Enhanced Fiber Tractography Using Edema Correction: Application and Evaluation in High-Grade Gliomas

Abstract

BACKGROUND A limitation of diffusion tensor imaging (DTI)-based tractography is peritumoral edema that confounds traditional diffusion-based magnetic resonance metrics. OBJECTIVE To augment fiber-tracking through peritumoral regions by performing novel edema correction on clinically feasible DTI acquisitions and assess the accuracy of the fiber-tracks using intraoperative stimulation mapping (ISM), task-based functional magnetic resonance imaging (fMRI) activation maps, and postoperative follow-up as reference standards. METHODS Edema correction, using our bi-compartment free water modeling algorithm (FERNET), was performed on clinically acquired DTI data from a cohort of 10 patients presenting with suspected high-grade glioma and peritumoral edema in proximity to and/or infiltrating language or motor pathways. Deterministic fiber-tracking was then performed on the corrected and uncorrected DTI to identify tracts pertaining to the eloquent region involved (language or motor). Tracking results were compared visually and quantitatively using mean fiber count, voxel count, and mean fiber length. The tracts through the edematous region were verified based on overlay with the corresponding motor or language task-based fMRI activation maps and intraoperative ISM points, as well as at time points after surgery when peritumoral edema had subsided. RESULTS Volume and number of fibers increased with application of edema correction; concordantly, mean fractional anisotropy decreased. Overlay with functional activation maps and ISM-verified eloquence of the increased fibers. Comparison with postsurgical follow-up scans with lower edema further confirmed the accuracy of the tracts. CONCLUSION This method of edema correction can be applied to standard clinical DTI to improve visualization of motor and language tracts in patients with glioma-associated peritumoral edema.

Significance of navigated transcranial magnetic stimulation and tractography to preserve motor function in patients undergoing surgery for motor eloquent gliomas

“…Limitations arise from the lack of intraoperative verification of the preoperative planning via electrophysiological monitoring and commonly known limitations of DTI [ 15 , 39 , 40 ].…”

Advancements in Diffusion MRI Tractography for Neurosurgery

“…55 This technique can precisely delineate tractography even when edema is strong in the peritumoral white matter. 56 However, there is limited research on the practical application of such technology, and there is a paucity of evidence of its use in real-world neurosurgical practice.…”

“…Furthermore, the bicompartmental free water modeling algorithm can now exclude the effects of edema from the tissue by estimating the quantity of extracellular free water in the voxel using a bicompartmental model 55 . This technique can precisely delineate tractography even when edema is strong in the peritumoral white matter 56 . However, there is limited research on the practical application of such technology, and there is a paucity of evidence of its use in real-world neurosurgical practice.…”

Modern preoperative imaging and functional mapping in patients with intracranial glioma

“…This relevant information is, however, overlaid by free-water contamination, which is particularly relevant for the peritumoral edematous region. Thus, several strategies have been developed to disentangle and bias-correct the "true" diffusion signal, which could increase the diagnostic value of DTI-derived metrics [28][29][30].…”