Improved cerebrospinal fluid flow measurements using phase contrast balanced steady-state free precession

We present a demonstration of phase contrast balanced steady-state free precession (PC-bSSFP) for measuring cerebrospinal fluid (CSF) flow in the brain and spine, and a comparison of measurements obtained with this technique to conventional phase contrast using incoherent gradient echoes (PC-GRE). With PC-GRE sequences, CSF images suffer from low signal-to-noise ratio (SNR), due to short repetition times required for adequate temporal resolution, and the long relaxation time of CSF. Furthermore, CSF flow is often nonlaminar, causing phase dispersion and signal loss in PC-GRE images. It is hypothesized that PC-bSSFP can improve CSF flow measurements with its high SNR and insensitivity to turbulent flow effects. CSF images acquired from the two techniques were compared in 13 healthy volunteers. Three measures were used to objectively evaluate the PC-bSSFP sequence: the CSF flow percentage, defined as the percentage of the total CSF region exhibiting pulsatile flow, net stroke volume and SNR. Images acquired with PC-bSSFP demonstrated pulsatile CSF flow in 35.8% (P<.005), 11.2% (P<.05) and 27.8% (P<.0005) more pixels than PC-GRE in the prepontine cistern, anterior and posterior cervical subarachnoid space (SAS), respectively. Likewise, measurements of stroke volume in these regions increased by 61.6% (P<.05), 16.8% (P<.001) and 48.3% (P<.0001), respectively. Similar comparisons in the aqueduct showed no statistical difference in stroke volumes between the two techniques (P=.5). The average gain in SNR was 3.3+/-1.7 (P<.001) in the prepontine cistern, 5.0+/-0.2 (P<.01) at the cervical level and 2.0+/-0.4 (P<.001) in the aqueduct in PC-bSSFP magnitude images over PC-GRE images. In addition to the obvious advantage of increased SNR, these results indicate that PC-bSSFP provides more complete measurements of CSF flow data than PC-GRE. PC-bSSFP can be used as a reliable technique for CSF flow quantification for the characterization of normal and altered intracranial CSF flow patterns.