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A, Schematic representation of IRF in a tissue with an intact (ie, impermeable to contrast molecules) BBB.
B, Schematic representation of an IRF, R(t), in tissue with a permeable BBB. The first plateau reflects the intravascular phase of the contrast material. The second (and much lower) plateau reflects the extravascular phase. The extraction fraction, E, is derived by dividing the second plateau height by the first plateau height.
