Characterization of cerebral infarction by multicomponent analysis of transverse magnetization decay curves.

RATIONALE AND OBJECTIVES: Individual components of the transverse magnetization decay curve (TDC) were assessed for their ability to characterize ischemia in photochemically induced cerebral infarcts. METHODS: Fifty rats were randomly divided into equal-sized experimental and control groups, which were subdivided into groups studied at five different time points, ranging from 6 hours to 22 days. All the rats received transcalvarial irradiation with 560-nm light. Five rats in each time group also received a sensitizing dye before irradiation. In these latter animals, lesions of uniform size and location developed. Lesions were compared with tissue of similar volume and location from the contralateral cortex of the experimental animals and with tissue from both hemispheres of the control animals. TDCs of all the samples were measured and fit with mono- and bi-exponential functions. RESULTS: Unlike the control tissue, infarcted tissue displayed definitive two-component TDC behavior. The time course of the bi-exponential parameters yielded information unavailable from mono-exponential analyses. CONCLUSIONS: Bi-exponential analysis of TDCs may have diagnostic use as a more sensitive indicator of cerebral infarction than mono-exponential analyses.

Differentiation of experimental white matter lesions using multiparametric magnetic resonance measurements.

The potential of multiparametric proton magnetic resonance (MR) measurements for characterizing white matter lesions was investigated. The authors compared acute experimental allergic encephalomyelitis (EAE), which is distinguished by inflammatory lesions, with an immunologically potentiated hyperacute form of the disease in which demyelinating lesions (DEM) also are present. Tissue samples containing cervical spinal cord and brain stem were excised and in vitro measurements of T1, T2, and two components of T2 were performed. Discriminant analysis was applied using MR parameters singly and in various combinations. When the disease was clearly manifested, discrimination between treated and normal animals was satisfactory with single parameters. The use of biexponential T2 components improved the distinction of normal from treated but asymptomatic animals, and differentiated between EAE and DEM. These results suggest that improved characterization of white matter lesions is possible with multiparametric MR in vivo, especially if sampling is performed with imaging and the T2 decay curves are obtained with a sufficient number of echoes to perform biexponential analysis.