High‐resolution diffusion‐weighted imaging with interleaved variable‐density spiral acquisitions

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Abstract
Purpose: To develop a multishot magnetic resonance imaging (MRI) pulse sequence and reconstruction algorithm for diffusion‐weighted imaging (DWI) in the brain with submillimeter in‐plane resolution.Materials and Methods: A self‐navigated multishot acquisition technique based on variable‐density spiral k‐space trajectory design was implemented on clinical MRI scanners. The image reconstruction algorithm takes advantage of the oversampling of the center k‐space and uses the densely sampled central portion of the k‐space data for both imaging reconstruction and motion correction. The developed DWI technique was tested in an agar gel phantom and three healthy volunteers.Results: Motions result in phase and k‐space shifts in the DWI data acquired using multishot spiral acquisitions. With the two‐dimensional self‐navigator correction, diffusion‐weighted images with a resolution of 0.9 × 0.9 × 3 mm3 were successfully obtained using different interleaves ranging from 8–32. The measured apparent diffusion coefficient (ADC) in the homogenous gel phantom was (1.66 ± 0.09) × 10−3 mm2/second, which was the same as measured with single‐shot methods. The intersubject average ADC from the brain parenchyma of normal adults was (0.91 ± 0.01) × 10−3 mm2/second, which was in a good agreement with the reported literature values.Conclusion: The self‐navigated multishot variable‐density spiral acquisition provides a time‐efficient approach to acquire high‐resolution diffusion‐weighted images on a clinical scanner. The reconstruction algorithm based on motion correction in the k‐space data is robust, and measured ADC values are accurate and reproducible. J. Magn. Reson. Imaging 2005;21:468–475. Published 2005 Wiley‐Liss, Inc.