Current and emerging MR imaging techniques for the diagnosis and management of CSF flow disorders: a review of phase-contrast and time-spatial labeling inversion pulse

Abstract

This article provides an overview of phase-contrast and time-spatial labeling inversion pulse MR imaging techniques to assess CSF movement in the CNS under normal and pathophysiologic situations. Phase-contrast can quantitatively measure stroke volume in selected regions, notably the aqueduct of Sylvius, synchronized to the heartbeat. Judicious fine-tuning of the technique is needed to achieve maximal temporal resolution, and it has limited visualization of CSF motion in many CNS regions. Phase-contrast is frequently used to evaluate those patients with suspected normal pressure hydrocephalus and a Chiari I malformation. Correlation with successful treatment outcome has been problematic. Time-spatial labeling inversion pulse, with a high signal-to-noise ratio, assesses linear and turbulent motion of CSF anywhere in the CNS. Time-spatial labeling inversion pulse can qualitatively visualize whether CSF flows between 2 compartments and determine whether there is flow through the aqueduct of Sylvius or a new surgically created stoma. Cine images reveal CSF linear and turbulent flow patterns.

Fig 1.

A 26-year-old healthy male volunteer. A, Geometry for the oblique-axial CSF phase-contrast scan. The section is positioned axially at a 90° angle through the aqueduct of Sylvius (rectangle, A). Aliasing (B) occurs if a phase value is greater than the maximum expected velocity, causing the phase to wrap back to a multiple of π, appearing black (black arrow) when it should appear white (or vice versa). Uncorrected (dotted line) and corrected (solid line) flow waveforms in milliliters per second represent bidirectional flow through the aqueduct (C). Aliasing can be corrected off-line by adding a multiple of 2 × π × V_enc to aliased pixels.

Fig 2.

An 18-year-old healthy female volunteer. A, A series of midline sagittal images depicting pulsatile CSF flow, where flow magnitude and direction are represented as gray-scale. Flow changes from positive to negative and back to positive (white indicates peak caudal flow; black, peak cranial flow). B, Depiction of a series of axial images at the level of the aqueduct (arrow). In both series, every odd phase of the 16 cardiac phases that were acquired is displayed.

Fig 3.

Hydrocephalus in a 74-year-old woman. The patient had undergone endoscopic third ventriculostomy. Patency of the fenestration on the floor of the third ventricle is readily and noninvasively confirmed postsurgery by the presence of CSF flow between the third ventricle and the basal cisterns (asterisk) emerging from the tagged region (dotted lines). (See On-line Video 1, which demonstrates postsurgical CSF flow between the third ventricle and the basal cisterns.)

Fig 4.

Idiopathic normal pressure hydrocephalus in a 78-year-old man. Time-SLIP has consistently shown the presence of reflux flow from the third ventricle into the lateral ventricle in adult patients without hydrocephalus (A). This flow is shown to be restricted in NPH (B). Time-SLIP in the same patient confirms that this flow is restored after surgical intervention by inserting a CSF diverting shunt (C, artifacts on the right are from the shunt valve). (See On-line Videos 2 and 3, which demonstrate restricted flow and restored flow pre- and postsurgery, respectively.)

Fig 5.

Chiari malformation in a 43-year-old woman pre- (top row) and post- (bottom row) surgery, shown at incremental TIs. Obliteration of the subarachnoid space at the craniocervical junction is associated with Chiari I malformation and a syrinx (top row, arrow). Following craniocervical decompression (bottom row, arrow), Time-SLIP shows CSF flow ventral to the brain stem and cervical spinal cord and a decrease in the size of the syrinx (bold arrow). (See On-line Videos 4 and 5, which demonstrate restricted flow and restored flow with a decrease in the size of the syrinx pre- and postsurgery, respectively.)