Biomedical subjects

Teng-Yi Huang

Publications and source records attributed to Teng-Yi Huang.

14 recordsLinked to original sources

PubMed2006

Purified vitamin K epoxide reductase alone is sufficient for conversion of vitamin K epoxide to vitamin K and vitamin K to vitamin KH2.

More than 21 million prescriptions for warfarin are written yearly in the U.S. Despite its importance, warfarin's target, vitamin K epoxide reductase (VKOR), has resisted purification since its identification in 1972. Here, we report its purification and reconstitution. HPC4, a calcium-specific antibody that recognizes a 12-aa tag, was used to purify and identify VKOR. Partial reconstitution is achieved on the column by washing with 0.4% dioleoylphosphatidylcholine/0.4% deoxycholate. Activity is completely recovered by dialysis against a buffer containing a reducing agent but lacking dioleoylphosphatidylcholine/deoxycholate. Removal of detergent from the eluted proteins apparently facilitates liposome formation. Purified recombinant VKOR with tag is approximately 21 kDa, as expected; fully active; and > 93% pure. The concentration of warfarin for 50% inhibition is the same for purified protein and microsomes. It has been reported that VKOR is a multisubunit enzyme. Our results, however, suggest that a single peptide can accomplish both the conversion of vitamin K epoxide to vitamin K and vitamin K to reduced vitamin K. This purification will allow further characterization of VKOR in relation to other components of the vitamin K cycle and should facilitate its structural determination.

Baculoviridae↗

PubMed2006

Electron-transfer reagent anion formation via electrospray ionization and collision-induced dissociation.

A strategy is described and demonstrated for the formation of reagent anions via electrospray ionization (ESI) for electron-transfer dissociation (ETD). To circumvent difficulties associated with formation of high mass-to-charge ratio (m/z) reagent anions, it is desirable to form ETD reagents via means other than those that require reagent molecule vaporization. ESI is a candidate method, but anions that are generally generated efficiently by ESI tend to react with multiply protonated polypeptides via proton transfer. The strategy described herein involves the use of a precursor reagent molecule that ionizes efficiently via electrospray ionization and that can subsequently be converted to an ETD reagent via gas-phase dissociation. The approach is demonstrated with arenecarboxylic acids that yield strong signals associated with the deprotonated molecule and that subsequently undergo collision-induced dissociation (CID) by loss of CO(2). In the present work, triply protonated KGAILKGAILR served as a test substrate for the CID product ions to give rise to ETD. Several precursor molecules were shown to be capable of generating ETD reagents via ESI followed by CID. These included 9-anthracenecarboxylic acid, 2-fluoro-5-iodobenzoic acid, and 2-(fluoranthene-8-carbonyl)benzoic acid. The latter molecule has the most attractive set of characteristics as a precursor for a relatively high m/z ratio ETD reagent.

Amino Acid Sequence↗

PubMed2006

Homologous response regulators KvgA, KvhA and KvhR regulate the synthesis of capsular polysaccharide in Klebsiella pneumoniae CG43 in a coordinated manner.

On the basis of phenotypic analysis, the Klebsiella pneumoniae CG43 derived mutants with deletions of the gene encoding respectively the response regulators KvgA, KvhA, and KvhR were classified into two groups. Group I bacteria carrying either kvgA- or kvhR- exhibited less mucoidy, lower level of capsular polysaccharide (CPS) synthesis and higher LD50 than the parental strain. No apparent change of the group II, including kvhA- and kvhA- kvhR- mutants, was observed. However, the mucoidy of kvhA- kvhR- mutant was found to be diminished after introducing into a kvhA- expressing plasmid. Via promoter-lacZ fusion analysis, kvhA deletion was found to reduce kvhR expression. A regulatory role of KvhA for the expression of kvhR was supported further by EMSA showing a specific binding of KvhA to the putative promoter of kvhR. The promoter activity measurement and EMSA also revealed that KvgA acted as an autoregulator and an activator for the expression of kvhAS and kvhR. In addition, deletion of kvgA suppressed slightly the promoter activity of the cps-orf16-17, and the expression of all three cps transcripts orf1-2, orf3-15, and orf16-17 were reduced in the kvhR- mutant. These suggest that the three homologous response regulators interact to control, in coordination, the bacterial cps expression.

Animals↗

PubMed2006

Tensor deflection (TEND) tractography with adaptive subvoxel stepping.

PURPOSE: To develop an adaptive subvoxel stepping scheme, as an adjunct to tensor deflection (TEND) tractography, that automatically adjusts the stepping size by considering the tensor linearity to properly trace fiber bundles in regions with different degrees of tensor anisotropy. MATERIALS AND METHODS: A theoretical investigation of the TEND algorithm was performed to assess the degree of deflection of the propagation vector toward the major eigenvector. Mathematically generated phantoms (one with curved fibers and the other with crossing fibers) at wide ranges of signal-to-noise ratio (SNR), and human brain images obtained in vivo were used to test the performance of the adaptive stepping algorithm. RESULTS: The degree of deflection was found to be inversely related to the stepping size. A small stepping size was advantageous for tracing single curved fiber bundles, whereas a large stepping size was beneficial for passing through fiber crossing regions. The performance of the adaptive stepping algorithm was superior to fixed stepping in both situations, leading to an approximately 0.17 voxel of deviation in curved fibers and a nearly 100% successful tracking rate in crossing fibers at typical SNR. Human brain images demonstrated similar results. CONCLUSION: The adaptive stepping algorithm is a helpful adjunct to TEND tractography.

Algorithms↗

PubMed2006

Temporal correlation-based dynamic contrast-enhanced MR imaging improves assessment of complex pulmonary circulation in congenital heart disease.

A temporal correlation (TC) mapping method is proposed to help bolus chasing during dynamic contrast-enhanced (DCE) MRI of complex pulmonary circulation (CPC) in patients with congenital heart disease. DCE-MRI was performed on five healthy male subjects (23-24 years old) and 25 patients (nine males and 16 females, 0.25-44 years old), and TC maps were generated by performing pixel-based computation of cross-correlations to the pulmonary artery with a series of time shifts in all subjects. Qualitative and quantitative evaluations were performed in comparison with original DCE images. TC maps exhibited a better signal-to-noise ratio (SNR) by factors of 4.3 and 1.3 in the lung parenchyma, pulmonary veins, and superior artery/vein; a better intraparenchymal contrast-to-noise ratio (CNR) by factors of 1.5-5.4; and a significantly higher conspicuity in all regions except the pulmonary arteries when graded with a five-point score. TC maps evaluated by two experienced clinicians significantly added relevant information (P<0.001), and in some cases affected the final diagnosis. We conclude that TC maps facilitate bolus chasing for DCE-MRI by reducing recirculation effects and interframe fluctuations, and hence complements morphological imaging of CPC in patients with complex congenital heart disease.

Adolescent↗

PubMed2006

PROPELLER-EPI with parallel imaging using a circularly symmetric phased-array RF coil at 3.0 T: application to high-resolution diffusion tensor imaging.

A technique integrating multishot periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) and parallel imaging is presented for diffusion echo-planar imaging (EPI) at high spatial resolution. The method combines the advantages of parallel imaging to achieve accelerated sampling along the phase-encoding direction, and PROPELLER acquisition to further decrease the echo train length (ETL) in EPI. With an eight-element circularly symmetric RF coil, a parallel acceleration factor of 4 was applied such that, when combined with PROPELLER acquisition, a reduction of geometric distortions by a factor substantially greater than 4 was achieved. The resulting phantom and human brain images acquired with a 256 x 256 matrix and an ETL of only 16 were visually identical in shape to those acquired using the fast spin-echo (FSE) technique, even without field-map corrections. It is concluded that parallel PROPELLER-EPI is an effective technique that can substantially reduce susceptibility-induced geometric distortions at high field strength.

Adult↗

PubMed2005

Functional MRI using regularized parallel imaging acquisition.

Parallel MRI techniques reconstruct full-FOV images from undersampled k-space data by using the uncorrelated information from RF array coil elements. One disadvantage of parallel MRI is that the image signal-to-noise ratio (SNR) is degraded because of the reduced data samples and the spatially correlated nature of multiple RF receivers. Regularization has been proposed to mitigate the SNR loss originating due to the latter reason. Since it is necessary to utilize static prior to regularization, the dynamic contrast-to-noise ratio (CNR) in parallel MRI will be affected. In this paper we investigate the CNR of regularized sensitivity encoding (SENSE) acquisitions. We propose to implement regularized parallel MRI acquisitions in functional MRI (fMRI) experiments by incorporating the prior from combined segmented echo-planar imaging (EPI) acquisition into SENSE reconstructions. We investigated the impact of regularization on the CNR by performing parametric simulations at various BOLD contrasts, acceleration rates, and sizes of the active brain areas. As quantified by receiver operating characteristic (ROC) analysis, the simulations suggest that the detection power of SENSE fMRI can be improved by regularized reconstructions, compared to unregularized reconstructions. Human motor and visual fMRI data acquired at different field strengths and array coils also demonstrate that regularized SENSE improves the detection of functionally active brain regions.

Brain Mapping↗

PubMed2005

PROPELLER EPI: an MRI technique suitable for diffusion tensor imaging at high field strength with reduced geometric distortions.

A technique suitable for diffusion tensor imaging (DTI) at high field strengths is presented in this work. The method is based on a periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) k-space trajectory using EPI as the signal readout module, and hence is dubbed PROPELLER EPI. The implementation of PROPELLER EPI included a series of correction schemes to reduce possible errors associated with the intrinsically higher sensitivity of EPI to off-resonance effects. Experimental results on a 3.0 Tesla MR system showed that the PROPELLER EPI images exhibit substantially reduced geometric distortions compared with single-shot EPI, at a much lower RF specific absorption rate (SAR) than the original version of the PROPELLER fast spin-echo (FSE) technique. For DTI, the self-navigated phase-correction capability of the PROPELLER EPI sequence was shown to be effective for in vivo imaging. A higher signal-to-noise ratio (SNR) compared to single-shot EPI at an identical total scan time was achieved, which is advantageous for routine DTI applications in clinical practice.

Algorithms↗

PubMed2005

FLAIR diffusion-tensor MR tractography: comparison of fiber tracking with conventional imaging.

BACKGROUND AND PURPOSE: Partial volume with CSF is known to contaminate the quantification of white matter anisotropy depicted by diffusion tensor imaging (DTI). We hypothesized that the FLAIR technique helps to improve DTI white matter tractography in the normal adult brain by eliminating CSF partial volume effects. METHODS: Seven healthy adults aged 23-37 underwent both conventional and FLAIR DTI at 1.5T. Each subject was imaged five times. Neural fiber tractography was performed with both sequences by using two algorithms: a voxel-based method (EZ-tracing) with global seed points and another based on subvoxel tractography (tensor deflection) by using manual encircling of local seed points. Total volume of the fibers tracked was compared for the two types of images. RESULTS: Fiber tracking was substantially most successful on FLAIR DTI near the lateral ventricles and the sulci, where CSF partial volume effects were likely present. Minor false tracts on FLAIR images, possibly due to a reduced signal-to-noise ratio, were found in regions relatively free of CSF contamination; however, they did not affect tracking of major periventricular white matter bundles, such as those related to the corpus callosum or the corona radiata. When we excluded false tracts, the FLAIR technique depicted an average of 17% more fibers in volume than conventional DTI in the periventricular regions (P < .0005, paired Student t test). CONCLUSION: Despite the reduction of signal-to-noise ratio and longer imaging times, FLAIR improved tractography by eliminating CSF partial volume effects.

Adult↗

PubMed2005

MR ventriculocisternography by using 3D balanced steady-state free precession imaging: technical note.

This study investigated the effects of flip angle setting in 3D balanced steady-state free precession (SSFP) imaging on CSF-parenchyma contrast and section aliasing artifacts. Theoretical derivations indicated that the extent of section aliasing artifacts decreased as the flip angle was lowered, at the expense of a sacrifice in CSF-parenchyma contrast. Experimental data agreed closely with theoretical predictions. A flip angle of about 40 degrees is therefore recommended for 3D balanced SSFP MR ventriculocisternography.

Artifacts↗

PubMed2004

Fat and water separation in balanced steady-state free precession using the Dixon method.

In this work the feasibility of separating fat and water signals using the balanced steady-state free precession (SSFP) technique is demonstrated. The technique is based on the observation (Scheffler and Hennig, Magnetic Resonance in Medicine 2003;49:395-397) that at the nominal values of TE = TR/2 in SSFP imaging, phase coherence can be achieved at essentially only two orientations (0 degrees and 180 degrees ) relative to the RF pulses in the rotating frame, under the assumption of TR << T2, and independently of the SSFP angle. This property allows in-phase and out-of-phase SSFP images to be obtained by proper choices of the center frequency offset, and thus allows the Dixon subtraction method to be utilized for effective fat-water separation. The TR and frequency offset for optimal fat-water separation are derived from theories. Experimental results from healthy subjects, using a 3.0 Tesla system, show that nearly complete fat suppression can be accomplished.

Abdomen↗

PubMed2004

Comparison of arterial spin labeling and first-pass dynamic contrast-enhanced MR imaging in the assessment of pulmonary perfusion in humans: the inflow spin-tracer saturation effect.

The flow-sensitive alternating inversion recovery (FAIR) and the first-pass dynamic contrast-enhanced MR imaging (CE-MRI) techniques have both been shown to be effective in the assessment of human pulmonary perfusion. However, no comprehensive comparison of the measurements by these two methods has been reported. In this study, healthy adults were recruited, with FAIR and CE-MRI performed for an estimation of the relative pulmonary blood flow (rPBF). Regions of interest were encircled from the right and left lungs, with right-to-left rPBF ratios calculated. Results indicated that, on posterior coronal slices, the rPBF ratios obtained with the FAIR technique agreed well with CE-MRI measurements (mean difference = -0.02, intraclass correlation coefficient RI = 0.78, 95% confidence interval = [0.67, 0.86]). On middle coronal slices, however, FAIR showed a substantially lower rPBF by up to 43% in the right lung compared with CE-MRI (mean difference = -0.38, RI = 0.34, 95% confidence interval = [-0.09, 0.68]). The location-dependent discrepancy between measurements by FAIR and CE-MRI methods is attributed to tracer saturation effects of arterial inflow when the middle coronal slice contains the in-plane-oriented right pulmonary artery, whereas the left lung rPBF is less affected due to oblique orientation of the left pulmonary artery. Intrasequence comparison on additional subjects using FAIR at different slice orientations supported the above hypothesis. It is concluded that FAIR imaging for pulmonary perfusion in the coronal plane provides equivalent rPBF information with CE-MRI only in the absence of tracer saturation effects; hence, FAIR should be carefully exercised to avoid misleading interpretations.

Adult↗

PubMed2004

Supratentorial cerebrospinal fluid production rate in healthy adults: quantification with two-dimensional cine phase-contrast MR imaging with high temporal and spatial resolution.

A method for objectively determining supratentorial cerebrospinal fluid (CSF) production rate is described. The method employs cine phase-contrast magnetic resonance imaging with high temporal and spatial resolution at the level of the aqueduct of Sylvius. Automatic encircling of the aqueduct was accomplished by using a pulsatility-based segmentation approach. Results in 23 healthy adults (18 men, five women; age range, 21-39 years) yielded an average CSF production rate of 305 microL/min +/- 145 (standard deviation); this rate is in good agreement with literature-reported values obtained with invasive ventriculolumbar perfusion measurements. Average operator imprecision was 23.1% if automatic segmentation was not used. The proposed method is potentially an effective means for measuring supratentorial CSF production rate in humans.

Adult↗

PubMed2002

Are TrueFISP images T2/T1-weighted?

Images acquired using the TrueFISP technique (true fast imaging with steady-state precession) are generally believed to exhibit T(2)/T(1)-weighting. In this study, it is demonstrated that with the widely used half-flip-angle preparation scheme, approaching the steady state requires a time length comparable to the scan time such that the transient-state response may dominate the TrueFISP image contrast. Two-dimensional images of the human brain were obtained using various phase-encoding matrices to investigate the transient-state signal behavior. Contrast between gray and white matter was found to change significantly from proton-density- to T(2)/T(1)-weighted as the phase-encoding matrix size increased, which was in good agreement with theoretical predictions. It is concluded that TrueFISP images in general exhibit T(2)/T(1)-contrast, but should be more appropriately regarded as exhibiting a transient-state combination of proton-density and T(2)/T(1) contrast under particular imaging conditions. Interpretation of tissue characteristics from TrueFISP images in clinical practice thus needs to be exercised with caution.

Brain↗