Long Versus Short Axial Field of View Immuno-PET/CT: Semiquantitative Evaluation for ⁸⁹Zr-Trastuzumab

The purpose of this study was to quantify any differences between the SUVs of ⁸⁹Zr immuno-PET scans obtained using a PET/CT system with a long axial field of view (LAFOV; Biograph Vision Quadra) compared to a PET/CT system with a short axial field of view (SAFOV; Biograph Vision) and to evaluate how LAFOV PET scan duration affects image noise and SUV metrics. Methods: Five metastatic breast cancer patients were scanned consecutively on SAFOV and LAFOV PET/CT scanners. Four additional patients were scanned using only LAFOV PET/CT. Scans on both systems lasted approximately 30 min and were acquired 4 d after injection of 37 MBq of ⁸⁹Zr-trastuzumab. LAFOV list-mode data were reprocessed to obtain images acquired using shorter scan durations (15, 10, 7.5, 5, and 3 min). Volumes of interest were placed in healthy tissues, and tumors were segmented semiautomatically to compare coefficients of variation and to perform Bland-Altman analysis on SUV metrics (SUV_max, SUV_peak, and SUV_mean). Results: Using 30-min images, 2 commonly used lesion SUV metrics were higher for SAFOV than for LAFOV PET (SUV_max, 16.2% ± 13.4%, and SUV_peak, 10.1% ± 7.2%), whereas the SUV_mean of healthy tissues showed minimal differences (0.7% ± 5.8%). Coefficients of variation in the liver derived from 30-min SAFOV PET were between those of 3- and 5-min LAFOV PET. The smallest SUV_max and SUV_peak differences between SAFOV and LAFOV were found for 3-min LAFOV PET. Conclusion: LAFOV ⁸⁹Zr immuno-PET showed a lower SUV_max and SUV_peak than SAFOV because of lower image noise. LAFOV PET scan duration may be reduced at the expense of increasing image noise and bias in SUV metrics. Nevertheless, SUV_peak showed only minimal bias when reducing scan duration from 30 to 10 min.