Postlabeling Delay Research Articles

Prognostic value of multi-PLD ASL-based cerebral perfusion ASPECTS in acute ischemic stroke.

We aimed to verify the application value of the Alberta Stroke Program Early CT Score (ASPECTS) based on multiple post-labeling delay (multi-PLD) arterial spin labeling (ASL) for outcome assessment in acute ischemic stroke (AIS) patients. The endpoint was modified Rankin scale score at 90 days (90-day mRS). Patients were divided into the good outcome (0-2) and poor outcome (3-6) groups. The independent samples t-test, Mann-Whitney U-test, and χ2-test were used to compare clinical and imaging parameters between groups. We used partial correlation analysis to evaluate the relationships between ASPECTS and outcomes. Multivariate logistic regression analysis was used to examine potential independent prognostic indicators. The receiver operating characteristic (ROC) curve analysis was used to evaluate the performance of the independent prognostic indicators in predicting outcomes. Fifty-five AIS patients were included. The good outcome group had a lower baseline National Institutes of Health Stroke Scale (NIHSS; Z = -3.413, P < 0.001) and infarct core volume (ICV; Z = -3.114, P = 0.002) as well as higher cerebral blood flow (CBF)-ASPECTS (Z = -3.835, P < 0.001) and cerebral blood volume (CBV)-ASPECTS (Z = -4.099, P < 0.001). Higher CBF-ASPECTS (r = -0.459, P = 0.001), and CBV-ASPECTS (r = -0.502, P < 0.001) were associated with a lower 90-day mRS. The baseline NIHSS, CBF-ASPECTS, and CBV-ASPECTS were identified as independent prognostic indicators. The AUCs of the baseline NIHSS, CBF-ASPECTS, and CBV-ASPECTS were 83.3, 87.4, and 89.9%, respectively. Combining NIHSS with CBF-ASPECTS and CBV-ASPECTS, the AUC significantly improved to 96.3%. The combined three factors showed a significant difference compared to the baseline NIHSS (Z = 2.039, P = 0.041) and CBF-ASPECTS (Z = 2.099, P = 0.036), but no difference with CBV-ASPECTS (Z = 1.176, P = 0.239). The ASPECTS based on multi-PLD ASL is a valuable tool for identifying independent prognostic indicators and assessing clinical outcomes in AIS patients. The baseline NIHSS, combined with CBF-ASPECTS and CBV-ASPECTS, enhances the predictive efficacy of clinical outcomes in AIS patients. The CBV-ASPECTS alone can offer comparable predictive efficacy to the combination.

Cerebral perfusion in patients with unilateral internal carotid artery occlusion by dual post-labeling delays arterial spin labeling imaging.

Global and regional cerebral blood flow (CBF) changes in patients with unilateral internal carotid artery occlusion (ICAO) are unclear when the dual post-labeling delays (PLD) arterial spin labeling (ASL) magnetic resonance imaging (MRI) technique is used. Manual delineation of regions of interest for CBF measurement is time-consuming and laborious. To assess global and regional CBF changes in patients with unilateral ICAO with the ASL-MRI perfusion technique. Twenty hospitalized patients with ICAO and sex- and age-matched controls were included in the study. Regional CBF was measured by Dr. Brain's ASL software. The present study evaluated differences in global, middle cerebral artery (MCA) territory, anterior cerebral artery territory, and Alberta Stroke Program Early Computed Tomography Score (ASPECTS) regions (including the caudate nucleus, lentiform nucleus, insula ribbon, internal capsule, and M1-M6) and brain lobes (including frontal, parietal, temporal, and insular lobes) between ICAO patients and controls at PLD 1.5 s and PLD 2.5 s. When comparing CBF between ICAO patients and controls, the global CBF in ICAO patients was lower at both PLD 1.5 s and PLD 2.5 s; the CBF on the occluded side was lower in 15 brain regions at PLD 1.5 s, and it was lower in 9 brain regions at PLD 2.5 s; the CBF in the contralateral hemisphere was lower in the caudate nucleus and internal capsule at PLD 1.5 s and in M6 at PLD 2.5 s. The global CBF in ICAO patients was lower at PLD 1.5 s than at PLD 2.5 s. The ipsilateral CBF at PLD 1.5 s was lower than that at PLD 2.5 s in 15 regions, whereas the contralateral CBF was lower at PLD 1.5 s than at PLD 2.5 s in 12 regions. The ipsilateral CBF was lower than the contralateral CBF in 15 regions at PLD 1.5 s, and in M6 at PLD 2.5 s. Unilateral ICAO results in hypoperfusion in the global and MCA territories, especially in the ASPECTS area. Dual PLD settings prove more suitable for accurate CBF quantification in ICAO.

Pseudo-continuous and territorial arterial spin labeling MRI for assessment of cerebral perfusion in moyamoya disease after revascularization: A comparative study with digital subtraction angiography

PurposeTo evaluate if pseudo-continuous arterial spin labeling (pcASL) and territorial ASL (tASL) can assess cerebral perfusion post-revascularization in Moyamoya disease and compare with digital subtraction angiography (DSA) outcomes. Materials and methodsPatients diagnosed with Moyamoya disease who underwent pcASL using two post-labeling delays (short ASL, 1,525 ms; delayed ASL, 2,525 ms), tASL, and DSA 3 months after surgery at a single institution were retrospectively evaluated. Manual delineation on pcASL cerebral blood flow (CBF) maps covered middle cerebral artery (MCA) territory on both sides, and cerebellum. Normalized CBF (nCBF) was calculated. Revascularization in the MCA territory was evaluated with external carotid angiography and tASL, graded on a three-point scale. Intermodality agreement was analyzed with weighted κ statistics. Correlation between pcASL-derived nCBF and tASL-measured revascularization, and revascularization grade from direct angiography, was determined. Diagnostic performance of pcASL and tASL was evaluated using DSA as a reference via receiver operating characteristic (ROC) curve analysis. ResultsA total of 32 hemispheres from 31 patients were assessed. On the operated side, sASL and dASL had nCBF values of 1.00 ± 0.30 and 1.31 ± 0.31, respectively. Revascularization area grading showed substantial intermodality agreement (weighted κ = 0.68; 95 % CI: 0.49, 0.87). DSA revascularization moderately correlated with sASL and dASL nCBF values (r = 0.56 and 0.47) and strongly correlated with tASL revascularization area (r = 0.73). ROC analysis revealed that sASL and dASL nCBF values reflected revascularization (area under the curve (AUC) = 0.86 and 0.77) and tASL revascularization area (AUC = 0.91). Combined pcASL and tASL had an AUC of 0.93, comparable to tASL alone, improving diagnostic performance. The diagnostic accuracy of nCBF for sASL was 87.5 %, superior to 75 % for dASL. The diagnostic accuracy of tASL external carotid artery revascularization area was 87.5 %, with sensitivity and specificity of 88 % and 85.7 %, respectively. ConclusionThe combination of pcASL and tASL outperformed pcASL alone in assessing cerebral perfusion post-Moyamoya disease revascularization.

Diagnostic Performance of ASL-MRI and FDG-PET in Frontotemporal Dementia: A Systematic Review and Meta-Analysis.

While the diagnosis of frontotemporal dementia (FTD) is based mostly on clinical features, [18F]-FDG PET has been investigated as a potential imaging golden standard in ambiguous cases, with arterial spin labeling (ASL) MRI gaining recent interest. The purpose of this study is to conduct a systematic review and meta-analysis on the diagnostic performance of ASL MRI in FTD patients and compare it to that of [18F]-FDG PET. A systematic search of PubMed, Scopus and EMBASE was conducted until March 13, 2024. Inclusion criteria were: original articles, patients with FTD and/or its variants, use of ASL MR perfusion imaging with or without [18F]-FDG PET, presence of sufficient diagnostic performance data. Exclusion criteria were: meeting abstracts, comments, summaries, protocols, letters and guidelines, longitudinal studies, overlapping cohorts. The quality of eligible studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2. Pooled sensitivity, specificity, and diagnostic odds ratio (DOR) for [18F]-FDG PET and ASL MRI were calculated, and a summary receiver operating characteristic curve was plotted. Seven eligible studies were identified, which included a total of 102 FTD patients. Aside from some of the studies showing at worst an unclear risk of bias in patient selection, index test, flow and timing, all studies showed low risk of bias and applicability concerns in all categories. Data from 4 studies was included in our meta-analysis for ASL MRI and 3 studies for [18F]-FDG PET. Pooled sensitivity, specificity and DOR were 0.70 (95% CI: 0.59-0.79), 0.81 (95% CI: 0.71-0.88) and 8.00 (95% CI: 3.74-17.13) for ASL MRI, and 0.88 (95% CI: 0.71-0.96), 0.89 (95% CI: 0.43-0.99) and 47.18 (95% CI: 10.77-206.75) for [18F]-FDG PET. The number of studies was relatively small, with a small sample size. The studies used different scanning protocols as well as a mix of diagnostic metrics, all of which might have introduced heterogeneity in the data. While ASL MRI performed worse than [18F]-FDG PET in the diagnosis of FTD, it exhibited a decent diagnostic performance to justify its further investigation as a quicker and more convenient alternative. 3DPCASL, 3D pseudocontinuous ASL; AD, Alzheimer's disease; ASL, arterial spin labeling; AUC, area under the curve; CI, confidence interval; DOR, diagnostic odds ratio; FN, false negative; FP, false positive; FTD, frontotemporal dementia; LE, limbic encephalitis; NLR, negative likelihood ratio; PASL, pulsed ASL; PLD, post-label delay; PLR, positive likelihood ratio; PRISMA, PSP, progressive supranuclear palsy; Preferred Reporting Items for Systematic Reviews and Meta-Analysis; SROC, summary receiver operative characteristic; TN, true negative; TP, true positive; QUADAS-2, Quality Assessment of Diagnostic Accuracy Studies-2.

Three-dimensional pseudocontinuous arterial spin labeling with dual postlabeling delay for reflecting cerebral blood flow regulation in patients with hydrocephalus: a retrospective cross-sectional study.

Three-dimensional pseudo-continuous arterial spin-labeling (3D pCASL) with dual postlabeling delay (PLD) captures both early and delayed cerebral blood flow (CBF), yet its potential in reflecting blood flow regulation in hydrocephalus patients remains uncertain. This study investigated the hemodynamic characteristics in patients with hydrocephalus and whether the difference in cerebral blood flow using short and long PLDs (ΔCBF = CBFPLD =2.5 s - CBFPLD =1.5 s) could reflect cerebral regulation and further aimed to demonstrate the associations between regional ΔCBF and the degree of ventricular dilatation. This retrospective study included consecutive patients with hydrocephalus and control participants attending The Second Affiliated Hospital of Nanchang University from December 2017 to December 2022. The CBF in 18 brain regions was manually delineated by two radiologists. Regional CBF and ΔCBF were compared via covariance analyses. The associations between ΔCBF and the degree of ventricular dilatation were investigated using linear regression analyses and interaction analysis. In total, 58 patients with communicating hydrocephalus, 57 patients with obstructive hydrocephalus, and 52 controls were analyzed. CBF of the hydrocephalus groups was lower than that of the control group at the shorter PLD. CBF was higher at a longer PLD, with no difference between the hydrocephalus groups and the control group in some regions. The hydrocephalus groups showed a higher ΔCBF compared to the control group. Furthermore, in the left medial watershed (10.6±5.66 vs. 7.01±5.88 mL/100 g/min; P=0.038), communicating hydrocephalus exhibited greater ΔCBF than did obstructive hydrocephalus. ΔCBF of the right posterior external watershed [adjusted β: 0.276; 95% confidence interval (CI): 0.047-0.505; P=0.019] and right parietal cortex (adjusted β: 0.277; 95% CI: 0.056-0.498; P=0.015) in the obstructive hydrocephalus group and ΔCBF of the left internal watershed (adjusted β: 0.274; 95% CI: 0.013-0.536; P=0.040) in the communicating hydrocephalus group were associated with the degree of ventricular dilatation, respectively. Patients with hydrocephalus showed cerebral regulation in maintaining adequate CBF, resulting in longer arterial transit times. The ability to regulate CBF in brain regions represented by the watershed was associated with the degree of ventricular dilation.

Spatial coefficient of variation of arterial spin labeling magnetic resonance imaging can predict decreased cerebrovascular reactivity measured by acetazolamide challenge single-photon emission tomography.

The aim of this study was to investigate whether the spatial coefficient of variation of arterial spin labeling (ASL-CoV) acquired in clinical settings can be used to estimate decreased cerebrovascular reactivity (CVR) measured with single-photon emission computed tomography (SPECT) and acetazolamide challenge in patients with atherosclerotic stenosis of intra- or extracranial arteries. We evaluated the data of 27 atherosclerotic stenosis patients who underwent pseudocontinuous ASL and SPECT. After spatial normalization, regional values were measured using the distributed middle cerebral artery territorial atlas of each patient. We performed comparisons, correlations, and receiver operating characteristic (ROC) curve analyses between ASL-cerebral blood blow (CBF), ASL-CoV, SPECT-CBF and SPECT-CVR. Although the ASL-CBF values were positively correlated with SPECT-CBF values (r = 0.48, 95% confidence interval (CI) = 0.28-0.64), no significant difference in ASL-CBF values was detected between regions with and without decreased CVR. However, regions with decreased CVR had significantly greater ASL-CoV values than regions without decreased CVR. SPECT-CVR was negatively correlated with ASL-CoV (ρ = -0.29, 95% CI = -0.49 - -0.06). The area under the ROC curve of ASL-CoV in predicting decreased CVR (0.66, 95% CI = 0.51-0.81) was greater than that of ASL-CBF (0.51, 95% CI = 0.34-0.68). An ASL-CoV threshold value of 42% achieved a high specificity of 0.93 (sensitivity = 0.42, positive predictive value = 0.77, and negative predictive value = 0.75). ASL-CoV acquired by single postlabeling delay without an acetazolamide challenge may aid in the identification of patients with decreased CVR on SPECT.

Quantitative transport mapping of multi-delay arterial spin labeling MRI detects early blood perfusion alterations in Alzheimer’s disease

BackgroundQuantitative transport mapping (QTM) of blood velocity, based on the transport equation has been demonstrated higher accuracy and sensitivity of perfusion quantification than the traditional Kety’s method-based cerebral blood flow (CBF). This study aimed to investigate the associations between QTM velocity and cognitive function in Alzheimer’s disease (AD) using multiple post-labeling delay arterial spin labeling (ASL) MRI.MethodsA total of 128 subjects (21 normal controls (NC), 80 patients with mild cognitive impairment (MCI), and 27 AD) were recruited prospectively. All participants underwent MRI examination and neuropsychological evaluation. QTM velocity and traditional CBF maps were computed from multiple delay ASL. Regional quantitative perfusion measurements were performed and compared to study group differences. We tested the hypothesis that cognition declines with reduced cerebral blood perfusion with consideration of age and gender effects.ResultsIn cortical gray matter (GM) and the hippocampus, QTM velocity and CBF showed decreased values in the AD group compared to NC and MCI groups; QTM velocity, but not CBF, showed a significant difference between MCI and NC groups. QTM velocity and CBF showed values decreasing with age; QTM velocity, but not CBF, showed a significant gender difference between male and female. QTM velocity and CBF in the hippocampus were positively correlated with cognition, including global cognition, memory, executive function, and language function.ConclusionThis study demonstrated an increased sensitivity of QTM velocity as compared with the traditional Kety’s method-based CBF. Specifically, we observed only in QTM velocity, reduced perfusion velocity in GM and the hippocampus in MCI compared with NC. Both QTM velocity and CBF demonstrated a reduction in AD vs. controls. Decreased QTM velocity and CBF in the hippocampus were correlated with poor cognitive measures. These findings suggest QTM velocity as potential biomarker for early AD blood perfusion alterations and it could provide an avenue for early intervention of AD.

The effect of post-labeling delay on cerebral blood flow is influenced by age and sex: a study based on arterial spin-labeling magnetic resonance imaging.

Whether the effect of post-labeling delay (PLD) on cerebral blood flow (CBF) is influenced by age and sex in adults is unknown. In this study, we mainly aimed to explore the potential influence of age and sex on the effect of PLD on CBF. This prospective study enrolled 90 healthy adult volunteers (49.47±15.63 years of age; age range, 20-77 years; 47 female; 43 male). All participants underwent 3-dimensional (3D) pseudo-continuous arterial spin labeling (ASL) imaging with 3 different PLDs (1,525, 2,025, and 2,525 ms). The CBF values for each PLD, the arterial transit time (ATT), and the spatial coefficient of variation (spatial CoV) were computed for 21 regions of interest (ROIs) in every participant. Multivariate regression analysis was conducted to assess the potential influence of age and sex on the effect of PLD on CBF and the relationships among CBF, ATT, PLD, age, sex, and spatial CoV. The CBF increased for 7.32 to 9.87 mL/100 g/min as the PLD increased per 1 second in the global gray matter, bilateral frontal, temporal lobes, the vascular territories of bilateral anterior and middle carotid artery. When the age increased per 1 year, the speed of the changes for CBF decreased for 0.26 to 0.3 mL/100 g/min/s in these regions. However, the CBF decreased for 12 to 17 mL/100 g/min as the PLD increased per 1 second in the bilateral limbic lobes, insula, and deep gray matter. In these regions, the speed of the changes for CBF increased for 0.2 to 0.28 mL/100 g/min/s as the age increased per 1 year. Furthermore, compared to the female, the speed of the changes for CBF decreased for 3.58 to 4.6 mL/100 g/min/s for the male in global gray matter, bilateral frontal, limbic lobes, and the vascular territories of bilateral anterior carotid artery, and the speed increased 4.49 to 5.09 mL/100 g/min/s for the male in the limbic lobes. In addition, the CBF decreased with aging and the CBF tended to be higher in females compared to males. At the same time, we found that the ATT of all ROIs increased with age and manifested higher in males than females. Moreover, we found that CBF decreased with the increase of ATT, and the effect of ATT on CBF was less influenced by PLD. Finally, we found that the spatial CoV of ASL in certain regions increased with the increase of ATT and age, and was greater in males. The effect of PLD on CBF can be influenced by age and sex. The relationships among CBF, ATT, PLD, age, sex, and spatial CoV found in this study may have certain significance for the study of ASL imaging in the future.

Evaluating cerebrovascular reactivity measured by velocity selective inversion arterial spin labeling with different post-labeling delays: The effect of fast flow.

Velocity selective arterial spin labeling (VSASL) quantification assumes that the labeled bolus continuously moves into the imaging voxel during the post-labeling delay (PLD). Faster blood flow could lead to a bolus duration shorter than the applied PLD of VSASL and cause underestimation of cerebral blood flow (CBF). This study aims to evaluate the performance of velocity-selective inversion (VSI) prepared arterial spin labeling (ASL) with different PLDs and pseudo-continuous ASL (PCASL) for quantification of hypercapnia-induced cerebrovascular reactivity (CVR), using phase-contrast (PC) MRI as a global reference. We compared CVR obtained by VSI-ASL with PLD of 1520 ms (VSASL-1520), 1000 ms (VSASL-1000), and 500 ms (VSASL-500), PCASL with PLD of 1800 ms (PCASL-1800), and PC MRI on eight healthy volunteers at two sessions. Compared with PC MRI, VSASL-1520 produced significantly lower global CVR values, while PCASL-1800, VSASL-1000, and VSASL-500 yielded more consistent results. The reduced CVR in VSASL-1520 was more pronounced in carotid territories including frontal and temporal lobes than in vertebral territories such as the occipital lobe. This is largely caused by the underestimated perfusion during hypercapnia due to the reduced bolus duration being less than the PLD. Although VSASL offers certain advantages over spatially selective ASL due to its reduced susceptibility to delayed ATT, this technique is prone to biases when the ATT is excessively short. Therefore, a short PLD should be employed for reliable perfusion and CVR quantification in populations or conditions with fast flow.

Evaluating Ocular Blood Flow in Diabetic Macular Edema using Three-dimensional Pseudocontinuous Arterial Spin Labeling.

Alterations in ocular blood flow play an important role in the pathogenesis of diabetic macular edema; however, this remains unclear. This study aimed to investigate ocular blood flow in eyes with or without diabetic macular edema using arterial spin labeling. This cross-sectional study included 118 eyes of 65 patients with diabetic retinopathy analyzed between November 2018 and December 2019. We included a total of 53 eyes without diabetic macular edema (mean [SD] age, 57.83 [7.23] years; 29 men [54.7%]) and 65 eyes with diabetic macular edema (mean [SD] age, 60.11 [7.63] years; 38 men [58.5%]). Using a 3.0-T magnetic resonance imaging, participants were imaged with arterial spin labeling with multiple post-labeling delays. The mean ocular blood flow at post-labeling delays of 1.5 and 2.5 s was significantly lower in eyes with diabetic macular edema among patients with diabetic retinopathy compared with the remaining subgroups (P=0.022 and P <0.001, respectively). The mean ocular blood flow exhibited a significant decrease in eyes with diabetic macular edema when the post-labeling delay was set at 2.5 s in the nonproliferative and proliferative diabetic retinopathy groups, compared with the remaining subgroups (P=0.005 and P=0.002, respectively). The cutoff points of ocular blood flow at post-labeling delays of 1.5 s and 2.5 s were 9.40 and 11.10 mL/100 g/min, respectively. Three-dimensional pseudocontinuous arterial spin labeling can identify differences in the ocular blood flow of patients with diabetic eyes with and without diabetic macular edema.

Influence of arterial transit time delays on the differentiation between tumor progression and pseudoprogression in glioblastoma by arterial spin labeling magnetic resonance imaging.

Arterial spin labeling (ASL) and dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI) have shown potential for differentiating tumor progression from pseudoprogression. For pseudocontinuous ASL with a single postlabeling delay, the presence of delayed arterial transit times (ATTs) could affect the evaluation of ASL-MRI perfusion data. In this study, the influence of ATT artifacts on the perfusion assessment and differentiation between tumor progression and pseudoprogression were studied. This study comprised 66 adult patients (mean age 60 ± 13 years; 40 males) with a histologically confirmed glioblastoma who received postoperative radio (chemo)therapy. ASL-MRI and DSC-MRI scans were acquired at 3months postradiotherapy as part of the standard clinical routine. These scans were visually scored regarding (i) the severity of ATT artifacts (%) on the ASL-MRI scans only, scored by two neuroradiologists; (ii) perfusion of the enhancing tumor lesion; and (iii) radiological evaluation of tumor progression versus pseudoprogression by one neuroradiologist. The final outcome was based on combined clinical and radiological follow-up until 9months postradiotherapy. ATT artifacts were identified in all patients based on the mean scores of two raters. A significant difference between the radiological evaluation of ASL-MRI and DSC-MRI was observed only for ASL images with moderate ATT severity (30%-65%). The perfusion assessment showed ASL-MRI tending more towards hyperperfusion than DSC-MRI in the case of moderate ATT artifacts. In addition, there was a significant difference between the prediction of tumor progression with ASL-MRI and the final outcome in the case of severe ATT artifacts (McNemar test, p= 0.041). Despite using ASL imaging parameters close to the recommended settings, ATT artifacts frequently occur in patients with treated brain tumors. Those artifacts could hinder the radiological evaluation of ASL-MRI data and the detection of true disease progression, potentially affecting treatment decisions for patients with glioblastoma.

Recommendations for quantitative cerebral perfusion MRI using multi-timepoint arterial spin labeling: Acquisition, quantification, and clinical applications.

Accurate assessment of cerebral perfusion is vital for understanding the hemodynamic processes involved in various neurological disorders and guiding clinical decision-making. This guidelines article provides a comprehensive overview of quantitative perfusion imaging of the brain using multi-timepoint arterial spin labeling (ASL), along with recommendations for its acquisition and quantification. A major benefit of acquiring ASL data with multiple label durations and/or post-labeling delays (PLDs) is being able to account for the effect of variable arterial transit time (ATT) on quantitative perfusion values and additionally visualize the spatial pattern of ATT itself, providing valuable clinical insights. Although multi-timepoint data can be acquired in the same scan time as single-PLD data with comparable perfusion measurement precision, its acquisition and postprocessing presents challenges beyond single-PLD ASL, impeding widespread adoption. Building upon the 2015 ASL consensus article, this work highlights the protocol distinctions specific to multi-timepoint ASL and provides robust recommendations for acquiring high-quality data. Additionally, we propose an extended quantification model based on the 2015 consensus model and discuss relevant postprocessing options to enhance the analysis of multi-timepoint ASL data. Furthermore, we review the potential clinical applications where multi-timepoint ASL is expected to offer significant benefits. This article is part of a series published by the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group, aiming to guide and inspire the advancement and utilization of ASL beyond the scope of the 2015 consensus article.

Arterial transit artifact as a short-term prognostic indicator in acute ischemic stroke

BackgroundArterial transit artifact (ATA) observed on arterial spin labeling (ASL) was recently suggested to be associated with improved functional outcomes following acute ischemic stroke (AIS). AIS is a heterogeneous disease with diverse pathogenic mechanisms depending on the stroke subtype. This study aimed to investigate the association between ATA and 3-month functional outcomes in AIS patients according to etiology subtypes.MethodsConsecutive patients with AIS were included. All patients underwent ASL MRI with postlabeling delay (PLD) of 1.5 and 2.5 s. ATA was assessed from the ASL images of both PLDs. Stroke etiologic subtypes were determined according to the modified TOAST (Trial of ORG 10172 in Acute Stroke Treatment) classification. Short-term functional outcomes were evaluated using the 3-month modified Rankin scale (mRS). Log-binomial regression was applied to analyze the association between ATA and functional outcomes at 3 months after stroke.ResultsNinety-eight AIS patients (62.73 ± 13.05 years; 68 men) were finally included. ATA was detected in forty-six patients and most frequently seen in the large-artery atherosclerosis (LAA) subtype (35/46). The ATA group exhibited a lower percentage of patients with mRS > 2 compared to the group without ATA (36.5% vs. 19.6%; P < 0.001). ATA was independently associated with better 3-month clinical outcomes (adjusted risk ratio, 0.35[95% CI, 0.16—0.74]) in the multivariate log-binomial regression model. After stratification by TOAST subtypes, a significant association was found between ATA and better outcomes in the LAA subtype (adjusted risk ratio, 0.20[ 95% CI, 0.05—0.72]) but not in cardioembolism and small artery occlusion (SVO) subtype.ConclusionATA is associated with better outcomes at 3 months in patients with AIS, especially in the LAA subtype, but this association attenuated in the cardioembolism and SVO subtypes.

Deeply Accelerated Arterial Spin Labeling Perfusion MRI for Measuring Cerebral Blood Flow and Arterial Transit Time.

Cerebral blood flow (CBF) indicates both vascular integrity and brain function. Regional CBF can be non-invasively measured with arterial spin labeling (ASL) perfusion MRI. By repeating the same ASL MRI sequence several times, each with a different post-labeling delay (PLD), another important neurovascular index, the arterial transit time (ATT) can be estimated by fitting the acquired ASL signal to a kinetic model. This process however faces two challenges: one is the multiplicatively prolonged scan time, making it impractically for clinical use due to the escalated risk of motions; the other is the reduced signal-to-noise-ratio (SNR) in the long PLD scans due to the T1 decay of the labeled spins. Increasing SNR needs more repetitions which will further increase the total scan time. Currently, there lacks a way to accurately estimate ATT from a parsimonious number of PLDs. In this paper, we proposed a deep learning-based algorithm to reduce the number of PLDs and to accurately estimate ATT and CBF. Two separate deep networks were trained: one is designed to estimate CBF and ATT from ASL data with a single PLD; the other is to estimate CBF and ATT from ASL data with two PLDs. The models were trained and tested using the large Human Connectome Project multiple-PLD ASL MRI. Performance of the DL-based approach was compared to the traditional full dataset-based data fitting approach. Our results showed that ATT and CBF can be reliably estimated using deep networks even with one PLD.

A comparative study of multi and single post labeling delay pseudocontinuous arterial spin labeling in patients with carotid artery stenosis

PurposeArterial Spin Labeling (ASL) allows for the non-invasive visualization of brain perfusion to detect abnormalities. In unilateral carotid artery stenosis, one hemisphere is less supplied with blood which results in a lower cerebral blood flow (CBF) compared to the healthy side. ASL can be performed time-resolved using multiple post labeling delay (PLD) times after labeling or static with a single delay, the latter allowing for a faster and more robust acquisition while bearing the risk of a falsely set delay resulting in unusable images. The purpose of this study is to compare the performance of multi-PLD and single-PLD ASL in patients with unilateral carotid artery stenosis both as means of diagnosis and therapeutic follow-up examination. MethodsASL perfusion data of 17 patients with known unilateral carotid artery stenosis was used to compare the diagnostic performance of the multi-PLD and single-PLD approach. Comparisons were made based on the CBF values and the added benefit of arrival time maps showing slower blood flow in multi-PLD ASL which might be overlooked in the individual delay images both before and after therapy. ResultsBoth the multi-PLD and the single-PLD data could identify the side of the stenosis with hemispheric differences in each approach (p < 0.001) and depict the normalization of CBF after therapy (p > 0.05). There were no differences between the individual methods (p > 0.05). ConclusionIn this work, we could show that multi-PLD ASL in patients with unilateral carotid artery stenosis is beneficial as it provides both CBF and arrival time maps, however when only a single-PLD acquisition is available, this appears sufficient in a clinical setting to investigate the presence of a unilateral stenosis.

Cerebral Blood Flow and Arterial Transit Time Variations in Elders with Long COVID

AbstractBackgroundMany COVID‐19 patients experience persistant neurological symptoms that often extend beyond the period of acute infection, referred to as “Long COVID”, where most patients reported brain fog and cognitive dysfunction. While elderly individuals are more vulnerable to possible enduring cognitive impairments after acute COVID‐19 requiring hospitalization, there is increasing concern that older patients with Long COVID will be at high risk for developing Alzheimer’s disease (AD) and dementia. Although there is emerging recognition of Long COVID, its underlying neuropathology remains unknown. This study aimed to investigate neurovascular function using advanced MRI perfusion in elder patients with Long COVID.MethodWell‐matched elderly Long COVID patients (n = 14, mean age = 60.1±4.3 years, 12F, 2M) and control subjects (n = 25, mean age = 60.4±7.2 years, 19F, 6M) underwent neurocognitive testing as well as neuroimaging. Patients were seen 711.57 ± 165.02 days after the initial mild non‐hospitalized COVID‐19 infection. Clinical cognitive complaints of Long COVID patients included memory changes (n = 12, 85.7%), attention (n = 12, 85.7%), speech/writing (n = 9, 64.3%), and multitasking (n = 9, 64.3%). Brain perfusion was evaluated using an advanced 3D pseudo‐continuous arterial spin labeling (pCASL) sequence with Hadamard encoded multiple post‐labeling delays (PLDs), enabling estimation of Cerebral Blood Flow (CBF) and Arterial Transit Time (ATT) ATT and ATT corrected CBF.ResultConventional MRI scans (T1, T2, and FlAIR) appear normal in all subjects. Voxelwise comparisons between Long‐COVID and control subjects showed a significant global decrease in the ATT (p &lt; 0.05, cluster corrected at a &lt; 0.05), along default mode and other key networks, where there is a trend of decreased CBF (p&lt;0.05, uncorrected) specifically in the frontal lobe in those with Long COVID.ConclusionThese preliminary results in an aging group indicate that neurocognitive effects of Long COVID could be attributed to neurovascular dysfunction, even in those cases with initial non‐hospitalized mild COVID‐19 of more than 500 days. The novel finding of diffusely decreased ATT could be something attributable to the unique neurovascular mechanism of Long COVID. Future longitudinal research following the progression of those elderly Long COVID patients with known abnormal neurovascular function to fully evaluate their risk for developing AD and dementia.

Cerebral Blood Flow and Arterial Transit Time Variations in Elders with Long COVID

AbstractBackgroundMany COVID‐19 patients experience persistant neurological symptoms that often extend beyond the period of acute infection, referred to as “Long COVID”, where most patients reported brain fog and cognitive dysfunction. While elderly individuals are more vulnerable to possible enduring cognitive impairments after acute COVID‐19 requiring hospitalization, there is increasing concern that older patients with Long COVID will be at high risk for developing Alzheimer’s disease (AD) and dementia. Although there is emerging recognition of Long COVID, its underlying neuropathology remains unknown. This study aimed to investigate neurovascular function using advanced MRI perfusion in elder patients with Long COVID.MethodWell‐matched elderly Long COVID patients (n = 14, mean age = 60.1±4.3 years, 12F, 2M) and control subjects (n = 25, mean age = 60.4±7.2 years, 19F, 6M) underwent neurocognitive testing as well as neuroimaging. Patients were seen 711.57 ± 165.02 days after the initial mild non‐hospitalized COVID‐19 infection. Clinical cognitive complaints of Long COVID patients included memory changes (n = 12, 85.7%), attention (n = 12, 85.7%), speech/writing (n = 9, 64.3%), and multitasking (n = 9, 64.3%). Brain perfusion was evaluated using an advanced 3D pseudo‐continuous arterial spin labeling (pCASL) sequence with Hadamard encoded multiple post‐labeling delays (PLDs), enabling estimation of Cerebral Blood Flow (CBF) and Arterial Transit Time (ATT) ATT and ATT corrected CBF.ResultConventional MRI scans (T1, T2, and FlAIR) appear normal in all subjects. Voxelwise comparisons between Long‐COVID and control subjects showed a significant global decrease in the ATT (p &lt; 0.05, cluster corrected at α &lt; 0.05), along default mode and other key networks, where there is a trend of decreased CBF (p&lt;0.05, uncorrected) specifically in the frontal lobe in those with Long COVID.ConclusionThese preliminary results in an aging group indicate that neurocognitive effects of Long COVID could be attributed to neurovascular dysfunction, even in those cases with initial non‐hospitalized mild COVID‐19 of more than 500 days. The novel finding of diffusely decreased ATT could be something attributable to the unique neurovascular mechanism of Long COVID. Future longitudinal research following the progression of those elderly Long COVID patients with known abnormal neurovascular function to fully evaluate their risk for developing AD and dementia.

Can combined high-resolution vessel wall imaging and multiple post-labeling delay 3D pseudo-continuous arterial spin labeling differentiate moyamoya disease from atherosclerotic moyamoya syndrome?

PurposeTo investigate whether moyamoya disease (MMD) and atherosclerotic moyamoya syndrome (AS-MMS) differ in vascular morphology and perfusion characteristics using T1w-CUBE imaging and multiple post-labeling delay 3D pseudo-continuous arterial spin labeling imaging (MP 3D-PcASL), and to explore the potential of the combined techniques for accurate diagnosis of both diseases. MethodThis prospective study enrolled 51 patients with moyamoya vasculopathy, including 26 with MMD and 25 with AS-MMS. All patients underwent digital subtraction angiography (DSA)/magnetic resonance angiography (MRA), T1w-CUBE imaging, and MP 3D-PCASL examinations. Morphological parameters, including the outer diameter, maximum wall thickness, luminal stenosis morphology, degree of wall enhancement, number of collateral vessels, and perfusion parameters, such as cerebral blood flow (CBF) and arterial transit time (ATT), were measured. After univariate analysis between the two groups, logistic regression models based on the derived parameters of T1w-CUBE imaging, MP 3D-PCASL, and combined imaging were implemented, and receiver operating characteristic (ROC) curves were generated to compare the discriminatory power of the different imaging methods for the diagnosis of MMD. ResultsWith T1w-CUBE imaging, MMD showed a smaller outer diameter (2.76 ± 0.39 vs. 3.07 ± 0.49 mm) and maximum wall thickness (1.27 ± 0.19 vs. 1.49 ± 0.24 mm) than AS-MMS (both P < 0.05). Using MP 3D-pcASL, the resultant CBF (36.64 ± 14.28 vs. 28.77 ± 8.63 mL/100 g/min) was higher in MMD relative to AS-MMS, while an opposite pattern was shown for ATT (1.61 ± 0.09 vs. 1.72 ± 0.13 s; both P < 0.05). Robust diagnostic efficacies for disease differentiation, confirmed by high areas under the ROC curve (AUCs) (>0.808), were separately shown with T1w-CUBE and MP 3D-pcASL derived parameters. However, the combined multivariate logistic regression model showed optimaldiagnostic efficacy(AUC: 0.938; P < 0.05). ConclusionsCombined T1w-CUBE imaging and MP 3D-PCASL provides distinctive morphological and functional features to evaluate vessel walls and cerebral perfusion, and might help distinguish MMD from AS-MMS.

ISMRM Open Science Initiative for Perfusion Imaging (OSIPI): ASL pipeline inventory.

To create an inventory of image processing pipelines of arterial spin labeling (ASL) and list their main features, and to evaluate the capability, flexibility, and ease of use of publicly available pipelines to guide novice ASL users in selecting their optimal pipeline. Developers self-assessed their pipelines using a questionnaire developed by the Task Force 1.1 of the ISMRM Open Science Initiative for Perfusion Imaging. Additionally, each publicly available pipeline was evaluated by two independent testers with basic ASL experience using a scoring system created for this purpose. The developers of 21 pipelines filled the questionnaire. Most pipelines are free for noncommercial use (n = 18) and work with the standard NIfTI (Neuroimaging Informatics Technology Initiative) data format (n = 15). All pipelines can process standard 3D single postlabeling delay pseudo-continuous ASL images and primarily differ in their support of advanced sequences and features. The publicly available pipelines (n = 9) were included in the independent testing, all of them being free for noncommercial use. The pipelines, in general, provided a trade-off between ease of use and flexibility for configuring advanced processing options. Although most ASL pipelines can process the common ASL data types, only some (namely, ASLPrep, ASLtbx, BASIL/Quantiphyse, ExploreASL, and MRICloud) are well-documented, publicly available, support multiple ASL types, have a user-friendly interface, and can provide a useful starting point for ASL processing. The choice of an optimal pipeline should be driven by specific data to be processed and user experience, and can be guided by the information provided in this ASL inventory.

Subject-specific timing adaption in time-encoded arterial spin labeling imaging

ObjectivesOne challenge in arterial spin labeling (ASL) is the high variability of arterial transit times (ATT), which causes associated arterial transit delay (ATD) artifacts. In patients with pathological changes, these artifacts occur when post-labeling delay (PLD) and bolus durations are not optimally matched to the subject, resulting in difficult quantification of cerebral blood flow (CBF) and ATT. This is also true for the free lunch approach in Hadamard-encoded pseudocontinuous ASL (H-pCASL).Material and methodsFive healthy volunteers were scanned with a 3 T MR-system. pCASL-subbolus timing was adjusted individually by the developed adaptive Walsh-ordered pCASL sequence and an automatic feedback algorithm. The quantification results for CBF and ATT and the respective standard deviations were compared with results obtained using recommended timings and intentionally suboptimal timings.ResultsThe algorithm individually adjusted the pCASL-subbolus PLD for each subject within the range of recommended timing for healthy subjects, with a mean intra-subject adjustment deviation of 47.15 ms for single-shot and 44.5 ms for segmented acquisition in three repetitions.DiscussionA first positive assessment of the results was performed on healthy volunteers. The extent to which the results can be transferred to patients and are of benefit must be investigated in follow-up studies.