Volumetric velocity measurements in restricted geometries using spiral sampling: a phantom study

Abstract

Object:To evaluate the accuracy of maximum velocity measurements using volumetric phase contrast imaging with spiral readouts in a stenotic flow phantom. Materials and Methods:In a phantom model, maximum velocity, flow, pressure gradient and streamline visualizations were evaluated using volumetric phase contrast MRI with velocity encoding in one (extending on current clinical practice) and three directions (for characterization of the flow field) using spiral readouts.Results of maximum velocity and pressure drop were compared to CFD simulations (Computational Fluid Dynamics), as well as corresponding low-TE Cartesian data. Flow was compared to 2D throughplane PC upstream from the restriction. Results:Results obtained with 3D throughplane PC as well as 4D PC at shortest TE using spiral readout showed excellent agreements with the maximum velocity values obtained with CFD (<1% for both methods), while larger deviations were seen using Cartesian readouts (-2% and 13%, respectively).Peak pressure drop calculated from 3D throughplane PC and 4D PC spiral sequences was 14% and 13% overestimated compared to CFD. Conclusion:Identification of the maximum velocity location as well as accurate velocity quantification can be obtained in stenotic regions using short-TE spiral volumetric PC imaging.3

Quantification of turbulence and velocity in stenotic flow using spiral three‐dimensional phase‐contrast MRI

“…However, the flow rate estimates seem to be less accurate when the estimation is performed in the region of the post-stenotic flow jet, especially for the OBL orientations. This corresponds well to previous observations of flow rate measured with 4D flow spiral measurements in jet regions (15). For 2D through-plane PC-MRI, a TE longer than 3 ms has been shown to cause severe underestimation of flow rate for actual flow rates over 300 mL/s (8).…”

“…Instead, we see a slight increase of the measurement of the maximum velocity in the jet for the oblique orientation. Measurements with spiral readouts on a similar phantom have shown that a TE longer than 3 ms will result in less accurate maximum velocity estimates . In the present work, TE was 1.9–2.5 ms and 4.3–4.5 ms for the spiral and Cartesian maximum velocity measurements, respectively.…”

“…Spiral trajectories have previously been shown to be suitable for 2D PC‐MRI of high‐speed flow jets and unsteady flow systems . A recent study, evaluated spiral 4D PC‐MRI and found that the short TE of spiral trajectories are advantageous when assessing maximum velocity and flow rate in stenotic nonpulsatile flow in vitro . However, the effect of spiral sampling on the assessment of TKE has not yet been investigated.…”

4D spiral imaging of flows in stenotic phantoms and subjects with aortic stenosis

“…Other methods that have adopted a stack of spirals for 4D flow acquisitions include Nilsson et al . In this work, which was tested under steady‐flow phantom experiments, velocities from MRI were compared to CFD simulations.…”

Retrospectively gated intracardiac 4D flow MRI using spiral trajectories

“…Spiral MRI has previously been used for 2D flow imaging , 3D MR angiography , and 2D myocardial phase velocity mapping . In addition to reducing the scan time, spiral k‐space trajectories also are inherently insensitive to flow‐induced displacement . Moreover, because spiral k–space trajectories start in the center of k‐space, they may be suitable for respiratory self‐gating.…”