Whereas phase effects are suppressed as fully as possible in TOF MRA, it is the flow-induced phase shift of the transverse magnetization that is employed to image blood vessels with phase contrast techniques. There are two ways of using phase effects to selectively depict blood flow:
• magnitude contrast (rephased-dephased) method
• phase contrast method
Today, magnitude contrast is only rarely used. Conversely, techniques that in a stricter sense are referred to as "phase contrast", have gained greater importance both as an imaging method and as an accurate approach to measuring blood flow velocity and direction.
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