Elsevier

Clinical Radiology

Volume 62, Issue 8, August 2007, Pages 804-807
Clinical Radiology

Technical report
MR small bowel enterography: optimization of imaging timing

https://doi.org/10.1016/j.crad.2007.02.010Get rights and content

Introduction

Requests to exclude underlying small bowel pathology are often associated with a low index of suspicion in routine clinical practice. Nonetheless, exclusion of such pathology is in the majority of cases a necessary early step in the assessment of such patients.

Small bowel imaging methods should allow visualization of small bowel luminal integrity, mucosal detail, mural thickness, and mesenteric, as well as peripheral visceral, morphology. The assessment of peristaltic activity and small bowel transit time, would also be advantageous. Patient acceptability, absence of associated ionizing radiation, and multiplanar imaging capabilities represent further desirable traits. Conventional small bowel enterography and enteroclysis fulfil a number of the above requirements, but score poorly with regard to mural, mesenteric, and visceral depiction, as well as involving considerable ionizing radiation exposure and occasionally intolerable patient discomfort, particularly so in the case of enteroclysis. Computed tomography (CT) addresses many of the short-comings of conventional fluoroscopy, allowing visualization of intraluminal, mural, and extramural components, as well as permitting multiplanar reformatting capabilities. However, the significant radiation exposure associated with this technique precludes repeated imaging in order to assess peristaltic activity, an important factor in small bowel imaging. It is for this reason that, in recent times, the attributes of magnetic resonance imaging (MRI), including superb contrast resolution, multiplanar imaging capabilities during single-breath hold acquisition times, real-time cine imaging, and lack of associated ionizing radiation exposure, have rekindled interest in the imaging of this anatomical region. This has resulted in the clinical application and investigation of a number of potential oral contrast media, with promising results.

The relative inaccessibility of the small bowel makes delivery of a uniform column of contrast medium and optimum distension very difficult. In an attempt to address this during fluoroscopic, CT or MRI evaluation, small bowel enteroclysis has in the past decades been extensively used. This technique, occasionally referred to as the “intubation–infusion technique” requires the fluoroscopic passage of a nasojejunal catheter (usually 8 F) and subsequent controlled infusion of significant volumes of contrast medium (often up to 3 l). One particularly useful technique for MR enteroclysis uses a combination of catheter-infused methylcellulose and intravenously-administered Gadopentetate dimeglumine.1 However, this technique is invariably associated with significant patient discomfort, particularly during catheter introduction and manipulation, and profuse diarrhoea often results once the infused contrast medium reaches the distal colon. Continuous infusion of contrast medium may result in gastro-esophageal reflux, particularly in the obstructed patient, with resultant potential for vomiting and aspiration.

As a result, many centres have investigated the application of enterography to MR small bowel evaluation, whereby contrast medium is orally ingested rather than infused, in an attempt to reach a compromise between patient tolerability and reproducible, predictable, diagnostic image acquisition. Efforts have been fuelled by encouraging reports such as that by Schreyer et al., who determined peroral MR enterography to be at least as useful as conventional enteroclysis or MR enteroclysis in the evaluation of patients with Crohn's disease.2

The aim of this study was the determination of a timing algorithm that would reduce the number of interval sequences performed after ingestion of a polyethylene glycol solution. In doing so, it was hoped that the timing of the imaging sequences would be optimized without compromising examination quality, the patient's experience of the examination would be improved, and the use of the MRI machine would be maximized.

Section snippets

Materials and methods

A retrospective, sequential evaluation was performed of 100 MR small-bowel examinations from a single institute performed over a 9 month interval. All patients fasted from midnight the previous night and then ingested a contrast agent consisting of one sachet of KleanPrep® (Norgine, Middlesex, UK) dissolved in 1 l water, over a period of 10 min. This preparation contains the following active ingredients: 59 g Macrogol (polyethylene glycol) 3350, 5.685 g sodium sulphate, 1.685 g sodium bicarbonate,

Results

Oral contrast medium ingestion and subsequent imaging was possible in all patients. One hundred MR enterographic examinations, from 96 different patients, were performed during the interval evaluated (46 males; 50 females). Overall average age was 46 years (males 46.86 years, females 45.13 years). Forty-three of these studies were of normal appearance, pathological features being detected in the remaining 57 studies (probable adhesions in 13, inflammatory bowel disease in 26, lymphoma in four,

Discussion

Optimization of small bowel enterography may be complicated by a number of variables. Presence or absence of disease, ability to ingest contrast medium over a short period of time, patient age, considerable individual variation in transit time independent of these factors, and the contrast medium regimen used all affect the duration and quality of the study. Initial attempts used tap water, which is readily available, cheap, acceptable to patients and has homogeneous signal intensity.3, 4

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References (13)

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