Multi-delay Arterial Spin Labeling Research Articles

354 Feasibility and Clinical Imaging of Pain States Based on Multi-Delay Arterial Spin Labeling in Chronic Low Back Pain Patients Implanted With Thoracic Spinal Cord Stimulation

INTRODUCTION: Multi-delay, pseudo-continuous arterial spin labelling (PCASL) is a novel technique capable of perfusion imaging without contrast. It overcomes the limitation of a low signal-to-noise ratio of pulsed-ASL, and multiple post-label delays allow it to account for and measure arterial transit time (ATT). This makes it a suitable tool for the perfusion assessment. To date, there have been no studies to assess changes in ASL-measured perfusion in chronic low-back pain (cLBP) patients treated with thoracic spinal cord stimulation (tSCS). METHODS: PCASL data was acquired in five patients post-tSCS and five healthy subjects. ATT was estimated using weighted delays from multiple delay times, and it was used to calculate cerebral blood flow (CBF) and cerebral blood volume (CBV). Maps were normalized into MNI space and smoothed. Averaged values of ATT, CBF and CBV from pain ROI atlas were extracted and compared between cLBP and healthy control groups. Statistics comparing perfusion changes between patients and healthy subjects were conducted after Box-Cox transformation of data using Wilcoxon rank sum. RESULTS: Our results demonstrated the feasibility of MRI scanning with ASL sequence in patients with SCS. Specific absorption rates ranged from 0.031–0.042W/kg. Wilcoxon test indicated that ATT was significantly greater in cLBP patients within the supplementary motor area, posterior short gyrus, and the orbitofrontal cortex. There were no significant differences in patients and controls in CBF or CBV. CONCLUSIONS: Rate of perfusion as indexed by PCASL-derived ATT is reduced in cLBP treated with SCS patients in regions associated with pain processing, cognition, and motor planning. Insignificant results in CBF and CBV measures are likely due to low sample size of patients.

Abstract TP139: Revascularization Improves Vascular Hemodynamics in Pediatric Moyamoya Patients

Introduction: Cerebrovascular reactivity (CVR) reflects the change in cerebral blood flow (CBF) in response to vasodilation. Studies have demonstrated that impaired CVR was associated with a higher risk of acute stroke in patients with intracranial vasculopathy and that bypass surgeries can reduce the risk of strokes. Moyamoya disease is a progress cerebrovascular disorder that begins during childhood. Arterial spin labeling (ASL) is a quantitative MRI technique for non-invasive CBF and CVR measurement; ASL with multiple delays can also measure arterial transit time (ATT). Here, we compare the CBF, CVR, and ATT in pediatric Moyamoya patients before and after bypass using multi-delay ASL. Hypothesis: CVR will increase significantly after bypass surgeries. Methods: Imaging data were acquired from 22 Moyamoya patients (11 months - 18 years, 14 females) using a 3T MRI system. All patients had unilateral or bilateral occlusion at ACA, MCA and/or PCA. Multi-delay ASL data (7 delays) were acquired at baseline and 15 minutes after acetazolamide administration. CBF and ATT were computed using the general kinetic model. CVR was computed as the percentage of CBF change compared with baseline CBF. Flow territories (right and left ACA, MCA, and PCA) were defined using the Harvard-Oxford atlases. Paired t-tests were conducted to compare the mean CVR, CBF, and ATT changes before and after bypass surgeries. Results: The figure shows the hemodynamic maps of an example patients. Overall, CVR and CBF in the affected regions increased after bypass; ATT in these regions decreased after bypass. For this cohort, our analysis showed that CVR of the affected regions increased significantly by 68% and ATT reduced significantly by 10.7% measured by multi-delay ASL, implying improved circulation and lower risk for strokes. Discussion: Multi-delay ASL was effective to detect improved CVR and reduced ATT in pediatric Moyamoya patients after bypass surgeries.

Effects of the Training Data Condition on Arterial Spin Labeling Parameter Estimation Using a Simulation-Based Supervised Deep Neural Network.

A simulation-based supervised deep neural network (DNN) can accurately estimate cerebral blood flow (CBF) and arterial transit time (ATT) from multidelay arterial spin labeling signals. However, the performance of deep learning depends on the characteristics of the training data set. We aimed to investigate the effects of the ground truth (GT) ranges of CBF and ATT on the performance of the DNN when training data were prepared using arterial spin labeling signal simulation. Deep neural networks were individually trained using 36 patterns of the training data sets. Simulation test data (1,000,000 points), 17 healthy volunteers, and 1 patient with moyamoya disease were included. The simulation test data were used to evaluate accuracy, precision, and noise immunity of the DNN. The best-performing DNN was determined by the normalized mean absolute error (NMAE), normalized root mean squared error (NRMSE), and normalized coefficient of variation over repeated training (CV Net ). Cerebral blood flow and ATT values and their histograms were compared between the GT and predicted values. For the in vivo data, the dependency of the predicted values on the GT ranges was visually evaluated by comparing CBF and ATT maps between the best-performing DNN and the other DNNs. Moreover, using the synthesized noisy images, noise immunity was compared between the best-performing DNN based on the simulation study and a conventional method. The simulation study showed that a network trained by the GT of CBF and ATT in the ranges of 0 to 120 mL/100 g/min and 0 to 4500 milliseconds, respectively, had the highest performance (NMAE CBF , 0.150; NRMSE CBF , 0.231; CV NET CBF , 0.028; NMAE ATT , 0.158; NRMSE ATT , 0.257; and CV NET ATT , 0.028). Although the predicted CBF and ATT varied with the GT range of the training data sets, the appropriate settings preserved the accuracy, precision, and noise immunity of the DNN. In addition, the same results were observed in in vivo studies. The GT ranges to prepare the training data affected the performance of the simulation-based supervised DNNs. The predicted CBF and ATT values depended on the GT range; inappropriate settings degraded the accuracy, whereas appropriate settings of the GT range provided accurate and precise estimates.

Transformer-based deep learning denoising of single and multi-delay 3D arterial spin labeling.

To present a Swin Transformer-based deep learning (DL) model (SwinIR) for denoising single-delay and multi-delay 3D arterial spin labeling (ASL) and compare its performance with convolutional neural network (CNN) and other Transformer-based methods. SwinIR and CNN-based spatial denoising models were developed for single-delay ASL. The models were trained on 66 subjects (119 scans) and tested on 39 subjects (44 scans) from three different vendors. Spatiotemporal denoising models were developed using another dataset (6 subjects, 10 scans) of multi-delay ASL. A range of input conditions was tested for denoising single and multi-delay ASL, respectively. The performance was evaluated using similarity metrics, spatial SNR and quantification accuracy of cerebral blood flow (CBF), and arterial transit time (ATT). SwinIR outperformed CNN and other Transformer-based networks, whereas pseudo-3D models performed better than 2D models for denoising single-delay ASL. The similarity metrics and image quality (SNR) improved with more slices in pseudo-3D models and further improved when using M0 as input, but introduced greater biases for CBF quantification. Pseudo-3D models with three slices achieved optimal balance between SNR and accuracy, which can be generalized to different vendors. For multi-delay ASL, spatiotemporal denoising models had better performance than spatial-only models with reduced biases in fitted CBF and ATT maps. SwinIR provided better performance than CNN and other Transformer-based methods for denoising both single and multi-delay 3D ASL data. The proposed model offers flexibility to improve image quality and/or reduce scan time for 3D ASL to facilitate its clinical use.

Hemodynamic imaging parameters in brain metastases patients – Agreement between multi-delay ASL and hypercapnic BOLD

Arterial spin labeling (ASL) MRI is a routine clinical imaging technique that provides quantitative cerebral blood flow (CBF) information. A related technique is blood oxygenation level-dependent (BOLD) MRI during hypercapnia, which can assess cerebrovascular reactivity (CVR). ASL is weighted towards arteries, whereas BOLD is weighted towards veins. Their associated parameters in heterogeneous tissue types or under different hemodynamic conditions remains unclear. Baseline multi-delay ASL MRI and BOLD MRI during hypercapnia were performed in fourteen patients with brain metastases. In the ROI analysis, the CBF and CVR values were positively correlated in regions showing sufficient reserve capacity (i.e. non-steal regions, rrm = 0.792). Additionally, longer hemodynamic lag times were related to lower baseline CBF (rrm = −0.822) and longer arterial arrival time (AAT; rrm = 0.712). In contrast, in regions exhibiting vascular steal an inverse relationship was found with higher baseline CBF related to more negative CVR (rrm = −0.273). These associations were confirmed in voxelwise analyses. The relationship between CBF, AAT and CVR measures seems to be dependent on the vascular status of the underlying tissue. Healthy tissue relationships do not hold in tissues experiencing impaired or exhausted autoregulation. CVR metrics can possibly identify at-risk areas before perfusion deficiencies become visible on ASL MRI, specifically within vascular steal regions.

Short- and Long-Term MRI Assessed Hemodynamic Changes in Pediatric Moyamoya Patients After Revascularization.

Cerebrovascular reserve (CVR) reflects the capacity of cerebral blood flow (CBF) to change following a vasodilation challenge. Decreased CVR is associated with a higher stroke risk in patients with cerebrovascular diseases. While revascularization can improve CVR and reduce this risk in adult patients with vasculopathy such as those with Moyamoya disease, its impact on hemodynamics in pediatric patients remains to be elucidated. Arterial spin labeling (ASL) is a quantitative MRI technique that can measure CBF, CVR, and arterial transit time (ATT) non-invasively. To investigate the short- and long-term changes in hemodynamics after bypass surgeries in patients with Moyamoya disease. Longitudinal. Forty-six patients (11 months-18 years, 28 females) with Moyamoya disease. 3-T, single- and multi-delay ASL, T1-weighted, T2-FLAIR, 3D MRA. Imaging was performed 2 weeks before and 1 week and 6 months after surgical intervention. Acetazolamide was employed to induce vasodilation during the imaging procedure. CBF and ATT were measured by fitting the ASL data to the general kinetic model. CVR was computed as the percentage change in CBF. The mean CBF, ATT, and CVR values were measured in the regions affected by vasculopathy. Pre- and post-revascularization CVR, CBF, and ATT were compared for different regions of the brain. P-values <0.05 were considered statistically significant. ASL-derived CBF in flow territories affected by vasculopathy significantly increased after bypass by 41 ± 31% within a week. At 6 months, CBF significantly increased by 51 ± 34%, CVR increased by 68 ± 33%, and ATT was significantly reduced by 6.6 ± 2.9%. There may be short- and long-term improvement in the hemodynamic parameters of pediatric Moyamoya patients after bypass surgery. 4 TECHNICAL EFFICACY: Stage 2.

Brain perfusion imaging by multi-delay arterial spin labeling: Impact of modeling dispersion and interaction with denoising strategies and pathology.

Arterial spin labeling (ASL) acquisitions at multiple post-labeling delays may provide more accurate quantification of cerebral blood flow (CBF), by fitting appropriate kinetic models and simultaneously estimating relevant parameters such as the arterial transit time (ATT) and arterial cerebral blood volume (aCBV). We evaluate the effects of denoising strategies on model fitting and parameter estimation when accounting for the dispersion of the label bolus through the vasculature in cerebrovascular disease. We analyzed multi-delay ASL data from 17 cerebral small vessel disease patients (50 ± 9 y) and 13 healthy controls (52 ± 8 y), by fitting an extended kinetic model with or without bolus dispersion. We considered two denoising strategies: removal of structured noise sources by independent component analysis (ICA) of the control-label image timeseries; and averaging the repetitions of the control-label images prior to model fitting. Modeling bolus dispersion improved estimation precision and impacted parameter values, but these effects strongly depended on whether repetitions were averaged before model fitting. In general, repetition averaging improved model fitting but adversely affected parameter values, particularly CBF and aCBV near arterial locations in patients. This suggests that using all repetitions allows better noise estimation at the earlier delays. In contrast, ICA denoising improved model fitting and estimation precision while leaving parameter values unaffected. Our results support the use of ICA denoising to improve model fitting to multi-delay ASL and suggest that using all control-label repetitions improves the estimation of macrovascular signal contributions and hence perfusion quantification near arterial locations. This is important when modeling flow dispersion in cerebrovascular pathology.

Multidelay Arterial Spin Labeling Versus Computed Tomography Perfusion in Penumbra Volume of Acute Ischemic Stroke.

Multidelay arterial spin labeling (ASL) is a novel perfusion method of ASL, with arterial transit time (ATT) calculated by multiple postlabeling delays to correct cerebral blood flow (CBF). We verify the accuracy of multidelay ASL in evaluating the ischemic penumbra and perfusion levels in patients with acute ischemic stroke, compared with computed tomography perfusion (CTP). Patients with acute ischemic stroke with anterior circulation large vessel occlusion received baseline CTP, multidelay ASL, and diffusion-weighted imaging (DWI) in succession. Multidelay ASL image was processed to reconstruct ATT, CBF without ATT correction, and CBF corrected by ATT. The consistency of hypoperfusion and ischemic penumbra volume calculated by CTP and multidelay ASL were quantified by intraclass correlation coefficient (ICC) in 2-way mixed effects, absolute agreement, and single measure. Wilcoxon signed-rank test was used to compare the difference in penumbra volume between CTP, corrected ASL, and uncorrected ASL. Thirty patients were included. Hypoperfusion volume based on multidelay ASL with different thresholds were 117.95 (87.77-151.49) mL for corrected relative CBF<40%, 130.29 (85.99-249.37) mL for CBF corrected by ATT<20 mL·100g-1·min-1, no statistical difference (P>0.05) compared with the volume of CTP, and consistency was almost excellent (ICC, 0.91) and substantial consistent (ICC, 0.727). The volumes of ischemic penumbra were 91.00 (42.68-125.27) mL for corrected relative CBF<40%-DWI, 108.94 (62.03-150.86) mL for CBF corrected by ATT<20 mL·100 g-1·min-1-DWI, which showed no statistical difference compared with the penumbra volume of CTP (P>0.05). The consistency was excellent (ICC, 0.822) and moderate (ICC, 0.501), respectively. The volume of uncorrected relative CBF <40%-DWI was 209.57 (123.21-292.45) mL, statistically larger than corrected relative CBF <40%-DWI (P<0.001) and CTP (P<0.001). The volume of uncorrected CBF<20 mL·100g-1·min-1-DWI was 186.23 (86.56-298.22) mL, statistically larger than CBF corrected by ATT<20 mL·100g-1·min-1-DWI (P<0.001) and CTP(P<0.001). The volume of ischemic penumbra determined by CBF/DWI mismatch based on multidelay ASL is consistent with CTP. The penumbra volume calculated by CBF adjusted by ATT is more accurate.

Cerebral blood flow quantification with multi-delay arterial spin labeling in ischemic stroke and the association with early neurological outcome

Restoring blood flow to brain tissue at risk of infarction is essential for tissue survival and clinical outcome. We used cerebral blood flow (CBF) quantified with multiple post-labeling delay (PLD) pseudocontinuous arterial spin labeling (ASL) MRI after ischemic stroke and assessed the association between CBF and early neurological outcome. We acquired ASL with 7 PLDs at 3.0 T in large vessel occlusion stroke patients at 24 h. We quantified CBF relative to the contralateral hemisphere (rCBF) and defined hyperperfusion as a ≥30% increase and hypoperfusion as a ≥40% decrease in rCBF. We included 44 patients (median age: 70 years, median NIHSS: 13, 40 treated with endovascular thrombectomy) of whom 37 were recanalized. Hyperperfusion in ischemic core occurred in recanalized but not in non-recanalized patients (65.8% vs 0%, p = 0.006). Hypoperfusion occurred only in the latter group (0% vs 85.7%, p < 0.001). In recanalized patients, hyperperfusion was also seen in salvaged penumbra (38.9%). Higher rCBF in ischemic core (aβ, −2.75 [95% CI: −4.11 to −1.40]) and salvaged penumbra (aβ, −5.62 [95% CI: −9.57 to −1.68]) was associated with lower NIHSS scores at 24 h. In conclusion, hyperperfusion frequently occurs in infarcted and salvaged brain tissue following successful recanalization and early neurological outcome is positively associated with the level of reperfusion.

The Boston ASL Template and Simulator: Initial development and implementation.

Templates are a hallmark of image analysis in neuroimaging. However, while numerous structural templates exist and have facilitated single-subject and large group studies, templates based on functional contrasts, such as arterial spin labeling (ASL) perfusion, are scarce, have an inherently low spatial resolution, and are not as widely distributed. Having such tools at one's disposal is desirable, for example, in the case of studies not acquiring structural scans. We here propose an initial development of an ASL adult template based on high-resolution fast spin echo acquisitions. High-resolution single-delay ASL, low-resolution multi-delay ASL, T1 -weighted magnetization prepared rapid acquisition 2 gradient echoes, and T2 fluid attenuated inversion recovery data were acquired in a cohort of 10 healthy volunteers (6 males and 4 females, 30± 7 years old). After offline reconstruction of high-resolution perfusion arterial transit time (ATT) and T1 maps, we built a multi-contrast template relying on the Advanced Normalization Toolbox multivariate template nonlinear construction framework. We offer examples for the registration of ASL data acquired with different sequences. Finally, we propose an ASL simulator based on our templates and a standard kinetic model that allows generating synthetic ASL contrasts based on user-specified parameters. Boston ASL Template and Simulator (BATS) offers high-quality, high-resolution perfusion-weighted and quantitative perfusion templates accompanied by ATT and different anatomical contrasts readily available in the Montreal Neurological Institute space. In addition, examples of use for data registration and as a synthetic contrast generator show various applications in which BATS could be used. We propose a new ASL template collection, named BATS, that also includes a simulator allowing the generation of synthetic ASL contrasts. BATS is available at http://github.com/manueltaso/batsasltemplate.

Customized whole brain-covering 3D GRASE in multi-delay pseudo-continuous arterial spin labeling for duplex distinct hemodynamic mapping contrasts of brain tissues and circulation pathways

Gradient and spin echo (GRASE) is widely employed in arterial spin labeling (ASL) as an efficient readout sequence. Hemodynamic parameter mappings of perfusion, such as cerebral blood flow (CBF) and arterial transit time (ATT), can be derived via multi-delay ASL acquisitions. Multi-delay ASL perfusion imaging inevitably suffers limited signal-to-noise ratio (SNR) since a motion-sensitized vessel suppressing module has to be employed to highlight perfusion signals. The present work reveals that in multi-delay ASL, manipulation of GRASE sequence on either planar imaging echo echo train for adjusted spatial resolutions or FSE echo train for modulated extent of T 2-blurring can significantly alter the mapping contrasts among tissues and among cerebral lobes under different pathways of blood circulation, and meanwhile regulates SNR. Four separate multi-delay ASL scans with different echo train designs in 3D whole brain covering GRASE were carried out for healthy subjects to evaluate the variations in regard to the parameter quantifications and SNR. Based on the quantification mappings, the GRASE acquisition with moderate spatial resolution (3.5 × 3.5 × 4 mm3) and segmented k z scheme was recognized for the first time to be recommended for more unambiguous CBF and ATT contrasts between GM and WM in conjunction with more enhanced ATT contrast between anterior and posterior cerebral circulations, with reasonably good SNR. The technical proposal is of great value for the cutting-edge research of a variety of neurological diseases of global concerns.

Potential Diagnostic Applications of Multi-Delay Arterial Spin Labeling in Early Alzheimer's Disease: The Chinese Imaging, Biomarkers, and Lifestyle Study.

BackgroundCerebral blood flow (CBF) alterations are involved in the onset and progression of Alzheimer’s disease (AD) and can be a potential biomarker. However, CBF measured by single-delay arterial spin labeling (ASL) for discrimination of mild cognitive impairment (MCI, an early stage of AD) was lack of accuracy. Multi-delay ASL can not only provide CBF quantification but also provide arterial transit time (ATT). Unfortunately, the technique was scarcely applied to the diagnosis of AD. Here, we detected the utility of ASL with 1-delay and 7-delay in ten regions of interest (ROIs) to identify MCI and AD.Materials and MethodsPseudocontinuous ASL (pCASL) MRI was acquired on a 3T GE scanner in adults from the Chinese Imaging, Biomarkers, and Lifestyle (CIBL) Study of AD cohort, including 26 normal cognition (NC), 37 MCI, and 39 AD. Receiver operating characteristic (ROC) analyses with 1-delay and 7-delay ASL were performed for the identification of MCI and AD. The DeLong test was used to compare ROC curves.ResultsFor CBF of 1-delay or 7-delay the AUCs showed moderate-high performance for the AD/NC and AD/MCI comparisons (AUC = 0.83∼0.96) (p < 0.001). CBF of 1-delay performed poorly in MCI/NC comparison (AUC = 0.69) (p < 0.001), but CBF of 7-delay fared well with an AUC of 0.79 (p < 0.001). The combination of CBF and ATT of 7-delay showed higher performance for AD/NC, AD/MCI, and MCI/NC comparisons with AUCs of 0.96, 0.89, and 0.89, respectively (p < 0.001). Furthermore, combination of CBF, ATT, sex, age, APOE ε4, and education improved further the accuracy (p < 0.001). In subgroups analyses, there were no significant differences in CBF of 7-delay ASL for identification of AD or MCI between age subgroups (p > 0.05).ConclusionThe combination of CBF and ATT with 7-delay ASL showed higher performance for identification of MCI than CBF of 1-delay, when adding to sex, age, APOE ε4 carrier status, and education years, the diagnostic performance was further increased, presenting a potential imaging biomarker in early AD.

Multidelay ASL of the pediatric brain.

Arterial spin labeling (ASL) is a powerful noncontrast MRI technique for evaluation of cerebral blood flow (CBF). A key parameter in single-delay ASL is the choice of postlabel delay (PLD), which refers to the timing between the labeling of arterial free water and measurement of flow into the brain. Multidelay ASL (MDASL) utilizes several PLDs to improve the accuracy of CBF calculations using arterial transit time (ATT) correction. This approach is particularly helpful in situations where ATT is unknown, including young subjects and slow-flow conditions. In this article, we discuss the technical considerations for MDASL, including labeling techniques, quantitative metrics, and technical artefacts. We then provide a practical summary of key clinical applications with real-life imaging examples in the pediatric brain, including stroke, vasculopathy, hypoxic-ischemic injury, epilepsy, migraine, tumor, infection, and metabolic disease.

Saturated multi‐delay renal arterial spin labeling technique for simultaneous perfusion and T1 quantification in kidneys

To propose a free-breathing simultaneous multi-delay arterial spin labeling (ASL) and T1 mapping technique with a stepwise kinetic model for renal assessment in a single 4-min scan at 3T. The proposed saturated multi-delay renal arterial spin labeling (SAMURAI) sequence used flow-sensitive alternating inversion recovery (FAIR) preparation, followed by acquisition of 9 images with Look-Locker spoiled gradient recalled echo (SPGR). Pre-saturation at the imaging slice was used to achieve saturation-based T1 mapping. A 4-step 2-compartment kinetic model was proposed to characterize water transition through artery- and tissue-compartment. The impact of the Look-Locker sampling scheme on the ASL signal was corrected in this model. T1 estimation with dictionary searching method and perfusion quantification based on the proposed kinetic model fitting were conducted after groupwise registration of the acquired images. The feasibility and repeatability of SAMURAI were validated in healthy subjects (n=11) and patients with different renal diseases (n=4). The proposed SAMURAI technique can provide accurate T1 map with strong correlation (R2 =0.98) with inversion recovery spin echo (IR-SE) on phantom. SAMURAI provided equally reliable whole kidney and cortical ASL and T1 quantification results compared with multi-TI FAIR (intraclass correlation coefficient [ICC], 0.880-0.958) and IR-SPGR (ICC, 0.875-0.912), respectively. Low renal blood flow and increased T1 were detected by SAMURAI in the affected kidneys of the patients. SAMURAI had excellent scan-rescan repeatability (ICC, 0.905-0.992) and significantly reduced scan time (4 min 6 s vs. 45 min for 9 TIs) compared to multi-TI FAIR. The proposed SAMURAI technique is feasible and repeatable for simultaneously quantifying T1 and perfusion of kidneys with high time-efficiency.

Brain abnormalities in children with attention-deficit/hyperactivity disorder assessed by multi-delay arterial spin labeling perfusion and voxel-based morphometry.

To obtain an understanding of the correlation between hemodynamic differences and morphological changes as well as potential sex differences in children with ADHD using multi-delay pseudo-continuous arterial spin labeling (pCASL) imaging and voxel-based morphometry (VBM), especially given that previous findings are limited for girls. We recruited 23 children with ADHD (mean age, 8.3years; 19 boys; 4 girls) and 24 children without ADHD (mean age, 9.1years; 13 boys; 11 girls) as controls. All participants underwent 3D multi-delay pCASL and T1-weighted imaging. The voxel-based statistical parameter mapping (SPM) method was used for group-wise comparisons. Compared with controls, children with ADHD exhibited decreased regional cerebral blood flow (rCBF) and gray matter volume (GMV) in the left middle frontal gyrus and left postcentral gyrus. Analysis by sex revealed reduced rCBF and GMV in the left lingual gyrus and left inferior occipital gyrus in boys with ADHD versus controls and increased rCBF and GMV in the left superior frontal gyrus in girls with ADHD. Although our results are preliminary because of small sample sizes, several brain regions exhibit changes in both cerebral perfusion and GMV in the same direction in patients with ADHD, with boys with ADHD showing decreased activity and girls with ADHD displaying increased activity in the fronto-parietal cortices.

K-space weighted image average (KWIA) for ASL-based dynamic MR angiography and perfusion imaging

A novel denoising algorithm termed k-space weighted image average (KWIA) was proposed to improve the signal-to-noise ratio (SNR) of dynamic MRI, such as arterial spin labeling (ASL)-based dynamic magnetic resonance angiography (dMRA) and perfusion imaging. KWIA divides the k-space of each time frame into multiple rings, the central ring of the k-space remains intact to preserve the image contrast and temporal resolution, while outer rings are progressively averaged with neighboring time frames to increase SNR. Simulations and in-vivo dMRA and multi-delay ASL studies were performed to evaluate the performance of KWIA under various MRI acquisition conditions. SNR ratios and temporal signal errors between KWIA-processed and the original data were measured. Visualization of dynamic blood flow signals as well as quantitative parametric maps were evaluated for KWIA-processed images as compared to the original images. KWIA achieved a SNR ratio of 1.73 for dMRA and 2.0 for multi-delay ASL respectively, which were in accordance with the theoretical predictions. Improved visualization of dynamic blood flow signals was demonstrated using KWIA in distal small vessels in dMRA and small brain structures in multi-delay ASL. Approximately 5% temporal errors were observed in both KWIA-processed dMRA and ASL signals. Fine anatomical features were revealed in the quantitative parametric maps of dMRA, and the residuals of model fitting were reduced for multi-delay ASL. Compared to other conventional denoising methods, KWIA is a flexible denoising algorithm that improves the SNR of ASL-based dMRA and perfusion MRI by up to 2-fold without compromising spatial and temporal resolution or quantification accuracy.

Usefulness of arterial spin labeling perfusion as an initial evaluation of status epilepticus

This study aimed to evaluate the sensitivity and prognostic value of arterial spin labeling (ASL) in a large group of status epilepticus (SE) patients and compare them with those of other magnetic resonance (MR) sequences, including dynamic susceptibility contrast (DSC) perfusion imaging. We retrospectively collected data of patients with SE in a tertiary center between September 2016 and March 2020. MR images were visually assessed, and the sensitivity for the detection of SE and prognostication was compared among multi-delay ASL, DSC, fluid-attenuated inversion recovery (FLAIR), and diffusion-weighted imaging (DWI). We included 51 SE patients and 46 patients with self-limiting seizures for comparison. Relevant changes in ASL were observed in 90.2% (46/51) of SE patients, a percentage higher than those for DSC, FLAIR, and DWI. ASL was the most sensitive method for initial differentiation between SE and self-limiting seizures. The sensitivity of ASL for detecting refractory SE (89.5%) or estimating poor outcomes (100%) was higher than those of other MR protocols or electroencephalography and comparable to those of clinical prognostic scores, although the specificity of ASL was very low as 9.4% and 15.6%, respectively. ASL showed a better ability to detect SE and predict the prognosis than other MR sequences, therefore it can be valuable for the initial evaluation of patients with SE.

Reliability and Sensitivity to Longitudinal CBF Changes in Steno-Occlusive Diseases: ASL Versus 123 I-IMP-SPECT.

Noninvasive cerebral blood flow (CBF) monitoring using arterial spin labeling (ASL) magnetic resonance imaging is useful for managing large cerebral artery steno-occlusive diseases. However, knowledge about its measurement characteristics in comparison with reference standard perfusion imaging is limited. To evaluate perfusion in a longitudinal manner in patients with steno-occlusive disease using ASL and compare with single-photon emission computed tomography (SPECT). Prospective. Moyamoya (n= 10, eight females) and atherosclerotic diseases (n= 2, two males). 3.0 T; gradient-echo three-dimensional T1 -weighted and spin-echo ASL. Multi-delay ASL and [123 I]-iodoamphetamine SPECT CBF measurements were performed both before and within 9 days of anterior-circulation revascularization. Reliability and sensitivity to whole-brain voxel-wise CBF changes (ΔCBF) and their postlabeling delay (PLD) dependency with varied PLDs (in milliseconds) of 1000, 2333, and 3666 were examined. Reliability and sensitivity to ΔCBF were examined using within-subject standard deviation (Sw) and intraclass correlation coefficients (ICCs). For statistical comparisons, standard deviation of longitudinal ΔCBF within the hemisphere contralateral to surgery, and the ratio between it and average ΔCBF within the ipsilateral regions of interest were subjected to paired t tests, respectively. P < 0.05 was considered statistically significant. ASL test-retest time interval was 31 ± 18 days. Test-retest reliability was significantly lower for SPECT (0.16 ± 0.02) than ASL (0.13 ± 0.04). Sensitivity to postoperative changes was significantly higher for ASL (2.71 ± 2.79) than SPECT (0.27 ± 0.62). Test-retest reliability was significantly higher for a PLD of 2333 (0.13 ± 0.04) than 3666 (0.19 ± 0.05), and sensitivity to ΔCBF was significantly higher for PLDs of 1000 (2.53 ± 2.50) and 2333 than 3666 (0.79 ± 1.88). ICC maps also showed higher reliability for ASL than SPECT. Higher test-retest reliability led to better ASL sensitivity than SPECT for postoperative ΔCBF. ASL test-retest reliability and sensitivity to ΔCBF were higher with a PLD of 2333. 1 TECHNICAL EFFICACY: Stage 2.

Association of Cerebral Blood Flow and Brain Tissue Relaxation Time With Neurodevelopmental Outcomes of Preterm Neonates: Multidelay Arterial Spin Labeling and Synthetic MRI Study.

Both cerebral blood flow (CBF) and brain tissue relaxation times are known to reflect maturation in the neonatal brain. However, we do not yet know if these factors are associated with neurodevelopmental outcomes. The objective of this study was to acquire CBF and relaxation time in preterm neonates, using multidelay arterial spin labeling and synthetic magnetic resonance imaging (MRI), and show their association with later neurodevelopmental outcomes. In this prospective study, preterm neonates were recruited, and multidelay arterial spin labeling and synthetic MRI were performed between September 2017 and December 2018. These neonates underwent the Bayley Scales of Infant Development test at 18 months of age, and both cognitive and motor outcome scores were measured. Transit time-corrected CBF and T1 and T2 relaxation time values were measured for different brain regions. The measured values were correlated with gestational age (GA) at birth and corrected GA at the MRI scan. Simple and multiple linear regression analyses were performed for the measured values and neurodevelopmental outcome scores. Forty-nine neonates (median [interquartile range] GA, 30 [2] weeks, 209 [17] days; 28 boys) underwent MRI scans at or near term-equivalent age (median [interquartile range] corrected GA, 37 [2] weeks, 258 [14] days). Transit time-corrected CBF (coefficient, 0.31-0.59) and relaxation time (coefficient, -0.39 to -0.86) values showed significant correlation with corrected GA but not with GA. After controlling for GA, the frontal white matter CBF in preterm neonates showed a negative relationship with cognitive outcome scores (β = -0.97; P = 0.029). Frontal white matter T1 relaxation times showed a positive relationship with cognitive outcome scores (β = 0.03; P = 0.025) after controlling for GA. Higher CBF values and lower T1 relaxation times in frontal white matter were associated with poorer cognitive outcomes. As quantitative neuroimaging markers, CBF and relaxation times may help predict neurodevelopmental outcomes in preterm neonates.

Arterial Transit Time-Based Multidelay Combination Strategy Improves Arterial Spin Labeling Cerebral Blood Flow Measurement Accuracy in Severe Steno-Occlusive Diseases.

Although perfusion imaging plays a key role in the management of steno-occlusive diseases, the clinical usefulness of arterial spin labeling (ASL) is limited by technical issues. To examine the effect of arterial transit time (ATT) prolongation on cerebral blood flow (CBF) measurement accuracy and identify the best CBF measurement protocol for steno-occlusive diseases. Prospective. Moyamoya (n=10) and atherosclerotic diseases (n= 8). A 3.0T/3DT1 -weighted and ASL. Hadamard-encoded multidelay ASL scans with/without vessel suppression (VS) and single-delay ASL scans with long-label duration (LD) and long postlabeling delay (PLD), referred to as long-label long-delay (LLLD), were acquired. CBF measurement accuracy and its ATT dependency, measured as the correlation between the relative CBF measurement difference (ASL-single-photon emission computed tomography [SPECT]) and ATT, were compared among 1) Combo (incorporating multidelay and LLLD data based on ATT), 2) standard (LD/PLD=1333/2333 msec), and 3) LLLD (LD/PLD=4000/4000 msec) protocols, using whole-brain voxel-wise correlation with reference standard SPECT CBF. The effect of VS on CBF measurement accuracy was also assessed. Pearson's correlation coefficient, repeated-measures analysis of variance, t-test. P< 0.05 was considered significant. Pearson's correlation coefficients between ASL and SPECT CBF measurements were as follows: Combo=0.55 ± 0.09; standard=0.52 ± 0.12; LLLD=0.41 ± 0.10. CBF measurement was least accurate in LLLD and most accurate in Combo. VS significantly improved overall CBF measurement accuracy in the standard protocol and in moyamoya patients for the Combo. ATT dependency analysis revealed that, compared with Combo, the standard and LLLD protocols showed significantly lower and negative and significantly higher and positive correlations, respectively (standard=-0.12 ± 0.04, Combo=-0.04 ± 0.03, LLLD=0.17 ± 0.03). By using ATT-corrected CBF derived from LD/PLD=1333/2333 msec as a base and by compensating underestimation in delayed regions using multidelay scans, the ATT-based Combo strategy improves CBF measurement accuracy compared with single-delay protocols in severe steno-occlusive diseases. 1 TECHNICAL EFFICACY: Stage 2.