水模型鉴定PET-CT同机融合图像配准误差

本文是应用水模型模拟PET-CT实际检查检测同机融合图像的配准误差。首先制备含59.2 MBq[氟18]-氟代脱氧葡萄糖的水模型,静置80 min,采集2D PET图像20 min,然后经形态学处理与阈值法得水的CT与PET图像,把两组图像的质心位置经线性回归方程拟合,求配准误差。并用Alignment软件测量CT与PET成像系统配准误差4次。得出水PET图像质心较CT图像在X轴偏移(0.011×层数+0.63)mm;在Y轴质心偏移(0.022×层数+1.35)mm,PET图像须经平移且X轴须旋转(0.06±0.07)、Y轴旋转(0.01±0.08)才能与CT图像配准。所以检查床的负载与分布不影响本PET/CT仪系统的配准校正,测量坐标轴旋转角度的随机误差易使PET与CT配准产生偏差。     

Towards Quantification of Functional Breast Images Using Dedicated SPECT With Non-Traditional Acquisition Trajectories

Quantification of radiotracer uptake in breast lesions can provide valuable information to physicians in deciding patient care or determining treatment efficacy. Physical processes (e.g., scatter, attenuation), detector/collimator characteristics, sampling and acquisition trajectories, and reconstruction artifacts contribute to an incorrect measurement of absolute tracer activity and distribution. For these experiments, a cylinder with three syringes of varying radioactivity concentration, and a fillable 800 mL breast with two lesion phantoms containing aqueous (99m)Tc pertechnetate were imaged using the SPECT sub-system of the dual-modality SPECT-CT dedicated breast scanner. SPECT images were collected using a compact CZT camera with various 3D acquisitions including vertical axis of rotation, 30° tilted, and complex sinusoidal trajectories. Different energy windows around the photopeak were quantitatively compared, along with appropriate scatter energy windows, to determine the best quantification accuracy after attenuation and dual-window scatter correction. Measured activity concentrations in the reconstructed images for syringes with greater than 10 μCi /mL corresponded to within 10% of the actual dose calibrator measured activity concentration for ±4% and ±8% photopeak energy windows. The same energy windows yielded lesion quantification results within 10% in the breast phantom as well. Results for the more complete complex sinsusoidal trajectory are similar to the simple vertical axis acquisition, and additionally allows both anterior chest wall sampling, no image distortion, and reasonably accurate quantification.     

一体化PET/MRI头部运动两种校正方法的对比

<正>电子发射断层成像(Position emission tomography,PET)/磁共振成像(Magnetic resonance imaging,MRI)问世以后,通过MRI获取扫描对象运动信息的准确度大为增加。为验证精确的运动信息条件下,基于响应线(Line of Response,LOR)的运动校正方法校正效果更为明显,我们对基于frame和基于LOR的两种头部运动校正方法的精度进行了对比研究。通过PET模拟数据完成两种校正算法的设计和结果比较,进而利用MRI成像速度快、图像质量高的特点,在上海联影医疗科技有限公司一体化PET/MRI上获取实验数据,通过配准MRI图像获取头部运动信息,并对PET数据进行运动补偿,实现对两种校正方法校正效果的验证和评估。通过对模拟和实验数据校正结果的定性定量分析,我们验证了PET/MRI环境中,基于LOR的方法,利用获取的高精度运动信息对于PET头部运动具有更好的补偿效果。     

多平行束准直器模拟研究

在平行束准直器中引用多通道技术设计了三通道的多平行束（Multi-parallel Beam,MPB）准直器。计算机模拟表明,MPB准直器在保持较高的空间分辨率下,有效地改善了系统的灵敏度。放射药物匀均分布的圆柱数字模具和Jaszczak数字模具（phantom）模拟表明,随重叠比例的增加,未出现重建环状伪影;虽然靠近准直器表面空间分辨率有所下降,但在FOV（Field of View）中心区域空间分辨率近似等同于平行束准直器,重建图像的匀均度有了改善。投影数据的重叠表明,MPB的投影有放大作用。该研究为高成像质量的临床SPECT成像提供一种新的准直器设计方法。     

Quantification in positron emission mammography (PEM) with planardetectors: contrast resolution measurements using a custom breastphantom and novel spherical hot-spots

The authors have previously demonstrated that their Positron Emission Mammography-1 (PEM-1) system can successfully detect small (<2 cm diameter) tumors. Images in the current system are judged qualitatively for the presence of focal uptake of ¹⁸F-FDG. The authors are presently taking steps toward quantifying the emission images. To this end they have constructed a breast phantom and developed a novel technique for fabricating very small wall-less radioactive hot-spots. The hot-spots are made by adding ¹⁸F-FDG to a 25 mg/cc solution of Agarose in water. The heated solution is poured into spherical molds which are separated upon congealing to yield robust wall-less radioactive hot-spots. The hot-spots were uniform to within 1-5 parts in 100. Less than 0.1% of the total hot-spot activity leaked into the background in 30 minutes. Contrast resolution experiments have been performed with 12 mm and 16 mm diameter hot-spots in the breast phantom containing water with various amounts of background activity. In both cases, the observed contrast values agree well with the ideal values. In the case of the 12 mm hot-spot with a 350-650 keV energy window, image contrast differed from the ideal by an average of 11%. The image contrast for 12 mm hot-spot improved by 40% and the number of detected events decreased by 35% when the low energy threshold was increased from 300 keV to 450 keV     

A high-resolution small animal SPECT system developed at Tsinghua

An SPECT system dedicated to small animal imaging shall be of a millimeter spatial resolution or even better.This study was aimed at achieving 0.5-mm spatial resolution for a small animal SPECT system at low cost.It was developed from a single-head clinical SPECT scanner,with a seven-pinhole collimator and a four-degree-offreedom motion control stage.Several key techniques were developed,including high-resolution image reconstruction algorithm,high accuracy geometrical calibration method,and optimized system matrix derivation scheme.The system matrix was derived from Monte-Carlo simulation and de-noised by fitting each point spread function to a two dimensional Gaussian function.Experiments of point source and ultra micro hot rod phantom were conducted.With a spatial resolution of 0.5-0.6 mm,this system provides a practical way for low-cost high-resolution animal imaging on a clinic SPECT system.     

心肌灌注显像常见伪影的辨析

为探讨心肌灌注显像常见伪影的特征，提高诊断的准确性，对132例心肌断层影像进行了回顾分析，并以冠脉造影结果为标准判断伪影的有关。在充分识别各种伪影的情况下采用盲法重新诊断，并与既往诊断结果进行了比较，结果显示，衰减伪影和位移为影多见于^201Tl显像者。其中胸壁衰减伪影女性多见，表现为位置固定的左室前壁或侧壁缺损；膈肌衰减伪影常见于男性，在垂直长轴上常表现为下壁由前向后逐渐变细。位移伪影常表现为室壁上的浓度与稀疏的同时存在，非靶器官放射性摄导致伪影，最多见于^99mTc-MIBI显像的病人，此时常在三个断面上同时发现有肝或肠道影，重新读片后，误诊率由原来的13．6％下降到6．8％，此结果表明，各种伪影均有其影像特征和出现的特定前提；多数伪影在实践过程中能为人们所认识，但仍有部分伪影难于识别，认真分析其特征有助于进一步提高诊断的准确性。     

Image quality of cone beam CT on respiratory motion

In this study, the influence of respiratory motion on Cone Beam CT (CBCT) image quality was investigated by a motion simulating platform, an image quality phantom, and a kV X-ray CBCT. A total of 21 motion states in the superior-inferior direction and the anterior-posterior direction, separately or together, was simulated by considering different respiration amplitudes, periods and hysteresis. The influence of motion on CBCT image quality was evaluated with the quality indexes of low contrast visibility, geometric accuracy, spatial resolution and uniformity of CT values. The results showed that the quality indexes were affected by the motion more prominently in AP direction than in SI direction, and the image quality was affected by the respiration amplitude more prominently than the respiration period and the hysteresis. The CBCT image quality and its characteristics influenced by the respiration motion, and may be exploited in finding solutions.     

Phantom experiments on a PSAPD-based compact gamma camera with submillimeter spatial resolution for small animal SPECT

We demonstrate a position sensitive avalanche photodiode (PSAPD) based compact gamma camera for the application of small animal single photon emission computed tomography (SPECT). The silicon PSAPD with a two-dimensional resistive layer and four readout channels is implemented as a gamma ray detector to record the energy and position of radiation events from a radionuclide source. A 2 mm thick monolithic CsI:Tl scintillator is optically coupled to a PSAPD with a 8mm×8mm active area, providing submillimeter intrinsic spatial resolution, high energy resolution (16% full-width half maximum at 140 keV) and high gain. A mouse heart phantom filled with an aqueous solution of 370 MBq (99m)Tc-pertechnetate (140 keV) was imaged using the PSAPD detector module and a tungsten knife-edge pinhole collimator with a 0.5 mm diameter aperture. The PSAPD detector module was cooled with cold nitrogen gas to suppress dark current shot noise. For each projection image of the mouse heart phantom, a rotated diagonal readout algorithm was used to calculate the position of radiation events and correct for pincushion distortion. The reconstructed image of the mouse heart phantom demonstrated reproducible image quality with submillimeter spatial resolution (0.7 mm), showing the feasibility of using the compact PSAPD-based gamma camera for a small animal SPECT system.     

高压型低能大功率辐照加速器电子枪研制

低能大功率辐照加速器广泛用于辐照加工产业。本工作研制出一台二极电子枪作为高压型低能大功率辐照加速器的电子源,并通过出束实验对其加以优化,最后确定了二极电子枪的最佳结构、尺寸及运行参数等。结果表明,从电子枪引出电子束的能量为5~25 keV,流强为60~100 mA,束斑为15~30 mm,半散角为0.6°~1.6°,不稳定度好于±0.6%。该电子枪工作稳定,寿命长于5 000 h。     

fMRI artifacts reduction using Bayesian image processing

Functional MRI is known to be prone to artifacts caused by spatio-temporally varying structural noise components such as gross head motion, CSF pulsation, physiological fluctuation, and magnetic susceptibility changes. The presence of these artifacts can cause negative and positive false activation and obscure true activated pixels. Thus the reliability of the functional images can be diminished. The authors have applied Bayesian image processing to reduce noise and artifacts in fMRI using local continuity information. The results indicate that Bayesian image processing reduces image-to-image signal fluctuation significantly, is effective in reducing fMRI noise and artifacts, and improves hue activity detection by enhancing the connectivity of the activated pixels     

基于基图像TV模型的CT射束硬化校正方法

X射线CT中,X射束硬化导致重建图像中出现伪影,严重影响了图像质量。论文深入分析了射束硬化对原始投影数据的影响,并提出了一种基于基图像TV模型的射束硬化校正方法。该方法首先依据射束硬化的物理特征建立了带有可调参数的初步校正模型;其次,在不同的可调参数条件下,原始投影数据经该模型预处理变换得到多组预处理投影序列;再次,分别对预处理投影序列进行重建得到一系列校正基图像;最后,将基图像的线性组合作为最终重建图像。其中,加权系数的最优解是以最终重建图像的全变分(Total Variation,TV)函数作为目标函数,通过迭代法求得。为验证该算法,对真实的铝柱体模和工业检测件进行了实验,结果表明,该算法对射束硬化引起的杯状和条状伪影均有显著的抑制效果。     

基于物理体模CT图像的1岁儿童体素体模构建

本文介绍了基于1岁儿童物理体模（Model 704-D）的CT图像和中国成年男性参考人体素体模(CRAM)的1岁儿童体素体模（CPP01）的构建,包括通过对物理体模扫描得到OCP01体模（基于儿童物理体模的CT图像建立的一粗略的体素体模）,进而构建和优化CPP01。该体素体模的各器官组织的质量与GBZ/T 200.2-2007所给数据的相对偏差约在5%以内,且其外部轮廓和主要器官的位置与Model 704-D相匹配。     

北京同步辐射软X射线偏振测量装置及其应用

在北京同步辐射装置(BSRF)设计建造了-套基于多层膜偏振元件的软X射线偏振测量分析装置,可工作在双反、双透、前反后透和前透后反四种工作模式,既可作为偏振测量装置,用于同步辐射光束线和多层膜偏振元件偏振特性测量,也可作为通用反射率计,用于多层膜和薄膜的反射或透射率测量,又可用于磁性材料的磁光效应研究等.利用自行研制的装置和光学元件对BSRF的3W1B光束线的偏振特性进行了系统的测量.测量结果指出,在206 eV时,输出光的线偏振度从起偏前的O.585上升到起偏后的0.995,同步光的线偏振度得到极大改善.利用非周期宽带Mo/Si多层膜开展了铁磁性材料的磁光法拉第效应测量,获得了Ni薄膜3p边附近(60-70 eV)的法拉第旋转角度,最大偏转角度在65.5 eV和68 eV分别为1.85±0.19°和-0.75±0.09°.     

Four-dimensional superquadric-based cardiac phantom for Monte Carlosimulation of radiological imaging systems

A four-dimensional (x,y,z,t) composite superquadric-based object model of the human heart for Monte Carlo simulation of radiological imaging systems has been developed. The phantom models the real temporal geometric conditions of a beating heart for frame rates up to 32 per cardiac cycle. Phantom objects are described by boolean combinations of superquadric ellipsoid sections. Moving spherical coordinate systems are chosen to model wall movement whereby points of the ventricle and atria walls are assumed to move towards a moving center-of-gravity point. Due to the non-static coordinate systems, the atrial/ventricular valve plane of the mathematical heart phantom moves up and down along the left ventricular long axis resulting in reciprocal emptying and filling of atria and ventricles. Compared to the base movement, the epicardial apex as well as the superior atria area are almost fixed in space. Since geometric parameters of the objects are directly applied on intersection calculations of the photon ray with object boundaries during Monte Carlo simulation, no phantom discretization artifacts are involved     

锥束微焦点CT系统对比度灵敏度测量研究

对比度灵敏度是描述计算机断层成像（CT）系统分辨图像细节特征能力的参数,其主要受图像统计噪声水平的影响。本文介绍了CT对比度灵敏度的测量方法,并用直径50 mm的均匀有机玻璃圆柱作样品测量225 kV-3D-ICT系统的对比度灵敏度,在X光机电压为160 kV的条件下,得出在0.3 mm×0.3 mm×0.3 mm范围内的对比度灵敏度约为1%。并讨论了系统的稳定性、硬化校正和重建滤波参数对测量结果的影响。     

Isotopic Enrichment and Thermal Neutron Cross Section Measurement of Erbium-167

The thermal neutron cross section of Er167 has been obtained by measuring the relative number of Erl68 atoms formed by radiative neutron capture, when isotopically pure Er167 samples were exposed to a highly-thermalized neutron flux. A four-stage mass spectrometer was used to provide a 106/1 isotopic enrichment of Er167. It was also employed it measure the postirradiation Er168/Er167 isotopic ratios of the samples, which were placed in the D2O moderated Argonne CP-5 reactor. The integrated neutron flux, and effective neutron temperature in this reactor were also monitored mass spectrometrically, by observing isotopic ratio changes in nuclides whose cross section as a function of temperature are known. Two rare earth isotopes Sm149 and Gd157, were selected as the "non-l/v" absorbers that yielded this data. The effective neutron cross section of Er167 was found to be 740 ± 21 barns, at an effective neutron temperature of 42.8 + 2.5°C, with an integrated neutron flux of 3.37 ± 0.08 × 1019 neutron/cm2. The thermal (2200 m/sec) neutron cross section of Er167 was then calculated to be 699 ± 20 barns.     

Quantification of the Multiplexing Effects in Multi-Pinhole Small Animal SPECT: A Simulation Study

Our goal is to study the trade-off between image degradation and improved detection efficiency and resolution from allowing multiplexing in multi-pinhole (MPH) SPECT, and to determine the optimal pinhole number for MPH design. We used an analytical 3D MPH projector and two digitized phantoms: the mouse whole body (MOBY) phantom and a hot sphere phantom to generate noise-free and noisy projections, simulating pinhole collimators fitted with pre-studied pinhole patterns. We performed three schemes to achieve different degrees of multiplexing: 1. Fixed magnification and detection efficiency; 2. Fixed detection efficiency and changed magnification; 3. Fixed magnification and changed detection efficiency. We generated various noisy data sets by simulating Poisson noise using differently scaled noise-free projections and obtained 20 noise realizations for each setting. All datasets were reconstructed using 3D MPH ML-EM reconstruction method. We analyzed the quantitative accuracy by the normalized-mean-square-error. We evaluated the image contrast for the hot sphere phantom simulation, and also the image noise by the average normalized-standard-deviation of certain pixels for different degrees of multiplexing. Generally, no apparent artifacts were observed in the reconstructed images, illustrating the effectiveness of reconstructions. Bias increased for increased degree of multiplexing. Contrast was not significantly affected by multiplexing in the specific simulation scheme (1). Scheme (2) showed that excessive multiplexing to improve image resolution would not improve the overall trade-off of bias and noise compared to no multiplexing. However, scheme (3) showed that when comparing to no multiplexing, the trade-off improved initially with increased multiplexing by allowing more number of pinholes to improve detection efficiency. The trade-off reached a maximum and decreased with further multiplexing due to image degradation from increased bias. The optimal pinhole number was 7 for a compact camera with size of 12 cm × 12 cm and 9 for a standard gamma camera with size of 40 cm × 40 cm in this scheme. We conclude that the gains in improved detection efficiency and resolution by increased multiplexing are offset by increased image degradations. All the aforementioned factors must be considered in the optimum MPH collimator design for small animal SPECT imaging.     

Comparison of 3D OS-EM and 4D MAP-RBI-EM reconstruction algorithms for cardiac motion abnormality classification using a motion observer

Using a heart motion observer, we compared the performance of two image reconstruction techniques, a 3D OS-EM algorithm with post Butterworth spatial filtering and a 4D MAP-RBI-EM algorithm. The task was to classify gated myocardial perfusion (GMP) SPECT images of beating hearts with or without regional motion abnormalities. Noise-free simulated GMP SPECT projection data was generated from two 4D NCAT beating heart phantom models, one with normal motion and the other with a 50% motion defect in a pie-shaped wedge region-of-interest (ROI) in the anterior-lateral left ventricular wall. The projection data were scaled to clinical GMP SPECT count level before Poisson noise was simulated to generate 40 noise realizations. The noise-free and noisy projection data were reconstructed using the two reconstruction algorithms, parameters chosen to optimize the tradeoff between image bias and noise. As a motion observer, a 3D motion estimation method previously developed was applied to estimate the radial motion on the ROI from two adjacent gates. The receiver operating characteristic (ROC) curves were computed for radial motion magnitudes corresponding to each reconstruction technique. The area under the ROC curve (AUC) was calculated as an index for classification of regional motion. The reconstructed images with better bias and noise tradeoff were found to offer better classification for hearts with or without regional motion defects. The 3D cardiac motion estimation algorithm, serving as a heart motion observer, was better able to distinguish the abnormal from the normal regional motion in GMP SPECT images obtained from the 4D MAP-RBI-EM algorithm than from the 3D OS-EM algorithm with post Butterworth spatial filtering.     

Recombination Centers in Gamma-Irradiated Arsenic-Doped Germanium

A comprehensive investigation has been performed of the properties of recombination centers introduced in As-doped Ge by Co60 gamma rays. Materials of three resistivities were used: ~0.2, ~1 and ~8 ?-cm. Measurements of lifetime versus temperature were made at low excess densities following various anneals. Numerous measurements of lifetime as a function of excess density with temperature as a parameter and with different annealing histories were performed. The position of the recombination center was observed to shift slightly with anneal temperature from Ev + 0. 346 ±.005 eV for room temperature stable defects to 0. 322 ±0.003 eV for samples which have been annealed in the range of ~70°C to ~120°C. These values are based on excess density measurements and assume unity statistical weight. The possible error from this assumption is estimated to be ±0.02 eV. The variation of electron capture probability with temperature was indicated by comparison with temperature dependence data; it varies approximately as T3/4. The hole-to-electron capture probability ratio near room temperature is 400 ±30 %. The arsenic atom appears to play no significant role in the process of recombination center creation or annihilation.