Abstract:
PURPOSE:In diffusion MRI, the actual b-value played out on the scanner may deviate from the nominal value due to magnetic field imperfections. A simple image-based correction method for this problem is presented. METHODS:The apparent diffusion constant (ADC) of a water phantom was measured voxel-wise along 64 diffusion directions at b = 1000 s/mm2 . The true diffusion constant of water was estimated, considering the phantom temperature. A voxel-wise correction factor, providing an effective b-value including any magnetic field deviations, was determined for each diffusion direction by relating the measured ADC to the true diffusion constant. To test the method, the measured b-value map was used to calculate the corrected voxel-wise ADC for additionally acquired diffusion data sets on the same water phantom and data sets acquired on a small water phantom at three different positions. Diffusion tensor was estimated by applying the measured b-value map to phantom and in vivo data sets. RESULTS:The b-value-corrected ADC maps of the phantom showed the expected spatial uniformity as well as a marked improvement in consistency across diffusion directions. The b-value correction for the brain data resulted in a 5.8% and 5.5% decrease in mean diffusivity and angular differences of the primary diffusion direction of 2.71° and 0.73° inside gray and white matter, respectively. CONCLUSION:The actual b-value deviates significantly from its nominal setting, leading to a spatially variable error in the common diffusion outcome measures. The suggested method measures and corrects these artifacts.
journal_name
Magn Reson Medjournal_title
Magnetic resonance in medicineauthors
Lee Y,Kettinger AO,Wilm BJ,Deichmann R,Weiskopf N,Lambert C,Pruessmann KP,Nagy Zdoi
10.1002/mrm.28078subject
Has Abstractpub_date
2020-06-01 00:00:00pages
2173-2184issue
6eissn
0740-3194issn
1522-2594journal_volume
83pub_type
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