VIRTUAL COLONOSCOPY USING CT AND MR-IMAGING

Purpose: To evaluate experimentally and in patients the sensitivity an d effective dose of virtual electron-beam tomography (EBT) colonoscopy for detecting small colon tumors and to compare the methods and resul ts with virtual colonoscopy using spiral CT and MR imaging in a review of the literature. Materials and methods: Six polyps with diameters b etween 3 and 12 mm were created and randomly placed in resected pig co lon. After distension with air,the pig colon was scanned with continou s volume scanning (CVS, 3 mm collimation) and a pitch of 0.4, 0.8 and 1.5. Twenty patients positive for the fecal blood test were examined a fter rectal CO2 insufflation and i.v. administration of 1 mg glucagon. A 13 s CVS scan was used to cover the entire colon within one breath- hold. 3D volume-rendered fly-throughs were evaluated by two independen t radiologists. Effective dose equivalent was estimated using an Alder son phantom equipped with thermoluminescence dosimeters. Results: In t he tumor model, all polyps were detectable at a pitch of 1.5. A furthe r reduction of the pitch ratio did not improve the conspicuity of the polyps. ln patient studies, all tumors (n = 4) and polyps (n = 3) were correctly identified on 3D fly-throughs. Two false positive results w ere obtained. Effective dose equivalent was calculated at 3.2 mSv per scan. Conclusions: Our preliminary results indicate that virtual EBT c olonoscopy holds promise for fast screening for colon polyps. The best technique for virtual colonoscopy (Spiral CT,EBT, MRI) has not yet be en determined and the future role of virtual colonoscopy must still be defined.