Quantitative MRI for analysis of peritumoral edema in malignant gliomas

Abstract

Background and purposeDamage to the blood-brain barrier with subsequent contrast enhancement is a hallmark of glioblastoma. Non-enhancing tumor invasion into the peritumoral edema is, however, not usually visible on conventional magnetic resonance imaging. New quantitative techniques using relaxometry offer additional information about tissue properties. The aim of this study was to evaluate longitudinal relaxation R1, transverse relaxation R2, and proton density in the peritumoral edema in a group of patients with malignant glioma before surgery to assess whether relaxometry can detect changes not visible on conventional images.MethodsIn a prospective study, 24 patients with suspected malignant glioma were examined before surgery. A standard MRI protocol was used with the addition of a quantitative MR method (MAGIC), which measured R1, R2, and proton density. The diagnosis of malignant glioma was confirmed after biopsy/surgery. In 19 patients synthetic MR images were then created from the MAGIC scan, and ROIs were placed in the peritumoral edema to obtain the quantitative values. Dynamic susceptibility contrast perfusion was used to obtain cerebral blood volume (rCBV) data of the peritumoral edema. Voxel-based statistical analysis was performed using a mixed linear model.ResultsR1, R2, and rCBV decrease with increasing distance from the contrast-enhancing part of the tumor. There is a significant increase in R1 gradient after contrast agent injection (P < .0001). There is a heterogeneous pattern of relaxation values in the peritumoral edema adjacent to the contrast-enhancing part of the tumor.ConclusionQuantitative analysis with relaxometry of peritumoral edema in malignant gliomas detects tissue changes not visualized on conventional MR images. The finding of decreasing R1 and R2 means shorter relaxation times closer to the tumor, which could reflect tumor invasion into the peritumoral edema. However, these findings need to be validated in the future.

Patient respiratory‐triggered quantitative T2 mapping in the pancreas

“…Unlike conventional MR sequences, which evaluate morphological alterations, T 2 mapping (or T 2 relaxometry) enables quantification of the transverse relaxation time of the underlying tissues . This evaluation is assumed to be more sensitive and reproducible than the visual assessment of T 2 ‐weighted MR images for identifying minor contrast changes (eg, tissue edema) . For this reason, it is applied for quantifying well‐defined pathologies (eg, cardiac iron overload or cartilage degeneration) …”

Quantitative histopathologic assessment of perfusion MRI as a marker of glioblastoma cell infiltration in and beyond the peritumoral edema region

“…In the clinical context, marginal infiltration typically occurs outside contrast‐enhancing regions, in a quasinormoxic microenvironment. Perfusion drops with increasing distance from the contrast‐enhancing part of the tumor partly due to limited angiogenesis . The vascular endothelial growth factor (VEGF) secreted by GBM cells appears to be involved not only in neovascularization but also in edema production through the induction of vascular permeability .…”

“…Decreased perfusion in tumor regions is commonly observed in rodent glioblastoma models and can be explained by the early stage of tumor progression, before contrast‐enhancement related to leaky vessels that arise from angiogenesis. In fact, newly formed tumor vessels are often nonfunctional, displaying low blood flow or not participating in the microcirculation . Functional angiogenesis requires solid tumor conditions (eg, significant tumor burden, hypoxia), that can be observed either in noninfiltrative models that lack clinical relevance, or when the tumors reach such large sizes that animal survival and welfare is compromised.…”

“…Despite the clear relationship between tumor cell density and perfusion shown in this work, a direct connection cannot be assumed and several potential mechanisms should be considered. Compression of the peritumoral tissue caused by edema in conjunction with increased intracranial pressure (ICP) is a known cause of reduced local perfusion with increasing distance from the contrast‐enhancing part of the tumor . ICP effects are expected to be minimal in this marginal infiltration model due to the relatively small tumor volumes.…”

“…Perfusion drops with increasing distance from the contrastenhancing part of the tumor partly due to limited angiogenesis. 31 The vascular endothelial growth factor (VEGF) secreted by GBM cells appears to be involved not only in neovascularization but also in edema production 32 through the induction of vascular permeability. 33 Distant from the hypoxic microenvironment of the tumor core, brain tumors may develop and grow using vascular co-option as the main mechanism of neovascularization, 33 without needing an angiogenic switch.…”