الفهرس 
Anatomy of The Small BowelOnly 14 pages are availabe for public view
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Abstract
Crohn disease is a multifactorial chronic inflammatory disease characterized by non caseating granuloma formation with a tendency toward remission and relapse, it affects any part of the GIT from mouth to anus with 80% small bowel involvement, most commonly the terminal ileum, with characteristic multiple discontinuous sites involvement (skip lesions) and transmural inflammation.
Crohn disease is common in North America, northern Europe and Japan with a peak involvement in 2nd and 3rd decades of life (young patient population) with tendency to remission and relapse and complications as fibrosing strictures, sinus tracts, fistulas and abscesses formation.
Barium studies and endoscopy are the basic modalities in diagnosing Crohn disease in early stages with endoscopic guided biopsy and histopathological verification. Cross-sectional imaging (M.D.C.T. and M.R. enterography) with intraluminal and intravenous contrast material are with limited role in depicting subtle mucosal lesions but are most useful in assessment of symptomatic patients with known small bowel Crohn disease providing excellent visualization of most intestinal lesions and demonstrate their mural and extramural extent, also demonstrating complications such as sinus tracts, fistulas and abscesses.
In clinical settings, M.D.C.T. has been the cross sectional imaging modality of choice at most institutions due to its widespread availability, low cost and higher spatial and temporal resolutions relative to M.R. imaging, yet it is based on ionizing radiation.
However, because Crohn disease is commonly involving the young persons with a peak involvement between 15 and 25 years of age, and also has a tendency for remission and relapse and the high cumulative radiation doses imparted to the patients from multiple serial examinations needed to assess progression of the disease, detect complications and monitor response to treatment (high radiation burden); it is preferable to use a non ionizing radiation based modality such as M.R. imaging for diagnostic and follow up evaluation that help reduce patient’s lifetime radiation exposure and provides superior soft tissue contrast and excellent depiction of fluid and edema, meanwhile have a high diagnostic sensitivity as that of the C.T. imaging and relatively higher safety profile of intravenous contrast material used in MR examination in relation to that used in C.T. examination.
Newer techniques such as parallel imaging help improve spatial and temporal resolution of MR imaging and so can detect early lesions. Also parallel imaging enables the acquisition of high-resolution three-dimensional data sets of isotropic voxels in one breath hold. These techniques allow high-quality dynamic imaging (MR fluoroscopy) with a combination of higher temporal resolution and higher spatial resolution.
When interpreting MR Enterographic findings, familiarity with the MR imaging features of acute and chronic Crohn disease and their mimics improves diagnostic accuracy and helps optimize management of Crohn disease.
MRI is able to detect significant variations in bowel wall thickness and contrast enhancement, reflecting favorable clinical response to medical treatment of CD’s relapse. In addition to its lack of ionizing radiation, this may allow MRI to be the imaging technique of choice for the follow-up of patients with active CD.
MRE is a promising modality as techniques improve and undergo further validation and standardization. Indications of MRE is expanding to include assessment of response to therapy in clinical trials.