Three-dimensional digital subtraction angiography

A dye-edge tracking algorithm was used to determine the corresponding points in the two images (anterior-posterior and lateral) of the digital subtraction biplane angiography. This correspondence was used to reconstruct three-dimensional images of cerebral arteries in a dog experiment and a clinical observation. The method was tested by comparing the measured image of oblique view to the computed reconstructed image. For the present study, we have developed three new algorithms. The first algorithm is to determine the corresponding dye-edge points using the fact that the density of contrast media at the moving edge shows the same changing pattern in the two projection views. This moving pattern of dye-edge density is computed using a matching method of cross correlation for the two sequential frames' dye density. The second algorithm is for simplified perspective transformation, and the third is to identify the corresponding points using a complementary method for locating the approximate points on the small vessels. The present method can be applied to compute the velocity of blood flow using the dye-edge displacement and the three-dimensional distance data.     

Flexible mask subtraction for digital angiography

A flexible-mask algorithm that effectively provides correction for motion artifacts and gray-level variations in digital subtraction angiography (DSA) images is presented. The algorithm makes use of a flexible local registration of the mask with the live image to minimize the main distortions caused by the complex motion of the heart, namely spatial translation, rotation, and nonisotropic scaling. It also reduces the gray-level variations caused by the diffusion of the contrast medium into parts of the heart other than the arteries. It is concluded from experiments on X-ray coronary angiograms that when the background near the arteries is rugged or provides significant interference, flexible mask subtraction offers important improvements in quantitative estimates of the sizes of the arteries. In all the X-ray images used in the experiments, the precision of the method was at the 0.1-pixel level. The computation is extensive. However, some improvements can be achieved by doing the subtraction only at the coronary arteries and the immediate neighborhood instead of the whole image. The algorithm lends itself to implementation by parallel-structured hardware.     

CCD camera for dual-energy digital subtraction angiography

A motion immune dual-energy subtraction technique in which X-ray tube voltage and beam filtration were switched at 30 Hz between 60 kVp (2.0 mm Al filter) and 120 kVp (2.00 mm Al+2.5 mm Cu filter) was previously reported. In this study the effects of camera lag on the dual-energy iodine signal is investigated. The temporal lag of the lead oxide vidicon tested reduced the dual-energy iodine signal by a factor of 2.3, as compared to a mode that included 4 scrub frames between low- and high-energy images, for an iodine phantom with thicknesses of 0-86.0 mg/cm(2), imaged over a 15 cm thick Lucite phantom. On the other hand, the Charge-Coupled Device (CCD) camera has inherently no temporal lag and its versatile scanning characteristics make it near ideal for dual-energy DSA. The CCD camera eliminates the reduction of dual-energy iodine signal, since it does not mix low- and high-energy image data. Another benefit of the CCD camera is that the separation time between low and high-energy images is not limited to the frame period, as is the lead oxide vidicon; and as small as a 5-msec time difference is possible. The short time interval between low and high-energy images minimizes motion misregistration artifacts. Due to these advantages, the CCD camera significantly improves the utility of dual-energy DSA.     

Motion detection and motion compensation for digital subtraction angiography image enhancement

For the enhancement of digital subtraction angiography (DSA) images, registration of mask and contrast image prior to subtraction is a pre-requisite. One of the main requirements of this task is that the region-of-interest used for the calculation of the registration parameters should contain the vascular structures of interest. This, however, is also one of the main problems in DSA because the contrasted vascular structures can be regarded as a distortion that makes the images to be compared dissimilar. In this paper we present a comparison between three frequently used similarity measures and histogram-based similarity measures. This reveals the advantages of the latter. The data-driven approach is especially suitable for registration of two images which are identical except for some structures visible in one but not in the other image. Based on an energy similarity measure, a motion vector field is obtained by template matching, which gives a set of homologous landmarks or control points in the mask and contrast image. A point-based registration is performed fitting the parameter of an appropriate transformation for patient motion correction. An affine and an elastic transformation are compared for an abdominal fluoroscopic scene.     

Limitations of the lead oxide vidicon for dual-energy digital subtraction angiography

Dual-energy digital subtraction angiography (DSA) can be performed, with some modifications, using existing systems designed for conventional DSA work. However, the video camera generally found in such installations, the lead oxide vidicon, places significant limitations on the image quality of dual-energy DSA. If the video camera is operated in a 60 Hz, 266 line progressive scanning mode to maintain a nominal 30 subtraction images/s frame rate, the maximum available X-ray pulse width is limited to 5 ms. The resulting required increase in low-energy kVp reduces the dual-energy signal-to-noise ratio by approximately 40% for cardiac dual-energy DSA imaging. In addition, the performance of the video camera with respect to read-out lag is much more important for dual-energy DSA than conventional single-energy imaging. Measurements show that lag reduces the iodine contrast in dual-energy DSA by up to 20% when a 30 Hz vertical scan mode is used, and by up to 27% when a 60 Hz vertical scan mode is employed. Replacement of the lead oxide vidicon with a CCD camera removes these limitations.     

Retrospective motion correction in digital subtraction angiography: a review

Digital subtraction angiography (DSA) is a well-established modality for the visualization of blood vessels in the human body. A serious disadvantage of this technique, inherent to the subtraction operation, is its sensitivity to patient motion. The resulting artifacts frequently reduce the diagnostic value of the images. Over the past two decades, many solutions to this problem have been put forward. In this paper, the authors give an overview of the possible types of motion artifacts and the techniques that have been proposed to avoid them. The main purpose of this paper is to provide a detailed review and discussion of retrospective motion correction techniques that have been described in the literature, to summarize the conclusions that can be drawn from these studies, and to provide suggestions for future research     

Respiratory-synchronized digital subtraction angiography based on a respiratory phase matching method

Catheter-based therapy is typically performed under fluoroscopic image observation. However, the vessel structure cannot be visualized on fluoroscopic images. To overcome this limitation, angiographic images are captured with a contrast agent, and digital subtraction angiography (DSA) images are acquired during the intervention. In thoracoabdominal DSA, patients have to hold their breath to match the respiratory phase during DSA acquisition. However, breath holding is difficult for some patients, including the elderly. If the organs move during DSA acquisition, artifacts can occur on DSA images, and the DSA acquisition must be performed again. In the present study, we describe and characterize a new respiratory phase matching method for respiratory-synchronized DSA acquisition under natural respiration. Preoperative angiographic and intra-operative fluoroscopic images were collected under natural respiration during the operation. For each fluoroscopic image, we used a pattern matching to select an angiographic image in the most similar respiratory phase. We then examined whether the method could be applied to both the free breathing DSA and the respiratory-synchronized roadmap. We found that our proposed respiratory phase matching method produced acceptable DSA images without breath holding, and that the processing could be performed in real time.     

高精度激光直写数字伺服滤波器的设计

为提高激光直写控制系统的定位精度、定位时间和系统响应度,设计了一种数字伺服滤波器.该滤波器以伺服系统的三环PID控制原理为基础,并在设计中加入了具有实际问题性的前馈补偿模块;建立了以TMS3202812处理器组成的数字伺服滤波器模型;并对该模型进行了模拟仿真分析,然后移植到处理器中;最后通过验证,提高了位置定位和速度稳定精度.实验结果表明,整个系统输入与输出时差小于100 Ls;无噪音无振荡,效果很好;定位精度误差控制±1μm范围内.     

A time domain fluorescence tomography system for small animal imaging

We describe the application of a time domain diffuse fluorescence tomography system for whole body small animal imaging. The key features of the system are the use of point excitation in free space using ultrashort laser pulses and noncontact detection using a gated, intensified charge-coupled device (CCD) camera. Mouse shaped epoxy phantoms, with embedded fluorescent inclusions, were used to verify the performance of a recently developed asymptotic lifetime-based tomography algorithm. The asymptotic algorithm is based on a multiexponential analysis of the decay portion of the data. The multiexponential model is shown to enable the use of a global analysis approach for a robust recovery of the lifetime components present within the imaging medium. The surface boundaries of the imaging volume were acquired using a photogrammetric camera integrated with the imaging system, and implemented in a Monte-Carlo model of photon propagation in tissue. The tomography results show that the asymptotic approach is able to separate axially located fluorescent inclusions centered at depths of 4 and 10 mm from the surface of the mouse phantom. The fluorescent inclusions had distinct lifetimes of 0.5 and 0.95 ns. The inclusions were nearly overlapping along the measurement axis and shown to be not resolvable using continuous wave (CW) methods. These results suggest the practical feasibility and advantages of a time domain approach for whole body small animal fluorescence molecular imaging, particularly with the use of lifetime as a contrast mechanism.      

Fourier domain techniques for digital angiography of the heart

Digital angiography is widely considered simply as a method in which images taken at different times are subtracted from each other. This paper presents some techniques which are performed in the frequency domain after the application of the Fourier transform. Nonselective bypass angiograms and intravenous ventriculograms are taken as examples to show that simple procedures utilizing these techniques exhibit the advantages of improved signal-to-noise ratio in the subtraction images, reduction of motion artifacts, easy application of phase-synchronous subtraction, integration, and quantitative visualization of blood propagation. It is furthermore shown that the storage of the angiographic image sequence as Fourier coefficients leads to data compression and convenient data access in an image database.     

一种高精度时钟同步电路

本文提出了一种基于交错延迟单元和动态补偿电路的高精度时钟同步电路结构,HPSC,并 可用在对时钟要求较高的大规模分布网络中。此电路采用了基于SMD的粗调结构和动态补偿 电路的细调结构,可在两个时钟周期内完成粗调并在接下来三个时钟周期内完成细调,其误 差小于3.8 ps。本电路使用SMIC 0.13 μm 1P6M 工艺设计并实现,供电电压1.2 V。其输入 频率为200MHz-800MHz,占空比为20%-80%,有效面积 245μm×134μm,功耗为1.64 mW@500MHz     

用于低压差线性稳压器的输出精密微调设计技术

提出了一种用于低压差线性稳压器(LDO:Low-Dropout regulator)的输出精密微调方法,通过在反馈网络中引入可微调电阻梯实现对LDO输出的精密调整,并采取伪电阻保护的版图布局方式提高电阻梯的匹配性能。基于65 nm CMOS工艺对LDO进行了设计,整个LDO线性调整率约为0.05mV/V,输出电压在1.02V~1.36V范围内能够按照0.02V/step的最小步长进行精密微调,能有效减小由电源电压、温度等因素引起的输出误差,适合嵌入式片上系统(So C:System-on-Chip)的应用。     

A high-frame rate duplex ultrasound biomicroscopy for small animal imaging in vivo

Much of the current knowledge of human cardiovascular pathologies and treatment strategies has been gained from understanding the cardiac physiologies and functions in small animal models, such as mice, rats, and zebrafish. In this paper, we present the development of a high-frame-rate duplex ultrasound biomicroscopy (UBM) capable of B-mode imaging and pulsed-wave (PW) Doppler measurement for in vivo cardiovascular investigation in small animals. A frame rate of 200 frames per second (fps) was accomplished at a view of 5 mm $times$ 8 mm, using a novel high-speed sector probe and specially designed lightweight transducers. In a reduced lateral view of 1.2 mm, a frame rate of 400 fps was achieved to examine more detailed cardiac motion. The UBM utilized transducers with different center frequencies (40–75 MHz) and geometries, which made it useful for various applications in small animal cardiac imaging. The highest spatial resolution the UBM achieved was 25 $mu$m $times$ 56 $mu$ m. In addition, the image-guided PW Doppler implemented in the UBM demonstrated the detection of the velocity of a moving wire as low as 0.1 mm/s, and flow in a polyimide tube as small as 200 $mu$ m in diameter. Furthermore, the UBM achieved a 15-$mu$ V minimal detectable signal and a 60-dB dynamic range using a low-cost PCB-based design. Finally, sample in vivo cardiac images of mouse and zebrafish hearts were given. These results showed that the UBM integrated with B-mode and PW Doppler is useful to investigate the pathophysiological mechanism in the cardiovascular studies.      

A low power and small area digital self-calibration technique for pipeline ADC

A digital self-calibration implementation with discontinuity-error and gain-error corrections for a pipeline analog-to-digital converter (ADC) is presented. In the proposed calibration method, the error owing to each reference unit capacitor of the multiplying D/A converter is measured separately using a calibration capacitor and an enhanced resolution back-end pipeline ADC acting as an error quantizer. The offset and finite open loop DC-gain of the operational amplifier and capacitor mismatches, the reference voltage mismatch can all be calibrated. The calibration can be achieved by that only used addition and subtraction. Hence, it needs low power and area consuming. A prototype ADC with the proposed calibration was fabricated on a 0.5 μm double-poly triple-metal CMOS process. The power consumption and area of the calibration circuit are only 10.1 mW and 1.05 mm², respectively. At a sampling rate of 30 MS/s, the calibration improves the DNL and INL from 2.59 LSB and 14.98 LSB to 0.72 LSB and 1.82 LSB, respectively. For a 1.25 MHz sinusoidal signal, the calibration improves the signal-to-noise-distortion ratio and spurious-free dynamic range from 43.1 dB and 52.1 dB to 75.51 dB and 83.61 dB, respectively. The 12.25 effective number of bits at 30 MS/s ADC consumes a total power of 136 mW.     

Intensity surface stretching technique for contrast enhancement of digital photography

In this paper we propose a contrast enhancement technique which stretches the intensity surfaces of an image to improve the quality of a digital photo. The proposed method enhances the contrast of an image by stretching the intensity surface of the original image to the maximum range of the output image. This is done in proportion to the distances between the original intensity surface, and the upper and lower intensity surfaces respectively. The upper and lower intensity surfaces are generated adaptively from the original intensity surface by gaussian smoothing and gamma transform. In our experiments, digital color images in a variety of illumination conditions were used, and the proposed method was compared with other algorithms such as histogram stretching, histogram equalization, gamma correction, and retinex. From the results of the experiments, it was proven that the proposed algorithm further enhanced the contrast more than other methods and resulted in a more natural image without deterioration of gradation.

A high-precision VLSI winner-take-all circuit for self-organizingneural networks

The design and implementation of a high-precision VLSI winner-take-all (WTA) circuit that can be arranged to process 1024 inputs are presented. The cascade configuration can be used to significantly increase the competition resolution and maintain high-speed operation for a large-scale network. The total bias current increases in proportion to the number of circuit cells so that a nearly constant response time is achieved. A unique dynamic current steering method is used to ensure that only a single winner exits in the final output. Experimental results for a prototype chip fabricated in a 2-μm CMOS technology show that a cell can be a winner if its input is larger than those of the other cells by 15 mV. The measured response time is around 50 ns at a 1-pF load capacitance. This analog winner-take-all circuit is a key module in the competitive layer of self-organizing neural networks     

Fluorescent protein tomography scanner for small animal imaging

Microscopy of fluorescent proteins has enabled unprecedented insights into visualizing gene expression in living systems. Imaging deeper into animals, however, has been limited due to the lack of accurate imaging methods for the visible. We present a novel system designed to perform tomographic imaging of fluorescent proteins through whole animals. The tomographic method employed a multiangle, multiprojection illumination scheme, while detection was achieved using a highly sensitive charge-coupled device camera with appropriate filters. Light propagation was modeled using a modified solution to the diffusion equation to account for the high absorption and high scattering of tissue at the visible wavelengths. We show that the technique can quantitatively detect fluorescence with sub millimeter spatial resolution both in phantoms and in tissues. We conclude that the method could be applied in tomographic imaging of fluorescent proteins for in vivo targeting of different diseases and abnormalities.     

A two-dimensional hot carrier injector for electron waveguide structures

The current-voltage characteristics for a constriction in a quantum waveguide channel are calculated. The constriction forms an effective barrier which can be employed as a tunneling injector. We find that such a structure may be useful in providing high-energy electrons in a single mode of the waveguide. We also examine the current in the far-from-linear response regime. Away from the linear region the current through the constriction saturates and the conductance falls to zero.     

一种面向智能传感器的低功耗高精度sigma-delta调制器设计

设计了一款工作在1.2 V电源电压下,功耗为196μW,精度为14 bit,FOM值达202.4,应用于物联网领域的ΣΔ调制器,其OSR为64,采用四阶前馈单位量化结构,大幅度降低了系统对OTA的要求。通过Matalb SD-TOOLBOX确定系统参数,进行行为级建模确定最优值,同时对系统架构和电路模块进行低功耗分析,针对调制器各级进行适当的增益缩放。该调制器采用SMIC0.18μCMOS工艺设计,输入信号频率为3.4 k Hz,采样时钟为1.28 MHz时,调制器SNDR达到88.6 d B,达到有效位14 bit精度,处理带宽10 k Hz的要求。     

一种基于提升小波变换的数字水印算法

根据提升方式的小波变换理论,提出了一种可以与JPEG2000标准完全兼容的静止图像数字水印算法,可以在图像中嵌入多个相同或不同的水印信息。实验证明,算法对包括JPEG2000在内的各种常见攻击手段都表现出了很好的鲁棒性。