Flow Effects and MR Angiography

Abstract

As described in Chapter 6, the choice of imaging parameters and the spin properties of the tissue determine the intensity of the MR signal and the resulting image contrast for a stationary medium. Ultimately it is the steady state values of the longitudinal magnetization and the resulting transverse magnetization during the detection period that will provide the signal. Blood is a composed of cellular and noncellular components and is about 80% water by weight. Therefore stationary blood will produce a signal similar to other tissue with long T1 and T2. In the presence of flow, the M _x, M _y, and M _z magnetizations are further modified to produce a variety of effects (flow void, flow saturation, ghosting, etc.), depending on the imaging pulse sequence and scan parameters. Before we examine these effects, it is important to understand the nature of blood flow in vessels.