A MODEL FOR MRI CONTRAST ENHANCEMENT USING T-1 AGENTS

Contrast in MRI relies on differences in the local environment of wate r and is often enhanced by using contrast agents. We present a simple model for evaluating the minimal contrast agent concentration required to produce ''satisfactory'' contrast enhancement in magnetic resonanc e images. Previous strategies have been based largely on empirical res ults for specific systems. The present tissue contrast model (TCM) can be applied to ''conventional,'' targeted, or biochemically responsive agents. The model results are formulated so that only a small number of parameters are required to analyze a given scenario. The TCM is a p articularly useful tool in the development of new classes of magnetic resonance contrast media. These agents will have the ability to target specific cells or tissue, and perhaps be able to report on their phys iological status. As an example of the applicability of the TCM, we te st it against irt vivo magnetic resonance microscopy results in frog e mbryos that have focal cell populations labeled with contrast agent by using calibrated single-cell microinjection techniques.