An-Najah Staff

PURPOSE
Bowel cleansing has been mandatory for MR colonography (MRC) thereby reducing patients’ acceptance. Administering oral contrast agents, the signal intensity of fecal material can be altered and stool can be virtually made invisible. We aimed to evaluate the accuracy of a new MRC protocol without colonic cleansing as for diagnostic accuracy and patients’ acceptance.
METHOD AND MATERIALS
340 screening patients older than 50 years were included. In addition to their regular meals they ingested 2000 ml of a tagging solution (5% gastrografin, 1% barium and 0.2% locust bean gum) starting 48 hours prior to the MR examination. No bowel cleansing was applied. MRC was performed in conjunction with a rectal water enema on a 1.5T MR System (Magnetom Sonata, Siemens) in patients’ prone position. A T1w 3D GRE sequence was acquired pre- and 75s after gadolinium administration (TR/TE/flip/FOV/matrix 3.08/1.13/35°/50/168x256). All patients underwent conventional colonoscopy within 3 weeks of the MR examination. MR data were analyzed concerning image quality and presence of colorectal masses. Additionally, patients’ acceptance was assessed for both methods.
RESULTS
Image quality of fecal tagging based MRC was diagnostic in 87% of the examinations. Reasons for non-diagnostic examinations were related to motion artifacts in 6% and signal-intense stool on the T1w images in 8% of the procedures. Adenomatous polyps > 5mm (>10mm) were detected with a sensitivity of 74% (93%) and a specificity of 95% compared to CC. Although MRC lacks therapeutic options 67 % of the patients preferred MRC for future examinations.
CONCLUSION
Fecal tagging MRC is applicable for screening purposes. Major advantages are related to the high patient acceptance and the specific detection of colorectal masses. However, further improvements such as parallel imaging techniques may help to improve the detection rate for smaller colorectal polyps.