Abstract
1724
Objectives: In cardiac PET-CT protocols, a low dose CT is used for attenuation correction of PET. Misregistration due to respiratory or patient motion between the subsecond CT scan and the PET acquisition may cause artifacts and, thus, diagnostic inaccuracy. We evaluated incidence and severity of PET/CT misregistration in myocardial Rb-82 perfusion scans. Methods: Ninety-two consecutive patients who underwent rest/dipyridamole Rb-82 perfusion imaging on a GE Discovery Rx 16-slice PET-CT for workup of CAD, were included. Two different scanning protocols were used: The first 57 patients had CT followed by PET at rest, then the table was moved out of the gantry for dipyridamole, then, after repositioning, stress PET followed by a second CT was done (2-CT-protocol). In the subsequent 35 patients, rest CT and PET, immediately followed by dipyridamole and stress PET were done without moving the table (1-CT-protocol). The rest CT was used for correction of stress PET and no second CT was obtained unless significant patient motion was observed during stress (n=6). Coregistration of the heart in PET and CT was visually scored with a 5-point scale (0=no, 1=minimal, 2= mild, 3=moderate and 4=severe misalignment). Results: Overall, alignment at rest was better than for stress (0.7+0.7 vs. 1.0+0.9, P=0.03). In rest studies, 60% of patients showed misregistration of the heart (42% minimal and 17% mild misalignment). In stress studies, 67% of patients showed misregistration of the heart (40% minimal and 23% mild misalignment). Comparison of the 2-CT-and 1-CT-protocols revealed no difference in the alignment of stress studies(1.0+0.9 vs. 1.0+0.9, P=0.9). Conclusions: Misregistration of the heart occurs in myocardial perfusion PET-CT studies, emphasizing the need for realignment algorithms for highest study quality. Routine acquisition of a second CT after the stress PET did not result in improved alignment, suggesting that radiation burden can be reduced by using a single CT protocol.
Research Support (if any): Dr. Lautamäki is supported by SNM/Bracco Fellowship for Cardiovascular Molecular Imaging.
- Society of Nuclear Medicine, Inc.