A phantom study of intracranial CSF signal loss due to pulsatile motion.

MR imaging of the head often reveals localized areas of decreased signal intensity (flow voids) within the CSF. These flow voids are caused by turbulence within the CSF resulting from its pulsatile back-and-forth flow through the cerebral aqueduct and foramina. We describe a phantom that mimics the essential features of the CSF flow, and discuss its use in studying the dependence of the CSF flow void (CFV) on spin-echo (SE) and inversion-recovery pulse sequence parameters. The phantom had fluid-filled spaces to represent ventricles, and channels connecting these spaces to represent the aqueduct and foramina. A pump pushed the fluid in a pulsing manner through the phantom at various rates. The CFV was quantified by measuring signal loss relative to nonflowing fluid. The CFV did not appear to depend on repetition time or inversion time. The CFV was, however, strongly dependent on echo time (TE), and for single-echo SE sequences CFV became less severe as TE decreased. An even-echo rephasing effect was observed for multiecho sequences. Slice thickness and field of view also affected the appearance of the CFV, as did gating with respect to the pulsatile motion. These results imply that TE, field of view, slice thickness, and gating must be considered when using the appearance or absence of the CFV in diagnosis.