Comparison of alignment of computer-registered data sets: combined PET/CT versus independent PET and CT of the thorax.

PURPOSE To retrospectively determine whether alignment of registered positron emission tomographic (PET) and computed tomographic (CT) data sets obtained independently varies significantly from alignment of data sets acquired from a combined PET/CT scanner. MATERIALS AND METHODS The study was approved by the institution's Human Research Committee with a waiver of informed consent and complied with HIPAA. Whole-body combined PET/CT data sets and separate routinely positioned thoracic CT data sets were obtained from 12 patients (six men, six women; mean age, 48.6 years; range, 24-62 years). Separate PET and thoracic CT data sets matched for patient positioning and respiration were acquired on the same day for nine patients (four men, five women; mean age, 71 years; range, 51-90 years). Computer nonlinear registration was performed on PET and CT data sets from combined PET/CT (fusion group 1), PET data sets from combined PET/CT with unmatched thoracic CT (fusion group 2), and data sets from separate PET and CT matched for patient positioning and respiration (fusion group 3). Quality of alignment was assessed by two radiologists in consensus blinded to the source of registered data in each fusion group at the following anatomic locations: diaphragm, aortic arch, heart, thoracic spine, and lung apices. Results were compared by using the Wilcoxon paired signed rank and unpaired rank sum tests. RESULTS Quality of alignment did not significantly differ between fusion group 1 and fusion group 3. Fusion group 1 provided significantly better alignment in two of five anatomic locations (P = .008 for diaphragm and P = .031 for heart) than fusion group 2. Fusion group 3 provided significantly better alignment in two of five anatomic locations (P = .037 for diaphragm and P = .009 for heart) than fusion group 2. CONCLUSION Thoracic anatomic alignment does not significantly differ between registered PET and CT data sets acquired on a combined PET/CT scanner or from separate PET and CT scanners obtained on the same day when carefully matched for anatomic positioning and respiration.