Spectral CT in the demonstration of the gastrocolic ligament: a comparison study

Purpose

To investigate the performance of spectral CT in the depiction of the gastrocolic ligament (GCL) compared to conventional polychromatic CT.

Methods

Gemstone spectral CT and conventionally polychromatic CT examinations were randomly allocated to be performed on 62 consecutive patients. A total of 11 groups of monochromatic images were generated on energy levels ranging from 40 to 140 keV at an interval of 10 keV. A five-score classification system was used to evaluate the performances of CT images in the demonstration of GCL. The inter-observer agreement between two radiologists in their evaluation of the GCL by each method was evaluated using kappa statistics.

Results

There were statistically significant differences between the spectral CT and polychromatic CT in their abilities to highlight the GCL (observer 1: χ² = 18.310, P < 0.001; observer 2: χ² = 19.780, P < 0.001). The distinct display (score ≥ 3) rates of the GCL by integrated monochromatic images were higher than that of polychromatic images (P < 0.001). The best energy level for displaying the GCL by spectral CT was 50–70 keV. The kappa value for the image scores on the integrated keV images between the two radiologists was higher than that for polychromatic CT images (P < 0.01).

Conclusions

Spectral CT can improve the visualisation of the GCL compared to polychromatic CT.     

基于深度学习的跨模态医学图像转换

运用深度学习的方法基于脑部CT扫描图像合成相应的MRI。将28例患者进行颅脑CT和MRI扫描得到的CT和MRI的断层图像进行刚性配准,随机选取20例患者的图像输入U-Net卷积神经网络进行训练,利用训练好的网络对未参与训练的8例患者的CT图像进行预测,得到合成的MRI。研究结果显示:通过对合成的MRI进行定量分析,利用基于L2损失函数构建的U-Net网络合成MRI效果良好,平均绝对平均误差（MAE）为47.81,平均结构相似性指数（SSIM）为0.91。本研究表明可以利用深度学习方法对CT图像进行转换,获得合成MRI,现阶段可以达到扩充MRI医学图像数据库的目的,随着合成图像精度的提高,可以用于帮助诊断等临床应用。     

Adaptive Voxel Matching for Temporal CT Subtraction

Temporal subtraction (TS) technique calculates a subtraction image between a pair of registered images acquired from the same patient at different times. Previous studies have shown that TS is effective for visualizing pathological changes over time; therefore, TS should be a useful tool for radiologists. However, artifacts caused by partial volume effects degrade the quality of thick-slice subtraction images, even with accurate image registration. Here, we propose a subtraction method for reducing artifacts in thick-slice images and discuss its implementation in high-speed processing. The proposed method is based on voxel matching, which reduces artifacts by considering gaps in discretized positions of two images in subtraction calculations. There are two different features between the proposed method and conventional voxel matching: (1) the size of a searching region to reduce artifacts is determined based on discretized position gaps between images and (2) the searching region is set on both images for symmetrical subtraction. The proposed method is implemented by adopting an accelerated subtraction calculation method that exploit the nature of liner interpolation for calculating the signal value at a point among discretized positions. We quantitatively evaluated the proposed method using synthetic data and qualitatively using clinical data interpreted by radiologists. The evaluation showed that the proposed method was superior to conventional methods. Moreover, the processing speed using the proposed method was almost unchanged from that of the conventional methods. The results indicate that the proposed method can improve the quality of subtraction images acquired from thick-slice images.     

基于循环一致性生成对抗网络的盆腔伪CT生成方法

目的:基于循环一致性生成对抗网络（CycleGAN）,利用非配对患者盆腔部位数据,实现MRI和CT图像之间的相互转换,并对基于该模型生成的盆腔伪CT（sCT）进行精度和剂量性能的评估。方法:该CycleGAN网络包含两个生成器和两个判别器。先基于全卷积网络（FCNs）构建两个生成器,一个将2D盆腔MRI转换为2D盆腔sCT图像,另一个将CT图像转换为伪MRI（sMRI）图像。再基于FCNs构建两个判别器,用于对真实图像和生成的伪图像进行判别,提升生成图像的质量。为保证sCT图像与MRI图像的一致性,引入归一化互信息作为相似性约束损失项,对模型进行改进。训练集包括35例患者盆腔部位的T1-MRI图像和另外36例患者盆腔部位的CT图像,测试集包括10例盆腔部位患者的MRI和CT图像,评估方法包括sCT与CT图像的误差和放疗剂量伽马通过率。结果:对于测试集中所有病例,生成的sCT与真实CT图像之间的平均绝对误差（MAE）为35.537（±4.537） HU;基于体素的平均剂量差异最大为0.49%;以3%/3 mm、2%/2 mm和1%/1 mm为标准的平均伽马通过率分别高于99%、98%和95%。结论:使用CycleGAN网络和非配对患者训练数据可以生成准确且符合临床剂量精度要求的盆腔部位sCT图像。     

Amide proton transfer MRI differentiates between progressive multifocal leukoencephalopathy and malignant brain tumors: a pilot study

Background and purpose

Synthetic MR imaging (SyMRI) allows the reconstruction of various contrast images, including double inversion recovery (DIR), from a single scan. This study aimed to investigate the advantages of SyMRI by comparing synthetic DIR images with synthetic T2-weighted fluid-attenuated inversion recovery (T2W-FLAIR) and conventional DIR images.

Materials and methods

We retrospectively reviewed the imaging data of 100 consecutive patients who underwent brain MRI between December 2018 and March 2019. Synthetic DIR, T2W-FLAIR, T1-weighted, and phase-sensitive inversion recovery (PSIR) images were generated from SyMRI data. For synthetic DIR, the two inversion times required to suppress white matter and cerebrospinal fluid (CSF) were manually determined by two radiologists. Quantitative analysis was performed by manually tracing the region of interest (ROI) at the sites of the lesion, white matter, and CSF. Synthetic DIR, synthetic T2W-FLAIR, and conventional DIR images were compared on the basis of using the gray matter-to-white matter, lesion-to-white matter, and lesion-to-CSF contrast-to-noise ratios.

Results

The two radiologists showed no differences in setting inversion time (TI) values, and their evaluations showed excellent interobserver agreement. The mean signal intensities obtained with synthetic DIR were significantly higher than those obtained with synthetic T2W-FLAIR and conventional DIR.

Conclusion

Synthetic DIR images showed a higher contrast than synthetic T2WFLAIR and conventional DIR images.

     

基于DenseCUT网络由头部锥形束CT图像生成合成CT图像

提出一种由头部锥形束CT(CBCT)图像生成合成CT(sCT)图像的无监督深度学习网络,并与循环生成对抗（CycleGAN）网络及对比非配对转换（CUT）网络进行比较。本研究共获取56例脑部肿瘤患者的计划CT(pCT)和CBCT数据（其中49例用于训练,7例用于测试）,分别使用CycleGAN网络、CUT网络以及本研究提出的密集对比非配对转换（DenseCUT）网络由CBCT图像生成sCT。DenseCUT网络有两点创新之处：将CUT网络与密集块网络结合;在损失函数中加入结构相似性。与pCT-CBCT相比,pCT-sCT(DenseCUT网络)的HU值平均绝对误差从34.38 HU降低到17.75 HU,峰值信噪比从26.19 dB提升到29.83 dB,结构相似性从0.78提升到0.87。本文方法可在不改变解剖结构的情况下从CBCT图像中生成高质量的sCT图像,同时降低图像伪影,使CBCT应用于剂量计算和自适应放疗计划成为可能。     

Determination of subjective similarity for pairs of masses and pairs of clustered microcalcifications on mammograms: comparison of similarity ranking scores and absolute similarity ratings

The presentation of images that are similar to that of an unknown lesion seen on a mammogram may be helpful for radiologists to correctly diagnose that lesion. For similar images to be useful, they must be quite similar from the radiologists' point of view. We have been trying to quantify the radiologists' impression of similarity for pairs of lesions and to establish a "gold standard" for development and evaluation of a computerized scheme for selecting such similar images. However, it is considered difficult to reliably and accurately determine similarity ratings, because they are subjective. In this study, we compared the subjective similarities obtained by two different methods, an absolute rating method and a 2-alternative forced-choice (2AFC) method, to demonstrate that reliable similarity ratings can be determined by the responses of a group of radiologists. The absolute similarity ratings were previously obtained for pairs of masses and pairs of microcalcifications from five and nine radiologists, respectively. In this study, similarity ranking scores for eight pairs of masses and eight pairs of microcalcifications were determined by use of the 2AFC method. In the first session, the eight pairs of masses and eight pairs of microcalcifications were grouped and compared separately for determining the similarity ranking scores. In the second session, another similarity ranking score was determined by use of mixed pairs, i.e., by comparison of the similarity of a mass pair with that of a calcification pair. Four pairs of masses and four pairs of microcalcifications were grouped together to create two sets of eight pairs. The average absolute similarity ratings and the average similarity ranking scores showed very good correlations in the first study (Pearson's correlation coefficients: 0.94 and 0.98 for masses and microcalcifications, respectively). Moreover, in the second study, the correlations between the absolute ratings and the ranking scores were also very high (0.92 and 0.96), which implies that the observers were able to compare the similarity of a mass pair with that of a calcification pair consistently. These results provide evidence that the concept of similarity for pairs of images is robust, even across different lesion types, and that radiologists are able to reliably determine subjective similarity for pairs of breast lesions.     

Dedicated phantom materials for spectral radiography and CT

As x-ray imaging technology moves from conventional radiography and computed tomography (CT) to spectral radiography and CT, dedicated phantom materials are needed for spectral imaging. The spectral phantom materials should accurately represent the energy-dependent mass-attenuation coefficients of different types of tissues. Although tissue-equivalent phantom materials were previously developed for CT and radiation therapy applications, these materials are suboptimal for spectral radiography and CT; they are not compatible with contrast agents, do not represent many of the tissue types and do not provide accurate values of attenuation characteristics of tissue. This work provides theoretical framework and a practical method for developing tissue-equivalent spectral phantom materials with a required set of parameters. The samples of the tissue-equivalent spectral phantom materials were developed, tested and characterized. The spectral phantom materials were mixed with iodine, gold and calcium contrast agents and evaluated. The materials were characterized by CT imaging and x-ray transmission experiments. The fabricated materials had nearly identical densities, mass attenuation coefficients, effective atomic numbers and electron densities as compared to corresponding tissue materials presented in the ICRU-44 report. The experimental results have shown good volume uniformity and inter-sample uniformity (repeatability of sample fabrication) of the fabricated materials. The spectral phantom materials were fabricated under laboratory conditions from readily available and inexpensive components. It was concluded that the presented theoretical framework and fabrication method of dedicated spectral phantom materials could be useful for researchers and developers working in the new area of spectral radiography and CT. Independently, the results could also be useful for other applications, such as radiation therapy.     

一种自动确定放疗原始等中心的新方法

目的:提出一种通过勾画标记点结构自动确定放疗原始等中心的方法（以下简称新方法）,通过与常规方法作比较分析测试新方法的应用价值。方法:选取40例接受放射治疗的腹部肿瘤患者的定位CT图像,其中标记点出现在1层、2层CT层面各20例。使用常规方法（通过Eclipse计划系统的十字定位工具手动确定原始等中心）,然后使用新方法（通过自动勾画标记点结构并进行位置计算自动确定放疗原始等中心）,分析两种方法确定的原始等中心之间坐标的差异。此外,还手动勾画了标记点结构。结果:与手动勾画标记点结构相比,自动勾画20例2层CT图像中标记点的Dice相似性指数（DSC）值为（0.79±0.06）,40例左右方向（x轴）偏差绝对值、腹背方向（y轴）偏差绝对值的均值分别为0.04、0.05 cm。标记点出现在2层CT图像的20例中,头脚方向（z轴）偏差绝对值的平均值、标准差、最大值、最小值分别为0.22、0.03、0.26、0.16 cm。结论:本文提出的新方法可以快速、精确地计算出放疗原始等中心坐标,特别是当标记点出现在2层CT图像时,可以有效弥补常规方法的缺陷。     

Robust feature-based registration using a Gaussian-weighted distance map and brain feature points for brain PET/CT images

Feature-based registration is an effective technique for clinical use, because it can greatly reduce computational costs. However, this technique, which estimates the transformation by using feature points extracted from two images may cause misalignments, particularly in brain PET and CT images that have low correspondence rates between features due to differences in image characteristics. To cope with this limitation, we propose a robust feature-based registration technique using a Gaussian-weighted distance map (GWDM) that finds the best alignment of feature points even when features of two images are mismatched. A GWDM is generated by propagating the value of the Gaussian-weighted mask from feature points of CT images and leads the feature points of PET images to be aligned on an optimal location even though there is a localization error between feature points extracted from PET and CT images. Feature points are extracted from two images by our automatic brain segmentation method. In our experiments, simulated and clinical data sets were used to compare our method with conventional methods such as normalized mutual information (NMI)-based registration and chamfer matching in accuracy, robustness, and computational time. Experimental results showed that our method aligned the images robustly even in cases where conventional methods failed to find optimal locations. In addition, the accuracy of our method was comparable to that of the NMI-based registration method.     

Automatic registration of the prostate for computed-tomography-guided radiotherapy

The recent development of integrated computed tomography (CT)/linear accelerator (LINAC) combinations, where the CT scanner and the LINAC use the same patient couch, and of kilovoltage cone-beam CT systems attached to the LINAC gantry, means that suitable hardware is now available for CT-guided localization of the prostate. Clinical implementation is, however, currently impeded by the lack of robust and accurate software tools to compare the position of the prostate in the CT images used for the treatment plan with its position in the daily CT images. Manual registration of the planning CT images with the daily CT images can be slow and can introduce significant inter-user variations. We have developed an automatic registration technique that is not adversely influenced by changes in prostate shape, size or orientation, presence of rectal gas, or bladder filling. The cost function used in the registration is the mean absolute difference in CT numbers voxel-by-voxel between the daily CT image and the planning CT image for a volume extracted from the planning CT images using the original physician-drawn gross tumor volume contours. To enhance soft tissue contrast in the prostate region and to reduce the impact of rectal gas calcifications and bone on the registration, voxels with CT numbers that represent gas or bone are filtered out from the calculation. The results of the automatic registration agreed with the mean results of seven human observers, with standard deviations of 0.5 mm, 0.5 mm, and 1.0 mm in the left/right (RL), anterior/posterior (AP), and superior/inferior (SI) directions, respectively, for a patient that was relatively easy to localize. Agreement (one standard deviation) for a patient that was difficult to localize was 0.6 mm, 1.4 mm, and 1.9 mm in the RL, AP, and SI directions, respectively. These results are better than the interuser uncertainties reported for a manual alignment technique and are close to the reported intrauser uncertainties. The results are independent of the shape of contours in the original treatment plan, reducing the impact of interobserver variations in contouring the prostate. The algorithm is fast and reliable, allowing the entire CT localization process to take place in 5-9 minutes. In 120 CT image sets from seven patients, the failure rate was found to be less than 1%. The use of this algorithm will facilitate the clinical implementation of CT-guided localization of the prostate.     

Imaging lobular breast carcinoma: comparison of synchrotron radiation DEI-CT technique with clinical CT, mammography and histology

Different modalities for imaging cancer-bearing breast tissue samples are described and compared. The images include clinical mammograms and computed tomography (CT) images, CT images with partly coherent synchrotron radiation (SR), and CT and radiography images taken with SR using the diffraction enhanced imaging (DEI) method. The images are evaluated by a radiologist and compared with histopathological examination of the samples. Two cases of lobular carcinoma are studied in detail. The indications of cancer are very weak or invisible in the conventional images, but the morphological changes due to invasion of cancer become pronounced in the images taken by the DEI method. The strands penetrating adipose tissue are seen clearly in the DEI-CT images, and the histopathology confirms that some strands contain the so-called 'Indian file' formations of cancer cells. The radiation dose is carefully measured for each of the imaging modalities. The mean glandular dose (MGD) for 50% glandular breast tissue is about 1 mGy in conventional mammography and less than 0.25 mGy in projection DEI, while in the clinical CT imaging the MGD is very high, about 45 mGy. The entrance dose of 95 mGy in DEI-CT imaging gives rise to an MGD of 40 mGy, but the dose may be reduced by an order of magnitude, because the contrast is very large in most images.     

Design of a high-speed,high-resolution teleradiology network

A teleradiology system acquires radiographic images from one location and transmits them to one or more distant sites where they are displayed and/or converted to hard-copy film recordings. The long-term goal of teleradiology research is to show that teleradiology systems can provide diagnostically equivalent results when compared with conventional radiographic film interpretation. If this hypothesis is proven, provision of the following radiology services will be improved: (1) providing for primary interpretation of radiological images for patients in underserved areas as well as in other medical facilities; (2) integration of radiological services for multihospital/clinic health care provider consortiums; (3) improving emergency service and intensive care unit coverage; (4) offering consulting-at-a-distance with subspecialty radiologists; and (5) providing radiologists in the community or in rural areas with immediate access to large academic centers for help in the interpretation of difficult and problematic cases. We are designing a high-speed, high-resolution teleradiology network that will communicate between our level 3 medical center and several outlying medical centers within the metropolitan area. Computed tomography (CT), magnetic resonance (MR), and screen-film examinations will be digitized to 2,000 x 2,000 or 4,000 x 4,000 pixels at the remote sites, transmitted to the central referral facility, and sent to a laser film printer, replicating the original film. This film may then be used for primary diagnosis, overreading/consultative purposes, or for emergency department preparation. Inherently digital modality data (eg, MR and CT) can be sent without digitization of the multiformat film if desired.     

A comparison of conventional screen-film radiography and hard copy of computed radiography in full and two-thirds sizes in detection of interstitial lung disease

This study examined whether hard-copy radiographs produced from computed radiography (CR) images show the subtle interstitial pulmonary disease equally well to conventional screen-film radiographs, because a digital radiography should be chosen for introduction of the digital picture archiving and communication system (PACS) for the new Osaka University Hospital.^1,2 Eleven radiologists examined 20 abnormal and 20 control chest radiographs presented in each of three groups: conventional screen-film radiographs and two sizes of hard-copy radiographs made from CR images. This study of digital image quality of chest examinations found that some findings on conventional screen-film radiography images are not reproduced by current CR (2,000×2,000×10 bits in matrix), especially when the experienced radiologists were observed. This finding suggested improvements are needed in CR before CR of chest should fully replace conventional screen-film radiography.     

Accelerating reconstruction of reference digital tomosynthesis using graphics hardware

The successful implementation of digital tomosynthesis (DTS) for on-board image guided radiation therapy (IGRT) requires fast DTS image reconstruction. Both target and reference DTS image sets are required to support an image registration application for IGRT. Target images are usually DTS image sets reconstructed from on-board projections, which can be accomplished quickly using the conventional filtered backprojection algorithm. Reference images are DTS image sets reconstructed from digitally reconstructed radiographs (DRRs) previously generated from conventional planning CT data. Generating a set of DRRs from planning CT is relatively slow using the conventional ray-casting algorithm. In order to facilitate DTS reconstruction within a clinically acceptable period of time, we implemented a high performance DRR reconstruction algorithm on a graphics processing unit of commercial PC graphics hardware. The performance of this new algorithm was evaluated and compared with that which is achieved using the conventional software-based ray-casting algorithm. DTS images were reconstructed from DRRs previously generated by both hardware and software algorithms. On average, the DRR reconstruction efficiency using the hardware method is improved by a factor of 67 over the software method. The image quality of the DRRs was comparable to those generated using the software-based ray-casting algorithm. Accelerated DRR reconstruction significantly reduces the overall time required to produce a set of reference DTS images from planning CT and makes this technique clinically practical for target localization for radiation therapy.     

Feature Selection and Performance Evaluation of Support Vector Machine (SVM)-Based Classifier for Differentiating Benign and Malignant Pulmonary Nodules by Computed Tomography

There are lots of work being done to develop computer-assisted diagnosis and detection (CAD) technologies and systems to improve the diagnostic quality for pulmonary nodules. Another way to improve accuracy of diagnosis on new images is to recall or find images with similar features from archived historical images which already have confirmed diagnostic results, and the content-based image retrieval (CBIR) technology has been proposed for this purpose. In this paper, we present a method to find and select texture features of solitary pulmonary nodules (SPNs) detected by computed tomography (CT) and evaluate the performance of support vector machine (SVM)-based classifiers in differentiating benign from malignant SPNs. Seventy-seven biopsy-confirmed CT cases of SPNs were included in this study. A total of 67 features were extracted by a feature extraction procedure, and around 25 features were finally selected after 300 genetic generations. We constructed the SVM-based classifier with the selected features and evaluated the performance of the classifier by comparing the classification results of the SVM-based classifier with six senior radiologists′ observations. The evaluation results not only showed that most of the selected features are characteristics frequently considered by radiologists and used in CAD analyses previously reported in classifying SPNs, but also indicated that some newly found features have important contribution in differentiating benign from malignant SPNs in SVM-based feature space. The results of this research can be used to build the highly efficient feature index of a CBIR system for CT images with pulmonary nodules.     

Investigation of an image artefact induced by projection noise inhomogeneity in multi-slice helical computed tomography

The introduction of multi-slice helical computed tomography has fundamentally changed the way radiologists view CT images. Increasing numbers of clinical cases are examined with advanced visualization tools, such as maximum intensity projection, multi-planar reformation and volume rendering. It has been discovered that new image artefacts, which do not appear in the traditional two-dimensional reconstructed images, become visible in images generated by these new tools. In this paper, we investigate the causes of one such artefact, the Venetian blind artefact, which appears as bright-and-dark bands superimposed on three-dimensional images. We demonstrate that such an artefact is caused by the periodical noise variation in the reconstructed images. The image noise variation is, in turn, caused by the interaction of the noise inhomogeneity in the projections with the helical weights. An analytical formula is developed that accurately predicts the presence of such artefacts. Based on our analysis, several approaches are proposed for the artefact reduction or elimination.     

High-resolution breast tomography at high energy: a feasibility study of phase contrast imaging on a whole breast

Previous studies on phase contrast imaging (PCI) mammography have demonstrated an enhancement of breast morphology and cancerous tissue visualization compared to conventional imaging. We show here the first results of the PCI analyser-based imaging (ABI) in computed tomography (CT) mode on whole and large (>12 cm) tumour-bearing breast tissues. We demonstrate in this work the capability of the technique of working at high x-ray energies and producing high-contrast images of large and complex specimens. One entire breast of an 80-year-old woman with invasive ductal cancer was imaged using ABI-CT with monochromatic 70 keV x-rays and an area detector of 92×92 μm2 pixel size. Sagittal slices were reconstructed from the acquired data, and compared to corresponding histological sections. Comparison with conventional absorption-based CT was also performed. Five blinded radiologists quantitatively evaluated the visual aspects of the ABI-CT images with respect to sharpness, soft tissue contrast, tissue boundaries and the discrimination of different structures/tissues. ABI-CT excellently depicted the entire 3D architecture of the breast volume by providing high-resolution and high-contrast images of the normal and cancerous breast tissues. These results are an important step in the evolution of PCI-CT towards its clinical implementation.     

Semiempirical analysis of materials' elemental composition to formulate tissue-equivalent materials: a preliminary study

Tissue-equivalent materials are used for simplifying quality control and quality assurance procedures, both in diagnostic and therapeutic radiology. Important information to formulate a tissue-equivalent material is elemental composition of its base materials. However, this information is not easily obtained. Therefore we propose a stoichiometric analysis method to investigate the elemental composition of the base materials that can potentially be used for manufacturing tissue-equivalent materials. In this technique, we combined the stoichiometric calibration and the basic data method to obtain the elemental composition of materials from measured computer tomography (CT) numbers. The elemental composition, with the maximum number of the elements of the material in question up to the available number of different tube voltages at the CT scanner, was analysed using the proposed approach. We tested eight different cylinders in this study. The estimated elemental compositions of unspecified materials in the cylinders were evaluated by comparing the calculated and the simulated CT numbers to the measured ones; the results showed good correlation with maximum absolute differences of 1.9 and 3.7 HU, respectively. The accuracy of the stoichiometric analysis method to estimate the elemental composition was influenced by the accuracy of the measured CT numbers. The method proposed allows for determining the elemental composition of the base materials which can then be applied further to formulate tissue-equivalent materials.     

双层探测器光谱CT虚拟平扫中重建层厚对肝细胞癌显示的影响

目的：探讨双层探测器光谱CT虚拟平扫（VNC）对肝细胞癌（HCC）显示的最佳层厚。方法：回顾性分析73例HCC患者腹部CT扫描的影像资料,分别获得5、3、1 mm不同层厚的常规平扫（TNC）、动脉期VNC(VNC-a)图像和门静脉期VNC(VNC-p)图像。比较3种不同层厚TNC、VNC-a和VNC-p图像的CT值、信噪比（SNR）、对比噪声比（CNR）和噪声（SD）。通过Bland-Altman plot散点图分析TNC图像和VNC图像的CT值一致性;采用5分法评价图像质量。结果：3种层厚VNC-a图像、VNC-p图像与TNC图像相比,SNR升高,SD降低,差异有统计学意义（P<0.05）,CT值和CNR的差异无统计学意义（P>0.05）;组内两两比较,5和3 mm层厚VNC-p图像比VNC-a图像SD更低,SNR更高（P<0.05）,1 mm图像VNC-p与VNC-a图像SD和SNR差异无统计学意义（P>0.05）。5和3 mm层厚VNC-a图像和VNC-p图像与TNC图像的CT值一致性良好,其中3 mm VNC-p图像LOA界限外的数据点比例最低（1.4%...