What is the relationship between ¹8F-FDG aortic aneurysm uptake on PET/CT and future growth rate?

PURPOSE: In this study we investigate the relationship between (18)F-fluorodeoxyglucose (FDG) metabolism and future aneurysm expansion measured by serial duplex ultrasound. Current screening programmes are increasing the identification of patients with abdominal aortic aneurysm (AAA). The management of these patients remains challenging and methods of risk stratification are sought. METHODS: Thirty-four consecutive patients [31 men, 3 women, median age 75 years, interquartile range (IQR) 71-78] with aortic aneurysms under routine surveillance with serial ultrasound were prospectively recruited for (18)F-FDG positron emission tomography (PET)/CT. A whole vessel type analysis was performed measuring the highest aortic wall (18)F-FDG uptake (standardized uptake value or SUV(max)), and target to background ratio (TBR) for each axial image and median SUV(max) and TBR value were calculated. Institutional Review Board permission and informed patient consent were obtained. RESULTS: Nine patients failed to undergo 12-month follow-up study (deceased n = 2, withdrew n = 1, failed to attend ultrasound scan n = 5, emergency aneurysm repair n = 1) leaving 25 patients for analysis. The median whole vessel SUV(max) was 1.70 (IQR 1.45-2.08). The median whole vessel TBR was 1.15 (IQR 1.00-1.40). The median aneurysm expansion at 12 months was 2.0 mm (IQR 0.5-5.0). The correlation (r) between (18)F-FDG SUV(max) and ultrasound expansion at 1 year was -0.501 (p = 0.011). CONCLUSION: The preliminary findings from this observational longitudinal pilot study suggest that there is an inverse trend between (18)F-FDG uptake on PET and future AAA expansion. Aortic aneurysms with lower metabolic activity may therefore be more likely to expand.

Assessment of left ventricular function at rest using rubidium-82 myocardial perfusion PET: comparison of four software algorithms with simultaneous 64-slice coronary CT angiography.

OBJECTIVE: Left ventricular function is prognostically important. Our aim was to validate different algorithms' measurements with rubidium-82 PET, using computed tomography (CT) acquired simultaneously on hybrid imaging. METHODS: Fifty patients (33 men, 17 women, mean age 59 years SD 12) referred for coronary artery disease evaluation underwent rubidium-82 PET myocardial perfusion scintigraphy and 64-slice CT coronary angiography simultaneously on hybrid PET/CT. Left ventricular ejection fraction, end-systolic volume and end-diastolic volume from quantitative gated PET at rest, were calculated using quantitative gated single-photon emission computed tomography (QGS), Emory Cardiac Toolbox (ECT), Myometrix and CardIQ Physio software and then compared with CT. The paired t-test and Bland-Altman plots were used for analysis. RESULTS: There was no significant difference between CT and both QGS and ECT for calculating ESV. Otherwise there were significant differences (t-test, P<0.05) between CT coronary angiography and all other software algorithms in calculating systolic and diastolic volumes. Bland-Altman analysis revealed a bias towards underestimating end-diastolic volume with mean differences of 32.3, 34.8, 42.6 and 35.7 ml for QGS, ECT, Myometrix and CardIQ Physio, respectively. The limits of agreement (mean bias+/-1.96 SD) for left ventricular ejection fraction (%) were 8.5+/-21.0, 12.9+/-21.0, 3.5+/-18.9 and 5.6+/-17.1, for QGS, ECT, Myometrix and CardIQ Physio, respectively. CONCLUSION: The systematic error (or mean bias) of the Myometrix algorithm is the smallest, and CardIQ Physio shows the least statistical error (or limits of agreement) when calculating ejection fraction from rubidium-82 myocardial perfusion PET, compared with QGS and ECT. The wide limits of agreement between the different algorithms mean that they are not interchangeable.