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M Zhao, W Huang,
Q Zhang,
F Gao,
L Wang,
G Zhang,
Y Su,
R Xiao,
J Zhang,
M Tang,
W Cheng,
Y Tan,
Q Lu
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ABSTRACT: Pemphigus vulgaris (PV) is an autoimmune blistering disorder with a complex aetiology involving genetic and environmental factors, most of which remain unknown. It has become increasingly evident that aberrant epigenetic modifications are associated with the occurrence and development of autoimmune skin disorders. However, it is not known whether epigenetic modifications play a role in the development of PV.
To analyse DNA methylation and histone modification patterns in peripheral blood mononuclear cells (PBMCs) of patients with PV.
PBMC samples were isolated from 24 patients with PV and 20 healthy controls. Skin lesion biopsies and control skin specimens were obtained from 25 patients with PV and 15 healthy controls. Global DNA methylcytosine levels, as well as histone acetylation and methylation levels, were measured by enzyme-linked immunosorbent assay. mRNA expression levels were determined using real-time reverse transcription-polymerase chain reaction.
Genomic DNA methylation in PBMCs of patients with PV was increased relative to controls. DNMT1 expression levels were significantly higher in PV PBMCs than in controls. MBD3 expression was repressed in PV PBMCs compared with healthy controls. Global histone H3/H4 acetylation and H3K4/H3K27 methylation levels were significantly decreased in patient PBMCs compared with healthy controls. These changes were accompanied by increased HDAC1, HDAC2 and SUV39H2 and decreased SUV39H1 and EZH2 in PV PBMCs.
Aberrant DNA methylation and histone modifications occur in PBMCs of patients with PV, possibly due to the deregulation of epigenetic modifier genes. These changes may contribute to the pathological immune responses in PV.
British Journal of Dermatology 04/2012; 167(3):523-31. · 3.67 Impact Factor
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ABSTRACT: We present an implementation of a reconfigurable 16-tap finite impulse response filter for post-processing applications. This filter exploits the distributed arithmetic technique for signal processing and floating-gate voltage references for setting tunable analog coefficients. The filter is fabricated in 0.5mum CMOS process, and its order can be increased at the cost of 0.011mm<sup>2</sup> of die area and 0.02mW of power per tap. Measurement results for low-pass and band-pass filters at 50kHz sampling frequency are presented.
Circuits and Systems, 2007. ISCAS 2007. IEEE International Symposium on; 06/2007
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ABSTRACT: This paper discusses the design of true redundant, N+l parallel voltage regulator module (VRM) system with low droop resistance. Average current mode control and limited gain for voltage compensation is used to achieve droop current sharing between parallel modules without single point failure. Small signal model of the current sharing scheme is derived and experimentally validated. A novel local sense feedback is used to improve the dynamic performance of the parallel system. Experimental results from a prototype confirm the current sharing between two VRMs to be within 10 % and the dynamic response improvement by 33 % due to local sense feedback
Industry Applications Conference, 2006. 41st IAS Annual Meeting. Conference Record of the 2006 IEEE; 11/2006
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ABSTRACT: In this paper, we present a new scheme to robustly detect a human attentive behavior, i.e., a frequent change in focus of attention (FCFA) from video sequences. The FCFA behavior can be easily perceived by people as temporal changes of human head pose. Here, we propose a non-linear head pose embedding and mapping algorithm to detect the pose in each frame of the sequence. Developed from ISOMAP, we learn a person-independent and non-linear embedding space (we call it a 2-D feature space) for different head poses. A non-linear interpolation mapping followed by an adaptive local fitting method is designed to map new frames into the 2-D feature space where head poses can be further obtained. An entropy classifier is then proposed on each sequence to detect the FCFA behavior. Experiments reported in this paper showed robust results
Multimedia Signal Processing, 2005 IEEE 7th Workshop on; 12/2005
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ABSTRACT: In this paper, a multiplexed multiplier architecture (MMA) for a field programmable gate array (FPGA) implementation of the least mean square (LMS) adaptive filter is developed and presented. In the proposed architecture, hardware multipliers are reused, i.e. multiplexed in time, for both filtering and adaptation. The number of multipliers may be chosen to achieve certain design trade-offs. The design trade-offs considered in this paper include on-chip area, filter size, maximum filter throughput, and power consumption.
Signals, Systems and Computers, 2003. Conference Record of the Thirty-Seventh Asilomar Conference on; 12/2003
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ABSTRACT: Distributed arithmetic (DA) is an efficient architecture for implementing finite impulse response (FIR) digital filters. The DA FIR filter calculates the filter output using look up tables (LUTs) instead of multipliers. Thus, a DA based implementation of an FIR filter is highly parameterizable and area efficient. Furthermore, the fundamental building blocks in the DA architecture map well to the architecture of today's field programmable gate arrays (FPGAs). In this paper, we analyze the design of an adaptive FIR filter using the DA architecture on an FPGA. The design trade-offs discussed in detail include throughput, number of logic elements utilized, memory usage, and power consumption estimates.
Signals, Systems and Computers, 2003. Conference Record of the Thirty-Seventh Asilomar Conference on; 12/2003
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ABSTRACT: The development of the first prototype active matrix flat-panel imager (AMFPI) capable of radiographic and fluoroscopic megavoltage operation is reported. The signal and noise performance of individual pixels is empirically quantified. Results of an observer-dependent study of imaging performance, using a contrast-detail phantom, are detailed and radiographic patient images are shown. Finally, a theoretical investigation of the zero-frequency detective quantum efficiency (DQE) performance of such imagers, using a cascaded systems formalism, is presented.
The imager is based on a 508-microm pitch, 26 x 26 cm2 array which detects radiation indirectly via an overlying copper plate + phosphor screen converter.
Due to its excellent optical coupling, the imager exhibits sensitivity superior to that of video-based systems. With an approximately 133 mg/cm2 Gd2O2S:Tb screen the system is x-ray quantum-noise-limited down to approximately 0.3 cGy, conservatively, and extensions of this behavior to even lower doses by means of reduced additive electronic noise is predicted. The observer-dependent study indicates performance superior to that of conventional radiotherapy film while the patient images demonstrate good image quality at 1 to 4 MU. The theoretical studies suggest that, with a 133 mg/cm2 Gd2O2S:Tb screen, the system would provide DQE performance equivalent to that of video-based systems and that almost a factor of two improvement in DQE is achievable through the incorporation of a 400 mg/cm2 screen.
The reported prototype imager is the first megavoltage AMFPI having performance characteristics consistent with practical clinical operation. The superior contrast-detail sensitivity of the imager allows the capture of high-quality 6- and 15-MV images at minimal dose. Moreover, significant performance improvements, including extension of the operational range up to full portal doses, appear feasible. Such capabilities could be of considerable practical benefit in patient localization and verification.
International Journal of Radiation OncologyBiologyPhysics 10/1998; 42(2):437-54. · 4.11 Impact Factor
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ABSTRACT: The performance of an indirect-detection, active matrix flat-panel imager (FPI) at diagnostic energies is reported in terms of measured and theoretical signal size, noise power spectrum (NPS), and detective quantum efficiency (DQE). Based upon a 1536 x 1920 pixel, 127 microns pitch array of a-Si:H thin-film transistors and photodiodes, the FPI was developed as a prototype for examination of the potential of flat-panel technology in diagnostic x-ray imaging. The signal size per unit exposure (x-ray sensitivity) was measured for the FPI incorporating five commercially available Gd2O2S:Tb converting screens at energies 70-120 kVp. One-dimensional and two-dimensional NPS and DQE were measured for the FPI incorporating three such converters and as a function of the incident exposure. The measurements support the hypothesis that FPIs have significant potential for application in diagnostic radiology. A cascaded systems model that has shown good agreement with measured individual pixel signal and noise properties is employed to describe the performance of various FPI designs and configurations under a variety of diagnostic imaging conditions. Theoretical x-ray sensitivity, NPS, and DQE are compared to empirical results, and good agreement is observed in each case. The model is used to describe the potential performance of FPIs incorporating a recently developed, enhanced array that is commercially available and has been proposed for testing and application in diagnostic radiography and fluoroscopy. Under conditions corresponding to chest radiography, the analysis suggests that such systems can potentially meet or even exceed the DQE performance of existing technology, such as screen-film and storage phosphor systems; however, under conditions corresponding to general fluoroscopy, the typical exposure per frame is such that the DQE is limited by the total system gain and additive electronic noise. The cascaded systems analysis provides a valuable means of identifying the limiting stages of the imaging system, a tool for system optimization, and a guide for developing strategies of FPI design for various imaging applications.
Medical Physics 06/1998; 25(5):614-28. · 2.83 Impact Factor
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ABSTRACT: Signal properties of the first large-area, high resolution, active matrix, flat-panel imager are reported. The imager is based on an array of 1536 x 1920 pixels with a pixel-to-pixel pitch of 127 microns. Each pixel consists of a discrete amorphous silicon n-i-p photodiode coupled to an amorphous silicon thin-film transistor. The imager detects incident x rays indirectly by means of an intensifying screen placed over the array. External acquisition electronics send control signals to the array and process analog imaging signals from the pixels. Considerations for operation of the imager in both fluoroscopic and radiographic modes are detailed and empirical signal performance data are presented with an emphasis on exploring similarities and differences between the two modes. Measurements which characterize the performance of the imager were performed as a function of operational parameters in the absence or presence of illumination from a light-emitting diode or x rays. These measurements include characterization of the drift and magnitude of the pixel dark signal, the size of the pixel switching transient, the temporal behavior of pixel sampling and the implied maximum frame rate, the dependence of relative pixel efficiency and pixel response on photodiode reverse bias voltage and operational mode, the degree of linearity of pixel response, and the trapping and release of charge from metastable states in the photodiodes. In addition, X-ray sensitivity as a function of energy for a variety of phosphor screens for both fluoroscopic and radiographic operation is reported. Example images of a line-pair pattern and an anthropomorphic phantom in each mode are presented along with a radiographic image of a human hand. General and specific improvements in imager design are described and anticipated developments are discussed. This represents the first systematic investigation of the operation and properties in both radiographic and fluoroscopic modes of an imager incorporating such an array.
Medical Physics 02/1997; 24(1):51-70. · 2.83 Impact Factor
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ABSTRACT: Noise properties of active matrix, flat-panel imagers under conditions relevant to diagnostic radiology are investigated. These studies focus on imagers based upon arrays with pixels incorporating a discrete photodiode coupled to a thin-film transistor, both fabricated from hydrogenated amorphous silicon. These optically sensitive arrays are operated with an overlying x-ray converter to allow indirect detection of incident x rays. External electronics, including gate driver circuits and preamplification circuits, are also required to operate the arrays. A theoretical model describing the signal and noise transfer properties of the imagers under conditions relevant to diagnostic radiography, fluoroscopy, and mammography is developed. This frequency-dependent model is based upon a cascaded systems analysis wherein the imager is conceptually divided into a series of stages having intrinsic gain and spreading properties. Predictions from the model are compared with x-ray sensitivity and noise measurements obtained from individual pixels from an imager with a pixel format of 1536 x 1920 pixels at a pixel pitch of 127 microns. The model is shown to be in excellent agreement with measurements obtained with diagnostic x rays using various phosphor screens. The model is used to explore the potential performance of existing and hypothetical imagers for application in radiography, fluoroscopy, and mammography as a function of exposure, additive noise, and fill factor. These theoretical predictions suggest that imagers of this general design incorporating a CsI: Tl intensifying screen can be optimized to provide detective quantum efficiency (DQE) superior to existing screen-film and storage phosphor systems for general radiography and mammography. For fluoroscopy, the model predicts that with further optimization of a-Si:H imagers, DQE performance approaching that of the best x-ray image intensifier systems may be possible. The results of this analysis suggest strategies for future improvements of this imaging technology.
Medical Physics 02/1997; 24(1):71-89. · 2.83 Impact Factor
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ABSTRACT: The creation of the first large-area, amorphous silicon megavoltage imager is reported. The imager is an engineering prototype built to serve as a stepping stone toward the creation of a future clinical prototype. The engineering prototype is described and various images demonstrating its properties are shown including the first reported patient image acquired with such an amorphous silicon imaging device. Specific limitations in the engineering prototype are reviewed and potential advantages of future, more optimized imagers of this type are presented.
The imager is based on a two-dimensional, pixelated array containing amorphous silicon field-effect transistors and photodiode sensors which are deposited on a thin glass substrate. The array has a 512 x 560-pixel format and a pixel pitch of 450 microns giving an imaging area of approximately 23 x 25 cm2. The array is used in conjunction with an overlying metal plate/phosphor screen converter as well as an electronic acquisition system. Images were acquired fluoroscopically using a megavoltage treatment machine.
Array and digitized film images of a variety of anthropomorphic phantoms and of a human subject are presented and compared. The information content of the array images generally appears to be at least as great as that of the digitized film images.
Despite a variety of severe limitations in the engineering prototype, including many array defects, a relatively slow and noisy acquisition system, and the lack of a means to generate images in a radiographic manner, the prototype nevertheless generated clinically useful information. The general properties of these amorphous silicon arrays, along with the quality of the images provided by the engineering prototype, strongly suggest that such arrays could eventually form the basis of a new imaging technology for radiotherapy localization and verification. The development of a clinically useful prototype offering high-quality images, ultimately with an approximately 52 x 52-cm2 detection surface, is anticipated.
International Journal of Radiation OncologyBiologyPhysics 11/1996; 36(3):661-72. · 4.11 Impact Factor
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ABSTRACT: As part of the development necessary for implementing a fully digital radiology department, the authors have investigated thin-film photodiodes and transistors for use in new photoelectronic imaging devices. One such device, a large-area, flat-panel, amorphous silicon imaging array, has been developed and is currently being tested. The array has a format of 512 x 560 pixels, a pixel-to-pixel pitch of 450 microns, and an area of 230 x 252 mm2, making it the largest self-scanning, solid-state imaging array developed to date. The array is used in conjunction with an overlying x-ray converter. Although specifically designed for megavoltage imaging, the device can produce high-quality, low spatial resolution, diagnostic x-ray images. Qualitative comparisons of array images of anthropomorphic head, chest, and pelvic phantoms and a spatial resolution pattern suggest that much of the information content of the film images at low spatial resolution is present in the corresponding array images. Current trends in the development of large-area, flat-panel imaging technology hold the promise of higher resolution arrays in the near future.
Radiographics 08/1995; 15(4):993-1000. · 2.85 Impact Factor
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ABSTRACT: An electronic data acquisition system for pixelated,
two-dimensional, amorphous silicon x-ray imaging arrays has been
developed. The system was designed in a modular fashion with digital
control provided by field-programmable logic devices. This approach
allows sections of the design to be upgraded with little impact an other
aspects of the system. Good analog noise performance was obtained by
matching the preamplifier design to the characteristics of the array
outputs. The design of this system is presented and its performance
quantified
IEEE Transactions on Nuclear Science 09/1994; · 1.45 Impact Factor
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ABSTRACT: The first diagnostic X-ray signal measurements for two-dimensional
amorphous silicon imaging arrays are presented. Data were acquired for a
variety of phosphor screens, for energies ranging from 70 to 120 kVp,
both in the presence and in the absence of a phantom simulating the
attenuation of a human chest. Results are reported in terms of pixel
charge per unit exposure at the array. Also, linearity of pixel response
with exposure as a function of sensor bias, pixel response as a function
of sensor bias, and the first data quantifying the degree of reciprocity
of the pixel response are reported. Significant results include: (a)
pixel response remained linear to within 1% for ~70% of the signal range
at 0.5 volts and ~95% at 3.0 volts; (b) from a partial response at 0
volts, pixel response is observed to increase rapidly up to ~1 volt
after which more gradual increases in response are observed; and (c) for
exposure rates varying by a factor of ~5, pixel response was
approximately consistent with reciprocal behavior although evidence of
limited (~6%) reciprocity failure is suggested
IEEE Transactions on Nuclear Science 09/1994; · 1.45 Impact Factor
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ABSTRACT: Electrical performance and printed circuit board routability
tradeoff are studied in ceramic ball grid array packages (CBGAs). CBGA
package design is described for a high speed chip with peripheral
drivers. Three general types of array patterns are compared. First, the
best routability design, where all the power and ground balls on the
CBGA are routed in the center area. Second, a design with four pairs of
P/G balls moved to the corners of the CBGA is evaluated, resulting in
improvement of electrical performance by 50%, as measured by SSN
reduction. The reasons for this improvement are analyzed. Third, even
more P/G balls are moved closer to the onchip drivers, achieving an
additional 30% reduction in SSN. In each case, the implications on board
routability and simultaneous switching noise are assessed
Electronic Components and Technology Conference, 1994. Proceedings., 44th; 06/1994
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ABSTRACT: The application of a controlled-collapse-chip-connection,
ceramic-ball-grid-array (C4/CBGA) module for a RISC microprocessor is
presented. The zero to second-level interconnection technologies and the
various design considerations, from the on-chip redistribution metal to
the single-chip module printed-circuit-board connection, are analysed.
In addition to an overview of the interconnect technology, we discuss
the: 1) electrical modeling and characterization, 2) board design and
routability, 3) thermal management, and 4) C4 and ball-grid-array
interconnection reliability
Electronic Components and Technology Conference, 1994. Proceedings., 44th; 06/1994
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ABSTRACT: A readout system is developed to facilitate the digitization and
subsequent display of image data from two-dimensional, pixellated,
flat-panel, amorphous silicon imaging arrays. These arrays are designed
specifically for medical X-ray imaging applications. The readout system
is based on hardware and software developed for various experiments at
CERN and Fermi National Accelerator Laboratory. Additional analog signal
processing and digital control electronics are constructed specifically
for this application. The form of the resulting data acquisition system
is reported, aspects of its performance are discussed, and the
compromises which were involved in its design are considered
IEEE Transactions on Nuclear Science 09/1993; · 1.45 Impact Factor
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ABSTRACT: Large area, two-dimensional, amorphous silicon arrays are under development for x-ray imaging applications. Theoretical limits on frame rates imposed by array design and operational requirements are examined. Measurements of image lag as a function of frame rate are reported.
MRS Proceedings. 12/1992; 297.
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ABSTRACT: The concept of composite imaging detectors in which a flat-panel
array precedes a second level of detection is presented. In
radiotherapy, a dual-energy X-ray projection imager would consist of a
pair of stacked, flat-panel imagers. The upper detection of level would
consist of a flat-panel array with an overlying X-ray converter and
would serve as a diagnostic imager. The lower detection level would
consist of a second array with an overlying metal sheet/phosphor screen
converter and would serve as a megavoltage imager. Such a composite
imager would be of significant assistance in helping to resolve the
patient localization problem in megavoltage radiotherapy by facilitating
the correlation of patient anatomy obtained with diagnostic images with
the position of the megavoltage portal field. In a second realization of
a composite imager, a flat-panel array placed directly over the crystal
in a SPECT (single photon emission computed tomography) camera, or
within the detector ring of a PET (positron emission tomography)
scanner, would allow the simultaneous collection of emission and
transmission projection data
Nuclear Science Symposium and Medical Imaging Conference, 1992., Conference Record of the 1992 IEEE; 12/1992
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ABSTRACT: Signal measurements for a variety of pixelated a-Si:H imaging
arrays irradiated by megavoltage beams are reported. Data are presented
for 6-, 10-, and 15-MV beam energies for screens containing
gadolinium-oxysulfide and calcium tungstate. These results are
quantitative radiation signal sizes reported for such arrays. The
initialization times of these arrays are reported. The performance of
arrays of various sizes and pitches with respect to these measured
values is compared. These results are part of an ongoing effort to
develop flat-panel, real-time gamma and X-ray imagers
IEEE Transactions on Nuclear Science 09/1992; · 1.45 Impact Factor
