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Hu Cheng

Publications and source records attributed to Hu Cheng.

9 recordsLinked to original sources
PubMed2006

SmartPhantom--an fMRI simulator.

Many informatics tools have emerged to process the voluminous and complex data generated by functional magnetic resonance imaging (fMRI). The interpretation of fMRI exams is largely determined by these tools. However, their performance is hard to evaluate because there is no independent means of calibration. A novel fMRI calibration system called SmartPhantom has been developed to simulate functional blood oxygen level dependent (BOLD) imaging. SmartPhantom contains a quadrature radio frequency coil, comprising two perpendicular planar loops that can be externally activated or deactivated. The system is able to produce reasonably uniform signal enhancements in a calibration sample surrounded by the two loops during an MRI scan. The enhancement is controlled well in both magnitude and predefined timing and produces BOLD-like signals. Characteristics of SmartPhantom are discussed in detail, followed by a comparison of fMRI informatics tools. Two fMRI data sets are acquired with the SmartPhantom. One with high signal-to-noise ratio provides the calibration. Another with lower SNR is input into three software packages (BrainVoyager, FSL and Statistical Parametric Mapping 2) for data preprocessing and statistical analysis. Results from the three packages are compared in both sensitivity of detecting the activation and correlation between the predicted activation and calibration.

Calibration↗
PubMed2006

Magnetic resonance imaging image intensity correction with extrapolation and adaptive smoothing.

A significant problem in magnetic resonance imaging (MRI) is the inhomogeneity of the image resulting from a number of factors that are hardware related. The obtained image can be treated as the true image multiplied by a signal modulator, which is usually smooth across the image. A class of MR image intensity correction methods extracts the slowly varying component from the image with low-pass filtering or smoothing to approximate the signal modulator. This usually causes the edge enhancement artifact in the corrected image. A novel method of extrapolating the image in advance is proposed to reduce this effect significantly. Closest point algorithm is implemented to minimize the calculation time for extrapolation. To remove bright spots caused by nonuniform sensitivity profiles, a gradient-weighted smoothing method is discussed in this work. The partial differential equations based model is applied for locally adaptive smoothing. The filtered gradient of the corrupted image is used as the weight for smoothing. Phantom and clinical data collected on various MRI systems are used for evaluation of our method. These experimental results show that the proposed method solves the edge enhancement and bright spots problem effectively and robustly.

Algorithms↗
PubMed2004

Tolerance of MRI procedures by the oldest old.

OBJECTIVES: The study aimed to evaluate the feasibility and discomfort of magnetic resonance imaging (MRI) procedures in the oldest-old subjects (age > 90 years) using a survey design in a university-affiliated neuroimaging research center. PARTICIPANTS: Forty-one community-dwelling, elderly subjects were considered for participation. Twenty-nine of them underwent voluntary, extensive MRI scanning (up to 1 h) as part of a project on brain function in the oldest old. Thirteen oldest old (OO, range 90-93 years, mean 92 years) were compared to 16 young old (YO, range 72-80 years, mean 76 years). MEASUREMENTS: Likert-style questionnaire on satisfaction following extensive MRI scanning session (up to 1 h) was administered. Data were analyzed by an analysis of variance (gender by age group). RESULTS: All subjects reported positive experiences with no significant difficulties or concerns. There were minor differences in some rated items, with the OO and males slightly less comfortable than YO and females, respectively. Overall, the OO tolerated the procedures as well as the YO. CONCLUSION: Very long MRI sessions are feasible, even in the oldest-old subjects, and are not associated with any significant discomfort. Prior screening and thorough education of the subjects probably help to minimize anxiety and dropout.

Adolescent↗
PubMed2003

[A study on biomarkers of styrene].

OBJECTIVE: To study the biomarkers of styrene and to provide theoretical basis for bio-monitoring of styrene. METHODS: Urinary mandalic acid (MA), phenylglyoxalic acid (PGA) and mercapturic acid (MUA) of styrene were examined by high performance liquid chromatography (HPLC). RESULTS: The correlation regression equations between exposure dose and MA, PGA and MUA level in morning urinary samples were: ŷ = 2.58x + 70.82; ŷ = 1.66x + 37.42; ŷ = 0.05x + 0.55 respectively. The correlation regression equations between exposure dose and MA, PGA and MUA level in post-shift urinary samples were: ŷ = 1.85x + 89.02; ŷ = 1.33x + 4.32; ŷ = 0.04x + 0.68 respectively. All showed close dose-response relationship. CONCLUSIONS: The level of MA, PGA and MUA in morning or post-shift urinary samples may be used as bio-monitoring indexes of styrene.

Acetylcysteine↗
PubMed2002

Environmental effects on phosphoryl group bonding probed by vibrational spectroscopy: implications for understanding phosphoryl transfer and enzymatic catalysis.

We have used vibrational spectroscopy to study bonding in monosubstituted dianionic phosphates, both to learn more about basic properties intrinsic to this important class of biological substrates and to assess the ability of vibrational spectroscopy to provide a "sensor" or probe of the local environment experienced by the phosphoryl group. We examined the bonding properties of the phosphoryl group via vibrational spectroscopy for a series of compounds in which the phosphoryl substituent was varied systematically and extensively. A broad linear correlation of the bridging P-O(R) bond length and the pK(a) of the substituent alcohol was observed. The results indicate that the P-O(R) bond changes by only approximately 0.04 A with alcohol substituents that vary in pK(a) by approximately 12 units, suggesting that phosphoryl group bonding responds in a subtle but regular manner to changes in the local environment. We also determined the effect on the phosphoryl bonding from changes in the solvent environment. Addition of dimethyl sulfoxide (DMSO) elongates the bridging bond, presumably as a result of lessened solvation to the nonbridging oxygens and conservation of bond order to phosphorus. Finally, we have addressed the relationship between ground-state bonding properties and reactivity, as changing the leaving group substituent and adding DMSO have large rate effects, and it was previously proposed that lengthening of the bond to be broken is the cause of the increased reactivity. The results herein suggest, however, that the change in the bridging bond energy is small compared to the changes in energy that accompany the observed reactivity differences. Further analysis indicates that electrostatic interactions can provide a common driving force underlying both bond lengthening and the observed rate increases. We suggest that ground-state distortions of substrates bound to enzymes can provide a readout of the electrostatic active site environment, an environment that is otherwise difficult to assess.

Binding Sites↗
PubMed2002

Physical properties of compounds promoting oral delivery of macromolecular drugs.

The spectroscopic and solution properties of a series of amidated acids (delivery agents), which promote the gastrointestinal absorption of USP heparin and other drugs that show poor oral bioavailability, are investigated using Raman and NMR spectroscopy. The results show evidence for self-association at low concentrations of delivery agents that increases as the concentration of the delivery agent is increased. The self-associate is characterized by ring-ring stacking interactions, and the best geometrical arrangement for the stacking is the parallel-shifted arrangement of the rings. In addition, the amide group participates in the formation of intermolecular hydrogen bonds in the self-associate. Unlike the rigid ring, the tails of these delivery agents remain relatively flexible in the self-associate. It is suggested that the limited solubility of the delivery agents at physiological pH arises from a percentage of protonated carboxyls. Their presence promotes the formation of intermolecular hydrophobic and ring stacking interactions, which are otherwise weakened by an ionized carboxyl group.

Acids↗
PubMed2002

Interactions of amidated acids with heparin.

Raman and NMR studies are performed to characterize the solution structures of complexes between heparin and a group of amidated acids, which act as delivery agents that facilitate the gastrointestinal absorption of orally administered heparin. At concentrations typically employed for the oral drug delivery of heparin, the contact points between heparin complexed with the delivery agents include points near the OH groups of heparin. The results suggest that heparin interacts rather nonspecifically with the amidated acids as monomers and with self-associated complexes of the delivery agents. It is also found that the carboxyl groups of at least one of the bioactive delivery agents easily protonates when it forms complexes with itself or heparin. This attribute may be one reason why this class of compounds is effective in the oral delivery of heparin.

Acids↗
PubMed2002

Leukocyte mitochondria alterations after aerobic exercise in trained human subjects.

UNLABELLED: Exercise is associated with intensity-dependent immune disturbances. Leukocyte mitochondrial alterations and apoptosis may contribute to this phenomenon. PURPOSE: To investigate the effects of different intensities of aerobic exercise (AE) on leukocyte mitochondrial transmembrane potential (MTP) and the propensity of apoptosis. METHODS: Blood samples were collected from 12 subjects who performed AE for 3 consecutive days (35% maximal oxygen consumption (VO2max)). Leukocyte MTP and apoptosis were measured by flow cytometry. The subjects performed two additional sessions of AE of higher intensities (60% and 85% VO2max) with an intervening 4-wk washout period. The measurements were repeated during each session. RESULTS: Leukocyte MTP declined during daily, repetitive AE at an intensity of 60% and 85% VO2max. Similar changes were not found during a more moderate AE (35% VO2max). Leukocytes increased their propensity of apoptosis a period (3-5 d) after the start of the AE. CONCLUSION: High-intensity AE has accumulative effects on the mitochondrial energization status and vitality of peripheral blood leukocytes. Leukocyte MTP is a potentially applicable indicator for monitoring immune distress due to overtraining.

Adult↗