PET/CT成像中的呼吸运动衰减校正仿真实验

目的衰减效应是影响肺部诊断图像的一个重要因素。基于正电子发射计算机断层摄影术/X线计算机体层摄影术(PET/CT),研究衰减校正对于基于PET/CT门控数据呼吸运动的影响。方法使用仿真PET/CT成像的软件GATE(Geant4 Application Tomographic Emission)和像素体模仿真软件NCAT(NURBS cardiac-torso),模拟肺部在PET/CT扫描过程中的运动。然后,利用得到的GATE仿真数据进行门控处理并进行衰减校正。结果经过衰减校正后的门控图像能够进一步有效地减少呼吸运动对PET/CT成像的影响,其图像质量好于未经过衰减校正的门控图像质量,图像的清晰度和准确度得到提高。结论通过利用在GATE仿真平台上进行NCAT像素体模的仿真研究,验证了基于PET/CT门控数据的呼吸运动衰减校正的图像相比于运动模糊的图像和仅仅经过门控校正后的图像,可以进一步提高图像的清晰度和准确度。     

LYSO闪烁晶体PET探测器设计及位置映射算法研究

目的分析LYSO闪烁晶体内光子的输运特性及正电子发射计算机断层扫描装置（positron emission tomography,PET）位置映射表的建立方法。方法在Linux fedora操作系统之上成功构建了GATE（geant4 application for tomographic emission）核医学仿真平台,模拟了LYSO闪烁晶体PET探测器内光子输运过程。并且基于仿真数据,分析了位置映射表。结果成功研制了8×8探测器模块,得到位置映射对照表。结论基于GATE进行探测器模块设计切实可行,得到的位置映射表对后期实际散点图的建立过程具有重要指导作用。     

GATE:一种用于辐射层析成像的蒙特卡罗模拟技术

描述了GATE的主要特点以及实现这些特点的GATE所具有的层级结构.通过测试由GATE软件包自带的GATE PET Benchmark的模拟结果,验证了GATE模拟引擎的正确性以及不同初始随机数下多次模拟实验的稳定性与可靠性.     

基于正弦图的正电子发射成像呼吸运动弹性配准校正

在患者胸部正电子发射成像(PET)过程中,呼吸运动会造成成像质量下降。本文使用三层网格B-样条弹性配准的方法修正重组和降噪后的正弦图来进行呼吸运动校正。使用GATE仿真NCAT呼吸运动体模数据进行实验,结果显示图像质量得到了很大地提高,运动伪影和结构信息得到了修复,表明本文的方法是有效的。     

基于剂量预测和自动勾画技术的PET/CT器官内照射剂量率快速评估方法

目的：实现一种基于深度学习的剂量预测和自动勾画技术的正电子发射断层成像（PET）/CT检查器官内照射剂量率的快速评估方法。方法：首先基于患者特定时刻的PET/CT图像,使用蒙特卡罗程序GATE进行内照射剂量率计算,获得每个患者的剂量率分布图。随后,基于U-Net构建深度神经网络,将患者的CT和PET图像作为输入,GATE计算的剂量率图作为金标准进行训练。训练后的深度学习模型能够根据患者的CT和PET图像预测对应的剂量率分布。同时,使用勾画软件DeepViewer对患者CT图像中的器官和组织进行自动勾画,结合预测得到的剂量率分布结果计算相应器官和组织的吸收剂量率。使用50名患者的PET/CT数据,其中10份用于测试,其余40份进行4折交叉训练,每次使用30份用于训练,10份用于验证。将测试集结果与GATE和GPU蒙特卡罗工具ARCHER-NM进行对比。结果：在自动勾画软件DeepViewer勾画的24个器官中,绝大部分器官的深度学习预测剂量率与GATE计算结果偏差在±10%以内。其中大脑、心脏、肝脏、左肺、右肺的平均偏差分别为3.3%、1.1%、1.0%、-1.1%、0.0%,与GATE...     

基于GATE的小动物PET原型机仿真验证与性能评估

小动物正电子发射断层成像(PET)在药代动力学、新药研发、疗效评估等预临床研究中具有重要意义, 但小动物PET的定量精度仍受限于探测器的空间分辨率与灵敏度的不足。为研发高性能的小动物专用PET探测器, 提出“小孔径、大轴向跨度”的小动物PET搭建方案, 并通过蒙特卡罗仿真技术, 对该方案进行仿真验证与评估。该方案设计的原型机由60个晶体探测模块, 分为5个连续的12边形探测环组成, 其中心孔径与轴向跨度分别为102和125.4 mm, 具备高达50.8°的光子最大接收角。采用GATE平台建立该原型机的仿真模型, 并对其空间分辨率、计数性能(散射分数与等效噪声计数率)、探测灵敏度以及成像质量共4个性能进行预评估与分析。结果显示, 该原型机的空间分辨率为1.62 mm, 探测灵敏度为9.26%, 散射分数为20.8, 等效噪声计数率为2, 256 kcps, 总体性能与西门子Inveon PET系统相近, 并在探测灵敏度及等效噪声计数率性能上分别取得21.36%以及35.14%的提升。基于GATE平台的仿真结果表明, 采用“小孔径、大轴向跨度”的设计, 能显著提升小动物PET系统的探测灵敏度, 有望进一步提升小动物PET应用的定量精度。     

无创双水平气道正压通气治疗系统建模及通气仿真

无需经口鼻腔或气道切口插管建立人工气道的无创双水平气道正压通气（Bi-PAP）广泛应用于各种呼吸病患者的通气治疗。为研究无创Bi-PAP通气下呼吸病患者的通气治疗状况及需要采取的通气措施,本文建立无创Bi-PAP通气治疗系统模型,进行仿真通气。所建系统模型包括无创Bi-PAP呼吸机模型、呼吸管路及面罩模型和呼吸病患者的呼吸模型。并在Matlab Simulink仿真环境设计系统仿真实验平台,模拟对无自主呼吸患者、慢性阻塞性肺疾病（COPD）患者和呼吸窘迫综合征（ARDS）患者进行仿真通气。运用SPSS统计分析,将仿真所得通气流量、通气压力和潮气量等数据与基于主动模拟肺实验平台的物理实验所得数据进行比较分析。结果表明：源自仿真实验和物理实验的数据未见明显差异（P> 0.1）,具有良好的相关性（R> 0.7）。所设计的无创BiPAP通气系统模型,能有效模拟实际通气系统进行通气实验,将有助于对无创Bi-PAP通气技术的研究,有助于临床医师对无创Bi-PAP通气技术的学习和了解。     

基于STM32的医学信号保存及USB传输

目的 为实现远程猝死监测系统中对采集数据的保存及传输,设计并实现了一种基于STM32的数据存储及传输系统.方法 系统将采集到的12位数据经过处理,变为212格式,然后将数据保存在W25Q128BV芯片中,最后经过USB接口上传至PC机进行后续的分析.结果 实验结果证明该系统有效地节省了Flash空间,数据传输速度快.结论 该数据存储及传输系统是远程猝死监测系统研究开发的基础.     

GATE在核医学成像和放射治疗中的蒙特卡洛模拟

目的:探讨GATE在核医学成像SPECT和PET、光子和质子放射治疗中的蒙特卡洛模拟,并利用GATE平台研究碳纤维床板对光子放疗时剂量的影响。方法:首先模拟运行GATE V6.1提供的三个例子,分别对应于SPECT、PET和RT,其中RT又分为光子治疗和质子治疗。对SPECT和PET模拟中光子的散射情况进行统计分析,详细比较RT模拟中光子束和质子束在水模体中的能量沉积特性。然后在GATE平台上编程模拟了光子治疗束分别在有碳纤维床板和无床板时射入水模体中,比较并分析这两种情况下水模体中的剂量分布差异。结果:GATE V6.1的三个例子模拟中,SPECT中的未散射光子稳定在36%左右,PET中未散射的真符合计数稳定在44.5%左右,RT模拟中质子相比于光子在深度方向上有明显的剂量分布优势,而光子在横向方向的剂量分布稍好于质子。在碳纤维床板对光子放疗时剂量影响的模拟中,有碳纤维床板相对于无床板时,水模体的表层剂量有明显的提高。结论:GATE能够稳定准确的对核医学成像SPECT和PET及放射治疗过程进行蒙特卡洛模拟。它可以为放射治疗剂量验证、临床放射治疗计划以及核医学成像引导放射治疗的研究提供强大帮助。     

基于支持向量回归的PET/CT图像衰减校正方法

目的在电子发射及计算机断层扫描系统(positron emission computed tomography/X-ray computed tomography,PET/CT)图像衰减校正的能量转换过程中,为了改进双线性转换法用线性关系来拟合非线性关系的不足,本文以支持向量回归为基础,提出了一种新的能量转换法即支持向量回归的PET/CT图像衰减校正方法来进行衰减校正,以寻找CT值和511 keV能量下线性衰减系数值之间的最佳转换关系。方法使用仿真软件GATE(Geant4 Application Tomographic Emission)模拟了11组不同材质的圆柱体体模。然后根据GATE仿真的不同材质圆柱体体模,求出其CT值和511 keV能量下线性衰减系数值并代入SVR模型中进行训练,建立CT值和511 keV能量下线性衰减系数值之间的SVR模型。最后与目前PET/CT衰减校正能量转换中常用的双线性能量转换法进行对比分析,并分别应用于GATE仿真的NCAT(NURBs Cardiac Torso)像素体模图像中,评估两种方法准确性的差异。结果支持向量回归的PET/CT图像衰减校正方法得到的511 keV能量下对应物质的线性衰减系数值的相对百分误差值较小(肺的相对百分误差值3.1%和肝脏的相对百分误差值1.08%),且经过支持向量回归法衰减校正的PET图像,其MSE评价值都是最小的(176.9230),其PSNR和AG的评价值都是最大的(31.8621和7.9083)。这说明经过支持向量回归法衰减校正的PET图像相比于双线性转换法衰减校正的PET图像,更接近于静态的图像。结论支持向量回归的PET/CT图像衰减校正方法在PET/CT图像的衰减校正应用中有更好的表现,可以更好地吻合CT值与511 keV能量下线性衰减系数之间的转换关系,从而提高了PET/CT图像的衰减校正效果,改善了PET/CT图像定量的准确性,便于医生做出更精确的临床诊断。     

Validation of the GATE Monte Carlo simulation platform for modelling a CsI(Tl) scintillation camera dedicated to small-animal imaging

Monte Carlo simulations are increasingly used in scintigraphic imaging to model imaging systems and to develop and assess tomographic reconstruction algorithms and correction methods for improved image quantitation. GATE (GEANT4 application for tomographic emission) is a new Monte Carlo simulation platform based on GEANT4 dedicated to nuclear imaging applications. This paper describes the GATE simulation of a prototype of scintillation camera dedicated to small-animal imaging and consisting of a CsI(Tl) crystal array coupled to a position-sensitive photomultiplier tube. The relevance of GATE to model the camera prototype was assessed by comparing simulated 99mTc point spread functions, energy spectra, sensitivities, scatter fractions and image of a capillary phantom with the corresponding experimental measurements. Results showed an excellent agreement between simulated and experimental data: experimental spatial resolutions were predicted with an error less than 100 microns. The difference between experimental and simulated system sensitivities for different source-to-collimator distances was within 2%. Simulated and experimental scatter fractions in a [98-182 keV] energy window differed by less than 2% for sources located in water. Simulated and experimental energy spectra agreed very well between 40 and 180 keV. These results demonstrate the ability and flexibility of GATE for simulating original detector designs. The main weakness of GATE concerns the long computation time it requires: this issue is currently under investigation by the GEANT4 and the GATE collaborations.     

GATE V6: a major enhancement of the GATE simulation platform enabling modelling of CT and radiotherapy

GATE (Geant4 Application for Emission Tomography) is a Monte Carlo simulation platform developed by the OpenGATE collaboration since 2001 and first publicly released in 2004. Dedicated to the modelling of planar scintigraphy, single photon emission computed tomography (SPECT) and positron emission tomography (PET) acquisitions, this platform is widely used to assist PET and SPECT research. A recent extension of this platform, released by the OpenGATE collaboration as GATE V6, now also enables modelling of x-ray computed tomography and radiation therapy experiments. This paper presents an overview of the main additions and improvements implemented in GATE since the publication of the initial GATE paper (Jan et al 2004 Phys. Med. Biol. 49 4543-61). This includes new models available in GATE to simulate optical and hadronic processes, novelties in modelling tracer, organ or detector motion, new options for speeding up GATE simulations, examples illustrating the use of GATE V6 in radiotherapy applications and CT simulations, and preliminary results regarding the validation of GATE V6 for radiation therapy applications. Upon completion of extensive validation studies, GATE is expected to become a valuable tool for simulations involving both radiotherapy and imaging.     

Integration of SimSET photon history generator in GATE for efficient Monte Carlo simulations of pinhole SPECT

The authors developed and validated an efficient Monte Carlo simulation (MCS) workflow to facilitate small animal pinhole SPECT imaging research. This workflow seamlessly integrates two existing MCS tools: simulation system for emission tomography (SimSET) and GEANT4 application for emission tomography (GATE). Specifically, we retained the strength of GATE in describing complex collimator/detector configurations to meet the anticipated needs for studying advanced pinhole collimation (e.g., multipinhole) geometry, while inserting the fast SimSET photon history generator (PHG) to circumvent the relatively slow GEANT4 MCS code used by GATE in simulating photon interactions inside voxelized phantoms. For validation, data generated from this new SimSET-GATE workflow were compared with those from GATE-only simulations as well as experimental measurements obtained using a commercial small animal pinhole SPECT system. Our results showed excellent agreement (e.g., in system point response functions and energy spectra) between SimSET-GATE and GATE-only simulations, and, more importantly, a significant computational speedup (up to approximately 10-fold) provided by the new workflow. Satisfactory agreement between MCS results and experimental data were also observed. In conclusion, the authors have successfully integrated SimSET photon history generator in GATE for fast and realistic pinhole SPECT simulations, which can facilitate research in, for example, the development and application of quantitative pinhole and multipinhole SPECT for small animal imaging. This integrated simulation tool can also be adapted for studying other preclinical and clinical SPECT techniques.     

Monte Carlo simulations of a scintillation camera using GATE: validation and application modelling

Geant4 application for tomographic emission (GATE) is a recently developed simulation platform based on Geant4, specifically designed for PET and SPECT studies. In this paper we present validation results of GATE based on the comparison of simulations against experimental data, acquired with a standard SPECT camera. The most important components of the scintillation camera were modelled. The photoelectric effect. Compton and Rayleigh scatter are included in the gamma transport process. Special attention was paid to the processes involved in the collimator: scatter, penetration and lead fluorescence. A LEHR and a MEGP collimator were modelled as closely as possible to their shape and dimensions. In the validation study, we compared the simulated and measured energy spectra of different isotopes: 99mTc, 22Na, 57Co and 67Ga. The sensitivity was evaluated by using sources at varying distances from the detector surface. Scatter component analysis was performed in different energy windows at different distances from the detector and for different attenuation geometries. Spatial resolution was evaluated using a 99mTc source at various distances. Overall results showed very good agreement between the acquisitions and the simulations. The clinical usefulness of GATE depends on its ability to use voxelized datasets. Therefore, a clinical extension was written so that digital patient data can be read in by the simulator as a source distribution or as an attenuating geometry. Following this validation we modelled two additional camera designs: the Beacon transmission device for attenuation correction and the Solstice scanner prototype with a rotating collimator. For the first setup a scatter analysis was performed and for the latter design. the simulated sensitivity results were compared against theoretical predictions. Both case studies demonstrated the flexibility and accuracy of GATE and exemplified its potential benefits in protocol optimization and in system design.     

GATE as a GEANT4-based Monte Carlo platform for the evaluation of proton pencil beam scanning treatment plans

Active scanning delivery systems take full advantage of ion beams to best conform to the tumor and to spare surrounding healthy tissues; however, it is also a challenging technique for quality assurance. In this perspective, we upgraded the GATE/GEANT4 Monte Carlo platform in order to recalculate the treatment planning system (TPS) dose distributions for active scanning systems. A method that allows evaluating the TPS dose distributions with the GATE Monte Carlo platform has been developed and applied to the XiO TPS (Elekta), for the IBA proton pencil beam scanning (PBS) system. First, we evaluated the specificities of each dose engine. A dose-conversion scheme that allows one to convert dose to medium into dose to water was implemented within GATE. Specific test cases in homogeneous and heterogeneous configurations allowed for the estimation of the differences between the beam models implemented in XiO and GATE. Finally, dose distributions of a prostate treatment plan were compared. In homogeneous media, a satisfactory agreement was generally obtained between XiO and GATE. The maximum stopping power difference of 3% occurred in a human tissue of 0.9?g cm(-3) density and led to a significant range shift. Comparisons in heterogeneous configurations pointed out the limits of the TPS dose calculation accuracy and the superiority of Monte Carlo simulations. The necessity of computing dose to water in our Monte Carlo code for comparisons with TPSs is also presented. Finally, the new capabilities of the platform are applied to a prostate treatment plan and dose differences between both dose engines are analyzed in detail. This work presents a generic method to compare TPS dose distributions with the GATE Monte Carlo platform. It is noteworthy that GATE is also a convenient tool for imaging applications, therefore opening new research possibilities for the PBS modality.     

Validation of a dose deposited by low-energy photons using GATE/GEANT4

The GATE Monte Carlo simulation platform based on the Geant4 toolkit has now become a diffused tool for simulating PET and SPECT imaging devices. In this paper, we explore its relevance for dosimetry of low-energy 125I photon brachytherapy sources used to treat prostate cancers. To that end, three 125-iodine sources widely used in prostate cancer brachytherapy treatment have been modelled. GATE simulations reproducing dosimetric reference observables such as radial dose function g(r), anisotropy function F(r, theta) and dose-rate constant (Lambda) were performed in liquid water. The calculations were splitted on the EGEE grid infrastructure to reduce the computing time of the simulations. The results were compared to other relevant Monte Carlo results and to measurements published and fixed as recommended values by the AAPM Task Group 43. GATE results agree with consensus values published by AAPM Task Group 43 with an accuracy better than 2%, demonstrating that GATE is a relevant tool for the study of the dose induced by low-energy photons.     

Comparison of GATE/GEANT4 with EGSnrc and MCNP for electron dose calculations at energies between 15 keV and 20 MeV

The GATE Monte Carlo simulation platform based on the GEANT4 toolkit has come into widespread use for simulating positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging devices. Here, we explore its use for calculating electron dose distributions in water. Mono-energetic electron dose point kernels and pencil beam kernels in water are calculated for different energies between 15 keV and 20 MeV by means of GATE 6.0, which makes use of the GEANT4 version 9.2 Standard Electromagnetic Physics Package. The results are compared to the well-validated codes EGSnrc and MCNP4C. It is shown that recent improvements made to the GEANT4/GATE software result in significantly better agreement with the other codes. We furthermore illustrate several issues of general interest to GATE and GEANT4 users who wish to perform accurate simulations involving electrons. Provided that the electron step size is sufficiently restricted, GATE 6.0 and EGSnrc dose point kernels are shown to agree to within less than 3% of the maximum dose between 50 keV and 4 MeV, while pencil beam kernels are found to agree to within less than 4% of the maximum dose between 15 keV and 20 MeV.