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Prone and Supine Positions in MRI Are Found to Be Equal in Lesion Detection and Feature Visualization in the Small Bowel

March 16, 2009
Written by: , Filed in: Abdominal Imaging
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The better the visualization of the abdomen, the better the chances of detection when it comes to the small bowel. Does one position, either the prone (face down) or supine (face up) position, yield better results than another in terms of lesion detection and feature visualisation?

In a recent study reported in the AJR, small-bowel distention was found to be greater with imaging in the prone position. Lesion detection and evaluation performance were comparable with both positions.

The Study
Objective:

The objective of the prospective analysis was to determine if the prone position or the supine position during MRI afforded better small-bowel distention, lesion detection, and evaluation.

The Study:
This study evaluated 40 patients, 22 women and 18 men, referred with known or suspected small-bowel abnormalities who underwent MR small-bowel follow-through examination in the prone and supine positions.

Clinical concerns included Crohn’s disease, small-bowel neoplasm, small-bowel lymphoma, or celiac disease.

The Methodology:

The first set of images of the small bowel was acquired in either the prone or supine position, followed by immediate imaging in the other position.

MR examinations were performed on a 1.5-Tesla system. T2-weighted 2-D true fast imaging with steady state precession sequences (FISP) in the coronal and axial planes were obtained.

Images were reviewed by 2 radiologists without knowledge of clinical information or symptomatology. The small bowel was arbitrarily divided into 5 distinct segments for purposes of image analysis:  duodenum, jejunum, proximal ileum, distal ileum, and terminal ileum.

Small bowel distention was graded on a 3-point scale for each of the supine and prone image sets:
1=poor distention
2=moderate distention
3=excellent distention.

Observers recorded number, location, and characteristics of intraluminal, mural, and extraluminal lesions found in each segment of the small bowel.

Results of The Study:
28 of 40 patients demonstrated pathologic findings of the small bowel and abdominal area on MR examination. Bowel abnormalities included Crohn’s disease, carcinoid, lymphoma, and polyps.

Extraluminal abnormalities included a splenic mass, mesenteric lymph nodes, and ovarian cyst.

The prone (face down) images were found to be superior to those obtained supine (face up) regarding degree of small-bowel distention for all segments.

All lesions encountered were identified on both prone and supine images. In addition, there was no statistically significant difference in lesion detection or characterization between the prone and supine images.

Conclusions
Although the prone position results in superior small-bowel distention during MRI small-bowel follow-through, both the prone and supine positions are equal in terms of lesion detection and feature visualization.

Reviewer’s Comments
The results of this study are helpful in demonstrating the benefit of prone positioning for MR small-bowel follow-through examinations to achieve better bowel distention.

This improvement would decrease the propensity to over-call normal collapsed bowel wall as being pathologically thickened, but the results did not translate to better lesion detection or characterization.

Therefore, it would probably not be of any added diagnostic benefit to image in the prone position.

But in addition to the better bowel distention, the comparable results achieved can be said to offer flexibility in tailoring the MRI to patients who are not able to tolerate 1 of the 2 positions.

One of the limitations to the study was that the observers could not be blinded to the patient positions, as evidenced by gravity-dependent findings on the images, such as fluid-levels.

Author: John C. Sabatino, MD
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Reference:
Cronin CG, Lohan DG, et al. MRI Small Bowel Follow-Through: Prone Versus Supine Patient Position for Best Small Bowel Distention and Lesion Detection. AJR; 2008; 191 (August): 502-506

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