Helical SPECT using axially truncated data

In this study, use of a helical orbit in performing a long object SPECT scan with parallel, cone, fan, rotated fan, varying focal-length cone, divergent, and astigmatic collimators is proposed. Sufficient-data scanning helical orbits for these collimation geometries are developed. Both a single-detector system and a multi-detector system are considered. In order to verify the authors' orbit design requirement, the iterative ML-EM algorithm is used to reconstruct images of a long Defrise phantom. The phantom height is five times the height of the detectors. Computer simulations are performed and exact reconstructions are obtained. The proposed sufficient helical orbit pitch will facilitate performing whole body SPECT and PET scans that demand an exact reconstruction     

A new multi-parallel-beam collimators with improved sensitivity for SPECT

In this paper, a new design of multi-parallel-beam (MPB) collimators with projection multiplexing is proposed. In the MPB system, two different oblique parallel channels are introduced in a conventional parallel-beam collimator. The sensitivity of the single photon emission computed tomography (SPECT) system is improved by allowing projection overlapping. Comparative simulation studies were performed in the MPB collimators, general purpose parallel-beam (GPPB) collimators and high sensitivity parallel-beam (HSPB) collimators. In the simulation, attenuation, scattering and the impact of detector response were neglected. Simulation results show that the sensitivity is improved for the MPB collimator comparing with parallel-beam collimator. The behavior of spatial resolution is only different near the front face of the collimators and approaches that of the GPPB with increasing depth. Proper pre-filtering is helpful for the image reconstruction in the MPB collimators. Comparing with the HSPB collimator, the MPB can achieve a similar sensitivity and better resolution. The simulation ot the U87 cells, and their expression levels were higher in the 10 Gy group than in the 0 Gy group. The differential gene expression in DCX-U87 cells before and after radiation is helpful for future investigations into the mechanisms of radiation therapy in neurogliocytoma cells.     

轫致辐射显像的初步探讨

应用Ｓｏｐｈｙ ＤＳＸ ＳＰＥＣＴ系统，以＾９０Ｙ、＾３２Ｐ纯β类核素作为辐射源，通过模型实验选用不同准直器、不同能量窗宽等进行轫致辐射显像，以探讨最佳显像条件。结果发现：轫致辐射光谱是连续的，最大光子分布约在７０ｋｅＶ，以高能准直器，取８０ｋｅＶ６０％的能量范围及窗宽或经验性窗宽、且准直器与放射源之间距离较短时图像最为满意，２例病人的显像效果良好。结果表明ＳＰＥＣＴ可以用作轫致辐射显像。     

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.     

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。     

单光子发射断层图像的人体衰减校正

本文论述了人体组织对γ射线的吸收给ＳＰＥＣＴ图像造成的影响，通过分析对比人体衰减的各种校正办法，提出了我们的新方法，采用偏置的线源和平行缝准直器，产生倾斜的扇形束投影，在同一台ＳＰＥＣＴ上获取透射型和发射型两种数据，从透射型数据重建出人体衰减系数的三维分布图。然后对发射型图像作精确的校正。     

γ相机准直器的质量指标对比研究

对比研究γ相机准直器的3个主要质量指标对评价和检测准直器质量的价值。用同型号低能通用低能高分辨平行孔准直器4只,参照NEMA标准（1994）,分别测试各准直器的系统均匀性,同时测试系统空间分辨率及灵敏度,对测试结果进行比较和分析。结果表明,同型号准直器的系统空间分辨率与灵敏度两项指标基本接近,而均匀性指标存在较大差异（当部分准直器存在质量问题时）。其中系统积分和微分均匀性分别超过6％和3％的3只准直器被证实存在质量问题。说明系统均匀性定量和定性地反映准直器的性能,是反映准直器质量问题的最基本和最有效指标。     

6 MV医用加速器电子对效应的蒙特卡罗模拟研究

以Geant4编程构建6 MV医用加速器机头和照射条件,并通过实测数据比对验证模型的正确性,模拟加速器粒子输运过程,获取不同射野和不同层面的粒子相空间文件,以正电子和湮没光子为指标研究射野及各机头部件对电子对效应产生的影响,模拟电子对效应对加速器射束及水模中剂量沉积的影响。结果表明：射野面积越小,电子对效应产生越多;在靶、均整器及次级准直器处均会有较明显的电子对效应发生,其中次级准直器是主要的发生部件;电子对效应使射束中污染电子增加了约4%,降低了射束的平均能量,使射束粒子分布更加分散,增加了模体表面剂量及射野外剂量。     

Monte carlo study on 6 MV photon beams of a CyberKnife(R) stereotactic radiosurgery system

In this paper, the beam quality and percent depth dose curves for different field sizes of Cyber Knife(R) system were investigated by Monte Carlo simulations using the PENELOPE code, which has been used to simulate 6 MV photon beam. In water phantom, the absolute doses were calculated for φ10-60 mm collimators, and percent depth dose curves were evaluated for φ30-60 mm collimators. The agreement ofdose distributions of the calculation with measurement was within 3.0%. The mean energy ofphoton spectrum was 1.46 MeV, and the beam quality index was 0.632, which was slightly smaller than that ofmeasurement.     

Investigation of SPECT/CT cardiac imaging using Geant4

The purpose of this paper is to propose a friendly computational framework able to investigate particles tracking through different compartments of the human being using dedicated numerical techniques.The main building blocks of this framework are:(i) convenient X-ray spectra calculator for different filter/anode combination,(ii) realistic voxelized computational human phantom,(iii)validated Geant4-based Monte Carlo simulation,and(iv)extendable and free image processing software.We studied the multimodality SPECT/CT cardiac imaging using specific spectrum of the ~(99m)Tc and 120 kVp X-ray beam,for internal and external exposure,respectively.The application of the framework to quantify the loss of information between combined and simultaneous coregistration was carried out.Two main objectives were addressed:(i) an ideal geometry was simulated for educational purposes(ii) a realistic case study was carried out,for research purposes,concerning the modeling of the GE Infinia II 3/800 Gamma Camera.We compared the effect of using a Na I(Tl) and CZT crystal detector,and a LEHR and MEGP collimator with different uptake values of the heart organ(1:1,5:1 and 50:1) for both simultaneous andcombined SPECT/CT images.We confirmed the usefulness of the Na I(Tl) crystal with the LEHR collimator for such kind of study.     

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.     

The Effects of Incorrect Modeling on Noise and Resolution Properties of ML-EM Images

The effects of incorrect compensation for collimator blur in single-photon emission computed tomography (SPECT) images are studied in terms of the noise and resolution properties of the reconstructed images. Qualitative analysis of images of the Hoffman brain phantom reconstructed using nonlinear maximum-likelihood-expectation maximization (ML-EM) show the behavior of longer noise correlations for high-pass filtered images. These qualitative observations are confirmed with more quantitative noise measures. The differences also appear in images reconstructed using linear Landweber iteration. However, the signal-to-noise ratio, in terms of the noise-equivalent quanta, remains largely unchanged. We conclude that the compensation model affects SPECT image properties, though the effect on human task performance remains to be studied.     

基于束流环形高斯模型对上海硬X射线自由电子激光装置的束流刮束器进行活化分析

在建的上海硬X射线自由电子激光装置(Shanghai HIgh repetition rate XFEL aNd Extreme light facility,SHINE)的加速器隧道内,采用束流刮束器刮掉束晕外围张角比较大的电子,刮束器的束流损失率为0.1‰。本文采用蒙特卡洛程序FLUKA,用SOURCE程序实现电子束在3σ_beam外的高斯分布,以尽量真实模拟电子在束流刮束器处的丢失情况,解决了低功率刮束情况下蒙特卡洛模拟无统计性结果的难题。利用束流环形高斯模型对刮束器的活化进行了分析,结果表明环形高斯模型可以更真实地再现电子在束流刮束器的丢失情况;5年运行后距刮束器30 cm处的剩余剂量率达到了数百μSv/h至数mSv/h,和国外类似装置计算结果相当;通过对放射性核素的种类分析,结果证明刮束器(钨)的放射性废物处置难度不大。     

Monte Carlo simulation of breast tumor imaging properties withcompact, discrete gamma cameras

Describes Monte Carlo simulation results for breast tumor imaging using a compact, discrete gamma camera. The simulations were designed to analyze and optimize camera design, particularly collimator configuration and detector pixel size. Simulated planar images of 5-15 mm diameter tumors in a phantom patient (including a breast, torso, and heart) were generated for imaging distances of 5-55 mm, pixel sizes of 2×2-4×4 mm², and hexagonal and square hole collimators with sensitivities from 4000 to 16,000 counts/mCi/sec. Other factors considered included T/B (tumor-to-background tissue uptake ratio) and detector energy resolution. Image properties were quantified by computing the observed tumor FWHM (full-width at half-maximum) and S/N (sum of detected tumor events divided by the statistical noise). Results suggest that hexagonal and square hole collimators perform comparably, that higher sensitivity collimators provide higher tumor S/N with little increase in the observed tumor FWHM, that smaller pixels only slightly improve tumor FWHM and S/N, and that improved detector energy resolution has little impact on either the observed tumor FWHM or the observed tumor S/N     

高能闪光照相中陡坡准直体成像性能实验研究

在针对FTO样品的高能闪光照相实验中,比较了一般准直体与陡坡准直体对FTO样品的成像性能。结果表明,陡坡准直体对降低散射及缩小照射量量程非常有效,可得到层次分明的底片图像;采用一般准直体则无法得到有意义的样品图像。对实验进行了蒙卡模拟,模拟结果与实验结果一致。     

The YAP camera: an accurate gamma camera particularly suitable fornew radiopharmaceuticals research

The YAP Camera represents refined research instrument in nuclear medicine and pharmacology because of its overall detection efficiency comparable to an Anger Camera and its submillimeter intrinsic spatial resolution. The YAP Camera consists of a YAP:Ce multicrystal matrix, whose pillars dimensions are 0.6 mm×0.6 mm×10 mm, optically coupled with a position sensitive PMT Hamamatsu R2486 and furnished with a parallel hole lead collimator 20 mm thick with holes diameter of 0.5 mm and septa of 0.15 mm. At this stage it is a miniature camera, with a field of view (FOV) of 40 mm×40 mm and a total spatial resolution of 1.0-1.2 mm, currently used for radiotracers studies on small biological specimens. A detailed analysis of the detector position linearity and energy responses are presented in this work. The intrinsic spatial resolution is studied with three different single hole collimators (1.0, 0.3, and 0.2 mm), and a theoretical equation is presented. Three different parallel hole collimators are tested to evaluate the optimal hole and septa dimensions. Finally, it is demonstrated that two correction procedures are capable of recovering the image spatial homogeneity and of removing the statistical noise. Some phantom images show the importance of the small-field YAP Camera in the radiopharmacological research     

Characteristics of parallel-hole and pinhole collimators for nuclear medicine imaging

In this paper,the spatial resolution and geometry sensitivity of parallel- and pin-hole collimators in compact gamma camera are presented,and quantitatively compared by GEANT4 code in Monte-Carlo library.The results show that the geometry sensitivity for pinhole collimator rapidly drops with increasing the gamma source-to- collimator distance(SCD);and for parallel-hole collimator,mildly.Meanwhile,the spatial resolution for pin-hole collimator mildly deteriorates;and for parallel-hole collimator,severely.The pin-hole collimator for close imaging objects has higher geometry sensitivity than parallel-hole collimator.Our findings are helpful for setting compact gamma camera collimators in nuclear medicine imaging.     

Thermal analysis and tests of W/Cu brazing for primary collimator scraper in CSNS/RCS

To the transverse beam collimation system in a rapid cycling synchrotron,an important component is the primary collimator,which improves emittance of the beam halo particles such that the particles outside the predefined trajectory can be absorbed by the secondary collimators.Given the material properties and power deposition distribution,the beam scraper of the primary collimator is a0.17 mm tungsten foil on a double face-wedged copper block of 121.5 mm x 20 mm.The heat is transferred to the outside by a φ34 mm copper rod.In this paper,for minimizing brazing thermal stress,we report our theoretical analysis and tests on brazing the tungsten and copper materials which differ greatly in size.We show that the thermal stress effect can be controlled effectively by creating stress relief grooves on the copper block and inserting a tungsten transition layer into the copper block.This innovation contributes to the successful RD of the primary collimator.And this study may be of help for working out a brazing plan of similar structures.     

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.     

蒙特卡罗方法选择 TGS 准直器的最佳形状

采用蒙特卡罗方法和技术，模拟ＴＧＳ连续扫描模式，对不同形状的准直器，计算了被测量废物桶中各个像素内的纵向效率的最大百分差，从中选取了棱形准直器和调整后的棱形准直器作为ＴＧＳ装置的扫描准直器。