Role of ischemia and deformation in the onset of compression-induced deep tissue injury: MRI-based studies in a rat model.

A rat model was used to distinguish between the different factors that contribute to muscle tissue damage related to deep pressure ulcers that develop after compressive loading. The separate and combined effects of ischemia and deformation were studied. Loading was applied to the hindlimb of rats for 2 h. Muscle tissue was examined using MR imaging (MRI) and histology. An MR-compatible loading device allowed simultaneous loading and measurement of tissue status. Two separate loading protocols incorporated uniaxial loading, resulting in tissue compression and ischemic loading. Uniaxial loading was applied to the tibialis anterior by means of an indenter, and ischemic loading was accomplished with an inflatable tourniquet. Deformation of the muscle tissue during uniaxial loading was measured using MR tagging. Compression of the tissues for 2 h led to increased T2 values, which were correlated to necrotic regions in the tibialis anterior. Perfusion measurements, by means of contrast-enhanced MRI, indicated a large ischemic region during indentation. Pure ischemic loading for 2 h led to reversible tissue changes. From the MR-tagging experiments, local strain fields were calculated. A 4.5-mm deformation, corresponding to a surface pressure of 150 kPa, resulted in maximum shear strain up to 1.0. There was a good correlation between the location of damage and the location of high shear strain. It was concluded that the large deformations, in conjunction with ischemia, provided the main trigger for irreversible muscle damage.

A novel magnetic method for examination of bowel motility.

In contrast to the well-developed methods for morphological diagnosis of the gastrointestinal tract, there is no comparatively satisfying technique for functional disorders. One important example is irritable bowel syndrome (IBS), a disorder that affects a high percentage of all individuals. It can only be diagnosed by excluding organic diseases and by considering symptom criteria. In this case, the examination of the motility of the bowel may be a promising way to differentiate between the two major mechanisms of IBS: increased sensitivity of the intestine and altered gastrointestinal motility. To this aim, a recently developed method for monitoring magnetic markers in the gastrointestinal tract was utilized that works without the use of ionizing radiation. We give a short description of this method, showing a spatial resolution of 3-4 mm and a temporal resolution of 330 ms, and report on examples of the first in vivo experiments. Typical monitoring results are shown for the esophagus, the stomach, and the duodenum. The motility behavior is described for the lower parts of the gut as well. The advantages and drawbacks of this type of magnetic marker monitoring are discussed with special consideration of the noninvasive examination of the motility in different sections of the gut.