Preparation, Technique, and Imaging of Computed Tomography/Magnetic Resonance Enterography

Min Ju Kim

doi:10.4166/kjg.2020.75.2.86

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Kim: Preparation, Technique, and Imaging of Computed Tomography/Magnetic Resonance Enterography

Review Article

Korean J Gastroenterol 2020;75(2):86-93.

Published online: 4 October 2020

DOI: https://doi.org/10.4166/kjg.2020.75.2.86

Preparation, Technique, and Imaging of Computed Tomography/Magnetic Resonance Enterography

Min Ju Kim

Department of Radiology, Korea University Anam Hospital, Korea University College of Medicine, Seoul, Korea

Correspondence to: Min Ju Kim, Department of Radiology, Korea University Anam Hospital, Korea University College of Medicine, 73 Goryeodae-ro, Seongbuk-gu, Seoul 02841, Korea. Tel: +82-2-920-5657, Fax: +82-2-920-3796, E-mail: mjkim7@korea.ac.kr, ORCID: https://orcid.org/0000-0003-0979-9835

Received 31 January 2020 Revised 17 February 2020 Accepted 19 February 2020

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

CT enterography and magnetic resonance (MR) enterography are widely used imaging modalities used to examine the small bowel. These radiologic tests are distinguished from routine abdominopelvic CT and MRI by the oral ingestion of a large amount of neutral contrast to distend the small bowel before scanning. For achievement of high quality, diagnostic images and proper technique are required. Conducted protocols still vary in patient preparation, enteric contrast, and CT and MRI acquisition sequences, resulting in heterogeneous diagnostic accuracy. The purpose of this article is to review the processes and techniques that optimize CT/MR enterography for patients with suspected Crohn's disease or other small bowel diseases.

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Keywords: Diagnostic imaging, Multidetector computed tomography, Magnetic resonance imaging, Intestine, small

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Fig. 1.

Computed tomography enterography of active Crohn's disease. Axial image (A) showed bowel wall thickening, mucosal enhancement and edema (arrows). (B) Coronal image demonstrated mesenteric vessel engorgement (comb sign, arrow) with lymph node enlargement (arrowhead). (C, D) Coronal image (C) and axial image (D) noted star-shaped entero-enteric fistula (arrows).

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Fig. 2.

Magnetic resonance enterography of active Crohn's disease. (A) Coronal scan of postcontrast T1-weighted image showed mucosal enhancement, wall thickening (arrow), and mesenteric vessel engorgement. (B) Coronal scan of true fast imaging with steady-state precession (FISP) noted intermediate signal intensity of involved ileal segment (arrow). (C, D) Diffusion-weighted image (C, high b-value=1,000) and apparent diffusion coefficient (ADC) (D) images demonstrated diffusion restriction presenting active inflammation (arrows).

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Table 1.

Summary of International Consensus Guidance^1,2,8,17

Patient preparation and technique
Patient preparation	• Fasting for 4–6 hours
	• Should not drink for 4–6 hours except nonsparkling water
Technique	• Hyperosmolar agent: mannitol, PEG, sorbitol and lactulose
	• Optimal volume of oral contrast: 1,000–1,500 mL
	• During 45–60 minutes
	• Laxative bowel preparation is not recommended
MR enterography technical considerations and sequence selection
Hardware	• Both 1.5 and 3 T
	• Phased-array coil is mandatory
Spasmolysis	• Spasmolytic agent is recommended
	• 20 mg IV hyoscine butylbromide or 1 mg IV glucagon
Positioning	• Prone or supine
Recommended sequences	• Axial and coronal T2 FSE without FS
	• Axial and coronal SSFPGE without FS
	• Axial or coronal T2 FSE with FS
	• 3D T1-weighted GRE sequence with FS before and after IV contrast
IV contrast	• For suspected IBD, enteric (45 s) or portal venous phase (70 s)
	• For chronic GI bleeding, arterial (30 s), enteric (45 s) or portal venous phase (70 s)
Optional sequences	• DWI are suggested not mandatory
	• DWI with free-breathing technique and maximal slice thickness ≤5 mm
Parameters	• FSE T2W and SSFPGE slice thickness ≤5 mm
	• FSE T2W performed 2D or 3D
	• T1W slice thickness ≤3 mm with 3D
Scan coverage and scan time	• Include small bowel, colon and perineum
	• Total acquisition time should be 30 minutes or less

PEG, polyethylene glycol; MR, magnetic resonance; IV, intravenous; FSE, fast-spin echo; FS, fat saturation; SSFPGE, steady-state free precession gradient-echo; 3D, three-dimensional; GRE, gradient-echo; IBD, inflammatory bowel disease; s, seconds; GI, gastrointestinal; DWI, diffusion-weighted image; T2W, T2-weighted image; 2D, two-dimensional; T1W, T1-weighted image.

Table 2.

CT and MR Techniques in Common Clinical Settings that Require Examination of Small Bowel^3,29

Indication	Preferred techniques	Comment
Suspected small bowel bleeding
Hemodynamic instability	Nonenterographic abdominopelvic CT	• Unenhanced+dynamic multiphasic contrastenhanced scans
Hemodynamic stability	CTE (MRE in limited cases)	• Unenhanced+dynamic multiphasic contrastenhanced scans
		• MRE may be used mainly in pediatric patents
Crohn's disease
Initial evaluation	CTE	• Single enteric-phase contrastenhanced scan
		• MRE if a history of multiple prior CT scans
Acutely severely ill	CTE or nonenterographic	• In patients who may not be able to hold still for the long acquisition time for
	abdominopelvic CT	MRE
		• Nonenterographic AP CT if unable to tolerate oral contrast
Young age	MRE	• Perhaps, <35 years old
Pregnancy	MRE	• Unenhanced scans only, because MRI contrast agents are contraindicated
Therapeutic monitoring	MRE	• As repeated imaging F/U are required
Suspicion of perianal disease	MRE	• A separate anal scan can be added to MRE
Suspected bowel obstruction or ischemia	Nonenterographic AP CT	• Unenhanced+dynamic multiphasic contrastenhanced scans if ischemia/ strangulation is suspected
		• Otherwise, single-phase contrastenhanced scan
Unexplained diarrhea	CTE or MRE	• Evaluate small bowel and pancreas
Malabsorption or celiac sprue	CTE or MRE	• Rule out lymphoma or refractory celiac disease
Polyposis	CTE or MRE	• Define polyp sizes and locations
		• May consider positive oral contrast at CT, because polyps are intraluminal filling defects

CT, computed tomography; MR, magnetic resonance; CTE, computed tomography enterography; MRE, magnetic resonance enterography; AP, abdomen and pelvis; MRI, magnetic resonance imaging; F/U, follow-up.

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ORCID iDs: Min Ju Kim
https://orcid.org/0000-0003-0979-9835
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