A. Broisat

Equivocal usefulness of FDG for the noninvasive imaging of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAA) usually progress asymp-tomatically and are undetected until rupture occurs. Onceruptured, the mortality rate of AAA is about 80 %. Amongall patients with ruptured AAA, about one-third die withoutreachinghospital,andaboutanotherquarterreachhospitalbutdie prior to surgical intervention. Among the remaining pa-tients (about 40 %) surviving AAA rupture long enough tobenefit from surgical intervention, the perioperative mortalityhas historically reached about 50 % [1], a value that hashowever recently decreased owing to the introduction ofendovascular repair [2]. On the other hand, elective AAArepair has a much lower in-hospital mortality rate, with re-cently reported values of 1.3 % and 4.7 % for endovascularand open surgical repair, respectively [3], thereby stronglyemphasizingtheneedforscreeningandidentificationofthosepatients with prone-to-rupture AAA.The crude estimate of AAA diameter remains the mostwidely used predictive risk factor for AAA rupture and thesole therapeutic management criterion. Indeed, in both the2014EuropeanSocietyofCardiologyandthe2011AmericanCollege of Cardiology/American Heart Association guide-lines, aortic repair is a class I indication if the AAA diameterexceeds55mm[4,5].However,thelimitationsofthisparam-eter are well acknowledged, and it is therefore unanimouslyagreed that a more robust noninvasive predictor of the indi-vidual riskofAAA rupture is required. Althoughbeing muchless documented than atherogenesis, the current knowledgeregarding the pathophysiology of AAA indicates that parietalinflammation, matrix degradation and smooth muscle cellapoptosis are required for AAA pathogenesis [6]. FDG hasbeen suggested as a potentially useful agent for the molecularimaging of vascular inflammation due to the elevated carbo-hydratemetabolismofextravasatedinflammatorycells[7].Assuch, the tracer has been extensively evaluated in both theexperimentalandclinicalsettingsforthenoninvasiveimagingof inflammatory processes in vulnerable atherosclerotic le-sions as well as in AAA.In the multicentre study by Barwick and colleagues pub-lished in this issue of the European Journal of Nuclear Med-icine&MolecularImaging[8],theauthorsusedPETimagingof FDG uptake to retrospectively compare the metabolicactivity in the abdominal aortic wall of 151 patients withAAA (mean aortic diameter, 50±13 mm) with that of 159individuals with no AAA (mean aortic diameter, 21±3 mm)and matched for age, sex, diabetes, smoking status, statin useand indication for PET/CT. This cohort is the largest so farused for the comparison of FDG uptake between AAA andnormal vessels in well-matched patients. FDG uptake wasanalysed by semiquantitative visual scoring as well as quan-titatively using SUVmax and target to background ratiosutilizing mediastinal blood pool or descending thoracic aortaactivities for normalization.Althoughthe retrospective natureand the design of the study limit the conclusions that can bedrawn with respect to the potential of FDG for predictingAAA growth or rupture, the results unequivocally show thatthere was no correlation between AAA size and FDG uptakeand that there was no statistically significant difference inFDG uptake between AAA and normal abdominal aortas.The study by Barwick et al. therefore joins the ranks ofthose suggesting the suboptimal usefulness of FDG for AAAevaluation, which face the ranks of previously publishedstudies that reached opposite conclusions by suggesting the

Translating Molecular Imaging of the Vulnerable Plaque—a Vulnerable Project?

Translating Molecular Imaging of the Vulnerable Plaque—a Vulnerable Project? Gezim Bala, Alexis Broisat, Tony Lahoutte, Sophie Hernot 1 In vivo Cellular and Molecular Imaging (ICMI/BEFY), Vrije Universiteit Brussel, Brussels, Belgium Department of Cardiology, UZ Brussel, Brussels, Belgium Radiopharmaceutiques Biocliniques, INSERM, 1039-Université de Grenoble, La Tronche, France Department of Nuclear Medicine, UZ Brussel, Brussels, Belgium

Myocardium segmentation on 3D spect images

This paper presents a segmentation process of the myocardium, endocardium and epicardium surfaces of the heart from 3D SPECT images to compute a heterogeneity index. This index represents the distribution of the activity in the myocardium. Because of the low resolution of SPECT images, the thickness of the myocardium is 1 to 4 voxels and a sub-voxel accuracy is therefore needed. The segmentation process is based on the minimization of an energy by dynamic programming after a coarse segmentation to define the center surface of the myocardium. A Gaussian mixture is fitted on the data to ensure subvoxel accuracy. The heterogeneity index is compared to the reference index on 58 SPECT images and the segmentation is visually validated on 300 SPECT images by a clinician.

Novel SPECT perfusion imaging agents with improved myocardial or liver kinetics: Experimental studies and the need for clinical evaluation

the suboptimalphysical characteristics of the historical agent Tl-201have prompted the development of Tc-99 m-labeledmyocardial perfusion imaging agents with more favor-able emission energy and dosimetry. For a number ofreasons that were addressed in the abovementionededitorial, and despite excellent myocardial extractionand encouraging clinical results, the neutral and lipo-philic tracers TcN-NOET and Tc-TEBOROXIME havenot reached routine clinical use.