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Polyethylene Glycol Solution as an Oral Contrast Agent for MR Imaging of the Small Bowel

¹ All authors: Department of Radiology, University of Rome "La Sapienza," Policlinico Umberto I, Viale Regina Elena 324, 00161 Rome, Italy.

Received April 27, 2001; accepted after revision June 19, 2001.

 
Address correspondence to A. Laghi.

Introduction

Top Introduction Subjects and Methods Results Discussion References

 
The development of fast single-shot heavy T2-weighted sequences that are able to provide motion-free images of static fluids has greatly increased interest in MR imaging of the small bowel. Various authors have advocated the use of a half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence as a reliable technique for imaging both the normal and abnormal small bowel [1,2,3]. However, poor distention of normal bowel loops in basal conditions has led researchers to perform small-bowel MR imaging using an oral contrast agent to distend the bowel lumen. Recently, two reports [4, 5] showed the utility of using tap water as an oral contrast agent in conjunction with the acquisition of a heavy T2-weighted sequence. However, the use of an absorbable agent, such as water, may not lead to optimal distention and visualization of distal ileal loops.

We evaluated an oral isosmotic polyethylene glycol solution as an oral contrast agent for MR imaging of the small bowel in a population of healthy volunteers. Polyethylene glycol solution simulates the properties of water as it relates to signal intensity, with the added advantage of nonabsorbability, thus providing good distention of all the small-bowel loops from the jejunum to the terminal ileum.

Subjects and Methods

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Subjects
Ten healthy nonobese volunteers (eight men and two women; age range, 26-32 years) with no history of known or suspected small-bowel disease, who were not currently receiving medication, and who had never undergone abdominal surgery were evaluated with MR imaging. After receiving approval for the study by the institutional review board at our institution, we obtained written consent from each participant. The research subjects fasted overnight, and immediately before the MR examination, a fixed amount (600 mL) of polyethylene glycol solution was administered orally. No antispasmodic or other drugs were given. Polyethylene glycol solution was freshly prepared by dissolving a granular powder containing polyethylene glycol 4000, 34.8 g; anhydrous sodium sulfate, 1.42 g; sodium bicarbonate, 0.42 g; sodium chloride, 0.36 g; and potassium chloride (Isocolan; Bracco, Milan, Italy), 0.18 g in 500 mL of tap water. Each volunteer was asked to drink 600 mL of contrast solution continuously, beginning 5-10 min before the examination.

MR Protocol
MR imaging was performed on a 1.5-T MR scanner (Magnetom Vision Plus; Siemens Medical Systems, Erlangen, Germany) with a maximum gradient field strength of 25 mT/m. We used a phased array body coil to examine the subjects, who were in a supine position. After obtaining localizing images in three axes, we acquired a coronal T2-weighted HASTE sequence using the following parameters: TR/TE, infinite/90; echotrain length, 104; section thickness, 6 mm; intersection gap, 20%; field of view, 350-400 mm; effective matrix, 192 x 256; signal average, 1; and half-Fourier reconstruction. Fifteen slices were obtained during a single breath-hold of 20 sec. Images were acquired every 5 min until the cecum was observed to be filled by the oral contrast agent for a maximum of 30 min.

Image Analysis
Images were reviewed by two radiologists who were experienced in both gastrointestinal and MR imaging. Agreement was by consensus. Small-bowel loops were divided into three segments including the jejunum, the proximal ileum, and the distal ileum—ileocecal region. The time required for the contrast agent to reach the ileocecal region was recorded.

Images were assessed for visibility of all three regions. Qualitative analysis consisted of luminal distention, performed as described by Minowa et al. [4], with small-bowel loops evaluated using a three-step scale (0 = poor, 1 = good, 2 = optimal).

The quantitative analysis included an evaluation of bowel caliber and wall thickness. A bowel caliber not exceeding 3 cm and wall thickness less than 3 mm were considered indicative of normal bowel.

Results

Top Introduction Subjects and Methods Results Discussion References

 
All 10 healthy volunteers tolerated our imaging study, and no volunteers experienced adverse side effects after ingesting 600 mL of the polyethylene glycol solution. The time to obtain complete visualization of the small bowel, from the jejunum to the ileocecal region, ranged from 15 to 25 min (mean, 22.3 min).

The jejunum showed optimal distention in all subjects in 5-10 min, whereas the proximal ileum showed good distention in four subjects and poor distention in the remaining six subjects in 5-10 min. Good to optimal distention was observed for the proximal ileum in all subjects and for the terminal ileum in seven subjects in 10-20 min (Fig. 1A,1B). Good to optimal evaluation of the ileocecal region was obtained in 25 min in all subjects (Fig. 2A,2B).

View larger version (94K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —30-year-old healthy female volunteer. Coronal MR image obtained using half-Fourier acquisition single-shot turbo spin-echo sequence shows optimal distention of jejunal loops with visualization of valvulae conniventes and thin bowel wall.

View larger version (185K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —30-year-old healthy female volunteer. MR image obtained few minutes later than A shows distention of both the jejunum and proximal ileum. Note visibility of different anatomic features of jejunal and ileal folds.

View larger version (107K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —30-year-old healthy female volunteer. Delayed MR image shows good evaluation of ileocecal region.

View larger version (109K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —30-year-old healthy female volunteer. MR image obtained using contiguous slice better depicts apex of cecum and terminal ileum (arrow) than A.

Bowel caliber evaluated at the level of the jejunum, the proximal ileum, and the distal ileum measured an average of 22.5 mm (range, 19-26.8 mm), 18.6 mm (range, 16.4-22 mm), and 15.4 mm (range, 12-16 mm), respectively; wall thickness measured an average of 2.6 mm (range, 2-2.9 mm) at the level of the jejunum, 2.2 mm (range, 1.4-2.8 mm) at the level of the proximal ileum, and 2.2 mm (range, 1.7-2.9 mm) at the level of the distal ileum.

Discussion

Top Introduction Subjects and Methods Results Discussion References

 
Luminal distention is required for small-bowel imaging because collapsed bowel loops can hide even large lesions and may falsely mimic wall thickening. In cases of lesions that obstruct the small bowel, luminal distention occurs naturally [2]. Otherwise, even in patients with small-bowel disease, bowel loops are often collapsed and MR imaging can be difficult, as shown by Lee et al. [1]. In their series of patients with disease, 88% of the patients showed fluid in less than 50% of their small-bowel loops.

The use of various oral contrast agents, both positive and negative, has been proposed; however, none of these have proved sufficiently successful to be widely used clinically [5].

Recently, water has been advocated as a contrast agent. Water is relatively safe, although water overload, vomiting, and related aspiration remain potential risks [5]. The major limitation of this method concerns early water reabsorption, which prevents the visualization of the ileocecal region in more than 30% of patients [4, 5].

A more invasive approach for obtaining optimal luminal distention is MR enteroclysis with methylcellulose, as reported by Umschaden et al. [6]. Methylcellulose presents the same signal properties as both water and polyethylene glycol solution, but methylcellulose cannot be ingested orally and therefore requires preliminary positioning of a nasoenteric tube. Patient discomfort is increased and vomiting inside the MR scanner, despite all precautions, may occur [6].

In this study, we used an isosmotic polyethylene glycol solution on the basis of a technique optimized for sonographic examination [7]. Once in the small bowel, the unabsorbable and unfermentable polyethylene glycol remains unmodified, linked with water molecules, fills the lumen, and distends the intestinal loops [7]. The relatively small amount of polyethylene glycol solution (600 mL) was easily ingested by each subject and did not cause substantial side effects; bowel distention was optimal in the jejunum and good to optimal in the proximal and distal ileum. Obtaining sequential images is mandatory to evaluate small-bowel loops when maximally distended and to characterize correctly any mobile filling defects in the lumen as either gas bubbles or food residue. The relatively rapid transit time of polyethylene glycol solution limited the examination to less than 30 min.

Our imaging technique included the acquisition of a HASTE sequence that was able to clearly show normal small-bowel loops, with a reduced amount of artifacts from physiologic (respiratory and cardiac) motion [8].

Our study has shown that MR imaging using polyethylene glycol solution as an oral contrast agent is feasible and provides a physiologic overview of the normal small bowel. Polyethylene glycol solution is easily prepared and administered and was well tolerated in all subjects. Additional studies in patients with small-bowel disease are necessary to evaluate the possible clinical value.

References

Top Introduction Subjects and Methods Results Discussion References

 

1. Lee JKT, Marcos HB, Semelka RC. MR imaging of the small bowel using the HASTE sequence. AJR 1998;170:1457 -1463[Abstract/Free Full Text]
2. Regan F, Beall DP, Bohlman ME, Khazan R, Sufi A, Schaefer DC. Fast MR imaging and the detection of small-bowel obstruction. AJR 1998;170:1465 -1469[Abstract/Free Full Text]
3. Ernst O, Asselah T, Cablan X, Sergent G. Breath-hold fast spin-echo MR imaging of Crohn's disease. AJR 1998;170:127 -128[Free Full Text]
4. Minowa O, Ozaki Y, Kyogoku S, Shindoh N, Sumi Y, Katayama H. MR imaging of the small bowel using water as a contrast agent in a preliminary study with healthy volunteers. AJR 1999;173:581 -582[Free Full Text]
5. Lomas DJ, Graves MJ. Small bowel MRI using water as a contrast medium. Br J Radiol 1999;72:994 -997[Abstract]
6. Umschaden HW, Szolar D, Gasser J, Umschaden M, Haselbach H. Small-bowel disease: comparison of MR enteroclysis images with conventional enteroclysis and surgical findings. Radiology 2000;215:717 -725[Abstract/Free Full Text]
7. Pallotta N, Baccini F, Corazzieri E. Small intestine contrast ultrasonography. J Ultrasound Med 2000;19:21 -26[Abstract]
8. Catasca J, Mirowitz SA. T2-weighted MR imaging of the abdomen: fast spin-echo vs conventional spin-echo sequences. AJR 1994;162:61 -67[Abstract/Free Full Text]

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