A stationary sampling scheme for multilayer positron tomographs

A stationary sampling scheme applicable to tomographic instruments incorporating two or more detector layers is described and tested. In this concept, the detectors in adjacent layers are angularly offset by half the interdetector distance. By reconstructing in one single slice all lines of response defined by two adjacent rings of detectors, a fourfold increase in the number of coincidence lines is obtained and a uniform sampling distance equal to one-quarter the interdetector spacing is achieved. Whereas this is obtained at the expense of a 100% degradation of the resolution in the axial direction, with the recent breed of PET (positron emission tomography) scanners using nearly square cross section detectors, the resolution loss may be tolerable in many situations. In addition, normal reconstruction of the individual coincidence planes is always possible. The sampling concept was investigated experimentally with the help of the Universite de Sherbrooke PET camera simulator.     

Non linear response and optimization of a new z-axis resonant micro-accelerometer

Micro-Electro-Mechanical Systems (MEMS) accelerometers are micro-sized devices largely used for detecting accelerations in the consumer and automotive market. Both capacitive and resonant sensing have been successfully employed in these devices.In the present work, the focus is on a z-axis resonant accelerometer recently proposed in [1] and fabricated with the Thelma^© surface-micromachining technique developed by STMicroelectronics [2].After a full non-linear dynamic study, two possible optimized designs are studied through an optimization procedure. The goal of the work is to find a novel design for the z-axis resonant accelerometer which meets the linearity and the reliability requirements for MEMS accelerometers whitout losses in terms of sensitivity.     

基于极大倾角光纤光栅的降钙素原免疫传感器

降钙素原(Procalcitonin,PCT)对于反映患者炎症甚至败血症患病程度具有重要意义。为实现低浓度PCT的免标记检测,利用极大倾角光纤光栅(Excessively Tilted Fiber Grating,Ex-TFG)的低温度交叉敏感性和高折射率灵敏度的优点,在光纤的表面修饰金黄色葡萄球菌(Staphylococcus Aureus Protein A,SPA),再将PCT单克隆抗体固定在SPA分子层,从而构成对PCT具有特异性检测功能的免疫传感器。实验结果表明:降钙素原含量为0.5ng/mL时,谐振波长红移约13pm;PCT的浓度为200ng/mL时,Ex-TFG的红移量基达约125pm;浓度为1 000ng/mL时,红移量趋于饱和,最大红移量约150pm。通过对实验数据拟合,发现Ex-TFG谐振波长的红移量与PCT浓度之间的关系满足Langmuir模型,相关性系数为0.98。该方法为低浓度PCT的检测提供了一种免标记、快速的检测方法。     

Spiral interpolation algorithms for multislice spiral CT--part II: measurement and evaluation of slice sensitivity profiles and noise at a clinical multislice system

The recently introduced multislice data acquisition for computed tomography (CT) is based on multirow detector design, increased rotation speed, and advanced z-interpolation and z-filtering algorithms. We evaluated slice sensitivity profiles (SSPs) and noise of a clinical multislice spiral CT (MSCT) scanner with M = 4 simultaneously acquired slices and adaptive axial interpolator (AAI) reconstruction software. SSPs were measured with a small gold disk of 50 microm thickness and 2-mm diameter located at the center of rotation (COR) and 100 mm off center. The standard deviation of CT values within a 20-cm water phantom was used as a measure of image noise. With a detector slice collimation of S = 1.0 mm, we varied spiral pitch p from 0.25 to 2.0 in steps of 0.025. Nominal reconstructed slice thicknesses were 1.25, 1.5, and 2.0 mm. For all possible pitch values, we found the full-width at half maximum (FWHM) of the respective sensitivity profile at the COR equivalent to the selected nominal slice thickness. The profiles at 100 mm off center are broadened less than 7 % on the average compared with the FWHM at the COR. In addition, variation of the full-width at tenth maximum (FWTM) at the COR was below 10% for p < or = 1.75. Within this range, image noise varied less than 10% with respect to the mean noise level. The slight increase in measured slice-width above p = 1.75 for nominal slice-widths of 1.25 and 1.50 mm is accompanied by a decrease of noise according to the inverse square root relationship. The MSCT system that we scrutinized provides reconstructed slice-widths and image noise, which can be regarded as constant within a wide range of table speeds. With respect to this, MSCT is superior to single-slice spiral CT. These facts can be made use of when defining and optimizing clinical protocols: the spiral pitch can be selected almost freely, and scan protocols can follow the diagnostic requirements without technical restrictions. In summary, MSCT offers constant image quality while scan times are reduced drastically. Volume scans with three-dimensional (3-D) isotropic resolution are routinely feasible for complete anatomical regions.     

一种应用于曝光机的新型z向系统方案及实验研究

z向系统是接触式曝光机的关键部件之一。设计了一种曝光机的新型z向系统方案,该方案采用气动控制的方式,通过控制气体压力来调整接触力,用空气轴承导向,完成找平、微分离的自动控制。对z向系统设计原理进行了详细介绍,并通过实验对其部分功能进行了验证。     

Fully 3-D PET reconstruction with system matrix derived from point source measurements

The quality of images reconstructed by statistical iterative methods depends on an accurate model of the relationship between image space and projection space through the system matrix The elements of the system matrix for the clinical Hi-Rez scanner were derived by processing the data measured for a point source at different positions in a portion of the field of view. These measured data included axial compression and azimuthal interleaving of adjacent projections. Measured data were corrected for crystal and geometrical efficiency. Then, a whole system matrix was derived by processing the responses in projection space. Such responses included both geometrical and detection physics components of the system matrix. The response was parameterized to correct for point source location and to smooth for projection noise. The model also accounts for axial compression (span) used on the scanner. The forward projector for iterative reconstruction was constructed using the estimated response parameters. This paper extends our previous work to fully three-dimensional. Experimental data were used to compare images reconstructed by the standard iterative reconstruction software and the one modeling the response function. The results showed that the modeling of the response function improves both spatial resolution and noise properties.     

HTS and PCT Reliability of Chips and Flex Substrates Assembled Using a Thermosonic Flip-Chip Bonding Process

This study assesses the high-temperature storage (HTS) test and the pressure-cooker test (PCT) reliability of an assembly of chips and flexible substrates. After the chips were bonded onto the flexible substrates, specimens were utilized to assess the HTS test and PCT reliability. After the PCT and HTS tests, the die-shear test was applied to examine changes in die-shear forces. The microstructure of the test specimens was analyzed to evaluate reliability and to identify possible failure mechanisms. When the duration of the HTS test was increased, the percentage of gold bumps that peeled off from the surface of the copper pads on the chip side increased, and a crack was present at the bonding interface between the gold bumps and chip bond pads. This crack was due to thermal stress generated during the HTS test, and degraded the die-shear force of the assembly of chips and flexible substrates. After the PCT, the crack was present at the interface between deposited layers of copper electrodes after the specimens were subjected to the PCT for various durations. Moisture penetrated into the deposited layers of the copper electrodes, deposited layers lost their adhesion, and the crack progressed from the corner into the central bond area as the test duration increased. To improve the PCT reliability of assemblies of chips and flexible substrates using the thermosonic flip-chip bonding process, one must prevent moisture from penetrating into deposited layers of copper electrodes and prevent crack formation at the interface between nickel and copper layers. Underfill would be an effective approach to prevent moisture from penetrating into deposited layers during the PCT, thereby improving the reliability of the samples during the PCT.     

Spiral interpolation algorithm for multislice spiral CT--part I: theory

This paper presents the adaptive axial interpolator (AAI), a novel spiral interpolation approach for multislice spiral computed tomography (CT) implemented in a clinical multislice CT scanner, the SOMATOM Volume Zoom (Siemens Medical Systems, Forchheim, Germany). The method works on parallel-beam data generated from the acquired fan-beam data by azimuthal rebinning. Spiral interpolation is performed by distance-dependent weighting; i.e., for each ray, its distance to the image plane is evaluated and serves as an argument to a freely selectable weighting function, resulting in a weight factor. A normalization step is applied to the weight factors to ensure that the sum of all corresponding weights (i.e., the weights applied to rays that contribute to the same ray in the interpolated sinogram) is 1. By selection of appropriate weighting functions and suitable adjustment of the tube current, it is possible to keep the slice sensitivity profiles (SSP) as well as the pixel noise constant for all pitch values in the relevant range. Also, a large range of slice-thickness can be reconstructed from a given collimation. The method is, thus, very versatile. Further advantages are that it uses the entire applied dose for imaging and allows for efficient implementation using a table lookup approach.     

A 3D reconstruction of vascular structures from two X-ray angiograms using an adapted simulated annealing algorithm

A three-dimensional (3D) reconstruction of the vessel lumen from two angiographic views, based on the reconstruction of a series of cross-sections, is proposed. Assuming uniform mixing of contrast medium and background subtraction, the cross-section of each vessel is reconstructed through a binary representation. A priori information about both the slice to be reconstructed and the relationships between adjacent slices are incorporated to lessen ambiguities on the reconstruction. Taking into account the knowledge of normal vessel geometry, an initial solution of each slice is created using an elliptic model-based method. This initial solution is then deformed to be made consistent with projection data while being constrained into a connected realistic shape. For that purpose, properties on the expected optimal solution are described through a Markov random field. To find an optimal solution, a specific optimization algorithm based on simulated annealing is used. The method performs well both on single vessels and on branching vessels possessing an additional inherent ambiguity when viewed at oblique angles. Results on 2D slice independent reconstruction and 3D reconstruction of a stack of spatially continuous 2D slices are presented for single vessels and bifurcations.     

Z-Axis anisotropic electrical conductor films in adhesive and standalone forms for electrical interconnection

Z-axis electrical conductor films in adhesive and standalone forms were made from nickel particles (one per conduction path) and a polymer matrix (polyvinylidene fluoride for the standalone film and epoxy for the adhesive film). The standalone film was found to exhibit resilience, conducting path pitch 125 μm and z-axis resistance 2 Ω. 4 Ω, 17, 48 Ω, and 160 Ω per connection at z-axis pressures of 1.39 MPa, 0.037 MPa, 0.0046 MPa, and 0 MPa respectively; each connection consisted of one nickel particle, which protruded from both sides of the film; the film exhibited no stress relaxation due to the absence of polymer deformation under z-axis pressure. The adhesive film exhibited pitch 64 μm and z-axis resistance 52 Ω per connection at zero pressure.     

Effect of a cylindrical refracting interface on ultrasoundintensity and the CW Doppler spectrum

The insonation of axisymmetric flow in a tube by an ultrasound beam which is refracted at the tube surface is considered. A three-dimensional (3-D) model for refraction at a cylindrical interface is developed. The incident beam, which is planar but otherwise arbitrary, is refracted at a single acoustic impedance interface between the medium within the tube and the surrounding medium. A ray approximation is used as the ultrasonic wavelength is small compared to the radius of curvature of the tube. A parametric form for the ray paths is obtained and used to derive an expression for the intensity. The intensity depends on the specific position within the tube, as well as the ratio of sound speeds, N, and the Doppler angle &thetas;_D. A diverging (N=1.2, &thetas;_D=45°) and a converging (N=0.8, &thetas;_D=45°) case are presented in detail. The converging interface results in more extreme intensity distortion. The regions of maximum and minimum intensity over a tube slice are immediately adjacent in both diverging and converging cases. Once the intensity distribution across a tube slice is known, the previously reported (Aldis and Thompson, 1992) volume integral method for the calculation of continuous wave (CW) Doppler spectral power density (spd) functions may be used. The effect of refraction of the incident beam on the spd function is shown for both an infinite beam and a circular beam with radius equal to the tube radius. A curved acoustic impedance interface, as may be encountered in vitro in flow phantoms or in vivo in vascular disease, leads to nonuniform insonation and spectral distortion which depends on transducer orientation     

Reliability of assembly of chips and flex substrates using thermosonic flip-chip bonding process with a non-conductive paste

This study investigates the reliability of the assembly of chips and flex substrates using the thermosonic flip-chip bonding process with non-conductive paste (NCP). The high-temperature storage (HTS) test, the temperature cycling test (TCT), the pressure cooker test (PCT) and the high-temperature/high-humidity (HT/HH) test were conducted to examine the reliability of chips that are bonded on flex substrates. The environmental parameters used in the various reliability tests were consistent with the JEDEC standards. After the reliability tests, a peeling test was performed and the microstructure of the tested specimen observed to evaluate further the reliability.The bonding strength increased with the storage period in the HTS test. After the peeling test, a layer of copper electrodes was observed to be stuck on gold bumps over the fractured morphology of the chips when the chips and flex substrates were assembled using an ultrasonic power of 14.46 W, indicating that the bonding strength between the gold bumps and the copper electrodes was even higher than the adhesive strength of the layers that were deposited on the flex substrates. The HTS test yielded sufficient thermal energy to promote atomic interdiffusion between gold bumps and copper electrodes. Metallurgical bonding between the gold bump and the copper electrode occurred, improving the bonding strength. In the assembly of chips and flex substrates without the application of ultrasonic power in bonding process, the adhesive strength of NCP was highly reliable after HTS test, because the bonding strength was maintained after HTS test for various storage periods. The typical failure mode of PCT was interfacial delamination between NCP and flex substrates. Approximately 80% of the specimens exhibited full separation after PCT at 336 h when chips and flex substrates were assembled without applied ultrasonic power to the bonding process, revealing that the NCP cannot withstand the PCT and lost its adhesive strength. Applying an adequate ultrasonic power of 14.46 W in the bonding process not only improved the bonding strength, but also enabled the bonding strength to be maintained at high level after PCT. The high bonding strength was attributable to the strong bonding of the gold bumps on the copper electrodes after PCT for various storage periods. This experimental result demonstrates that ultrasonic power can increase the reliability of PCT on chips and flex substrates that were assembled with the NCP. The bonding strength of the gold bumps on the flex substrates did not change significantly after the TCT, revealing the great reliability of TCT on chips and flex substrates that were assembled using the thermosonic flip-chip bonding process with the NCP. The bonding strength of chips bonded to flex substrates increased with the storage periods of the HT/HH test if ultrasonic power was applied to bonding process. Neither delamination nor any defect at the bonding interface was observed. The reliability of the HT/HH test for chips bonded on flex substrates using the thermosonic flip-chip process with the NCP fulfills the requirements stated in the JEDEC standards.According to the experimental findings of various reliability tests, the chips that were bonded to flex substrates using the thermosonic bonding process with NCP met the JEDEC specifications; with the exception of the adhesive strength of NCP under PCT which must be improved.     

Exact and approximate rebinning algorithms for 3-D PET data

This paper presents two new rebinning algorithms for the reconstruction of three-dimensional (3-D) positron emission tomography (PET) data. A rebinning algorithm is one that first sorts the 3-D data into an ordinary two-dimensional (2-D) data set containing one sinogram for each transaxial slice to be reconstructed; the 3-D image is then recovered by applying to each slice a 2-D reconstruction method such as filtered-backprojection. This approach allows a significant speedup of 3-D reconstruction, which is particularly useful for applications involving dynamic acquisitions or whole-body imaging. The first new algorithm is obtained by discretizing an exact analytical inversion formula. The second algorithm, called the Fourier rebinning algorithm (FORE), is approximate but allows an efficient implementation based on taking 2-D Fourier transforms of the data. This second algorithm was implemented and applied to data acquired with the new generation of PET systems and also to simulated data for a scanner with an 18° axial aperture. The reconstructed images were compared to those obtained with the 3-D reprojection algorithm (3DRP) which is the standard “exact” 3-D filtered-backprojection method. Results demonstrate that FORE provides a reliable alternative to 3DRP, while at the same time achieving an order of magnitude reduction in processing time     

Effect of amplitude modulation on selective excitation in NMR imaging

If NMR imaging uses selective excitation, then it has to do it correctly as it affects the image resolution. We have related the properties of the selected slice, such as its width, its rate of attenuation, and its side lobes to the amplitude modulation of the radio frequency pulse. An interesting observation was that multiplying sinc(t) function by a triangle can give better results than multiplying it with a Gauss function. We have used computer simulation and tried to emphasize the qualitative relationship between the properties. We conclude with some practical requirements and show the need of a numerical design procedure if the slice properties have to be optimized.     

电容式z轴微机械陀螺的噪声抑制

将z轴微机械陀螺两个模态的机械噪声效应等效为各自在单位噪声力作用下的振动,根据陀螺的工作原理得到两个噪声力作用下陀螺敏感模态的机械输出噪声。建立了包含运放和电路板非理想因素在内的接口电路的噪声模型。结合机械噪声模型和接口电路模型噪声,建立了包括结构参数和电路最小检测电容量在内的陀螺的噪声等效输入角速度模型,为陀螺的设计优化提供了参考。分析了结构参数对陀螺等效输入角速度噪声影响,并采用两个参数不同的电容式z轴微机械陀螺进行了实验。结果表明,通过结构参数的调整,将电容式z轴微机械陀螺的输出噪声从414μV/Hz降低至235μV/Hz。     

Quad-Detector Arrangement and Sampling Characteristics in Rotary Positron Tomography: POSITOLOGICA II

This paper clarifies that a method of rotary positron-emission computed tomography (PCT) with quad (tri or bi)-detector units can provide the satisfactory sampling characteristics with negligible sacrifice (less than 1 percent) of the detector packing ratio. This paper also presents the array design of quad-BGO (bismuth germanate) units and the sampling characteristics of a rotary PCT system named POSITOLOGICA II. In the rotary PCT, detector units are mounted unequally spaced on a ring so as to provide fine and uniform linear sampling during a 360 degrees rotation of the ring around its center. This principle was applied to a system named POSITOLOGICA I, but it has unidetector units [one detector-one photomultiplier tube (PMT)]. The quad-detector unit consists of four BGO crystals, two PMT's, and a circuit positioning the address of the crystal by which a gamma ray is detected. Merits of the quad units are an effective coupling between rectangular crystals and a photocathode of PMT and reduction of the number of PMT's.     

Computation of integrated-circuit yields from the distribution of slice yields for the individual devices

This correspondence calculates the average yieldbar{Y_{N}}forNmultiple devices as a function of the average yield (bar{Y_{1}}) of single devices assuming several simple forms of distribution function for slice yields. It shows that the usual calculationbar{Y_{N}}= (bar{Y_{1}})^{N}is too pessmistic by an appreciable factor even when no "within slice" correlation exists. Using an actual distribution of transistor slice yields, the (bar{Y_{1}})^{N}calculation is shown to give a yield which is a factor of 5 too low for groups of eight good devices.     

张量切片稀疏表示在宽带信号波达方向估计中的应用

本文提出了一种新颖的宽带信号波达方向（Direction of Arrival, DOA）估计方法。首先,本文利用窄带滤波器将阵元接收到的宽带信号分解成了若干窄带分量。接着,利用这些分离出来的窄带分量,计算出任意两个相邻阵元间的一系列频率互相关函数（Frequency Cross correlations, FCCS）并用于构造一个Toeplitz矩阵。在所有相邻阵元间进行相同的处理,将构造出的所有Toeplitz矩阵堆叠成一个张量。最后,本文利用切片稀疏表示（Slice sparse Representation, SSR）的思想实现该张量的稀疏表示并提出了相应的恢复算法实现其稀疏重构,宽带信号DOA估计也随之实现。在仿真中,本文将所提算法与现有代表性算法进行了对比,仿真结果展现了本文算法的有效性。      

Automatically Controlled 2-Vessel Pressure-Cooker Test-Equipment

A highly accelerated humidity test for plastic encapsulated IC reliability short-term evaluation has been studied. 2-Vessel pressure cooker test (PCT) equipment capable of controlling relative humidity and temperature independently, and of keeping specimens free from water droplet condensation, has been designed. This equipment consists of a test chamber and a vapor chamber. Humidity conditions are set by controlling the temperature difference between the test chamber and the vapor chamber. Humidity levels are controlled with the direct pressure adjustment. The whole test chamber is heated in an oven, thereby obtaining temperature stability and uniformity. Using this equipment, humidity tests were carried out on plastic molded ICs. As a result, good test reproducibility and excellent correlation in test results between PCT and conventional humidity test such as 85°C/85%RH, were obtained. As a consequence, it was found possible, in a short time, to evaluate plastic molded IC reliability quantitatively in humidity ambients using this 2-vessel PCT equipment. This equipment can be used for quality assurance testing of plastic-encapsulated ICs in a short time.     

Electrochemical impedance spectroscopic study of encapsulatedtriple tracks test (TTT) circuits

Electrochemical impedance spectroscopy (EIS) is effective for studying the reliability of protective coatings on microelectronic packaging devices. Triple track test (TTT) circuits were evaluated as a function of exposure time at 121°C and 2 atm pressure. Specimens were deliberately contaminated by various chemicals and particles before coating. The impedance of some specimens decreased after the first 10 hours in the Pressure Cooker Test (PCT) while some lasted more than 150 hours in the PCT without an appreciable change in the impedance values. Impedance of the specimens changed appreciably due to water uptake in the epoxy coatings. The ionic contamination trapped under the coating caused faster failure in the TTT with respect to clean specimens. Water diffused to the polymer/gold interface causing a change in the dielectric properties of the specimen, shown as a shift in the EIS spectrum. This shift was observed in EIS spectra for most of the specimens which were exposed for more than 150 hours. The change suggests water that penetrated the coating made a conductive pathway to the interfacial region, a common cause of debonding between the metal (or ceramic) polymer interface. In one case (specimens contaminated by SiO₂ particles) the shift was not observed-suggesting that SiO₂ particles do not accelerate the adhesive failure at the metal (or ceramic)/polymer interface. The calculated saturated volume fraction of water at the metal (or ceramic)/polymer interface was 1.1±0.1