Objective: The purpose of this study was to compare the diagnostic performance of manually fused PET images obtained using 18F-FDG and CT images with that of CT alone, PET alone, and conventional side-by-side review of PET images and CT images (hereafter referred to as "PET + CT") in patients with suspected recurrent colorectal cancer.
Materials and methods: Ethics committee approval and informed consent were obtained. Sixty-three patients with suspected recurrent colorectal cancer underwent whole-body 18F-FDG PET followed by diagnostic CT. The acquired PET and CT images were merged on a workstation on a pixel-to-pixel basis. CT, PET, PET + CT, and fused images were evaluated separately in terms of the presence or absence of recurrence, new metastases, or both using a 5-point grading scale (0 = definitely negative, 1 = probably negative, 2 = equivocal, 3 = probably positive, and 4 = definitely positive). Lesions determined to be grade 3 or 4 were considered positive, and diagnostic accuracy and certainty were evaluated with statistical analysis using the chi-square test for independence.
Results: Of 119 pathologically or clinically confirmed lesions in 36 patients, evaluation of CT, PET, PET + CT, and fused images resulted in the detection of 75 (63%), 84 (71%), 91 (76%), and 111 (93%) lesions, respectively (p < 0.01) with the number of grade 4 lesions detected being 59 (50%), 72 (61%), 84 (71%), and 108 (91%), respectively (p < 0.01). Overall, the diagnostic accuracy of CT, PET, PET + CT, and fused images according to patient were 78%, 79%, 84%, and 92%, respectively (p = 0.13).
Conclusion: Interpreting fused images provided more accurate diagnoses than interpreting CT, PET, or PET + CT images. This method of manually fusing separately obtained PET and CT images increased the diagnostic certainty for detecting colorectal cancer recurrence and decreased the number of equivocal cases.