Intracranial lesions: flow-related enhancement on MR images using time-of-flight effects

Many physico-anatomic variables and instrument parameters influence the relative magnetic resonance signal intensity of vascular channels. The interaction of these mechanisms is complex, but their composite effects can be accounted for by two main categories of flow phenomena: time-of-flight effects and spin-phase changes. Of these two mechanisms only the time-of-flight effect known as flow-related enhancement produces augmentation of intravascular signal. Flow-related enhancement can potentially provide positive contrast of diagnostic value in terms of anatomic depiction of vascular detail as well as physiologic characterization of blood flow. The authors have used a single-section, selectively irradiated, spin-echo pulse sequence to maximize flow-related enhancement within a variety of intracranial lesions, as a supplement to their regular imaging. The technique was found to be diagnostically useful in improving the conspicuity of vascular lesions, in determining vessel patency, in distinguishing flow void from calcification, and in obtaining semiquantitative information about flow dynamics.