Original article Assessment of non-reperfused and reperfused myocardial infarction using diffusible or deposited radiolabelled perfusion imaging agents L. M. Riou 1 , A. Broisat 1 , C. Lartizien 2 , M. C. Toufektsian 3 , S. Maitrejean 4 , M. Janier 2 , G. Vanzetto 1 , D. Fagret 1 , C. Ghezzi 1 1 INSERM, U340 Radiopharmaceutiques Biocliniques; Université de Grenoble, 38700 La Tronche, France 2 Plateforme ANIMAGE, CERMEP, Lyon, France 3 Laboratoire NVMC, Faculté de Médecine de Grenoble, Grenoble, France 4 Biospace Mesures, Paris, France Received: 10 May 2006 / Accepted: 17 July 2006 / Published online: 27 September 2006 © Springer-Verlag 2006 Abstract. Purpose: Incomplete microvascular reperfusion is often observed in patients undergoing thrombolytic therapy or angioplasty for acute myocardial infarction and has important prognostic implications. We compared the myocardial uptake of diffusible ( 201 Tl) and deposited ( 99m TcN-NOET) perfusion imaging agents in the setting of experimental infarction. Methods: Rats were subjected to permanent coronary occlusion (OCC, n=10) or to 45-min occlusion and reperfusion (REP, n=17). Seven days later, the tracers were co-injected and the animals were euthanised 15 min (all ten rats in the OCC group and 12 rats in the REP group) or 120 min (five rats from the REP group, euthanised at this time point to evaluate any redistribution of the tracers: REP- RED group) afterwards. Infarct size determination and 99m TcN-NOET/ 201 Tl ex vivo imaging were performed. Regional flow and tissue oedema were quantified using radioactive microspheres and 99m Tc-DTPA, respectively. Results: 99m TcN-NOET and 201 Tl defect magnitudes were similar in OCC animals (0.11±0.01 vs 0.13±0.01). In REP animals, 201 Tl defect magnitude (0.25±0.02) was signifi- cantly lower than the magnitude of 99m TcN-NOET and flow defects (0.14±0.03 and 0.17±0.01, respectively; p<0.05), despite the lack of 201 Tl redistribution (REP-RED animals). 99m Tc-DTPA indicated the presence of oedema in the reperfused area. Blood distribution studies showed that, unlike 99m TcN-NOET, 201 Tl plasma activity was mostly unbound to plasma proteins. Conclusion: 99m TcN-NOET and 201 Tl delineated the non- viable area in chronic non-reperfused and reperfused myo- cardial infarction. The significantly decreased 201 Tl defect in reperfused infarction was likely due to partial diffusion of the tracer from the plasma into the oedema present in the infarcted area. Deposited perfusion tracers might be better suited than diffusible agents for the assessment of regional flow following reperfusion of myocardial infarction. Keywords: Radiopharmaceuticals – Myocardial blood flow – Nuclear imaging – Myocardial infarction Eur J Nucl Med Mol Imaging (2007) 34:330–337 DOI 10.1007/s00259-006-0230-3 Introduction Reperfusion of infarcted myocardium is often incomplete, and numerous studies have demonstrated a progressive impairment in regional myocardial blood flow (RMBF) following reperfusion of a previously ischaemic area [1–5]. Clinically, areas of microvascular obstruction as identified with myocardial contrast-enhanced echocardiography are observed in a significant proportion of patients achieving thrombolysis in myocardial infarction (TIMI) grade 3 flow following coronary angioplasty [6]. In this regard, the presence of microvascular obstruction in the reperfused area is predictive of late wall thinning and poor functional recovery [7] and is a prognostic marker of post-infarction complications [8]. Radiolabelled perfusion imaging agents are routinely used for the assessment of myocardial perfusion and viability in patients with known or suspected coronary artery disease [9]. Lund et al. have shown that patients with microvascular obstruction have larger infarct sizes as determined using the diffusible radiolabelled perfusion tracer thallium-201 ( 201 Tl) [10]. It has also been suggested that microvascular dysfunction without angiographically significant coronary artery disease may be evidenced with the diffusible perfusion tracer 99m Tc-sestamibi [11]. L. M. Riou ()) INSERM, U340 Radiopharmaceutiques Biocliniques; Université de Grenoble, 38700 La Tronche, France e-mail: Laurent.Riou@ujf-grenoble.fr Tel.: +33-47-6637509, Fax: +33-47-6637142 European Journal of Nuclear Medicine and Molecular Imaging Vol. 34, No. 3, March 2007