Comparison of measures of left ventricular function from electrocardiographically gated82Rb PET with contrast-enhanced CT ventriculography: A hybrid PET/CT analysis

Because of the ultrashort tracer half-life and high positron energy of ⁸²Rb, PET images acquired with this tracer are noisier and of lower resolution than those obtained with other PET tracers. The validity of electrocardiographic gating using ⁸²Rb for assessment of left ventricular (LV) function is not well established. To support feasibility, we compared functional parameters from gated ⁸²Rb PET with simultaneous high-resolution contrast-enhanced CT ventriculography, obtained as a byproduct a CT coronary angiography during hybrid cardiac PET/CT. Methods: A total of 24 patients underwent PET/CT, consisting of rest and dipyridamole ⁸²Rb perfusion studies and contrast-enhanced CT angiography, using a 64-slice scanner, for the workup of coronary artery disease. From gated PET images, LV ejection fraction (EF), end-diastolic volume (EDV), and end-systolic volume (ESV) were calculated using 2 commercial products. For functional CT analysis, commercial software using endocardial contour detection was applied. Results: Inter- and intraobserver agreement was good for all methods. On CT, EF was 66% ± 13%, ESV was 41 ± 29 mL, and EDV was 115 ± 36 mL. On PET, EF during dipyridamole was 56% ± 15% and 52% ± 15% using the 2 commercial products (P <0.05 vs. CT), ESV was 36 ± 28 and 47 ± 35 mL (P = not significant vs. CT), and EDV was 75 ± 30 and 91 ± 33 mL (P <0.05 vs. CT). Correlations with CT were 0.85 and 0.87 for EF using commercial software, 0.76 and 0.88 for ESV, and 0.60 and 0.68 for EDV (P <0.01 for all). Bland-Altman analysis confirmed systematic underestimation of EF and EDV by PET versus CT but did not show a significant deviation from linearity. Conclusion: Global LV function can be measured reproducibly from gated ⁸²Rb PET, using different available software products. However, underestimation of EF by ⁸²Rb PET, compared with CT ventriculography, is present, which is a result of underestimation of EDV from countpoor ED frames. This underestimation needs to be considered for clinical interpretation of ⁸²Rb PET.