Postlabeling Delay Research Articles

The influence of obesity on cerebral blood flow in young adults using arterial spin labeling MRI.

Obesity causes damage to several organs, including the brain. Recent studies have been focusing on understanding the mechanisms through which obesity affects brain structure and function using neuroimaging techniques. A functional biomarker, such as cerebral blood flow (CBF), is a powerful tool that can be used to explore neural dysfunction. However, there is currently limited information regarding the association between CBF and obesity. The study was conducted to investigate the potential effect of obesity on brain perfusion in a young cohort aged 20-30 years. A total of 21 obese (body mass index (BMI) > 26 kg/m2 ) and 21 lean (BMI < 24 kg/m2 ) right-handed volunteers were included in this study. CBF was acquired using the 2D single post-labeling delay (PLD) arterial spin labeling (ASL) technique on a 3 T MRI scanner. A multiple regression analysis was performed to examine the difference in global and regional gray matter (GM) CBF between the groups. CBF value was assigned as the dependent variable, whereas age, sex, and group (obese or lean) were considered as the independent variables. Results showed that group-related differences in CBF were homogeneous across brain regions, as obese subjects had significantly lower global GM CBF than lean subjects (P < 0.05). In the voxelwise analysis, obese individuals had significantly lower CBF in the left pulvinar of the thalamus and visual association areas, including Brodmann area (BA) 7, BA18, and BA19, than lean subjects. Although the signal-to-noise ratio was slightly compromised for 2D sequences and subject-specific arterial transit time was not estimated due to a single PLD sequence, this study demonstrated alterations in CBF in obese subjects, particularly in regions of the pulvinar of the thalamus and its synchronously related areas such as visual association areas. These results suggest that ASL provides a potential platform for further obesity-related research.

Test-retest reliability and reproducibility of long-label pseudo-continuous arterial spin labeling

PurposeArterial spin labeling MRI can quantify the cerebral blood flow (CBF) without exogenous tracer. However, the variation of arterial transit time across different brain regions introduces bias for measuring local CBF, especially for those subjects with long arterial transit time (ATT). Long post-labeling delay (PLD) or multi-PLD methods could mitigate the problem of heterogenous ATT at the expense of the signal-to-noise ratio (SNR). Long-label ASL might address the low SNR problem by increasing the amount of labeled arterial blood. Thus, we hypothesized that with the same relatively long PLD, long-label pCASL may be more robust and reproducible than standard-label pCASL in population with potentially prolonged ATT. The purpose of the study was to investigate the reliability and reproducibility of long-label pCASL in the whole brain and vascular regions of interest in an elderly population, compared with standard-label pCASL. MethodTwenty adult volunteers (14 males, 6 females; age, 56.6 ± 17.2 years) were scanned twice on one 3.0 T scanner by standard-label pCASL (label duration (LD) = 1500 ms, PLD = 2000 ms) and long-label pCASL (LD = 3500 ms, PLD = 2000 ms). The intraclass correlation coefficient (ICC), within-subject coefficient of variation (wsCV), random noise and signal coefficient of variation(CoV) were used to assess global and regional reliability and reproducibility. Measurement agreement and difference were compared in different brain regions using correlation coefficient plots and Bland-Altman plots respectively. ResultsCBF value measured by long-label pCASL was overall higher than standard-label pCASL in all ROIs. Long-label pCASL had higher ICC than standard-label pCASL in most ROIs, and lower wsCV, random noise and CoV in all ROIs. Regardless of ASL method used, anterior circulation flow territories (ICC, 0.93–0.97; wsCV, 0.03–0.06) had higher CBF reliability and reproducibility than posterior circulation flow territories (ICC, 0.89; wsCV, 0.06–0.08). In all ROIs, the correlation analysis showed higher test-retest agreement (rlong-label > rstandard-label) and the Bland-Altman plots demonstrated lower measurement difference in long-label pCASL. ConclusionThe study demonstrated good reliability and reproducibility of long-label pCASL in anterior brain regions in the elderly population. To further improve CBF quantification in a long-ATT population while proper PLD is already used, increasing the label duration may help.

Assessment of Renal Perfusion in Transplanted Kidney Patients Using Pseudo-Continuous Arterial Spin Labeling with Multiple Post-Labeling Delays

PurposeTo investigate technical issues for implementing pseudo-continuous arterial spin labeling (pCASL) for renal perfusion measurements in transplanted kidney patients (TK) in the early postoperative recovery phase. MethodsEleven subjects were scanned: TK (N = 4, 42 ± 8.1Y) and normal volunteers (NV) (N = 7, 25 ± 3Y). In 3.0 T clinical MRI, pCASL with a 2D balanced steady-state free precession readout was applied with four different post-labeling delays: 0.5/1.0/1.5/2.0 s. Perfusion images were acquired with and without background suppression and processed with and without registration for comparison. Renal blood flow (RBF) and arterial transit time (ATT) values were calculated from each pixel of images. The F-test, Wilcoxon signed-rank test, and Wilcoxon rank-sum test were used for statistical analyses. ResultsBackground suppression decreased signal variations for both NV and TK. Registration suppressed effects of kidney motion for NV, which was not critical for TK. The renal cortex showed greater perfusion than the renal medulla in both NV and TK(p < 0.01). TK showed greater renal perfusion than NV(p < 0.05). Cortical and medullary RBF values were 271.8 ± 43.5, 119.1 ± 15.1 ml/100 g/min for NV and 358.3 ± 36.4, 141.0 ± 11.5 ml/100 g/min for TK. TK showed longer ATT values than NV(p < 0.01). ATT values in the cortex and medulla were 641 ± 141 and 746 ± 150 ms for NV and 919 ± 49 and 935 ± 81 ms for TK. ConclusionsWe demonstrated that although there is no discernible motion of the transplanted kidney, background suppression is necessary to suppress signal fluctuations in renal perfusion measurements. Also, relatively high RBF and long ATT values were observed in the transplanted kidneys in the early postoperative recovery phase, which requires further longitudinal studies.

Imaging Pulmonary Blood Flow Using Pseudocontinuous Arterial Spin Labeling (PCASL) With Balanced Steady-State Free-Precession (bSSFP) Readout at 1.5T.

Quantitative assessment of pulmonary blood flow and visualization of its temporal and spatial distribution without contrast media is of clinical significance. To assess the potential of electrocardiogram (ECG)-triggered pseudocontinuous arterial spin labeling (PCASL) imaging with balanced steady-state free-precession (bSSFP) readout to measure lung perfusion under free-breathing (FB) conditions and to study temporal and spatial characteristics of pulmonary blood flow. Prospective, observational. Fourteen volunteers; three patients with pulmonary embolism. 1.5T, PCASL-bSSFP. The pulmonary trunk was labeled during systole. The following examinations were performed: 1) FB and timed breath-hold (TBH) examinations with a postlabeling delay (PLD) of 1000 msec, and 2) TBH examinations with multiple PLDs (100-1500 msec). Scan-rescan measurements were performed in four volunteers and one patient. Images were registered and the perfusion was evaluated in large vessels, small vessels, and parenchyma. Mean structural similarity indices (MSSIM) was computed and time-to-peak (TTP) of parenchymal perfusion in multiple PLDs was evaluated. Image quality reading was performed with three independent blinded readers. Wilcoxon test to compare MSSIM, perfusion, and Likert scores. Spearman's correlation to correlate TTP and cardiac cycle duration. The repeatability coefficient (RC) and within-subject coefficient of variation (wCV) for scan-rescan measurements. Intraclass correlation coefficient (ICC) for interreader agreement. Image registration resulted in a significant (P < 0.05) increase of MSSIM. FB perfusion values were 6% higher than TBH (3.28 ± 1.09 vs. 3.10 ± 0.99 mL/min/mL). TTP was highly correlated with individuals' cardiac cycle duration (Spearman = 0.89, P < 0.001). RC and wCV were better for TBH than FB (0.13-0.19 vs. 0.47-1.54 mL/min/mL; 6-7 vs. 19-60%). Image quality was rated very good, with ICCs 0.71-0.89. ECG-triggered PCASL-bSSFP imaging of the lung at 1.5T can provide very good image quality and quantitative perfusion maps even under FB. The course of labeled blood through the lung shows a strong dependence on the individuals' cardiac cycle duration. 2 TECHNICAL EFFICACY STAGE: 2 J. MAGN. RESON. IMAGING 2020;52:1767-1782.

Arterial transit artifacts observed by arterial spin labeling in Moyamoya disease

Objectives: Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI) technique used to assess cerebral perfusion. When tissue perfusion is impaired, such as in Moyamoya disease, a hyperintense band called the arterial transit artifact (ATA) may occur, which interferes with accurate measurements on ASL-MRI. In this study, we evaluated the correlation of ATAs with magnetic resonance angiography (MRA) and single-photon emission computed tomography (SPECT) imaging results in Moyamoya disease. The aim of our study was to elucidate the pathophysiology of ATAs and risk factors for high ATA scores. Materials and Methods: This retrospective study included 28 patients (56 hemispheres) with Moyamoya disease treated at our institution. MRI, MRA, ASL perfusion, and N-isopropyl-[123I] b-iodoamphetamine (123I-IMP) SPECT were performed. In order to semi-quantitatively evaluate the degree of ATA, the ATA scores were measured according to the number of hyperintense signal bands in the cerebral cortex. The relationship between the ATA scores and clinical and radiological factors were analyzed. Results: Regional cerebral blood flow (rCBF) determined with ASL weakly correlated with that determined by 123I-IMP SPECT (ρ=0.31, p=0.027). There was no significant association between the ATA scores and rCBF values determined with 123I-IMP SPECT (p=0.872, 0.745, 0.743 at PLD1000 (post-labeling delay), 1500, and 2000, respectively). However, there was a significant correlation between ATA scores and MRA scores (ρ=0.427 p=0.001; ρ=0.612 p=0.001; ρ=0.563 p=0.001 at PLD1000, 1500, and 2000, respectively). An analysis of patient background characteristics revealed a significantly higher incidence of high ATA scores in female patients, patients with high MRA scores, and patients with a distinguishable ivy sign. A multivariate analysis confirmed that female sex, high MRA score, and presence of an ivy sign were risk factors for high ATA scores. Conclusion: ATA scores were moderately correlated with MRA scores, and presence of an ivy sign was the most predictive factor for high ATA scores. A high ATA score determined using ASL in a patient with Moyamoya disease might suggest an advanced disease stage and a reduction in cerebrovascular reserve capacity.

Improved velocity‐selective‐inversion arterial spin labeling for cerebral blood flow mapping with 3D acquisition

To further optimize the velocity-selective arterial spin labeling (VSASL) sequence utilizing a Fourier-transform based velocity-selective inversion (FT-VSI) pulse train, and to evaluate its utility for 3D mapping of cerebral blood flow (CBF) with a gradient- and spin-echo (GRASE) readout. First, numerical simulations and phantom experiments were done to test the susceptibility to eddy currents and B1 field inhomogeneities for FT-VSI pulse trains with block and composite refocusing pulses. Second, the choices of the post-labeling delay (PLD) for FT-VSI prepared 3D VSASL were evaluated for the sensitivity to perfusion signal. The study was conducted among a young-age and a middle-age group at 3T. Both signal-to-noise ratio (SNR) and CBF were quantitatively compared with pseudo-continuous ASL (PCASL). The optimized 3D VSI-ASL was also qualitatively compared with PCASL in a whole-brain coverage among two healthy volunteers and a brain tumor patient. The simulations and phantom test showed that composite refocusing pulses are more robust to both eddy-currents and B1 field inhomogeneities than block pulses. 3D VSASL images with FT-VSI preparation were acquired over a range of PLDs and PLD = 1.2 s was selected for its higher perfusion signal. FT-VSI labeling produced quantitative CBF maps with 27% higher SNR in gray matter compared to PCASL. 3D whole-brain CBF mapping using VSI-ASL were comparable to the corresponding PCASL results. FT-VSI with 3D-GRASE readout was successfully implemented and showed higher sensitivity to perfusion signal than PCASL for both young and middle-aged healthy volunteers.

Ternary encoded super-selective arterial spin labeling for time-resolved flow territory mapping

Arterial spin labeling (ASL) is a non-contrast enhanced method for perfusion measurements. The obtained information is in general a snap-shot of the whole-brain perfusion. Image acquisition is performed after a certain delay time after the labeling of the arterial blood. Time-resolved information alongside flow territory mapping of individual arteries can become useful for the collection of important information such as arterial crossflow, and revascularization. Therefore, a method is presented that combines time-resolved flow territory mapping within a single scan based on encoding of the acquisition cycle using a ternary matrix approach.The super-selective tagging process is divided in individual blocks following a ternary matrix encoding scheme. In each block, the position of the labeling focus changes its position to each of the major brain feeding arteries. Contrary to conventional ASL approaches, no control condition is acquired and the individual flow territories are calculated by combining the label images only.The method was successfully evaluated in healthy volunteers. Each flow territory could be visualized over several post labeling delays within a single scan of approximately five minutes. Comparison of signal intensity (relative perfusion) did not show statistically significant differences between the methods.Encoding super-selective ASL using a ternary matrix allows for the vessel-selective and time-resolved acquisition of perfusion territories within a single scan.

Arterial spin labeling magnetic resonance imaging at short post-labeling delay reflects cerebral perfusion pressure verified by oxygen-15-positron emission tomography in cerebrovascular steno-occlusive disease.

Arterial transit time correction by data acquisition with multiple post-labeling delays (PLDs) or relatively long PLDs is expected to obtain more accurate imaging in cases of the cerebrovascular steno-occlusive disease. However, there have so far been no reports describing the significance of arterial spin labeling (ASL) images at short PLDs regarding the evaluation of cerebral circulation in ischemic cerebrovascular disease. To clarify the role of short-PLD ASL in cerebrovascular steno-occlusive disease. Fifty-three patients with cerebrovascular steno-occlusive disease were included in this study. All patients underwent ASL magnetic resonance imaging and 15O-PET within two days of each modality. To compare the ASL findings with each parameter of PET, the right-to-left (R/L) ratio, defined as the right middle cerebral artery (MCA) value/left MCA value, was calculated. There is a significant correlation between the ASL images at a short PLD and the ratio of cerebral blood flow and cerebral blood volume by 15O-PET, which may accurately reflect the cerebral perfusion pressure. A receiver operating characteristic curve analysis indicated that ASL images at PLD 1000 and 1500 ms were more accurate than at PLD 2000-3000 ms for the detection of a ≥10% change in the PET cerebral blood flow. ASL images at shorter PLDs may be useful at least as a screening modality to detect the changes in the cerebral circulation in cerebrovascular steno-occlusive disease. We must evaluate ASL images at multiple PLDs while considering the arterial transit time of each case at present.

Arterial spin-labeling perfusion MR images with dual postlabeling delay reveals hemodynamic changes in dural arteriovenous fistulas following endovascular surgery

BackgroundPrevious studies have demonstrated that, in patients with dural arteriovenous fistulas (DAVF), magnetic resonance perfusion images with arterial spin labeling (ASL) with a conventional single postlabeling delay (PLD) of 1.5 s, can be used to depict dural sinus and cortical venous reflux (CVR). However, because ASL is highly sensitive to arterial transit time (ATT), slow-flowing CVR cannot be fully evaluated. Furthermore, cerebral blood flow in the entire cortex can be underestimated because of prolonged ATT associated with venous congestion. To overcome these problems, we used a simple ASL technique with dual PLD settings with a longer PLD of 2.5 s in addition to 1.5 s. MethodsWe retrospectively selected two patients with DAVF who underwent endovascular surgery, and visually analyzed the diagnostic performance of the dual PLD method for evaluating perioperative changes of dural sinus and slow-flowing CVR and the associated hemodynamic state. Patient 1 had left transverse sinus-DAVF with severe venous congestion and Patient 2 developed an intracerebral hemorrhage in the left temporal lobe associated with left tentorial DAVF. ResultsPreoperatively, slow-flowing CVR in the left frontal lobe in Patient 1 and CVR in the vein of Trolard in Patient 2 were not detected using ASL with PLD at 1.5 s, but became apparent at 2.5 s. In both patients, the preoperative ATT of the entire brain was prolonged; ASL signals of the entire brain were decreased at 1.5 s and somewhat increased at 2.5 s. Postoperatively, the dural sinus and CVR disappeared. Furthermore, the prolonged ATT of the entire brain was improved. ConclusionAlthough further research with a large number of the patients is required, ASL with dual PLD method may enhance the detection of slow-flowing CVR and allow the evaluation of perioperative hemodynamic changes, including the improvement of prolonged ATT caused by venous congestion.

Influence of labeling parameters and respiratory motion on velocity-selective arterial spin labeling for renal perfusion imaging.

PurposeArterial transit time uncertainties and challenges during planning are potential issues for renal perfusion measurement using spatially selective arterial spin labeling techniques. To mitigate these potential issues, a spatially non‐selective technique, such as velocity‐selective arterial spin labeling (VSASL), could be an alternative. This article explores the influence of VSASL sequence parameters and respiratory induced motion on VS‐label generation.MethodsVSASL data were acquired in human subjects (n = 15), with both single and dual labeling, during paced‐breathing, while essential sequence parameters were systematically varied; (1) cutoff velocity, (2) labeling gradient orientation and (3) post‐labeling delay (PLD). Pseudo‐continuous ASL was acquired as a spatially selective reference. In an additional free‐breathing single VSASL experiment (n = 9) we investigated respiratory motion influence on VS‐labeling. Absolute renal blood flow (RBF), perfusion weighted signal (PWS), and temporal signal‐to‐noise ratio (tSNR) were determined.Results(1) With decreasing cutoff velocity, tSNR and PWS increased. However, undesired tissue labeling occurred at low cutoff velocities (≤ 5.4 cm/s). (2) Labeling gradient orientation had little effect on tSNR and PWS. (3) For single VSASL high signal appeared in the kidney pedicle at PLD < 800 ms, and tSNR and PWS decreased with increasing PLD. For dual VSASL, maximum tSNR occurred at PLD = 1200 ms. Average cortical RBF measured with dual VSASL (264 ± 34 mL/min/100 g) at a cutoff velocity of 5.4 cm/s, and feet‐head labeling was slightly lower than with pseudo‐continuous ASL (283 ± 55 mL/min/100 g).ConclusionWith well‐chosen sequence parameters, tissue labeling induced by respiratory motion can be minimized, allowing to obtain good quality RBF maps using planning‐free labeling with dual VSASL.

Abstract WP171: Are We Correctly Measuring Cerebrovascular Reserve Capacity: A Study on Multiple Sequential Post-Acetazolamide Injection Cerebral Blood Flow Measurements Using Arterial Spin Labeling in a Moyamoya Patient Population?

Introduction: Cerebrovascular reserve capacity (CVRC), an important predictor and prognostic factor for patients with moyamoya disease (MMD), can be derived by measuring cerebral blood flow (CBF) before and after administration of acetazolamide (ACZ). Commonly, a single CBF measurement is performed after ACZ injection at a time point varying between 5 to 20 minutes, whereas the dynamic temporal response using sequential CBF measurements has not been studied extensively. Furthermore, current literature reports group averaged CVRCs with high standard deviations indicating a patient-specific CVRC is spread over a wide range of values. The aim of this study was to assess the temporal dynamic response of CBF and derived CVRC during the ACZ challenge using arterial spin labeling in patients with MMD. Methods: Ten patients with MMD were included before and/or after revascularisation surgery and examined on a 3T MR scanner. CBF maps, based on 3D-pseudocontineous arterial spin labeling, were acquired before and 5, 15 and 25 minutes after an i.v. ACZ injection and registered to each patient’s 3D-T1-weighted image. A vascular territory template was spatially normalised to patient-specific space, defined by the 3D-T1-weighted image, including bilateral ACA, MCA and PCA. A post label delay of 2500 ms and large regions-of-interests were used to account for possible arterial transit time artefacts. CVRC was calculated as CBF augmentation post-ACZ injection relative to baseline. Results: A total of sixteen examinations were analysed. Average peak CBF augmentation occurred at 5 min post-ACZ injection, successively decreasing at 15 - and 25 min post-ACZ injection . CVRC followed a similar pattern. Peak CBF augmentation mostly occurred at 5 min for all vascular regions (frequency distribution 5 min: 64 %, 15 min: 23 %, 25 min: 13 %). Average ratio between CVRC calculated using 15 min CBF augmentation and CVRC using true peak CBF augmentation (5, 15 or 25 min) was 0.80 to 0.90 for all vascular regions. Conclusion: CVRC assessed using 15 min as a single post-ACZ injections time point may underestimate CVRC in average by 10 % to 20 % because of individual temporal patient response. The use of multiple post-injection time points is warranted.

Usefulness of Post-labeling Delay for the Assessment of Bright Vessel Appearance by Arterial Spin Labeling.

This study was performed to clarify the differences in blood flow strength, blood vessel diameter, and post-labeling delay (PLD) by physical experiments, and to examine whether bright vessel appearance (BVA) can be observed by arterial spin labeling (ASL). We introduced simulated blood flow (25 cm/sec, 12.5 cm/sec) using a specially made phantom of fixed tubes in a plastic container. At each speed, we scanned at several points of PLD using ASL imaging. We measured the signal in the tube to obtain a signal intensity (SI). We revised the T1 level from the SI and obtained SIblood. We used SItissue with normal perfusion measured from obtained clinical images by ASL and compared it with SIblood. In tubes with a narrow inner diameter, the signal slightly decreased. SI also decreased under slow flow compared with fast flow. At each flow rate, SIblood significantly exceeded SItissue. PLD distinguishes spin in brain tissue from 1525 msec to 2525 msec, and it can be observed. As spin signal decreases when the flow rate is slow, attention is necessary for observation. Assessment at PLD1525-2525 msec where normal perfusion was obtained suggested that BVA can be observed.

NI-08 TRIAL AND PROBLEM OF USING ASL IN INTRAOPERATIVE MRI

INTRODUCTIONMagnetic resonance perfusion imaging is considered to be available as grading of brain tumor and follow-up of brain treatment. One of the methods, arterial spin labeling (ASL), is a test that is useful for patients with renal impairment and contrast agent allergy and has low invasiveness because it does not use a contrast agent. However, there have been no reports of ASL in intraoperative MRI (iMRI).PURPOSEIn this hospital iMRI (1.5T), it was examined whether ASL could be used to evaluate residual tumor in patients under general anesthesia.CASE STUDYA 75-year-old woman with right temporal lobe Glioblastoma. 43-year-old man, left temporal lobe Diffuse astrocytoma. All performed ASL at the time of MRI imaging for navigation before induction of anesthesia just before surgery and iMRI. In all cases, the blood pressure at iMRI was maintained, and Post Label Delay (PLD) calculated the optimal PLD from the carotid artery velocity measured by iMRI, and defined it as 1800–2200 ms, and performed ASL.RESULTSActually, imaging by iMRI was almost difficult to visualize, and reflux was not recognized not only in the tumor but also in the gray matter.DISCUSSIONThe blood flow velocity measurement in the internal carotid artery is performed by the phase contrast method by intraoperative MRI, and the CBF decreases because propofol used during the operation decreases the CBF and also the brain metabolism. However, it has been suggested that it is one of the factors that make evaluation with ASL difficult. Although the iMRI of our hospital is 1.5 T, which is also a subject of investigation, it is thought that there is a limit to ASL imaging in the case of general anesthesia with propofol even from the calculated PLD.CONCLUSIONASL in iMRI at our hospital was not useful.

Detection of hemodynamic impairment on 15O gas PET using visual assessment of arterial spin-labeling MR imaging in patients with moyamoya disease

It is unclear whether the visual assessment of noninvasive arterial spin labeling magnetic resonance imaging (ASL) can identify instances of hemodynamic compromise including an elevated oxygen extraction fraction (OEF) measured by 15O-gas positron emission tomography (PET). Here we evaluated the relationship between a four-point visual assessment system referred to as 'ASL scores' using ASL with two postlabeling delays (PLDs; 1525 ms and 2525 ms) and some quantitative hemodynamic parameters measured by PET. We retrospectively evaluated the cases of 18 Japanese patients with moyamoya disease who underwent ASL and PET. We compared the patients' regional ASL scores on two ASL images to the regional values of PET parameters, and we observed a significant trend in accord with the presumed clinical severity among all PET parameters and ASL scores (p < .003). The ASL score of the long PLD (2525 ms) showed the highest specificity (98.5%) for elevated OEF. Our results suggest that hemodynamic impairment (including elevated OEF) in patients with moyamoya disease may be grossly assessed by a visual assessment of noninvasive ASL images, which can be easily obtained in clinical settings.

Longitudinal Reproducibility of MR Perfusion Using 3D Pseudocontinuous Arterial Spin Labeling With Hadamard-Encoded Multiple Postlabeling Delays.

Arterial spin labeling (ASL) can be confounded by varying arterial transit times (ATT) across the brain and with disease. Hadamard encoding schemes can be applied to 3D pseudocontinuous ASL (pCASL) to acquire ASL data with multiple postlabeling delays (PLDs) to estimate ATT and then correct cerebral blood flow (CBF). To assess the longitudinal reproducibility of 3D pCASL with Hadamard-encoded multiple PLDs. Prospective, longitudinal. Fifty-two healthy, right-handed male subjects who underwent imaging at four timepoints over 45 days. A Hadamard-encoded 3D pCASL sequence was acquired at 3.0T with seven PLDs from 1.0-3.7 sec. ATT and corrected CBF (cCBF) were computed. Conventional uncorrected CBF (unCBF) was also estimated. Within- and between-subject coefficient of variation (wCV and bCV, respectively) and intraclass correlation coefficient (ICC) were evaluated across four time intervals: 7, 14, 30, and 45 days, in gray matter and 17 independent regions of interest (ROIs). A power analysis was also conducted. A repeated-measures analysis of variance (ANOVA) was used to compare ATT, cCBF, and unCBF across the four scan sessions. A paired two-sample t-test was used to compare cCBF and unCBF. Pearson's correlation was used to examine the relationship between the cCBF and unCBF difference and ATT. Power calculations were completed using both the cCBF and unCBF variances. ATT showed the lowest wCV and bCV (3.3-4.4% and 6.0-6.3%, respectively) compared to both cCBF (10.5-11.7% and 20.6-22.2%, respectively) and unCBF (12.0-13.6% and 22.7-23.7%, respectively). wCV and bCV were lower for cCBF vs. unCBF. A significant difference between cCBF and unCBF was found in most regions (P = 5.5 × 10-5 -3.8 × 10-4 in gray matter) that was highly correlated with ATT (R2 = 0.79-0.86). A power analysis yielded acceptable power at feasible sample sizes using cCBF. ATT and ATT-corrected CBF were longitudinally stable, indicating that ATT and CBF changes can be reliably evaluated with Hadamard-encoded 3D pCASL with multiple PLDs. 1 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;51:1846-1853.

Optimizing MRF-ASL scan design for precise quantification of brain hemodynamics using neural network regression.

Arterial Spin Labeling (ASL) is a quantitative, non-invasive alternative for perfusion imaging that does not use contrast agents. The magnetic resonance fingerprinting (MRF) framework can be adapted to ASL to estimate multiple physiological parameters simultaneously. In this work, we introduce an optimization scheme to increase the sensitivity of the ASL fingerprint. We also propose a regression based estimation framework for MRF-ASL. To improve the sensitivity of MRF-ASL signals to underlying parameters, we optimized ASL labeling durations using the Cramer-Rao Lower Bound (CRLB). This paper also proposes a neural network regression based estimation framework trained using noisy synthetic signals generated from our ASL signal model. We tested our methods in silico and in vivo, and compared with multiple post labeling delay (multi-PLD) ASL and unoptimized MRF-ASL. We present comparisons of estimated maps for the six parameters of our signal model. The scan design process facilitated precise estimates of multiple hemodynamic parameters and tissue properties from a single scan, in regions of normal gray and white matter, as well as regions with anomalous perfusion activity in the brain. In particular, there was a 86.7% correlation of perfusion estimates with the ground truth in silico, using our proposed techniques. In vivo, there was roughly a 7 fold improvement in the Coefficient of Variation (CoV) for white matter perfusion, and 2 fold improvement in gray matter perfusion CoV in comparison to a reference Multi PLD method. The regression based estimation approach provided perfusion estimates rapidly, with estimation times of around 1s per map. Scan design optimization, coupled with regression-based estimation is a powerful tool for improving precision in MRF-ASL.

Quantification of ASL Perfusion MRI in MCI Patients Using Single-Post Labeling Delay Model-Fitting Approach

Purpose: Neuroimaging techniques hold many promises to detect Alzheimer Disease (AD) at early stages before clinical symptoms fully develop, suggesting decreased regional Cerebral Blood Flow (CBF). Perfusion deficiencies are present from very early clinical phases of AD, i.e. Mild Cognitive Impairment (MCI) and persist well into the latest stages, demonstrating a pattern of increased hypo-perfusion with the disease development. Accurate quantification such as quantification model and noise reduction method is necessary to achievement of good results in insufficient Post Labeling Delay (PLD) time. Materials and Methods: Arterial Spin Labeling (ASL) is a non-invasive MRI technique to extract brain regional CBF, which in recent years gained wide acceptance for its value in clinical and neuroscience applications. In the present work, 44 participants in 2 groups were imaged (normal control and MCI) using single-Post Label Delay (single-PLD) model-fitting ASL Perfusion at 1.5T. Images were de-noised with Independent Component Analysis (ICA) algorithm and then preprocessing such as motion correction, distortion correction, normalization, and tissue segmentation analyzed with SPM12. Calibration image that needed to calculate absolute perfusion was estimated from the data by fitting a curve to the control images in the dataset. Absolute CBF values were finally extracted from the kinetic model quantification. Results: Perfusion decreases in the right precuneus (28%), right inferior partial cortex (22%) and right middle frontal cortex (20%) cortex in MCI subjects. Conclusion: According to the results, ASL-MRI is able to calculate perfusion changes associated with MCI.

Application of Postlabeling Delay Time in 3-Dimensional Pseudocontinuous Arterial Spin-Labeled Perfusion Imaging in Normal Children.

To explore the application value of postlabeling delay (PLD) in 3D pseudocontinuous arterial spin-labeled (3D-pcASL) perfusion imaging in normal children and to find the optimal PLD values for children at each age group. Five groups of children, with 50 patients in each group, who underwent routine magnetic resonance imaging scans with normal results were included. The patients were stratified according to the following ages: younger than 1 month, more than 1 month to 6 months, more than 6 months to 12 months, more than 1 year to 3 years, more than 3 years to 6 years, and more than 6 years to 18 years. All patients received 3D-pcASL perfusion magnetic resonance scanning. The PLD values were set to 1025, 1525, or 2025 milliseconds. In subjective evaluations, the signal-to-noise ratio (SNR) and cerebral blood flow (CBF) of 3D-pcASL perfusion images under different PLD values were compared and analyzed. For patients in the <1-month group and >1-month to 6-month group, the images were mainly grade A when the PLD value was 1025 milliseconds, which equaled 43 and 46 cases, respectively. The brain CBF values and SNR values were higher than those of the images with PLD values of 1525 and 2025 milliseconds. For patients in the >6-month to 12-month group, >1-year to 3-year group, >3-year to 6-year group, and >6-year to 18-year group, the images were mainly grade A when the PLD value was 1525 milliseconds, which equaled 43, 45, 43, and 46 cases, respectively. The brain CBF values and SNR values were higher than those of the images with PLD values of 1025 and 2025 milliseconds. The optimal PLD values for 3D-pcASL perfusion imaging are different in children of different ages. The optimal PLD value for infants who are 6 months younger is 1025 milliseconds. The optimal PLD value for children older than 6 months to 18 years is 1525 milliseconds.

Application of a 3D pseudocontinuous arterial spin-labeled perfusion MRI scan combined with a postlabeling delay value in the diagnosis of neonatal hypoxic-ischemic encephalopathy.

BackgroundCurrently, there are many studies on the application of the 3D pseudocontinuous arterial spin-labeled (3D-pcASL) perfusion MRI technique for adult brain examinations, but few studies exist on the application of the technique for child brain examinations.PurposeTo explore the application of a 3D-pcASL perfusion MRI scan combined with postlabeling delay (PLD) for assessing neonatal hypoxic-ischemic encephalopathy (HIE).Materials and methodsTwo-hundred neonates diagnosed with neonatal HIE were equally divided into five groups (40/group): 0- to <24-hour-old HIE group, 1- to <3-day-old HIE group, 3- to <7-day-old HIE group, 7- to <15-day-old HIE group and 15- to 28-day-old HIE group; 200 healthy neonates were equivalently divided. All 10 groups received a conventional and a 3D-pcASL perfusion MRI scan. For groups <3 days old, PLD values for the 3D-pcASL cerebral perfusion MRI scan were preset at 1025 ms; in all other groups, PLD values were preset at 1525 ms. CBF values for the 3D-pcASL cerebral perfusion MRI were compared between the HIE and corresponding control groups to determine the distinguishing characteristics of CBF values in HIE neonates.ResultsOn the 3D-pcASL cerebral perfusion MRI scan, in the 1- to <3-day-old groups, HIE neonate CBF values were higher than those of controls in all brain regions (excluding the frontal lobe); in the 0- to <24-hour-old and 3- to <7-day-old groups, HIE neonate CBF values were lower than those of corresponding controls in all brain regions; in the 7- to <15-day-old and 15- to 28-day-old groups, there were no significant differences in the CBF values between groups in any brain regions.ConclusionsThe 3D-pcASL perfusion MRI scan combined with a PLD can assist in the early diagnosis of neonatal HIE, as this method more comprehensively reflects the HIE pathological process.

ICA-based denoising for ASL perfusion imaging

Arterial Spin Labelling (ASL) imaging derives a perfusion image by tracing the accumulation of magnetically labeled blood water in the brain. As the image generated has an intrinsically low signal to noise ratio (SNR), multiple measurements are routinely acquired and averaged, at a penalty of increased scan duration and opportunity for motion artefact. However, this strategy alone might be ineffective in clinical settings where the time available for acquisition is limited and patient motion are increased. This study investigates the use of an Independent Component Analysis (ICA) approach for denoising ASL data, and its potential for automation.72 ASL datasets (pseudo-continuous ASL; 5 different post-labeling delays: 400, 800, 1200, 1600, 2000 m s; total volumes = 60) were collected from thirty consecutive acute stroke patients. The effects of ICA-based denoising (manual and automated) where compared to two different denoising approaches, aCompCor, a Principal Component-based method, and Enhancement of Automated Blood Flow Estimates (ENABLE), an algorithm based on the removal of corrupted volumes. Multiple metrics were used to assess the changes in the quality of the data following denoising, including changes in cerebral blood flow (CBF) and arterial transit time (ATT), SNR, and repeatability. Additionally, the relationship between SNR and number of repetitions acquired was estimated before and after denoising the data.The use of an ICA-based denoising approach resulted in significantly higher mean CBF and ATT values (p < 0.001), lower CBF and ATT variance (p < 0.001), increased SNR (p < 0.001), and improved repeatability (p < 0.05) when compared to the raw data. The performance of manual and automated ICA-based denoising was comparable. These results went beyond the effects of aCompCor or ENABLE. Following ICA-based denoising, the SNR was higher using only 50% of the ASL-dataset collected than when using the whole raw data.The results show that ICA can be used to separate signal from noise in ASL data, improving the quality of the data collected. In fact, this study suggests that the acquisition time could be reduced by 50% without penalty to data quality, something that merits further study. Independent component classification and regression can be carried out either manually, following simple criteria, or automatically.