The oscillating gradient spin echo (OGSE) sequence enables measurement of diffusion weighting with a short diffusion time. The apparent diffusion coefficient (ADC) values of diffusion-weighted imaging (DWI) depend on the effective diffusion time (Δeff), which is the time allowed for water molecules to diffuse and probe the microstructural information in vivo. The aim of this study was to determine the utility of DWI with shorter diffusion times when observing microstructural changes due to acute cerebral infarction. Twenty-seven lesions in 22 subjects (18 men and 4 women ; mean age, 69.1 years) with acute cerebral infarction were observed. A 3T MR scanner (MAGNETOM Prisma, Siemens Healthcare, Erlangen, Germany) with a 20-channel head coil was used. DWI was performed using b-values of 0 and 1500 s/mm2 and three diffusion-encoding directions with the following parameters : Δeff of the pulsed gradient spin echo (PGSE), 47.3 ms ; Δeff of the OGSE, 8.5 ms. On the DWI/ADC map, one region of interest was placed within the lesion of an acute cerebral infarction. The ratios of the PGSE ADC values to the OGSE ADC values fluctuated during the time course after the onset of acute cerebral infarction. This fluctuation can be caused by microstructural changes, which may lead to structurally restricted diffusion and/or viscosity. No study has determined the relationship between ADC values with such a short diffusion time and time course from the onset of acute cerebral infarction in a live human brain. In vivo, the ADC measured in the lesion of the acute brain infarction of a live adult mouse brain presented tissue-dependent frequency dependence. This study suggests that a human ADC should also depend on the diffusion time, with non-invasive OGSE methods.
Koshino et al. (Mon,) studied this question.
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