An-Najah Staff

Magnet resonance colonography (MRC) is a promising method for the depiction of colorectal pathologies. For colorectal masses exceeding 10mm, high accuracy values (92% to 100%) have been reported (1). However, due to limited spatial resolution, the detection rate of smaller pathologies is only fair. Another limitation of current MRC protocols is related to relatively long data acquisition of up to 25 seconds, which need to be performed under breath-hold conditions. Especially in elderly patients or patients with diseases of the respiratory tract, this can result in severe motion artefacts hampering a reliable assessment of the colon. The underlying problems may be solved by new image acquisition techniques providing a higher spatial resolution and / or a decreased acquisition time. These parallel acquisition techniques (PAT) have recently been successfully applied for MR colonography in an in-vitro study (2). Aim of the current trial was to prove the practicability of PAT imaging for MR colonography in-vivo.

The aim of our study was to assess the effect of oral and rectal stool softeners on dark-lumen magnetic resonance (MR) colonography without bowel cleansing. Ten volunteers underwent MR colonography without colonic cleansing. A baseline examination was performed without oral or rectal administration of stool softeners. In a second set, volunteers ingested 60 ml of lactulose 24 h prior to MR examination. In a third examination, water as a rectal enema was replaced by a solution of 0.5%-docusate sodium (DS). A fourth MR examination was performed, in conjunction with both oral administration of lactulose and rectal application of DS. A T1-weighted data set was acquired at scanning times of 0, 5 and 10 min after colonic filling. A fourth data set was acquired 75 s after i.v. injection of contrast agent. Signal intensity of stool was calculated for all colonic segments. Without oral ingestion of lactulose or rectal enema with DS stool signal intensity was high and did not decrease over time. However, lactulose and DS caused a decrease in stool signal intensity. Both substances together led to a decreasing signal intensity of feces. Combination of lactulose and DS provided the lowest signal intensity of stool. Thus, feces could hardly be distinguished from dark rectal enema allowing for the assessment of the colonic wall.

In the last few years virtual colonography using MR imaging has shown a proceeding development regarding detection and quantification of colorectal pathologies. Dark-lumen MR colonography (MRC) has been a leading tool for the diagnosis of the entire colon and their pathologies. This review article describes some of the underlying techniques of MRC concerning data acquisition, the need for intravenously applied paramagnetic contrast agent, as well as indications, results and limitations of MRC for the detection of colorectal pathologies. In addition, new techniques to improve patient acceptance are discussed.