Diffusion-weighted MR imaging of the gastrointestinal tract: technique, indications, and imaging findings.

Diffusion-weighted magnetic resonance (MR) imaging has emerged as an important tool in the diagnostic work-up of patients with bowel cancer and inflammatory conditions of the gastrointestinal tract. It functions on the basis of the microscopic motion of water molecules in a cellular environment and provides functional information about the water in body tissues. Diffusion-weighted imaging serves to complement conventional MR imaging, and its use may improve the accuracy of tumor detection and staging. It does not rely on the use of intravenous contrast material and may be performed in patients with renal impairment. Because it provides quantitative information about tissue cellularity, diffusion-weighted imaging may be used to distinguish between tissues with altered cellularity (eg, tumors and metastases) and normal tissues. Data from diffusion-weighted MR images enable the calculation of apparent diffusion coefficient (ADC) values, which provide useful information about response to treatment. Malignant gastrointestinal tract tumors have low ADC values, which increase after successful therapy. Diffusion-weighted imaging also plays a role in the evaluation of patients with inflammatory bowel disease and may help assess inflammation and complications, such as abscesses and fistulas. Quantitative measurements of signal intensity at diffusion-weighted imaging may help differentiate actively inflamed bowel from normal bowel, and ADC values provide useful information about disease activity and response to treatment.

Multidetector computed tomography of the mesocolon: review of anatomy and pathology.

The anatomy of the mesocolon can be seen on multidetector computed tomography (MDCT) scans, and its most important anatomic landmarks are the mesocolic vessels. The high spatial resolution of the current generation scanner coupled with the ability to generate high quality multiplanar images is very helpful in the delineation of the mesocolon. These vessels include the ileocolic and right colic vessels for the ascending mesocolon, the middle colic vessels for the transverse mesocolon, and the inferior mesenteric vein for the sigmoid and descending mesocolon. Knowledge of the anatomic landmarks of the mesocolon can help the radiologist identify the pathways for the spread of diseases of the colon and pancreas. Abnormalities of the mesocolon may also herald primary disease in the adjacent viscera. In the current context, this knowledge of the anatomy of the mesocolon and vascular landmarks can also be helpful for surgical planning, especially for minimal access or laparoscopic surgery.