Acute cerebral infarction: Quantification of spin-density and T2 shine-through phenomena on diffusion-weighted MR images

PURPOSE: To quantify the relative contributions of spin density and T2 effe cts ("shine through'') on diffusion-weighted (DW) magnetic resonance (MR) i mages of acute and subacute cerebral infarction. MATERIALS AND METHODS: in 30 patients, 1.5-T imaging was performed within t he first 7 days after onset of cerebral infarction. Estimates of T2, spin d ensity, and apparent diffusion coefficient (ADC) in the region of stroke an d contralateral normal brain were computed by means of standard regression techniques after quadruple-echo conventional MR imaging and single-shot ech o-planar DW imaging with a maximum b value of 1,000 sec/mm(2). Expected sig nal intensity (SI) enhancement ratios resulting from independent changes in T2, spin density and ADC were then calculated for the DW sequence. RESULTS: The overall SI of cerebral infarction on DW images was significant ly higher than that of normal brain throughout the Ist week after stroke(me an relative SI enhancement ratio, 2.29; P < .001). During the first 2 days after stroke, decreased ADC within the stroke region made the dominant cont ribution to increased SI on DW images. By day 3, increased T2 values in the stroke region became equally important, and, from days 3-7, the contributi on to SI from T2 effects became dominant. A slight increase of spin density in the stroke region made a relatively small and constant contribution to DW SI over the 1st week. CONCLUSION:The increased SI of subacute cerebral infarction on DW images re flects not only a shortening of ADC but a prolongation of T2 and spin-densi ty values.