Person: Sun, Phillip
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Phillip
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Sun, Phillip
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Publication Quantitative chemical exchange saturation transfer (CEST) MRI of glioma using Image Downsampling Expedited Adaptive Least-squares (IDEAL) fitting(Nature Publishing Group UK, 2017) Zhou, Iris Yuwen; Wang, Enfeng; Cheung, Jerry S.; Zhang, Xiaoan; Fulci, Giulia; Sun, PhillipChemical Exchange Saturation Transfer (CEST) MRI is sensitive to dilute metabolites with exchangeable protons, allowing tissue characterization in diseases such as acute stroke and tumor. CEST quantification using multi-pool Lorentzian fitting is challenging due to its strong dependence on image signal-to-noise ratio (SNR), initial values and boundaries. Herein we proposed an Image Downsampling Expedited Adaptive Least-squares (IDEAL) fitting algorithm that quantifies CEST images based on initial values from multi-pool Lorentzian fitting of iteratively less downsampled images until the original resolution. The IDEAL fitting in phantom data with superimposed noise provided smaller coefficient of variation and higher contrast-to-noise ratio at a faster fitting speed compared to conventional fitting. We further applied the IDEAL fitting to quantify CEST MRI in rat gliomas and confirmed its advantage for in vivo CEST quantification. In addition to significant changes in amide proton transfer and semisolid macromolecular magnetization transfer effects, the IDEAL fitting revealed pronounced negative contrasts of tumors in the fitted CEST maps at 2 ppm and −1.6 ppm, likely arising from changes in creatine level and nuclear overhauser effects, which were not found using conventional method. It is anticipated that the proposed method can be generalized to quantify MRI data where SNR is suboptimal.Publication A General MRI-CEST Ratiometric Approach for pH Imaging: Demonstration of in Vivo pH Mapping with Iobitridol(American Chemical Society, 2014) Longo, Dario L.; Sun, Phillip; Consolino, Lorena; Michelotti, Filippo C.; Uggeri, Fulvio; Aime, SilvioChemical exchange saturation transfer (CEST) is a novel contrast mechanism for magnetic resonance imaging (MRI). CEST MRI selectively saturates exchangeable protons that are transferred to MRI-detectable bulk water signal. MRI-CEST (pH)-responsive agents are probes able to map pH in the microenvironment in which they distribute. To minimize the confounding effects of contrast agent concentration, researchers have developed ratiometric CEST imaging, which investigates contrast agents containing multiple magnetically non-equivalent proton groups, whose prototropic exchange have different pH responses. However, conventional ratiometric CEST MRI imposes stringent requirements on the selection of CEST contrasts agents. In this study, a novel ratiometric pH MRI method based on the analysis of CEST effects under different radio frequency irradiation power levels was developed. The proposed method has been demonstrated using iobitridol, an X-ray contrast agent analog of iopamidol but containing a single set of amide protons, both in vitro and in vivo.Publication Developing a Multiscale, Multi-Resolution Agent-Based Brain Tumor Model by Graphics Processing Units(BioMed Central, 2011) Zhang, Le; Jiang, Beini; Wu, Yukun; Strouthos, Costas; Sun, Phillip; Su, Jing; Zhou, XiaoboMultiscale agent-based modeling (MABM) has been widely used to simulate Glioblastoma Multiforme (GBM) and its progression. At the intracellular level, the MABM approach employs a system of ordinary differential equations to describe quantitatively specific intracellular molecular pathways that determine phenotypic switches among cells (e.g. from migration to proliferation and vice versa). At the intercellular level, MABM describes cell-cell interactions by a discrete module. At the tissue level, partial differential equations are employed to model the diffusion of chemoattractants, which are the input factors of the intracellular molecular pathway. Moreover, multiscale analysis makes it possible to explore the molecules that play important roles in determining the cellular phenotypic switches that in turn drive the whole GBM expansion. However, owing to limited computational resources, MABM is currently a theoretical biological model that uses relatively coarse grids to simulate a few cancer cells in a small slice of brain cancer tissue. In order to improve this theoretical model to simulate and predict actual GBM cancer progression in real time, a graphics processing unit (GPU)-based parallel computing algorithm was developed and combined with the multi-resolution design to speed up the MABM. The simulated results demonstrated that the GPU-based, multi-resolution and multiscale approach can accelerate the previous MABM around 30-fold with relatively fine grids in a large extracellular matrix. Therefore, the new model has great potential for simulating and predicting real-time GBM progression, if real experimental data are incorporated.Publication Magnetic Resonance Characterization of Ischemic Tissue Metabolism(Bentham Open, 2011) Cheung, Jerry S; Wang, Xiaoying; Sun, PhillipMagnetic resonance imaging (MRI) and spectroscopy (MRS) are versatile diagnostic techniques capable of characterizing the complex stroke pathophysiology, and hold great promise for guiding stroke treatment. Particularly, tissue viability and salvageability are closely associated with its metabolic status. Upon ischemia, ischemic tissue metabolism is disrupted including altered metabolism of glucose and oxygen, elevated lactate production/accumulation, tissue acidification and eventually, adenosine triphosphate (ATP) depletion and energy failure. Whereas metabolism impairment during ischemic stroke is complex, it may be monitored non-invasively with magnetic resonance (MR)-based techniques. Our current article provides a concise overview of stroke pathology, conventional and emerging imaging and spectroscopy techniques, and data analysis tools for characterizing ischemic tissue damage.