Recent progress in ASL

Hernandez‐García, Luis; Lahiri, Anish; Schollenberger, Jonas

doi:10.1016/j.neuroimage.2017.12.095

Cited by 97 publications

(83 citation statements)

References 118 publications

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“…In the VS-ASL experiment, [95][96][97][98][99][100][101][102] uni-directional flow encoding is combined with nonselective (partial or full) RF saturation or excitation of arterial water protons. As the pulses are non-selective, excitation is close to the tissue of interest and long PLDs not required.…”

Section: Velocity Encodingmentioning

confidence: 99%

CEST, ASL, and magnetization transfer contrast: How similar pulse sequences detect different phenomena

Knutsson

Ahlgren

et al. 2018

Magnetic Resonance in Med

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Chemical exchange saturation transfer (CEST), arterial spin labeling (ASL), and magnetization transfer contrast (MTC) methods generate different contrasts for MRI. However, they share many similarities in terms of pulse sequences and mechanistic principles. They all use RF pulse preparation schemes to label the longitudinal magnetization of certain proton pools and follow the delivery and transfer of this magnetic label to a water proton pool in a tissue region of interest, where it accumulates and can be detected using any imaging sequence. Due to the versatility of MRI, differences in spectral, spatial or motional selectivity of these schemes can be exploited to achieve pool specificity, such as for arterial water protons in ASL, protons on solute molecules in CEST, and protons on semi-solid cell structures in MTC. Timing of these sequences can be used to optimize for the rate of a particular delivery and/or exchange transfer process, for instance, between different tissue compartments (ASL) or between tissue molecules (CEST/MTC). In this review, magnetic labeling strategies for ASL and the corresponding CEST and MTC pulse sequences are compared, including continuous labeling, single-pulse labeling, and multi-pulse labeling. Insight into the similarities and differences among these techniques is important not only to comprehend the mechanisms and confounds of the contrasts they generate, but also to stimulate the development of new MRI techniques to improve these contrasts or to reduce their interference. This, in turn, should benefit many possible applications in the fields of physiological and molecular imaging and spectroscopy.

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Section: Velocity Encodingmentioning

confidence: 99%

CEST, ASL, and magnetization transfer contrast: How similar pulse sequences detect different phenomena

Knutsson

Ahlgren

et al. 2018

Magnetic Resonance in Med

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“…Healthy brain function relies on the appropriate regulation of regional cerebral blood flow (CBF) for the delivery of oxygen and glucose to support brain metabolism. Over the past decade, arterial spin labeling (ASL) has emerged as a robust and noninvasive method for acquiring regional CBF maps (Hernandez-Garcia, Lahiri, & Schollenberger, 2018) with high reproducibility (Gevers et al, 2011;Hermes et al, 2007). In contrast to imaging methodologies that depend on the administration of a contrast agent to measure perfusion, such as dynamic susceptibility contrast (DSC)-magnetic resonance imaging (MRI), computed tomography (CT) perfusion imaging, single-photon emission tomography (SPECT), and H 2 [ 15 O] positron emission tomography (PET), ASL generates an image by magnetically "labeling" water molecules as an endogenous tracer (Williams, Detre, Leigh, & Koretsky, 1992).…”

Section: Introductionmentioning

confidence: 99%

Increased resting perfusion of the hippocampus in high positive schizotypy: A pseudocontinuous arterial spin labeling study

Modinos

Egerton

McMullen

et al. 2018

Human Brain Mapping

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Arterial spin labeling (ASL) provides absolute quantification of resting tissue cerebral blood flow (CBF) as an entirely noninvasive approach with good reproducibility. As a result of neurovascular coupling, ASL provides a useful marker of resting neuronal activity. Recent ASL studies in individuals at clinical high risk of psychosis (CHR) have reported increased resting hippocampal perfusion compared with healthy controls. Schizotypy refers to the presence of subclinical psychotic‐like experiences in healthy individuals and represents a robust framework to study neurobiological mechanisms involved in the extended psychosis phenotype while avoiding potentially confounding effects of antipsychotic medications or disease comorbidity. Here we applied pseudo‐continuous ASL to examine differences in resting CBF in 21 subjects with high positive schizotypy (HS) relative to 22 subjects with low positive schizotypy (LS), as determined by the Oxford and Liverpool Inventory of Feelings and Experiences. Based on preclinical evidence that hippocampal hyperactivity leads to increased activity in mesostriatal dopamine projections, CBF in hippocampus, midbrain, and striatum was assessed. Participants with HS showed higher CBF of the right hippocampus compared to those with LS (p = .031, family‐wise error corrected). No differences were detected in the striatum or midbrain. The association between increased hippocampal CBF and HS supports the notion that hippocampal hyperactivity might be a central characteristic of the extended psychosis phenotype, while hyperactivity in subcortical dopamine pathways may only emerge at a higher intensity of psychotic experiences.

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“…Therefore, these could also be linked to later arriving label, causing a possible underestimation of the EV signal component due to reduced ASL signal at short PLDs. 31,32 This is reflected by enlarged occipital compartmentalization uncertainties relative to other regions in two subjects, which are especially dominant at PLD = 0.9 s. A possibility for considering this influence consists of a PLDand ATT-dependent masking to ensure that the compartmentalization is only performed for sufficiently large signal. Comparatively rapid F I G U R E 7 (A) Frequency distributions of estimated EV ASL signal fractions f EV in GM-ROI for all postlabeling delays (PLD = 0.9/1.2/1.5/1.8 s) by using subject-specific T 2,IV and T 2,EV , moving average filter smoothed data (gray) and detected peaks f EV,peak .…”

Section: Discussionmentioning

confidence: 99%

Blood–brain barrier permeability measurement by biexponentially modeling whole‐brain arterial spin labeling data with multiple T₂‐weightings

et al. 2020

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Blood–brain barrier (BBB) permeability assessment remains of ongoing interest in clinical practice and research. Transitions between intravascular (IV) and extravascular (EV) gray matter (GM) compartments may provide information regarding the microstructural status of the BBB. Due to different transverse relaxation times (T2) of water protons in vessels and GM, it is possible to determine the compartment in which these protons are located. This work presents and investigates the feasibility of a simplified analytical approach for compartmentalizing the proportions of magnetically marked water protons into IV and EV GM components by biexponentially modeling T2‐weighted arterial spin labeling (ASL) data. Numerous model assumptions were used to stabilize the fit and achieve in vivo applicability. Particularly, transverse relaxation times of IV and EV water protons were determined from the analysis of two supporting T2‐weighted ASL measurements, utilizing a monoexponential signal model. This stabilized a two‐parameter biexponential fit of ASL data with T2 preparation (PLD = 0.9/1.2/1.5/1.8 s, TET2Prep = 0/30/40/60/80/120/160 ms), which thereby robustly provided estimates of the IV and EV compartment fractions. Experiments were conducted with three healthy volunteers in a 3 T scanner. Averaged over all subjects, the labeled water protons inherit T2,IV = 200 ± 18 ms initially and adapt T2,EV = 91 ± 2 ms with a longer retention time in cerebral structures. Accordingly, the EVlocated ASL signal fraction rises with increasing PLD from 0.31 ± 0.11 at the shortest PLD of 0.9 s to 0.73 ± 0.02 at the longest PLD of 1.8s. These results indicate a transition of the water protons from IV to EV space. The findings support the potential of biexponential modeling for compartmentalizing ASL spin fractions between IV and EV space. The novel integration of monoexponential parameter estimates stabilizes the two‐compartment model fit, suggesting that this technique is suitable for robustly estimating the BBB permeability in vivo.

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Recent progress in ASL

Cited by 97 publications

References 118 publications

CEST, ASL, and magnetization transfer contrast: How similar pulse sequences detect different phenomena

CEST, ASL, and magnetization transfer contrast: How similar pulse sequences detect different phenomena

Increased resting perfusion of the hippocampus in high positive schizotypy: A pseudocontinuous arterial spin labeling study

Blood–brain barrier permeability measurement by biexponentially modeling whole‐brain arterial spin labeling data with multiple T₂‐weightings

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Recent progress in ASL

Cited by 97 publications

References 118 publications

CEST, ASL, and magnetization transfer contrast: How similar pulse sequences detect different phenomena

CEST, ASL, and magnetization transfer contrast: How similar pulse sequences detect different phenomena

Increased resting perfusion of the hippocampus in high positive schizotypy: A pseudocontinuous arterial spin labeling study

Blood–brain barrier permeability measurement by biexponentially modeling whole‐brain arterial spin labeling data with multiple T2‐weightings

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Blood–brain barrier permeability measurement by biexponentially modeling whole‐brain arterial spin labeling data with multiple T₂‐weightings