正电子发射断层扫描图像部分容积效应的模拟研究及实验检验

用模拟实验研究了正电子发射断层扫描(PET)部分容积效应与相关影响因素间的关系。依据形成部分容积效应的理论,由计算机模拟PET各种分辨率情况下各种大小热灶的图像。计算图像的最大恢复系数、平均恢复系数及图像热灶半高宽,并用PET实验进行了检验。结果表明：PET实验的结果与模拟结果一致;当热灶直径以PET分辨率为单位时,图像热灶的最大及平均恢复系数随热灶直径的变化与分辨率无关,且热灶半高宽／分辨率与热灶直径的关系不受分辨率影响。     

一种简单校正PET图像部分容积效应的方法

部分容积效应使PET图像中的病灶失真,影响临床定量诊断.本文建立一种临床实用的校正病灶失真的方法.方法:根据部分容积效应形成的原理,并基于柱形病灶的模拟实验结果,分析病灶断层图像特征剖线数据和一维病灶图像的关系.由此将二维病灶图像部分容积效应校正问题转化为一维问题,称之为一维校正法.并通过柱型病灶模型的PET、实验,对所建校正法进行实验检验.结果:①一维校正法:校正方法的三步骤及数学公式.②实验验证:直径大于分辨率(FWHM)的病灶,得到了很好的直径校正值,偏差在±6%内.直径小于分辨率的病灶,直径校正偏差较大.病灶放射性浓度均值受部分容积效应的影响随病灶变小而加重,对应病灶直径29-3 mm,相对偏差从～-17%增加到-80%以上.经校正后,偏差大幅减少,尤其对直径大于分辨率的病灶,放射性浓度基本得到了完全校正恢复,偏差都在±7%内.对直径小于分辨率的病灶(4.7mm、3mm),虽然没有完全校正恢复,但使偏差平均减小了近一半.结论:提出了一种二维病灶PET图像部分容积效应校正的方法--一维校正法,此方法简单快速,其校正效果令人鼓舞.     

校正PET图像上病灶SUV值的研究

进行定量分析是PET技术重要的优势,但由于部分容积效应(PVE)的影响,使图像定量值失真.本研究建立一种校正PET图像上病灶标准摄取值(SUV)的方法.基于PET图像PVE形成原理及模拟实验,分析病灶图像上最大SUV与病灶真实大小、病灶真实SUV之间的关系,建立由图像上最大值校正SUV的方法,称之为最大值校正法.并通过PET模型实验,对建立的方法进行验证.结果:①最大值校正法:建立了用图像上病灶SUV最大值计算SUV校正值的公式.②实验验证:对不同大小的病灶,其SUV均得到了一定程度的校正,尤其对小于分辨率的病灶(4.7mm、3mm),校正效果更显著,SUV校正值的准确度提高了53.55%、54.17%和50.37%、68.52%.结论:建立了一种简单校正PET图像上病灶SUV的方法--最大值校正法.     

双探头符合图像中冷灶的部分容积效应

部分容积效应是影响图像质量的重要因素,它使图像的像素值与实际值产生偏差.本文探讨部分容积效应对双探头符合图像中冷灶的影响.采用GE.Hawkeye符合成像设备及东芝AZ-618 ECT模型.18F-FDG的总活度从15.15 MBq到204.33 MBq分18次扫描.图像重建采用OSEM算法,Hanning后滤波.由重建数据确定冷灶的恢复系数,分析部分容积效应.结果显示,冷灶恢复系数随其背景实际放射性浓度的增高而增大,并随冷灶尺寸的增加而减小.说明部分容积效应不仅随病灶尺寸的减小而增强,且随本底活度的增加而加剧.     

脑专用PET显像探测器自由结构符合与初步实验测试

采用脑PET进行人脑功能的研究对生物医学起到至关重要的作用,为了显著提高脑PET显像质量,增加探测效率、实时显示图像,本文设计一种脑专用PET显像大面积平板型探测系统,该探测系统由两个大面积探头组成,每个大面积探头包含3×3阵列的位置灵敏光电倍增管和多个紧密排布的硅酸钇镥闪烁晶体（Ce：LYSO)阵列。并利用1 μCi的²²Na点源对晶格大小为0.7 mm×0.7 mm等六种LYSO晶体阵列进行晶体性能测试,并选用两块晶格大小为1.5 mm×1.5 mm的LYSO晶体阵列进行一对一符合探测初步断层显像。结果显示,各种晶格大小的LYSO晶体阵列的位置区分轮廓的半高宽平均值在0.38~0.49 mm之间,平均能量分辨率（半高宽）在17.61%~30.40%之间;在对²²Na点源的初步图像断层扫描实验测试中,通过滤波反投影算法获得重建图像的空间分辨率为1.5 mm,验证了大面积平板型探测系统的可行性。     

双探头符合成像系统的分辨率及其影响因素

研究双探头符合成像系统的分辨率及其影响因素。采用Hawkeye双探头符合成像设备,对Toshiba椭圆柱分辨率模型成像。用X线透射扫描进行衰减校正,在不同的活度下做18次扫描。OS-EM算法选择4种后滤波截止频率重建图像。计算线源横断层面上扩展函数的半高宽（FWHM）。在视野中活度较低时（〈101．00MBq）,FWHM基本不随活度变化;但在较高的活度区,FWHM随视野中活度的增加而缓慢增加;在视野中心至横向12cm范围内,视野中心区径向FWHMx最大,越靠边缘越小,而切向FWH嗨基本不随位置变化;FWHM随重建算法中后滤波截止频率的增加而减小。结论是视野中的总活度、位置及重建算法均影响双探头符合成像系统的分辨率。     

LMS自适应滤波数字峰值估计方法研究

在小动物PET成像系统中,脉冲峰值精度决定着能量分辨率和位置分辨率,对成像质量极为重要。我们通过精确仿真评估了LMS自适应滤波方法峰值估计的性能,结果表明相对传统直接取最大值方法,在窄脉冲及较大噪声时可以给出很高的精度;并且由于简单通用,该方法在数字峰值估计上有很高的应用价值。     

单侧部分开口方腔自然对流数值模拟

为研究开口度对自然对流和传热的影响,采用有限容积法对单侧部分开口（2个开口）方腔自然对流进行了二维层流稳态数值模拟。计算结果表明：Ra和开口度的改变对方腔内的温度场分布和涡流结构有显著影响。相同开口度下,平均Nu和无量纲流量随Ra的增加而增加;相同Ra下,无量纲流量随开口度的增加而增加。当Ra>10⁴,可能存在最佳开口度,此时平均Nu取得最大值。     

满江红鱼腥藻中氘的生物学同位素效应研究

用含重水０％、１０％、３０％、６０％、９０％的ＢＧ－１１培养基培养满江红鱼腥藻（Ａｎａｂａｅｎａａｚｏｌｌａｅ）并测定不同生长时间的光合活性、呼吸活性、固氮酶活性以及生长曲线，同时测定了室温吸收光谱及低温荧光光谱，用扫描电镜观察了细胞形态的变化。实验结果表明，重水使指数生长期后延，显著抑制光合活性、呼吸活性和固氮酶活性；随着重水含量的增加，藻胆素和类胡萝卜素的相对含量逐渐降低，光系统Ⅰ与光系统Ⅱ的相对荧光强度Ｆ＿（７３３）／Ｆ＿（６９５）变小，光合作用光能分配趋向于光系统Ⅱ。根据净光合最大值和固氮酶最大值讨论了氘的同位素效应。     

双层错位DOI脑PET探测器晶体厚度组合优化设计

双层错位晶体阵列是正电子发射断层成像（PET）仪获取作用深度（DOI）信息的一种低成本且简便的方案。为获得晶体厚度最优组合方案,本文使用GATE软件进行蒙特卡罗仿真研究。模拟兼容核磁共振成像（MRI）的嵌入式脑PET,环内径345 mm,使用硅酸钇镥（LYSO）晶体,2层晶体总厚度20 mm,内层晶体从0 mm到10 mm共11种厚度（间隔1 mm）;进行点源模拟实验,点源位于中心断层x轴上,偏移从x=0 cm到x=10 cm共6种情况（间隔2 cm）。计算中心点灵敏度;采用滤波反投影算法重建图像,评估径向空间分辨率。结果显示,双层晶体的设计相比于单层晶体灵敏度略有下降,但系统径向空间分辨率显著提高且其均匀性得到改善。随着内层晶体厚度的增大,视野平均径向空间分辨率先减小后增大,在内层晶体厚度为8 mm时达到最小。综上所述,所设计的双层错位DOI脑PET探测器晶体厚度最优组合方案为内层晶体厚度8 mm、外层晶体厚度12 mm。     

~(18)F-FDG PET/CT in diagnosis of skeletal metastases

This work is to evaluate correlated lesions in PET and CT images of patients suffering skeletal metastases so as to improve efficacy of ~(18)F-FDG PET/CT in diagnosing bone metastases. PET and CT images of 25 patients with malignant tumor suspected bone metastases were reviewed independently by three experts. A region of interest was placed over each lesion, and the standardized uptake value (SUV) was calculated at the maximal single pixel value.The t and χ~2 tests were used for statistical analysis. Of the 203 lesions detected on the PET and CT images, 189 were malignant and 14 were benign lesions. PET alone identified 159 malignant lesions and 6 benign lesions, CT alone identified 152 malignant lesions and 11 benign lesions. For PET, the diagnostic sensitivity, specificity and accuracy were 84.1%, 71.4% and 83.3%, respectively, while 80.4%, 71.4% and 83.3% for CT. No significant difference was found between PET and CT in detecting bone metastases (χ~2=0.89, 0.19, 0.59,P>0.05). Statistical difference of positive ratio of PET was found between osteoblastic and osteolytic or mixed lesions (χ~2=47.33, 7.93, both P<0.05).Of the 122 positive lesions on both CT and PET scan, the mean SUV was 5.76±3.41, 8.52±5.37 and 7.78±4.96 in osteoblastic lesions, osteolytic lesions and mixed lesions, respectively. Significant difference was found between osteoblast lesions and osteolytic lesions (t=2.28, P<0.05). PET images alone may leave out half of osteoblastic letions,but combined analysis of PET and CT images gives better diagnosis.     

Imaging studies for evaluating impact of position sampling techniques in PET scanners

Previously we have evaluated two crystal calibration techniques that can be applied to pixelated detector designs to improve system spatial resolution without detector motion. The inter-crystal positioning technique utilizes sub-sampling in the crystal flood map to better sample the Compton scatter events in the detector. The Compton scatter rejection technique, on the other hand, rejects those events that are located further from individual crystal centers in the flood map. Here we performed imaging studies with a Mini Deluxe hot rod phantom and a hot sphere phantom (sphere diameters of 4.95 and 7.86-mm with 6:1 uptake relative to background) using the standard crystal calibration technique, as well as the inter-crystal and Compton rejection calibration techniques. Our results show improved separation of 1.6-mm diameter hot rods with the two new crystal calibration techniques that is consistent with improved spatial resolution. For the hot sphere phantom the contrast recovery is improved with both the inter-crystal and Compton rejection calibration techniques over the standard calibration technique. The only drawback of the inter-crystal calibration technique is the increase in the number of possible lines-of-response (LORs) (factor of 16) that may slow image reconstruction. With the Compton rejection calibration technique, loss of counts leads to increased noise in the images.     

Compton Scattering in Clinical PET/CT With High Resolution Half Ring PET Insert Device

The integration of a high resolution PET insert into a conventional PET system can significantly improve the resolution and the contrast of its images within a reduced imaging field of view. For the rest of the scanner imaging field of view, the insert is a highly attenuating and scattering media. In order to use all available coincidence events (including coincidences between 2 detectors in the original scanner, namely the scanner-scanner coincidences), appropriate scatter and attenuation corrections have to be implemented. In this work, we conducted a series of Monte Carlo simulations to estimate the composition of the scattering background and the importance of the scatter correction. We implemented and tested the Single Scatter Simulation (SSS) algorithm for a hypothetical system and show good agreement between the estimated scatter using SSS and Monte Carlo simulated scatter contribution. We further applied the SSS to estimate scatter contribution from an existing prototype PET insert for a clinical PET/CT scanner. The results demonstrated the applicability of SSS to estimate the scatter contribution within a clinical PET/CT system even when there is a high resolution half ring PET insert device in its imaging field of view.     

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。     

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     

基于TGV正则化的MP-PET图像恢复

针对光子计数较少导致心肌灌注PET(MP-PET)图像质量严重退化问题,提出基于TGV正则化的MP-PET图像恢复模型。模型结合低秩稀疏分解理论对MP-PET序列图像的目标区域和背景区域进行分离,针对目标区域进行TGV约束从而改善图像质量。分别对仿真数据及临床扫描数据进行实验,采用视觉及不同的量化指标进行恢复效果评价。实验结果表明,提出的TGV模型具有优质的恢复效果。     

Imaging performance evaluation in depth-of-interaction PET with a new method of sinogram generation:A Monte Carlo simulation study

In conventional PET systems,the parallax error degrades image resolution and causes image distortion.To remedy this,a PET ring diameter has to be much larger than the required size of field of view(FOV),and therefore the cost goes up.Measurement of depth-of-interaction(DOI)information is effective to reduce the parallax error and improve the image quality.This study is aimed at developing a practical method to incorporate DOI information in PET sinogram generation and image reconstruction processes and evaluate its efficacy through Monte Carlo simulation.An animal PET system with 30-mm long LSO crystals and 2-mm DOI measurement accuracy was simulated and list-mode PET data were collected.A sinogram generation method was proposed to bin each coincidence event to the correct LOR location according to both incident crystal indices and DOI positions of the two annihilation photons.The sinograms were reconstructed with an iterative OSMAPEM(ordered subset maximum a posteriori expectation maximization)algorithm.Two phantoms(a rod source phantom and a Derenzo phantom)were simulated,and the benefits of DOI were investigated in terms of reconstructed source diameter(FWHM)and source positioning accuracy.The results demonstrate that the proposed method works well to incorporate DOI information in data processing,which not only overcomes the image distortion problem but also significantly improves image resolution and resolution uniformity and results in satisfactory image quality.     

Hot sphere detection limits for a dual head coincidence imagingsystem

Phantom studies were performed to investigate detectability limits for a dual head coincidence imaging system. Spheres of 2.8, 2.2, 1.6, 1.2, 1.0, 0.8 cm inner diameter were placed at a radius of 5.75 cm in a 22 cm diameter cylindrical phantom. The contrast to noise ratio (CNR) of the spheres to background was used as the authors' metric of detectability. CNR values were determined for three different sphere to background ratios (10:1, 5:1, and 3:1); for three different background count densities (high, medium, and low); and for three different energy window requirements (photopeak only, photopeak and photopeak-Compton, and all combinations). Based upon the authors' visual observation, the smallest detectable spheres were 0.8 cm, 1.2 cm and 1.6 cm for a 2.5 million event photopeak-Compton image set with sphere to background ratios of 10:1, 5:1 and 3:1, respectively. The CNR values for these spheres were 5.1, 7.8, and 4.8. Over all observations, spheres with a CNR greater than 4 were detectable