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Biomedical subjects

Y C Tai

Publications and source records attributed to Y C Tai.

9 recordsLinked to original sources
PubMed2003

Feasibility of T-cell receptor gamma (TCRgamma) gene rearrangement on formalin-fixed, paraffin-embedded tissues by PCR assays.

INTRODUCTION: T- and B-lymphocytes are involved in recognition of foreign antigen by the specificity of their surface T-cell receptor and immunoglobulin, generated by gene rearrangement. Each T- and B-lymphocyte carries unique rearranged TCR or immunoglobulin gene, which has been applied to detect clonal from non-clonal T- and B-cell proliferation. METHODS: Paraffin-embedded biopsy tissues of 85 T-, 24 B-cell non-Hodgkin's lymphomas (NHL) of various subtypes, and seven reactive lymphoid hyperplasia were retrieved from the archives for determining the feasibility of TCRgamma gene rearrangement analysis by PCR assays in our laboratory. DNA was extracted by Proteinase K digestion. The analyses were performed by five PCR assays, and analysed on polyacrylamide gel. RESULTS: Clonal TCRgamma gene rearrangement was demonstrated in 69/85 (81.2%) of the cases. Selective rearrangement of specific Vgamma segment was observed, especially in peripheral T-cell lymphoma-unspecified and nasal NK/T-cell lymphoma. Clonal TCRgamma rearranged band was also demonstrated in 4/24 (16.7%) and 2/7 (28.6%) of B-NHL and reactive lymphoid tissues respectively. CONCLUSION: PCR assays were able to demonstrate clonal TCRgamma gene rearrangement in a high proportion of T-NHL. However, the PCR results should be interpreted carefully. A neoplasm should only be considered as T-cell type if it does not express any B-cell marker because TCRgamma is not lineage specific as shown by the presence of clonal TCRgamma gene rearrangement in B-NHL. Hence, the results for TCR gene rearrangement should always be interpreted in conjunction with histology and immunophenotyping.

B-Lymphocytes↗
PubMed2002

Model-based normalization for iterative 3D PET image reconstruction.

We describe a method for normalization in 3D PET for use with maximum a posteriori (MAP) or other iterative model-based image reconstruction methods. This approach is an extension of previous factored normalization methods in which we include separate factors for detector sensitivity, geometric response, block effects and deadtime. Since our MAP reconstruction approach already models some of the geometric factors in the forward projection, the normalization factors must be modified to account only for effects not already included in the model. We describe a maximum likelihood approach to joint estimation of the count-rate independent normalization factors, which we apply to data from a uniform cylindrical source. We then compute block-wise and block-profile deadtime correction factors using singles and coincidence data, respectively, from a multiframe cylindrical source. We have applied this method for reconstruction of data from the Concorde microPET P4 scanner. Quantitative evaluation of this method using well-counter measurements of activity in a multicompartment phantom compares favourably with normalization based directly on cylindrical source measurements.

Algorithms↗
PubMed2001

Silicon couplers for microfluidic applications.

Several types of silicon fluidic coupler have been designed, fabricated, and tested to facilitate external connections to MEMS (microelectromechanical systems) fluidic devices. By using both bulk micromachining and DRIE (deep reactive ion-etching) techniques, couplers of different geometry have been produced for use with any standard MEMS fluidic port. In addition, couplers are easily modified to accommodate any arbitrary fluidic port geometry. For ease of use, these couplers interface with PEEK (polyetheretherketone) and fused-silica capillary tubing, both of which are commonly used in HPLC (high-performance liquid chromatography) systems and are supported by a wide range of plumbing products. Coupler performance was evaluated and an operating range of at least 0-8,963 kPa (0-1,300 psig) is attainable.

Journal Article↗
PubMed2001

Detector development for microPET II: a 1 microl resolution PET scanner for small animal imaging.

We are currently developing a small animal positron emission tomography (PET) scanner with a design goal of 1 microlitre (1 mm3) image resolution. The detectors consist of a 12 x 12 array of 1 x 1 x 10 mm lutetium oxyorthosilicate (LSO) scintillator crystals coupled to a 64-channel photomultiplier tube (PMT) via 5 cm long optical fibre bundles. The optical fibre connection allows a high detector packing fraction despite the dead space surrounding the active region of the PMT. Optical fibre bundles made from different types of glass were tested for light transmission, and also their effects on crystal identification and energy resolution, and compared to direct coupling of the LSO arrays to the PMTs. We also investigated the effects of extramural absorber (EMA) in the fibre bundles. Based on these results, fibre bundles manufactured from F2 glass were selected. We built three pairs of prototype detectors (directly coupled LSO array, fibre bundle without EMA and fibre bundle with EMA) and measured flood histograms, energy resolution, intrinsic spatial resolution and timing resolution. The results demonstrated an intrinsic spatial resolution (FWHM) of 1.12 mm (directly coupled), 1.23 mm (fibre bundle without EMA coupling) and 1.27 mm (fibre bundle with EMA coupling) using an approximately 500 microm diameter Na-22 point source. Using a 330 microm outer diameter steel needle line source filled with F-18, spatial resolution for the detector with the EMA optical fibre bundle improved to 1.05 mm. The respective timing and energy FWHM values were 1.96 ns, 21% (directly coupled), 2.20 ns, 23% (fibre bundle without EMA) and 2.99 ns, 30% (fibre bundle with EMA). The peak-to-valley ratio in the flood histograms was better with EMA (5:1) compared to the optical fibre bundle without EMA (2.5:1), due to the decreased optical cross-talk. In comparison to the detectors used in our current generation microPET scanner, these detectors substantially improve on the spatial resolution, preserve the timing resolution and provide adequate energy resolution for a modern high-resolution animal PET tomograph.

Animals↗
PubMed2000

A micromachined chip-based electrospray source for mass spectrometry.

A micromachining process is described for fabricating a mass spectrometry electrospray source on a silicon chip. The process utilizes polymer (parylene) layers to form a system of chambers, filters, channels, and hollow needle structures (electrospray emitters) that extend more than a millimeter beyond the edge of the silicon substrate. The use of photoresist as the sacrificial layer facilitates the creation of long channels. Access to the channel structures on the chip is through a port etched through the silicon substrate that also serves as a sample reservoir. A reusable chip holder consisting of two plastic plates and an elastomer gasket provides the means to mount the chip in front of the mass spectrometer inlet and make electrical and gas connections. The electrospray emitters have tapered tips with 5 microns x 10 microns rectangular openings. The shape of the tip can be varied depending on the shape of the mask used to protect the parylene structures during the final plasma etch. The parylene emitters are physically robust and require only a high electric field to achieve stable electrospray operation over a period of a few hours. Direct comparisons with conventional glass or fused silica emitters indicated very similar performance with respect to signal strength and stability, spectral quality, and endurance. The automated MS/MS analysis of a mixture of tryptic peptides was no more difficult and yielded nearly identical results as the analysis of the same sample using a conventional nanospray device. This work demonstrates that an efficient electrospray interface to mass spectrometry can be integrated with other on-chip structures and mass-produced using a batch process.

Mass Spectrometry↗
PubMed2000

ROC and LROC analyses of the effects of lesion contrast, size, and signal-to-noise ratio on detectability in PET images.

UNLABELLED: Image quality in PET is typically assessed using measures such as contrast recovery, noise variation, and signal-to-noise ratio (SNR). However, these criteria do not directly reflect performance in the clinical use of the images. Lesion detection is a critical task in the clinical interpretation of many PET studies. A receiver operating characteristic (ROC) study is an accepted method for quantitatively evaluating detection performance with respect to factors that influence image quality. ROC and localization ROC (LROC) analyses were conducted to investigate the effects of lesion contrast, SNR, and size on detectability of hot lesions in PET images. METHODS: A thorax phantom was imaged with spheres of 3 sizes simulating lesions (0.45, 1.0, and 1.9 mL). The relative activity in the lesions and the total number of counts acquired were each varied by factors of 2 to ascertain the effects of contrast and SNR, respectively. Measured attenuation correction and a standard reconstruction protocol were used. Three nuclear medicine physicians and 6 medical physicists participated as readers, rating each image and indicating the suspected lesion location. The area under the calculated ROC and LROC curves (Az and Az,LROC) were used as measures of detection performance. RESULTS: Detection performance was shown to increase from virtually random (Az approximately 0.5, Az,LROC approximately 0.2) to superior (Az > 0.9, Az,LROC > 0.9) as lesion contrast was increased by 50% and as lesion SNR was doubled. Detection performance was not seen to vary when comparison was made using image-based measures alone. CONCLUSION: This study quantitatively shows that moderate increases in the image-based measures of lesion contrast and SNR give a relatively large increase in the task-based measure of lesion detection as measured by ROC and LROC analyses. Thus, techniques that give modest increases in lesion contrast or SNR are expected to improve detection. Results will be useful in evaluating improvement in detection for various reconstruction, acquisition, and data analysis methods that enhance contrast or noise performance.

Heart↗
PubMed1999

The neurochip: a new multielectrode device for stimulating and recording from cultured neurons.

The neurochip is a silicon micromachined device upon which cultured mammalian neurons can be continuously and individually monitored and stimulated. The neurochip is based upon a 4 x 4 array of metal electrodes, each of which has a caged well structure designed to hold a single mature cell body while permitting normal outgrowth of neural processes. We demonstrate that this device is capable of maintaining cell survival, and that the electrodes can both record and stimulate electrical activity in individual cells with no crosstalk between channels.

Algorithms↗
PubMed1999

Microstructures for studies of cultured neural networks.

A description is given of a functional silicon micromachined device that permits non-invasive, bidirectional, highly specific communication with cultured mammalian neurons. The heart of the system is a well structure that holds the cell in close proximity to a metal extracellular electrode while permitting normal outgrowth of axons and dendrites. An iterative approach is used to create a design that allows normal growth of the neurons while preventing their escape. An array of 16 such neurowells makes it possible to perform studies of biological neural network development and function with unprecedented detail.

Animals↗