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Single‐shot ADC imaging for fMRI

It has been suggested that apparent diffusion coefficient (ADC) contrast can be sensitive to cerebral blood flow (CBF) changes during brain activation. However, current ADC imaging techniques have an inherently low temporal resolution due to the requirement of multiple acquisitions with different b‐factors, as well as potential confounds from cross talk between the deoxyhemoglobin‐induced background gradients and the externally applied diffusion‐weighting gradients. In this report a new method is proposed and implemented that addresses these two limitations. Specifically, a single‐shot pulse sequence that sequentially acquires one gradient‐echo (GRE) and two diffusion‐weighted spin‐echo (SE) images was developed. In addition, the diffusion‐weighting gradient waveform was numerically optimized to null the cross terms with the deoxyhemoglobin‐induced background gradients to fully isolate the effect of diffusion weighting from that of oxygenation‐level changes. The experimental results show that this new single‐shot method can acquire ADC maps with sufficient signal‐to‐noise ratio (SNR), and establish its practical utility in functional MRI (fMRI) to complement the blood oxygenation level‐dependent (BOLD) technique and provide differential sensitivity for different vasculatures to better localize neural activity originating from the small vessels. Magn Reson Med 57:417–422, 2007. © 2007 Wiley‐Liss, Inc.