Publications by authors named "Zungho Zun"

19 Publications

  • Page 1 of 1

Hyperpolarized C MR Spectroscopy Depicts in Vivo Effect of Exercise on Pyruvate Metabolism in Human Skeletal Muscle.

Radiology 2021 Jun 22:204500. Epub 2021 Jun 22.

From the Advanced Imaging Research Center (J.M.P., C.E.H., J.M., J.C., J.R., J.L., G.D.R., A.C., C.R.M.), Department of Radiology (J.M.P., A.C., C.R.M.), Department of Neurology and Neurotherapeutics (R.G.H.), and Department of Internal Medicine (C.R.M.), University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8568; Department of Electrical and Computer Engineering, University of Texas at Dallas, Dallas, Tex (J.M.P.); Department of Diagnostic Imaging and Radiology, Developing Brain Institute, Children's National Hospital, Washington, DC (Z.Z.); Department of Pediatrics and Radiology, George Washington University, Washington, DC (Z.Z.); GE Healthcare, Dallas, Tex (G.D.R.); Department of Biochemistry and Molecular Medicine, University of California, Davis, Davis, Calif (T.J.); and Veterans Affairs North Texas Healthcare System, Dallas, Tex (C.R.M.).

Background Pyruvate dehydrogenase (PDH) and lactate dehydrogenase are essential for adenosine triphosphate production in skeletal muscle. At the onset of exercise, oxidation of glucose and glycogen is quickly enabled by dephosphorylation of PDH. However, direct measurement of PDH flux in exercising human muscle is daunting, and the net effect of covalent modification and other control mechanisms on PDH flux has not been assessed. Purpose To demonstrate the feasibility of assessing PDH activation and changes in pyruvate metabolism in human skeletal muscle after the onset of exercise using carbon 13 (C) MRI with hyperpolarized (HP) [1-C]-pyruvate. Materials and Methods For this prospective study, sedentary adults in good general health (mean age, 42 years ± 18 [standard deviation]; six men) were recruited from August 2019 to September 2020. Subgroups of the participants were injected with HP [1-C]-pyruvate at resting, during plantar flexion exercise, or 5 minutes after exercise during recovery. In parallel, hydrogen 1 arterial spin labeling MRI was performed to estimate muscle tissue perfusion. An unpaired test was used for comparing C data among the states. Results At rest, HP [1-C]-lactate and [1-C]-alanine were detected in calf muscle, but [C]-bicarbonate was negligible. During moderate flexion-extension exercise, total HP C signals (tC) increased 2.8-fold because of increased muscle perfusion ( = .005), and HP [1-C]-lactate-to-tC ratio increased 1.7-fold ( = .04). HP [C]-bicarbonate-to-tC ratio increased 8.4-fold ( = .002) and returned to the resting level 5 minutes after exercise, whereas the lactate-to-tC ratio continued to increase to 2.3-fold as compared with resting ( = .008). Conclusion Lactate and bicarbonate production from hyperpolarized (HP) [1-carbon 13 {C}]-pyruvate in skeletal muscle rapidly reflected the onset and the termination of exercise. These results demonstrate the feasibility of imaging skeletal muscle metabolism using HP [1-C]-pyruvate MRI and the sensitivity of in vivo pyruvate metabolism to exercise states. © RSNA, 2021
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1148/radiol.2021204500DOI Listing
June 2021

Longitudinal Trajectories of Regional Cerebral Blood Flow in Very Preterm Infants during Third Trimester Ex Utero Development Assessed with MRI.

Radiology 2021 06 30;299(3):691-702. Epub 2021 Mar 30.

From the Division of Diagnostic Imaging and Radiology, Children's National Hospital, 111 Michigan Ave NW, Washington, DC 20010 (Z.Z., K.K., N.A., J.M., C.L.); Division of Fetal and Transitional Medicine, Children's National Hospital, Washington, DC (Z.Z., A.d.P., C.L.); Departments of Pediatrics (Z.Z., M.J., S.B., M.S., J.M., T.C., A.d.P., C.L.) and Radiology (Z.Z., J.M., C.L.) and Divisions of Neonatology (S.B., M.S.) and Neurology (T.C.), Children's National Hospital, George Washington University School of Medicine and Health Sciences, Washington, DC; Division of Biostatistics and Study Methodology, Children's National Research Institute, Washington, DC (M.J.).

Background The third trimester of gestation is a crucial phase of rapid brain development, but little has been reported on the trajectories of cerebral blood flow (CBF) in preterm infants in this period. Purpose To quantify regional CBF in very preterm infants longitudinally across the ex utero third trimester and to determine its relationship with clinical factors associated with brain injury and premature birth. Materials and Methods In this prospective study, very preterm infants were enrolled for three longitudinal MRI scans, and 22 healthy full-term infants were enrolled for one term MRI scan between November 2016 and February 2019. Global and regional CBF in the cortical gray matter, white matter, deep gray matter, and cerebellum were measured using arterial spin labeling with postlabeling delay of 2025 msec at 1.5 T and 3.0 T. Brain injury and clinical risk factors in preterm infants were investigated to determine associations with CBF. Generalized estimating equations were used to account for correlations between repeated measures in the same individual. Results A total of 75 preterm infants (mean postmenstrual age [PMA]: 29.5 weeks ± 2.3 [standard deviation], 34.9 weeks ± 0.8, and 39.3 weeks ± 2.0 for each scan; 43 male infants) and 22 full-term infants (mean PMA, 42.1 weeks ± 2.0; 13 male infants) were evaluated. In preterm infants, global CBF was 11.9 mL/100 g/min ± 0.2 (standard error). All regional CBF increased significantly with advancing PMA ( ≤ .02); the cerebellum demonstrated the most rapid CBF increase and the highest mean CBF. Lower CBF was associated with intraventricular hemorrhage in all regions ( ≤ .05) and with medically managed patent ductus arteriosus in the white matter and deep gray matter ( = .03). Mean CBF of preterm infants at term-equivalent age was significantly higher compared with full-term infants ( ≤ .02). Conclusion Regional cerebral blood flow increased significantly in preterm infants developing in an extrauterine environment across the third trimester and was associated with intraventricular hemorrhage and patent ductus arteriosus. © RSNA, 2021 .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1148/radiol.2021202423DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8165945PMC
June 2021

Feasibility of QSM in the human placenta.

Magn Reson Med 2021 03 16;85(3):1272-1281. Epub 2020 Sep 16.

Developing Brain Institute, Division of Diagnostic Imaging and Radiology, Children's National Hospital, Washington, DC, USA.

Purpose: Quantitative susceptibility mapping (QSM) is an emerging tool for the precise characterization of human tissue, including regional oxygenation. A critical function of the human placenta is oxygen transfer to the developing fetus, which remains difficult to study in utero. The purpose of this study is to investigate the feasibility of performing QSM in the human placenta in utero.

Methods: In healthy pregnant women, 3D gradient echo data of the placenta were acquired with prospective respiratory gating at 1.5 Tesla and 3 Tesla. A brief period (6-7 min) of maternal hyperoxia was induced to increase placental oxygenation in a subset of women scanned at 3 Tesla, and data were acquired before and during oxygen administration. Susceptibility and / maps were reconstructed from gradient echo data, and mean and SD of these measures within the whole placenta were calculated.

Results: A total of 54 women were studied at a mean gestational age of 30.7 ± 4.2 (range: 24 5/7-38 4/7) weeks. Susceptibility and maps demonstrated lobular contrast reflecting regional oxygenation difference at both field strengths. SD of susceptibilities, mean , and SD of of the placenta showed a linear relationship with gestational age (P < .01 for all). These measures were also responsive to maternal hyperoxia, and there was an increasing response with advancing gestational age (P < .01 for all).

Conclusion: This study demonstrates the feasibility of performing placental QSM in pregnant women and supports the potential for placental QSM to provide noninvasive in vivo assessment of placental oxygenation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mrm.28502DOI Listing
March 2021

Placental perfusion imaging using velocity-selective arterial spin labeling.

Magn Reson Med 2018 09 13;80(3):1036-1047. Epub 2018 Feb 13.

Division of Diagnostic Imaging and Radiology, Children's National Medical Center, Washington, DC.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mrm.27100DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5980687PMC
September 2018

Non-Invasive Placental Perfusion Imaging in Pregnancies Complicated by Fetal Heart Disease Using Velocity-Selective Arterial Spin Labeled MRI.

Sci Rep 2017 11 23;7(1):16126. Epub 2017 Nov 23.

Division of Diagnostic Imaging and Radiology, Children's National Medical Center, Washington, DC, United States.

The placenta is a vital organ for fetal growth and development during pregnancy. Congenital heart disease (CHD) is a leading cause of morbidity and mortality in newborns. Despite the parallel development of the placenta and fetal heart early in pregnancy, very few studies suggested an association between placental dysfunction and fetal CHD. In this study, we report placental perfusion of healthy pregnancies and pregnancies complicated by fetal CHD measured using advanced fetal MRI techniques. We studied forty-eight pregnant women (31 healthy volunteers and 17 with fetal CHD) that underwent fetal MRI during their second or third trimester of pregnancy. Placental perfusion imaging was performed using velocity-selective arterial spin labeling (VSASL) and 3D image acquisition with whole-placenta coverage. In pregnancies with fetal CHD, global placental perfusion significantly decreased and regional variation of placental perfusion significantly increased with advancing gestational age; however, no such correlation was found in healthy pregnancies. Also, global placental perfusion was significantly higher in fetal CHD versus controls, in the lateral side-lying patient position versus supine, and in the posterior placental position versus anterior placental position. This study reports for the first time non-invasive whole-placenta perfusion imaging in utero. These data suggest that placental VSASL may serve as a potential biomarker of placental dysfunction in fetuses diagnosed with CHD.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-017-16461-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5700998PMC
November 2017

Semi-automatic segmentation of the placenta into fetal and maternal compartments using intravoxel incoherent motion MRI.

Proc SPIE Int Soc Opt Eng 2017 Mar;10137

Dept. of Diagnostic Imaging and Radiology, Children's National Medical Center, Washington, DC, USA.

Intravoxel incoherent motion (IVIM) magnetic resonance imaging is an emerging non-invasive technique that has been recently applied to quantify in vivo global placental perfusion. We propose a robust semi-automated method for segmenting the placenta into fetal and maternal compartments from IVIM data, using a multi-label image segmentation algorithm called ''. Placental IVIM data were acquired on a 1.5T scanner from 16 healthy pregnant women between 21-37 gestational weeks. The voxel-wise perfusion fraction was then estimated after non-rigid image registration. The seed regions of the fetal and maternal compartments were determined using structural T2-weighted reference images, and improved progressively through an iterative process of the GrowCut algorithm to accurately encompass fetal and maternal compartments. We demonstrated that the placental perfusion fraction decreased in both fetal (-0.010/week) and maternal compartments (-0.013/week) while their relative difference (f-f) gradually increased with advancing gestational age (+0.003/week, p=0.065). Our preliminary results show that the proposed method was effective in distinguishing placental compartments using IVIM.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1117/12.2254610DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5609721PMC
March 2017

Composite iron oxide-Prussian blue nanoparticles for magnetically guided T-weighted magnetic resonance imaging and photothermal therapy of tumors.

Int J Nanomedicine 2017 5;12:6413-6424. Epub 2017 Sep 5.

The Sheikh Zayed Institute for Pediatric Surgical Innovation, Children's National Health System, Washington, DC, USA.

Theranostic nanoparticles offer the potential for mixing and matching disparate diagnostic and therapeutic functionalities within a single nanoparticle for the personalized treatment of diseases. In this article, we present composite iron oxide-gadolinium-containing Prussian blue nanoparticles ([email protected]) as a novel theranostic agent for T-weighted magnetic resonance imaging (MRI) and photothermal therapy (PTT) of tumors. These particles combine the well-described properties and safety profiles of the constituent FeO nanoparticles and gadolinium-containing Prussian blue nanoparticles. The [email protected] nanoparticles function both as effective MRI contrast agents and PTT agents as determined by characterizing studies performed in vitro and retain their properties in the presence of cells. Importantly, the [email protected] nanoparticles function as effective MRI contrast agents in vivo by increasing signal:noise ratios in T-weighted scans of tumors and as effective PTT agents in vivo by decreasing tumor growth rates and increasing survival in an animal model of neuroblastoma. These findings demonstrate the potential of the [email protected] nanoparticles to function as effective theranostic agents.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.2147/IJN.S144515DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5592912PMC
March 2018

Comparing accuracy and reproducibility of sequential and Hadamard-encoded multidelay pseudocontinuous arterial spin labeling for measuring cerebral blood flow and arterial transit time in healthy subjects: A simulation and in vivo study.

J Magn Reson Imaging 2018 04 9;47(4):1119-1132. Epub 2017 Aug 9.

Department of Radiology, Stanford University, Stanford, California, USA.

Purpose: To compare performance of sequential and Hadamard-encoded pseudocontinuous arterial spin labeling (PCASL).

Materials And Methods: Monte Carlo simulations and in vivo experiments were performed in 10 healthy subjects. Field strength and sequence: 5-delay sequential (5-del. Seq.), 7-delay Hadamard-encoded (7-del. Had.), and a single-delay (1-del.) PCASL, without and with vascular crushing at 3.0T. The errors and variations of cerebral blood flow (CBF) and arterial transit time (ATT) from simulations and the CBF and ATT estimates and variations in gray matter (GM) with different ATT ranges were compared. Pairwise t-tests with Bonferroni correction were used.

Results: The simulations and in vivo experiments showed that 1-del. PCASL underestimated GM CBF due to insufficient postlabeling delay (PLD) (37.2 ± 8.1 vs. 47.3 ± 8.5 and 47.3 ± 9.0 ml/100g/min, P ≤ 6.5 × 10 ), while 5-del. Seq. and 7-del. Had. yielded comparable GM CBF (P ≥ 0.49). 5-del. Seq. was more reproducible for CBF (P = 4.7 × 10 ), while 7-del. Had. was more reproducible for ATT (P = 0.033). 5-del. Seq. was more prone to intravascular artifacts and yielded lower GM ATTs compared to 7-del. Had. without crushing (1.13 ± 0.18 vs. 1.23 ± 0.13 seconds, P = 2.3 × 10 ), but they gave comparable ATTs with crushing (P = 0.12). ATTs measured with crushing were longer than those without crushing (P ≤ 6.7 × 10 ), but CBF was not affected (P ≥ 0.16).

Conclusion: The theoretical signal-to-noise ratio (SNR) gain through Hadamard encoding was confirmed experimentally. For 1-del., a PLD of 1.8 seconds is recommended for healthy subjects. With current parameters, 5-del. Seq. was more reproducible for CBF, and 7-del. Had. for ATT. Vascular crushing may help reduce variations in multidelay experiments without compromising tissue CBF or ATT measurements.

Level Of Evidence: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1119-1132.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jmri.25834DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5807238PMC
April 2018

Cerebral blood flow, transit time, and apparent diffusion coefficient in moyamoya disease before and after acetazolamide.

Neuroradiology 2017 Jan 2;59(1):5-12. Epub 2016 Dec 2.

Stanford University Medical Center, Department of Radiology, Neuroradiology Division, Lucas Center, 1201 Welch Rd, Stanford, CA, 94305, USA.

Introduction: The goal of this study was to assess the changes in arterial spin labeling (ASL) cerebral blood flow (CBF) and arterial transit time (ATT), and in apparent diffusion coefficient (ADC), before and after an acetazolamide challenge in moyamoya patients, as function of arterial stenosis severity.

Methods: Pre-operative patients diagnosed with moyamoya disease who could undergo MRI at 3.0T were recruited for this study. A multi-delay pseudo-continuous ASL and a diffusion-weighted sequence were acquired before and 15 min after acetazolamide injection. The severity of anterior, middle, and posterior cerebral artery pathology was graded on time-of-flight MR angiographic images. CBF, ATT, and ADC were measured on standardized regions of interest as function of the vessel stenosis severity.

Results: Thirty patients were included. Fifty-four percent of all vessels were normal, 28% mildly/moderately stenosed, and 18% severely stenosed/occluded. Post-acetazolamide, a significantly larger CBF (ml/100 g/min) increase was observed in territories of normal (+19.6 ± 14.9) compared to mildly/moderately stenosed (+14.2 ± 27.2, p = 0.007), and severely stenosed/occluded arteries (+9.9 ± 24.2, p < 0.0001). ATT was longer in territories of vessel anomalies compared with normal regions at baseline. ATT decreases were observed in all territories post-acetazolamide. ADC did not decrease after acetazolamide in any regions, and no correlation was found between ADC changes and baseline ATT, change in ATT, or CVR.

Conclusion: The hemodynamic response in moyamoya disease, as measured with ASL CBF, is impaired mostly in territories with severe arterial stenosis/occlusion, while ATT was prolonged in all non-normal regions. No significant changes in ADC were observed after acetazolamide.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00234-016-1766-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8006793PMC
January 2017

Imaging of cerebrovascular reserve and oxygenation in Moyamoya disease.

J Cereb Blood Flow Metab 2017 Apr 1;37(4):1213-1222. Epub 2016 Jan 1.

1 Department of Radiology, Stanford University, Stanford, CA, USA.

This study aimed to determine whether measurements of cerebrovascular reserve and oxygenation, assessed with spin relaxation rate R2', yield similar information about pathology in pre-operative Moyamoya disease patients, and to assess whether R2' is a better measure of oxygenation than other proposed markers, such as R2* and R2. Twenty-five pre-operative Moyamoya disease patients were scanned at 3.0T with acetazolamide challenge. Cerebral blood flow mapping with multi-delay arterial spin labeling, and R2*, R2, and R2' mapping with Gradient-Echo Sampling of Free Induction Decay and Echo were performed. No baseline cerebral blood flow difference was found between angiographically abnormal and normal regions (49 ± 12 vs. 48 ± 11 mL/100 g/min, p = 0.44). However, baseline R2' differed between these regions (3.2 ± 0.7 vs. 2.9 ± 0.6 s, p < 0.001), indicating reduced oxygenation in abnormal regions. Cerebrovascular reserve was lower in angiographically abnormal regions (21 ± 38 vs. 41 ± 26%, p = 0.001). All regions showed trend toward significantly improved oxygenation post-acetazolamide. Regions with poorer cerebrovascular reserve had lower baseline oxygenation (Kendall's τ = -0.24, p = 0.003). A number of angiographically abnormal regions demonstrated preserved cerebrovascular reserve, likely due to the presence of collaterals. Finally, of the concurrently measured relaxation rates, R2' was superior for oxygenation assessment.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1177/0271678X16651088DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5453445PMC
April 2017

Robust preprocessing for stimulus-based functional MRI of the moving fetus.

J Med Imaging (Bellingham) 2016 Apr 5;3(2):026001. Epub 2016 Apr 5.

Children's National Medical Center, Department of Diagnostic Imaging and Radiology, 111 Michigan Avenue N.W., Washington, DC 20852, United States; George Washington University, School of Medicine and Health Sciences, Department of Radiology, 2300 Eye Street N.W., Washington, DC 20037, United States; Children's National Medical Center, Department of Fetal and Transitional Medicine, 111 Michigan Avenue N.W., Washington, DC 20852, United States; George Washington University, School of Medicine and Health Sciences, Department of Pediatrics, 2300 Eye Street N.W., Washington, DC 20037, United States.

Fetal motion manifests as signal degradation and image artifact in the acquired time series of blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) studies. We present a robust preprocessing pipeline to specifically address fetal and placental motion-induced artifacts in stimulus-based fMRI with slowly cycled block design in the living fetus. In the proposed pipeline, motion correction is optimized to the experimental paradigm, and it is performed separately in each phase as well as in each region of interest (ROI), recognizing that each phase and organ experiences different types of motion. To obtain the averaged BOLD signals for each ROI, both misaligned volumes and noisy voxels are automatically detected and excluded, and the missing data are then imputed by statistical estimation based on local polynomial smoothing. Our experimental results demonstrate that the proposed pipeline was effective in mitigating the motion-induced artifacts in stimulus-based fMRI data of the fetal brain and placenta.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1117/1.JMI.3.2.026001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4821892PMC
April 2016

Improved multislice perfusion imaging with velocity-selective arterial spin labeling.

J Magn Reson Imaging 2015 May 6;41(5):1422-31. Epub 2014 May 6.

Department of Radiology, School of Medicine, Stanford University, Stanford, California, USA.

Purpose: To improve the multislice performance of velocity-selective arterial spin labeling (VS-ASL) imaging for cerebral blood flow (CBF) measurement such that it might be routinely applied for clinical applications with whole brain coverage.

Materials And Methods: VS-ASL was performed with improvements such as timing optimization, stimulated echo removal, and slice profile sharpening. Each improvement was evaluated in volunteers by measuring temporal noise in the CBF measurement. VS-ASL with all these improvements was performed in 20 patients with Moyamoya disease some of whom also underwent xenon-enhanced CT (xeCT) imaging which was the reference standard for CBF measurement.

Results: Sequence timing optimization and inter-slice crosstalk reduction using stimulated echo removal and slice profile sharpening all contributed to reduction of temporal noise. VS-ASL imaging with all these improvements performed in Moyamoya disease patients showed significant reduction of temporal noise (P < 0.0001) and increased correlation coefficient with xeCT CBF imaging (from 0.07 to 0.62).

Conclusion: We demonstrated that timing optimization, stimulated echo removal, and slice profile improvement have a large effect on image quality and robustness of VS-ASL in clinical imaging applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jmri.24652DOI Listing
May 2015

Comparison of R2' measurement methods in the normal brain at 3 Tesla.

Magn Reson Med 2015 Mar 18;73(3):1228-36. Epub 2014 Apr 18.

Department of Radiology, Stanford University, Stanford, California, USA; Department of Electrical Engineering, Stanford University, Stanford, California, USA.

Purpose: R2', the reversible component of transverse relaxation, is an important susceptibility measurement for studies of brain physiology and pathologies. In existing literature, different R2' measurement methods are used with assumption of equivalency. This study explores the choice of measurement method in healthy, young subjects at 3T.

Methods: In this study, a modified gradient-echo sampling of free induction decay and echo (GESFIDE) sequence was used to compare four standard R2' measurement methods: asymmetric spin echo (ASE), standard GESFIDE, gradient echo sampling of the spin echo (GESSE), and separate R2 and R2* mapping.

Results: GESSE returned lower R2' measurements than other methods (P < 0.05). Intersubject mean R2' in gray matter was found to be 2.7 s(-1) using standard GESFIDE and GESSE, versus 3.4-3.8 s(-1) using other methods. In white matter, mean R2' from GESSE was 2.3 s(-1) while other methods produced 3.7-4.3 s(-1) . R2 correction was applied to partially reduce the discrepancies between the methods, but significant differences remained, likely due to violation of the fundamental assumption of a single-compartmental tissue model, and hence monoexponential decay.

Conclusion: R2' measurements are influenced significantly by the choice of method. Awareness of this issue is important when designing and interpreting studies that involve R2' measurements.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mrm.25232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4308575PMC
March 2015

Pseudocontinuous arterial spin labeling with prospective motion correction (PCASL-PROMO).

Magn Reson Med 2014 Oct 14;72(4):1049-56. Epub 2013 Nov 14.

Department of Radiology, Stanford University, Stanford, California, USA.

Purpose: Arterial spin labeling (ASL) perfusion imaging with a segmented three-dimensional (3D) readout is becoming increasing popular, yet conventional motion correction approaches cannot be applied in segmented imaging. The purpose of this study was to demonstrate the integration of 3D pseudocontinuous ASL (PCASL) and PROMO (PROspective MOtion correction) for cerebral blood flow measurements.

Methods: PROMO was integrated into 3D PCASL without increasing repetition time. PCASL was performed with and without PROMO in the absence of motion. The performance of PCASL-PROMO was then evaluated with controlled motions using separate scans with and without PROMO and also with random motion using an interleaved scan where every repetition time is repeated twice, once with and once without PROMO.

Results: The difference in the average ASL signal of the 3D volume between conventional and PROMO implementations was negligible (<0.2%). ASL image artifacts from both controlled and random motions were removed significantly with PROMO, showing improved correlation with reference images. Multiple combinations of data acquired using the interleaved scan revealed that PROMO with real-time motion updating alone reduces motion artifact significantly and that rescanning of corrupted segments is more critical in tagged images than control images.

Conclusion: This study demonstrates that PROMO is a successful approach to motion correction for PCASL cerebral blood flow imaging.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mrm.25024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4048655PMC
October 2014

Near-contiguous spin echo imaging using matched-phase RF and its application in velocity-selective arterial spin labeling.

Magn Reson Med 2014 Jun 15;71(6):2043-50. Epub 2013 Jul 15.

Department of Radiology, Stanford University, Stanford, California, USA.

Purpose: The minimum slice spacing in multislice imaging is limited by inter-slice crosstalk due to an imperfect slice profile. This study sought to minimize the slice spacing using matched-phase RF pulses and demonstrate its application in cerebral blood flow imaging using velocity-selective arterial spin labeling.

Methods: A spin-echo matched-phase 90°-180° RF pair was designed using Shinnar-Le Roux algorithm in order to improve the slice profile of longitudinal magnetization, which plays a more critical role in creating interslice crosstalk than transverse magnetization. Both transverse and longitudinal slice profiles were compared between matched-phase RF and sinc-based RF pulses in simulations and measurements. Velocity-selective arterial spin labeling was performed in normal volunteers using both RF pulses and standard deviation of cerebral blood flow time series was calculated to examine ASL signal stability.

Results: Using designed matched-phase RF, the longitudinal slice profile was sharpened without signal-to-noise ratio loss. In velocity-selective arterial spin labeling imaging, the temporal standard deviation of cerebral blood flow measurements was reduced from 48 mL/100 g/min to 32 mL/100 g/min by 33% using matched-phase RF pulses, and as a result, cerebral blood flow image quality improved.

Conclusion: This study reports that near-contiguous multislice imaging can be achieved using matched-phase RF pulses without compromising signal-to-noise ratio and signal stability.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mrm.24866DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4087163PMC
June 2014

CBF measurements using multidelay pseudocontinuous and velocity-selective arterial spin labeling in patients with long arterial transit delays: comparison with xenon CT CBF.

J Magn Reson Imaging 2012 Jul 22;36(1):110-9. Epub 2012 Feb 22.

Department of Radiology, Stanford University, Stanford, California, USA.

Purpose: To test the theory that velocity-selective arterial spin labeling (VSASL) is insensitive to transit delay.

Materials And Methods: Cerebral blood flow (CBF) was measured in ten Moyamoya disease patients using xenon computed tomography (xeCT) and magnetic resonance imaging (MRI), which included multiple pseudo-continuous ASL (pcASL) with different postlabel delays, VSASL, and dynamic susceptibility contrast (DSC) imaging. Correlation coefficient, root-mean-square difference, mean CBF error between ASL, and gold-standard xeCT CBF measurements as well the dependence of this error on transit delay (TD) as estimated by DSC time-to-peak of the residue function (Tmax) were determined.

Results: For pcASL with different postlabel delay time (PLD), CBF measurement with short PLD (1.5-2 sec) had the strongest correlations with xeCT; VSASL had a lower but still significant correlation with a mean coefficient of 0.55. We noted the theoretically predicted dependence of CBF error on Tmax and on PLD for pcASL; VSASL CBF measurements had the least dependence of the error on TD. We also noted effects suggesting that the location of the label decay (blood vs. tissue) impacted the measurement, which was worse for pcASL than for VSASL.

Conclusion: We conclude that VSASL is less sensitive to TD than conventional ASL techniques and holds promise for CBF measurements in cerebrovascular diseases with slow flow.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jmri.23613DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3368036PMC
July 2012

Arterial spin labeled CMR detects clinically relevant increase in myocardial blood flow with vasodilation.

JACC Cardiovasc Imaging 2011 Dec;4(12):1253-61

Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA.

Objectives: This study sought to determine whether arterial spin labeled (ASL) cardiac magnetic resonance (CMR) is capable of detecting clinically relevant increases in regional myocardial blood flow (MBF) with vasodilator stress testing in human myocardium.

Background: Measurements of regional myocardial perfusion at rest and during vasodilatation are used to determine perfusion reserve, which indicates the presence and distribution of myocardial ischemia. ASL CMR is a perfusion imaging technique that does not require any contrast agents, and is therefore safe for use in patients with end-stage renal disease, and capable of repeated or continuous measurement.

Methods: Myocardial ASL scans at rest and during adenosine infusion were incorporated into a routine CMR adenosine induced vasodilator stress protocol and was performed in 29 patients. Patients who were suspected of having ischemic heart disease based on first-pass imaging also underwent x-ray angiography. Myocardial ASL was performed using double-gated flow-sensitive alternating inversion recovery tagging and balanced steady-state free precession imaging at 3-T.

Results: Sixteen patients were found to be normal and 13 patients were found to have visible perfusion defect based on first-pass CMR using intravenous gadolinium chelate. In the normal subjects, there was a statistically significant difference between MBF measured by ASL during adenosine infusion (3.67 ± 1.36 ml/g/min), compared to at rest (0.97 ± 0.64 ml/g/min), with p < 0.0001. There was also a statistically significant difference in perfusion reserve (MBF(stress)/MBF(rest)) between normal myocardial segments (3.18 ± 1.54) and the most ischemic segments in the patients with coronary artery disease identified by x-ray angiography (1.44 ± 0.97), with p = 0.0011.

Conclusions: This study indicates that myocardial ASL is capable of detecting clinically relevant increases in MBF with vasodilatation and has the potential to identify myocardial ischemia.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jcmg.2011.06.023DOI Listing
December 2011

Design and use of variable flip angle schedules in transient balanced SSFP subtractive imaging.

Magn Reson Med 2010 Feb;63(2):537-42

Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089-2564, USA.

In subtractive imaging modalities, the differential longitudinal magnetization decays with time, necessitating signal-efficient scanning methods. Balanced steady-state free precession pulse sequences offer greater signal strength than conventional spoiled gradient echo sequences, even during the transient approach to steady state. Although traditional balanced steady-state free precession requires that each excitation pulse use the same flip angle, operating in the transient regimen permits the application of variable flip angle schedules that can be tailored to optimize certain signal characteristics. A computationally efficient technique is presented to generate variable flip angle schedules efficiently for any optimization metric. The validity of the technique is shown using two phantoms, and its potential is demonstrated in vivo with a variable angle schedule to increase the signal-to-noise ratio (SNR) in myocardial tissue. Using variable flip angles, the mean SNR improvement in subtractive imaging of myocardial tissue was 18.2% compared to conventional, constant flip angle, balanced steady-state free precession (P = 0.0078).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mrm.22255DOI Listing
February 2010

Assessment of myocardial blood flow (MBF) in humans using arterial spin labeling (ASL): feasibility and noise analysis.

Magn Reson Med 2009 Oct;62(4):975-83

Ming Hsieh Department of Electrical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California 90089-2564, USA.

Arterial spin labeling (ASL) is a powerful tool for the quantitative measurement of tissue blood flow, and has been extensively applied to the brain, lungs, and kidneys. ASL has been recently applied to myocardial blood flow (MBF) measurement in small animals; however, its use in humans is limited by inadequate signal-to-noise ratio (SNR) efficiency and timing restrictions related to cardiac motion. We present preliminary results demonstrating MBF measurement in humans, using cardiac-gated flow-sensitive alternating inversion recovery (FAIR) tagging and balanced steady-state free precession (SSFP) imaging at 3T, and present an analysis of thermal and physiological noise and their impact on MBF measurement error. Measured MBF values in healthy volunteers were 1.36 +/- 0.40 ml/ml/min at rest, matching the published literature based on quantitative (13)N-ammonia positron emission tomography (PET), and increased by 30% and 29% with passive leg elevation and isometric handgrip stress, respectively. With thermal noise alone, MBF can be quantified to within +/- 0.1 ml/ml/min with 85.5% confidence, for 3.09 cm(3) regions averaged over 6 breath-holds. This study demonstrates the feasibility of quantitative assessment of myocardial blood flow in humans using ASL, and identifies SNR improvement and the reduction of physiological noise as key areas for future development.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mrm.22088DOI Listing
October 2009
-->