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Background: Arterial spin labeling (ASL) based-noncontrast-enhanced 4D MR angiography (NCE 4D MRA) shows potential in characterizing cerebrovascular hemodynamics in cerebrovascular disorders. Ultrahigh-field theoretically benefits ASL signal with increased inherent signal-to-noise ratio (SNR) and prolonged blood T 1 , which may provide improved delineation of vasculature in 4D MRA., Purpose: To investigate the feasibility of NCE 4D MRA using 3D Cartesian trajectory and stack-of-stars (SOS) golden angle radial trajectory at 7T., Study Type: A prospective study., Subjects: Six normal volunteers and eight patients with arteriovenous malformation (AVM)., Field Strength/sequence: NCE 4D MRA with Cartesian and radial trajectories were performed at 3T and 7T., Assessment: Subjective image quality of 4D MRA was evaluated using a 4-point scale by two experienced neuroradiologists. The characterization of AVM components with 4D MRA and DSA was also graded using the Spetzler-Martin grading scale., Statistical Tests: Cohen's kappa coefficient was calculated to evaluate the agreement between two readers within each 4D MRA technique (Cartesian and Radial). A Wilcoxon signed-rank test was performed to compare the subjective image quality scores of 4D MRA between Cartesian and radial trajectories, and between 7T and 3T, respectively., Results: Good-to-excellent image quality was achieved in 4D MRA with both Cartesian (3.83 ± 0.41) and radial (3.42 ± 0.49) acquisitions in healthy volunteers at 7T. However, markedly reduced scan time was needed with radial acquisition. 4D MRA at 7T (3.31 ± 0.59) shows better delineation of AVM lesion features, especially the vein drainage, compared with that of 3T (2.83 ± 0.75), although no statistical significance was achieved (P = 0.180)., Data Conclusion: The feasibility of ASL based 4D MRA at 7T with Cartesian and SOS golden angle radial acquisition was demonstrated. The clinical evaluation of 4D MRA in AVMs between 3T and 7T suggested 7T 4D MRA images acquired with radial acquisition demonstrate excellent delineation of AVM features, especially the draining veins., Level of Evidence: 2 Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2017., (© 2017 International Society for Magnetic Resonance in Medicine.)

Purpose: To investigate whether arterial spin labeling (ASL) MRI could detect renal hemodynamic impairment in diabetes mellitus (DM) along different stages of chronic kidney disease (CKD)., Materials and Methods: Three Tesla (3T) ASL-MRI was performed to evaluate renal blood flow (RBF) in 91 subjects (46 healthy volunteers and 45 type 2 diabetic patients). Patients were classified according to their estimated glomerular filtration rate (eGFR) as group I (eGFR > 60 mL/min/1.73 m 2 ), group II (60 ≥ eGFR>30 mL/min/1.73 m 2 ), or group III (eGFR ≤ 30 mL/min/1.73 m 2 ), to determine differences depending on renal function. Studies were performed at 3T using a 12-channel flexible body array combined with the spine array coil as receiver., Results: A 28% reduction in cortical RBF was seen in diabetics in comparison with healthy controls (185.79 [54.60] versus 258.83 [37.96] mL/min/100 g, P < 3 × 10 -6 ). Differences were also seen between controls and diabetic patients despite normal eGFR and absence of overt albuminuria (RBF [mL/min/100 g]: controls=258.83 [37.96], group I=208.89 [58.83], P = 0.0018; eGFR [mL/min/1.73 m 2 ]: controls = 95.50 [12.60], group I = 82.00 [20.76], P > 0.05; albumin-creatinine ratio [mg/g]: controls = 3.50 [4.45], group I = 17.50 [21.20], P > 0.05). A marked decrease in RBF was noted a long with progression of diabetic nephropathy (DN) through the five stages of CKD (χ 2  = 43.58; P = 1.85 × 10 -9 ). Strong correlation (r = 0.62; P = 4 × 10 -10 ) was obtained between RBF and GFR estimated by cystatin C., Conclusion: ASL-MRI is able to quantify early renal perfusion impairment in DM, as well as changes according to different CKD stages of DN. In addition, we demonstrated a correlation of RBF quantified by ASL and GFR estimated by cystatin C., Level of Evidence: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017;46:1810-1817., (© 2017 International Society for Magnetic Resonance in Medicine.)

Purpose: 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., Materials and Methods: 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., Results: 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)., Conclusion: 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., (© 2015 Wiley Periodicals, Inc.)

Purpose: To investigate the hemodynamic changes of normal-appearing white matter (NAWM) in hypertension using the 3D pseudocontinuous arterial spin labeling (pCASL) technique., Materials and Methods: Seventy-three subjects, including a patient group (n = 41; 30 males; age = 47.7 ± 8.3 years; test-time blood pressure [BP] = 155 ± 23/98 ± 11 mmHg) and an age-matched control group (n = 32; 14 males; age = 46 ± 8.3 years; test-time BP = 117 ± 8/76 ± 10 mmHg), were recruited and scanned on a 3.0T magnetic resonance imaging (MRI) system using routine MRI sequences and 3D pCASL sequence. The routine MRI sequences were used to further define the NAWM. The cerebral blood flow (CBF) values in various regions of interest (ROIs) were extracted. One-way analysis of variance (ANOVA) and unpaired t-test were performed to evaluate the significance of the intergroup difference in CBF modifications., Results: Compared to healthy volunteers, CBF values in global gray matter (GM) and various NAWM regions were found to be lower (P < 0.05) in hypertensive patients, except for genu of corpus callosum (CC), cingulate gyrus, amygdala, pallidum, putamen, and thalamus (P > 0.05). Furthermore, compared to the control group, mild hypertension showed significantly reduced CBF in various ROIs (P < 0.05), but no intergroup differences in GM, R anterior horn of periventricular WM, and genu of CC (P > 0.05), while moderate hypertension showed reduced CBF in all ROIs (P < 0.05). However, it was observed that, between mild and moderate hypertensive patients, there were no statistically significant difference in CBF values except for genu of CC (P < 0.05)., Conclusion: 3D pCASL has the ability to detect subtle hemodynamic abnormalities in NAWM regions at relatively early stages of hypertension. The observed decreases in CBF in these regions may suggest an increased risk of cerebral small vessel diseases., (© 2015 Wiley Periodicals, Inc.)

Purpose: To investigate the reliability and accuracy of two pseudo-continuous arterial spin labeling (pCASL) sequences, using two-dimensional (2D) gradient-echo echo planar imaging (EPI) and 3D gradient and spin echo (GRASE) as the readout, respectively., Materials and Methods: Each sequence was performed twice 4 weeks apart on six normal control subjects, six elderly subjects with mild cognitive impairment (MCI), and one participant with Alzheimer's disease (AD). Eight of these subjects also underwent H2 (15) O positron emission tomography (PET) scans on the same day or proximal to their second MRI scan. The longitudinal repeatability of EPI and GRASE pCASL were evaluated with the intraclass correlation coefficient (ICC) and within-subject coefficient of variation (wsCV)., Results: The ICCs of global perfusion measurements were 0.697 and 0.413 for GRASE and EPI based pCASL respectively. GRASE pCASL also demonstrated a higher longitudinal repeatability for regional perfusion measurements across 24 regions-of-interests (ICC = 0.707; wsCV = 10.9%) compared with EPI pCASL (ICC = 0.362; wsCV = 15.3%). When compared with PET, EPI pCASL showed a higher degree of spatial correlation with PET than GRASE pCASL, although the difference was not statistically significant., Conclusion: The 3D GRASE pCASL offers better repeatability than 2D EPI pCASL, thereby may provide a reliable imaging marker for the evaluation of disease progression and treatment effects in MCI and early AD subjects., (Copyright © 2013 Wiley Periodicals, Inc.)

Purpose: To explore the use of approximate entropy (ApEn) as an index of the complexity and the synchronicity of resting state blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in normal aging and cognitive decline associated with familial Alzheimer's disease (fAD)., Materials and Methods: Resting state BOLD fMRI data were acquired at 3T from two independent cohorts of subjects consisting of healthy young (age 23 ± 2 years, n = 8) and aged volunteers (age 66 ± 3 years, n = 8), as well as 22 fAD associated subjects (14 mutation carriers, age 41.2 ± 15.8 years; and eight nonmutation carrying family members, age 28.8 ± 5.9 years). Mean ApEn values were compared between the two age groups and correlated with cognitive performance in the fAD group. Cross-ApEn (C-ApEn) was further calculated to assess the asynchrony between precuneus and the rest of the brain., Results: Complexity of brain activity measured by mean ApEn in gray and white matter decreased with normal aging. In the fAD group, cognitive impairment was associated with decreased mean ApEn in gray matter as well as decreased regional ApEn in right precuneus, right lateral parietal regions, left precentral gyrus, and right paracentral gyrus. A pattern of asynchrony between BOLD fMRI series emerged from C-ApEn analysis, with significant regional anti-correlation with cross-correlation coefficient of functional connectivity analysis., Conclusion: ApEn and C-ApEn may be useful for assessing the complexity and synchronicity of brain activity in normal aging and cognitive decline associated with neurodegenerative diseases., (Copyright © 2012 Wiley Periodicals, Inc.)

Purpose: To compare the performance of pulsed and pseudocontinuous arterial spin-labeling (PASL and pCASL) methods in measuring CO(2) -induced cerebrovascular reactivity (CVR)., Materials and Methods: Subjects were scanned using both ASL sequences during a controlled hypercapnia procedure and visual stimulation. CVR was computed as the percent CO(2) -induced increase in cerebral blood flow (Δ%CBF) per mmHg increase in end-tidal PCO(2) . Visually evoked responses were expressed as Δ%CBF. Resting CBF and temporal signal-to-noise ratio were also computed. Regionally averaged values for the different quantities were compared in gray matter (GM) and visual cortex (VC) using t-tests., Results: Both PASL and pCASL yielded comparable respective values for resting CBF (56 ± 3 and 56 ± 4 mL/min/100g) and visually evoked responses (75 ± 5% and 81 ± 4%). Values of CVR determined using pCASL (GM 4.4 ± 0.2, VC 8 ± 1 Δ%CBF/mmHg), however, were significantly higher than those measured using PASL (GM 3.0 ± 0.6, VC 5 ± 1 Δ%CBF/mmHg) in both GM and VC. The percentage of GM voxels in which statistically significant hypercapnia responses were detected was also higher for pCASL (27 ± 5% vs. 16 ± 3% for PASL)., Conclusion: pCASL may be less prone to underestimation of CO(2) -induced flow changes due to improved label timing control., (Copyright © 2012 Wiley Periodicals, Inc.)

Perfusion provides oxygen and nutrients to tissues and is closely tied to tissue function while disorders of perfusion are major sources of medical morbidity and mortality. It has been almost two decades since the use of arterial spin labeling (ASL) for noninvasive perfusion imaging was first reported. While initial ASL magnetic resonance imaging (MRI) studies focused primarily on technological development and validation, a number of robust ASL implementations have emerged, and ASL MRI is now also available commercially on several platforms. As a result, basic science and clinical applications of ASL MRI have begun to proliferate. Although ASL MRI can be carried out in any organ, most studies to date have focused on the brain. This review covers selected research and clinical applications of ASL MRI in the brain to illustrate its potential in both neuroscience research and clinical care., (Copyright © 2012 Wiley Periodicals, Inc.)

Purpose: To compare the test-retest reproducibility of three variants of arterial spin labeling (ASL): pseudo-continuous (pCASL), pulsed (PASL) and continuous (CASL)., Materials and Methods: Twelve healthy subjects were scanned on a 3.0T scanner with PASL, CASL, and pCASL. Scans were repeated within-session, after 1 hour, and after 1 week to assess reproducibility at different scan intervals., Results: Comparison of within-subject coefficients of variation (wsCV) demonstrated high within-session reproducibility (ie, low wsCV) for CASL-based methods (gray matter [GM] wsCV for pCASL: 3.5% ± 0.02%, CASL: 4.1% ± 0.07%) compared to PASL (wsCV: 7.5% ± 0.06%), due to the higher signal-to-noise ratio (SNR) associated with continuous labeling, evident in the 20% gain in temporal SNR and 58% gain in raw SNR for pCASL relative to PASL. At the 1-week scan interval, comparable reproducibility between PASL (GM wsCV 9.2% ± 0.12%) and pCASL (GM wsCV 8.5% ± 0.14%) was observed, indicating the dominance of physiological fluctuations., Conclusion: Although all three approaches are capable of measuring cerebral blood flow within a few minutes of scanning, the high precision and SNR of pCASL, with its insensitivity to vessel geometry, make it an appealing method for future ASL application studies., (Copyright © 2011 Wiley-Liss, Inc.)