Method which enables analysis of blood vessels generated by a tumor.
Dynamic contrast enhanced magnetic resonance imaging and Dynamic susceptibility weighted contrast enhanced perfusion imaging represent a widely accepted method to assess glioblastoma microvasculature.
This method makes use of a contrast agent which is blocked by the regular brain-blood-barrier but is not blocked in the blood vessels generated by the tumor. In this method the images taken are MRI T1-weighted after an intravenous injection of the contrast agent. The concentration of the contrast agent is measured, when it passes from the blood vessels to the extra-cellular space of the tissue (it cannot enter inside the cells) and whether it goes back to the blood vessels.
The contrast agents used are often gadolinium-based. Gadolinium injection causes the relaxation time to decrease, and therefore images done after gadolinium injection have higher contrast. First a regular T1-weighted MRI scan is done (with no gadolinium), then gadolinium is injected (usually dose of 0.05-0.1 mmol/kg) and another T1-weighted scan is done. By comparing the values of T1 in both scans, for each voxel, it is possible to identify permeable blood vessel and a tissue with active tumor. When there are many healthy cells in the tissue, the gadolinium gets back to the blood since it cannot enter the cells. If tissue is damaged and there are fewer cells, the gadolinium stays in the extracellular space of the tissue and gets out to the blood vessels very slowly.
To ascertain if the volume transfer constant (Ktrans) derived from T1 dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) correlates with the immunohistological markers of angiogenesis in high-grade gliomas.
Fifty-one image-guided biopsy specimens in 34 patients with newly presenting high-grade gliomas (grade III = 16; grade IV = 18) underwent preoperative imaging (conventional imaging and T1 DCE-MRI). We correlated vascular endothelial growth factor (VEGF) expression and the microvessel density (MVD) of MRI-guided biopsy specimens with the corresponding DCE-derived Ktrans . Histological sections were stained with VEGF and CD34, and examined under light microscopy. These histological and molecular markers of angiogenesis were correlated with the Ktrans of the region of interest corresponding to the biopsy specimen.
The Ktrans showed a significant positive correlation with VEGF expression (ρ = 0.582, P = 0.001) but not with MVD stained with CD34 antibody (ρ = 0.328, P = 0.072).
The Ktrans derived from DCE-MRI can reflect the VEGF expression of high-grade gliomas but not the MVD 1).
Spratt et al. report the first analysis on the utility of DCE-MRI for metastatic sarcoma spine metastases treated with SBRT. They demonstrate that early assessment at two months post-SBRT using size and subjective neuroradiology impressions is insufficient to judge ultimate disease progression, and that a combination of perfusion parameters provides excellent correlation to local control 2).
performed conventional and dynamic susceptibility-contrast MRI imaging in 38 patients with brain tumours: 20 with metastases (breast carcinoma: two; renal carcinoma: five; colorectal carcinoma: one; lung carcinoma: seven; melanoma: five), and 18 with high-grade astrocytomas. We obtained cerebral blood volume (CBV) maps and calculated the relative CBV (rCBV) in different areas using the ratio between the CBV in the pathological area (CBVp) and in the contralateral white matter (CBVn). We calculated the maximum rCBV (rCBVmax) for each tumour and compared the mean rCBVmax in each group of tumours. The mean rCBV of melanoma metastases (5.35+/-2.32, range 3.14-9.23) and of renal carcinoma metastases (8.17+/-2.39, range 5.41-11.64) were significantly greater than those of high-grade astrocytomas (2.61+/-1.17, range 1.3-5.0) ( P=0.002 and <0.001, respectively) and of lung carcinoma metastases (2.94+/-0.86, range 1.43-4.04) ( P=0.003 and 0.002). There was no statistically significant difference between the mean rCBV of lung metastases and of high-grade astrocytomas ( P=0.59). Large, solitary, necrotic metastases can be indistinguishable from high-grade astrocytomas using conventional MRI. Demonstration of an elevated rCBV which may suggest a hypervascular lesion such as renal carcinoma or melanoma 3).