DCE-MRI imaging techniques are still evolving and methods of image analysis remain mostly qualitative, variable, and nonstandard, making these techniques unsuitable for comparisons between different institutions or different study protocols. In the attempt to standardize and make this analysis quantitative, a number of pharmacokinetic multicompartment models have been proposed that would serve to infer "absolute" physiological quantities from the data gathered with the dynamic scan.
When the contrast agent is injected, it equilibrates with the blood plasma and is rapidly delivered to the different tissues. The blood plasma (the central compartment) and the extra-vascular, extra-cellular space of the inflamed tissue lesion (the peripheral compartment) are connected by linear exchange processes in both directions. The measurement of microvessel permeability is possible by assessment of the rate at which a contrast agent transfers from the blood pool to the extra-vascular extra-cellular space. Similarly, the transfer of the contrast agent back to the blood can be expressed as the reflux coefficient. In addition, the measurement of increased blood volume is possible by permitting calculation of fractional plasma volume . This method offers the great advantage of being quantitative, i.e., not measurement-dependent but pathology-dependent, so that the results from different studies/sites can be directly compared.
Clinical scoring (such as the Crohn's disease activity index , biologic indexes , endoscopy, and imaging studies have all been used to monitor activity, but no established gold standard exists. Assessment of activity is usually made using a combination of clinical symptoms, physical findings, laboratory investigations, endoscopy, and imaging tests. The assessment of biologic activity, based on the positiv-ity for three of four acute phase reactants (WBC, ery-throcyte sedimentation rate, and C-reactive protein), has been found to be a sensitive determinant of activity, especially when supported by endoscopic or imaging findings.
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