Improved Conspicuity and Delineation of High-Grade Primary and Metastatic Brain Tumors Using “Restriction Spectrum Imaging”: Quantitative Comparison with High B-Value DWI and ADC

Abstract

Background and Purpose Restriction spectrum imaging (RSI) is a sensitive DWI technique for probing separable water diffusion compartments in tissues. Here, we evaluate RSI tumor cellularity maps (RSI-CM) derived from the spherically-restricted water compartment for improved tumor conspicuity and delineation from non-tumor tissue and reduced sensitivity to edema compared with high b-value DWI and ADC. Materials and Methods RSI was performed in 10 pre-surgical patients: 4 with glioblastoma, 3 with primary CNS lymphoma, and 3 with metastatic brain tumors. Multi-directional DWI data was collected at b = 500, 1500, and 4000 sec/mm2. Quantification of tumor conspicuity (TC), edema conspicuity (EC), and relative sensitivity to edema (RSE) for RSI-CM, DWI at b = 4000 (DWI-4000), and ADC were compared in manually drawn VOIs. Receiver operating characteristic (ROC) curves were used to evaluate the sensitivity and specificity of each method for delineating tumor from NAWM. Results Significant TC was seen with both RSI-CM and DWI-4000, but not ADC. Significant EC was seen with ADC, but not RSI-CM or DWI-4000. Significantly greater TC was seen with RSI-CM compared with DWI-4000. Significantly reduced RSE was seen with RSI-CM compared with both DWI-4000 and ADC. Greater sensitivity and specificity for delineating tumor from NAWM was seen with RSI-CM (AUC = .91) compared with both DWI-4000 (AUC = .77) and ADC (AUC = .66). Conclusion RSI-CM offers improved conspicuity and delineation of high-grade primary and metastatic brain tumors and reduced sensitivity to edema compared with high b-value DWI and ADC.

Diffusion-Weighted Imaging in Cancer: Physical Foundations and Applications of Restriction Spectrum Imaging

“…The RSI design matrix includes a distribution (or “spectrum”) of effective diffusion pools spanning hindered and restricted length scales with both isotropic and anisotropic geometries. In Fig 4 we illustrate both a schematic for the RSI spectrum model and the resultant fit of the model to data collected in a 51 year-old patient with right frontal GBM prior to surgical intervention (47). Note the separation of diffusion components in different tissue types, with the primary lesion exhibiting a large volume fraction of spherically-restricted water likely stemming from water trapped within cancer cells.…”

“…Also note the large fraction of free and hindered water in areas of necrosis and edema. The volume fraction of spherically restricted water (either with or without additional filtering of white matter signal using a technique called “beamforming” (48)) has been coined the RSI cellularity index or cellularity map (47, 49–51). In addition, the signal from the restricted anisotropic component can be use to map the density and orientation of surrounding white matter tracts (50).…”

Pretreatment ADC Histogram Analysis Is a Predictive Imaging Biomarker for Bevacizumab Treatment but Not Chemotherapy in Recurrent Glioblastoma

“…These limitations have resulted in a surge of more advanced imaging biomarkers aimed at predicting response to therapy, as summarized in various review articles. 7,8 Among these new imaging biomarkers showing promise are diffusion MR imaging techniques, [9][10][11][12][13][14][15][16][17][18] including ADC histogram analysis. Previous results have shown that pretreatment ADC histogram analysis performed within the contrast-enhancing tumor regions can stratify patients with recurrent GBM into high-and low-risk groups.…”

Targeted Prostate Biopsy: Lessons Learned Midst the Evolution of a Disruptive Technology

“…Moreover, pulse sequences such as RSI may allow standardization of diffusion imaging across scanners, which is currently lacking. When RSI was applied to diagnosis of brain tumors, the tumor signal was enhanced by 10-fold over conventional diffusion imaging 45 . Preliminary studies indicate that RSI may also be of great value in prostate cancer 44 .…”