Postlabeling Delay Research Articles

Quantification of liver perfusion using multidelay pseudocontinuous arterial spin labeling.

To develop a free-breathing multidelay pseudocontinuous arterial spin labeling (pCASL) technique for quantitative measurement of liver perfusion of the hepatic artery and portal vein, respectively. A navigator-gated pCASL sequence with balanced steady-state free precession (bSSFP) readout was developed and applied on five healthy young volunteers at 3T. Two labeling schemes were performed with the labeling plane applied on the descending aorta above the liver, and perpendicular to the portal vein before its entry to liver to label the hepatic artery and portal vein, respectively. For each labeling scheme, pCASL scans were performed at five or six postlabeling delays between 200 and 2000 msec or 2500 msec with an interval of 400 or 500 msec. Multidelay pCASL images were processed offline with nonrigid motion correction, outlier removal, and fitted for estimation of liver perfusion and transit time. Estimated liver perfusion of the hepatic artery and hepatic portal vein were 21.8 ± 1.9 and 95.1 ± 8.9 mL/100g/min, with the corresponding transit time of 1227.3 ± 355.5 and 667.2 ± 85.0 msec, respectively. The estimated liver perfusion and transit time without motion correction were less reliable with greater residual variance compared to those processed with motion correction (P < 0.05). The liver perfusion measurement using multidelay pCASL showed good correspondence with values noted in the literature. The capability to noninvasively and selectively label the hepatic artery and portal vein is a unique strength of pCASL as compared to other liver perfusion imaging techniques, such as computed tomography perfusion and dynamic contrast-enhanced MRI.

Three-dimensional Pseudo-continuous Arterial Spin Label Non-contrast Enhanced Perfusion Imaging of Head and Neck Tumors with High-field MR System

To evaluate the feasibility of three-dimensional pseudo-continuous arterial spin label (3D pCASL) non-contrast enhanced perfusion imaging applied to head and neck tumors in high-field MR and detect the effects of different postlabeling delay (PLD) time on image quality and the reliability of repeated measurements of tumor blood flow (BF) in different 3D pCASL groups. In this prospective study,all the 25 patients received neck 3D pCASL non-contrast enhanced perfusion examinations in a 3.0 T MR system by using an 8-channel head and neck joint coil. Conventional T1-weighted (TIWI) and T2-weighted imaging (T2WI) were performed firstly. Finally,three 3D pCASL with different PLD time [ASL1(PLD1=1525 ms),ASL2 (PLD2=2025 ms), ASL3(PLD3=2525 ms)] were acquired. Patients' perfusion-weighted images acquired from different 3D pCASL sequences underwent the analysis of signal to noise ratio (SNR) and contrast noise ratio (CNR) for tumors. Two observers performed the qualitative assessments on spiral artifacts and vascular artifacts of perfusion-weighted images from different 3D pCASL sequences. Blood flow (BF) of tumors from different 3D pCASL sequences were measured by the two observers respectively for the first time and by observer 2 for the second time. Seventeen enrolled patients (age:50.1 ± 12.7 years,M/F=10:7) with histopathologic. underwent the evaluation of image quality and measurements of BF values. The SNRs and CNRs of ASL1,ASL2, and ASL3 showed a descending trendency. SNRs (P=0.011) and CNRs (P=0.009) of ASL1 were significant higher than those of ASL3. There was no significant difference of scores of spiral artifacts among the three ASL groups (P=0.932). The scores of vascular artifacts of ASL1,ASL2,and ASL3 showed a descending trendency,also. And scores of ASL1 was significant higher than that of ASL3(P=0.000). The intraclass correlation coefficient (ICC) of intre-and intraobserver were high (ICC>0.9). Although the BF values of ASL1,ASL2, and ASL3 showed an ascending trendency,there was no significant difference among the three groups (P=0.977). The 3D pCASL no-contrast enhanced perfusion MR imaging can be used for head and neck tumor. The image quality of perfusion weighted images and reliability of BF measurements were satisfied. The 3D pCASL series with PLD of 1525 ms and 2025 ms have better image quality than PLD of 2525 ms. And BF values do not show significant statistic difference among the three groups. Therefore, 3D pCASL series with PLD of 1525 ms and 2025 ms are more suitable for the perfusion imaging of head and neck tumors

Arterial Spin Labeling Perfusion Magnetic Resonance Image with Dual Postlabeling Delay: A Correlative Study with Acetazolamide Loading 123I-Iodoamphetamine Single-Photon Emission Computed Tomography

Perfusion magnetic resonance image with arterial spin labeling (ASL) provides a completely noninvasive measurement of cerebral blood flow (CBF). However, arterial transient times can have a marked effect on the ASL signal. For example, a single postlabeling delay (PLD) of 1.5 seconds underestimates the slowly streaming collateral pathways that maintain the cerebrovascular reserve (CVR). To overcome this limitation, we developed a dual PLD method. A dual PLD method of 1.5 and 2.5 seconds was compared with (123)I-iodoamphetamine single-photon emission computed tomography with acetazolamide loading to assess CVR in 10 patients with steno-occlusive cerebrovascular disease. In 5 cases (Group A), dual PLD-ASL demonstrated low CBF with 1.5-second PLD in the target area, whereas CBF was improved with 2.5-second PLD. In the other 5 cases (Group B), dual PLD-ASL depicted low CBF with 1.5-second PLD, and no improvement in CBF with 2.5-second PLD in the target area was observed. On single-photon emission computed tomography, CVR was maintained in Group A but decreased in Group B. Although dual PLD methods may not be a completely alternative test for (123)I-iodoamphetamine single-photon emission computed tomography with acetazolamide loading, it is a feasible, simple, noninvasive, and repeatable technique for assessing CVR, even when employed in a routine clinical setting.

Voxel-Wise Perfusion Assessment in Cerebral White Matter with PCASL at 3T; Is It Possible and How Long Does It Take?

PurposeTo establish whether reliable voxel-wise assessment of perfusion in cerebral white matter (WM) is possible using arterial spin labeling (ASL) at 3T in a cohort of healthy subjects.Materials and MethodsPseudo-continuous ASL (PCASL) with background suppression (BS) optimized for WM measurements was performed at 3T in eight healthy male volunteers aged 25–41. Four different labeling schemes were evaluated by varying the labeling duration (LD) and post-labeling delay (PLD). Eight slices with voxel dimension 3.75x3.75x5 mm3 were acquired from the anterosuperior aspect of the brain, and 400 image/control pairs were collected for each run. Rigid head immobilization was applied using individually fitted thermoplastic masks. For each voxel in the resulting ASL time series, the time needed to reach a 95% significance level for the ASL signal to be higher than zero (paired t-test), was estimated.ResultsThe four protocols detected between 88% and 95% (after Bonferroni correction: 75% and 88%) of WM voxels at 95% significance level. In the most efficient sequence, 80% was reached after 5 min and 95% after 53 min (after Bonferroni correction 40% and 88% respectively). For all protocols, the fraction of significant WM voxels increased in an asymptotic fashion with increasing scan time. A small subgroup of voxels was shown to not benefit at all from prolonged measurement.ConclusionAcquisition of a significant ASL signal from a majority of WM voxels is possible within clinically acceptable scan times, whereas full coverage needs prohibitively long scan times, as a result of the asymptotic trajectory.

Evaluation of cerebral blood flow using multi-phase pseudo continuous arterial spin labeling at 3-tesla

PurposeArterial spin labeling (ASL) methods have been widely used for evaluation of cerebral blood flow (CBF) by magnetic resonance imaging. However, ASL methods require setting of the post labeling delay (PLD) time for obtaining images. As the hemodynamic status cannot be estimated in each patient, the resultant quantitative values of blood flow may not be accurate. The multi-phase pseudo continuous arterial spin labeling (pCASL) method can be used to obtain images at various time-points. The purpose of this study was to create the transit-time maps for correcting the delayed blood flow and evaluate CBF using the transit-time maps obtained by the multi-phase pCASL method. Materials and MethodsTwelve patients who underwent both 3.0-tesla magnetic resonance imaging (MRI) and single photon emission computed tomography with iodine-123-N-isopropyl-p-iodoamphetamine (123I-IMP) were investigated. This study was approved by the institutional review board of our institution. MRI acquisitions included PLD time-fixed (1525ms) and multi-phase pCASL sequences. The transit-time maps were calculated from multi-phase pCASL images by software. The transit-time maps were applied to PLD-fixed pCASL images pixel by pixel, for calculating the CBF value corrected for peak blood transit time. Regions of interest were drawn on the brain. IMP-CBF, ASL-CBF (default and corrected) and transit time were measured for each segment. ResultsTwelve patients and 264 segments were investigated. The mean IMP-CBF, ASL-CBF (default, corrected) and transit time were 28.4, 23.0, 29.6, [ml/min/100g] and 1977.5 [ms], respectively. There were no significant differences between IMP-CBF and ASL-CBF (corrected). ConclusionCBF values can be corrected by using the transit-time maps obtained using the multi-phase pCASL method.

How far is arterial spin labeling MRI from a clinical reality? Insights from arterial spin labeling comparative studies in Alzheimer's disease and other neurological disorders.

How far is arterial spin labeling MRI from a clinical reality? Insights from arterial spin labeling comparative studies in Alzheimer's disease and other neurological disorders.

Different post label delay cerebral blood flow measurements in patients with Alzheimer's disease using 3D arterial spin labeling

PurposeTo evaluate cerebral blood flow (CBF) in patients with Alzheimer's disease (AD) using a three-dimensional pseudocontinuous arterial spin labeling (PCASL). We aimed to study the effects of different post label delay on the resulting CBF maps and to investigate the characteristics and clinical applications of brain perfusion. Materials and methodsSixteen AD patients and nineteen healthy control subjects were recruited. 3D PCASL was performed using a 3.0T MR scanner. ASL was performed twice with different post label delays (PLD). Comparisons of CBF were made between AD patients and healthy control subjects respectively with PLD of 1.5s and PLD of 2.5s. Relationship between the CBF values and cognition was investigated using correlation analysis. A receiver operating characteristic (ROC) curve was generated for CBF measurements in posterior cingulate region. ResultAD patients with PLD of 1.5s showed lower CBF values primarily in bilateral temporal lobes, precuneus, middle and posterior cingulate gyri, left inferior parietal gyrus, left angular gyrus and left superior frontal gyrus. Lowered cerebral values were also observed in similar regions with PLD of 2.5s, but the clusters of voxel were smaller. CBF values were associated with cognition scores in most of gyri mentioned above. ConclusionHypoperfusion areas were observed in AD patients. PLD of 1.5s was sufficient to display CBF. Considering the complicated AD pathology, multiple PLDs are strongly recommended.

Abstract T P297: Arterial Spin Labeled MRI Quantifies Cerebral Blood Flow Changes with Blood Pressure from Acute to Subacute Stroke

Background: Hemodynamic interventions, such as blood pressure (BP) manipulation, are often utilized to optimize perfusion of the ischemic territory. Scant data support theoretical effects of permissive hypertension or BP reduction, yet arterial-spin labeled (ASL) MRI may chronicle quantitative cerebral blood flow (CBF) changes. We used serial ASL to measure CBF changes associated with hemodynamic interventions, based on arterial occlusion site and collaterals. Methods: Serial ASL acquired in 148 consecutive cases of acute ischemic stroke at a single center during a 3-year period. A pseudo-continuous ASL pulse sequence with background suppressed 3D GRASE (gradient and spin echo) readout with 4 post-labeling delays was used, with normalization of quantitative CBF on a standard neurovascular template. CBF values and relative changes were measured in the affected hemisphere and in discrete regions of infarct core and collateral territories. Results: 148 cases (median age 68 years (IQR 62-82), 73 women) were studied. Overall, CBF (ml/100g/min) was related to age (r=-0.40, p&lt;0.001) but not gender (male: 39±9.7, female: 40.6±8.2; r=.05, p=NS). Serial studies were obtained in 126 cases, including 2 studies in 91, 3 in 32, and 4 in 3. Median time to 1 st , 2 nd , 3 rd , and 4 th ASL study was 11.3, 39.7, 140.7, and 121.3 hrs and median CBF at these timepoints was 39.9 (IQR 28-48); 42.2 (IQR 29-52); 47.1 (IQR 36-56); and 35.6 (IQR 34-41). Average changes in CBF from study 1 to 2, 2 to 3, 3 to 4 were +2.2; +3.4; -14.8. Average CBF ratio between leptomeningeal and perforating MCA regions was 1.1. The correlation of initial delta CBF (study 1 to 2) with initial delta BP (1 to 2) was r=-0.1, p=NS. Average delta CBF/delta mmHg SBP was 0.25. At studies 1 and 2, lower BP was related to higher CBF (r=-0.148, p=0.102). Overall, delta BP was not linked with CBF (r=0.002, p=NS) or delta CBF (r=-0.108, p=NS). For those with low initial CBF (&lt;40), positive delta BP was strongly associated with lower CBF at study 2 (r=-0.552, p=0.006). Conclusions: Blood pressure modification, permissive or interventional, may differentially affect CBF in the ischemic core and collateral regions. ASL provides a novel method for non-invasive mapping of serial changes in absolute CBF quantification in the ICU and beyond.

Multi-TI Arterial Spin Labeling MRI with Variable TR and Bolus Duration for Cerebral Blood Flow and Arterial Transit Time Mapping.

Arterial spin labeling (ASL) is an MRI perfusion imaging method from which quantitative cerebral blood flow (CBF) can be calculated. We present a multi-TI ASL method (multi-TI integrated ASL) in which variable post-labeling delays and variable TRs are used to improve the estimation of arterial transit time (ATT) and CBF while shortening the scan time by 41% compared to the conventional methods. Variable bolus widths allow for T1 and M0 estimation from raw ASL data. Multi-TI integrated pseudo-continuous ASL images were collected at 7 TI times ranging 100-4300 ms. Voxel-wise T1 and M0 maps were estimated, then CBF and ATT maps were created using the estimated T1 tissue map. All maps were consistent with physiological values reported in the literature. Based on simulations and in vivo comparisons, this method demonstrates higher CBF and ATT estimation efficiency than other ATT acquisition methods and better fit to the perfusion model. It produces CBF maps with reduced sensitivity to errors from ATT and tissue T1 variations. The estimated M0, T1, and ATT maps also have potential clinical utility. The method requires a single scan acquired within a clinically acceptable scan time (under 6 minutes) and with low sensitivity to motion.

Optimization and Reliability of Multiple Postlabeling Delay Pseudo-Continuous Arterial Spin Labeling during Rest and Stimulus-Induced Functional Task Activation

Arterial spin labeling (ASL) sequences that incorporate multiple postlabeling delay (PLD) times allow estimation of when arterial blood signal arrives within a region of interest. Sequences that account for such variability may improve the reliability of ASL and therefore make the technique well suited for future clinical and experimental investigations of cerebral perfusion. This study assessed the within- and between-session reproducibility of an optimized pseudo-continuous ASL (pCASL) functional magnetic resonance imaging (FMRI) sequence that incorporates multiple postlabeling delays (multi-PLD pCASL). Healthy subjects underwent four identical scans separated by 30 minutes, 1 week, and 1 month using multi-PLD pCASL to image absolute perfusion (cerebral blood flow (CBF) and arterial arrival time (AAT)) during both rest and a visual-cued motor task. We show good test-retest reliability, with strong consistency across subjects and sessions during rest (inter-session within-subject coefficient of variation: gray matter (GM) CBF=6.44%; GM AAT=2.20%). We also report high sensitivity and reproducibility during the functional task, where we show robust task-related decreases in AAT corresponding with regions of increased CBF. Importantly, these results give insight into optimal PLD selection for future investigations using single-PLD ASL to image different brain regions, and highlight the necessity of multi-PLD ASL when imaging perfusion in the whole brain.

Increased SNR efficiency in velocity selective arterial spin labeling using multiple velocity selective saturation modules (mm-VSASL).

Velocity-selective arterial spin labeling (VSASL) is theoretically insensitive to transit delay (TD) effects. However, it uses saturation instead of inversion, resulting in compromised signal to noise ratio (SNR). In this study we explore the use of multiple velocity-selective saturation (VSS) modules in VSASL (mm-VSASL) to improve SNR. Theoretical SNR efficiency improvement and optimized parameters were calculated from simulations for mm-VSASL. VSASL with two VSS modules (VSASL-2VSS) was implemented to measure cerebral blood flow in vivo, compared with conventional VSASL (VSASL-1VSS), pulsed ASL (PASL), and pseudo-continuous ASL (PCASL). TDs and bolus durations (BDs) were measured to validate the simulations and to examine the TD sensitivity of these preparations. Compared with VSASL-1VSS, VSASL-2VSS achieved a significant improvement of SNR (22.1 ± 1.9%, P = 1.7 × 10(-6) ) in vivo, consistent with a 22.7% improvement predicted from simulations. The SNR was comparable to or higher (in gray matter, P = 4.3 × 10(-3) ) than that using PCASL. VSASL was experimentally verified to have minimal TD effects. Utilizing multiple VSS modules can improve the SNR efficiency of VSASL. Mm-VSASL may result in an SNR that is comparable to or even higher than that of PCASL in applications where long postlabeling delays are required.

Regional cerebral arterial transit time hemodynamics correlate with vascular risk factors and cognitive function in men with coronary artery disease.

Arterial transit time is the time needed for blood to travel from large arteries to capillaries, as estimated from arterial spin-labeling MR imaging. The purpose of this study was to determine whether vascular risk factors and cognitive performance are related to regional differences in cerebral arterial transit time in patients with coronary artery disease who are at risk for cognitive decline. Arterial transit time was estimated from multiple postlabel delay pseudocontinuous arterial spin-labeling images obtained from 29 men with coronary artery disease. Tests of memory, attention, processing speed, and executive function were administered. Principal component analysis was used to create separate models of cognition and vascular risk, which were related to brain regions through voxelwise analyses of arterial transit time maps. Principal component analysis identified 2 components of vascular risk: 1) "pressor" (age, systolic blood pressure, and pulse pressure) and 2) "obesity" (body fat percentage and body mass index). Obesity was inversely related to arterial transit time in the posterior cingulate, precuneus, lateral occipital cortices, middle temporal gyrus, and frontal pole (P corrected < .05), whereas pressor was not significant. Cognitive scores were factored into a single component. Poor performance was inversely related to precuneus arterial transit time (P corrected < .05). The average arterial transit time in regions identified by obesity was associated with poorer cognitive function (r(2) = 0.21, t = -2.65, P = .01). Altered cerebral hemodynamics, notably in nodal structures of the default mode network, may be one way that vascular risk factors impact cognition in patients with coronary artery disease.

SU‐D‐18C‐05: Variable Bolus Arterial Spin Labeling MRI for Accurate Cerebral Blood Flow and Arterial Transit Time Mapping

Purpose:Arterial spin labeling (ASL) is an MRI perfusion imaging method from which quantitative cerebral blood flow (CBF) maps can be calculated. Acquisition with variable post‐labeling delays (PLD) and variable TRs allows for arterial transit time (ATT) mapping and leads to more accurate CBF quantification with a scan time saving of 48%. In addition, T1 and M0 maps can be obtained without a separate scan. In order to accurately estimate ATT and T1 of brain tissue from the ASL data, variable labeling durations were invented, entitled variable‐bolus ASL.Methods:All images were collected on a healthy subject with a 3T Siemens Skyra scanner. Variable‐bolus Psuedo‐continuous ASL (PCASL) images were collected with 7 TI times ranging 100‐4300ms in increments of 700ms with TR ranging 1000‐5200ms. All boluses were 1600ms when the TI allowed, otherwise the bolus duration was 100ms shorter than the TI. All TI times were interleaved to reduce sensitivity to motion. Voxel‐wise T1 and M0 maps were estimated using a linear least squares fitting routine from the average singal from each TI time. Then pairwise subtraction of each label/control pair and averaging for each TI time was performed. CBF and ATT maps were created using the standard model by Buxton et al. with a nonlinear fitting routine using the T1 tissue map.Results:CBF maps insensitive to ATT were produced along with ATT maps. Both maps show patterns and averages consistent with literature. The T1 map also shows typical T1 contrast.Conclusion:It has been demonstrated that variablebolus ASL produces CBF maps free from the errors due to ATT and tissue T1 variations and provides M0, T1, and ATT maps which have potential utility. This is accomplished with a single scan in a feasible scan time (under 6 minutes) with low sensivity to motion.

Nonenhanced arterial spin labeled carotid MR angiography using three‐dimensional radial balanced steady‐state free precession imaging

To optimize and preliminarily evaluate a three-dimensional (3D) radial balanced steady-state free precession (bSSFP) arterial spin labeled (ASL) sequence for nonenhanced MR angiography (MRA) of the extracranial carotid arteries. The carotid arteries of 13 healthy subjects and 2 patients were imaged on a 1.5 Tesla MRI system using an undersampled 3D radial bSSFP sequence providing a scan time of ∼4 min and 1 mm(3) isotropic resolution. A hybridized scheme that combined pseudocontinuous and pulsed ASL was used to maximize arterial coverage. The impact of a post label delay period, the sequence repetition time, and radiofrequency (RF) energy configuration of pseudocontinuous labeling on the display of the carotid arteries was assessed with contrast-to-noise ratio (CNR) measurements. Faster, higher undersampled 2 and 1 min scans were tested. Using hybridized ASL MRA and a 3D radial bSSFP trajectory, arterial CNR was maximized with a post label delay of 0.2 s, repetition times ≥ 2.5 s (P < 0.05), and by eliminating RF energy during the pseudocontinuous control phase (P < 0.001). With higher levels of undersampling, the carotid arteries were displayed in ≤ 2 min. Nonenhanced MRA using hybridized ASL with a 3D radial bSSFP trajectory can display long lengths of the carotid arteries with 1 mm(3) isotropic resolution.

Multi-delay arterial spin labeling perfusion MRI in moyamoya disease–comparison with CT perfusion imaging

To present a multi-delay pseudo-continuous ASL (pCASL) protocol that offers simultaneous measurements of cerebral blood flow (CBF) and arterial transit time (ATT), and to study correlations between multi-delay pCASL and CT perfusion in moyamoya disease. A 4 post-labeling delay (PLD) pCASL protocol was applied on 17 patients with moyamoya disease who also underwent CT perfusion imaging. ATT was estimated using the multi-delay protocol and included in the calculation of CBF. ASL and CT perfusion images were rated for lesion severity/conspicuity. Pearson correlation coefficients were calculated across voxels between the two modalities in grey and white matter of each subject respectively and between normalized mean values of ASL and CT perfusion measures in major vascular territories. Significant associations between ASL and CT perfusion were detected using subjective ratings, voxel-wise analysis in grey and white matter and region of interest (ROI)-based analysis of normalized mean perfusion. The correlation between ASL CBF and CT perfusion was improved using the multi-delay pCASL protocol compared to CBF acquired at a single PLD of 2 s (P < 0.05). There is a correlation between perfusion data from ASL and CT perfusion imaging in patients with moyamoya disease. Multi-delay ASL can improve CBF quantification, which could be a prognostic imaging biomarker in patients with moyamoya disease. • Simultaneous measurements of CBF and ATT can be achieved using multi-delay pCASL. • Multi-delay ASL was compared with CT perfusion in patients with moyamoya disease. • Statistical analyses showed significant associations between multi-delay ASL and CT perfusion. • Multi-delay ASL can improve CBF quantification in moyamoya disease.

Abstract W MP114: Arterial Spin Label Perfusion Imaging in Acute Neonatal Stroke Reveals Hyperperfusion in Association With Cerebral Ischemic Injury

Introduction: Perfusion magnetic resonance imaging (pMRI) in adults reveals a hypoperfused region, the ischemic penumbra, related to the fixed ischemic injury shown by diffusion weighted imaging (DWI) in acute stroke. Neonatal stroke has pathophysiology and optimum treatment that remain elusive. We hypothesized that altered regional perfusion accompanies the ischemic injury in focal neonatal stroke. Methods: Neonates (0-28 days of life) underwent MR imaging at 3T fieldstrength. pMRI employed a pseudocontinuous arterial spin labeling (PCASL) sequence with multi-slice echo planar readouts at 3x3x5mm3 resolution with TE/TR = 12ms/3.5s, labeling time = 1.6s, a post-labeling delay = 1.5s, 9 axial slices acquired, scan time ~5 min. Forty label/control image pairs were acquired, subtracted and averaged to obtain contrast maps proportional to quantified cerebral blood flow (CBF). DWI, susceptibility weighted imaging and T2-weighted series were obtained with standard protocols. Acute stroke was classified as arterial or venous. Core infarction was considered to lie in hypointense regions on DWI apparent diffusion coefficient maps. Regional perfusion signal was compared to the ischemic core on DWI and to the homologous uninvolved region in the contralesional hemisphere. Results: Data were collected on 20 neonates, (13 males; median/mean gestational age=38/38.5 weeks) with acute stroke (11 arterial ischemic stroke (AIS); 9 venous) scanned at median postnatal age=1.5 days. Evidence of regional hyperperfusion existed in 10/11 (91%) neonates with AIS and 4/9 (44%) with venous stroke. Hyperperfusion was part of a heterogeneous pattern of hypo- and hyperperfusion in 4 infants with AIS and 3 infants with venous infarct. Electroencephalography data obtained at presentation were available for 19 (95%) of the neonates. Fourteen infants (70%) had either electrographic seizure or focal sharp waves in the same hemisphere as the acute infarction. Conclusion: Arterial spin labeling pMRI can be successfully obtained in acute neonatal stroke. Unlike adults, pMRI often reveals hyperperfusion rather than hypoperfusion in neonates. This hyperperfusion may be due to early spontaneous reperfusion or to the neuronal hyperexcitability of stroke-associated seizure.

Time‐encoded pseudocontinuous arterial spin labeling: Basic properties and timing strategies for human applications

In this study, the basic properties and requirements of time-encoded pseudocontinuous arterial spin labeling (te-pCASL) are investigated. Also, the extra degree of freedom delivered by changing block durations is explored. First, the minimal duration of encoding blocks, the influence of cardiac triggering, and the effect of dividing the labeling period into blocks are evaluated. Two new strategies for timing the encoding blocks in te-pCASL are introduced: variable block duration to compensate for T1-decay and the free lunch approach that uses the postlabeling delay time that is idle in standard pCASL to acquire arterial transit time (ATT) information. Simulations are used to probe possible signal losses. No signal loss was found when dividing the labeling period into blocks with duration >50 ms. In time-encoded perfusion imaging, no cardiac triggering is required. Summation of results for individual blocks in te-pCASL postprocessing causes severe loss of temporal SNR. Quality of cerebral blood flow (CBF) maps was not affected by the encoding line order. Adjusting the timing of encoding blocks in te-pCASL allows for tailoring the acquisition to specific applications. With the free lunch setup, te-pCASL delivers CBF and high resolution ATT maps within a single scan, with a small penalty in tSNR.

Arterial Spin-Labeling Evaluation of Cerebrovascular Reactivity to Acetazolamide in Healthy Subjects

Arterial spin-labeling MR imaging permits safe, repeated CBF measurement. We investigated the potential and technical factors of arterial spin-labeling imaging in assessing cerebrovascular reactivity to acetazolamide. The regional CBF was measured in 8 healthy volunteers by use of a 3D pseudocontinuous arterial spin-labeling sequence. Arterial spin labeling imaging was performed at rest and every 2 minutes after intravenous acetazolamide injection. To evaluate repeatability, regional CBF measurements were repeated without acetazolamide within an imaging session and on a separate day. Additionally, arterial spin-labeling imaging was performed at rest and after acetazolamide injection with different postlabeling delays, and regional cerebrovascular reactivity was calculated. The regional CBF started to increase immediately after acetazolamide injection and peaked at approximately 10 minutes, followed by a slow decrease. Favorable intrasession repeatability was demonstrated, especially when scanner tuning was omitted between scans. Rest regional CBF was slightly lower with a postlabeling delay of 2525 ms than with a postlabeling delay of 1525 ms, and the postlabeling delay-dependent difference was more evident for regional CBF after acetazolamide injection and regional cerebrovascular reactivity. Arterial spin-labeling imaging allows evaluation of the distribution, magnitude, and time course of cerebrovascular response to acetazolamide. The influence of the postlabeling delay on the estimated cerebrovascular reactivity should be noted.

Measurement of cerebral white matter perfusion using pseudocontinuous arterial spin labeling 3T magnetic resonance imaging--an experimental and theoretical investigation of feasibility.

PurposeThis study was aimed to experimentally and numerically investigate the feasibility of measuring cerebral white matter perfusion using pseudocontinuous arterial spin labeling (PCASL) 3T magnetic resonance imaging (MRI) at a relatively fine resolution to mitigate partial volume effect from gray matter.Materials and MethodsThe Institutional Research Ethics Committee approved this study. On a clinical 3T MR system, ten healthy volunteers (5 females, 5 males, age = 28±3 years) were scanned after providing written informed consent. PCASL imaging was performed with varied combinations of labeling duration (τ = 1000, 1500, 2000, and 2500 ms) and post-labeling delay (PLD = 1000, 1400, 1800, and 2200 ms), at a spatial resolution (1.56x1.56x5 mm3) finer than commonly used (3.5x3.5 mm2, 5-8 mm in thickness). Computer simulations were performed to calculate the achievable perfusion-weighted signal-to-noise ratio at varied τ, PLD, and transit delay.ResultsBased on experimental and numerical data, the optimal τ and PLD were found to be 2000 ms and 1500-1800 ms, respectively, yielding adequate SNR (~2) to support perfusion measurement in the majority (~60%) of white matter. The measurement variability was about 9% in a one-week interval. The measured white matter perfusion and perfusion ratio of gray matter to white matter were 15.8-27.5 ml/100ml/min and 1.8-4.0, respectively, depending on spatial resolution as well as the amount of deep white matter included.ConclusionPCASL 3T MRI is able to measure perfusion in the majority of cerebral white matter at an adequate signal-to-noise ratio by using appropriate tagging duration and post-labeling delay. Although pixel-wise comparison may not be possible, region-of-interest based flow quantification is feasible.

Reliability of Three-Dimensional Pseudo-Continuous Arterial Spin Labeling MR Imaging for Measuring Visual Cortex Perfusion on Two 3T Scanners

Cerebral blood flow (CBF) in the human primary visual cortex is correlated with the loss of visual function in neuro-ophthalmological diseases. Advanced three-dimensional pseudo-continuous arterial spin labeling (3D pCASL), as a non-invasive method to access the CBF, can be a novel measurement to detect the visual cortex. The objective of the study was to assess the intra- and inter-scanner reliability of 3D pCASL of the visual cortex in healthy adults and suggest the selection of different post-labeling delay times (PLDs). For this reason, 3D pCASL was conducted in two 3.0T MR three times with twelve healthy volunteers at an interval of 10–15 days. The 1st and 3rd tests were performed on scanner-1, and the 2nd test was performed on scanner-2. The value of the CBF was abstracted from the visual cortex with two PLDs. The intra- and inter-scanner reliability and reproducibility were evaluated with the intraclass correlation coefficient (ICC) and Bland-Altman plots. By estimating the mean value of the CBF in the visual cortex, the intra-scanner results demonstrated the higher reliability (ICC for PLD = 1.5 second presented at 0.743 compared with 0.829 for PLD = 2.5 seconds), and the Bland-Altman plots showed the reproducibility at a longer PLD. We conclude that the calibrated 3D pCASL approach provides a highly reproducible measurement of the CBF of the visual cortex that can serve as a useful quantitative probe for research conducted at multiple centers and for the long-term observation of the clinical effects of neuro-opthalmological diseases.