Shared velocity encoding: A method to improve the temporal resolution of phase‐contrast velocity measurements

Abstract

Phase contrast magnetic resonance imaging (PC-MRI) is used routinely to measure fluid and tissue velocity with a variety of clinical applications. PC-MRI methods require acquisition of additional data to enable phase difference reconstruction, making real-time imaging problematic. Shared Velocity Encoding (SVE), a method devised to improve the effective temporal resolution of PC-MRI, was implemented in a real-time pulse sequence with segmented echo planar readout. The effect of SVE on peak velocity measurement was investigated in computer simulation, and peak velocities and total flow were measured in a flow phantom and in volunteers and compared with a conventional ECG-triggered, segmented k-space phase-contrast sequence as a reference standard. Computer simulation showed a 36% reduction in peak velocity error from 8.8% to 5.6% with SVE. A similar reduction of 40% in peak velocity error was shown in a pulsatile flow phantom. In the phantom and volunteers, volume flow did not differ significantly when measured with or without SVE. Peak velocity measurements made in the volunteers using SVE showed a higher concordance correlation (0.96) with the reference standard than non-SVE (0.87). The improvement in effective temporal resolution with SVE reconstruction has a positive impact on the precision and accuracy of real-time PC-MRI peak velocity measurements.

Real-time phase contrast magnetic resonance imaging for assessment of haemodynamics: from phantom to patients

“…Overall our results are in line with recently published data [22]. They show close agreement for velocities and flow in initial comparisons of a shared velocity-encoding-based realtime PC sequence and a conventional segmented PC sequence in a pulsatile flow phantom and healthy volunteers.…”

“…Shared velocity encoding with two-sided velocity encoding improved the effective frame rate by a factor of 2 by sharing data between two adjacent frames [22]. Temporal generalized autocalibrating partially parallel acquisition (TGRAPPA) with an acceleration rate of 3 was used to further speed up image acquisition resulting in an effective temporal resolution of 39.7 ms per frame.…”

“…echo planar imaging (EPI), parallel and split acquisition techniques) [19][20][21]. In this paper, shared velocity encoding is used in addition to further speed up the acquisition [22].…”

Respiratory Effects on Fontan Circulation During Rest and Exercise Using Real-Time Cardiac Magnetic Resonance Imaging

“…The imaging protocol, which utilized parallel imaging, began with an anatomic survey using static steady state free precession; this data was reformatted to acquire slice orientations and positions perpendicular to flow for rtPCMR acquisitions. The rtPCMR was an echoplanar sequence utilizing shared velocity encoding, the details of which have been described previously [15]. It utilized, in general, the following parameters: Repetition time =9.5 msec, Echo time =4.1 msec, Flip angle of 30 degrees, Field of view=320–400 mm, Slice thickness=8–10 mm, and Bandwidth=2841 Hz/pixel.…”

Advanced flow MRI: emerging techniques and applications

“…To achieve sufficiently high frame rates needed for real-time flow acquisitions, optimised and accelerated 2D flow imaging pulse sequences have been developed, which combine effective data readout modules (e.g., echo planar imaging, EPI) with data undersampling and parallel imaging data reconstruction (e.g., compressed sensing, k-t-acceleration in spatial and temporal dimension). In addition, shared velocity encoding 10,163 has been proposed to further improve temporal resolution and is based on the concept of sharing sets of full k-space data between adjacent time frames in order to double the effective frame rate. Based on these developments, 2D real-time flow imaging with through-plane velocity encoding can be performed with temporal update rates on the order of 30–50 ms (see Fig.…”