影响PET/CT图像质量技术因素的探讨

目的对受检者体内18F-脱氧葡萄糖使用正电子发射体层摄影术/计算机体层摄影术（PET/CT）进行扫描,评价技术因素与图像质量的相关性,充分理解获得高质量PET/CT图像的必要条件,指导临床工作。方法采用GE公司Discovery LS16型PET/CT一体扫描仪对患者进行2D数据采集,对原始数据进行图像重建,使用CT对PET图像进行衰减校正。随机选取2005～2009年期间受检患者900例进行回顾性分析。结果伪影分为自身因素和设备技术因素,自身因素所致伪影中以运动伪影和高密度物质伪影最常见;设备技术因素伪影以截断伪影、放射性污染及注射点外漏较多见。不常见的生理性摄取包括乳腺摄取、子宫内膜摄取和脂肪摄取。结论受检者体内足够的放射性计数以及规范化操作是获得高质量PET/CT图像的前提和保证,且相辅相成。     

CT图像伪影的分析

CT图像伪影就是指扫描重建出来的CT图像中出现不属于图像本身的信息。根据伪影产生的原因不同,CT图像伪影可分为两类：与扫描、采集有关的伪影及与CT机系统本身有关的伪影。扫描伪影的产生与扫描过程中扫描方法、参数的选择有关。主要包括X线硬化伪影、部分体积效应伪影、金属伪影、运动伪影等。     

胃螺旋CT扫描技术探讨

目的研究比较不同充填剂与不同扫描体位在胃的螺旋CT扫描中的应用。方法分别对80例胃病患者采用不同的充填剂（水和低浓度泛影葡胺），与不同的体位（单体位和双体位），进行螺旋CT扫描，评价不同的充填剂与不同体位的优缺点。结果水作为充填剂组病灶显示情况明显优于低浓度泛影萄胺组且伪影少，选择双体位组的图像质量也明显优于常规体位组。结论胃螺旋CT扫描时应首选水作为充填剂，根据病变需要选择双体位，有利于图像质量的提高，从而提高临床诊断率。     

CT9800 Quick─特例环形伪影故障分析检修

CT是一个全电子数字成像设备。它应用现代图像理论，将透过人体的反映人体组织衰减特性的X线通过计算机控制，完成测量数据采集，经处理、运算，然后用不同灰度在视频显示器上进行图像输出（1）。由于我院采用G．E公司9800QuickCT属第三代CT产品，图像质量较好，但出现图像伪影故障的机会较多。这里就一特例环形伪影问题与大家商讨。一、故障现象：病人作头部CT扫描时，突然出现颅骨外围高密度粗线条同心圆环状伪影，随往头顶颅骨扫描，扫描面积缩小，伪影增加。当扫描条件提高，脑组织内亦出现环形伪影。尤以中心为甚。腹部扫描时，图…     

CT图像伪影的产生及消除

CT图像伪影就是指扫描重建出来的CT图像中出现的不属于图像本身的信息。不管CT机制造、校准、维护的多么好，图像伪影都是不可避免的。CT图像伪影可分为两类：与扫描、采集有关的伪影及与CT机系统本身有关的伪影。扫描伪影的产生与扫描过程中扫描方法、参数的选择有关。主要包括部分体积效应伪影、X线硬化伪影、金属伪影、运动伪影等。当X线穿过人体时，人体内各点密度不同，而探测器不可能做的太小，因而就会出现在同一个探测器单元上一半有高密度的测量数据，另一半有低密度的测量数据，而探测器的输出信号是按一个信号来自一个探测…     

CT增强扫描发生变态反应的护理

CT检查中，碘造影剂的增强扫描大大提高了CT诊断的准确率。尽管泛影葡胺毒性很低，但由于用量大，注射速度快，在日常工作中常有变态反应发生。现将其急救处理和护理分析报道如下：     

东芝Aquilion 16型CT机环形伪影故障分析与排除1例

在CT扫描过程中,我们常常会遇到很多图像伪影,如温度变化使探测器性能漂移造成的伪影、球管老化造成的伪影等。一般情况下,我们先采取空气扫描校正或者模具（水模、头模、体模）扫描校正,这些伪影大都能解决;如果以上方法都无法解决,我们应该通过检查相关部件来排除类似故障。下面就我院东芝产Aquilion 16型CT机1例环形伪影做简要分析,供同行参考。     

探讨GE Light speed 16 CT扫描在急性胰腺炎诊断中的应用价值

目的 探讨如何准确、合理运用GE Light speed 16 CT扫描技术及重建技术对急性胰腺炎的诊断。方法 扫描前30 min口服三种胃肠道对比剂:水、2%、5%泛影葡胺溶液300 mL,扫描前再服水,2%、5%泛影葡胺溶液300mL。扫描参数120 kV,320 mA,层厚2~5 mm,先行常规扫描,后行双期增强扫描:①20~30s内先行动脉期扫描;②40~50s再行平衡期扫描。再用三维重建(3D)MPR进行后处理。结果 急性胰腺炎时表现胰腺弥漫性增大,密度低,轮廓不清,边缘模糊,周围渗出积液等改变。胃肠道对比剂以2%泛影葡胺溶液后行增强扫描所得图象最清晰,能提高阳性诊断率。结论 GE Light speed 16 CT对急性胰腺炎及并发症显示细微、准确,有较特征性表现,对其诊断价值较大。     

全腹CT扫描前两种胃肠道准备方法的应用研究

目的 比较全腹CT扫描前两种胃肠道准备方法的应用效果。方法 将93例全腹CT扫描检查的患者按照进院检查顺序随机分组,观察组47例,对照组46例,对照组采用常规方法,口服泛影葡胺准备肠道进行全腹CT扫描检查,对照组采用口服并灌肠泛影葡胺用于全腹CT扫描检查。结果 观察组患者肠道造影剂充盈时间平均(1.01±0.20) h,成功率100%,对照组患者肠道造影剂充盈时间平均(2.93±0.32) h,成功率82.6%。两组对比差异有统计学意义(P < 0.01)。结论 表明口服并灌肠泛影葡胺用于全腹CT扫描的准备时间大大缩短。提高了影像检查质量和正确诊断率。     

CT成像质量影响因素

目的探讨在应用于医学诊断的过程中，CT成像质量的影响因素以及影响的质量控制。方法研究不同的CT图像的专有特征及其评价方法．并对照不同分析方法的特异性。结果对CT成像的典型图像进行分析，发现影响CT成像质量的主要影响因素中。CT成像质量的主要评价指标有空间分辨率、噪声、低对比度分辨率与伪影；其主要影响因素包括X射线源、球管焦点的尺寸、扫描层厚、探测器孔径的大小和采样间距、重建算法。结论CT成像质量直接关系到患者诊断的准确性，影响CT成像质量的因素比较多，主要分为机器因素和人为因素两大类。机器固有的性能无法改变的情况下要熟悉器械操作，最大程度避免机器因素造成的影响，充分发挥机器的优点，在此基础上避免人为因素造成的机器伪影和运动伪影，降低操作误差．并通过多种方法提高CT图像的质量，提高临床诊断率。     

Quantifying the effects of iodine contrast media on standardised uptake values of FDG PET/CT images: an anthropomorphic phantom study

This study aimed to quantify the amount of change in Standardised Uptake Values (SUVs) of PET/CT images by simulating the set-up as closely as possible to the actual patient scanning. The experiments were conducted using an anthropomorphic phantom, which contained an amount of radioactivity in the form of Fluorodeoxyglucose (FDG) in a primary plastic test tube and one litre saline bags, including the insertion of bony structures and another two test tubes containing different concentrations of iodine contrast media. Standard scanning protocols were employed for the PET/CT image acquisition. The highest absolute differences in the SUVmax and SUVmean values of the saline bags were found to be about 0.2 and 0.4, respectively. The primary test tube showed the largest change of 1.5 in both SUVs; SUV max and SUVmean. However, none of these changes were found to be statistically significant. The clinical literature also contains no evidence to suggest that the changes of this magnitude would change the final diagnosis. Based on these preliminary data, we propose that iodine contrast media can be used during the CT scan of PET/CT imaging, without significantly affecting the diagnostic quality of this integrated imaging modality.     

Motion effects on SUV and lesion volume in 3D and 4D PET scanning

To assess the effect of lesion motion and respiration rate on Standardised Uptake Value (SUV) and the ability of 4D PET to restore any loss in SUV and distortion of lesion volume on two PET/CT systems. A Perspex phantom with four cylindrical reservoirs filled with ¹⁸F-FDG was used in this study. The cylinders measured 5, 10, 15, and 20 mm in diameter. A GE Discovery STE8 (GE Medical Systems Milwaukee, WI) and a Siemens Biograph 64/40 (Siemens Medical Solutions, Erlangen, Germany) scanner was used to acquire a stationary un-gated PET scan of the phantom. Multiple 10 min list mode 4D PET scans were acquired using the Varian RPM on the GE camera and the Anzai Gating system on the Siemens camera. The phantom was scanned at five different respiratory rates and motion amplitudes in a sinusoidal fashion, 15 RPM/1 cm, 15 RPM/2 cm, 15 RPM/4 cm, 30 RPM/2 cm and 7.5 RPM/2 cm (RPM-respirations per minute). Each scan was reconstructed into ten bins and as an un-gated static image. The SUVmax, SUVmean and volume were measured for all four reservoirs using Siemens TrueD analysis software. With increasing lesion movement the SUVmax and SUVmean decreased and the volume increased with the SUVmax in the smallest lesion underestimated by up to a factor of four. The SUVmax, SUVmean and volume were mostly recovered using 4D imaging regardless of amount of lesion displacement. The larger lesions showed better count recovery and volume correction than the smaller lesions. The respiratory rate had no effect of SUV or volume. Un-gated imaging of moving lesions decreases apparent SUV in small lesions significantly and overestimates volumes. 4D PET scanning recovers most of the apparent loss in SUV and distortion of volumes.     

PET/CT中CT自动管电流调制模式下受检者有效剂量的研究

目的 研究PET/CT中CT自动管电流模式下受检者有效剂量与管电流阈值及噪声指数的关系,为确定最优化采集条件提供理论基础。方法 选用GE Discovery ST-16型和Discovery Elite型PET/CT,使用RS-550型仿真人体模型获得PET/CT中CT所致受检者有效剂量。两机型采用相同采集条件,即管电压120 kV,螺距为1.375,转速0.8 s/转,噪声指数（NI）8-30,间隔为2,自动管电流低限均为30 mA,高限为200~350mA,间隔为50 mA。模拟临床PET/CT的头颈部和体部分段扫描方式对仿真人体模型进行扫描。记录各种采集条件下剂量长度乘积（DLP）,计算有效剂量（ED_CT）。结果 采用相同采集条件,CT扫描所致有效剂量随噪声指数增大而降低,且曲线随自动管电流高限的增加而陡峭;Discovery Elite型扫描CT所致受检者全身有效剂量低于Discovery ST-16型。结论 对确定的受检者,PET/CT中CT所致有效剂量随扫描条件不同有较大差异。可以根据不同临床需求,选择最优化采集方案,从而尽可能降低受检者的有效剂量。     

The clinical application of 4D 18F-FDG PET/CT on gross tumor volume delineation for radiotherapy planning in esophageal squamous cell cancer

A combination of four-dimensional computed tomography with ¹⁸F-fluorodeoxyglucose positron emission tomography (4D CT-FDG PET) was used to delineate gross tumor volume (GTV) in esophageal cancer (EC). Eighteen patients with EC were prospectively enrolled. Using 4D images taken during the respiratory cycle, the average CT image phase was fused with the average FDG PET phase in order to analyze the optimal standardized uptake values (SUV) or threshold. PET-based GTV (GTV_PET) was determined with eight different threshold methods using the auto-contouring function on the PET workstation. The difference in volume ratio (VR) and conformality index (CI) between GTV_PET and CT-based GTV (GTV_CT) was investigated. The image sets via automatic co-registrations of 4D CT-FDG PET were available for 12 patients with 13 GTV_CT values. The decision coefficient (R²) of tumor length difference at the threshold levels of SUV 2.5, SUV 20% and SUV 25% were 0.79, 0.65 and 0.54, respectively. The mean volume of GTV_CT was 29.41 ± 19.14 ml. The mean VR ranged from 0.30 to 1.48. The optimal VR of 0.98, close to 1, was at SUV 20% or SUV 2.5. The mean CI ranged from 0.28 to 0.58. The best CI was at SUV 20% (0.58) or SUV 2.5 (0.57). The auto-contouring function of the SUV threshold has the potential to assist in contouring the GTV. The SUV threshold setting of SUV 20% or SUV 2.5 achieves the optimal correlation of tumor length, VR, and CI using 4D-PET/CT images.     

成像条件对不同机型PET/CT图像空间分辨率的影响

目的 探讨PET/CT成像条件（采集时间、床位重叠、重建矩阵、迭代次数、滤波核、衰减校正）对图像空间分辨率的影响。方法 使用GE Discovery Elite型和GE Discovery ST-16型2种PET/CT设备分别对椭圆柱分辨率模型进行1个和2个床位扫描（List mode模式,采集时间为6 min）;使用临床常用重建条件（Elite型：VPFX-S算法;ST-16型：VUE Point HD算法）分别按1～6 min/床、不同迭代次数2～10次、滤波核2.0～10.0 mm(Elite型)、不同的重建矩阵以及是否进行衰减校正对图像进行重建;用线源扩展函数的半高宽（FWHM）表示PET重建图像的空间分辨率。结果 在临床采集条件下,当采集时间为1 min、2 min、3 min、4 min、5 min、6 min时,中心位置图像空间分辨率FWHMElite分别为（4.06±0.08）mm、（4.05±0.20）mm、（4.01±0.01）mm、（4.05±0.07）mm、（4.05±0.03）mm、（4.08±0.06）mm;FWHMST-16分别为（5.76±0.12）mm...     

Optimization of a shorter variable-acquisition time for legs to achieve true whole-body PET/CT images

The present study aimed to qualitatively and quantitatively evaluate PET images as a function of acquisition time for various leg sizes, and to optimize a shorter variable-acquisition time protocol for legs to achieve better qualitative and quantitative accuracy of true whole-body PET/CT images. The diameters of legs to be modeled as phantoms were defined based on data derived from 53 patients. This study analyzed PET images of a NEMA phantom and three plastic bottle phantoms (diameter, 5.68, 8.54 and 10.7 cm) that simulated the human body and legs, respectively. The phantoms comprised two spheres (diameters, 10 and 17 mm) containing fluorine-18 fluorodeoxyglucose solution with sphere-to-background ratios of 4 at a background radioactivity level of 2.65 kBq/mL. All PET data were reconstructed with acquisition times ranging from 10 to 180, and 1200 s. We visually evaluated image quality and determined the coefficient of variance (CV) of the background, contrast and the quantitative %error of the hot spheres, and then determined two shorter variable-acquisition protocols for legs. Lesion detectability and quantitative accuracy determined based on maximum standardized uptake values (SUV_max) in PET images of a patient using the proposed protocols were also evaluated. A larger phantom and a shorter acquisition time resulted in increased background noise on images and decreased the contrast in hot spheres. A visual score of ≥?1.5 was obtained when the acquisition time was ≥?30 s for three leg phantoms, and ≥?120 s for the NEMA phantom. The quantitative %errors of the 10- and 17-mm spheres in the leg phantoms were ±?15 and ±?10%, respectively, in PET images with a high CV (scan < 30 s). The mean SUV_max of three lesions using the current fixed-acquisition and two proposed variable-acquisition time protocols in the clinical study were 3.1, 3.1 and 3.2, respectively, which did not significantly differ. Leg acquisition time per bed position of even 30–90 s allows axial equalization, uniform image noise and a maximum?±?15% quantitative accuracy for the smallest lesion. The overall acquisition time was reduced by 23–42% using the proposed shorter variable than the current fixed-acquisition time for imaging legs, indicating that this is a useful and practical protocol for routine qualitative and quantitative PET/CT assessment in the clinical setting.     

68Ge源与PET/CT的质量控制

目的:探讨68Ge校正源在PET/CT质量控制中的重要作用。方法:对68Ge源校正前、后正常体检患者的PET/CT图像和设备的质量图和参数报告进行对比分析。结果:校正前后采集的图像质量图和参数报告存在显著差异。患者全身PET图像:68Ge源校正前,横断位图像前胸部前方放射性分布较胸背部放射性分布明显稀疏,视野右侧较左侧放射性分布稀疏;右肺区呈放射性缺损,背部肌肉放射性分布增浓,SUV值明显升高;冠状位图像可见膀胱周围区放射性分布缺损;不符合正常人FDG代谢的分布特点。68Ge源校正后,图像横断位和冠状位全身显像未见异常的放射性分布增浓或稀疏区;放射性分布符合正常人FDG代谢分布特点。结论:68Ge校正源是PET正常运行中必不可少的配置。     

CT低剂量扫描的探讨

目的:用西门子Volume Zoom CT机扫描CT模体与人体,探讨降低常规CT扫描剂量的可能性。方法:扫描CT模体,用120kV,mAs在260～180(每次递减20)。共5次。再对50例患者随机分为5组,用120kV,mAs在260～180(每次递减20),进行头颅CT扫描,扫描图像由3名高年资放射诊断医师进行盲审,结果与模体扫描结果进行对比分析。结果:当头颅CT扫描时,mAs由260降至220时,CT剂量指数由62.4降为52.8,降幅16%,两者差异有统计学意义,而图像质量无明显下降,但头颅CT扫描的mAs达到180时,图像噪声大,影响诊断,与模体扫描结果相关。结论:在降低mAs值得情况下,受检者所接受的X线剂量明显减少,在本CT机上,头颅扫描在200mAs以上的图像质量可以满足诊断要求。     

An investigation of the challenges in reconstructing PET images of a freely moving animal

Imaging the brain of a freely moving small animal using positron emission tomography (PET) while simultaneously observing its behaviour is an important goal for neuroscience. While we have successfully demonstrated the use of line-of-response (LOR) rebinning to correct the head motion of confined animals, a large proportion of events may need to be discarded because they either ‘miss’ the detector array after transformation or fall out of the acceptance range of a sinogram. The proportion of events that would have been measured had motion not occurred, so-called ‘lost events’, is expected to be even larger for freely moving animals. Moreover, the data acquisition in the case of a freely moving animal is further complicated by a complex attenuation field. The aims of this study were (a) to characterise the severity of the ‘lost events’ problem for the freely moving animal scenario, and (b) to investigate the relative impact of attenuation correction errors on quantitative accuracy of reconstructed images. A phantom study was performed to simulate the uncorrelated motion of a target and non-target source volume. A small animal PET scanner was used to acquire list-mode data for different sets of phantom positions. The list-mode data were processed using the standard LOR rebinning approach, and multiple frame variants of this designed to reduce discarded events. We found that LOR rebinning caused up to 86 % ‘lost events’, and artifacts that we attribute to incomplete projections, when applied to a freely moving target. This fraction was reduced by up to 18 % using the variant approaches, resulting in slightly reduced image artifacts. The effect of the non-target compartment on attenuation correction of the target volume was surprisingly small. However, for certain poses where the target and non-target volumes are aligned transaxially in the field-of-view, the attenuation problem becomes more complex and sophisticated correction methods will be required. We conclude that there are limitations with the LOR rebinning approach and simplified attenuation correction for freely moving animals requiring the development and validation of more sophisticated approaches.