In our protocol; We need at least 6 hours of fasting from every patient, 5 gr.of methylcellulose is mixed with 500 ml water, then 667 mg/ml Osmolac, Biofarma, Turkey which constitutes about 150-200 mg Lactulose and 250 mg/ml E.Z-CAT, E-Z-EM, Quebec,Canada which involves 250 ml Barium with sorbitol, are added to the first mixture in which water and methycellulose exist. Afterwards, cold water is added to the mixture to make it about 1.5 lt. We request from each patient to drink this mixture with a rate of 300 ml/10 min. so in about 50 min, all the enterographic OCA will be finished by the patient. This mixture is a biphasic OCA, well tolerated by the patients with less side effects including nausea-vomiting and abdominal ache. It provides an adequate bowel wall distention which aids in the visualization of intestinal folds and loops4510.

20 mg intravenous(IV) Buscopan, Hyoscine-N-butyl bromide can be administered to prevent intestinal spasm and abdominal dyscomfort of the patients, 1 mg Glucagon subcutaneously or 0.3 mg IV Scopolamine can also be used as spasmolytic agents45.Current MRE protocol is: Fat-saturated(FS) T2 weighted(W) sequences in axial and coronal planes, T2W gradient echo breath-hold sequence in axial plane, precontrast T1W-WATS and fat-saturated 3D-T1W gradient-echo sequence in coronal planes, post-contrast dynamic T1W-gradient echo sequences in axial and coronal planes25710111213.Post-contrast dynamic images are often obtained at arterial-portal and late venous phases. The all MRE acquisitions are about 20-25 min of duration per patient.All MR-Enterography procedure was performed at 1.5 T Magnet, Achievva HB, Philips,Netherland..

Diffusion-weighted imaging(DWI) and magnetization transfer imaging(MTI) are the new imaging sequences and techniques that can be performed for the accurate diagnosis of Crohn’s disease2910. In case of active inflammation, restricted diffusion on high-b-value is conducted at DWI in case of Crohn’s disease, whereas infrequent for ulcerative colitis. To my experience, DWI may play a collaborating role in the imaging of patients who can’t tolerate OCA’s or in patients in whom IV contrast agent use is contraindicated59.MTI may reflect the enteric fibrosis and stricture development in Crohn’s disease via transfer of energy from the free water protons inside the lumen, to the macromolecules especially for the collagen fibers at the bowel wall9101112. Motility of the small intestine can be visualized by cine MRI via fast T2W images or true fast steady-state precession imaging, abnormal bowel motility and inflammatory activity in Crohn’s disease can be shown, based on wall thickness, ulceration and T2 signal intensity 9111213 (Figure 1a-b).

Crohn’s disease is a chronic inflammatory bowel disease with transmural invasion, causes damage to bowel wall with progression from inflammation to fibrosis over time69,121314151617.It is mostly seen in young adults between 15-30 years of age and slightly predominant in females, can be seen in any part of bowel, but predominant in terminal ileum with invasion to ileoceccal valve, forms enteric abcesses and via fistulization, invades adjacent bowel loops and wall26710131418. It has three main subgroups: Ulcerative-fistulizing and stenosing types, ulcerations of hypertrofied ileum and ileoceccal valve are predominant in ulcerative form, entero-enteric and entero-colic fistulas are the characteristic findings of fistulising form and stenotic segments with skip lesions and dilated pre-obstructed segments are the pathognomonic presentations of stenosing form61114,1617181920. Surgical approaches are most evident at stenosing form whereas medical conservative therapy aids more in ulcerative form. In fistulising form, both medical and surgical therapies can be applied67891011.

Pathognomonic signs of Crohn’s disease are; Bowel wall thickness must be higher than 2 mm in small intestine, 3 mm in colon, valvula conniventes has to be less than 3 mm, and small intestine diameter will be less than 3 cm, long segment intestinal infiltration, creeping fat sign, loss of haustration in colonic segments, skip lesions between normal and diseased segments and transmural invasion of bowel wall251214,181920. In endoscopy; Aftos ulcerations and erosions are found out initially in the normal bowel mucosa than at later stages, mural stratification with longitudinal and transverse ulcerations are observed7142021. On MRI; High bowel wall enhancement is particular at active inflammation, increased signal at bowel wall and adjacent mesentery on T2W images, strictures-fistulization and abcesses are the main complications and hyperintense on T2W images, asymmetrically thickened mucosal folds and lymphadenopathy, mesenteric stranding of the effected bowel wall and prominent draining vessels of the inflamed intestinal loops(comb sign), presence of intramural fat at chronic phase and target sign due to wall thickening at acute phase, surrounding peri-intestinal edema in acute phase are the main findings of Crohn’s disease71214,18192021 (Figure 2a-b)

Mucosal irregularities and ulcerations, strictures and fistulas at chronic stage can also be visualized by enteroclysis34141522 (Figure 3a-b-c).Clinical signs of Crohn’s disease are; Abdominal ache, diarrhea, fever, loss of weight, malnutrition, hemorrhage and fistulas, its extra-intestinal manifestations are: Arthritis, iridocyclitis, erthytema nodosum, aftoz stomatitis, cholelithiasis, primary sclerosing cholangitis and ankylosing spondylitis8910111213141516,202122.In the differential diagnosis; Ulcerative colitis(UC), ischemic colitis(IC), infectious-fungal and tuberculous(Tbc) enteritis, radiation enteritis, Lymphoma, Behcet’s disease have to be thought567,18192021 . UC involves the entire colon, small intestine involvement is extremely rare, it tends to involve only the mucosal part of bowel with continuous pattern and skip lesions-transmural pattern of Crohn’s disease involvement can never be seen in UC, fistulization and abscess formations are not evident, terminal ileum involvement of UC is named as backwash ileitis, UC is a pre-malignant inflammatory disease which often causes rectal adenocarcinoma, Malignant transformation of Crohn’s disease is extremely rare 6810141819

IC is particularly seen in elder patients with predominant vascular changes, especially thrombosis of mesenteric arteries, resulting the reduced blood flow to small intestine, presents low perfusion and loss of contrast enhancement on the bowel wall with submucosal edema or hemorrhage678. Infectious involvement of bowel loops may also mimic Crohn’s disease, Tbc enteritis mainly involve ceccum, then comes the terminal ileum, transverse and star shaped ulcerations on the intestinal mucosa with more evident bowel wall thickening, low segment concentric stenosis, are the major pathognomonic findings of it, lung involvement-calcified mesenteric lymphadenopathy and peritonitis are the common manifestations of Tbc242526. In the infectious enteritis, short clinical history and increased peristaltism of involved segments are the major clues in the differential diagnosis, radiation enteritis mostly causes luminal narrowing, mural thickening, adhesions and obstruction, abnormal contrast enhancement in the thickened intestinal wall, especially at terminal ileum and distal colon can frequently be observed14,2324252627. Lymphomas are also most commonly seen in ileum, luminal dilatation with mucosal necrosis and asymmetric bowel wall thickening are the major characteristics of lymphoma’s, moderate contrast enhancement of intestinal wall, preserved mesenteric tissues with lymphadenopathies , long segment involvement, increased wall signal on T2W images are the other common findings, obstruction of intestinal lumen due to lymphoma is quite rare14222326. Behcet’s disease often presents aftos lineer ulcerations in the terminal ileum and ileoceccal valve, also regard genital-oral and orbital ulcerations but histopathological differentiation from Crohn’s disease, can be necessary in most of the cases due to their similar involvement patterns 142628.

Standard MR imaging protocole generally include T2W-enhanced and unenhanced T1W sequences, their importance is mainly based on presenting mural and mucosal characteristics, including ulceration-wall thickness and mural involvement, seen with T2 signal intensity and contrast enhancement, histologically active Crohn’s disease has to be an inflammatory transmural process234567,141516171819. Active disease activity is also consistently associated with extramural inflammation such as comb sign, lymph node involvement, fat wrapping and edema of the bowel wall1114152029. Due to the lack of OCA application, standard MR imaging has a limited role in the diagnosis, management and follow-up of Crohn’s disease236. At this point of view, MRE may be currently used for accurate diagnosis and treatment of inflammatory bowel diseases(1234,789. Most standard MRE protocols achieve adequate intestinal distention via OCA, mural involvement and enhancement can be depicted by suboptimal bowel distention but, however mucosal ulcerations, skip lesions or strictures may be compromised3678910.

MRE examines; the number, distribution, shape and thickness of the plicae of intestine, diameter of the intestinal lumen and presence of intra or extra-luminal mass, thickness and contour of colonic wall, presence of abnormal bowel wall enhancement, mural or transmural inflammation, edema or hyperemia of bowel wall, irregularity and ulceration of mucosa, halo or target sign, stenosis or perforation of intestinal segments, mesenteric lympadenopathies, fistula formation, vascular engorgement and presence of other extra-intestinal pathologies 71214,1617181920. Summary of MRE findings in Crohn’s disease are as follows: