title: High-resolution diffusion-weighted imaging with interleaved variable-density spiral acquisitions.
abstract: OBJECTIVE
  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.
  
  
  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 x 0.9 x 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) x 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) x 10(-3) mm2/second, which was in a good agreement with the reported literature values.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disease and Stroke, National Institute of Health, Bethesda, Maryland 20892, USA. litie@ninds.nih.gov
authors.forename: Tie-Qiang
authors.initials: TQ
authors.lastname: Li
authors.forename: Dong-Hyun
authors.initials: DH
authors.lastname: Kim
authors.forename: Michael E
authors.initials: ME
authors.lastname: Moseley
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005782:Gels; D006801:Humans; D019047:Phantoms, Imaging
chemical_list: D005782:Gels