MR-Gated Intracranial CSF Dynamics: Evaluation of CSF pulsatile flow
Magnetic resonance imaging (MRI) was used to evaluate cerebrospinal fluid (CSF) pulsatile flow in eleven patients with hydrocephalus and three normal subjects. Multislice images were acquired using Siemens MRI system, operating at 1.0 Tesla. Each individual was positioned in a head coil and images of 5 mm slice-thickness were acquired. The echo time (TE) was 50 msec. The radiofrequency (RF) stimulation and all scan data acquisitions were gated to the QRS complex, such that the repetition time (TR) was at least twice the subject’s R-R interval and was always between 1700–2000 msec. A bipolar pulse was inserted between the 90 degrees RF pulse and the readout gradient, which induces a phase shift proportional to the velocity of the moving CSF. Images of the diastolic time data acquisition (DTDA) and systolic time data acquisition (STDA) were obtained at 40 msec and 300 msec after the R wave respectively. Scan times were approximately 10 minutes. The final flow images were acquired offline by subtraction at the same slice position. Higher intensities in the CSF and vascular pathways correspond to higher flow velocities. A comparison of the signal intensity in the DTDA and STDA images shows that the foramen of Monro expands in systole and contracts in diastole. The aqueduct appears narrower in diastole. The height of the third ventricle was greater in diastole than in systole. No significant change in signal intensity was observed in the basal cisterns. These dynamic changes in CSF compartments shown in figure (a-b) are probably related to transmission of arterial pulse pressure, which causes a rhythmic squeeze of the two thalami, referred to as “thalamic pump.” In the presence of obstruction of CSF flow, as shown in figure (c-d), there is absence of flow-related signal intensity.