Tract Orientation and Angular Dispersion Deviation Indicator (TOADDI): A framework for single-subject analysis in diffusion tensor imaging

Cheng G. Koay^{1,2}, Ping-Hong Yeh^{2,3}, John M. Ollinger^{2}, M. Okan İrfanoğlu^{1,3}, Carlo Pierpaoli^{1}, Peter J. Basser^{1}, Terrence R. Oakes^{2}, and Gerard Riedy^{2}

The salient features of the proposed framework are rigorous statistical quantification of orientation or shape deviation on a per-voxel basis, the incorporation of FDR and FNR methods for controlling the proportions of false positives and false negatives for an orientation deviation test and a nonparametric approach to testing shape deviation of the elliptical cones of uncertainty.

The most interesting preliminary biological finding from our clinical data is that the frontal portion of the superior longitudinal fasciculus seemed to be implicated in both tests (orientation and shape) as being significantly different from that of the control group. Another interesting result is that the Shape Deviation Indicator was able to separate the TBI patients from the single non-TBI subject at the chosen FDR level. The most puzzling result of this pilot study is that statistically significant voxels were found in the non-TBI subject under the orientation deviation test. Based on this preliminary test, we learned that the proposed orientation deviation test may be more sensitive to orientation changes in white matter tracts and perhaps at the cost of encountering more false positives.

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(A) The Gnomonic projection maps a point, s, on the unit
sphere to a point, p, on the u-v plane in which the line connecting both points
also passes through the center of the unit sphere. The u-v plane is tangent to
the unit sphere at (0,0,1). The inverse Gnomonic projection is the inverse of
the Gnomonic projection. (B) An ellipse on the u-v plane and its inverse
Gnomonic projection on the unit sphere. (C) The elliptical cone of uncertainty
with its center aligned along the z-axis.

Given two distinct centers (control group [red] and individual subject [blue]) of the elliptical COUs, two
scenarios are possible. (A) has
a lower Type II error than (B) because the center of the
control group is also deemed significantly different from that of the
individual subject. In (B), the center of the control group is not
significantly different from that of the individual subject because it is located within the confidence cone of the individual
subject.

Results of statistically significant deviation in orientation shown in (A) red, (B) blue and (C) yellow for TBI patient I, TBI patient II and single non-TBI subject, respectively. Results of statistically significant deviation in shape of the elliptical COU shown in (D) red and (E) blue for TBI patient I and TBI patient II, respectively. No voxel was found to be statistically significant under the shape deviation test for the non-TBI subject (F).

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

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