Publications by authors named "Yiu-Cho Chung"

47 Publications

Evaluation of trigeminal nerve tractography using two-fold-accelerated simultaneous multi-slice readout-segmented echo planar diffusion tensor imaging.

Eur Radiol 2021 Feb 1;31(2):640-649. Epub 2020 Sep 1.

Department of Diagnostic Radiology, Singapore General Hospital, Outram Rd, Singapore, 169608, Singapore.

Objectives: Simultaneous multi-slice (SMS) imaging with short repetition time (TR) accelerates diffusion tensor imaging (DTI) acquisitions. However, its impact when combined with readout-segmented echo planar imaging (RESOLVE) on the cranial nerves given the challenging skull base/posterior fossa terrain is unexplored. We evaluated the reliability of trigeminal nerve DTI metrics using SMS with RESOLVE-DTI.

Methods: Eight healthy controls and six patients with unilateral trigeminal neuralgia (TN) underwent brain MRI scan. Three different RESOLVE-DTI protocols were performed on a 3-T MRI system: non-SMS (TR = 4330 ms), SMS with identical TR (4330 ms), and SMS with short TR (2400 ms). Pontine signal-to-noise ratio (SNR) and DTI metrics of the trigeminal nerve streamlines tracked by two independent raters using deterministic tractography and standardized tracking protocol were obtained. These were statistically analyzed and compared across the three protocols using intra-rater and inter-rater intraclass correlation coefficients (ICCs), one-way analysis of variance (ANOVA), post hoc analysis, and linear regression.

Results: On visual screening, there were no artifacts across the trigeminal nerves. All data also cleared objective image quality assurance analysis. Pontine SNR was similar for the two SMS protocols and higher for the non-SMS RESOLVE-DTI (F = 4.40, p = 0.02). Intra-rater and inter-rater ICCs were very good (> 0.85). Trigeminal nerve DTI metrics were consistently measured by the three protocols, revealing significant linear relationships between non-SMS- and SMS-derived DTI metrics.

Conclusion: SMS RESOLVE-DTI enables fast and reliable evaluation of microstructural integrity of the trigeminal nerve, with potential application in the clinical management of TN.

Key Points: • Readout-segmented diffusion-weighted echo planar imaging (RESOLVE-DTI) reduces image distortion artifacts in the posterior fossa but its long acquisition time limits clinical utility. • Simultaneous multi-slice (SMS) imaging combined with RESOLVE-DTI provides reliable trigeminal nerve tractography with potential applications in trigeminal neuralgia. • Two-fold-accelerated RESOLVE-DTI yields comparable trigeminal nerve streamlines and DTI metrics while near-halving acquisition time.
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http://dx.doi.org/10.1007/s00330-020-07193-xDOI Listing
February 2021

TSTIR preparation for single-shot cardiovascular magnetic resonance myocardial edema imaging.

J Cardiovasc Magn Reson 2019 11 21;21(1):72. Epub 2019 Nov 21.

Siemens Healthcare Pte Ltd., 60 MacPherson Road, Singapore, 348615, Singapore.

Background: Myocardial edema in acute myocardial infarction (AMI) is commonly imaged using dark-blood short tau inversion recovery turbo spin echo (STIR-TSE) cardiovascular magnetic resonance (CMR). The technique is sensitive to cardiac motion and coil sensitivity variation, leading to myocardial signal nonuniformity and impeding reliable depiction of edematous tissues. T-prepared balanced steady state free precession (Tp-bSSFP) imaging has been proposed, but its contrast is low, and averaging is commonly needed. T mapping is useful but requires a long scan time and breathholding. We propose here a single-shot magnetization prepared sequence that increases the contrast between edema and normal myocardium and apply it to myocardial edema imaging.

Methods: A magnetization preparation module (TSTIR) is designed to exploit the simultaneous elevation of T and T in edema to improve the depiction of edematous myocardium. The module tips magnetization down to the -z axis after T preparation. Transverse magnetization is sampled at the fat null point using bSSFP readout and allows for single-shot myocardial edema imaging. The sequence (TSTIR-bSSFP) was studied for its contrast behavior using simulation and phantoms. It was then evaluated on 7 healthy subjects and 7 AMI patients by comparing it to Tp-bSSFP and T mapping using the contrast-to-noise ratio (CNR) and the contrast ratio as performance indices.

Results: In simulation and phantom studies, TSTIR-bSSFP had improved contrast between edema and normal myocardium compared with the other two edema imaging techniques. In patients, the CNR of TSTIR-bSSFP was higher than Tp-bSSFP (5.9 ± 2.6 vs. 2.8 ± 2.0, P < 0.05) but had no significant difference compared with that of the T map (T map: 6.6 ± 3.3 vs. 5.9 ± 2.6, P = 0.62). The contrast ratio of TSTIR-bSSFP (2.4 ± 0.8) was higher than that of the T map (1.3 ± 0.1, P < 0.01) and Tp-bSSFP (1.4 ± 0.5, P < 0.05).

Conclusion: TSTIR-bSSFP has improved contrast between edematous and normal myocardium compared with commonly used bSSFP-based edema imaging techniques. TSTIR-bSSFP also differentiates between fat that was robustly suppressed and fluids around the heart. The technique is useful for single-shot edema imaging in AMI patients.
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http://dx.doi.org/10.1186/s12968-019-0583-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6873416PMC
November 2019

Joint intracranial and carotid vessel wall imaging in 5 minutes using compressed sensing accelerated DANTE-SPACE.

Eur Radiol 2020 Jan 1;30(1):119-127. Epub 2019 Aug 1.

Siemens Healthcare Pte. Ltd, Singapore, Singapore.

Objectives: To compare visualization of joint intracranial and carotid vessel walls between 5× compressed sensing accelerated three-dimensional DANTE-SPACE sequence (CS VWI) acquired in 5 min and the same sequence accelerated by 2.7× parallel imaging (PI VWI) which takes 9-10 min currently.

Methods: Following institutional review board approval and informed consent, 28 subjects including 20 stroke patients underwent PI and CS VWI examinations with an acquired spatial resolution of isotropic 0.55 mm and joint coverage of intracranial and carotid arteries. Quantitative wall thickness measurements of CS VWI and PI VWI were compared on healthy volunteers and patients with wall thickening respectively. Subjective wall visualizations of the two VWI methods on patients were scored by two radiologists blindly and independently using a 4-point scale followed by inter-rater reproducibility analysis.

Results: Linear regression analysis of wall thickness measurements showed excellent agreement between CS VWI and PI VWI in both healthy volunteers (r = 0.99) and stroke patients with wall thickening (r = 0.99). Subjective wall visualization score of CS VWI was slightly lower than PI VWI (3.13 ± 0.41 vs. 3.31 ± 0.79) but still had good diagnostic quality (> 3 based on a 4-point scale). The two radiologists' scores agreed excellently, evidenced by the intraclass correlation coefficient (ICC) values being higher than 0.75 (p < 0.001).

Conclusions: Compressed sensing expedients joint intracranial and carotid VWI acquired at an isotropic resolution of 0.55 mm in 5 min without compromising quantitative vessel wall thickness measurement or diagnostic wall visualization.

Key Points: • CS VWI facilitates comprehensive visualization of intracranial and carotid vessel walls at an acquired isotropic resolution of 0.55 mm in a single 5-min scan. • CS VWI affords comparable vessel wall visualization and morphology measurement as PI VWI with a shortened acquisition time by 45%. • CS VWI alleviates the intensive trade-off between imaging resolution and scan time, and benefits the scan efficiency, motion robustness, and patient tolerance of high-resolution joint intracranial and carotid VWI.
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http://dx.doi.org/10.1007/s00330-019-06366-7DOI Listing
January 2020

Platelet inhibition to target reperfusion injury trial: Rationale and study design.

Clin Cardiol 2019 Jan 17;42(1):5-12. Epub 2018 Dec 17.

The Hatter Cardiovascular Institute, Institute of Cardiovascular Science, University College London, London, UK.

Background: In ST-segment elevation myocardial infarction (STEMI) patients treated with primary percutaneous coronary intervention (PPCI), current oral P2Y12 platelet inhibitors do not provide maximal platelet inhibition at the time of reperfusion. Furthermore, administration of cangrelor prior to reperfusion has been shown in pre-clinical studies to reduce myocardial infarct (MI) size. Therefore, we hypothesize that cangrelor administered prior to reperfusion in STEMI patients will reduce the incidence of microvascular obstruction (MVO) and limit MI size in STEMI patients treated with PPCI.

Methods: The platelet inhibition to target reperfusion injury (PITRI) trial, is a phase 2A, multi-center, double-blinded, randomized controlled trial, in which 210 STEMI patients will be randomized to receive either an intravenous (IV) bolus of cangrelor (30 μg/kg) followed by a 120-minute infusion (4 μg/kg/min) or matching saline placebo, initiated prior to reperfusion (NCT03102723).

Results: The study started in October 2017 and the anticipated end date would be July 2020. The primary end-point will be MI size quantified by cardiovascular magnetic resonance (CMR) on day 3 post-PPCI. Secondary endpoints will include markers of reperfusion, incidence of MVO, MI size, and adverse left ventricular remodeling at 6 months, and major adverse cardiac and cerebrovascular events.

Summary: The aim of the PITRI trial is to assess whether cangrelor administered prior to reperfusion would reduce acute MI size and MVO, as assessed by CMR.
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http://dx.doi.org/10.1002/clc.23110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6436500PMC
January 2019

Cardiovascular magnetic resonance evidence of myocardial fibrosis and its clinical significance in adolescent and adult patients with Ebstein's anomaly.

J Cardiovasc Magn Reson 2018 09 27;20(1):69. Epub 2018 Sep 27.

Department of Cardiology, West China Hospital, Sichuan University, Chengdu, 610041, Sichuan Province, China.

Background: Myocardial fibrosis is a common pathophysiological process that is related to ventricular remodeling in congenital heart disease. However, the presence, characteristics, and clinical significance of myocardial fibrosis in Ebstein's anomaly have not been fully investigated. This study aimed to evaluate myocardial fibrosis using cardiovascular magnetic resonance (CMR) late gadolinium enhancement (LGE) and T1 mapping techniques, and to explore the significance of myocardial fibrosis in adolescent and adult patients with Ebstein's anomaly.

Methods: Forty-four consecutive patients with unrepaired Ebstein's anomaly (34.0 ± 16.2 years; 18 males), and an equal number of age- and gender-matched controls, were included. A comprehensive CMR protocol consisted of cine, LGE, and T1 mapping by modified Look-Locker inversion recovery (MOLLI) sequences were performed. Ventricular functional parameters, native T1, extracellular volume (ECV), and LGE were analyzed. Associations between myocardial fibrosis and disease severity, ventricular function, and NYHA classification were analyzed.

Results: LGE was found in 10 (22.7%) patients. Typical LGE in Ebstein's anomaly was located in the endocardium of the septum within the right ventricle (RV). The LV ECV of Ebstein's anomaly were significantly higher than those of the controls (30.0 ± 3.8% vs. 25.3 ± 2.3%, P < 0.001). An increased ECV was found to be independent of the existence of LGE. Positive LGE or higher ECV (≥30%) was associated with larger fRV volume, aRV volume, increased disease severity, and worse NYHA functional class. In addition, ECV was significantly correlated with the LV ejection fraction (P <  0.001).

Conclusions: Both focal and diffuse myocardial fibrosis were observed in adolescent and adult patients with Ebstein's anomaly. Increased diffuse fibrosis is associated with worse LV function, increased Ebstein's severity, and worse clinical status.
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http://dx.doi.org/10.1186/s12968-018-0488-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6158838PMC
September 2018

Diffusion effect on T2 relaxometry in triple-echo steady state free precession sequence.

J Magn Reson 2018 07 2;292:25-35. Epub 2018 May 2.

Siemens Healthcare Pte. Ltd, Singapore.

Purpose: The purpose of this study is to evaluate the effect of diffusion on SSFP (Steady-state Free Precession) signals in triple-echo steady state (TESS) sequence and ultimately on the accuracy of T2 relaxometry.

Methods: The extended phase graph (EPG) algorithm was used to study the effect of diffusion on SSFP signals and T2 relaxometry. The simulation results were verified by a commercial phantom and in vivo studies. Based on the simulation results, a correction scheme was proposed to correct the estimated T2 values.

Results: T2 underestimation in TESS was evident in case of small flip angle and large unbalanced gradient moment on objects with large T2 and D values. The T2 underestimation mainly originated from the diffusion sensitivity of SSFP-echo. It was also observed that SSFP-FID (Free Induction Decay) signals increased with increasing diffusion weighting under some specific conditions. The proposed correction scheme corrected the T2 underestimation, which verified that the underestimation was due to the neglect of diffusion effect. For clinical practice of TESS in tissues with short T2 such as cartilage and muscle, the diffusion effect of TESS is negligible.

Conclusion: The effect of diffusion cannot be neglected during TESS T2 quantification as it is the main source of T2 underestimation when small flip angle and large unbalanced gradient moment is used, especially for objects with large T2 and D values.
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http://dx.doi.org/10.1016/j.jmr.2018.04.018DOI Listing
July 2018

High resolution simultaneous imaging of intracranial and extracranial arterial wall with improved cerebrospinal fluid suppression.

Magn Reson Imaging 2017 12 12;44:65-71. Epub 2017 Aug 12.

Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen key laboratory for MRI, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China. Electronic address:

Purpose: To develop a technique for three dimensional (3D) high resolution joint imaging of intracranial and extracranial arterial walls with improved cerebrospinal fluid (CSF) suppression and good blood suppression based on T1 weighted sampling perfection with application optimized contrast using different angle evolutions (T1w-SPACE) and to compare this technique (hereafter, iSPACE) with alternating with nutation for tailored excitation (DANTE) prepared SPACE sequence (DANTE-SPACE) for their CSF suppression performance around the mid cerebral arteries (MCA) and blood suppression at carotid arteries.

Materials And Methods: Eight volunteers and twelve patients were prospectively recruited in this institutional review board approved study. A custom designed 32-channel coil set covering the intracranial and extracranial arteries was used for signal reception. Imaging was performed in each subject using DANTE-SPACE and iSPACE. Signal-to-noise ratios (SNR) of the vessel walls at the MCA and carotid arteries, and contrast-to-noise ratios (CNR) between vessel wall and CSF at the MCA and between vessel wall and lumen at carotid arteries from the two sequences were compared.

Results: In volunteers, contrast between CSF and white matter (surrogate for vessel wall signal) at the M2 segments in iSPACE was 67.9% higher than in DANTE-SPACE. At the carotid region, the SNR of vessel wall in iSPACE was 11.6% higher than DANTE-SPACE while the CNR in iSPACE was 13% higher than DANTE-SPACE. In patients, images with 0.6mm isotropic resolution were obtained in 7.5min. iSPACE showed 70.9% improvement in CNR between plaque and CSF at the M2 segments compared to DANTE-SPACE.

Conclusion: Simultaneous extracranial and intracranial arterial wall imaging using iSPACE improved CSF suppression significantly at the M2 segment of MCA while blood suppression was comparable to DANTE-SPACE. The technique achieved 3D images with 0.6mm isotropic spatial resolution and took 7.5min using a custom made coil set. Using this technique, intracranial plaque visualization was improved with no observable image SNR degradation.
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http://dx.doi.org/10.1016/j.mri.2017.08.004DOI Listing
December 2017

Reference value of left and right atrial size and phasic function by SSFP CMR at 3.0 T in healthy Chinese adults.

Sci Rep 2017 06 9;7(1):3196. Epub 2017 Jun 9.

Cardiology Division, West China Hospital, Sichuan University, Chengdu, Sichuan Province, 610041, China.

The size and function of the left atrium (LA) and right atrium (RA) are related closely with the prognosis of cardiovascular diseases. However, their normal reference values, as measured by cardiac magnetic resonance (CMR), are not well established in Chinese populations. Healthy Chinese subjects (n = 135, 66 males, age 23-83 years) without cardiovascular risk factors were recruited. We imaged the LA and RA of all subjects using short axis and long axis slices by steady-state free precession (SSFP) sequences using a 3.0T scanner. The size and functional parameters were measured. Age and gender differences in LA were further explored. The normal reference values of atrial dimensions, volumes, and empty fractions (EFs) were provided by short axis (SAX) and area-length methods. Volumes and EFs derived by the area-length method showed correlated well with those derived by the by SAX method, but significantly underestimated the volumes (all P < 0.001) and overestimated the LA EFs (all P < 0.001). Atrial dimensions and volumes were generally larger in males. Conduit EFs and total EFs showed gender differences. Most atrial parameters correlated with age. In general, our results showed that gender and age have considerable impact on LA and RA size and function.
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http://dx.doi.org/10.1038/s41598-017-03377-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5466635PMC
June 2017

Improved workflow for quantifying left ventricular function via cardiorespiratory-resolved analysis of free-breathing MR real-time cines.

J Magn Reson Imaging 2017 09 27;46(3):905-914. Epub 2017 Jan 27.

Cardiology Division, West China Hospital, Sichuan University, Chengdu, Sichuan, P.R. China.

Purpose: To evaluate the feasibility of a proposed cardiorespiratory-resolved analysis in left ventricular (LV) function quantification from real-time cines in a cohort of cardiac patients.

Materials And Methods: Electrocardiograph (ECG)-free free-breathing real-time cine imaging based on the balanced steady-state free precession technique was performed on short-axis slices of 20 cardiac patients at 3T. K-means cluster segmentation was used to delineate the endocardial contours, from which the LV centroid and cavity area were determined. Respiratory and cardiac signals were respectively resolved from the filtered LV centroid displacement and time-varied LV cavity area to identify end-expiratory end-diastolic (ED) and end-systolic (ES) images. The obtained LV cavity areas and derived volumetric function indices, including ED volume (EDV), ES volume (ESV), stroke volume (SV), and ejection fraction (EF), were compared with those measured from manual analysis using two-tailed paired Student's t-tests, linear regression analyses, and Bland-Altman plots. Interobserver variability was calculated.

Results: The LV cavity area was strongly correlated between the proposed and conventional manual methods (r > 0.87) for three representative slices at the base, middle ventricle, and apex. The average differences between the two methods were 0.66 ± 3.22 mL for EDV, -0.02 ± 2.68 mL for ESV, 0.67 ± 3.73 mL for SV, and 0.17 ± 2.30% for EF. All paired measures exhibited strong correlations (r > 0.96) without significant differences (P = 0.38-0.98). Acceptable interobserver variability (0.19-3.55%) and strong correlations (r > 0.96) were shown for all measures between the two observers.

Conclusion: The proposed method is feasible for efficient measurement of LV function from real-time cines.

Level Of Evidence: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:905-914.
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http://dx.doi.org/10.1002/jmri.25618DOI Listing
September 2017

Assessing exercise cardiac reserve using real-time cardiovascular magnetic resonance.

J Cardiovasc Magn Reson 2017 Jan 23;19(1). Epub 2017 Jan 23.

National Heart Centre Singapore, 5 Hospital Drive, Singapore, 169609, Singapore.

Background: Exercise cardiovascular magnetic resonance (ExCMR) has great potential for clinical use but its development has been limited by a lack of compatible equipment and robust real-time imaging techniques. We developed an exCMR protocol using an in-scanner cycle ergometer and assessed its performance in differentiating athletes from non-athletes.

Methods: Free-breathing real-time CMR (1.5T Aera, Siemens) was performed in 11 athletes (5 males; median age 29 [IQR: 28-39] years) and 16 age- and sex-matched healthy volunteers (7 males; median age 26 [interquartile range (IQR): 25-33] years). All participants underwent an in-scanner exercise protocol on a CMR compatible cycle ergometer (Lode BV, the Netherlands), with an initial workload of 25W followed by 25W-increment every minute. In 20 individuals, exercise capacity was also evaluated by cardiopulmonary exercise test (CPET). Scan-rescan reproducibility was assessed in 10 individuals, at least 7 days apart.

Results: The exCMR protocol demonstrated excellent scan-rescan (cardiac index (CI): 0.2 ± 0.5L/min/m) and inter-observer (ventricular volumes: 1.2 ± 5.3mL) reproducibility. CI derived from exCMR and CPET had excellent correlation (r = 0.83, p < 0.001) and agreement (1.7 ± 1.8L/min/m). Despite similar values at rest (P = 0.87), athletes had increased exercise CI compared to healthy individuals (at peak exercise: 12.2 [IQR: 10.2-13.5] L/min/m versus 8.9 [IQR: 7.5-10.1] L/min/m, respectively; P < 0.001). Peak exercise CI, where image acquisition lasted 13-17 s, outperformed that at rest (c-statistics = 0.95 [95% confidence interval: 0.87-1.00] versus 0.48 [95% confidence interval: 0.23-0.72], respectively; P < 0.0001 for comparison) in differentiating athletes from healthy volunteers; and had similar performance as VO (c-statistics = 0.84 [95% confidence interval = 0.62-1.00]; P = 0.29 for comparison).

Conclusions: We have developed a novel in-scanner exCMR protocol using real-time CMR that is highly reproducible. It may now be developed for clinical use for physiological studies of the heart and circulation.
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http://dx.doi.org/10.1186/s12968-017-0322-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5256575PMC
January 2017

A fast screening protocol for carotid plaques imaging using 3D multi-contrast MRI without contrast agent.

Magn Reson Imaging 2017 06 28;39:89-97. Epub 2016 Oct 28.

Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology of Chinese Academy of Sciences, Shenzhen Key Laboratory for MRI, Shenzhen, China. Electronic address:

Purpose: To implement a fast (~15min) MRI protocol for carotid plaque screening using 3D multi-contrast MRI sequences without contrast agent on a 3Tesla MRI scanner.

Materials And Methods: 7 healthy volunteers and 25 patients with clinically confirmed transient ischemic attack or suspected cerebrovascular ischemia were included in this study. The proposed protocol, including 3D T1-weighted and T2-weighted SPACE (variable-flip-angle 3D turbo spin echo), and T1-weighted magnetization prepared rapid acquisition gradient echo (MPRAGE) was performed first and was followed by 2D T1-weighted and T2-weighted turbo spin echo, and post-contrast T1-weighted SPACE sequences. Image quality, number of plaques, and vessel wall thicknesses measured at the intersection of the plaques were evaluated and compared between sequences.

Results: Average examination time of the proposed protocol was 14.6min. The average image quality scores of 3D T1-weighted, T2-weighted SPACE, and T1-weighted magnetization prepared rapid acquisition gradient echo were 3.69, 3.75, and 3.48, respectively. There was no significant difference in detecting the number of plaques and vulnerable plaques using pre-contrast 3D images with or without post-contrast T1-weighted SPACE. The 3D SPACE and 2D turbo spin echo sequences had excellent agreement (R=0.96 for T1-weighted and 0.98 for T2-weighted, p<0.001) regarding vessel wall thickness measurements.

Conclusion: The proposed protocol demonstrated the feasibility of attaining carotid plaque screening within a 15-minute scan, which provided sufficient anatomical coverage and critical diagnostic information. This protocol offers the potential for rapid and reliable screening for carotid plaques without contrast agent.
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http://dx.doi.org/10.1016/j.mri.2016.10.028DOI Listing
June 2017

A 32-channel coil system for MR vessel wall imaging of intracranial and extracranial arteries at 3T.

Magn Reson Imaging 2017 Feb 27;36:86-92. Epub 2016 Oct 27.

Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology of Chinese Academy of Sciences, China; Shenzhen Key Laboratory for MRI, Shenzhen, China. Electronic address:

Purpose: To develop a RF coil system for joint imaging of intracranial and extracranial arterial vessel wall at 3T.

Materials And Method: The coil system consists of a 24-channel head coil combined with an 8-channel carotid coil. It is compared with a standard coil configuration (12-channel head coil+4-channel neck coil+8-channel carotid coil) for SNR and g-factors in phantoms and healthy volunteers. The clinical relevance of the proposed coil system is also evaluated in patients.

Results: In phantom experiments, the SNR of the proposed coil system is 53% higher than the maximum SNR of the standard coil configuration at the center of the phantom which usually corresponds to the intracranial region of the head. The g-factors of the proposed coil system in the sagittal plane are lower than the standard coil configuration (by 10.8% and 26.6% for R=2 and 4 respectively) in the same experiment. In healthy volunteer experiments, 55% of the pixels have SNR above 100 for the proposed coil system, which is 33% more than that of the standard coil configuration. The maximum g-factors in the standard configuration are higher than those from the new coil design by 12% at R=2 and up to 36% at R=4 in the sagittal plane. In patients, in-vivo intracranial and extracranial arterial wall images at an isotropic spatial resolution of 0.6mm can be acquired using the proposed coil system. Plaques are well depicted from the images.

Conclusions: The performance of the proposed coil set is superior to the standard coil configuration, providing high SNR, low g-factor and good spatial coverage needed for simultaneous high resolution imaging of intracranial and extracranial arterial walls. Images acquired in 7.6min using the proposed coil system can achieve an isotropic spatial resolution of 0.6mm and can be used to depict plaques on the intracranial and extracranial arterial walls in patients.
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http://dx.doi.org/10.1016/j.mri.2016.10.018DOI Listing
February 2017

Fast T1 mapping of the brain at high field using Look-Locker and fast imaging.

Magn Reson Imaging 2017 Feb 27;36:49-55. Epub 2016 Oct 27.

Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, China; Shenzhen Key Laboratory for MRI, Shenzhen, Guangdong, China.

This study aims to develop and evaluate a new method for fast high resolution T1 mapping of the brain based on the Look-Locker technique. Single-shot turboflash sequence with high temporal acceleration is used to sample the recovery of inverted magnetization. Multi-slice interleaved acquisition within one inversion slab is used to reduce the number of inversion pulses and hence SAR. Accuracy of the proposed method was studied using simulation and validated in phantoms. It was then evaluated in healthy volunteers and stroke patients. In-vivo results were compared to values obtained by inversion recovery fast spin echo (IR-FSE) and literatures. With the new method, T values in phantom experiments agreed with reference values with median error <3%. For in-vivo experiments, a T1 map was acquired in 3.35s and the T1 maps of the whole brain were acquired in 2min with two-slice interleaving, with a spatial resolution of 1.1×1.1×4mm. The T values obtained were comparable to those measured with IR-FSE and those reported in literatures. These results demonstrated the feasibility of the proposed method for fast T1 mapping of the brain in both healthy volunteers and stroke patients at 3T.
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http://dx.doi.org/10.1016/j.mri.2016.10.022DOI Listing
February 2017

Referenceless MR thermometry-a comparison of five methods.

Phys Med Biol 2017 01 14;62(1):1-16. Epub 2016 Dec 14.

Paul C Lauterbur Research Center for Biomedical Imaging, Shenzhen Key Laboratory for MRI, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, People's Republic of China.

Proton resonance frequency shift (PRFS) MR thermometry is commonly used to measure temperature in thermotherapy. The method requires a baseline temperature map and is therefore motion sensitive. Several referenceless MR thermometry methods were proposed to address this problem but their performances have never been compared. This study compared the performance of five referenceless methods through simulation, heating of ex vivo tissues and in vivo imaging of the brain and liver of healthy volunteers. Mean, standard deviation, root mean square, 2/98 percentiles of error were used as performance metrics. Probability density functions (PDF) of the error distribution for these methods in the different tests were also compared. The results showed that the phase gradient method (PG) exhibited largest error in all scenarios. The original method (ORG) and the complex field estimation method (CFE) had similar performance in all experiments. The phase finite difference method (PFD) and the near harmonic method (NH) were better than other methods, especially in the lower signal-to-noise ratio (SNR) and fast changing field cases. Except for PG, the PDFs of each method were very similar among the different experiments. Since phase unwrapping in ORG and NH is computationally demanding and subject to image SNR, PFD and CFE would be good choices as they do not need phase unwrapping. The results here would facilitate the choice of appropriate referenceless methods in various MR thermometry applications.
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http://dx.doi.org/10.1088/1361-6560/62/1/1DOI Listing
January 2017

An 8-channel RF coil array for carotid artery MR imaging in humans at 3 T.

Med Phys 2016 Apr;43(4):1897

Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology of Chinese Academy of Sciences, Shenzhen 518055, China and Shenzhen Key Laboratory for MRI, Shenzhen 518055, China.

Purpose: Carotid artery diseases due to plaque buildup at the carotid bifurcation are a leading cause of stroke. Accurate plaque quantification and characterization of plaque composition and morphology by magnetic resonance imaging (MRI) is essential to identifying high-risk patients. Difficulties in detecting plaque, which is physically small, and the unique physiological structure of the carotid artery make use of a radio frequency (RF) coil array with high resolution, large longitudinal coverage, and deep penetration ideal for clinical examinations. The goal of this project was to design and fabricate a sensitive RF coil array with sufficient imaging coverage and signal-to-noise ratio (SNR) for carotid artery imaging at 3 T.

Methods: Based on clinical requirements and the anatomical structure of the human carotid artery, an 8-channel carotid coil array was designed and fabricated for 3 T MRI of the carotid artery in humans. The performance of the proposed 8-channel carotid coil array was validated through bench tests and MR imaging experiments on a 3 T whole body MRI scanner. Its performance was also compared experimentally to the performance of a commercial 4-channel phased array carotid coil designed by Machnet BV (Machnet BV coil, Roden, Netherlands).

Results: The 8-channel carotid coil array performed significantly better in imaging the carotid artery than the commercial 4-channel Machnet BV coil in terms of the SNR, coverage, and penetration depth. In parallel imaging, the proposed 8-channel carotid coil array demonstrated a much lower maximum value and average value of the geometry factor in the region of interest. Carotid artery images acquired in vivo using the proposed 8-channel carotid artery coil and the commercial 4-channel Machnet BV coil were also compared, demonstrating the former's potential for clinical diagnosis.

Conclusions: Based on the analyses of phantom and in vivo imaging studies, the proposed 8-channel carotid coil array has the potential for use in clinical diagnosis, performing better in terms of SNR, imaging coverage, and penetration depth than the commercial 4-channel carotid artery coil array at 3 T. In future studies, the proposed 8-channel carotid coil array can also serve as an important part of a large-scale multichannel coil array for imaging the whole carotid artery system, including the extracranial and intracranial arteries.
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http://dx.doi.org/10.1118/1.4944500DOI Listing
April 2016

Middle Cerebral Artery Atherosclerotic Plaques in Recent Small Subcortical Infarction: A Three-Dimensional High-resolution MR Study.

Biomed Res Int 2015 11;2015:540217. Epub 2015 Oct 11.

Department of Neurology, Xuan Wu Hospital, Capital Medical University, Beijing 100053, China ; Beijing Key Laboratory of Geriatric Cognitive Disorders, Beijing 100053, China ; Neurodegenerative Laboratory of Ministry of Education of the People's Republic of China, Beijing 100053, China.

Purpose: Conventional two-dimensional vessel wall imaging has been used to depict the middle cerebral artery (MCA) wall in patients with recent small subcortical infarctions (RSSIs). However, its clinical use has been limited by restricted spatial coverage, low signal-to-noise ratio (SNR), and long scan time. We used a novel three-dimensional high-resolution MR imaging (3D HR-MRI) technique to investigate the presence, locations, and contrast-enhanced patterns of MCA plaques and their relationship with RSSI.

Methods: Nineteen consecutive patients with RSSI but no luminal stenosis on MR angiography were prospectively enrolled. 3D HR-MRI was performed using a T1w-SPACE sequence at 3.0 T. The presence, locations, and contrast-enhanced patterns of the MCA plaques on the ipsilateral and contralateral sides to the RSSI were analyzed.

Results: Eighteen patients successfully completed the study. MCA atherosclerotic plaques occurred more frequently on the ipsilateral than the contralateral side to the RSSI (72.2% versus 33.3%, P = 0.044). The occurrence of superiorly located plaques was significantly higher on the ipsilateral than the contralateral side of the MCA (66.7% versus 27.8%; P = 0.044).

Conclusions: Superiorly located plaques are closely associated with RSSI. 3D high-resolution vessel wall imaging may be a potential tool for etiologic assessment of ischemic stroke.
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http://dx.doi.org/10.1155/2015/540217DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4619811PMC
August 2016

High resolution three dimensional intracranial arterial wall imaging at 3 T using T1 weighted SPACE.

Magn Reson Imaging 2015 Nov 2;33(9):1026-1034. Epub 2015 Jul 2.

Shenzhen Key Laboratory for MRI, Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China. Electronic address:

Objective: To study the effect of imaging parameters on the contrast of T1 weighted SPACE (Sampling Perfection with Application optimized Contrast using different angle Evolutions, a 3D TSE variant) at 3 T for high resolution imaging of intracranial plaques before contrast and with post-gadolinium induced enhancement, and evaluate its relevance to patients with intracranial atherosclerosis.

Materials And Methods: Optimized parameters giving good T1 contrast between intracranial vessel wall and cerebrospinal fluid within a specific scan time and reasonable coverage were found by simulation and validated in a healthy volunteer study. Based on the results, a clinical protocol covering the three major intracranial arteries (middle cerebral arteries, basilar arteries, and petrous internal carotid arteries) was developed. It was applied in ten patients diagnosed with intracranial arterial lesions. The accuracy of the technique in depicting vessel lumen was assessed by comparison to contrast enhanced MR angiography. The contrast enhancement ratios of the vessel wall/plaque identified were analyzed.

Results: Simulation and volunteer study showed that using T1 weighted SPACE, good T1 contrast between vessel wall and cerebrospinal fluid occurred at TR of around 1000 ms using an echo train length of 21 within 10 minutes at an isotropic spatial resolution of 0.5 mm. In the 10 patients, 24 plaques were identified in the various segments of the intracranial arterial system of which eight appeared normal on MR angiography. Post-contrast enhancement ratio of these plaques varied from 0% up to 156%.

Conclusions: T1 weighted SPACE provides good T1 contrast between intracranial arterial wall and cerebrospinal fluid with high resolution and good coverage within a clinically acceptable scan time. It can depict plaques pre- and post-contrast along the vessels surrounded by cerebrospinal fluid in the intracranial arterial system, and would be a useful tool in the clinical assessment of intracranial arterial diseases.
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http://dx.doi.org/10.1016/j.mri.2015.06.006DOI Listing
November 2015

Efficient method for analyzing MR real-time cines: Toward accurate quantification of left ventricular function.

J Magn Reson Imaging 2015 Oct 2;42(4):972-80. Epub 2015 Mar 2.

Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Key Laboratory for MRI, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China.

Background: To develop and assess an efficient method to identify end-expiratory end-diastolic (ED) and end-systolic (ES) images for accurate quantification of left ventricular (LV) function in real-time cine imaging.

Methods: ECG-free free-breathing real-time cine imaging was performed on short-axis slices of thirteen healthy volunteers at 3 Tesla. K-means cluster segmentation was applied to delineate the endocardial contour, from which the LV centroid and cavity area were determined in each cine image. LV centroid displacement along the superior-inferior direction was filtered to extract respiratory motion in each slice. End-expiratory ED and ES images were then identified and used for LV function quantification. Accuracy was evaluated with that measured from the slice-matched standard ECG-gated breathhold segmented cines using two-tail paired Student's t-tests, linear regression analyses and Bland-Altman plots. Intra- and interobserver variability was calculated for each imaging technique.

Results: Qualitatively, end-expiratory ED and ES images identified with the proposed method agreed with those determined by frame-by-frame visual inspection in 97.5% of cases (P > 0.05). Quantitatively, good agreement of LV function indices between the real-time cine and the standard segmented cine was observed with averaged differences of 0.1 ± 0.9 g for myocardium mass, -0.3 ± 1.0 mL for ED volume, 0.2 ± 1.2 mL for ES volume, -0.2 ± 1.3 mL for stroke volume, and -0.3 ± 0.8% for ejection fraction. Paired LV function values exhibited strong correlation (r ≥ 0.96) and no significant difference (P > 0.05). The real-time cine and the standard segmented cine showed similar intra- (1.2-3.3% and 1.1-2.8%, respectively) and interobserver variability (2.6-6.9% and 1.8-4.8%, respectively) with all P-values > 0.05. All the variability was comparable with published results.

Conclusion: Compared with the laborious frame-by-frame visual inspection, as conventionally adopted, the proposed method is efficient in analyzing real-time cines for the accurate quantification of LV function without excessively manual interactions.
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http://dx.doi.org/10.1002/jmri.24869DOI Listing
October 2015

Noncontrast MRA of pedal arteries in type II diabetes: effect of disease load on vessel visibility.

Acad Radiol 2015 Apr 15;22(4):513-9. Epub 2015 Jan 15.

Biomedical Imaging Research Institute, Cedars Sinai Medical Center, Los Angeles, California.

Rationale And Objectives: Noncontrast magnetic resonance angiography (NC-MRA) of pedal artery remains challenging because of the global and regional disease load, tissue integrity, and altered microcirculation. This study aims to investigate the feasibility of the NC-MRA of pedal arteries with flow-sensitive dephasing-prepared steady-state free precession (FSD-SSFP) and to explore the effect of disease load of type II diabetes on the vessel depiction.

Materials And Methods: FSD-SSFP was performed on a 1.5-T magnetic resonance system before the contrast-enhanced MRA (CE-MRA) as a reference standard in 39 consecutive diabetic subjects (29 men and 16 women, aged 57.9 ± 11.4 years). Two experienced radiologists evaluated the overall artery visibility (VA) and the contamination from soft tissue (SC) and veins (VC) with a four-point scale. Chronic complications and measures including random blood glucose (RBG), lipid panel, body mass index, risk of diabetic foot ulcers (RDF), and glycated hemoglobin (HbA1c) by the imaging were recorded as disease load indicators. Spearman rank correlation and ordinal regression were performed to investigate the effect of disease load on the depiction of pedal arteries.

Results: The measurement of RBG and RDF were significantly correlated with the VC in CE-MRA and with the overall visibility of pedal arteries in NC-MRA (P < .025 and P < .001, respectively). Blood pressure was the only parameter that was significantly associated with SC in NC-MRA with FSD-SSFP (P < .025). For CE-MRA the effect of RDF on the overall VA manifested a significant linear trend (P < .001), and the level of RBG was substantially associated with the VC (P < .025) without significantly impacting VA and SC. Hypertension only correlated with SC in NC-MRA. VA was found independent of the presence of diabetic nephropathy, coronary artery disease, abnormal lipid panel, HbA1c (75.0%), or optimized m1 value that ranged from 70 to 160 mT⋅ms(2)/m (mean, 125 ± 18 mT⋅ms(2)/m) in this study.

Conclusions: FSD-SSFP proved to be a useful modality of NC-MRA for pedal artery imaging in diabetic patients. The vessel depiction is subject to the local and systemic disease load of type II diabetes. Technical optimization of the flow-sensitive dephasing gradient moment and properly choosing candidate would help augment the potential of this technique in patient care of peripheral artery disease.
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http://dx.doi.org/10.1016/j.acra.2014.11.010DOI Listing
April 2015

Non-rigid registration and KLT filter to improve SNR and CNR in GRE-EPI myocardial perfusion imaging.

J Biomed Sci Eng 2012 Dec;5(12A):871-877

Department of Internal Medicine, Cardiovascular Division, Dorothy M. Davis Heart and Lung Research Institute, Columbus, USA.

The purpose of the study was to evaluate the effect of motion compensation by non-rigid registration combined with the Karhunen-Loeve Transform (KLT) filter on the signal to noise (SNR) and contrast-to-noise ratio (CNR) of hybrid gradient-echo echoplanar (GRE-EPI) first-pass myocardial perfusion imaging. Twenty one consecutive first-pass adenosine stress perfusion MR data sets interpreted positive for ischemia or infarction were processed by non-rigid Registration followed by KLT filtering. SNR and CNR were measured in abnormal and normal myocardium in unfiltered and KLT filtered images following non-rigid registration to compensate for respiratory and other motions. Image artifacts introduced by filtering in registered and nonregistered images were evaluated by two observers. There was a statistically significant increase in both SNR and CNR between normal and abnormal myocardium with KLT filtering (mean SNR increased by 62.18% ± 21.05% and mean CNR increased by 58.84% ± 18.06%; p = 0.01). Motion correction prior to KLT filtering reduced significantly the occurrence of filter induced artifacts (KLT only-artifacts in 42 out of 55 image series vs. registered plus KLT-artifacts in 3 out of 55 image series). In conclusion the combination of non- rigid registration and KLT filtering was shown to increase the SNR and CNR of GRE-EPI perfusion images. Subjective evaluation of image artifacts revealed that prior motion compensation significantly reduced the artifacts introduced by the KLT filtering process.
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http://dx.doi.org/10.4236/jbise.2012.512A110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3738217PMC
December 2012

A fast referenceless PRFS-based MR thermometry by phase finite difference.

Phys Med Biol 2013 Aug 1;58(16):5735-51. Epub 2013 Aug 1.

Paul C Lauterbur Research Center for Biomedical Imaging and Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, People's Republic of China.

Proton resonance frequency shift-based MR thermometry is a promising temperature monitoring approach for thermotherapy but its accuracy is vulnerable to inter-scan motion. Model-based referenceless thermometry has been proposed to address this problem but phase unwrapping is usually needed before the model fitting process. In this paper, a referenceless MR thermometry method using phase finite difference that avoids the time consuming phase unwrapping procedure is proposed. Unlike the previously proposed phase gradient technique, the use of finite difference in the new method reduces the fitting error resulting from the ringing artifacts associated with phase discontinuity in the calculation of the phase gradient image. The new method takes into account the values at the perimeter of the region of interest because of their direct relevance to the extrapolated baseline phase of the region of interest (where temperature increase takes place). In simulation study, in vivo and ex vivo experiments, the new method has a root-mean-square temperature error of 0.35 °C, 1.02 °C and 1.73 °C compared to 0.83 °C, 2.81 °C, and 3.76 °C from the phase gradient method, respectively. The method also demonstrated a slightly higher, albeit small, temperature accuracy than the original referenceless MR thermometry method. The proposed method is computationally efficient (~0.1 s per image), making it very suitable for the real time temperature monitoring.
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http://dx.doi.org/10.1088/0031-9155/58/16/5735DOI Listing
August 2013

The Asymptotic Noise Distribution in Karhunen-Loeve Transform Eigenmodes.

J Health Med Inform 2013 Jun;4(2):122

Davis Heart and Lung Research Institute, The Ohio State University, Columbus, USA ; Department of Internal Medicine, The Ohio State University, Columbus, USA ; Department of Biomedical Engineering, The Ohio State University, Columbus, USA ; Department of Radiology, The Ohio State University, Columbus, USA.

Karhunen-Loeve Transform (KLT) is widely used in signal processing. Yet the well-accepted result is that, the noise is uniformly distributed in all eigenmodes is not accurate. We apply a result of the random matrix theory to understand the asymptotic noise distribution in KLT eigenmodes. Noise variances in noise-only eigenmodes follow the Marcenko-Pastur distribution, while noise variances in signal-dominated eigenmodes still follow the uniform distribution. Both the mathematical expectation of noise level in each eigenmode and an analytical formula of KLT filter noise reduction effect with a hard threshold were derived. Numerical simulations agree with our theoretical analysis. The noise variance of an eigenmode may deviate more than 60% from the uniform distribution. These results can be modified slightly, and generalized to non-IID (independently and identically-distributed) noise scenario. Magnetic resonance imaging experiments show that the generalized result is applicable and accurate. These generic results can help us understand the noise behavior in the KLT and related topics.
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http://dx.doi.org/10.4172/2157-7420.1000122DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4666531PMC
June 2013

Myocardial T₂ mapping with respiratory navigator and automatic nonrigid motion correction.

Magn Reson Med 2012 Nov 3;68(5):1570-8. Epub 2012 Jan 3.

Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA.

Quantitative T₂ mapping was recently shown to be superior to T₂-weighted imaging in detecting T₂ changes across myocardium. Pixel-wise T₂ mapping is sensitive to misregistration between the images used to generate the parameter map. In this study, utility of two motion-compensation strategies-(i) navigator gating with prospective slice correction and (ii) nonrigid registration-was investigated for myocardial T₂ mapping in short axis and horizontal long axis views. Navigator gating provides respiratory motion compensation, whereas registration corrects for residual cardiac and respiratory motion between images; thus, the two strategies provided complementary functions. When these were combined, respiratory-motion-induced T₂ variability, as measured by both standard deviation and interquartile range, was comparable to that in breath-hold T₂ maps. In normal subjects, this combined motion-compensation strategy increased the percentage of myocardium with T₂ measured to be within normal range from 60.1% to 92.2% in short axis and 62.3% to 92.7% in horizontal long axis. The new motion-compensated T₂ mapping technique, which combines navigator gating, prospective slice correction, and nonrigid registration to provide through-plane and in-plane motion correction, enables a method for fully automatic and robust free-breathing T₂ mapping.
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http://dx.doi.org/10.1002/mrm.24139DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4512252PMC
November 2012

Simultaneous right and left heart real-time, free-breathing CMR flow quantification identifies constrictive physiology.

JACC Cardiovasc Imaging 2012 Jan;5(1):15-24

The Ohio State University, Columbus, Ohio 43210, USA.

Objectives: The purpose of this study was to evaluate the ability of a novel cardiac magnetic resonance (CMR) real-time phase contrast (RT-PC) flow measurement technique to reveal the discordant respirophasic changes in mitral and tricuspid valve in flow indicative of the abnormal hemodynamics seen in constrictive pericarditis (CP).

Background: Definitive diagnosis of CP requires identification of constrictive hemodynamics with or without pericardial thickening. CMR to date has primarily provided morphological assessment of the pericardium.

Methods: Sixteen patients (age 57 ± 13 years) undergoing CMR to assess known or suspected CP and 10 controls underwent RT-PC that acquired simultaneous mitral valve and tricuspid valve inflow velocities over 10 s of unrestricted breathing. The diagnosis of CP was confirmed via clinical history, diagnostic imaging, cardiac catheterization, intraoperative findings, and histopathology.

Results: Ten patients had CP, all with increased pericardial thickness (6.2 ± 1.0 mm). RT-PC imaging demonstrated discordant respirophasic changes in atrioventricular valve inflow velocities in all CP patients, with mean ± SD mitral valve and tricuspid valve inflow velocity variation of 46 ± 20% and 60 ± 15%, respectively, compared with 16 ± 8% and 24 ± 11% in patients without CP (p < 0.004 vs. patients with CP for both) and 17 ± 5% and 31 ± 13% in controls (p < 0.001 vs. patients with CP for both). There was no difference in atrioventricular valve inflow velocity variation between patients without CP compared with controls (p > 0.3 for both). Respiratory variation exceeding 25% across the mitral valve yielded a sensitivity of 100%, a specificity of 100%, and an area under the receiver-operating characteristic curve of 1.0 to detect CP physiology. Using a cutoff of 45%, variation of transtricuspid valve velocity had a sensitivity of 90%, a specificity of 88%, and an area under the receiver-operating characteristic curve of 0.98.

Conclusions: Accentuated and discordant respirophasic changes in mitral valve and tricuspid valve inflow velocities characteristic of CP can be identified noninvasively with RT-PC CMR. When incorporated into existing CMR protocols for imaging pericardial morphology, RT-PC CMR provides important hemodynamic evidence with which to make a definite diagnosis of CP.
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http://dx.doi.org/10.1016/j.jcmg.2011.07.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4560101PMC
January 2012

Assessment of carotid stenosis using three-dimensional T2-weighted dark blood imaging: Initial experience.

J Magn Reson Imaging 2012 Feb 6;35(2):449-55. Epub 2011 Dec 6.

Department of Internal Medicine, Division of Cardiovascular Medicine, Ohio State University, Columbus, Ohio, USA.

Purpose: To evaluate the use of a T2-weighted SPACE sequence (T2w-SPACE) to assess carotid stenosis via several methods and compare its performance with contrast-enhanced magnetic resonance angiography (ceMRA).

Materials And Methods: Fifteen patients with carotid atherosclerosis underwent dark blood (DB)-MRI using a 3D turbo spin echo with variable flip angles sequence (T2w-SPACE) and ceMRA. Images were coregistered and evaluated by two observers. Comparisons were made for luminal diameter, luminal area, degree of luminal stenosis (NASCET: North American Symptomatic Endarterectomy Trial; ECST: European Carotid Surgery Trial, and area stenosis), and vessel wall area. Degree of NASCET stenosis was clinically classified as mild (<50%), moderate (50%-69%), or severe (>69%).

Results: Excellent agreement was seen between ceMRA and T2w-SPACE and between observers for assessment of lumen diameter, lumen area, vessel wall area, and degree of NASCET stenosis (r > 0.80, P < 0.001). ECST stenosis was consistently higher than NASCET stenosis (48 ± 14% vs. 24 ± 22%, P < 0.001). Area stenosis (72 ± 2%) was significantly higher (P < 0.001) than both ESCT and NASCET stenosis.

Conclusion: DB-MRI of carotid arteries using T2w-SPACE is clinically feasible. It provides accurate measurements of lumen size and degree of stenosis in comparison with ceMRA and offers a more reproducible measure of ECST stenosis than ceMRA.
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http://dx.doi.org/10.1002/jmri.22839DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4807862PMC
February 2012

Shared velocity encoding: a method to improve the temporal resolution of phase-contrast velocity measurements.

Magn Reson Med 2012 Sep 2;68(3):703-10. Epub 2011 Dec 2.

Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA.

Phase-contrast magnetic resonance imaging (PC-MRI) is used routinely to measure fluid and tissue velocity with a variety of clinical applications. Phase-contrast magnetic resonance imaging methods require acquisition of additional data to enable phase difference reconstruction, making real-time imaging problematic. Shared Velocity Encoding (SVE), a method devised to improve the effective temporal resolution of phase-contrast magnetic resonance imaging, was implemented in a real-time pulse sequence with segmented echo planar readout. The effect of SVE on peak velocity measurement was investigated in computer simulation, and peak velocities and total flow were measured in a flow phantom and in volunteers and compared with a conventional ECG-triggered, segmented k-space phase-contrast sequence as a reference standard. Computer simulation showed a 36% reduction in peak velocity error from 8.8 to 5.6% with SVE. A similar reduction of 40% in peak velocity error was shown in a pulsatile flow phantom. In the phantom and volunteers, volume flow did not differ significantly when measured with or without SVE. Peak velocity measurements made in the volunteers using SVE showed a higher concordance correlation (0.96) with the reference standard than non-SVE (0.87). The improvement in effective temporal resolution with SVE reconstruction has a positive impact on the precision and accuracy of real-time phase-contrast magnetic resonance imaging peak velocity measurements.
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http://dx.doi.org/10.1002/mrm.23273DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3339280PMC
September 2012

Post-interventional three-dimensional dark blood MRI in the adult with congenital heart disease.

Int J Cardiol 2012 Jul 18;158(2):267-71. Epub 2011 Feb 18.

Department of Internal Medicine, Division of Cardiovascular Medicine, Adolescent/Adult Congenital Heart Disease Program, The Ross Heart Hospital, The Ohio State University, United States.

Background: Investigate a novel three-dimensional (3D) turbo spin echo (TSE) magnetic resonance imaging (MRI) sequence to assess stented segments in adults with congenital heart disease (CHD) after transcatheter intervention.

Methods: Adults with CHD referred for computed tomography (CT) after transcatheter intervention underwent MR exam with a 3D respiratory gated TSE sequence. Data obtained at the time of the study included type of CHD, radiation dose, length of time between exams, and luminal diameters of stented segments from each exam. Continuous variables were analyzed using Student'st and Bland-Altman plots performed to analyze measurements obtained from both examinations.

Results: Eleven patients underwent both examinations. Type of defects included coarctation of the aorta (n=6) and tetralogy of Fallot. Average radiation dose was 19.6 mSv and average time between CT and MRI was 99 ± 160 days. Luminal diameters of stented vessels correlated closely between TSE MRI and CT (r(2)=.85) with a bias toward overestimation with MRI (mean 22.4 ± 4.3mm and 20.9 ± 3.7 mm, p<.01).

Conclusion: This novel 3D respiratory gated TSE MR technique provides a feasible method to reduce metallic artifact and improve visualization of stented segments and surrounding anatomic structures without exposure to radiation.
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http://dx.doi.org/10.1016/j.ijcard.2011.01.050DOI Listing
July 2012

A new approach to autocalibrated dynamic parallel imaging based on the Karhunen-Loeve transform: KL-TSENSE and KL-TGRAPPA.

Magn Reson Med 2011 Jun 19;65(6):1786-92. Epub 2011 Jan 19.

Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio 43210, USA.

TSENSE and TGRAPPA are autocalibrated parallel imaging techniques that can improve the temporal resolution and/or spatial resolution in dynamic magnetic resonance imaging applications. In its original form, TSENSE uses temporal low-pass filtering of the undersampled frames to create the sensitivity map. TGRAPPA uses a sliding-window moving average when finding the autocalibrating signals. Both filtering methods are suboptimal in the least-squares sense and may give rise to mismatches between the undersampled k-space raw data and the corresponding coil sensitivities. Such mismatches may result in aliasing artifacts when imaging patients with heavy breathing, as in real-time imaging of wall motion by MRI following a treadmill exercise stress test. In this study, we demonstrate the use of an optimal linear filter, i.e., the Karhunen-Loeve transform filter, to estimate the channel sensitivity for TSENSE and acquire the autocalibration signals for TGRAPPA. Phantom experiments show that the new reconstruction method has comparable signal-to-noise ratio performance to traditional TSENSE/TGRAPPA reconstruction. In vivo real-time cardiac cine experiments performed in five healthy volunteers post-exercise during rapid respiration show that the new method significantly reduces the chest wall aliasing artifacts caused by respiratory motion (P < 0.001).
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http://dx.doi.org/10.1002/mrm.22766DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3097269PMC
June 2011

Carotid arterial wall MRI at 3T using 3D variable-flip-angle turbo spin-echo (TSE) with flow-sensitive dephasing (FSD).

J Magn Reson Imaging 2010 Mar;31(3):645-54

Department of Radiology, Northwestern University, Chicago, Illinois 60611, USA.

Purpose: To evaluate the effectiveness of flow-sensitive dephasing (FSD) magnetization preparation in improving blood signal suppression of three-dimensional (3D) turbo spin-echo (TSE) sequence (SPACE) for isotropic high-spatial-resolution carotid arterial wall imaging at 3T.

Materials And Methods: The FSD-prepared SPACE sequence (FSD-SPACE) was implemented by adding two identical FSD gradient pulses right before and after the first refocusing 180 degrees -pulse of the SPACE sequence in all three orthogonal directions. Nine healthy volunteers were imaged at 3T with SPACE, FSD-SPACE, and multislice T2-weighted 2D TSE coupled with saturation band (SB-TSE). Apparent carotid wall-lumen contrast-to-noise ratio (aCNR(w-l)) and apparent lumen area (aLA) at the locations with residual-blood (rb) signal shown on SPACE images were compared between SPACE and FSD-SPACE. Carotid aCNR(w-l) and lumen (LA) and wall area (WA) measured from FSD-SPACE were compared to those measured from SB-TSE.

Results: Plaque-mimicking flow artifacts identified in seven carotids on SPACE images were eliminated on FSD-SPACE images. The FSD preparation resulted in slightly reduced aCNR(w-l) (P = 0.025), but significantly improved aCNR between the wall and rb regions (P < 0.001) and larger aLA (P < 0.001). Compared to SB-TSE, FSD-SPACE offered comparable aCNR(w-l) with much higher spatial resolution, shorter imaging time, and larger artery coverage. The LA and WA measurements from the two techniques were in good agreement based on intraclasss correlation coefficient (0.988 and 0.949, respectively; P < 0.001) and Bland-Altman analyses.

Conclusion: FSD-SPACE is a time-efficient 3D imaging technique for carotid arterial wall with superior spatial resolution and blood signal suppression.
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http://dx.doi.org/10.1002/jmri.22058DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2841222PMC
March 2010
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