Validation of monitored end expiration breath-hold computed tomography (CT) acquisition technique for the minimization of respiratory PET/CT image misregistration. A comparative study with averaged cine CT corrected image

Objectives To compare the monitored end expiration breath-hold and averaged Cine CT corrected image for the minimization of the respiratory PET/CT image mis-registration.

Methods Out of the 50 patients refereed for FDG PET/CT, 25 patients each underwent end expiration breathhold helical CT and cine CT (multiple low dose CT images) respectively during a respiratory cycle. In the first group, patients were instructed to hold breath at the end of forced expiration and helical CT was acquired. PET attenuated corrected images were reconstructed. In the second group, two scouts i.e. end inspiration & end expiration and cine CT scan were acquired over the entire diaphragm as delineated by the scout scans. Attenuated corrected cine and helical CT images were matched with the corresponding attenuated corrected PET images. The nuclear physicians who were blinded for the presence of the mis-registration and the motion artifacts, interpreted the data sets independently.

Results In the first group, the respiratory motion associated artifacts (liver) were noted in 4/25 patients. Misregistration in cranio-caudal and axial directions were seen in 10/25 and 13/25 patients respectively. The respiratory motion artifacts (Fig.) were noted in 13/25 patients in the 2nd group. Cranio-caudal and axial mis-registrations were seen in 20/25 and 22/25 patients respectively. A significant (p<0.05) proportion of patients showed difference in respiratory motion artifacts & mis-registration. The mean mis-registration in axial direction for breath hold protocol (6.2mm) was significantly (p <0.05) different from that for the cine protocol (12.9mm). However, the mis-registration (=7.4mm) as derived from breath hold CT did not differ significantly as compared to the value (=12.3mm) calculated in the craniocaudal direction.

Conclusions The simple end expiratory breath hold CT as compared to cine CT protocol was better in minimizing motion artifacts & mis-registration of PET/CT data