降低儿童X射线CT检查辐射剂量的研究进展

目的：归纳总结减少儿童X射线CT检查所致受检者辐射剂量的方法,为降低儿童接受X射线CT检查的辐射危害风险提供参考。方法：针对X射线CT检查所致儿童的辐射剂量,通过调研相关文献,基于各自研究的目的和原理,归纳总结降低儿童受照剂量的方法。结果：自动管电流调制技术能根据儿童受检者体型自行改变管电流,自动管电压选择技术能根据预先设定的影像质量水平并结合X射线在受检者的衰减自动选择管电压,这两种技术均能自动降低个体的受照剂量;先进的影像重建技术可减少低剂量扫描影像的噪声,间接起到降低个体和群体的受照剂量;非扫描区的合理屏蔽也能有效降低个体和群体的受照剂量;制定剂量参考水平有助于优化X射线CT检查扫描参数,起到降低群体受照剂量的作用。结论：可结合儿童受检者的体型、扫描部位以及X射线CT机的性能,综合运用自动管电流或管电压调制技术、影像重建技术以及屏蔽防护等多种方法,可最大限度地降低儿童X射线CT检查的受照剂量。     

低剂量CT检查在儿童中的应用

低剂量CT就是利用降低管电流的方法,来减少CT射线的剂量的方法,既能保证图像质量,又降低患者受辐射水平,对儿童检查中应用低剂量CT扫描具有重要意义。     

DR组织均衡技术在低剂量鼻骨侧位X射线摄影中的应用

目的探寻在鼻骨侧位X射线摄影中利用数字化X射线摄影(DR)组织均衡技术获取满足诊断需要的图像并降低患者辐射剂量的研究。方法利用人体模型进行常规的鼻骨侧位摄影,然后固定千伏值,在原有的mAs值上分别降低0.4、0.8、1.2 mAs进行摄片,再将降低剂量的图像采用DR组织均衡技术进行处理,比较不同图像对于满足诊断的需要和患者所接受的辐射剂量。结果常规摄影技术得到的图像需反复调节不同的窗宽、窗位才能显示密度、厚度不同的鼻骨与软组织;降低0.4、0.8 mAs,虽然图像的空间分辨率降低,但是采用DR组织均衡技术可在同一幅图像上清晰显示鼻骨与邻近软组织结构,同时降低患者的辐射剂量;降低1.2 mAs,不但图像的空间分辨率降低,而且无法采用DR组织均衡技术使图像达到满足诊断需要。结论采用DR组织均衡技术不仅能将密度、厚度不同的鼻骨及邻近软组织在同一副图像上清晰显示,而且能够有效降低患者的辐射剂量。     

Principal analysis on radiation dosimetry of CT-SD16 detector and its parameter setting

目的 介绍了一种用半导体电离室测量多排CT辐射剂量的原理和方法,为完善我国现有医疗CT检测规范提供技术信息.方法 通过介绍X射线辐射剂量计Barracuda的测量原理和多排CT辐射剂量测量的参数设置依据,并结合在Philip Brilliance iCT 256机器上的应用实例,阐述了用半导体电离室的探测器测量多排CT辐射剂量的关键技术.结果 基于CT扫描参数合理设置探测器参数后,多排CT辐射剂量空间分布情况得以较好展示.100 mm长杆空气电离室的测量范围远小于多排CT线束覆盖范围,需要对多排CT辐射剂量测量方法和技术进行更新.结论 新型探测器有利于揭示多排CT辐射剂量的特性规律.     

一种基于全局字典学习的小动物低剂量计算机断层扫描降噪方法

在小动物计算机断层扫描(CT)实验中,因需考虑小动物存活率以及实验的连续性等问题,一般较少采用高剂量的X射线进行实验;而低剂量的X射线会导致重建图像被噪声污染,影响图像质量,不利于后续实验分析。为解决此问题,本文介绍了一种基于全局字典学习的降噪方法,并将其应用于提升低剂量小动物CT重建图像质量的研究中。针对真实的小动物CT重建数据,选择高剂量的小动物CT重建图像作为训练样本,利用逐列更新的字典学习算法(K-SVD),构建包含图像信息的全局字典;利用正交匹配追踪算法(OMP)将低剂量重建图像利用全局字典进行稀疏分解,分离噪声,最后将重建图像复原,达到降噪、提升图像质量、降低小动物CT实验的拍摄剂量、提高小动物存活率的目的。实验结果表明,本文提出的方法能够有效减少低剂量动物CT图像的噪声,并能够较好地保留图像细节。     

CT-SD16探测器辐射剂量测量原理和参数设定

目的 介绍了一种用半导体电离室测量多排CT辐射剂量的原理和方法,为完善我国现有医疗CT检测规范提供技术信息.方法 通过介绍X射线辐射剂量计Barracuda的测量原理和多排CT辐射剂量测量的参数设置依据,并结合在Philip Brilliance iCT 256机器上的应用实例,阐述了用半导体电离室的探测器测量多排CT辐射剂量的关键技术.结果 基于CT扫描参数合理设置探测器参数后,多排CT辐射剂量空间分布情况得以较好展示.100 mm长杆空气电离室的测量范围远小于多排CT线束覆盖范围,需要对多排CT辐射剂量测量方法和技术进行更新.结论 新型探测器有利于揭示多排CT辐射剂量的特性规律.     

光耦功率放大技术在CT超低剂量扫描的研究

目的将全新的光电耦合高电压强电流放大处理技术用于CT机的前置放大处理中,隔离噪声和高电压大电流放大图像信号,实现超低剂量扫描,高清晰成像。方法将光电耦合放大器制作成射线剂量仪,并用CT机等超低剂量120KV、3-6mA…对其曝光,并与标准射线剂量仪校准,使其输出值不仅为射线剂量值,更能显示为高电压和大电流的优质图像信噪比。结果超小电流扫描经探测和光耦放大后最大值为87.5V和0.96A,而噪声电压为0.13μV、电流仅为0.02μA,给超低剂量扫描和传输处理时的功耗及高电压的宽动态范围显示留了很大空间。结论 CT超低剂量扫描时光耦放大器可在源头彻底隔离各种噪声并超高倍放大、高电压大电流输出图像信号,可保证高清晰高分辨率成像。     

医用诊断X射线源的研究进展

通过研究医用诊断X线机射线源、CT设备X射线源、特殊X射线源等比较X射线产生的物理原理和应用,探索基于韧致辐射的X射线源技术的局限性,提出X线机球管的未来发展方向。X射线的最大应用领域是在医学诊断中基于医学图像引导的诊断和治疗。通过研究其他等效X射线源如液态金属喷射轫致辐射源等,拓宽了X射线的应用领域。展望了X射线球管的关键特性和材料在医学诊断技术发展的前景。     

体质量指数指导Z轴自动管电流调制技术在胸部CT扫描中应用价值

目的评价体质量指数（BMI）指导下降低Z轴自动管电流调制技术最大毫安值在胸部CT扫描中的图像质量和辐射剂量,降低辐射剂量应用价值。方法连续选取100例BMI正常同时胸部CT定位像扫描显示无明显异常的受检者,随机分2组,每组50例。低剂量组,男性30例,女性20例,年龄18～75岁,中位年龄为39.74岁;对照组,男性30例,女性20例,年龄18～75岁,中位年龄为41.8岁。2组均使用Z轴自动管电流调制技术,Z轴自动管电流设置范围低剂量组30～200mA,对照组30～350mA。记录CT扫描后机显示容积CT剂量指数（CTDIvol）和剂量长度乘积（DLP）,计算有效剂量（ED）。取每例患者肺尖部、主动弓部、肺底部3幅图像,共计300幅。由2名副主任医师采用5分制双盲法评判,测量相应部位的噪声。所有数据记录录入Excel,分析采用SPSS13.0。结果低剂量组和对照组的图像质量主观评判均符合临床诊断要求。低剂量组的图像噪声肺尖部为12.27±2.64,主动弓部为10.83±2.03,肺底部为13.67±2.98。对照组图像噪声肺尖部10.96±2.42,主动脉弓部为9.71±2.72,肺底部为11.17±2.06。低剂量组噪声值高于对照组,两组比较,差异有统计学意义（P〈0.05）。低剂量组平均CTDIvol、ED分别为（5.89±1.63）mGy、（3.26±0.92）mSv,对照组平均CTDIvol、ED分别为（8.07±2.13）mGy、（4.47±1.20）mSv。结论BMI指导下降低Z轴自动管电流调制技术最大毫安值在胸部CT扫描中既能保证图像满足诊断要求,又大幅降低了受检者辐射剂量。     

肝脏低剂量计算机断层灌注的研究进展

肝脏计算机断层(CT)灌注成像是一种定量的无创性检测肝脏功能的影像学检查技术,主要用于肝脏肿瘤的诊断、鉴别诊断以及肝脏慢性疾病状态下的肝脏功能评价。过去,肝脏CT灌注由于辐射剂量高而限制了其在临床的应用。近年来,低剂量CT技术的开发和应用已经可以在保证图像质量的前提下大辐度降低患者的辐射剂量。本文将从X射线源、重建算法以及设备改进及扫描参数优化三个方面介绍低剂量CT灌注的研究进展。目前肝脏低剂量CT灌注的研究较少,仍有许多问题需要解决,但其在临床的应用前景将十分令人期许。     

Prior image constrained compressed sensing (PICCS): a method to accurately reconstruct dynamic CT images from highly undersampled projection data sets

When the number of projections does not satisfy the Shannon/Nyquist sampling requirement, streaking artifacts are inevitable in x-ray computed tomography (CT) images reconstructed using filtered backprojection algorithms. In this letter, the spatial-temporal correlations in dynamic CT imaging have been exploited to sparsify dynamic CT image sequences and the newly proposed compressed sensing (CS) reconstruction method is applied to reconstruct the target image sequences. A prior image reconstructed from the union of interleaved dynamical data sets is utilized to constrain the CS image reconstruction for the individual time frames. This method is referred to as prior image constrained compressed sensing (PICCS). In vivo experimental animal studies were conducted to validate the PICCS algorithm, and the results indicate that PICCS enables accurate reconstruction of dynamic CT images using about 20 view angles, which corresponds to an under-sampling factor of 32. This undersampling factor implies a potential radiation dose reduction by a factor of 32 in myocardial CT perfusion imaging.     

Ultra-low dose CT attenuation correction for PET/CT

A challenge for positron emission tomography/computed tomography (PET/CT) quantitation is patient respiratory motion, which can cause an underestimation of lesion activity uptake and an overestimation of lesion volume. Several respiratory motion correction methods benefit from longer duration CT scans that are phase matched with PET scans. However, even with the currently available, lowest dose CT techniques, extended duration cine CT scans impart a substantially high radiation dose. This study evaluates methods designed to reduce CT radiation dose in PET/CT scanning. We investigated selected combinations of dose reduced acquisition and noise suppression methods that take advantage of the reduced requirement of CT for PET attenuation correction (AC). These include reducing CT tube current, optimizing CT tube voltage, adding filtration, CT sinogram smoothing and clipping. We explored the impact of these methods on PET quantitation via simulations on different digital phantoms. CT tube current can be reduced much lower for AC than that in low dose CT protocols. Spectra that are higher energy and narrower are generally more dose efficient with respect to PET image quality. Sinogram smoothing could be used to compensate for the increased noise and artifacts at radiation dose reduced CT images, which allows for a further reduction of CT dose with no penalty for PET image quantitation. When CT is not used for diagnostic and anatomical localization purposes, we showed that ultra-low dose CT for PET/CT is feasible. The significant dose reduction strategies proposed here could enable respiratory motion compensation methods that require extended duration CT scans and reduce radiation exposure in general for all PET/CT imaging.     

基于参考图像的压缩感知磁共振扩散张量成像

基于参考图像的压缩感知磁共振扩散张量成像方法,利用相邻方向的扩散加权图像差异较小的特点,采用压缩感知理论实现快速扩散张量成像,回顾性选取扩散张量图像数据进行实验研究,在采样率为50%的均匀分布辐射线欠采样方式下进行基于参考图像的压缩感知扩散张量图像重建,结果表明重建后的扩散加权图的平均结构相似性（MSSIM）和峰值信噪比（PSNR）分别为0.904±0.044、（37.92±3.89） dB,各向异性分数图的MSSIM和PSNR分别为0.992、41.64 dB。因此,该方法在保证重建图像质量的前提下,可显著缩短数据采集时间,减少由于时间过长引起的图像伪影等问题。     

Improved compressed sensing-based cone-beam CT reconstruction using adaptive prior image constraints

Volumetric cone-beam CT (CBCT) images are acquired repeatedly during a course of radiation therapy and a natural question to ask is whether CBCT images obtained earlier in the process can be utilized as prior knowledge to reduce patient imaging dose in subsequent scans. The purpose of this work is to develop an adaptive prior image constrained compressed sensing (APICCS) method to solve this problem. Reconstructed images using full projections are taken on the first day of radiation therapy treatment and are used as prior images. The subsequent scans are acquired using a protocol of sparse projections. In the proposed APICCS algorithm, the prior images are utilized as an initial guess and are incorporated into the objective function in the compressed sensing (CS)-based iterative reconstruction process. Furthermore, the prior information is employed to detect any possible mismatched regions between the prior and current images for improved reconstruction. For this purpose, the prior images and the reconstructed images are classified into three anatomical regions: air, soft tissue and bone. Mismatched regions are identified by local differences of the corresponding groups in the two classified sets of images. A distance transformation is then introduced to convert the information into an adaptive voxel-dependent relaxation map. In constructing the relaxation map, the matched regions (unchanged anatomy) between the prior and current images are assigned with smaller weight values, which are translated into less influence on the CS iterative reconstruction process. On the other hand, the mismatched regions (changed anatomy) are associated with larger values and the regions are updated more by the new projection data, thus avoiding any possible adverse effects of prior images. The APICCS approach was systematically assessed by using patient data acquired under standard and low-dose protocols for qualitative and quantitative comparisons. The APICCS method provides an effective way for us to enhance the image quality at the matched regions between the prior and current images compared to the existing PICCS algorithm. Compared to the current CBCT imaging protocols, the APICCS algorithm allows an imaging dose reduction of 10-40 times due to the greatly reduced number of projections and lower x-ray tube current level coming from the low-dose protocol.     

Statistical image reconstruction from limited projection data with intensity priors

The radiation dose generated from x-ray computed tomography (CT) scans and its responsibility for increasing the risk of malignancy became a major concern in the medical imaging community. Accordingly, investigating possible approaches for image reconstruction from low-dose imaging protocols, which minimize the patient radiation exposure without affecting image quality, has become an issue of interest. Statistical reconstruction (SR) methods are known to achieve a superior image quality compared with conventional analytical methods. Effective physical noise modeling and possibilities of incorporating priors in the image reconstruction problem are the main advantages of the SR methods. Nevertheless, the high computation cost limits its wide use in clinical scanners. This paper presents a framework for SR in x-ray CT when the angular sampling rate of the projection data is low. The proposed framework is based on the fact that, in many CT imaging applications, some physical and anatomical structures and the corresponding attenuation information of the scanned object can be a priori known. Therefore, the x-ray attenuation distribution in some regions of the object can be expected prior to the reconstruction. Under this assumption, the proposed method is developed by incorporating this prior information into the image reconstruction objective function to suppress streak artifacts. We limit the prior information to only a set of intensity values that represent the average intensity of the normal and expected homogeneous regions within the scanned object. This prior information can be easily computed in several x-ray CT applications. Considering the theory of compressed sensing, the objective function is formulated using the ?(1) norm distance between the reconstructed image and the available intensity priors. Experimental comparative studies applied to simulated data and real data are used to evaluate the proposed method. The comparison indicates a significant improvement in image quality when the proposed method is used.     

小剂量造影剂联合不同电压对CT肺动脉造影图像质量的影响

目的:观察小剂量造影剂联合不同电压对CT肺动脉造影（CTPA）图像质量的影响。方法:选取2016年1月至2018年5月在滦州市人民医院就诊高度怀疑为肺动脉栓塞患者90例,拟行CTPA明确诊断,以随机数字表法分为A、B、C组,造影剂、电压不同。A组电压为120 kV,造影剂剂量为50 mL;B组电压为100 kV,造影剂剂量为50 mL;C组电压为80 kV,造影剂剂量为30 mL。3组均基于自动管电流调制技术设置管电流,其他参数一致。对比各组图像质量及辐射剂量。结果:B、C组肺动脉主干、左右肺动脉、肺段动脉CT值均明显高于A组,信噪比与对比噪声比均明显低于A组（P<0.05）。3组患者的图像质量主观评分均能达到3~6分,且评分未见统计学差异（P>0.05）。B、C组扫描后实际容积CT剂量指数、扫描长度与剂量长度之积及有效剂量明显低于A组（P<0.05）。结论:与传统扫描条件比较,小剂量造影剂联合低管电压（80 kV）扫描条件下行CTPA检查可在明显降低造影剂剂量的同时保证图像质量,有效减少辐射剂量。     

The Analysis of Effective Radiation Dose during PET/CT Examination

Objective: In order to reduce the effective dose level of the patients to explore the best scanning conditions, various factors affecting the level of PET/CT examination were analyzed. Methods: The effective doses of CT and pet were calculated respectively during PET/CT examination, Scanning parameters of CT and PET were optimized to reduce the effective dose of patients to a minimum while maintaining the image quality. Results: The tube voltage and tube current of CT, the injection dose during PET examination can affect the effective dose of the patients significantly. Conclusion: According to different types of patients and diseases to develop personalized scanning program, the effective dose level of the patients can be significantly reduced.     

Generalized multi-dimensional adaptive filtering for conventional and spiral single-slice, multi-slice, and cone-beam CT

In modern computed tomography (CT) there is a strong desire to reduce patient dose and/or to improve image quality by increasing spatial resolution and decreasing image noise. These are conflicting demands since increasing resolution at a constant noise level or decreasing noise at a constant resolution level implies a higher demand on x-ray power and an increase of patient dose. X-ray tube power is limited due to technical reasons. We therefore developed a generalized multi-dimensional adaptive filtering approach that applies nonlinear filters in up to three dimensions in the raw data domain. This new method differs from approaches in the literature since our nonlinear filters are applied not only in the detector row direction but also in the view and in the z-direction. This true three-dimensional filtering improves the quantum statistics of a measured projection value proportional to the third power of the filter size. Resolution tradeoffs are shared among these three dimensions and thus are considerably smaller as compared to one-dimensional smoothing approaches. Patient data of spiral and sequential single- and multi-slice CT scans as well as simulated spiral cone-beam data were processed to evaluate these new approaches. Image quality was assessed by evaluation of difference images, by measuring the image noise and the noise reduction, and by calculating the image resolution using point spread functions. The use of generalized adaptive filters helps to reduce image noise or, alternatively, patient dose. Image noise structures, typically along the direction of the highest attenuation, are effectively reduced. Noise reduction values of typically 30%-60% can be achieved in noncylindrical body regions like the shoulder. The loss in image resolution remains below 5% for all cases. In addition, the new method has a great potential to reduce metal artifacts, e.g., in the hip region.