Daniel Krainak PhD, Presenter: Nothing to Disclose

David Thomasson, Abstract Co-Author: Nothing to Disclose

Jennifer Hufton, Abstract Co-Author: Nothing to Disclose

Nadia Madelaine Biassou MD, PhD, Abstract Co-Author: Nothing to Disclose

Sunder S. Rajan PhD, Abstract Co-Author: Nothing to Disclose

Clinicians and researchers have begun to use diffusion tensor imaging (DTI) to characterize and assess a variety of conditions. To date, these DTI markers have not been thoroughly examined for slice angulation effects. Using an anisotropic phantom, we investigated how slice angulation alters DTI imaging characteristics.

DTI data of an anisotropic phantom (Brain Innovations, Inc, Maastricht, NL) were acquired at 3 Tesla with a 2D single-shot EPI sequence consisting of 160 slices of 160x160mm FOV; voxel size 1x1x1mm3, TR/TE of 33845/64ms, SENSE factor 2, and medium directional resolution (b-value=0 and 15 gradient orientations b-value= 900 s/mm2). Slice angle data consisted of 7 acquisitions moving from transverse to coronal acquisition in 15° steps. Additionally, six combinations of slice select and phase encode orientations were acquired (foot-head, right-left anterior-posterior). We used Nipype (Neuroimaging in Python Pipelines and Interfaces) to invoke FSL (Oxford, UK) utilities for data processing. Measures of fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) were extracted from the same region-of-interest (ROI) of an anisotropic fiber bundle. One-factor (slice acquisition angle) ANOVAs were used to examine the data. Post hoc comparisons were made with t-tests accounting for multiple comparisons (Bonferroni).

We observed significant differences in the DTI-derived metrics within the ROI for FA (F=5.986, p<0.001), RD (F=8.54, p<0.001) and MD (F=3.79, p<0.001). Across all pairs of acquisition angles, between pairs differences of up to 5% were observed in FA and MD, up to 12% in RD. Data acquired with phase encoding in the foot-head (z) orientation had coefficients of variation for FA and MD 3-5 times greater than right-left (x) or anterior-posterior (y).

DTI-derived metrics are sensitive to the MRI slice angulation. Data acquired with the phase encoding gradient in the foot-head orientation contain greater variability than other orientations. Clinicians and researchers should consider systematic differences in outcome metrics due to slice acquisition angle.

Clinicians need to avoid acquiring DTI data with phase-encode in the foot-head direction and consider systematic differences in DTI-metrics due to slice acquisition angle.

Krainak, D, Thomasson, D, Hufton, J, Biassou, N, Rajan, S, Slice Acquisition Angle Affects DTI Derived Metrics.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043875.html