Technological advances in MRI measurement of brain perfusion (original) (raw)
Related papers
2019
For standard clinical applications, ASL images are typically acquired with 4-8 mm thick slices and 3-4 mm in-plane resolution. However, in this paper we demonstrate that high-resolution continuous arterial spin labeling (CASL) perfusion images can be acquired in a clinically relevant scan time using current MRI technology. CASL was implemented with a separate neck coil for labeling the arterial blood on a 4.7T MRI using standard axial 2D GE-EPI. Typical-resolution to high-resolution (voxels of 95, 60, 45, 27, or 7 mm 3) images were compared for qualitative and quantitative cerebral blood flow analysis (CBF) in nine healthy volunteers (ages: 24-32 years). The highest resolution (1.5x1.5x3 = 7 mm 3) CASL implementation yielded perfusion images with improved cortex depiction and increased cortical CBF measurements (53 ± 8 ml/100g/min), consistent with reduced partial volume averaging. The 7 mm 3 voxel images were acquired with 6 cm brain coverage in a clinically relevant scan of 6 minutes. Improved spatial resolution facilitates CBF measurement with reduced partial volume averaging and may be valuable for the detection of perfusion deficits in small lesions and perfusion measurement in small brain regions.
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.
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.
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.
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.
Construction and evaluation of a quantitative arterial spin labeling brain perfusion template at 3T
2011
Abstract Arterial spin labeling (ASL) allows non-invasive imaging and quantification of brain perfusion by magnetically labeling blood in the brain-feeding arteries. ASL has been used to study cerebrovascular diseases, brain tumors and neurodegenerative disorders as well as for functional imaging. The use of a perfusion template could be of great interest to study inter-subject regional variation of perfusion and to perform automatic detection of individual perfusion abnormalities.
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...
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.