Nan-kuei Chen
Associate Professor, BIO5 Institute
Associate Professor, Biomedical Engineering
Primary Department
Department Affiliations
(520) 626-0060
Research Interest
I am an MR physicist with extensive expertise in fast image acquisition methodology, pulse sequence design, and artifact correction for neuro MRI. In the past 18 years, I have developed novel approaches effectively addressing various types of challenging MRI artifacts, ranging from echo-planar imaging (EPI) geometric distortions, to susceptibility effect induced signal loss, to EPI Nyquist artifact, to motion-induced phase errors and aliasing artifacts in interleaved EPI based diffusion-weighted imaging. I am the original developer of multiplexed sensitivity encoded (MUSE) MRI, which can measure human brain connectivity in vivo at high spatial-resolution and accuracy, as shown in the publications listed below. More generally, my research involves the application of MR protocols in translational contexts. I have served as PI on NIH-funded R01, R21 and R03 grants, and have had extensive experience as a co-investigator on NIH-funded projects. The current focus of my research includes: * Development of high-throughput and motion-immune clinical MRI for imaging challenging patient populations * Imaging of neuronal connectivity networks for studies of neurological diseases * High-fidelity and multi-contrast MRI guided intervention * Characterization and correction of MRI artifacts * Signal processing and algorithm development * MRI studies of human development

Publications

Wu, M., Chang, H., Chao, T., & Chen, N. (2015). Efficient imaging of midbrain nuclei using inverse double-echo steady-state acquisition. Medical physics, 42(7), 4367-74.

Imaging of midbrain nuclei using T2- or T2*-weighted MRI often entails long echo time, leading to long scan time. In this study, an inverse double-echo steady-state (iDESS) technique is proposed for efficiently depicting midbrain nuclei.

Meade, C. S., Cordero, D. M., Hobkirk, A. L., Metra, B. M., Chen, N., & Huettel, S. A. (2016). Compensatory activation in fronto-parietal cortices among HIV-infected persons during a monetary decision-making task. Human brain mapping, 37(7), 2455-67.

HIV infection can cause direct and indirect damage to the brain and is consistently associated with neurocognitive disorders, including impairments in decision-making capacities. The tendency to devalue rewards that are delayed (temporal discounting) is relevant to a range of health risk behaviors. Making choices about delayed rewards engages the executive control network of the brain, which has been found to be affected by HIV. In this case-control study of 18 HIV-positive and 17 HIV-negative adults, we examined the effects of HIV on brain activation during a temporal discounting task. Functional MRI (fMRI) data were collected while participants made choices between smaller, sooner rewards and larger, delayed rewards. Choices were individualized based on participants' unique discount functions, so each participant experienced hard (similarly valued), easy (disparately valued), and control choices. fMRI data were analyzed using a mixed-effects model to identify group-related differences associated with choice difficulty. While there was no difference between groups in behavioral performance, the HIV-positive group demonstrated significantly larger increases in activation within left parietal regions and bilateral prefrontal regions during easy trials and within the right prefrontal cortex and anterior cingulate during hard trials. Increasing activation within the prefrontal regions was associated with lower nadir CD4 cell count and risk-taking propensity. These results support the hypothesis that HIV infection can alter brain functioning in regions that support decision making, providing further evidence for HIV-associated compensatory activation within fronto-parietal cortices. A history of immunosuppression may contribute to these brain changes. Hum Brain Mapp 37:2455-2467, 2016. © 2016 Wiley Periodicals, Inc.

Meade, C. S., Hobkirk, A. L., Towe, S. L., Chen, N. K., Bell, R. P., & Huettel, S. A. (2017). Cocaine dependence modulates the effect of HIV infection on brain activation during intertemporal decision making. Drug and alcohol dependence, 178, 443-451.

Both HIV infection and chronic cocaine use alter the neural circuitry of decision making, but the interactive effects of these commonly comorbid conditions have not been adequately examined. This study tested how cocaine moderates HIV-related neural activation during an intertemporal decision-making task.

Bruce, I. P., Chang, H. C., Petty, C., Chen, N. K., & Song, A. W. (2017). 3D-MB-MUSE: A robust 3D multi-slab, multi-band and multi-shot reconstruction approach for ultrahigh resolution diffusion MRI. NeuroImage, 159, 46-56.

Recent advances in achieving ultrahigh spatial resolution (e.g. sub-millimeter) diffusion MRI (dMRI) data have proven highly beneficial in characterizing tissue microstructures in organs such as the brain. However, the routine acquisition of in-vivo dMRI data at such high spatial resolutions has been largely prohibited by factors that include prolonged acquisition times, motion induced artifacts, and low SNR. To overcome these limitations, we present here a framework for acquiring and reconstructing 3D multi-slab, multi-band and interleaved multi-shot EPI data, termed 3D-MB-MUSE. Through multi-band excitations, the simultaneous acquisition of multiple 3D slabs enables whole brain dMRI volumes to be acquired in-vivo on a 3 T clinical MRI scanner at high spatial resolution within a reasonably short amount of time. Representing a true 3D model, 3D-MB-MUSE reconstructs an entire 3D multi-band, multi-shot dMRI slab at once while simultaneously accounting for coil sensitivity variations across the slab as well as motion induced artifacts commonly associated with both 3D and multi-shot diffusion imaging. Such a reconstruction fully preserves the SNR advantages of both 3D and multi-shot acquisitions in high resolution dMRI images by removing both motion and aliasing artifacts across multiple dimensions. By enabling ultrahigh resolution dMRI for routine use, the 3D-MB-MUSE framework presented here may prove highly valuable in both clinical and research applications.

Chou, Y., Chen, N., & Madden, D. J. (2013). Functional brain connectivity and cognition: effects of adult age and task demands. Neurobiology of aging, 34(8), 1925-34.

Previous neuroimaging research has documented that patterns of intrinsic (resting state) functional connectivity (FC) among brain regions covary with individual measures of cognitive performance. Here, we examined the relation between intrinsic FC and a reaction time (RT) measure of performance, as a function of age group and task demands. We obtained filtered, event-related functional magnetic resonance imaging data, and RT measures of visual search performance, from 21 younger adults (19-29 years old) and 21 healthy, older adults (60-87 years old). Age-related decline occurred in the connectivity strength in multiple brain regions, consistent with previous findings. Among 8 pairs of regions, across somatomotor, orbitofrontal, and subcortical networks, increasing FC was associated with faster responding (lower RT). Relative to younger adults, older adults exhibited a lower strength of this RT-connectivity relation and greater disruption of this relation by a salient but irrelevant display item (color singleton distractor). Age-related differences in the covariation of intrinsic FC and cognitive performance vary as a function of task demands.