Commentary: 5-Aminolevulinic Acid and Contrast-Enhanced Ultrasound: The Combination of the 2 Techniques to Optimize the Extent of Resection in Glioblastoma Surgery

Application of intraoperative B-mode ultrasound and shear wave elastography for glioma grading

Background

To evaluate the value of intraoperative B-mode ultrasound and shear wave elastography (SWE) in differentiating low-grade and high-grade gliomas.

Methods

A total of 172 patients with glioma were examined by B-mode ultrasound to obtain a tumor sonogram. Intraoperative SWE was performed on 52 patients to obtain Young's modulus values of peritumor tissue and tumor tissue, and the differences in conventional B-mode signs and Young's modulus values of gliomas of different grades were then compared. The diagnostic performance of SWE in glioma grading was assessed by receiver operating characteristic (ROC) curve analysis, and the intra- and interobserver reliability of SWE was analyzed by the intraclass correlation coefficient (ICC).

Results

For B-mode ultrasound, patient age, cystic degeneration, and peritumor edema were independent risk factors for high-grade glioma (P<0.05, OR >1). For SWE, Young's modulus values of peritumor tissue, low-grade glioma, and high-grade glioma tissues were 8.20 (7.50, 9.70) kPa, 19.65 (15.30, 24.75) kPa, and 9.55 (8.50, 13.80) kPa, respectively. The area under the ROC curve for the diagnosis of high-grade glioma by SWE was 0.859 (95% CI: 0.758-0.961, P<0.05), and the optimal cutoff value was 12.1 kPa, with 89.3% sensitivity and 75.0% specificity. The intra- and interobserver reliability of SWE in grading gliomas was excellent, with ICCs ranging from 0.921 to 0.965.

Conclusions

High-grade glioma is associated with significantly more severe necrotic cystic degeneration and peritumoral edema on B-mode ultrasound and lower stiffness on SWE. Further, SWE exhibits excellent intra- and interobserver reliability. Intraoperative B-mode ultrasound combined with SWE helps differentiate different grades of gliomas.

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

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.