David Yang

Followers

Following

Public Views

Address: Beijing, Beijing, China

less

Interests

Uploads

Papers by David Yang

Evaluation of Preoperative Chemotherapy Using PET with Fluorine18Fluorodeoxyglucose in Breast Cancer

We retrospectively investigated the value of PET with fluorine-18 fluorodeoxyglucose (FDG) for pr... more We retrospectively investigated the value of PET with fluorine-18 fluorodeoxyglucose (FDG) for preoperative chemotherapy response in patients with locally advanced breast cancer. Methods: FDG-PET studies were performed on 16 consecutive patients. All patients had PET studies before chemotherapy, 13 patients between the end of the first cycle and at the midpoint of chemotherapy, and 14 patients before surgery. Visual diagnoses and the standardized uptake values (SUV) of PET scans were compared with pathology findings at surgery and with the results of mammography, ultrasonography (US) or both, which were performed before chemotherapy and before local surgery for residual disease. Each patient's clinical course was monitored for up to 3 yr. Results: Sensitivity for detection of pathologically proven primary lesions was 100%, 62.5% and 87.5% with FDG-PET, mammography and US, respec tively; and sensitivity for detection of initial nodal involvement was 77%, 70% and 87.5%, respectively. Sensitivity for detection of residual primary tumor was 75%, 71.4% and 87.5%, respectively; and sensitivity for detection of residual nodal involvement was 41.6%, 71.4% and 66.6%, respectively. The mean SUV value of primary lesions was 9.4 (range 2.0-20.7, n = 16), with only two lesions showing an SUV below 3. Clinical improvement of primary lesions was seen in all patients; improvement with smaller size and less FDG uptake was visible as early as the second study in 11 patients (69%). Mean SUV values obtained at the second and third studies decreased significantly from those obtained in the first study. In four patients, the disease recurred after breast surgery with high SUV values. The mammograms and sonograms obtained before surgery showed a decrease in the diameter of 6 and 12 primary lesions of the 13 and 14 patients examined, respectively. Conclusion: FDG-PET is valuable for monitoring the effects of preoperative chemotherapy in patients with locally advanced breast cancer with better sensitivity for primary tumor and better specificity for nodal metastasis in comparison with ultrasonography.

format_quoteSignificant clinical improvement observed in 69% of patients by the second PET study, indicating early chemotherapy response.format_quote

Download

Changes in blood lipids during six days of overfeeding with medium or long chain t rig I yce r i d es

Although medium chain triglyceride (MCT) is less calorically dense than long chain triglyceride (... more Although medium chain triglyceride (MCT) is less calorically dense than long chain triglyceride (LCT), it produces a greater thermic effect following ingestion. We hypothesized that the previously observed high rate of thermogenesis produced by MCT overfeeding was due to hepatic de novo synthesis of long chain fatty acids (LCFA) from the excess medium chain fatty acids (MCFA). To study this, we compared the effects of overfeeding MCT-and LCT-containing diets on blood lipid profiles. Ten in-patient, nonobese males were overfed (150 % of estimated energy requirements) two formula diets for 6 days each, in a randomized crossover design. Diets differed only in the composition of the fat and contained either 40% of energy as MCT or LCT (soybean oil). The major differences between diets in the resulting pattern of blood lipids were: 1) a reduction in fasting serum total cholesterol concentrations with the LCT, but not the MCT diet; and 2) a threefold increase in fasting serum triglyceride concentrations with MCT, but not LCT, diet. Moreover, 10% of the fasting triglyceride fatty acids were medium chain and 40% were 16:O with the MCT diet. This compared to 1 % and 20% for medium chain and 16:0, respectively, with the LCT diet. In addition, there were increases in 16:1, 18:0, and 18:l in the triglycerides during MCT feeding.

format_quoteMCT diet resulted in a 50% increase in thermic effect of food (TEF) over LCT diet after 6 days, indicating enhanced energy expenditure.format_quote

Download

Thermogenesis in humans during overfeeding with medium-chain triglycerides

Metabolism-clinical and Experimental, 1989

(LCT), ten male volunteers (ages 22 to 44) were overfed (150% of estimated energy requirement) li... more (LCT), ten male volunteers (ages 22 to 44) were overfed (150% of estimated energy requirement) liquid formula diets containing 40% of fat as either MCT or LCT. Each patient was studied for one week on each diet in a double-blind. crossover design. Resting metabolic rate (RMR) did not change during either week of overfeeding. The thermic response to food (TEF) was greater on day 1 following a meal (1,000 kcal) containing MCT than following an isocaloric meal containing LCT (8 ? .8% Y 5.8 + 5% of ingested energy; P < .05). Moreover, the TEF observed after a 1,000 kcal meal containing MCT increased significantly to 12% (+ 1.3%) of ingested energy after five days of MCT overfeeding. The TEF of the 1,000 kcal meal containing LCT was unchanged by five days of LCT overfeeding (6.6 + 1 .O% of ingested energy). Energy expenditure during a 20-hour continuous enteral infusion of the diet on day 7 was also significantly higher with the MCT diet than with the LCT diet (15.7 + 1.7% v 7.3 -+ .9% of ingested energy; P < .05). Our results demonstrate that excess dietary energy as MCT stimulates thermogenesis to a greater degree than does excess energy as LCT. This increased energy expenditure, most likely due to lipogenesis in the liver, provides evidence that excess energy derived from MCT is stored with a lesser efficiencv than is excess energy derived from dietary LCT.

format_quoteEnergy expenditure was significantly higher on an MCT diet (15.7%) compared to LCT (7.3%) during a continuous enteral infusion (P < 0.05).format_quote

Download

Carcinoid Tumors: Imaging Procedures and Interventional Radiology

World Journal of Surgery, 1996

The hypervascular nature of carcinoid tumors and their metastases allows a more aggressive role b... more The hypervascular nature of carcinoid tumors and their metastases allows a more aggressive role by the radiologist in diagnosis and interventional management. Double-contrast gastrointestinal studies still best define the primary neoplasms. Appendiceal tumors, the most frequent site of carcinoids, frequently escape radiologic detection until large enough to be discovered by computed tomography (CT). Superior mesenteric arteriography of the small bowel and cecum is useful when the scanning procedures are not revealing. The ''spokewheel'' configuration of the desmoplastic mesenteric masses and lymph node metastases are best seen by CT, whereas hepatic metastases can be demonstrated by CT, CT-angioportography (CTAP), ultrasonography (US), magnetic resonance imaging (MRI), and octreotide scintigraphy. Percutaneous needle biopsy with radiologic guidance confirms the diagnosis of carcinoid tumors and their metastases. Hepatic arteriography is frequently performed in preparation for hepatic embolization or chemoembolization. Hepatic vascular occlusion therapy, the procedure of choice for the management of inoperable carcinoid liver metastases, results in a partial response in at least 50% of patients and a mortality rate of 5%. Chemoembolization with microencapsulated cytotoxic agents and direct percutaneous ethanol injection should also be considered for the treatment of liver metastases.

format_quoteOnly 2% of carcinoid tumors <1 cm metastasize, while 80% of tumors >2 cm are metastatic, showing tumor size directly correlates with metastasis likelihood.format_quote

Download

A CMOS Area Image Sensor With Pixel Level A/D Conversion

A CMOS 64 × 64 pixel area image sensor chip using Sigma-Delta modulation at each pixel for A/D co... more A CMOS 64 × 64 pixel area image sensor chip using Sigma-Delta modulation at each pixel for A/D conversion is described. The image data output is digital. The chip was fabricated using a 1.2µm two layer metal single layer poly n-well CMOS process. Each pixel block consists of a phototransistor and 22 MOS transistors. Test results demonstrate a dynamic range potentially greater than 93dB, a signal to noise ratio (SNR) of up to 61dB, and dissipation of less than 1mW with a 5V power supply.

format_quoteThe image sensor demonstrates a dynamic range greater than 93dB and SNR up to 61dB while consuming less than 1mW power.format_quote

Download

Test structures for characterization and comparative analysis of CMOS image sensors

A set of test structures designed to characterize and compare the performance of CMOS passive and... more A set of test structures designed to characterize and compare the performance of CMOS passive and active pixel image sensors is presented. The test structures are deigned so that they can be rapidly ported from one process to another. They are also designed so that individual photodetectors and pixel circuits as well as entire image sensor arrays can be characterized and compared based on: quantum efficiency, spectral response, fixed pattern noise, sensitivity, blooming, input referred read noise, reduction of quantum efficiency caused by silicide/salicide, lag, digital switching noise sensitivity, impact ionization noise sensitivity, dynamic range, and temperature dependency of all measured parameters. Four test chips that include a variety of these structures have been built in two different 0.35 micrometer CMOS processes. The test chips include nineteen types of individual photodetectors and thirty eight types of 64 by 64 pixel arrays. The test methodology and preliminary test results from these chips are presented.

A CMOS area image sensor with pixel-level A/D conversion

Charge-coupled devices (CCD) are at present the most widely used technology for implementing area... more Charge-coupled devices (CCD) are at present the most widely used technology for implementing area image sensors. However, they suffer from low yields, consume too much power, and are plagued with SNR limitations due to the shifting and detection of analog charge packets, and the fact that data is communicated off chip in analog form. This paper describes an area image sensor that can potentially circumvent the limitations of CCDs and their alternatives. It uses a standard CMOS process and can therefore be manufactured with high yield. Digital circuitry for control and signal processing can be integrated with the sensor. Moreover, CMOS technology advances such as scaling and extra layers of metal can be used to improve pixel density and sensor performance. The analog image data is immediately converted to digital at each pixel using a one-bit sigma-delta modulator. The use of sigma-delta modulation allows the data-conversion circuitry to be simple and insensitive to process variations. A global shutter provides variable light input attenuation to achieve wide dynamic range. Data is communicated off chip in a digital form, eliminating the SNR degradation of analog data communication. To demonstrate the viability of the approach, an area image sensor chip is fabricated in a 1.2 /spl mu/m CMOS technology. The device consists of an array of 64x64 pixel blocks, a clock driver, a 6:64 row address decoder, 64 latched sense amplifiers, and 16 4:1 column multiplexers. The chip also contains data compression circuitry.>

Download

A Method for Estimating Quantum Efficiency for CMOS Image Sensors

The standard method for measuring QE for a CCD sensor is not adequate for CMOS APS since it does ... more The standard method for measuring QE for a CCD sensor is not adequate for CMOS APS since it does not take into consideration the random offset, gain variations, and nonlinearity introduced by the APS readout circuits. The paper presents a new method to accurately estimate QE of an APS. Instead of varying illumination as in the CCD method, illumination is kept constant and the pixel output is continuously observed -sampling at regular intervals. This makes it possible to eliminate random offset. The experiment is repeated multiple times to obtain good estimates of the pixel output mean and variance at each sample time. The sensor response is approximated by a piecewise linear function and using the Poisson statistics of shot noise (which are also used in the CCD method) gain, charge and read noise are estimated for each line segment. This procedure is repeated at no illumination so that dark charge may be estimated and subtracted from the total charge estimates. The method can also be used to estimate readout noise and gain FPN. Results from 64×64 pixel APS test structures implemented in a 0.35 um CMOS process are reported. Using 6 different chips and 16 pixels per chip QE=0.37, gain FPN=2%, dark charge=832e-, and readout noise= 40e-, are estimated.

Download

Comparative analysis of SNR for image sensors with enhanced dynamic range

Dynamic range is a critical figure of merit for image sensors. Often a sensor with higher dynamic... more Dynamic range is a critical figure of merit for image sensors. Often a sensor with higher dynamic range is regarded as higher quality than one with lower dynamic range. For CCD and CMOS sensors operating in the integration mode the sensor SNR monotonically increases with the signal. Therefore, a sensor with higher dynamic range, generally, produces higher quality images than one with lower dynamic range. This, however, is not necessarily the case when dynamic range enhancement schemes are used. For example, using the well capacity adjusting scheme dynamic range is enhanced but at the expense of substantial degradation in SNR. On the other hand, using multiple sampling dynamic range can be enhanced without degrading SNR. Therefore, even if both schemes achieve the same dynamic range the latter can produce higher image quality than the former. The paper provides a quantitative framework for comparing SNR for image sensors with enhanced dynamic range. We introduce a simple model to describe the sensor output response as a function of the photogenerated signal, dark signal, and noise for sensors operating in integration mode with and without dynamic range enhancement schemes. We use the model to quantify and compare dynamic range and SNR for three sensor operation modes, integration with shuttering, using the well capacity adjusting scheme, and using multiple sampling. 8473 * In the paper, lower case letters will indicate constant values, e.g. mean of a signal, and upper case letters will indicate random variables. † This assumes that the min is always positive, which is true with high probability, since with high probability the integrated shot noise is much less than the signal charge (including dark current).

Download

A 640×512 CMOS image sensor with ultrawide dynamic range floating-point pixel-level ADC

IEEE Journal of Solid-state Circuits, 1999

Analysis results demonstrate that multiple sampling can achieve consistently higher signal-to-noi... more Analysis results demonstrate that multiple sampling can achieve consistently higher signal-to-noise ratio at equal or higher dynamic range than using other image sensor dynamic range enhancement schemes such as well capacity adjusting. Implementing multiple sampling, however, requires much higher readout speeds than can be achieved using typical CMOS active pixel sensor (APS). This paper demonstrates, using a 640 2 2 2 512 CMOS image sensor with 8-b bit-serial Nyquist rate analog-todigital converter (ADC) per 4 pixels, that pixel-level ADC enables a highly flexible and efficient implementation of multiple sampling to enhance dynamic range. Since pixel values are available to the ADC's at all times, the number and timing of the samples as well as the number of bits obtained from each sample can be freely selected and read out at fast SRAM speeds. By sampling at exponentially increasing exposure times, pixel values with binary floating-point resolution can be obtained. The 640 2 2 2 512 sensor is implemented in 0.35-m CMOS technology and achieves 10.5 2 2 2 10.5 m pixel size at 29% fill factor. Characterization techniques and measured quantum efficiency, sensitivity, ADC transfer curve, and fixed-pattern noise are presented. A scene with measured dynamic range exceeding 10 000 : 1 is sampled nine times to obtain an image with dynamic range of 65 536 : 1. Limits on achievable dynamic range using multiple sampling are presented.

Download

A 640×512 CMOS image sensor with ultra wide dynamic range floating-point pixel-level ADC

The dynamic range of an image sensor is often not wide enough to capture scenes with both high li... more The dynamic range of an image sensor is often not wide enough to capture scenes with both high lights and dark shadows. A 640/spl times/512 image sensor with Nyquist rate pixel level ADC implemented in a 0.35 /spl mu/m CMOS technology shows how a pixel level ADC enables flexible efficient implementation of multiple sampling. Since pixel values are available to the ADCs at all times, the number and timing of the samples as well as the number of bits obtained from each sample can be freely selected without the long readout time of APS. Typically, hundreds of nanoseconds of settling time per row are required for APS readout. In contrast, using pixel level ADC, digital data is read out at fast SRAM speeds. This demonstrates another fundamental advantage of pixel level ADC-the ability to programmably widen dynamic range with no loss in SNR.

Download

Pixel Level Processing — Why, What, and How

Pixel level processing promises many significant advantages including high SNR, low power, and th... more Pixel level processing promises many significant advantages including high SNR, low power, and the ability to adapt image capture and processing to different environments by processing signals during integration. However, the severe limitation on pixel size has precluded its mainstream use. In this paper we argue that CMOS technology scaling will make pixel level processing increasingly popular. Since pixel size is limited primarily by optical and light collection considerations, as CMOS technology scales, an increasing number of transistors can be integrated at the pixel. We first demonstrate that our argument is supported by the evolution of CMOS image sensors from PPS to APS. We then briefly survey existing work on analog pixel level processing and pixel level ADC. We classify analog processing into intrapixel and interpixel. Intrapixel processing is mainly used to improve sensor performance, while interpixel processing is used to perform early vision processing. We briefly describe the operation and architecture of our recently developed pixel level MCBS ADC. Finally we discuss future directions in pixel level processing. We argue that interpixel analog processing is not likely to become mainstream even for computational sensors due to the poor scaling of analog compared to digital circuits. We argue that pixel level A/D conversion will become increasingly popular since it minimizes analog processing, and requires only simple and imprecise circuits to implement. We then discuss the inclusion of digital memory and interpixel digital processing in future technologies to implement programmable digital pixel sensors.

Download

A Nyquist-rate pixel-level ADC for CMOS image sensors

IEEE Journal of Solid-state Circuits, 1999

A multichannel bit-serial (MCBS) analog-to-digital converter (ADC) is presented. The ADC is ideal... more A multichannel bit-serial (MCBS) analog-to-digital converter (ADC) is presented. The ADC is ideally suited to pixel-level implementation in a CMOS image sensor. The ADC uses successive comparisons to output one bit at a time simultaneously from all pixels. It is implemented using a 1-bit comparator/latch pair per pixel or per group of neighboring pixels, and a digital-to-analog-converter/controller shared by all pixels. The comparator/latch pair operates at very slow speeds and can be implemented using simple robust circuits. The ADC's can be fully tested by applying electrical signals without any optics or light sources. A CMOS 320 2 2 2 256 sensor using the MCBS ADC is described. The chip measures 4.14 2 2 2 5.16 mm 2 . It achieves 10 2 2 2 10 m 2 pixel size at 28% fill factor in 0.35m CMOS technology. Each 2 2 2 2 2 pixel block shares an ADC.

Download

ENDOGENOUS INNOVATION GROWTH THEORY AND REGIONAL INCOME CONVERGENCE IN CHINA

Endogenous innovation growth theory is tested by using panel data for 27 provinces across China. ... more Endogenous innovation growth theory is tested by using panel data for 27 provinces across China. R&D expenditure and openness are added to the standard convergence regressions to control for different structural characteristics in each province. A standardized`t-bar' test for unit roots is applied to examine the properties of the data and identify a long-run relationship among the variables. By allowing for differences in the aggregate production function across regions, we ®nd evidence of convergence. The empirical results support the endogenous innovation growth model in which regional per capita income can converge given technological diffusion, transfer and imitation.

Download

David Yang

Uploads

Papers by David Yang

Log In