ROC analysis for assessment of lesion detection performance in 3D PET: influence of reconstruction algorithms

Image quality in positron emission tomography (PET) can be assessed with physical parameters, as spatial resolution and signal-to-noise ratio, or using psychophysical approaches, which include the observer performance and the considered task (ROC analysis). For PET in oncology, such a task is the detection of hot lesions. The aim of the present study was to assess the lesion detection performance due to adequate modeling of the scanner and the measurement process in the image reconstruction process. We compared the standard OSEM software of the manufacturer with a sophisticated fully 3D iterative reconstruction technique (USC MAP). A rectangular phantom with 6 oblique line sources in a homogeneous background (2.6 kBq/ml 18F) was imaged dynamically with an ECAT EXACT HR+ scanner in 3D mode. Reconstructed activity contrasts varied between 15 and 0, as the line sources were filled with 11C (3.2 MBq/ml). Measured attenuation and standard randoms, dead time, and scatter corrections of the manufacturer were employed. For the ROC analysis, a software tool presented a cut-out of the phantom (15 x 15 pixels) to two observers. These cut-outs were rated (5 classes) and the area Az under the ROC curve was determined as a measure of detection performance. The improvement for Az with USC MAP compared to the OSEM reconstructions ranged between 0.02 and 0.23 for signal-to-noise ratios of the background between 2.8 and 3.1 and lesion contrast between 2.1 and 4.2. This study demonstrates that adequate modeling of the measurement process in the reconstruction algorithm improves the detection of small hot lesions markedly.     

Artifact analysis of approximate helical cone-beam CT reconstruction algorithms

In this paper, four approximate cone-beam CT reconstruction algorithms are compared: Advanced single slice rebinning (ASSR) as a representative of algorithms employing a two dimensional approximation, PI, PI-SLANT, and 3-PI which all use a proper three dimensional back-projection. A detailed analysis of the image artifacts produced by these techniques shows that aliasing in the z-direction is the predominant source of artifacts for a 16-row scanner with 1.25 mm nominal slice thickness. For a detector with isotropic resolution of 0.5 mm, we found that ASSR and PI produce different kinds of artifacts which are almost at the same level, while PI-SLANT produces none of these artifacts. It is shown that the use of redundant data in the 3-PI method suppresses aliasing artifacts efficiently for both scanners.     

Image reconstruction and performance evaluation for ECG-gated spiral scanning with a 16-slice CT system

We present an image reconstruction approach and a performance evaluation for ECG-gate cardiac spiral scanning with recently introduced 16-slice CT equipment. We present an extension of the Adaptive Cardio Volume (ACV) reconstruction approach for ECG-gated multislice spiral scanning. We discuss the image z reformation introduced to control the spiral slice width of the final images and give an overview of the reformation functions chosen. We investigate image quality and discuss the maximum number of slices that can be reconstructed without severe cone-beam artifacts. Slice sensitivity profiles (SSPs) and transverse resolution are evaluated as a function of the patient's heart rate. We demonstrate the influence of slice width on the visualization of stents and plaques and show the impact of reduced gantry rotation time (0.42 s) on temporal resolution. Deviating from general purpose spiral scanning cone-beam reconstruction is not required for ECG-gated cardiac CT with up to 16 slices. Using the ACV approach with image reformation, SSPs are well defined and independent of the patient's heart rate. With 0.75 mm collimated slice width, the measured full width at half-maximum (FWHM) of the smallest reconstructed slice is about 0.83 mm. Using this slice width and overlapping image reconstruction, cylindrical holes 0.6-0.7 mm in diameter can be resolved in a z-resolution phantom. Adequate visualization of the coronary arteries requires reconstruction slice widths not larger than 1.5 mm. Visualization of stents and severe calcifications is significantly improved with sub-mm slice width. Experimental evidence for the theoretically predicted temporal resolution and for the variation of temporal resolution depending on the position in the field of measurement (FOM) is presented. With 0.42 s gantry rotation temporal resolution reaches its optimum of 105 ms in the center of the FOM at 81 bpm. First scans on human subjects demonstrate the potential to expand the range of heart rates accessible to routine clinical examinations. A 16-slice platform can cover the heart with sub-mm slices within short breath-hold times, allowing for improved cardiac imaging due to isotropic sub-mm spatial resolution.     

A performance study of 3D reconstruction algorithms for positron emission tomography

This paper investigates the statistical and systematic accuracy of five three-dimensional reconstruction algorithms for multi-ring PET scanners operated without septa: the reprojection method, the direct Fourier reconstruction, the FAVOR algorithm, and the single-slice and multi-slice rebinning algorithms. Simulated data of a uniform cylinder, of Gaussian sources, and of spherical sources are used to compare respectively the noise properties, the modulation transfer function, and the recovery coefficients of the algorithms. Brain scans reconstructed with the different algorithms are compared by calculating the linear regression of the mean values within regions of interest. The most significant observations are a slight loss of transaxial resolution with the reprojection algorithm in the external slices of the scanner, and increased noise in the images reconstructed using multi-slice rebinning.     

The performance of monotonic and new non-monotonic gradient ascent reconstruction algorithms for high-resolution neuroreceptor PET imaging

Iterative expectation maximization (EM) techniques have been extensively used to solve maximum likelihood (ML) problems in positron emission tomography (PET) image reconstruction. Although EM methods offer a robust approach to solving ML problems, they usually suffer from slow convergence rates. The ordered subsets EM (OSEM) algorithm provides significant improvements in the convergence rate, but it can cycle between estimates converging towards the ML solution of each subset. In contrast, gradient-based methods, such as the recently proposed non-monotonic maximum likelihood (NMML) and the more established preconditioned conjugate gradient (PCG), offer a globally convergent, yet equally fast, alternative to OSEM. Reported results showed that NMML provides faster convergence compared to OSEM; however, it has never been compared to other fast gradient-based methods, like PCG. Therefore, in this work we evaluate the performance of two gradient-based methods (NMML and PCG) and investigate their potential as an alternative to the fast and widely used OSEM. All algorithms were evaluated using 2D simulations, as well as a single [(11)C]DASB clinical brain dataset. Results on simulated 2D data show that both PCG and NMML achieve orders of magnitude faster convergence to the ML solution compared to MLEM and exhibit comparable performance to OSEM. Equally fast performance is observed between OSEM and PCG for clinical 3D data, but NMML seems to perform poorly. However, with the addition of a preconditioner term to the gradient direction, the convergence behaviour of NMML can be substantially improved. Although PCG is a fast convergent algorithm, the use of a (bent) line search increases the complexity of the implementation, as well as the computational time involved per iteration. Contrary to previous reports, NMML offers no clear advantage over OSEM or PCG, for noisy PET data. Therefore, we conclude that there is little evidence to replace OSEM as the algorithm of choice for many applications, especially given that in practice convergence is often not desired for algorithms seeking ML estimates.     

Quantitative assessment of the rat intrahepatic biliary system by three-dimensional reconstruction

The anatomical details of the biliary tree architecture of normal rats and rats in whom selective proliferation was induced by feeding alpha-naphthylisothiocyanate (ANIT) were reconstructed in three dimension using a microscopic-computed tomography scanner. The intrahepatic biliary tree was filled with a silicone polymer through the common bile duct and each liver lobe embedded in Bioplastic; specimens were then scanned by a microscopic-computed tomography scanner and modified Feldkamp cone beam backprojection algorithm applied to generate three-dimensional images. Quantitative analysis of bile duct geometry was performed using a customized software program. The diameter of the bile duct segments of normal and ANIT-fed rats progressively decreased with increasing length of the biliary tree. Diameter of bile ducts from ANIT-fed rats (range, 21 to 264 microm) was similar to that of normal rats (22 to 279 microm). In contrast, the number of bile duct segments along the major branch reproducibly doubled, the length of the bile duct segments decreased twofold, and the length of the biliary tree remained unchanged after ANIT feeding. Moreover, the total volume of the biliary tree of ANIT-fed rats was significantly greater (855 microl) than in normal rats (47 microl). Compared with normal rats, the total surface area of the biliary tree increased 26 times after ANIT-induced bile duct proliferation. Taken together, these observations quantitate the anatomical remodeling after selective cholangiocyte proliferation and strongly suggest that the proliferative process involves sprouting of new side branches. Our results may be relevant to the mechanisms by which ducts proliferate in response to hepatic injury and to the hypercholeresis that occurs after experimentally induced bile duct proliferation.     

Modeling and measurement of the detector presampling MTF of a variable resolution x-ray CT scanner

The detector presampling modulation transfer function (MTF) of a 576-channel variable resolution x-ray (VRX) computed tomography (CT) scanner was evaluated in this study. The scanner employs a VRX detector, which provides increased spatial resolution by matching the scanner's field of view (FOV) to the size of an object being imaged. Because spatial resolution is the parameter the scanner promises to improve, the evaluation of this resolution is important. The scanner's pre-reconstruction spatial resolution, represented by the detector presampling MTF, was evaluated using both modeling (Monte Carlo simulation) and measurement (the moving slit method). The theoretical results show the increase in the cutoff frequency of the detector presampling MTF from 1.39 to 43.38 cycles/mm as the FOV of the VRX CT scanner decreases from 32 to 1 cm. The experimental results are in reasonable agreement with the theoretical data. Some discrepancies between the measured and the modeled detector presampling MTFs can be explained by the limitations of the model. At small FOVs (1-8 cm), the MTF measurements were limited by the size of the focal spot. The obtained results are important for further development of the VRX CT scanner.     

Improved quantitation for PET/CT image reconstruction with system modeling and anatomical priors

Accurate quantitation of positron emission tomography (PET) tracer uptake levels in tumors is important for staging and monitoring response to treatment. Quantitative accuracy in PET is particularly poor for small tumors because of system partial volume errors and smoothing operations. This work proposes a reconstruction algorithm to reduce the quantitative errors due to limited system resolution and due to necessary image noise reduction. We propose a method for finding and using the detection system response in the projection matrix of a statistical reconstruction algorithm. In addition, we use aligned anatomical information, available in PET/CT scanners, to govern the penalty term applied during each image update. These improvements are combined with Fourier rebinning in a clinically feasible algorithm for reconstructing fully three-dimensional PET data. Results from simulation and measured studies show improved quantitation of tumor values in terms of bias and variance across multiple tumor sizes and activity levels with the proposed method. At common clinical image noise levels for the detection task, the proposed method reduces the error in maximum tumor values by 11% compared to filtered back-projection and 5% compared to conventional iterative methods.     

Thermal depth profiling of vascular lesions: automated regularization of reconstruction algorithms

Pulsed photo-thermal radiometry (PPTR) is a non-invasive, non-contact diagnostic technique used to locate cutaneous chromophores such as melanin (epidermis) and hemoglobin (vascular structures). Clinical utility of PPTR is limited because it typically requires trained user intervention to regularize the inversion solution. Herein, the feasibility of automated regularization was studied. A second objective of this study was to depart from modeling port wine stain PWS, a vascular skin lesion frequently studied with PPTR, as strictly layered structures since this may influence conclusions regarding PPTR reconstruction quality. Average blood vessel depths, diameters and densities derived from histology of 30 PWS patients were used to generate 15 randomized lesion geometries for which we simulated PPTR signals. Reconstruction accuracy for subjective regularization was compared with that for automated regularization methods. The objective regularization approach performed better. However, the average difference was much smaller than the variation between the 15 simulated profiles. Reconstruction quality depended more on the actual profile to be reconstructed than on the reconstruction algorithm or regularization method. Similar, or better, accuracy reconstructions can be achieved with an automated regularization procedure which enhances prospects for user friendly implementation of PPTR to optimize laser therapy on an individual patient basis.     

正常犬肺动脉三维CT重建中不同剂量对比剂的比较

背景：行CT血管成像时,需要静脉注入碘对比剂,并且随着对比剂应用剂量的增大,对患者带来的危害也相应增大。 目的：验证低剂量对比剂在多层螺旋CT肺动脉成像中的可行性。 方法：12只健康家犬参照临床上人的碘海醇(300 mgI/mL)使用剂量,根据《药理实验中动物间和动物与人体间的等效剂量换算》得出相应犬的3个剂量组分别为碘海醇2.40 mL/kg,2.02 mL/kg,1.62 mL/kg组。12只犬分别接受3种剂量各1次,每次实验扫描间隔时间至少48 h,共进行36次CT扫描。根据原始图像、容积重现像和最大密度投影像,对3种方案肺动脉分支的显示情况、肺动脉边缘清晰程度及肺静脉充盈程度进行评分,并测量肺动脉内对比剂的浓度。 结果与结论：3种方案均能清晰显示犬肺动脉4级分支,血管边缘清晰,显示程度评分各组差异无显著性意义(P > 0.05)。3种方案肺静脉显影程度均较低,与肺动脉有很好的密度对比,各组差异无显著性意义(P > 0.05)。3种方案肺动脉内的对比剂浓度均维持在较高的水平,差异无显著性意义(P > 0.05)。提示低剂量对比剂在多层螺旋CT犬肺动脉成像中是可行的,图像质量可以满足临床诊断要求,从而为临床应用低剂量对比剂行肺动脉成像提供实验依据。     

用两种体模作CT性能检测的对比研究

本文介绍使用两种不同的标准体模(AAPM体模和RMI461A体模),对3台新安装的CT设备作性能检测,把两组实验数据进行双边对比研究.结果:大多数性能项目,包括高对比度分辨率、影像均匀性和噪声、层厚偏差和CT值线性等的测量数据有较好的一致性.发现低对比度分辨率的测量值存在明显差异,可能是体模(插件)长期受X线照射,化学效应引起材料CT值漂移及本底对比度升高所致,需要用对比度-细节反比关系校正.本文还就当前CT性能检测的若干技术问题,包括检测方法与评价标准的改进等进行探讨.     

Isotope computed tomography using cone-beam geometry: a comparison of two reconstruction algorithms

A CT scanner has been constructed specifically to determine the three-dimensional distribution of bone mineral in the medullary cavities of the radius, ulna and femur. A source of x-rays (153Gd) and a multiwire proportional counter (MWPC) are mounted at opposite ends of a diameter of an annular mounting. The limb is placed on the axis of rotation of the annulus and a series of two-dimensional transmission projections are obtained at equal angular spacings over 360 degrees. The distribution of bone mineral is reconstructed from the projections either by the method of maximum entropy (ME) or by convolution and back projection (CBP). These two methods have been evaluated by reconstructing a single slice of a phantom, representing the forearm, from projections simulated by computer. With a clinically acceptable exposure time, the mean medullary densities of the ulna and radius were determined with systematic errors of less than 3.5% (ME) and 11% (CBP), although for the latter method of reconstruction the systematic error was reduced to less than 2% by increasing the number of views. The mean medullary densities of the ulna and radius were determined with precisions better than 2.5% (ME) and 3.5% (CBP).     

肝脏三维重建技术较传统CT成像技术对肿瘤体积可提供更准确的术前评估

文题释义：肝后下腔静脉：下腔静脉是体内最大的静脉干,为下腔静脉系的主干,在第5腰椎平面,由左、右髂总静脉合成,沿腹主动脉右侧上升,经肝的后方,穿膈的腔静脉孔入胸腔,进入右心房,收集下肢、盆腔和腹腔的静脉血。当下腔静脉阻塞时,在腹壁的两侧、脐平面以下可见到曲张血管。肝钳切肝法：肝钳切肝法是利用特制器械——肝钳钳夹将要切除之肝组织,阻断其血供后进行切肝的手术方法。适用于肝部分切除或左外叶切除,有时亦可用于右半肝切除。具体操作：先将欲要切除的肝叶或半肝充分游离,按此肝组织大小选择适合的钳翼,将钳翼套到相应肝组织上,收紧钳翼,使肝局部血供完全阻断,离钳翼一定间距(2 cm左右)切开肝包膜,分离肝实质,结扎切面上的所有管道结构,然后把相应肝组织切除。此法具有简便、术中出血少、省时及相当安全等优点,但不能用于肝中叶切除。对于要切除的肝组织较厚者,止血效果不够确切。背景：在进行肝脏的精准治疗时,目前临床上常采取多排螺旋CT和高场强MRI对肝实质疾病、Child-Pugh分级、门静脉高压和ICG滞留率等参数分析,相对准确地评估剩余肝脏储备功能并确定个体患者肝切除的安全极限。目的：探讨肝脏三维重建技术在精准肝脏外科临床应用上的优势。方法：随机选取辽宁省肿瘤医院肝胆外科接受肝脏切除手术治疗的原发性肝癌患者100例,分为2组。对照组：二维CT检查,对肝脏肿瘤位置、切除范围以及残余肝量进行经验性评估,术中采用部分缓解Pringle法进行肝门阻断;试验组：手术前应用三维重建系统进行肝内、肝周管道以及肿瘤性状位置的立体成像,肝脏切除范围以及残余肝量进行量化评估,术中采用选择性肝门阻断方法。比较两组术后肝切除体积与术前影像评估的差异,并观察术后患者的恢复情况。研究方案的实施符合辽宁省肿瘤医院的相关伦理要求,参与者及其家属对治疗过程完全知情同意。结果与结论：①试验组术后切除肝肿瘤体积与术前计算比较无显著性意义;对照组有显著性意义(P < 0.05);对照组患者的住院时间和并发症的发生率明显高于试验组(P < 0.05);②术后1个月试验组患者的血清胰岛素样生长因子Ⅱ、人转化生长因子α、表皮细胞生长因子和甲胎蛋白水平较对照组均显著降低(P < 0.05);③与对照组相比,试验组谷丙转氨酶在术后第14天已经趋于正常,术后腹腔引流腹水计量两组逐渐减少,试验组明显低于对照组(P < 0.05);④术后1个月两组患者的KPS评分较术前均显著提高(P < 0.05),试验组明显高于对照组(P < 0.05);⑤对照组总有效率显著低于试验组(92%,100%,P < 0.05);⑥结果说明,与传统的CT成像技术比,肝脏三维重建技术可以在术前对肿瘤的体积提供更准确的术前评估,同时可以降低患者术中的手术风险、缩短患者的住院时间和降低术后并发症的发生率。ORCID: 0000-0002-4039-242X(李博)中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

基于CT数据肠系膜上动脉三维重建及解剖学研究

目的:研究肠系膜上动脉(SMA)CT数据三维重建方法及相关解削.方法:搜集140例患者64排螺旋CT腹部增强扫描数据,采用Mimics 10.01软件进行SMA三维重建,观察、测量3D模型中SMA的相关解剖学指标.结果:SMA 3D模型真实反映了其形态学结构,效果逼真,发现变异肝右动脉或肝总动脉来源于SMA者占9.3%(13例).SMA与腹主动脉的夹角为(62.3±18.6)°;在左肾静脉水平,SMA与腹主动脉的距离为(1.2±0.5)cm.结论:SMA 3D模型能很好显示其解剖学特征,术前可提供患者的个体化信息,将其运用于临床具有重要意义.