Diffusion weighted imaging (DWI) has been at the forefront of cancer imaging since the early 2000’s. Prior to its application in clinical oncology, this powerful technique had already achieved widespread recognition due to its utility in the diagnosis of cerebral infarction. Following this initial success, the ability of DWI to detect inherent tissue contrast began to be exploited in the field of oncology. Although the initial oncologic applications for tumor detection and characterization, assessing treatment response, and predicting survival were primarily in the field of neuro-oncology, the scope of DWI has since broadened to include oncologic imaging of the prostate gland, breast, and liver. Despite its growing success and application, misconceptions as to the underlying physical basis of the DWI signal exist among researchers and clinicians alike. In this review, we provide a detailed explanation of the biophysical basis of diffusion contrast, emphasizing the difference between hindered and restricted diffusion, and elucidating how diffusion parameters in tissue are derived from the measurements via the diffusion model. We describe one advanced DWI modeling technique, called Restriction Spectrum Imaging (RSI). This technique offers a more direct in vivo measure of tumor cells, due to its ability to distinguish separable pools of water within tissue based on their intrinsic diffusion characteristics. Using RSI as an example, we then highlight the ability of advanced DWI techniques to address key clinical challenges in neuro-oncology, including improved tumor conspicuity, distinguishing actual response to therapy from pseudoresponse, and delineation of white matter tracts in regions of peritumoral edema. We also discuss how RSI, combined with new methods for correction of spatial distortions inherent diffusion MRI scans, may enable more precise spatial targeting of lesions, with implications for radiation oncology, and surgical planning.

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.

Background and Purpose Brain radiotherapy is limited in part by damage to white matter, contributing to neurocognitive decline. We utilized diffusion tensor imaging (DTI) with multiple b-values (diffusion weightings) to model the dose-dependency and time course of radiation effects on white matter. Materials and Methods Fifteen patients with high-grade gliomas treated with radiotherapy and chemotherapy underwent MRI with DTI prior to radiotherapy, and after months 1, 4-6, and 9-11. Diffusion tensors were calculated using three weightings (high, standard, and low b-values) and maps of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (λ‖), and radial diffusivity (λ⊥) were generated. The region of interest was all white matter. Results MD, λ‖, and λ⊥increased significantly with time and dose, with corresponding decrease in FA. Greater changes were seen at lower b-values, except for FA. Time-dose interactions were highly significant at 4-6 months and beyond (p < .001), and the difference in dose response between high and low b-values reached statistical significance at 9-11 months for MD, λ‖, and λ⊥ (p < .001, p < .001, p = .005 respectively) as well as at 4-6 months for λ‖ (p = .04). Conclusions We detected dose-dependent changes across all doses, even <10 Gy. Greater changes were observed at low b-values, suggesting prominent extracellular changes possibly due to vascular permeability and neuroinflammation.

Purpose:To determine the ability of fully automated volumetric magnetic resonance (MR) imaging to depict hippocampal atrophy (HA) and to help correctly lateralize the seizure focus in patients with temporal lobe epilepsy (TLE). Materials and Methods:This study was conducted with institutional review board approval and in compliance with HIPAA regulations.