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Nguyen, Christopher

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Nguyen

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Christopher

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Nguyen, Christopher
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    Atherosclerosis T1-weighted characterization (CATCH): evaluation of the accuracy for identifying intraplaque hemorrhage with histological validation in carotid and coronary artery specimens
    (BioMed Central, 2018) Liu, Wen; Xie, Yibin; Wang, Chuan; Du, Yanni; Nguyen, Christopher; Wang, Zhenjia; Fan, Zhaoyang; Dong, Li; Liu, Yi; Bi, Xiaoming; An, Jing; Gu, Chengxiong; Yu, Wei; Li, Debiao
    Background: Coronary high intensity plaques (CHIPs) detected using cardiovascular magnetic resonance (CMR) coronary atherosclerosis T1-weighted characterization with integrated anatomical reference (CATCH) have been shown to be positively associated with high-risk morphology observed on intracoronary optical coherence tomography (OCT). This study sought to validate whether CHIPs detected on CATCH indicate the presence of intraplaque hemorrhage (IPH) through ex vivo imaging of carotid and coronary plaque specimens, with histopathology as the standard reference. Methods: Ten patients scheduled to undergo carotid endarterectomy underwent CMR with the conventional T1-weighted (T1w) sequence. Eleven carotid atherosclerotic plaques removed at carotid endarterectomy and six coronary artery endarterectomy specimens removed from patients undergoing coronary artery bypass grafting (CABG) were scanned ex vivo using both the conventional T1w sequence and CATCH. Both in vivo and ex vivo images were examined for the presence of IPH. The sensitivity, specificity, and Cohen Kappa (k) value of each scan were calculated using matched histological sections as the reference. k value between each scan in the discrimination of IPH was also computed. Results: A total of 236 in vivo locations, 328 ex vivo and matching histology locations were included for the analysis. Sensitivity, specificity, and k value were 76.7%, 95.3%, and 0.75 for in vivo T1w imaging, 77.2%, 97.4%, and 0.78 for ex vivo T1w imaging, and 95.0%, 92.1%, and 0.84 for ex vivo CATCH, respectively. Moderate agreement was reached between in vivo T1w imaging, ex vivo T1w imaging, and ex vivo CATCH for the detection of IPH: between in vivo T1w imaging and ex vivo CATCH (k = 0.68), between ex vivo T1w imaging and ex vivo CATCH (k = 0.74), between in vivo T1w imaging and ex vivo T1w imaging (k = 0.83). None of the coronary artery plaque locations showed IPH. Conclusion: This study demonstrated that carotid CHIPs detected by CATCH can be used to assess for IPH, a high-risk plaque feature.
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    Three-dimensional Cardiomyocytes Structure Revealed By Diffusion Tensor Imaging and Its Validation Using a Tissue-Clearing Technique
    (Nature Publishing Group UK, 2018) Lee, Sang-Eun; Nguyen, Christopher; Yoon, Jongjin; Chang, Hyuk-Jae; Kim, Sekeun; Kim, Chul Hoon; Li, Debiao
    We characterized the microstructural response of the myocardium to cardiovascular disease using diffusion tensor imaging (DTI) and performed histological validation by intact, un-sectioned, three-dimensional (3D) histology using a tissue-clearing technique. The approach was validated in normal (n = 7) and ischemic (n = 8) heart failure model mice. Whole heart fiber tracking using DTI in fixed ex-vivo mouse hearts was performed, and the hearts were processed with the tissue-clearing technique. Cardiomyocytes orientation was quantified on both DTI and 3D histology. Helix angle (HA) and global HA transmurality (HAT) were calculated, and the DTI findings were confirmed with 3D histology. Global HAT was significantly reduced in the ischemic group (DTI: 0.79 ± 0.13°/% transmural depth [TD] and 3D histology: 0.84 ± 0.26°/%TD) compared with controls (DTI: 1.31 ± 0.20°/%TD and 3D histology: 1.36 ± 0.27°/%TD, all p < 0.001). On direct comparison of DTI with 3D histology for the quantitative assessment of cardiomyocytes orientation, significant correlations were observed in both per-sample (R2 = 0.803) and per-segment analyses (R2 = 0.872). We demonstrated the capability and accuracy of DTI for mapping cardiomyocytes orientation by comparison with the intact 3D histology acquired by tissue-clearing technique. DTI is a promising tool for the noninvasive characterization of cardiomyocytes architecture.
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    Optimized CEST cardiovascular magnetic resonance for assessment of metabolic activity in the heart
    (BioMed Central, 2017) Zhou, Zhengwei; Nguyen, Christopher; Chen, Yuhua; Shaw, Jaime L.; Deng, Zixin; Xie, Yibin; Dawkins, James; Marbán, Eduardo; Li, Debiao
    Background: Previous studies have linked cardiac dysfunction to loss of metabolites in the creatine kinase system. Chemical exchange saturation transfer (CEST) is a promising metabolic cardiovascular magnetic resonance (CMR) imaging technique and has been applied in the heart for creatine mapping. However, current limitations include: (a) long scan time, (b) residual cardiac and respiratory motion, and (c) B0 field variations induced by respiratory motion. An improved CEST CMR technique was developed to address these problems. Methods: Animals with chronic myocardial infarction (N = 15) were scanned using the proposed CEST CMR technique and a late gadolinium enhancement (LGE) sequence as reference. The major improvements of the CEST CMR technique are: (a) Images were acquired by single-shot FLASH, significantly increasing the scan efficiency. (b) All images were registered to reduce the residual motion. (c) The acquired Z-spectrum was analyzed using 3-pool-model Lorentzian-line fitting to generate CEST signal, reducing the impact of B0 field shifting due to respiratory motion. Feasibility of the technique was tested in a porcine model with chronic myocardial infarction. CEST signal was measured in the scar, border zone and remote myocardium. Initial studies were performed in one patient. Results: In all animals, healthy remote myocardial CEST signal was elevated (0.16 ± 0.02) compared to infarct CEST signal (0.09 ± 0.02, P < 0.001) and the border zone (0.12 ± 0.02, P < 0.001). For both animal and patient studies, the hypointense regions in the CEST contrast maps closely match the bright areas in the LGE images. Conclusions: The proposed CEST CMR technique was developed to address long scan times, respiratory and cardiac motion, and B0 field variations. Lower CEST signal in bright region of the LGE image is consistent with the fact that myocardial infarction has reduced metabolic activity.