Virtual tagging for laxative-free CT colonography: pilot evaluation.

Laxative-free computed tomographic colonography (lfCTC) could significantly improve patient adherence to colorectal screening. However, the interpretation of lfCTC data is complicated by the presence of poorly tagged feces and partial-volume artifacts that imitate colorectal lesions. The authors developed a method for virtual tagging of such artifacts. A probabilistic model of colonic wall was developed, and virtual tagging was performed on artifacts that were identified by the model. The method was evaluated with 46 clinical lfCTC cases that were prepared with dietary fecal tagging only. Visual examples show that the method can label partial-volume artifacts, poorly tagged feces, nonadhering completely untagged feces, and artifacts such as rectal tubes. The effect of virtual tagging was evaluated by comparing the detection accuracy of a fully automated polyp detection scheme without and with the method. With virtual tagging, the per-lesion detection sensitivity was 100% for lesions > or = 10 mm (n = 4) with 3.8 false positives per patient (per two CT scan volumes) and 90% for lesions > or = 6 mm (n = 10) with 5.4 false positives per patient on average. The improvement in detection performance by virtual tagging was statistically significant (p = 0.03; JAFROC and JAFROC-1).