Probabilistic MRI Tractography of the Optic Radiation Using Constrained Spherical Deconvolution: A Feasibility Study

Abstract

Background and PurposeImaging the optic radiation (OR) is of considerable interest in studying diseases affecting the visual pathway and for pre-surgical planning of temporal lobe resections. The purpose of this study was to investigate the clinical feasibility of using probabilistic diffusion tractography based on constrained spherical deconvolution (CSD) to image the optic radiation. It was hypothesized that CSD would provide improved tracking of the OR compared with the widely used ball-and-stick model.MethodsDiffusion weighted MRI (30 directions) was performed on twenty patients with no known visual deficits. Tractography was performed using probabilistic algorithms based on fiber orientation distribution models of local white matter trajectories. The performance of these algorithms was evaluated by comparing computational times and receiver operating characteristic results, and by correlation of anatomical landmark distances to dissection estimates.ResultsThe results showed that it was consistently feasible to reconstruct individual optic radiations from clinically practical (4.5 minute acquisition) diffusion weighted imaging data sets using CSD. Tractography based on the CSD model resulted in significantly shorter computational times, improved receiver operating characteristic results, and shorter Meyer’s loop to temporal pole distances (in closer agreement with dissection studies) when compared to the ball-and-stick based algorithm.ConclusionsAccurate tractography of the optic radiation can be accomplished using diffusion MRI data collected within a clinically practical timeframe. CSD based tractography was faster, more accurate and had better correlation with known anatomical landmarks than ball-and-stick tractography.

Automated retinofugal visual pathway reconstruction with multi-shell HARDI and FOD-based analysis

“…Our average distance values between the temporal pole and the Meyer’s loop were 30.7 and 30.9 for the left and right hemispheres, respectively. This falls very close to the average value found in many dissection studies (Ebling & Reulen, 1988; Choi et al, 2006) as well as dMRI studies (Sherbondy et al, 2008; Lim et al, 2015). For future work, we work also introduce more flexible curvature controls that are adaptive to anatomical priors about the shape of the fiber tracts along different parts of the retinofugal pathway.…”

“…Thus the final curvature constraint of 1mm was chosen to reconcile the two goals of fully capturing Meyer’s loop while maintaining accurate fiber orientations closer to the visual cortex. A common metric used to judge tractographic representations of Meyer’s loop is the measurement of the distance between its anterior tip and the temporal pole (Lim et al, 2015; Sherbondy et al, 2008). This is an important indicator especially for surgical planning applications.…”

“…For example, mean distance to the temporal pole was almost 16mm larger than the results reported in postmortem dissection studies (Ebeling & Reulen, 1988). On a sample of 20 patients, a recent study by Lim et al (2015) developed a probabilistic tractography method for optic radiation reconstruction based on constrained spherical deconvolution (CSD) (Tournier et al, 2007). This study utilized data collected via common clinical scan protocols (30 gradient directions, single b-value, voxel size 2.5×2.5×2.5mm) and demonstrated feasibility for temporal lobe surgery planning.…”

Implementation of clinical tractography for pre-surgical planning of space occupying lesions: An investigation of common acquisition and post-processing methods compared to dissection studies

“…For the OR, two previous studies have quantitatively compared tractography results to the Jülich atlas as a 'gold standard' [16,51]. These studies used a modified receiver operating characteristics (ROC) analysis to obtain an objective threshold which optimises the overlap between tractography and the Jülich atlas for three consecutive coronal slices within the core of the OR.…”

“…Similar to our results they reported no significant difference in ML-TP distance between diffusion tensor based tractography and probabilistic tractography with a threshold of 0.05. Measurements of ML-TP distance have also recently been investigated by [51], for CSD-based probabilistic tractography implemented using the MRTrix package (as we report here). In their study, they report a mean ML-TP distance of 30mm (range 20-34mm), which is greater than that reported in dissection studies.…”