Time-of-Flight PET/CT Imaging of Ga-68-Dotatate: Normal Pattern, SUV Quantification, and Differences from...

Purpose  The biodistribution of gallium-68-dotatate (Ga-68-dotatate) and standardized uptake values (SUVs) using non-time-of-flight (TOF) positron emission tomography/computed tomography (PET/CT) cameras is well established. However, with the eventual retirement of older PET cameras and their replacement with newer, highly sensitive TOF PET/CT cameras, where SUV _max measurements are reportedly higher, updated knowledge of normal SUV _max range is needed and, to our knowledge, not previously reported. Our objectives are as follows: To establish normal Ga-68-dotatate TOF SUV _max database for common structures and to aid the visual detection of abnormalities objectively. To compare SUV _max values using the TOF and non-TOF algorithms. Methods  Fifty consecutive patients referred routinely to our nuclear medicine service (20 men, 30 women; median age 55 years) with presumed neuroendocrine tumors underwent Ga-68-dotatate scans on a PET-CT camera having capability of reconstructing both TOF/non-TOF images. Region of interests (ROIs) were drawn around 24 normal structures as well as the primary lesion with abnormal radiotracer uptake and SUV _max was measured. The same ROI was analyzed using both algorithms simultaneously and both TOF and non-TOF SUV _max values were compared. Results  Twelve hundred ROIs were evaluated. Non-TOF Ga-68-dotatate uptake in normal structures was in alignment with previously published studies. As compared to non-TOF, TOF images had better target to background ratios visually. TOF SUV _max was higher for all structures except for lung and brain. TOF SUV _max was more than double in adrenals/uncinate process of the pancreas; approximately 1.8 times in abnormal lesions, lymph nodes, pineal gland; and greater than 1.5 times in thyroid, breast, and pancreatic head. Conclusion  Normal database of Ga-68-dotatate TOF SUV _max is provided for common structures to aid visual detection of abnormalities objectively. Overall, TOF SUV _max measures higher in identical ROIs, with abnormal lesions measuring approximately 1.8 times higher versus non-TOF technology. These findings need to be taken in consideration when comparing patient scans imaged on different PET/CT technologies.