Perfusion MRI of the Small Bowel to Assess Mesenteric Ischemia

Perfusion imaging as a noninvasive method has been widely used for the determination of myocardial blood flow [34]. Cardiac perfusion examinations are usually performed during baseline conditions as well as during pharmacologically induced hyperemia [35,36]. Thus, a "myocardial perfusion reserve" can be determined, which accurately depicts individual graded coronary lesions [35]. This pathophysiological background can be transferred from myocardial perfusion to visceral perfusion, since processes in coronary artery disease are fairly comparable to those in mesenteric ischemia. Instead of increasing the blood flow and heart activity by the intravenous application of pharmaceutical drugs, the blood flow and "bowel activity" can be enlarged by the oral administration of a high caloric foodstuff. In fact, the reserve capacity of bowel wall perfusion, which is comparable to the myocardial perfusion reserve, has proven to be a reliable parameter for the differentiation between healthy volunteers and patients with mesenteric ischemia. The baseline examination alone without caloric stimulation should not be considered for the assessment of mesenteric ischemia as in our experience there have hardly been any differences between our reference and patient groups. Interestingly, both for the examination with caloric stimulation as well as for the examination concerning the reserve capacity, differences turned out to be most significant during the first pass of the intravenous contrast material. Hence evaluation of dynamic perfusion MRI should be based mainly on this first pass period.

Perfusion MRI of the bowel wall is a feasible method for the assessment of mesenteric ischemia [37].Among its advantages is its non-invasiveness.

Arterial Wall Ischemia
Fig. 12. Volume rendered 3D CE MRA data set (0.1 mmol/kg Gd-BOPTA) in a patient with Osler's disease. Multiple diffusely distributed hepatic arterio-venous malformations lead to hepatic shunting resulting in an enlarged celiac trunk and hepatic artery (arrows) [Image courtesy of Dr. G. Schneider]

In addition, direct information of the bowel wall can be obtained. Although only patients with proven artherosclerosis of the SMA were examined, the concept should be suitable for the evaluation of changes to each of the mesenteric arteries. To this end, the perfusion values of the colonic wall should be analyzed to exclude or confirm pathologies of the IMA.

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