Process, and American Trade Policy[END_REF][START_REF] Lohmann | Divided Government and US Trade Policy: Theory and Evidence[END_REF][START_REF] Gilligan | Empowering exporters: reciprocity, delegation, and collective action in American trade policy[END_REF] In these account, industry lobbying might not have an impact on trade policy, but only because politicians were sufficiently insulated from industry pressure or because firms were unable to act collectively.

3 Safeguards still remain a popular target of lobbying activities by sectoral groups. Import duties applied by the US government on March 2002 on steel imports or the activity of European textile producers confronted to Chinese imports are among the latest. 4 The reader interested in the differences between the three political systems may turn to [START_REF] Shaffer | Defending Interests: Public-Private Partnerships in WTO Litigation[END_REF] and [START_REF] Schneider | Organzing Interests and Coalitions in the Politics of Market Reform in Latin America[END_REF].

5 Almost all interviews have been conducted in the native language of the interviewees. For simplicity, the quotes used in the following text have been translated into English by the authors.

6 By political opportunity structure, we mean the configuration of resources, formal and informal institutional arrangements and historical precedents that facilitate or constrain the access of nongovernmental actors to the policy process (Kitschelt, 1986: 58).

7 An interesting counter-example of this trend can be found in the difficulties that certain accessing countries have in implementing the WTO agenda: in the rather obscure lobby opportunity structure of Russia, big rent-seeking industrial groups will resist trade liberalization on grounds of protectionism, but also because they apprehend the costs of an increased transparency of the process (see [START_REF] Peregudov | Gruppy interesov i rossiiskoe gosudarstvo[END_REF]). 8 For instance, in Brazil's textile sector foreign firms operating on national soil during the 1990s did not support liberalizing policies due to their world corporate strategy, and this even though the sector remained competitive at an international level. 9 Interview with a government official of the Ministry of Foreign Affairs in Brasilia, September 2002. 10 The authors refers here to individual firms and specifically to existing branch associations at the beginning of the 1990 such as ABIT and Sinditextil. 11 Ibid.

12 Interview with a representative from Deutsche Telekom, July 2003. 32 Business representatives of MTN textile firms in Brazil acknowledged that their branch was not always informed of issues being negotiated and that it was not uncommon for them to activate their MTN networks and to receive expertise from other subsidiary firms.

  And industry is not used to working with them […] except in the UK."23 Nonetheless, the Commission tries quite actively to involve business representatives, not the least reason being that it needs to keep up with the wealth of technical information that the US government can provide due to its business consultation. A representative of an EU business association explained: "Quite often, the Commission will approach us to keep them informed about market barriers encountered: 'If you have a problem, please tell us!'" 24 Indeed, the Commission has made an enormous effort to cooperate more closely with business representatives in order to obtain technical expertise necessary to keeping up with their American counterparts. This effort has led to the creation of the Transatlantic Business Dialogue (TABD) in 1995 and smaller associations such as the European Service Forum, where European business leaders were given a chance to enter into contact and consultation with Commission officials[START_REF] Cowles | The Transatlantic Business Dialogue and Domestic Business-Government Relations[END_REF] Pollack & Shaffer, 2001). At the opening of the European Service Forum, former European trade Commissioner Sir Leon[START_REF] Brittan | European Service Leaders' Group, Speech at launching meeting of ESF[END_REF] underlined: represents very diverse interests. The only agreement they can find is liberalization. In Europe, what is possible is finding the common good. That's the reason why the position papers of AEA are almost 'extremist' -I say this without any negative connotation. They are radical; they push the logic to their very end. That's understandable. When you demand very specific things, you cannot always choose what you obtain [in the end]. And they do not want to give birth to Frankenstein. 25

The US administration has for a long time asked private sector representatives to join them. According to a European observer, sometimes "the US private sector delegation would be as large as the government delegation." 21 A US business representative confirmed that, "if you are a significant American company, a lot of times the government might ask you to be part of the delegation."

22

In Europe, the Commission also tries to work with business representatives but often find firms surprisingly uninterested. According to one US business representative, "[t]he difference is that governments [in Europe] are not used to working with industry.

I am in your hands to listen to what your objectives are. . . . I count on your support and input . . . so that we can refine our strategy and set out clear, priority negotiating objectives, which will make a difference in the international expansion of business.

For firms that want to work with the Commission, however, these forums imply a very particular kind of logic. Since the Commission can decide to consider or ignore business input, firms need to make constructive suggestions that help increase the Commission's political decisions. For the Association of European Airlines (AEA), this logic was quite noticeable: AEA

Figure 1: Drivers of International Trade

	High
	Oligopolistic Competition	Regulated Competition
	Global
	Concentration
	Comparative Advantage	Political Competition
	Low
	Low	High
	Government Intervention

Table 1 : Two types of business-government relations pressure lobbying on trade regulatory trade lobbying

 1 Earlier versions have been presented at the Third ECPR General Conference in Budapest in September 2005 and during a workshop on "Trade, regulation and non-governmental actors" at the Institut d'Etudes Politiques and the Centre d'Etudes en Relations Internationales (CERI) in Paris in June 2004

	goal of multilateral negotiations	opening/closing of domestic markets to foreign goods	internationalization of regulatory regimes in order to facilitate trade and trans-border operations
	typical means for achieving goal	tariffs or non-tariff barriers	regulatory reform or creation of international regulatory standards
	stake for economic actors	demands for or against market-opening	participating in the elaboration of targeted rules specifying how to liberalize
	lobbying mode	exerting pressure, consultation	consultation, cooperation
	principal resource	political support (financial or electoral)	technical expertise
			dependence on government
	principal constraint	competition between groups	solicitation; complexity and
			uncertainty

  13 Interview with a US business representative, Washington, D.C., 2 July 2003. 'None' answers the question about remaining market access restrictions.14 Ibid.15 Interviews in Brussels,Washington and São Paulo, November 2002, July 2003 and June 2003 respectively. 16 Interview with a Brazilian government representative, Brasilia, 15 September 2002.17 Interview with several textile representatives during 2002-2003. 18 Interview with a US government representative, Washington, D.C., 20 June 2003. 19 Interview with a US government representative, Washington, D.C., 18 June 2003. 20 Interview with a US government representative, Washington, D.C. 20 June 2003. Very similar statement were made by representatives from the European Commission and the Council Secretariat. 21 Interview, Brussels, 3 September 2003. 22 Interview with a US telecom operator, Washington, D.C., 25 June 2003. 23 Interview with a US based telecommunication service provider, Washington, D.C., 25 June 2003. 24 Interview in Brussels, 14 February 2003. 25 Interview with an official from the European Commission, 21 October 2003. 26 Interview with a US telecom provider, Washington, D.C., 24 June 2003. 27 Interview, Washington, D.C., 18 June 2003. 28 Telephone interview on 22 October 2003.

29

Telephone interview, 5 November 2003.

30

Interview in Brussels, 3 September 2003.

31

Interview with a European airline representative, 18 November 2002.

In the case of Latin America, free-trade agreements signed with the US have progressively included areas beyond WTO standards, inspired by the NAFTA(Roffe and Santa Cruz ,

2006).


Caroline Nadeau

Hongliang Ren

Alexandre Krupa

Pierre Dupont

Intensity-based Visual Servoing for Instrument and Tissue Tracking in 3D Ultrasound Volumes

Intensity-based Visual Servoing for Instrument and Tissue Tracking in 3D Ultrasound Volumes Caroline Nadeau, Hongliang Ren, Member, IEEE, Alexandre Krupa, Member, IEEE, and Pierre Dupont, Fellow, IEEE Abstract-This paper presents a three dimensional ultrasound (3DUS)-based visual servoing technique for intraoperative tracking of the motion of both surgical instruments and tissue targets. In the proposed approach, visual servoing techniques are used to control the position of a virtual ultrasound probe so as to keep a target centered within the virtual probe's field of view. Multiple virtual probes can be servoed in parallel to provide simultaneous tracking of instruments and tissue. The technique is developed in the context of robotic beating-heart intracardiac surgery in which the goal of tracking is to both provide guidance to the operator as well as to provide the means to automate the surgical procedure. To deal with the low signal-to-noise ratio (SNR) of the 3DUS volumes, an intensity-based method is proposed that requires no primitive extraction or image segmentation since it directly utilizes the image intensity information as a visual feature. This approach is computationally efficient and can be applied to a wide range of tissue types and medical instruments. This paper presents the first validation of these techniques through off-line robot and tissue tracking using actual in vivo cardiac volume sequences from a robotic beating-heart surgery.

Note to Practitioners-This article is motivated by the practical navigation problem in 3DUS-guided beating-heart robotic surgery. A real-time and robust robot guidance system is of great significance in computer-assisted and computer-navigated robotic surgeries. The current position-based ultrasound guidance systems typically involve sequential feature extraction followed by position estimation, while the proposed intensity-based ultrasound virtual servoing can directly track both tissue and instruments from the raw 3D images. Without necessitating segmentation or feature extraction, the proposed approach is efficient enough to be used in guiding the surgical robot to the target using real-time 3DUS. The implementation is based on virtual probe servoing and can be extended to other similar volumetric image-based servoing problems in industrial applications. The proposed algorithm can be implemented as a plug-in module, which could be easily integrated into existing imageguided robotic surgery platforms.

Index Terms-3D Ultrasound, Visual Servoing, Instrument Tracking, Robotic Surgery, Real-time

I. INTRODUCTION

T HREE dimensional US-guided robotic beating heart surgery is an emerging computer-assisted surgical technique [START_REF] Gosline | Percutaneous Intracardiac Beating-heart Surgery using Metal MEMS Tissue Approximation Tools[END_REF], [START_REF] Vasilyev | Percutaneous Steerable Robotic Tool Delivery Platform and Metal MEMS Device for Tissue Manipulation and Approximation: Initial Experience with Closure of Patent Foramen Ovale[END_REF]. As shown in Fig. 1 heart through the vasculature to deploy tools and devices. Substantial challenges to surgeon-guided robot navigation and tissue manipulation arise, however, owing to both the 3D nature of the image sets as well as to image noise. These issues can lead to surgeon disorientation and lack of precision. These challenges can be greatly reduced by automatically tracking the robot tip as well as the surgical tissue targets and using this information to create virtual overlays [START_REF] Peters | Image-guidance for surgical procedures[END_REF]- [START_REF] Hungr | A 3-D Ultrasound Robotic Prostate Brachytherapy System With Prostate Motion Tracking[END_REF] or to automate certain surgical motions [START_REF] Padoy | Human-machine collaborative surgery using learned models[END_REF].

While exhibiting a lower signal-to-noise ratio compared to other imaging modalities, 3DUS does offer the possibility to extract, intra-operatively and in real time, the motion of multiple targets. Owing to the differences in acoustic impedance of tissue and metal instruments [START_REF] Huang | Imaging Artifacts of Medical Instruments in Ultrasound-Guided Interventions[END_REF], however, prior work has focused on either instrument tracking or tissue tracking as summarized below.

As 3DUS technology is emerging recently in practice, there is a modest amount of prior work on this topic and algorithms typically utilize knowledge of the instrument's geometry to perform tracking [START_REF] Novotny | GPU based real-time instrument tracking with three dimensional ultrasound[END_REF], [START_REF] Yuen | Robotic motion compensation for beating heart intracardiac surgery[END_REF]. Most of these techniques are dedicated to straight tool shaft detection based on linear discrimination algorithms including Principle Component Analysis (PCA) [START_REF] Stoll | Passive Markers for Tracking Surgical Instruments in Real-time 3D Ultrasound Imaging[END_REF], Hough transforms [START_REF] Ding | Automatic needle segmentation in 3d ultrasound images[END_REF] or Radon transforms [START_REF] Novotny | GPU based real-time instrument tracking with three dimensional ultrasound[END_REF]. In [START_REF] Ren | Detection of curved robots using 3d ultrasound[END_REF], [START_REF] Ren | Tubular Enhanced Geodesic Active Contours for Continuum Robot Detection using 3D Ultrasound[END_REF], a new decoupled method was proposed to detect robots of known curvature, however, it was limited to objects of a specific geometry. In contrast, the method presented here is an intensity-based visual servoing approach that does not require a priori knowledge of the target shape and can therefore be applied to a wide range of surgical instruments and robots.

Real-time tissue tracking in 3DUS volumes has been investigated in several contexts. For example, tracking of the blood-tissue boundary inside the heart has been performed in order to maintain a given offset distance between an instrument tip and the tissue [START_REF] Yuen | Robotic Tissue Tracking for Beating Heart Mitral Valve Surgery[END_REF]. Tissue tracking in this approach is facilitated by tracking the instrument axis. Other proposed approaches for US-based tissue tracking predominantly use 2D images. In [START_REF] Abolmaesumi | Image-guided control of a robot for medical ultrasound[END_REF], five feature extraction methods, based on image similarity measure or on contour segmentation, are compared to track an anatomical point corresponding to the center of an artery as a 2DUS probe is moved robotically along the vessel. A segmentation step is also required in [START_REF] Koizumi | Construction Methodology for NIUTS Bed Servoing System for Body Targets[END_REF] in order to compute the 3D position of a kidney stone in a lithotripsy procedure and in [START_REF] Mebarki | 2D ultrasound probe complete guidance by visual servoing using image moments[END_REF], where six geometric features are used for the tracking of an anatomic target. Contour segmentation proves to be effective with convex targets, but is generally time-consuming and not adapted for complex organ shapes, nor to the use of noisy 3DUS volumes provided by a matrix- array 3D probe.

In the proposed approach, visual servoing algorithms are utilized to perform both instrument and tissue tracking without requiring any assumption on object geometry or any segmentation step. This is a new method compared with conventional 3DUS-based target motion tracking or imageless motion tracking as surveyed in [START_REF] Ren | Detection of curved robots using 3d ultrasound[END_REF]. Previous work [START_REF] Nadeau | Intensity-based ultrasound visual servoing: modeling and validation with 2D and 3D probes[END_REF] in ultrasound-based visual servoing involved physically moving a robot-mounted probe to maintain a tissue target within the probe's field of view and so to compensate for organ motion. In contrast, the approach proposed here is to track the target motion using a virtual probe's field of view defined by a 3D region of interest (ROI). The ROI is automatically moved within the 3DUS volume to compensate for both target and probe motions. With respect to our previous work [START_REF] Nadeau | Intensity-based ultrasound visual servoing: modeling and validation with 2D and 3D probes[END_REF], we present here the first results of the intensity-based approach using 3D information provided by a matrix array probe. We are then able to demonstrate the robustness of the approach for actual surgical volume sets that include fast disturbance motion arising from the heartbeat. Moreover, the visual servoing is applied here for tracking not only the cardiac motion but also the insertion of a surgical tool into the heart.

The structure of this paper is as follows. Section II defines the proposed visual servoing technique, it includes subsections describing the use of image intensity as a visual feature and also provides the model for the interaction matrix that relates intensity variations to motion. Section III describes the collection of surgical image data and off-line robot and tissue tracking performed with the surgical data. Conclusions appear in the final section of the paper.

II. TRACKING USING VIRTUAL PROBE VISUAL SERVOING

The principle of the image-based visual servoing applied to the virtual probe is illustrated in Fig. 2. A closed-loop approach is considered where at each time t, a set of current visual features s(t) extracted from the image acquired by the visual sensor is compared to the set of desired visual features s * , characterizing the target.

The control velocity v p applied to the virtual US probe is computed so as to minimize the visual error e(t) = s(t)-s * . To obtain an exponential decrease in the visual error, the classical control law [START_REF] Espiau | A new approach to visual servoing in robotics[END_REF] is used

v p = -λ L s + (s(t) -s * ) , ( 1
)
where λ is the controller gain and L s + is the pseudo-inverse of an estimate of the interaction matrix L s that relates the variation of the visual features to the velocity v p .

In the proposed approach, v p defines the velocity of a virtual 3DUS probe (defined by a 3D ROI) that moves with respect to the actual ultrasound probe so as to maintain the visual features within the virtual probe's field of view. In other words, v p is applied to the ROI within the actual US probe's field of view so as to track the motion of the considered target.

A. Image intensity as visual feature

With visual servoing techniques, the efficiency of the control law is highly dependent of the choice of visual features. Typically, geometric features, which can be extracted by various methods based on image similarity measures, contour segmentation or image processing (threshold and morphological operators), are well adapted for controlling the motion of the visual sensor. However, the processing of US images is often more complex than with other imaging modalities due to the speckle generated by the propagation of the US waves in soft tissues. To avoid the computational complexity of such approaches, an alternate technique is adopted here in which the intensity values of the voxels of the 3D ROI are used as the visual features, s,

s = (I 1,1,1 , ..., I u,v,w , ..., I M,N,L ) , (2)
where M, N and L are respectively the width, the height and the depth of the ROI, I u,v,w is the intensity, expressed in grey level and (u, v, w) are the 3D voxel coordinates in the US volume. In consequence, the image processing step of the original ultrasound volume reduces to extracting the intensities of the voxels contained in the ROI. Computing ROI velocity from the intensity-based feature vector depends on formulating the interaction matrix L s , as described below, that links the variation of these image features to the motion of the virtual 3DUS probe.

B. Formulation of the interaction matrix

The interaction matrix involved in the control law (1) can be derived from the time derivative of the visual features vector s(t). The objective is then to determine an analytic form for the time variation of a single voxel intensity in the 3DUS image as a function of the virtual probe velocity v p , that is to find L I u,v,w such as:

İu,v,w (t) = L I u,v,w v p .

At time t, I u,v,w (t) corresponds to the amplitude I US (x(t),t) of the US echo reflected by the physical point P with coordinates x(t) = [x(t); y(t); z(t)] in the US probe frame. Given a fixed 3DUS probe, these coordinates are time varying due to the motion of the scene (physiological motion of the patient or motion of a surgical instrument) and the total derivative of the amplitude

I US (x(t),t) is İUS (x(t),t) = ∂ I US (x(t),t) ∂ x ẋ(t) + ∂ I US (x(t),t) ∂t (3)
The interaction matrix estimation relies on the hypothesis of the constancy of the US wave reflection from a physical 3D point. While this is a strong hypothesis since the intensity of the US echo reflected by an organ interface is dependent on the relative orientation of the US probe to this interface, this conservation equation has been empirically validated in [START_REF] Nadeau | Intensity-based ultrasound visual servoing: modeling and validation with 2D and 3D probes[END_REF] where a 2D intensity-based approach was applied to move a real 2D US probe interacting with an abdominal phantom.

The time invariance of the intensity of a 3D point is written as ∂ I US (x(t),t) ∂t = 0, which allows the reduction of eq.( 3) as follows:

İUS (x(t),t) ≈ ∂ I US (x(t),t) ∂ x ẋ(t). (4)
Here, the interaction matrix associated with a 3D point, L x , can be introduced and defined as:

ẋ(t) = L x v p . (5)
According to Varignon's formula for velocity composition in a solid [19], this interaction matrix is computed with the skew-symmetric matrix of the vector cross product [x] × , that only depends of the coordinates of the 3D point:

L x = I 3 -[x] × =   1 0 0 0 z -y 0 1 0 -z 0 x 0 0 1 y -x 0   . (6)
Combining ( 4), ( 5) and ( 6) results in

İUS (x(t),t) ≈ ∇I u,v,w I 3 -[x] × v p (7)
with ∇I u,v,w = [∇I x ∇I y ∇I z ] defined as the 3D image gradient associated with the voxel (u, v, w). It is comprised of three components,

∇I x = ∂ I u,v,w ∂ x , ∇I y = ∂ I u,v,w ∂ y and ∇I z = ∂ I u,v,w
∂ z that describe the intensity variation of the voxel (u, v, w) along the three orthogonal axes of the US image frame. With a 3D probe, these three components are directly obtained with three 3D derivative filters applied to the current 3DUS image [START_REF] Nadeau | Intensity-based ultrasound visual servoing: modeling and validation with 2D and 3D probes[END_REF].

The interaction matrix L I u,v,w ∈ ℜ 1×6 associated with the visual feature I u,v,w can now be written as

L I u,v,w = [ ∇I x ∇I y ∇I z y∇I z -z∇I y -x∇I z + z∇I x x∇I y -y∇I x ] , (8)
in which the coordinates of the 3D point are deduced from the coordinates of the voxel (u, v, w) in the ROI and from the intrinsic parameters of the 3D probe:

  x y z   =   sz x (u -u 0 ) sz y (v -v 0 ) sz z (w -w 0 )   , (9)
with (sz x , sz y , sz z ) the size of one voxel and (u 0 , v 0 , w 0 ) the coordinates of the ROI center.

The complete interaction matrix L s , built by stacking the L × M × N matrices L I u,v,w , can then be computed at each iteration of the algorithm using information entirely contained in the current 3DUS image:

L s =    L I 1,1,1 . . . L I M,N,L   . (10)

III. EXPERIMENTS

To evaluate the tracking algorithm, 3DUS image sequences were collected at the maximum rate of the scanner (25Hz) during a robotic beating-heart Patent Foramen Ovale (PFO) closure procedure in a porcine model as shown schematically in Fig. 1 (See [START_REF] Gosline | Percutaneous Intracardiac Beating-heart Surgery using Metal MEMS Tissue Approximation Tools[END_REF], [START_REF] Vasilyev | Percutaneous Steerable Robotic Tool Delivery Platform and Metal MEMS Device for Tissue Manipulation and Approximation: Initial Experience with Closure of Patent Foramen Ovale[END_REF]). As described below, these sequences were then imported into a software simulation program that implemented the proposed tracking algorithm at the same 25Hz rate used for data collection. Yorkshire pigs (50-70 kg) were used in these experiments to approximate human procedures and their use and treatment followed a protocol approved by the Animal Care and Use Committee of the host institution (BCH).

During the procedure, a concentric tube robot [START_REF] Dupont | Design and control of concentric-tube robots[END_REF] comprised of three telescoping curved sections was inserted into the jugular vein and navigated to the right atrium of the heart under 3DUS guidance. The robot sections include a long proximal section for Navigation through the jugular vein (segment 1N in Fig. 1) and two distal Manipulation sections (segments 2M and 3M in Fig. 1) for tissue manipulation and device deployment inside the atrium.

As shown in Fig. 3, the matrix-array 3D probe was positioned epicardially on the porcine heart to image the robotic instrument tip as well as the tissue inside the right atrium. Note that the position of the porcine lung precluded the use of a transesophageal probe as would be employed in a human procedure.

The 3D image acquisition system was an IE33 system (Philips Medical Systems) which was used to acquire US volumes at a frame rate of 25 Hz for a duration of 10 seconds. Standard settings of the imaging parameters were used during image generation, including 50% overall gain, 50% compression rate, high density scan line spacing, 6 cm image depth, and zero dB power level. The resulting voxels have anisotropic spacing of 0.290 mm, 0.342 mm, 0.456 mm in the x, y and z directions, respectively.

A tracking and rendering software package was implemented as shown in Fig. 4 that could load 3DUS imaging sequences and perform visual-servoing-based tracking on userdefined ROI's. The surgical volume sequence consisted of 250 Beating-heart intracardiac surgery with 3DUS probe manually positioned on the epicardial surface.

Porcine heart 3D US probe

US volumes that could be played back at the real-time 25Hz rate in the simulator. All image processing to execute the visual-servoing-based tissue tracking is performed at the realtime rate (25Hz) corresponding to the acquisition time of a US volume by the 3D probe.

Heart motion is visualized using two orthogonal images (with green and red contours as shown in Fig. 4, left) as well as an additional view displaying the virtual probe controlled by the proposed intensity-based visual servoing. The first image volume of the data set is used to graphically allow the user to delineate the desired anatomic structure by a bounding box (see Fig. 4, right) that is then used as the 3D ROI by the tracking control law.

In the current implementation, the tracking law assumes rigid motions. While this applies directly to the robot tip, the ROI for tissue tracking must be selected to be sufficiently small so that its motion is approximately rigid. For the tested data set, this corresponds to a ROI size of 40 × 25 × 10 voxels for tissue tracking and of 25 × 25 × 10 voxels for robot tracking.

A. Tissue Target Tracking

For PFO closure, a device must be inserted into the septal ridge above the PFO channel. In order to track the anatomic motion of this ridge, we define it as our tissue target and include it in an ROI. This ROI is a volume of about 1.2 cm × 0.9 cm × 0.5 cm that is manually defined in the first US image of the acquired sequence (see cyan rectangle in Fig. 5(a), which corresponds to a central slice of the ROI). The visual features vector involved in the control law is then constituted of all the voxel intensities belonging to the ROI. During the subsequent tracking, the velocity computed by visual servoing (1) is applied to this ROI. The gain λ is manually adjusted to ensure the best dynamics of the system while keeping it stable and the visual control law is applied several times on the same US volume until a new one is available. This strategy ensures a good tracking accuracy and is possible since the control loop period is about 10 ms while the image acquisition time is 40 ms. In this example, the motion compensated through tracking is predominantly due to beating of the heart. Fig. 5 provides a visual validation of the tracking performance by comparing the ultrasound images of an ROI fixed with respect to the 3D volume (Fig. 5(c)) with an ROI that is updated by tracking compensation (Fig. 5(e)).

The difference image, I di f f , between the current image I and the desired one I * is defined by

I di f f =
(I -I * ) + 255 2 and depicted for the cases of no compensation (Fig. 5(d)) and compensation (Fig. 5(f)). The effectiveness of the compensation can be seen by comparing the uniformly gray ROI in Fig. 5(f) that results from compensation with the strong gradients occurring in the uncompensated difference image ROI of Fig. 5(d). Image tracking error can also be defined quantitatively as the Euclidean norm of the visual vector normalized by the number of voxels N vox in the considered ROI, as given in ( 11) and as appears in Fig. 5(b). It can be seen that compensation reduces the norm of the error vector by a factor of about 3.5.

C = (s -s * ) (s -s * ) N vox . (11)

B. Robot motion tracking

Experiments were also performed to evaluate the intensitybased visual servoing for tracking robot motion during surgery. In this case, the desired ROI was defined to include the robot tip and once again the visual features vector was constructed with the intensities of every voxel belonging to this ROI (see cyan rectangle in Fig. 6). The image volume sequence analyzed corresponded to the operator moving the tip inside the right atrium of the beating porcine heart. The motion corresponds to a forward and backward translation along the direction of the tool shaft.

Robot tip motion is automatically tracked by the proposed intensity approach during its movement as shown in Fig. 6. In order to most effectively visualize the performance of the tracking algorithm, the 2D US slice passing through the center of the defined ROI is displayed for both non-compensated (Fig. 6 140) and removal (from iteration 140 to iteration 250) of the robot. Indeed, the detected displacement axis, shown as the red dotted line in Fig. 6(a), can be seen to be approximately given by the the 3D vector (1 -1 0) .

IV. CONCLUSIONS The new direct visual servoing method proposed in this paper provides a real-time estimation and compensation of rigid motions in 3DUS volume sequences. Its effectiveness has been illustrated using data from an actual robotic beating-heart surgery. These experiments provide validation of the proposed approach both for tracking the rigid motion of robotic tools and also for tracking the quasi-rigid motion of heart tissue.

As a next step, the methods will be extended to investigate non-rigid tissue motions using a deformable 3D grid instead of a rigid ROI. Deformation will be accommodated using parametric model based, for example, on 3D thin-plate splines. The objective will be to estimate the variation of the deformable model parameters directly from intensity difference as measured in successive volumes. In future applications, the proposed target tracking approach will be employed to automatically reach and track a target of interest inside the beating heart.

Fig. 1 .

 1 Fig. 1. Schematic of beating heart closure of a Patent Foramen Ovale (PFO) using real-time 3DUS guidance. Robot is comprised of three telescoping sections. Section 1N is for navigation through the jugular vein into the right atrium. Sections 2M and 3M are used to position and orient the robot tip within the right atrium.

Fig. 2 .

 2 Fig. 2. Image-based visual servoing applied to the virtual probe.

Fig. 3 .

 3 Fig. 3.Beating-heart intracardiac surgery with 3DUS probe manually positioned on the epicardial surface.

Fig. 4 .

 4 Fig. 4. Visualization of the tracking results with a simulator developed with the VTK library [22]. (left) The US volume loaded in the simulator is displayed with two orthogonal planes. (right) Two different ROI, displayed in orange in purple, can be tracked using the proposed visual servoing.

Fig. 5 .

 5 Fig. 5. Tracking results for cardiac tissue. (a) Desired anatomic target is selected by defining the ROI. (b) Visual error with and without compensation. (c) Uncompensated cardiac motion leads to target tissue moving out of ROI. (d) Difference image without compensation. (e) With compensation target tissue remains within ROI. (f) Difference image with compensation.

ACKNOWLEDGMENT

  This work was supported by the National Institutes of Health under USA grants R01HL073647, R01HL087797, Singapore Academic Research Grant R-397-000-139-133 and the US-Comp project of the French National Research Agency.

  -No compensation (b)-With compensation

Fig. 6 .

 6 Fig. 6. Robot tracking results. (a) Without compensation, robot tip moves wrt the ROI (displayed in cyan). (b) With compensation, robot tip is kept centered in the ROI. (c) ROI position and orientation wrt the initial image frame when the robot tip is tracked. The θ u representation of orientation is considered, where u = (u x u y u z ) is a unit vector representing the rotation axis and θ is the rotation angle.