An optimized velocity selective arterial spin labeling module with reduced eddy current sensitivity for improved perfusion quantification

Abstract

Velocity-selective (VS) arterial spin labeling is a promising method for measuring perfusion in areas of slow or collateral flow by eliminating the bolus arrival delay associated with other spin labeling techniques. However, B(0) and B(1) inhomogeneities and eddy currents during the VS preparation hinder accurate quantification of perfusion with VS arterial spin labeling. In this study, it is demonstrated through simulations and experiments in healthy volunteers that eddy currents cause erroneous tagging of static tissue. Consequently, mean gray matter perfusion is overestimated by up to a factor of 2, depending on the VS preparation used. A novel eight-segment B(1) insensitive rotation VS preparation is proposed to reduce eddy current effects while maintaining the B(0) and B(1) insensitivity of previous preparations. Compared to two previous VS preparations, the eight-segment B(1) insensitive rotation is the most robust to eddy currents and should improve the quality and reliability of VS arterial spin labeling measurements in future studies.

Quantitative measurement of cerebral blood volume using velocity‐selective pulse trains

“…For the VS pulse trains using DRHT (Figure 3a), the normalized subtraction errors (mean ± SD) for velocity-encoding along L-R, A-P and S-I directions were 0.08 ± 0.15%, −0.17 ± 0.18%, and −1.37 ± 0.46%, respectively, which showed lower sensitivity to eddy currents (slightly higher mean errors but much lower SD) than the corresponding ones with DRCP (Figure 3b), despite shorter gaps between gradient lobes and refocusing pulses (4.0 ms vs. 5.7 ms). The stripe patterns in the images acquired with gradients along L-R direction (Figure 3) is related to specific characteristics of the gradient imperfections in this direction (most likely eddy currents), as previously observed in VSASL work (42,44). It might also be partially caused by incomplete refocusing due to B1 inhomogeneities, as suggested in two MRA papers using VS pulse trains (54,64).…”

An optimized design to reduce eddy current sensitivity in velocity-selective arterial spin labeling using symmetric BIR-8 pulses

“…In the phantom experiments with BIR‐4, strong EC effects across the L/R and A/P axes were observed on scanner B [also noticed in ] but not on scanner A (Fig. and Fig.…”

“…In the following derivations, a single exponential decay with a time constant T is considered. The ECs generated by a trapezoidal waveform can be modeled as : where and are the times of the rise and fall portions of the trapezoid, t is the time from the initial start of the sequence, and is the initial amplitude of the gradient generated by EC at the end of the ramp for each transition. Assuming that the gradient pulses have the same shape and size (Fig.…”

Improved sensitivity and temporal resolution in perfusion FMRI using velocity selective inversion ASL

“…The bottom panel shows the phase of the RF pulse. FIGURE S2 Diagram of the BIR‐8 velocity selective saturation pulses proposed in Meakin and Jezzard and Guo et al FIGURE S3 Velocity Profiles for the velocity selective inversion pulse used for labeling (left panel), and for the velocity selective saturation pulse used for arterial suppression (right panel). The first zero‐crossing for the velocity saturation pulse happens at 0.7 cm/s.The efficiency of the velocity selective inversion pulse varies with velocity.…”