MRI in the diagnosis of small bowel disease: use of positive and negative oral contrast media in combination with enteroclysis

Technical challenges and clinical applications of magnetic resonance enteroclysis

With the advent of gradient systems the image quality of ultrafast pulse sequences, i.e., half Fourier acquisition single shot turbo spin echo (HASTE), true fast imaging with steady-state processing and fast low angle shot (FLASH), improved substantially and clinical applications including small bowel imaging became feasible. Within this context, magnetic resonance enteroclysis was developed as a comprehensive examination of the small bowel, providing luminal, transmural, and exoenteric diagnostic information of small bowel abnormalities. Clinical applications of magnetic resonance enteroclysis include diagnostic evaluation and follow-up of patients with inflammatory or neoplastic diseases and small bowel obstruction.

Small bowel magnetic resonance imaging for inflammatory bowel disease

The presented concept of hydro-magnetic resonance imaging (MRI) using a 2.5% mannitol solution as an orally applicable intraluminal contrast agent is a meaningful, reproducible, and reliable imaging method for the depiction of the small bowel. Especially in patients with Crohn's disease, hydro-MRI is the imaging method of first choice because hydro-MRI offers the advantage of a superior depiction of the inflamed bowel wall and the extramural complications of this disease without radiation exposure. In addition, hydro-MRI allows for a reliable assessment of the inflammatory activity, especially for the differentiation between an active and an inactive (scarred) stenosis. In particular, the mural enhancement, the length as well as the wall thickness of inflamed bowel segments, are considered to be significant MR parameters for the determination of the activity of Crohn's disease. Hydro-MRI of the colon is suitable for the depiction of pathologic changes in ulcerative colitis, but in contrast to Crohn's disease, the assessment of disease activity by hydro-MRI is unreliable in ulcerative colitis, probably because of the low spatial resolution (mucositis in ulcerative colitis vs. transmural inflammation in Crohn's disease). Hydro-MRI does not allow a reliable classification of inflammatory bowel diseases, but in ambiguous cases, hydro-MRI may provide helpful information for the differentiation of Crohn's disease and ulcerative colitis. There are no data of larger patient groups published regarding MR findings in inflammatory bowel diseases besides Crohn's disease and ulcerative colitis, but hydro-MRI is a promising imaging tool for these entities, which should be assessed in additional studies.

Ultrasound and magnetic resonance imaging assessmentof active bowel segments in Crohn's disease

AIM

Determining bowel disease activity in Crohn's patients can be difficult on clinical and laboratory assessment. Endoscopy is invasive and barium studies use ionising radiation. The aim of this study was to compare ultrasound and magnetic resonance imaging (MRI) in detecting Crohn's disease activity in the small or large bowel.

MATERIALS AND METHODS

Thirty patients, previously diagnosed with Crohn's disease, had bowel ultrasound and MR imaging, and were deemed active or inactive on each test. The 'gold standard' was based on clinical assessment and one or more of the following: endoscopy, barium studies or surgery.

RESULTS

For determining Crohn's disease activity, the sensitivities and specificities of bowel ultrasound and MRI were 87 percent and 100 percent, and 87 percent and 71 percent, respectively. Significant parameters that defined disease activity were bowel wall thickening on ultrasound and MRI, and contrast enhancement of the bowel wall and mesenteric vascularity/stranding on MRI.

CONCLUSION

Ultrasound and MRI were both sensitive for determining Crohn's disease activity in the bowel, but MRI with gadolinium enhancement was less specific.

Combining infliximab with 6-mercaptopurine/azathioprine for fistula therapy in Crohn's disease

OBJECTIVES

Fistulas occur in about one third of patients with Crohn's disease and rarely heal spontaneously. Conventional medical and surgical therapy often fails. The anti-TNF-alpha antibody infliximab offers a novel therapeutic option. By this approach, closure of fistulas was reported in 45% of cases. However, after discontinuation of therapy, most fistulas recurred. Azathioprine and 6-mercaptopurine (6-MP) are effective drugs in Crohn's disease and lead to closure of fistulas in 30-40% of cases. Thus, the aim of this study was to evaluate the combination of infliximab with 6-mercaptopurine/azathioprine as therapy for fistulas in patients with Crohn's disease.

METHODS

A total of 16 patients (mean age 37 yr) with Crohn's fistulas resistant to conventional measures were treated with a combination of three or four infusions of infliximab and long term 6-MP/azathioprine. In all, 13 patients had perianal fistulas, two had abdominal fistulas, and one patient had both perianal and recto-vaginal fistulas. Therapy success was defined as complete closure of fistulas for a minimum observation period of 6 months after fistula closure.

RESULTS

In 12 (75%) of the 16 patients, we observed complete closure of the fistulas that persisted for >6 months (median follow-up 10 months, range 6-11 months). The median time to complete closure of fistulas was 14 days (range 2-36 days). In four patients, therapy success was not achieved.

CONCLUSION

Our pilot study reveals that concomitant and long term 6-MP/azathioprine therapy could prolong the effect of an initial infliximab therapy on fistula closure in patients with Crohn's disease. These data prompt larger controlled trials.

MR colonography with barium-based fecal tagging: initial clinical experience

PURPOSE

To assess a strategy for fecal tagging with barium sulfate as an inexpensive tagging agent in conjunction with magnetic resonance (MR) colonography in patients suspected of having colorectal lesions.

MATERIALS AND METHODS

Twenty-four patients suspected of having colonic lesions because of rectal bleeding, positive fecal occult blood test results, or altered bowel habits underwent MR colonography and subsequent conventional colonoscopy. A 200-mL dose of a barium sulfate-containing contrast agent was ingested with each of four low-fiber meals, beginning 36 hours before the examination. For MR colonography, the colon was filled with tap water. Gadobenate dimeglumine was injected intravenously. Images were acquired 75 seconds after gadobenate dimeglumine administration by using only a T1-weighted three-dimensional gradient-echo sequence. Images were reviewed by two radiologists blinded to conventional colonoscopic data. By using colonoscopy as the reference standard, sensitivity and specificity of MR colonography were determined for detecting colorectal masses.

RESULTS

On the basis of MR colonography, 15 polyps of 5-20 mm and 10 carcinomas were detected and later confirmed with conventional colonoscopy. Conventional colonoscopy depicted three additional lesions less than 8 mm in diameter. Thus, sensitivity of MR colonography was 89.3% (25 of 28) for lesions and 91.7% (22 of 24) for patients.

CONCLUSION

Barium-tagged MR colonography obviates bowel cleansing and depicts all lesions exceeding 8 mm in diameter.

Non-invasive distension of the small bowel for magnetic-resonance imaging

Magnetic resonance enteroclysis is a promising technique that allows assessment of the small bowel but needs invasive nasoduodenal intubation. We propose a non-invasive distension method for magnetic-resonance imaging (MRI) in which ispaghula, dissolved in an aqueous solution with meglumine gadoterate taken orally over 4 h forms a viscous hydrogel within the intestinal lumen. MRI results from ten volunteers showed good luminal distension, constant signal homogeneity, optimum demarcation of the bowel content from surrounding tissues, and a low rate of artefacts. Our method permits non-invasive high quality MRI of the small bowel.

Dynamic studies of gadolinium uptake in brain tumors using inversion-recovery echo-planar imaging

Echo-planar imaging has been used to observe the dynamics of Gd-DTPA uptake in brain tumors. It has been possible to examine both vascular uptake and diffusion across the blood-brain barrier in a single experiment, by using the IR-MBEST echo-planar sequence which combines a high temporal resolution (approximately 3 s) with strong T1 weighting. To model the uptake it is necessary to know the arterial concentration of Gd-DTPA; in this study the signal in the sagittal sinus was measured to avoid the need to take repeated blood samples. The time constant for transfer across the blood-brain barrier was measured to be between 20 and 1050 s for different tumors. The results of the modeling correlated with the results of other assessments of tumor vascularity.