Thomas Lauenstein MD, PRESENTER: Nothing to Disclose

Abstract: HTML Purpose: MR colonography is an appropriate diagnostic tool for detecting colorectal polyps exceeding 8mm in size. Different techniques of MRC based on different contrast mechanisms have been described. Our goal was to compare a dark lumen MRC approach using a T1w VIBE sequence with a TrueFISP based bright lumen technique concerning sensitivity and specificity for the detection of colorectal masses. Methods and Materials: 31 patients with suspected colorectal lesions were examined. MR examinations were performed on a 1.5 T MR system (Magnetom Sonata, Siemens, Erlangen, Germany). The colon was filled with 2000ml of tap water. The TrueFISP sequence was acquired both in supine and prone position (TR/TE 4.45 / 2.23 ms, flip angle 70, slice thickness 3 mm, acquisition time 21 sec). For the dark lumen technique, data acquisition was performed with the patient in prone position, only. A 3D VIBE GRE sequence was acquired with the following parameters: TR/TE 1.64 / 0.6 ms, flip angle 15, effective slice thickness 1.57mm, acquisition time 23 sec. Paramagnetic contrast (Gd-BOPTA, Multihance, Bracco, Italy) was administered i.v. at a dosage of 0.2 mmol/kg and a flow rate of 3.0 ml/s. After a delay of 75 s, the pre-contrast 3D acquisition was repeated with identical imaging parameters. All patients underwent conventional colonoscopy on the same day of the MR exam. Results: In 11 patients 20 colorectal polyps and in three other patients each one colorectal cancer was detected by conventional colonoscopy. In the dark-lumen MRC data sets, all polyps > 5mm were correctly diagnosed, whereas 4 little polyps <5mm were missed. Thus, sensitivity of dark-lumen MRC amounted to 83%. There were no false-positive results: residual stool could correctly be differentiated from colorectal masses due to the lack of contrast enhancement after the intravenous application of paramagnetic contrast. The TrueFISP based bright lumen MRC, however, failed to detect two additional polyps (7 and 9mm in diameter). Furthermore, the bright lumen MRC led to false positive results in 5 patients. Conclusion: Bright lumen MRC based on the acquisition of TrueFISP scans is harmed by certain limitations: colorectal lesions larger than 5mm were missed in this trial. Besides, there are a considerable number of false positive findings due to the lacking differentiation between residual stool and colorectal masses. However, we believe that further improvements will enhance the impact of the TrueFISP approach, e.g. by the application of 3D TrueFISP sequences or the use of parallel imaging techniques.      

Lauenstein MD, T, TrueFISP versus VIBE: Comparison of Different Techniques for MR Colonography.  Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL. http://archive.rsna.org/2003/3103152.html