Magnetic resonance colonography in clinical use: How far have we come?

Magnetic resonance colonography (MRC) is a noninvasive method of imaging the colon that has been developed over the past decade. Despite promising results, MRC has mainly been used in a few centers around the world and is not used in daily routine in many hospitals. The indications for MRC include diagnosing of polyps and cancers in patients with an incompleteor expected difficult colonoscopy. Other indications such as inflammatory bowel disease, screening and evaluation of anastomoses or stenoses have been described, but the modalities need to be developed further. MRC can be done as either ‘‘bright’’ lumen (dark bowel wall/lesion against a brightly distended colonic lumen) or ‘‘dark’’ lumen (bright bowel wall/lesion against a dark distended colonic lumen) with or without bowel preparation. So far, the results have been promising, especially regarding the sensitivities/specificities for larger, clinically relevant lesions. Currently, MRC is ready to be implemented as a diagnostic alternative after difficult or incomplete colonoscopies. However, this procedure should only be carried out in highly specialized MR centers in order to maintain high diagnostic accuracy. MRC is a good diagnostic alternative to difficult or incomplete colonoscopy, but the method needs validation in larger multicenter, multireader trials in low-risk populations before MRC can be considered a serious rival to colonoscopy for routine examination of the colon. Virtual colonoscopy, which was first described in 1994 by Vining et al. [1], involves helical computed tomography (CT) scans and 2Dand 3D reconstructions to create a non-invasive colon imaging method. In 1997 virtual colonoscopy using magnetic resonance (MR) [2] was introduced, and since then the two modalities have been continuously developed. In 2002, we reviewed the literature on the two methods for virtual colonoscopy, CT and MR colonography [3]. Since then, the methods have evolved as a number of different non-invasive diagnostic submethods (e.g. 3D double contrast, fecal tagging, fecal cracking, colon dissection display, digital subtraction, computer-assisted detection, translucency rendering [4 11]) centered mainly on the two key modalities, CT and MRC. The potential gain in early detection of colorectal cancer has been a powerful motivator in the continuing development and research into CTand MRC. Thus, in the past decade, colonography has progressed from an innovative technique to daily routine. CT colonography (CTC) has developed rapidly since its inception, owing to good diagnostic outcome, widespread accessibility and low costs. CTC is already one of the standard daily diagnostic methods in most of the larger hospitals and medical centers, whereas MRC has for the most part been developed in a few specialized centers around the world, is less readily used in everyday routines and still needs larger randomized trials in low-risk populations. Despite this, MRC [12,13] has shown equal or better results in comparison with CTC, approaching 100% for larger polyps, and is not associated with the risks from radiation. CTC radiation yields around 9.7 mSv per examination, a dose that has not significantly decreased since 2004