Rapid and continuous monitoring of cerebral perfusion by magnetic resonance line scan assessment with arterial spin tagging (original) (raw)
Related papers
Arterial Spin Labeling: a One-stop-shop for Measurement of Brain Perfusion in the Clinical Settings
2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007
Arterial Spin Labeling (ASL) has opened a unique window into the human brain function and perfusion physiology. Altogether fast and of intrinsic high spatial resolution, ASL is a technique very appealing not only for the diagnosis of vascular diseases, but also in basic neuroscience for the follow-up of small perfusion changes occurring during brain activation. However, due to limited signal-to-noise ratio and complex flow kinetics, ASL is one of the more challenging disciplines within magnetic resonance imaging. In this paper, the theoretical background and main implementations of ASL are revisited. In particular, the different uses of ASL, the pitfalls and possibilities are described and illustrated using clinical cases.
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.
Challenges for non-invasive brain perfusion quantification using arterial spin labeling
The neuroradiology journal, 2011
Arterial Spin Labeling (ASL) sequences for perfusion Magnetic Resonance Imaging (MRI) have recently become available to be used in the clinical practice, offering a completely non-invasive technique for the quantitative evaluation of brain perfusion. Despite its great potential, ASL perfusion imaging still presents important methodological challenges before its incorporation in routine protocols. Specifically, in some pathological conditions in which the cerebrovascular dynamics is altered, the standard application of ASL may lead to measurement errors. In these cases, it would be possible to estimate perfusion, as well as arterial transit times, by collecting images at multiple time points and then fitting a mathematical model to the data. This approach can be optimized by selecting a set of optimal imaging time points and incorporating knowledge about the physiological distributions of the parameters into the model estimation procedures. In this study, we address the challenges th...
International Congress Series, 2004
The development of arterial spin labeling (ASL) techniques has provided a useful strategy for quantitative measurement of cerebral blood flow (CBF). However, quantification of transit time has historically been difficult to achieve without prolonged scan times, since ASL has suffered from low signal-to-noise ratio (SNR). Continuous ASL (CASL) has recently been implemented on the 3T magnetic resonance (MR) system, which can provide a more favorable perfusion signal SNR because of the higher Lamor frequency and prolonged T1 times. Therefore, the goal of the present study was to determine whether CASL perfusion imaging on the 3T MR system could evaluate transit time within a reasonable scan time. This study describes a theoretical framework for measuring arterial transit time using a two-compartment model, followed by application of the model to CASL perfusion data obtained from six normal subjects. CBF and arterial arrival time maps were successfully created using a two-parameter fitting procedure, and the transit time obtained with this model was consistent with those obtained from previous reports. However, the CBF values calculated with the present model were lower than those reported when using 1.5T. Possible reasons for this discrepancy, including transit time, CBV, label efficiency and MT effect, are discussed. D
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.
Magnetic resonance imaging of perfusion using spin inversion of arterial water
Proceedings of the National Academy of Sciences, 1992
A technique has been developed for proton magnetic resonance imaging (MRI) of perfusion, using water as a freely diffusable tracer, and its application to the measurement of cerebral blood flow (CBF) in the rat is demonstrated. The method involves labeling the inflowing water proton spins in the arterial blood by inverting them continuously at the neck region and observing the effects of inversion on the intensity of brain MRI. Solution to the Bloch equations, modified to include the effects of flow, allows regional perfusion rates to be measured from an image with spin inversion, a control image, and a T1 image. Continuous spin inversion labeling the arterial blood water was accomplished, using principles of adiabatic fast passage by applying continuous-wave radiofrequency power in the presence of a magnetic field gradient in the direction of arterial flow. In the detection slice used to measure perfusion, whole brain CBF averaged 1.39 +/- 0.19 ml.g-1.min-1 (mean +/- SEM, n = 5). T...
Perfusion imaging using dynamic arterial spin labeling (DASL
Magnetic Resonance in Medicine, 2001
Recently, a technique based on arterial spin labeling, called dynamic arterial spin labeling (DASL (Magn Reson Med 1999;41:299 -308)), has been introduced to measure simultaneously the transit time of the labeled blood from the labeling plane to the exchange site, the longitudinal relaxation time of the tissue, and the perfusion of the tissue. This technique relies on the measurement of the tissue magnetization response to a time varying labeling function. The analysis of the characteristics of the tissue magnetization response (transit time, filling time constant, and perfusion) allows for quantification of the tissue perfusion and for transit time map computations. In the present work, the DASL scheme is used in conjuction with echo planar imaging at 4.7 T to produce brain maps of perfusion and transit time in the anesthetized rat, under graded hypercapnia. The data obtained show the variation of perfusion and transit time as a function of arterial pCO 2 . Based on the data, CO 2 reactivity maps are computed. Magn Reson Med 45:1021-
Measurement of cerebral perfusion with arterial spin labeling: Part 1. Methods
Journal of The International Neuropsychological Society, 2007
Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI) method that provides a highly repeatable quantitative measure of cerebral blood flow (CBF). As compared to the more commonly used blood oxygenation level dependent (BOLD) contrast-based methods, ASL techniques measure a more biologically specific correlate of neural activity, with the potential for more accurate estimation of the location and magnitude of neural function. Recent advances in acquisition and analysis methods have improved the somewhat limited sensitivity of ASL to perfusion changes associated with neural activity. In addition, ASL perfusion measures are insensitive to the low-frequency fluctuations commonly observed in BOLD experiments and can make use of imaging sequences that are less sensitive than BOLD contrast to signal loss caused by magnetic susceptibility effects. ASL measures of perfusion can aid in the interpretation of the BOLD signal change and, when combined with BOLD, can measure the change in oxygen utilization accompanying changes in behavioral state. Whether used alone to probe neural activity or in combination with BOLD techniques, ASL methods are contributing to the field's understanding of healthy and disordered brain function. (JINS, 2007, 13, 1-9.)
Technological advances in MRI measurement of brain perfusion
Journal of Magnetic Resonance Imaging, 2005
Measurement of brain perfusion using arterial spin labeling (ASL) or dynamic susceptibility contrast (DSC) based MRI has many potential important clinical applications. However, the clinical application of perfusion MRI has been limited by a number of factors, including a relatively poor spatial resolution, limited volume coverage, and low signalto-noise ratio (SNR). It is difficult to improve any of these aspects because both ASL and DSC methods require rapid image acquisition. In this report, recent methodological developments are discussed that alleviate some of these limitations and make perfusion MRI more suitable for clinical application. In particular, the availability of high magnetic field strength systems, increased gradient performance, the use of RF coil arrays and parallel imaging, and increasing pulse sequence efficiency allow for increased image acquisition speed and improved SNR. The use of parallel imaging facilitates the trade-off of SNR for increases in spatial resolution. As a demonstration, we obtained DSC and ASL perfusion images at 3.0 T and 7.0 T with multichannel RF coils and parallel imaging, which allowed us to obtain high-quality images with in-plane voxel sizes of 1.5 ϫ 1.5 mm 2 .
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.