Abstract
Simple SummaryMRI plays an important role in the classification of structural brain changes and quantitative MRI can provide more and different information than conventional MRI. A comparison with neuropathological parameters helps to expand the understanding of (patho)physiological concepts but has hardly been carried out so far. In this prospective study, we correlated quantitative MRI data with histological features of 25 patients with isocitrate dehydrogenase (IDH) wild-type glioma. We found that the relative shortening of T1 relaxation time after the application of contrast agent was pronounced in the presence of tumor cells and vascular proliferates, indicating a disruption of the blood brain barrier (BBB). T2′ relaxation time, depending on local deoxyhemoglobin concentration, correlated with the vessel density but not with immunopositivity for endogenous markers of hypoxia.Quantitative MRI allows to probe tissue properties by measuring relaxation times and may thus detect subtle changes in tissue composition. In this work we analyzed different relaxation times (T1, T2, T2* and T2′) and histological features in 321 samples that were acquired from 25 patients with newly diagnosed IDH wild-type glioma. Quantitative relaxation times before intravenous application of gadolinium-based contrast agent (GBCA), T1 relaxation time after GBCA as well as the relative difference between T1 relaxation times pre-to-post GBCA (T1rel) were compared with histopathologic features such as the presence of tumor cells, cell and vessel density, endogenous markers for hypoxia and cell proliferation. Image-guided stereotactic biopsy allowed for the attribution of each tissue specimen to its corresponding position in the respective relaxation time map. Compared to normal tissue, T1 and T2 relaxation times and T1rel were prolonged in samples containing tumor cells. The presence of vascular proliferates was associated with higher T1rel values. Immunopositivity for lactate dehydrogenase A (LDHA) involved slightly longer T1 relaxation times. However, low T2′ values, suggesting high amounts of deoxyhemoglobin, were found in samples with elevated vessel densities, but not in samples with increased immunopositivity for LDHA. Taken together, some of our observations were consistent with previous findings but the correlation of quantitative MRI and histologic parameters did not confirm all our pathophysiology-based assumptions.
Highlights
MRI is crucial for diagnosis, therapy planning and monitoring of gliomas
T1 indicates how fast the excited tissue protons emit the energy absorbed from the radio-frequency pulse and realign with the external magnetic field
T2 can be considered a version of T2* which is corrected for spin–spin interactions, being defined by 1/T2* = 1/T2 + 1/T2. Both T2* and T2 values sensitively reflect modifications in tissue composition, though T2 better indicates the impact of blood oxygenation [2]
Summary
MRI is crucial for diagnosis, therapy planning and monitoring of gliomas. At present, it is mainly used for determining morphological features, such as the tumor size, contrast enhancement, necrosis and its spatial relationship to functional brain structures. T2 is the time constant of the decay process of transverse magnetization due to interactions between the magnetic fields of adjacent protons. The time constant T2* is influenced by several dephasing processes, such as magnetic field inhomogeneity, magnetic susceptibility, chemical shift and spin–spin interaction [1]. T2 can be considered a version of T2* which is corrected for spin–spin interactions, being defined by 1/T2* = 1/T2 + 1/T2 Both T2* and T2 values sensitively reflect modifications in tissue composition, though T2 better indicates the impact of blood oxygenation [2]
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