Clinical Value of Manual Fusion of PET and CT Images in Patients with Suspected Recurrent Colorectal Cancer

Abstract

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. 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. 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). 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.