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

The purpose of this study was to quantify any differences between the SUVs of Zr 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. 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 Zr-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, SUV, and SUV). Using 30-min images, 2 commonly used lesion SUV metrics were higher for SAFOV than for LAFOV PET (SUV, 16.2% ± 13.4%, and SUV, 10.1% ± 7.2%), whereas the SUV 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 and SUV differences between SAFOV and LAFOV were found for 3-min LAFOV PET. LAFOV Zr immuno-PET showed a lower SUV and SUV 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 showed only minimal bias when reducing scan duration from 30 to 10 min.