Pulsed Arterial Spin Labeling Research Articles

Test-retest reliability of resting-state cerebral blood flow quantification using pulsed Arterial Spin Labeling (PASL) over 3 weeks vs 8 weeks in healthy controls

Arterial Spin Labeling is a valuable functional imaging tool for both clinical and research purposes. However, little is known about the test-retest reliability of cerebral blood flow measurements over longer periods. In this study, we investigated the reliability of pulsed Arterial Spin Labeling in assessing cerebral blood flow over a 3 (n = 28) vs 8 (n = 19) weeks interscan interval in 47 healthy participants. As a measure of cerebral blood flow reliability, we calculated voxel-wise, whole-brain, and regions of interest intraclass correlation coefficients. The whole-brain mean resting-state cerebral blood flow showed good to excellent reliability over time for both periods (intraclass correlation coefficients = 0.85 for the 3-week delay, intraclass correlation coefficients = 0.53 for the 8-week delay). However, the voxel-wise and regions of interest intraclass correlation coefficients fluctuated at 8-week compared to the 3-week interval, especially within cortical areas. These results confirmed previous findings that Arterial Spin Labeling could be used as a reliable method to assess brain perfusion. However, as the reliability seemed to decrease over time, caution is warranted when performing correlations with other variables, especially in clinical populations.

Identifying delay in glymphatic clearance of labeled protons post-acute head trauma utilizing 3D ASL MRI (arterial spin labeling): a pilot study.

This study correlated mild traumatic brain injury (mTBI) cognitive changes with ASL-MRI glymphatic clearance rates (GCRs) and recovery with GCR improvement. mTBI disrupts the blood brain barrier (BBB), reducing capillary mean transit time and GCRs. mTBI is clinically diagnosed utilizing history/examination findings with no physiologic biomarkers. 3D TGSE (turbo-gradient spin-echo) pulsed arterial spin-labeling 3T MRI with 7 long inversion times (TIs) assessed the signal clearance of labeled protons 2800-4000ms postlabeling in bifrontal, bitemporal, and biparietal regions within 7days of mTBI and once clinically cleared to resume activities. The Sport Concussion Assessment Tool Version 5 (SKAT5) and Brief Oculomotor/Vestibular Assessment evaluated injured athletes' cognitive function prior to MRIs. The pilot study demonstrated significant GCRs improvement (95% CI -0.06 to -0.03 acute phase; to CI-recovery CI 0.0772 to -0.0497; P < 0.001 in frontal lobes; and parietal lobes (95% CI -0.0584 to -0.0251 acute; CI -0.0727 to -0.0392 recovery; P = 0.024) in 9 mTBI athletes (8 female, 1 male). Six age/activity-matched controls (4 females, 2 males) were also compared. mTBI disrupts the BBB, reducing GCR measured using the 3D ASL MRI technique. ASL MRI is a potential noninvasive biomarker of mTBI and subsequent recovery.

Optimizing background suppression for dual-module velocity-selective arterial spin labeling: Without using additional background-suppression pulses.

Background suppression (BS) is recommended in arterial spin labeling (ASL) for improved SNR but is difficult to optimize in existing velocity-selective ASL (VSASL) methods. Dual-module VSASL (dm-VSASL) enables delay-insensitive, robust, and SNR-efficient perfusion imaging, while allowing efficient BS, but its optimization has yet to be thoroughly investigated. The inversion effects of the velocity-selective labeling pulses, such as velocity-selective inversion (VSI), can be used for BS, and were modeled for optimizing BS in dm-VSASL. In vivo experiments using dual-module VSI (dm-VSI) were performed to compare two BS strategies: a conventional one with additional BS pulses and a new one without any BS pulse. Their BS performance, temporal noise, and temporal SNR were examined and compared, with pulsed and pseudo-continuous ASL (PASL and PCASL) as the reference. The in vivo experiments validated the BS modeling. Strong positive linear correlations (r > 0.82, p < 0.0001) between the temporal noise and the tissue signal were found in PASL/PCASL and dm-VSI. Optimal BS can be achieved with and without additional BS pulses in dm-VSI; the latter improved the ASL signals by 8.5% in gray matter (p = 0.006) and 12.2% in white matter (p = 0.014) and tended to provide better temporal SNR. The dm-VSI measured significantly higher ASL signal (p < 0.016) and temporal SNR (p < 0.018) than PASL and PCASL. Complex reconstruction was found necessary with aggressive BS. Guided by modeling, optimal BS can be achieved without any BS pulse in dm-VSASL, further improving the ASL signal and the SNR performance.

A Novel 5-Stage Visual Rating Scale for Global Arterial Spin Labeling Perfusion Assessment in the Brain: Simplifying Evaluation for Clinical Implementation

ObjectivesThe aim of this study was to develop and validate a visual rating scale for evaluating global arterial spin labeling (ASL) perfusion changes in the brain, with potential applications in a variety of conditions that impact general brain blood supply and perfusion. MethodsWe employed a five-stage scale (0 being normal and 4 indicating the most severe perfusion decline) to assess 156 patients using a 3D pulsed ASL technique. Three radiologists independently reviewed the images, and inter-rater reliability of the visual rating scale was evaluated. ResultsThe ASL stages showed a consistent distribution among the patients. The inter-rater reliability among the three radiologists, as measured by the Intraclass Correlation Coefficient (ICC), was 0.982. ConclusionOur findings suggest that this visual rating scale can be effectively implemented in everyday practice to evaluate global perfusion changes in the context of cardiovascular diseases, cerebrovascular diseases, cerebral small vessel disease, and other conditions that alter brain vascularization and perfusion. Further research is needed to explore the full range of clinical applications and to refine the scale for optimal utility.

Regional cerebral blood flow is associated with PET and plasma biomarkers of tau pathology in middle age

AbstractBackgroundCerebrovascular dysfunction and vascular brain injury are associated with risk and progression of clinical Alzheimer’s disease (AD), but it is unclear whether they contribute directly to disease pathogenesis. Animal models of small vessel cerebrovascular disease suggest that transient cerebral hypoperfusion may promote tau pathology independent of amyloidosis. In the current study, we used pulsed arterial spin labeling (PASL) magnetic resonance imaging (MRI) to examine the association of regional cerebral blood flow (CBF) with two biomarkers of tau pathology, plasma phosphorylated tau 181 (ptau181) concentrations and PET MK6240 SUVR, in middle aged adult participants from the Offspring Study of Mechanisms for Racial Disparities in Alzheimer’s Disease.MethodAt the time of analysis, 469 Offspring Study participants (54.0±10.6‐years‐old; 64% women; 67% Latinx, 22% non‐Latinx Black, 6% non‐Latinx white) had available PASL and ptau181 plasma concentrations (Quanterix Simoa HDx platform). Sixty‐four participants (59.9±5.4‐years‐old age; 67% women; 64% Latinx, 22% non‐Latinx Black, 8% Latinx white) with PASL CBF data received tau PET imaging with MK6240 and mean SUVR was computed across all grey matter regions for each participant. Voxelwise correlational analyses were run to examine the relationship between ptau181 concentrations and regional CBF and between tau PET SUVR and regional CBF.ResultIncreased ptau181 concentrations were associated with clusters of decreased CBF in frontal grey matter, striatum, hippocampus, and periventricular white matter. These correlations were asymmetrical, with the largest clusters found in the left hemisphere. Higher PET SUVR was associated with clusters of lower CBF in frontal, parietal, and occipital grey matter.ConclusionThese findings demonstrate a codependency between regional blood flow and tau pathology, indexed by fluidic and imaging biomarkers. Future studies will clarify the directionality and possible causality of these associations, but these cross‐sectional findings are consistent with a hypothesis that subtle diminished blood flow gives rise to tau abnormalities.

Regional White Matter Hyperintensities are Associated with Diminished Blood Flow and Microstructure in Middle Age

AbstractBackgroundWhite matter hyperintensities (WMH) are areas of increased signal visualized on T2‐weighted FLAIR magnetic resonance imaging (MRI), thought to reflect macrostructural damage due to small vessel cerebrovascular disease. Previous work established an association of WMH severity, particularly in posterior regions, with risk and progression of AD in late onset and genetic forms of AD, suggesting a vascular component to disease pathogenesis and course. Examination of the emergence and correlates of cerebrovascular changes in middle age, a critical time when vascular risk appears to be most penetrant, can give insight into mechanisms linking vascular brain injury and risk for AD. In the current study, we examined the association of cerebral blood flow (CBF) and white matter microstructure with total and regional WMH volume in middle‐aged, community dwelling adults.MethodFour hundred and ninety‐two middle‐aged participants (55+/‐11 age = 28 ‐85 years) from the community‐based Offspring Study of Mechanisms for Racial Disparities in Alzheimer’s Disease received multi‐modal MRI scanning. Regional WMH volumes were derived with in‐house software that labeled clusters of voxels within a hyperintense intensity distribution. Pulsed arterial spin labeling (PASL) sequences were processed to quantify CBF. Fractional anisotropy (FA) maps were obtained from diffusion weighted data. Total and regional WMH volumes were used as predictors for whole brain voxel‐wise correlation analyses in separate models for CBF and FA.ResultThere were negative associations between WMH volume and CBF in frontal, parietal, and occipital regions. Higher white matter hyperintensity volume was associated with lower FA, particularly in the periventricular region.ConclusionWe found associations of increased WMH volume with diminished blood flow and white matter microstructure. Future studies are needed to explain the relationship between these changes and the risk of cognitive impairment in middle aged adults and risk for AD.

Behavioural Deficits and Regional Cerebral Perfusion Map in Cognitively Normal and Pre‐Dementia Stages

AbstractBackgroundOur previous work has shown increased presence of early behavioural impairment in Asian than Western cohorts(Soo et al.,2021). Such impairments include mild behavioural changes, sleep disruptions and higher depression, anxiety and stress, in turn representing an at‐risk state which may predict later development of dementia(Müller‐Spahn,2003;Soo et al.,2021). Additionally, growing evidence illustrates that cerebrovascular changes are a key component in the pathological sequelae and may be detectable years before clinical presentation of dementia (de la Torre,2018). However, the influence of cerebral perfusion on behaviour, especially in pre‐dementia stages remains to be elucidated. Thus, we examined the association between regional grey matter perfusion and behaviour in cognitively normal(CN) and subjects with mild cognitive impairment(MCI) or subjective cognitive decline(SCD). We hypothesized that grey matter perfusion deficits would be related to behaviour impairment even in early stages of SCD/MCI.MethodWe studied 35 CN and 248 pre‐dementia (MCI/SCD) from a community‐based research cohort from the Dementia Research Centre (Singapore) with neuroimaging, neuropsychological and behavioural assessments(Table 1). We investigated the association between regional grey matter perfusion across 31 regions of interest spanning frontal, parietal, temporal and occipital lobes using 2D pulsed Arterial Spin Labelling and performance on the mild behaviour impairment‐checklist(MBI‐C), Pittsburgh Sleep Quality Index(PSQI) and Depression, Anxiety and Stress Scale(DASS). These associations were examined in CN and MCI/SCD groups separately and respective Pearson’s correlation matrices were derived.ResultOverall, greater behavioural impairment on the MBI‐C, DASS and PSQI was associated with hypoperfusion across multiple grey matter regions. This association was stronger in CN than in the pre‐dementia group. Specifically, among CN, hypoperfusion in the frontal, parietal and occipital lobes related most strongly to greater behavioural impairment, especially MBI‐C and DASS depression(Fig.1). In the MCI+SCD group, only hypoperfusion in the frontal and temporo‐occipital regions related to worse behavioural impairment across the MBI, PSQI and DASS(Fig.2).ConclusionIn this study, we illustrate differential associations between cerebral hypoperfusion and behavioural impairment in CN and MCI/SCD groups, with CN individuals showing more widespread and stronger associations between behavioural impairment and hypoperfusion across the brain. In SCD/MCI, hypoperfusion in frontal and temporo‐occipital regions were associated with behavioural impairment.

Relationship between Arterial Transit Time and Framingham Risk Score in the U.S. POINTER lifestyle intervention trial

AbstractBackgroundThe U.S. Study to Protect Brain Health Through Lifestyle Intervention to Reduce Risk (U.S. POINTER) is a two‐year randomized controlled trial designed to evaluate the effects of lifestyle interventions on older adults aged 60‐79 years. The POINTER Imaging ancillary study employs arterial spin labeling (ASL) magnetic resonance imaging (MRI) with two inversion times, enabling the mapping of arterial transit time (ATT) and the investigation of its relationship with dementia risk factors. This study examines the effect of the Framingham Risk Score (FRS) on ATT, which provides hemodynamic information on the cerebral vasculature.MethodA subset of POINTER Imaging participants (n = 134; F/M = 81/53; age = 68.1±5.1; FRS = 11.3±10.4) from two imaging sites underwent two ASL MRI scans during the baseline session. Two 3D Pulsed ASL scans were obtained with TI1 of 790ms and TI2 values of 2000ms or 2750ms, providing delay times (between labeling and imaging) of 1210ms or 1960ms. ATT, the time required for blood to travel from the neck to the tissue, was estimated in the range of 1210ms and 1960ms using a kinetic model (Figure 1). ATT maps were normalized to a standard space, and a voxel‐wise linear regression (ATT∼age+sex+log(FRS)) was performed on ATT maps in gray matter to assess the effect of FRS on ATT. To control false positives, clusters smaller than 1.4ml were removed based on a simulation with α = 0.05.ResultFigure 2 depicts three clusters found in the occipital, precuneus and frontal gray matter regions, all of which demonstrate a positive relationship between ATT and log(FRS). Participants with higher FRS exhibit prolonged mean ATT values in the clusters as shown in Figure 3. After stratifying into sex groups, both groups show the same direction.ConclusionAlthough the detectable range of ATT with two ASL scans was limited, the analysis suggests that an increased risk of cardiovascular disease, as quantified by the Framingham Risk Score, can serve as an indicator of potential cerebrovascular disease leading to prolonged ATT, which is associated with arterial stiffness, and vascular resistance. The clusters demonstrating the association between FRS and ATT are the brain regions that may have heightened vulnerability to vascular risk factors, according to previous studies.

Arterial Spin Labeling-Based MR Angiography for Cerebrovascular Diseases: Principles and Clinical Applications.

Arterial spin labeling (ASL) is a noninvasive imaging technique that labels the proton spins in arterial blood and uses them as endogenous tracers. Brain perfusion imaging with ASL is becoming increasingly common in clinical practice, and clinical applications of ASL for intracranial magnetic resonance angiography (MRA) have also been demonstrated. Unlike computed tomography (CT) angiography and cerebral angiography, ASL-based MRA does not require contrast agents. ASL-based MRA overcomes most of the disadvantages of time-of-flight (TOF) MRA. Several schemes have been developed for ASL-based MRA; the most common method has been pulsed ASL, but more recently pseudo-continuous ASL, which provides a higher signal-to-noise ratio (SNR), has been used more frequently. New methods that have been developed include direct intracranial labeling methods such as velocity-selective ASL and acceleration-selective ASL. MRA using an extremely short echo time (eg, silent MRA) or ultrashort echo-time (TE) MRA can suppress metal susceptibility artifacts and is ideal for patients with a metallic device implanted in a cerebral vessel. Vessel-selective 4D ASL MRA can provide digital subtraction angiography (DSA)-like images. This review highlights the principles, clinical applications, and characteristics of various ASL-based MRA techniques. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

ASL lexicon and reporting recommendations: A consensus report from the ISMRM Open Science Initiative for Perfusion Imaging (OSIPI).

The 2015 consensus statement published by the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group and the European Cooperation in Science and Technology ( COST) Action ASL in Dementia aimed to encourage the implementation of robust arterial spin labeling (ASL) perfusion MRI for clinical applications and promote consistency across scanner types, sites, and studies. Subsequently, the recommended 3D pseudo-continuous ASL sequence has been implemented by most major MRI manufacturers. However, ASL remains a rapidly and widely developing field, leading inevitably to further divergence of the technique and its associated terminology, which could cause confusion and hamper research reproducibility. On behalf of the ISMRM Perfusion Study Group, and as part of the ISMRM Open Science Initiative for Perfusion Imaging (OSIPI), the ASL Lexicon Task Force has been working on the development of an ASL Lexicon and Reporting Recommendations for perfusion imaging and analysis, aiming to (1) develop standardized, consensus nomenclature and terminology for the broad range of ASL imaging techniques and parameters, as well as for the physiological constants required for quantitative analysis; and (2) provide a community-endorsed recommendation of the imaging parameters that we encourage authors to include when describing ASL methods in scientific reports/papers. In this paper, the sequences and parameters in (pseudo-)continuous ASL, pulsed ASL, velocity-selective ASL, and multi-timepoint ASL for brain perfusion imaging are included. However, the content of the lexicon is not intended to be limited to these techniques, and this paper provides the foundation for a growing online inventory that will be extended by the community as further methods and improvements are developed and established.

Screening of postoperative cerebral hyperperfusion syndrome in moyamoya disease: a three-dimensional pulsed arterial-spin labeling magnetic resonance imaging approach

IntroductionMoyamoya disease (MMD) is associated with a risk of postoperative cerebral hyperperfusion syndrome (CHS) after revascularization surgery. This study aimed to explore the feasibility of using three-dimensional pulsed arterial spin labeling (3D PASL) and phase contrast (PC) magnetic resonance imaging (MRI) for predicting CHS occurrence in patients with MMD before revascularization surgery.MethodsOverall, 191 adult patients (207 hemispheres) with MMD who underwent combined revascularization surgery were included in this study. Preoperative 3D PASL-MRI and PC-MRI were performed before surgery. The PASL-MRI data were analyzed using SPM12. Patient clinical information, average flow, and preoperative cerebral blood flow (CBF) were compared between the non-CHS and CHS groups.ResultsAmong the patients, 45 (21.74%) developed CHS after revascularization surgery. No significant differences were noted in age, sex, clinical symptoms, hypertension, diabetes, surgical side, or history of revascularization surgery between the non-CHS and CHS groups. However, the average flow in the superficial temporal artery was significantly lower in the CHS group than in the non-CHS group (p &amp;lt; 0.05). Furthermore, 11 clusters of preoperative CBF values were significantly greater in the CHS group than in the non-CHS group [p &amp;lt; 0.05, false discovery rate (FDR) corrected]. A significant correlation was also observed between the preoperative time-to-flight MR angiography (MRA) scores and CBF values in patients with MMD (p &amp;lt; 0.05).ConclusionCompare patients with lower preoperative CBF and higher preoperative average flow in the STA, patients with higher preoperative CBF and lower preoperative average flow in the STA are more likely to develop postoperative CHS Preoperative PASL-MRI and PC-MRI examinations may help to screen patients at high risk of developing CHS after revascularization surgery.

Extracting functional connectivity brain networks at the resting state from pulsed arterial spin labeling data

IntroductionFunctional connectivity in the brain is often studied with blood oxygenation level dependent (BOLD) resting state functional magnetic resonance imaging (rsfMRI), but the BOLD signal is several steps removed from neuronal activity. Arterial spin labeling (ASL), particularly pulsed ASL (PASL), has also the capacity to measure the blood-flow changes in response to activity. In this paper, we investigated the feasibility of extracting major brain networks from PASL data, in contrast with rsfMRI analsyis. Materials and methodsIn this retrospective study, we analyzed a cohort dataset that consists of 21 mild traumatic brain injury (mTBI) patients and 29 healthy controls, which was collected in a previous study. By extracting 10 major brain networks from the data of both PASL and rsfMRI, we contrasted their similarities and differences in the 10 networks extracted from both modalities. ResultsOur data demonstrated that PASL could be used to extract all 10 major brain networks. Eight out of 10 networks demonstrated over 60 ​% similarity to rsfMRI data. Meanwhile, there are similar but not identical changes in networks detected between mTBI patients and healthy controls with both modalities. Notably, the PASL-extracted default mode network (DMN), other than the rsfMRI-extracted DMN, includes some regions known to be associated with the DMN in other studies. It demonstrated that PASL data can be analyzed to identify resting state networks with reasonable reliability, even without rsfMRI data. ConclusionOur analysis provides an opportunity to extract functional connectivity information in heritage datasets in which ASL but not BOLD was collected.

Functional Brain Network Connectivity Changes in Children and Adolescents with Attention- Deficit Hyperactivity Disorder: A Resting-State Brain Functional Magnetic Resonance Imaging Study

Background: ADHD is one of the most common psychiatric disorders in children and adolescents. Altered functional connectivity has been associated with ADHD symptoms. This study aimed to investigate abnormal changes in the functional connectivity of resting-state brain networks (RSNs) among children and adolescents with different subtypes of ADHD.&#x0D; Methods: This study was performed on 50 participants Group A: included 30 children and adolescents with ADHD Group B: included 20 normal typically developing controls. All participants aged between 7 and 16 years. All study patients. All participants underwent a neuropsychological assessment by applying the DSM-5 criteria to them. All study children and adolescents will undergo a R-fMRI examination, including Blood oxygenation level dependent BOLD-MRI and pulsed Arterial spin labeling MRI (PASL-MRI).&#x0D; Results: According to Conner’s Rating scale, there was a significant difference between ADHD subtypes and severity. Children with combined subtype were more likely to have severe degree in both teacher and parent editions of Conner’s Rating Scale. On the other hand, children with inattentive subtype had less severe degrees by both teacher and parent edition. There were a statistically significance difference between both genders as regard ADHD severity according to Conner’s Rating scale (Teacher and parent editions) (P value = 0.049, 0.028 respectively). Males were significantly affected by moderate and severe type compared to females whose affection were mostly mild and moderate. According to CBCL, most of ADHD children had low competence parameters. There was a statistically significant difference (P value &lt; 0.001) on the type of ADHD and social competence in the studied children, where the lowest parameters were found in children with hyperactive type.&#x0D; Conclusion: There was a statistically significant difference on the type of ADHD and social competence, where the lowest parameters were found in children with hyperactive type.

Insights Into Meningioma Visibility on Arterial Spin Labeling MRI: Location Outweighs Size.

Background Arterial Spin Labeling (ASL) MRI is a non-invasive imaging technique with potential applications for assessing meningiomas. This retrospective study aimed to investigate the impact of tumor location, size, age, and sex on the ASL visibility of meningiomas. Methods We retrospectively analysed 40 patients with meningiomas, who underwent 3 Tesla MRI examinations using a three-dimensional (3D) pulsed ASL technique. Tumor location was categorized as around the skull base or elsewhere, and size was determined by the area in the transverse plane. Results Our findings revealed that meningiomas around the skull base were significantly more likely to be ASL-visible compared to those located elsewhere (p < 0.001), whereas tumor size, age, and sex did not show a significant correlation with ASL visibility. This observation suggests that tumor location is a critical factor in determining the visibility of meningiomas on ASL MRI. Conclusion The results contribute to a better understanding of ASL visibility in meningiomas, highlighting the importance of tumor location over size. Further research, including larger cohorts and additional factors, such as histological variants, is needed to expand upon these findings and explore their clinical implications.

Pathophysiology of multiple sclerosis damage and repair: Linking cerebral hypoperfusion to the development of irreversible tissue loss in multiple sclerosis using magnetic resonance imaging.

Reduced cerebral perfusion has been observed in multiple sclerosis (MS) and may contribute to tissue loss both acutely and chronically. Here, we test the hypothesis that hypoperfusion occurs in MS and relates to the presence of irreversible tissue damage. In 91 patients with relapsing MS and 26 healthy controls (HC), gray matter (GM) cerebral blood flow (CBF) was assessed using pulsed arterial spin labeling. GM volume, T1 hypointense and T2 hyperintense lesion volumes (T1LV and T2LV, respectively), and the proportion of T2-hyperintense lesion volume that appears hypointense on T1-weighted magnetic resonance imaging (T1LV/T2LV) were quantified. GM CBF and GM volume were evaluated globally, as well as regionally, using an atlas-based approach. Global GM CBF was lower in patients (56.9 ± 12.3 mL/100 g/min) than in HC (67.7 ± 10.0 mL/100 g/min; p < 0.001), a difference that was widespread across brain regions. Although total GM volume was comparable between groups, significant reductions were observed in a subset of subcortical structures. GM CBF negatively correlated with T1LV (r = -0.43, p = 0.0002) and T1LV/T2LV (r = -0.37, p = 0.0004), but not with T2LV. GM hypoperfusion occurs in MS and is associated with irreversible white matter damage, thus suggesting that cerebral hypoperfusion may actively contribute and possibly precede neurodegeneration by hampering tissue repair abilities in MS.

Hypo- and hyper-perfusion in MCI and AD identified by different ASL MRI sequences.

Arterial spin labeling (ASL) perfusion MRI has been increasingly used in Alzheimer's Disease (AD) research. However, ASL MRI sequences differ greatly in terms of arterial blood signal preparations and data acquisition strategies, both leading to a large difference of signal-to-noise ratio (SNR). It is of great translational importance to compare the several widely used ASL MRI sequences regarding sensitivity of ASL measured cerebral blood flow (CBF) for detecting the between-group difference across the AD continuum. To this end, this study compared three ASL MRI sequences in AD research, including the 2D Pulsed ASL (PASL), 3D Background Suppressed (BS) PASL, and 3D BS Pseudo-Continuous ASL (PCASL). We used data from 100 healthy and cognitively normal elderly control (NC) subjects, 75 patients with mild cognitive impairment (MCI), and 57 Alzheimer's disease (AD) subjects from the AD neuroimaging initiative (ADNI). Both cross-sectional perfusion difference and perfusion versus clinical assessment correlations were examined. The major findings included: 3D PCASL sequence identified stronger patient versus control CBF/rCBF differences than 2D PASL and 3D PASL; MCI showed reduced CBF and CBF redistribution; CBF in orbito-frontal cortex presents a new U-shape change pattern from normal aging to MCI and to AD; 3D PCASL identified a negative rCBF to memory correlation while 2D PASL showed a positive correlation.

Hybrid adiabatic pulse with asymmetry (HAPY): An asymmetric adiabatic pulse with an application in pulsed arterial spin labeling at 7T.

A new class of asymmetric adiabatic radiofrequency (RF) pulses, Hybrid Adiabatic Pulse with asYmmetry (HAPY), is designed to be used as the labeling pulse for Pulsed Arterial Spin labeling (PASL) at 7T to reduce overall specific absorption rate (SAR) while maintaining high labeling efficiency with and inhomogeneities. Realistic and distributions were extracted from multiple in vivo scans. The proposed class of asymmetric pulses was parameterized and optimized considering these conditions. Simulation and phantoms experiments were performed to compare the optimized pulses with HS-3, GOIA, and trFOCI pulses. In vivo experiments were conducted to demonstrate the application of HAPY in PICORE PASL at 7T, compared with the GOIA and trFOCI pulses. HAPYs with different amounts of pulse energy reduction are obtained by the proposed optimization framework. Both simulation and phantom experiments demonstrate that HAPY achieves high labeling efficiency and high selectivity along the critical side despite off-resonance and low amplitude. In vivo experiments reveal that HAPY is able to generate robust perfusion signal with less overall SAR or shorter pulse repetition time, compared to the GOIA and trFOCI pulses. The HAPY class of pulses, obtained via systematic optimization tailored to the application of PASL at 7T, reduces power deposition without affecting labeling efficiency, which provides a prospect of further exploiting the benefits of ultra-high field in ASL.

Alteration of intracranial blood perfusion in temporal lobe epilepsy, an arterial spin labeling study

BackgroundA critical necessity before surgical resection in mesial temporal lobe epilepsy (mTLE) is lateralizing the seizure focus in the temporal lobe. This study aimed to investigate the differences in perfusion pattern changes in right and left mTLE. Methods42 mTLE patients (22 left and 20 right mTLE) and 14 controls were surveyed with pulsed arterial spin labeling at 3.0 T. The mean cerebral blood flow (CBF) and asymmetry index (AI) were calculated in the bilateral temporal lobe, amygdala, hippocampus, parahippocampus, and nine bilateral vascular territories ROIs. The alterations in whole-brain CBF were identified using statistical parametric mapping (SPM). ResultsCBF decreased in ipsilateral sides in both epilepsy subcohorts, with right mTLE showing a significant difference in most ROIs while left mTLE exhibiting no significant change. CBF comparison of left mTLE and controls showed a significant drop in ROI analysis in left middle temporal and left intermediate posterior cerebral artery and in AI analysis in parahippocampus, distal anterior cerebral artery, distal middle cerebral artery, and intermediate anterior cerebral artery. CBF hypoperfusion was seen in ROI analysis in the left intermediate anterior cerebral artery, left middle temporal, right middle temporal, left superior temporal in the right mTLE compared to controls. Left mTLE CBF differed significantly from right mTLE CBF in right distal middle cerebral artery ROI and AI of proximal middle cerebral artery. ConclusionOur result revealed that mTLE affects extratemporal regions and both mTLE subcohorts with different perfusion patterns, which may enhance the performance of preoperative MRI assessment in lateralization procedures.

Detection of ictal and periictal hyperperfusion with subtraction of ictal-interictal 1.5-Tesla pulsed arterial spin labeling images co-registered to conventional magnetic resonance images (SIACOM).

Our recent report showed that 1.5-T pulsed arterial spin labeling (ASL) magnetic resonance (MR) perfusion imaging (1.5-T Pulsed ASL [PASL]), which is widely available in the field of neuroemergency, is useful for detecting ictal hyperperfusion. However, the visualization of intravascular ASL signals, namely, arterial transit artifact (ATA), is more remarkable than that of 3-T pseudocontinuous ASL and is easily confused with focal hyperperfusion. To eliminate ATA and enhance the detectability of (peri) ictal hyperperfusion, we developed the subtraction of ictal-interictal 1.5-T PASL images co-registered to conventional MR images (SIACOM). We retrospectively analyzed the SIACOM findings in four patients who underwent ASL during both (peri) ictal and interictal states and examined the detectability for (peri) ictal hyperperfusion. In all patients, the ATA of the major arteries was almost eliminated from the subtraction image of the ictal-interictal ASL. In patients 1 and 2 with focal epilepsy, SIACOM revealed a tight anatomical relationship between the epileptogenic lesion and the hyperperfusion area compared with the original ASL image. In patient 3 with situation-related seizures, SIACOM detected minute hyperperfusion at the site coinciding with the abnormal electroencephalogram area. SIACOM of patient 4 with generalized epilepsy diagnosed ATA of the right middle cerebral artery, which was initially thought to be focal hyperperfusion on the original ASL image. Although it is necessary to examine several patients, SIACOM can eliminate most of the depiction of ATA and clearly demonstrate the pathophysiology of each epileptic seizure.

Abstract TMP66: Correlation Of Cerebrovascular Reserve Assessed By Acetazolamide-stress Spect With Collaterals On Arterial Spin-labeling MRI In Patients With Carotid Occlusive Disease

Introduction: We investigated the relationship between the level of cerebral collateral circulation on arterial spin-labeling (ASL) magnetic resonance imaging (MRI) and cerebrovascular reserve (CVR) on acetazolamide (ACZ)-stress single photon emission computed tomography (SPECT) brain scans in internal carotid artery (ICA) stenosis. Methods: This study enrolled 129 patients with severe ICA stenosis (&gt;70%). Collateral circulation was assessed in pulsed ASL images based on the presence of arterial transit artifact (ATA) that late-arriving flow appears as serpiginous high ASL signal within cortical vessels. CVR based on rest-SPECT and ACZ-stress SPECT with Tc-99m-ECD was calculated. The ASL CBF maps were independently assessed by two neuroradiologists blinded to clinical information. The two neuroradiologists graded on two slices of ASL images corresponding to Alberta Stroke Program Early Computed Tomography Score (ASPECTS) location using a 4-point scale for ASL intensity. Results: With ACZ-stress SPECT, the 88/129 (68%) patients showed normal CVR and 41/129 (32%) patients showed decreased CVR. In 73/88 (82%) of the normal CVR group patients, ASL showed ATA in ipsilateral to the stenosis. In 19/41 (46%) of the decreased CVR group patients, ASL showed no evidence of ATA in ipsilateral to the stenosis. Significant positive relationship was observed between the normal CVR group and the ATA showing group in ICA stenosis patients (p = 0.001, chi-square test). The ASL-based ASPECTS scores of brain in the ipsilateral side was lower than the scores in the contralateral side to the ICA stenosis (p &lt; 0.0001, Wilcoxon signed rank test). The ASL-based ASPECTS scores of brain ipsilateral side to the ICA stenosis was lower in the reduced CVR group than normal CVR group (p = 0.005). Conclusion: This study demonstrated the statistically significant positive correlation between good collaterals on ASL MRI and intact CVR in patients with ICA stenosis.