3D PET/CT 82Rb PET myocardial blood flow quantification: comparison of half-dose and full-dose protocols.

Abstract

Quantification of myocardial blood flow (MBF) has become central in the clinical application of Rubidium-82 (82Rb) PET myocardial perfusion scans. Current recommendations suggest injections of 1100-1500MBq of 82Rb in bolus form, which poses a potential risk of PET system saturation on most 3D PET/CT systems currently being used. We aimed to evaluate the frequency and impact of PET system saturation and to test the potential use of a half-dose acquisition protocol. This study comprised 20 patients who underwent repeated rest scans in a single imaging session, one employing a full-dose (FD), and the other scan a half-dose (HfD) protocol. Datasets were evaluated for saturation based on visual assessments of input functions and sinograms. We compared FD and HfD MBF measurements using Bland-Altman plots, coefficients of variation (CV), and paired t tests. A correction factor permitting serial analyses using FD/HfD imaging protocols was obtained using only the datasets without saturation. A dose reduction of 47% was reported for the HfD protocol (FD, 1247 ± 196MBq; HfD, 662 ± 115MBq). Saturation effects were observed in 4/20 (20%) FD scans, with none observed in the 20 HfD scans. Assessment of MBFs for FD and HfD protocols revealed bias in the MBF assessments of 0.09ml/g/min (global MBF, FD = 1.03 ± 0.29 vs HfD = 0.94 ± 0.22ml/g/min (p = 0.001)). Exclusion of patients with visually identified saturation effects (N = 4) reduced the bias to 0.05ml/g/min (global MBF, FD = 0.97 ± 0.28 vs HfD = 0.92 ± 0.23ml/g/min (p = 0.02)). From the datasets without saturation effect, it was possible to generate a bias-correction: Corrected MBFHfD = 1.09*MBFHfD-0.03ml/g/min. MBFFD and MBFHfD did not differ following the bias correction (MBFFD = 0.97 ± 0.28, MBFHfD,corrected = 0.98 ± 0.25ml/g/min, p = 0.77). Saturation effects can be problematic in 82Rb MBF studies using the recommended FD protocols for 3D PET/CT scanners. The use of HfD protocol eliminates the risks of saturation and should be used instead of clinical protocols to avoid erroneous results.