Acceleration of ASL‐based time‐resolved MR angiography by acquisition of control and labeled images in the same shot (ACTRESS)

Abstract

PurposeNoncontrast 4D‐MR‐angiography (MRA) using arterial spin labeling (ASL) is beneficial because high spatial and temporal resolution can be achieved. However, ASL requires acquisition of labeled and control images for each phase. The purpose of this study is to present a new accelerated 4D‐MRA approach that requires only a single control acquisition, achieving similar image quality in approximately half the scan time.MethodsIn a multi‐phase Look‐Locker sequence, the first phase was used as the control image and the labeling pulse was applied before the second phase. By acquiring the control and labeled images within a single Look‐Locker cycle, 4D‐MRA was generated in nearly half the scan time of conventional ASL. However, this approach potentially could be more sensitive to off‐resonance and magnetization transfer (MT) effects. To counter this, careful optimizations of the labeling pulse were performed by Bloch simulations. In in‐vivo studies arterial visualization was compared between the new and conventional ASL approaches.ResultsOptimization of the labeling pulse successfully minimized off‐resonance effects. Qualitative assessment showed that residual MT effects did not degrade visualization of the peripheral arteries.ConclusionThis study demonstrated that the proposed approach achieved similar image quality as conventional ASL‐MRA approaches in just over half the scan time. Magn Reson Med 79:224–233, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Optimization of the spatial modulation function of vessel‐encoded pseudo‐continuous arterial spin labeling and its application to dynamic angiography

“…When looking into more detail at the in‐plane spatial modulation, however, it will be noted that the transition between the labeling and the control conditions is much more gradual than the PASL profile by, e.g., a hyperbolic secant or frequency offset corrected inversion (FOCI) pulse . This more gradual transition could easily lead to partial labeling of untargeted arteries, leading to reduced SNR efficiency and the requirement for complex postprocessing to separate out the individual contributions from each vessel.…”

Acceleration of vessel‐selective dynamic MR Angiography by pseudocontinuous arterial spin labeling in combination with Acquisition of ConTRol and labEled images in the Same Shot (ACTRESS)

“…In this manuscript, we have presented a novel vessel‐selective 4D‐MRA acquisition which combines vessel‐selective pCASL with the ACTRESS acceleration approach . In the original ACTRESS approach based upon PASL for labeling, the application of vessel‐selective labeling was hampered by elevated background signal as a result of the disturbance of the equilibrium magnetization of the static tissue arising from the intersection of the labeling slab with the imaging slices.…”

“…In this manuscript, we have presented a novel vessel-selective 4D-MRA acquisition which combines vessel-selective pCASL with the ACTRESS acceleration approach. 3 In the original ACTRESS approach based upon PASL for labeling, the application of vessel-selective labeling was hampered by elevated background signal as a result of the disturbance of the equilibrium magnetization of the static tissue arising from the intersection of the labeling slab with the imaging slices. By using pCASL for labeling, in which the labeling pulses are applied approximately parallel to the imaging slices and, F I G U R E 7 Comparison of images acquired by the pCASL-ACTRESS approach (scan time of 2 min 40 s) and conventional approach (5 min 19 s) therefore, do not interfere with the magnetization in the imaging slices, the combination of vessel-selective labeling and ACTRESS acceleration became possible.…”

“…In the original ACTRESS approach using PASL, it is very important that the control image acquired in the first phase of the Look-Locker readout does not contain the residual labeled blood from the previous Look-Locker readout cycle. 3 Such a carryover of the labeled blood to the next Look-Locker cycle is unlikely to happen in pCASL-ACTRESS, because the WET presaturation module applied before the pCASL labeling cancels the residual labeling remaining within the imaging volume. In this study, 4D-MRA using the true pCASL-ACTRESS approach was not acquired in the in vivo studies due to restricted examination time.…”

Simultaneous acquisition of perfusion image and dynamic MR angiography using time‐encoded pseudo‐continuous ASL

“…Arterial spin labeling (ASL) techniques are used both for noncontrast 4D‐MRA as well as for perfusion imaging. Because both imaging modalities are based on a similar ASL preparation module, a combined acquisition seems feasible.…”