Washington University School of Medicine
Campus Box 8131
510 South Kingshighway
St. Louis, MO 63110
Associate Professor of Radiology
Associate Director, Center for Clinical Imaging Research
Our primary research interest is to develop novel imaging methods to deepen our understanding on pathophysiology and improve clinical diagnosis and patient management. We have focused on quantitative MR and PET/MR imaging. Our expertise are in MR physics, MR pulse sequence design and programming, image reconstruction, data processing and statistical analysis.
We have extensive experience in MR oxygen metabolic imaging, perfusion (Dynamic Susceptibility Contrast and Arterial Spin Labeling) imaging, susceptibility weighted imaging (SWI), diffusion tensor imaging (DTI), phase contrast imaging, MR spectroscopy, quantitative T1 and T2 measurements, and attenuation and motion correction for simultaneous PET/MR measurements.
Cerebral oxygenation measurements using MRI and its validation using simultaneous PET/MR
Abnormal oxygen metabolism occurs in neurological diseases such as ischemic stroke, intracranial stenosis, carotid occlusion, moyamoya disease, cerebral trauma, and brain tumors. It has been demonstrated that elevation of oxygen extraction fraction (OEF) in brain tissue portends a 6-7 fold increased risk of subsequent stroke in patients with chronic atherosclerotic carotid artery occlusion. Moreover, during acute ischemic stroke, “misery perfusion”, marked by an elevation of OEF and decreased blood flow, has been used as an indicator of “at-risk” tissue that is a target of therapeutic treatments. On the other hand, indiscriminate treatment without screening for “at-risk” tissue may lead to serious treatment-related complications. Therefore, a reliable and non-invasive measure of OEF that can be obtained with a routine clinical setup will have a great impact on appropriate patient diagnosis and treatment. In this study, the overall objectives are (1) to develop a novel MR OEF measurement that is rapid and robust to meet the need of clinical studies; and (2) to validate the MR OEF measurements using simultaneous O15 PET measurements in patients with focal pathology.
MR-Derived Cerebral Blood Flow and Oxygen Metabolism to Stratify Stroke Risk in Childhood Sickle Cell Disease
As the most common inherited blood disorder, sickle cell disease (SCD) affects one in 400 African-Americans. Among SCD complications, ischemic stroke is common and disabling, beginning in infancy — “overt” strokes cause acute neurological deficits and “silent” strokes manifest as intellectual decline. The current transcranial Doppler ultrasound (TCD) screening mechanism is insensitivity for predicting those at risk for silent strokes. Moreover, nearly half of children continue to have recurrent overt strokes, silent strokes, and/or progressive vasculopathy, despite screening and being placed on transfusions. In this study, we hypothesize that the brain’s hemodynamic and metabolic compensatory responses to reduced blood oxygen content in SCD will reveal mechanisms leading to ischemic stroke. We will determine if MR-derived cerebral blood flow (CBF) and oxygen extraction fraction (OEF), as metrics of this hemodynamic and metabolic stress, may provide novel tools to stratify stroke risk in SCD children so that treatment may be individualized, identifying those at highest risk for more aggressive therapies, while sparing those at lower risk any unnecessary adverse effects of treatment.
PET/MR attenuation correction and motion correction and the clinical applications
Simultaneous PET/MR imaging offers unprecedented opportunities to synergize the physiological and molecular imaging capability of PET and the excellent anatomical and functional imaging capability of MR. This instrument opens up many possibilities for previously impossible investigations for tumor, Alzheimer disease, Parkinson’s disease, and Epilepsy. Simultaneous PET/MR presents both unique challenges (in attenuation correction) and opportunities (in motion correction) in PET/MR. We are developing novel MR techniques for PET/MR attenuation correction (MRAC) method for brain and for pelvis. We have developed both atlas and UTE based MRAC methods and tested them extensively in brain studies. We will continue to develop approaches for MRAC in pelvic PET imaging. Simultaneous PET/MR imaging offers a unique opportunity for motion correction. We will develop a free-breathing, self-gated MR technique for respiratory motion correction in upper abdominal PET/MR imaging and respiratory and cardiac motion in heart PET/MR imaging.
- An H*, Ford AL*, Eldeniz C, Chen Y, Vo KD, Zhu H, Powers WJ, Lin W, Lee JM. Reperfusion Beyond 6 Hours Reduces Infarct Probability in Moderately Ischemic Brain Tissue, Stroke. 2016 Jan;47(1):99-105.10.1161/STROKEAHA.115.010656. Epub 2015 Nov 19. PMID: 26585394 (Manuscript was features on the 2016 January Stroke cover)
- Cihat Eldeniz, Jürgen Finsterbusch, Weili Lin and Hongyu An, TOWERS: T-One with Enhanced Robustness and Speed, Magn Reson Med. 2015 Jul 31. doi: 10.1002/mrm.25864. [Epub ahead of print], PMID: 26228530.
- Juttukonda MR, Mersereau BG, Chen Y, Su Y, Rubin BG, Benzinger TL, Lalush DS, An H. MR-based attenuation correction for PET/MRI neurological studies with continuous-valued attenuation coefficients for bone through a conversion from R2* to CT-Hounsfield units. Neuroimage. 2015 Mar 14;112:160-168. doi: 10.1016/j.neuroimage.2015.03.009. [Epub ahead of print], PMID: 25776213
- An H*, Ford AL*, Chen Y, Zhu H, Ponisio R, Kumar G, Modir-Shanechi A, Khoury N, Vo KD, Williams JA, Derdeyn CP, Diringer MN, Panagos P, Powers WJ, Lee JM†, Lin W†. Defining the Ischemic Penumbra using Magnetic Resonance Oxygen Metabolic Index. Stroke. 2015 Apr;46(4):982-8. doi: 10.1161/STROKEAHA.114.008154. Epub 2015 Feb 26. PMID: 25721017.
- Yasheng Chen, Meher Juttukonda, Yi Su, Tammie Benzinger, Brian G Rubin, Yueh Z Lee, Weili Lin, Dinggang Shen, David Lalush, and Hongyu An. Probabilistic Air Segmentation and Sparse Regression estimated pseudo CT for PET/MR attenuation correction, Radiology, 2014 Dec 17:140810. [Epub ahead of print] PMID: 25521778
- An H, Ford AL, Vo KD, Liu Q, Chen Y, Lee JM, Lin W. Imaging Oxygen Metabolism In Acute Stroke Using MRI. Curr Radiol Rep. 2014 Mar 1;2(3):39. PMID: 24707451
- Yasheng Chen, Hongtu Zhu, Hongyu An, Diane Armao, Dinggang Shen, John H. Gilmore, Weili Lin, More insights into early brain development through statistical analyses of eigen-structural elements of diffusion tensor imaging using multivariate adaptive regression splines, Brain Struct Funct. 2014 Mar;219(2):551-69. doi: 10.1007/s00429-013-0517-7. Epub 2013 Mar 1. PMID: 23455648
- Qingwei Liu, Yu Cai, Weili Lin, Gregory H. Turner, Hongyu An, A Magnetic Resonance (MR) Compatible Selective Brain Temperature Manipulation System for Pre-clinical Study, Medical Devices: Evidence and Research,2012:5,13–22. PMID: 23166453
- Hongyu An, Souvik Sen, Yasheng Chen, William J Powers, and Weili Lin, Noninvasive measurements of cerebral blood flow, oxygen extraction fraction, and oxygen metabolic index in human with inhalation of air and carbogen using Magnetic Resonance Imaging, Translational Stroke Research, 2012, 3(2):246–254, DOI 10.1007/s12975-011-0142-9
- Yu Cai; Matthew S. McMurray; Ipek Oguz; Hong Yuan; Martin A Styner; Weili Lin; Josephine Johns; and Hongyu An, High resolution 3D Diffusion tensor imaging to study brain white matter development in live neonatal rats, Frontiers in Child and Neurodevelopmental Psychiatry, 2011; 2:54. Epub 2011 Oct 10. PMID: 22013426
- Hongyu An*, Andria L. Ford*, Katie Vo, Cihat Eldeniz, Rosana Ponisio, Hongtu Zhu, Yimei Li, Yasheng Chen, William J. Powers, Jin-Moo Lee, and Weili Lin, Early Changes of Tissue Perfusion after tPA in Hyperacute Ischemic Stroke, Stroke. 2011;42:65-72, published online Dec 9, 2010, PMID: 21148444
- An H, Liu Q, Chen Y, Lin W. Evaluation of MR-Derived Cerebral Oxygen Metabolic Index in Experimental Hyperoxic Hypercapnia, Hypoxia, and Ischemia. Stroke. 2009 Jun;40(6):2165-72. Epub 2009 Apr 9.
- H An and W Lin. Impact of intravascular signal on quantitative measures of cerebral oxygen extraction and blood volume under normo- and hypercapnic conditions using an asymmetric spin echo approach, Magnetic Resonance in Medicine, 50:708–716, 2003
- H An and W Lin. Cerebral Oxygen Extraction Fraction and Cerebral Venous Blood Volume Measurements Using Magnetic Resonance Imaging: Effects of Magnetic Field Variation, Magnetic Resonance in Medicine 47:958-966, 2002.
- H An, W Lin, Quantitative Measurement of Cerebral Blood Oxygen Saturation Using Magnetic Resonance Imaging, Journal of Cerebral Blood Flow and Metabolism, 20: 1225-1236, 2000.
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For an up-to-date list of Dr. An's publications please see her entry on PubMed.