Simultaneous Multi-slice Turbo-FLASH Imaging with CAIPIRINHA for Whole Brain Distortion-Free Pseudo-Continuous Arterial Spin Labeling at 3 and 7T (2025)

Influence of selecting EPI readout-encoding bandwidths on arterial spin labeling perfusion MRI

Magnetic Resonance Materials in Physics, Biology and Medicine, 2009

Object The objective of this study was to investigate effects of varying readout bandwidths on the arterial spin labeling (ASL)-perfusion MRI measurements at a high magnetic field MRI system. Materials and methods Brain perfusion studies were performed on nine volunteers (four males, five females) using flow sensitive alternating inversion recovery (FAIR) ASL single-shot echo-planar imaging (EPI)-MRI. To investigate EPI bandwidth effects on the time-series perfusion-weighted imaging (PWI) data, two regions-of-interest (ROI) were placed outside the brain to determine the level of noise and another ROI inside the brain to determine the level of signal. Coefficients of variations (CoV) were calculated for the timeseries PWI data. One-way analysis of variance (ANOVA) was used to investigate voxel-wise differences in the time-series PWI data between two different bandwidth values. Results At the level of ROI, there was no significant effect of changing EPI bandwidths on the time-series PWI data in any of the volunteers (P > 0.031). In contrast, CoV values over the dynamic PWI data varied with depending on selecting EPI bandwidths and voxel-based tests showed that N2 ghosting, modulated by EPI bandwidth, can appear in some brain regions, especially in areas that overlap with the spatial distribution of N2 ghosting artifacts.

Multiple boli arterial spin labeling for high signal-to-noise rodent brain perfusion imaging

Magnetic Resonance in Medicine

A systematic method is proposed for optimising a promising preclinical arterial spin labelling (ASL) sequence based on the use of a train of adiabatic radio-frequency pulses labelling successive boli of blood water. Methods: The sequence optimisation is performed and evaluated using brain imaging experiments in mice and in rats. It involves the investigation of several parameters, ranging from the number of adiabatic pulses and labelling duration, to the properties of the adiabatic hyperbolic secant pulses (i.e. amplitude and frequency modulation). Results: Species dependant parameters are identified, allowing for robust fast optimisation protocols to be introduced. The resulting optimised multiple boli ASL (mbASL) sequence provides with significantly higher average signal-to-noise ratios (SNR) per voxel volume than currently encountered in ASL studies (278 mm-3 in mice and 172 mm-3 in rats). Comparing with the commonly used Flowsensitive Alternating Inversion Recovery technique (FAIR), mbASL-to-FAIR SNR ratios reach 203 % for mice and 725 % for rats. Conclusion: When properly optimised, mbASL can offer a robust, high SNR ASL alternative for rodent brain perfusion studies

Comparison of quantitative perfusion imaging using arterial spin labeling at 1.5 and 4.0 Tesla

Magnetic Resonance in Medicine, 2002

High-field arterial spin labeling (ASL) perfusion MRI is appealing because it provides not only increased signal-to-noise ratio (SNR), but also advantages in terms of labeling due to the increased relaxation time T1 of labeled blood. In the present study, we provide a theoretical framework for the dependence of the ASL signal on the static field strength, followed by experimental validation in which a multislice pulsed ASL (PASL) technique was carried out at 4T and compared with PASL and continuous ASL (CASL) techniques at 1.5T, both in the resting state and during motor activation. The resting-state data showed an SNR ratio of 2.3:1.4:1 in the gray matter and a contrast-to-noise ratio (CNR) of 2.7:1.1:1 between the gray and white matter for the difference perfusion images acquired using 4T PASL, 1.5T CASL, and 1.5T PASL, respectively. However, the functional data acquired using 4T PASL did not show significantly improved sensitivity to motor cortex activation compared with the 1.5T functional data, with reduced fractional perfusion signal change and increased intersubject variability. Possible reasons for these experimental results, including susceptibility effects and physiological noise, are discussed. Magn Reson Med 48:242–254, 2002. © 2002 Wiley-Liss, Inc.

Implementation of quantitative perfusion imaging techniques for functional brain mapping using pulsed arterial spin labeling

NMR in Biomedicine, 1997

We describe here experimental considerations in the implementation of quantitative perfusion imaging techniques for functional MRI using pulsed arterial spin labeling. Three tagging techniques: EPISTAR, PICORE, and FAIR are found to give very similar perfusion results despite large differences in static tissue contrast. Two major sources of systematic error in the perfusion measurement are identified: the transit delay from the tagging region to the imaging slice; and the inclusion of intravascular tagged signal. A modified technique called QUIPSS II is described that decreases sensitivity to these effects by explicitly controlling the time width of the tag bolus and imaging after the bolus is entirely deposited into the slice. With appropriate saturation pulses the pulse sequence can be arranged so as to allow for simultaneous collection of perfusion and BOLD data that can be cleanly separated. Such perfusion and BOLD signals reveal differences in spatial location and dynamics that may be useful both for functional brain mapping and for study of the BOLD contrast mechanism. The implementation of multislice perfusion imaging introduces additional complications, primarily in the elimination of signal from static tissue. In pulsed ASL, this appears to be related to the slice profile of the inversion tag pulse in the presence of relaxation, rather than magnetization transfer effects as in continuous arterial spin labeling, and can be alleviated with careful adjustment of inversion pulse parameters. © Abbreviations used: ASL, arterial spin labeling; BOLD, blood oxygenation level dependent; CBF, cerebral blood flow; EPISTAR, echo-planar imaging with signal targetting using alternating RF; FAIR, flow alternated inversion recovery; fMRI, functional magnetic resonance imaging; MRI, magnetic resonance imaging; MT, magnetization transfer; PICORE, proximal inversion with a control for off resonance effects; QUIIPSS II, quantitative imaging of perfusion using a single subtraction (version II); RF, radiofrequency; SNR, signal-to-noise ratio.

Improved pseudo-continuous arterial spin labeling for mapping brain perfusion

Journal of Magnetic Resonance Imaging, 2010

Purpose-To investigate arterial spin labeling (ASL) methods for improved brain perfusion mapping. Previously, Pseudo-continuous arterial spin labeling (pCASL) was developed to overcome limitations inherent with conventional continuous arterial spin labeling (CASL), but the control scan (null pulse) in the original method for pCASL perturbs the equilibrium magnetization, diminishing the ASL signal. Here, a new modification of pCASL, termed mpCASL is reported, in which the perturbation caused by the null pulse is reduced and perfusion mapping improved. Materials and Methods-Improvements with mpCASL are demonstrated using numerical simulations and experiments. ASL signal intensity as well as contrast and reproducibility of invivo brain perfusion images were measured in four volunteers who had MRI scans at 4 Tesla and the data compared across the labeling methods. Results-Perfusion maps with mpCASL showed, on average, higher ASL signal intensity and higher image contrast than those from CASL or pCASL. Furthermore, mpCASL yielded better reproducibility in repeat scans than the other methods. Conclusion-The experimental results are consistent with the hypothesis that the new null pulse of mpCASL leads to improved brain perfusion images.

STAR-HASTE: Perfusion imaging without magnetic susceptibility artifact

Magnetic Resonance in Medicine, 1997

A novel magnetic resonance imaging technique (STAR-HASTE) based on pulsed arterial spin labeling using a single shot acquisition method is described for perfusion imaging. The method is similar to EPISTAR in using STAR (Signal Targeting with Alternating Radiofrequency) technique for pulsed radiofrequency labeling of inflowing blood, but uses a half-Fourier single shot turbo spin-echo (HASTE) sequence for data acquisition instead of echo-planar imaging (EPI). Our preliminary studies show that STAR-HASTE permits perfusion imaging to be performed without many of the artifacts encoluntered with other imaging methods based on EPI acquisition. The novel method not only provides similar perfusion information to that obtained by EPISTAR, as demonstrated in the functional brain imaging study, but also eliminates magnetic susceptibility artifacts and image distortion commonly observed in EPI images. Furthermore, this technique can be readily implemented in MR systems without EPI capability.

Amplitude-modulated Continuous Arterial Spin-labeling 3.0-T Perfusion MR Imaging with a Single Coil: Feasibility Study

Radiology, 2005

Abbreviations: ASL ϭ arterial spin labeling CASL ϭ continuous ASL CBF ϭ cerebral blood flow ⌬M ϭ mean signal change PASL ϭ pulsed ASL RF ϭ radiofrequency ROI ϭ region of interest SAR ϭ specific absorption rate SNR ϭ signal-to-noise ratio

Multislice imaging of quantitative cerebral perfusion with pulsed arterial spin labeling

Magnetic Resonance in Medicine, 1998

A method is presented for multislice measurements of quantitative cerebral perfusion based on magnetic labeling of arterial spins. The method combines a pulsed arterial inversion, known as the FAIR (Flow-sensitive Alternating Inversion Recovery) experiment, with a fast spiral scan image acquisition. The short duration (22 ms) of the spiral data collection allows simultaneous measurement of up to 10 slices per labeling period, thus dramatically increasing efficiency compared to current single slice acquisition protocols. Investigation of labeling efficiency, suppression of unwanted signals from stationary as well as intraarterial spins, and the FAIR signal change as a function of inversion delay are presented. The assessment of quantitative cerebral blood flow (CBF) with the new technique is demonstrated and shown to require measurement of arterial transit time as well as suppression of intraarterial spin signals. CBF values measured on normal volunteers are consistent with results obtained from H,0i5 positron emission tomography (PET) studies and other radioactive tracer approaches. In addition, the new method allows detection of activation-related perfusion changes in a fingertapping experiment, with locations of activation corresponding well to those observed with blood oxygen level dependent (BOLD) fMRI.

Perfusion imaging of the human brain at 1.5 T using a single-shot EPI spin tagging approach

Magnetic Resonance in Medicine, 1996

Single-shot echo planar imaging (EPI) techniques have been applied, in conjunction with arterial spin tagging approaches, to obtain images of cerebral blood flow in a single axial slice in the human brain. Serial studies demonstrate that cerebral blood flow images acquired in 8 rnin are reproducible, with a statistical precision of approximately 210 cc/lOO g/min. The average value of cerebral blood flow in the slice is 51 k 11 ccll00 glmin for six normal subjects. The cerebral blood flow images contain two types of artifact, probably due to arterial and venous blood volume contributions, which must be overcome before the arterial spin tagging approach can be used for routine clinical studies.

Evaluation of segmented 3D acquisition schemes for whole-brain high-resolution arterial spin labeling at 3 T

NMR in biomedicine, 2014

Recent technical developments have significantly increased the signal-to-noise ratio (SNR) of arterial spin labeled (ASL) perfusion MRI. Despite this, typical ASL acquisitions still employ large voxel sizes. The purpose of this work was to implement and evaluate two ASL sequences optimized for whole-brain high-resolution perfusion imaging, combining pseudo-continuous ASL (pCASL), background suppression (BS) and 3D segmented readouts, with different in-plane k-space trajectories. Identical labeling and BS pulses were implemented for both sequences. Two segmented 3D readout schemes with different in-plane trajectories were compared: Cartesian (3D GRASE) and spiral (3D RARE Stack-Of-Spirals). High-resolution perfusion images (2 × 2 × 4 mm(3) ) were acquired in 15 young healthy volunteers with the two ASL sequences at 3 T. The quality of the perfusion maps was evaluated in terms of SNR and gray-to-white matter contrast. Point-spread-function simulations were carried out to assess the im...