Assistant Professor of Radiology Tehran University of Medical Sciences, Tehran, Iran
Gliomas are the most common primary brain tumor in adults. The prognosis of brain tumors, whether primary or metastatic, is strongly related with their grades. High-grade gliomas usually have more angiogenesis, neoangiogenesis and increased blood-brain barrier (BBB) permeability. The perfusion MRI can depict tissue vascularization, angioneogenesis, microcirculation, tissue blood volume and flow. The signal changes in vessels during the passage of paramagnetic contrast agent can be calculated as relative cerebral blood volume (rCBV) and cerebral blood flow (rCBF) parameters. The increased vascular permeability causes an increase in extravasations ofcontrastmedium and changes in rCBV and rCBF. Permeability MRI estimates vascular permeability by measuring contrast medium leakage through the BBB and has two main parameters: (1) vascular transfer constant (Ktrans), which describes the permeability of blood vessels to contrast medium based on a two-compartment pharmacokinetic model and (2) Extravascular and extracellular volume fraction (Ve), the interstitial volume in which extracellular contrast agents accumulate if they cross the BBB. The main purpose of this lecture is to describe the diagnostic accuracy of the perfusion and permeability MRI in differentiating the high- and low-grade brain gliomas and also gliomas versus primary lymphoma and metastasis.