Research Highlights

Single-Shot ADC Imaging

It has been suggested that apparent diffusion coefficient (ADC) contrast can be sensitive to cerebral blood flow changes during brain activation. However, current ADC imaging techniques inherently have a low temporal resolution due to the requirement of multiple acquisitions with different b factors, as well as potential confound from cross-talks 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 and two diffusion-weighted spin-echo 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 showed that this new single-shot method could acquire ADC maps with sufficient signal-to-noise ratio, establishing its practical utility in fMRI to complement the blood oxygenation level-dependent (BOLD) technique and allow differential sensitivity for different vasculatures to better localize neural activity originating from the small vessels.

Citation: Song, A.W., Guo, H., Truong, T.-K., Single-shot ADC imaging for fMRI, Magn. Reson. Med. 2006 (in press).