Dosisoptimierung in der thorakalen Computertomographie

Radiation exposure in computed tomography (CT) by far exceeds radiation dose in chest radiography. Dose requirements in CT of the chest, however, are much smaller than for the abdomen because of low x-ray absorption in the lungs. This article describes scanner parameters that influence patient exposure and image quality. Suitable compromises will be explained that allow for dose reduction in chest CT without jeopardising image quality. Dose reduction in chest CT should be performed depending on the clinical indication and requires active reduction of mAs settings. For helical CT, a pitch of 1.5 to 2 should be employed. Dedicated low-dose techniques for screening of bronchogenic carcinoma are described. Dose reduction decreases image quality but the detrimental effects can be reduced by applying proper parameters for scanning and image reconstruction. Thus, images of the mediastinum should be reconstructed with a smoothing filter, while a higher resolution filter should be used for the lungs. In multislice CT, reconstruction of thicker axial or multiplanar sections retains spatial resolution but keeps image noise and thus dose requirements low. The effective, weighted CT dose index (CTDIw,eff) can serve as a rough estimate of the effective patient dose (E) in helical or multislice CT of the whole chest: for most scanners and age groups the conversion factors are 0.5 mSv/mGy for females and 0.4 mSv/mGy for males.     

Quality control and diagnostic reference levels in intraoral dental radiographic facilities

OBJECTIVES: A quality control program in intraoral radiographic equipment was conducted aiming to verify compliance with the latest legal requirements and to measure radiation dose in order to contribute to the establishment of appropriate diagnostic reference levels. METHODS: This study was performed in 191 intraoral radiographic facilities in Northern Greece. The quality control program included visual inspection of the unit, registration of its characteristics, measurement and calculation of several radiological parameters, including entrance surface dose, and overall compliance with legislation requirements. RESULTS: Most units (61.8%) were found to perform within their corresponding specifications. Exposure timer accuracy was the parameter that the dental units showed the poorest performance. Inadequate beam filtration was found in almost half of the older 50 kVp units. Entrance surface dose showed significant discrepancies, varying from 0.30 mGy to 16.09 mGy with a third quartile value of 3.37 mGy. CONCLUSIONS: A diagnostic reference level of 3.5 mGy is considered to be a realistic value for all intraoral equipment currently operating in Greece. However, for newly installed units, a value of 2.8 mGy is considered to be more appropriate.     

Leksell Icon型伽玛刀锥形束CT的常规质量控制与评价

目的分析Leksell Icon型伽玛刀锥形束CT的常规质量控制结果,评估其长期稳定性。方法使用QA TOOL plus验证锥形束CT精度;扫描Catphan 503模体,分析图像空间分辨率、对比度-噪声比和均匀性。结果锥形束CT图像体积的最大偏差为0.09~0.17 mm,均通过精度测试;预设的CT剂量指数2.5和6.3 mGy扫描模式下,空间分辨率很稳定,分别为7和8 lp/cm;对比度-噪声比和均匀性均符合参考要求。结论12个月的Leksell Icon型伽玛刀锥形束CT的常规质量控制比较稳定。锥形束CT的质量控制除了参考厂商的调试基线值外,针对伽玛刀统一的分析评价标准有待进一步完善。     

Radimetrics系统在CT辐射剂量评估上的初步应用

目的通过Radimetrics系统对CT辐射剂量的数据分析,评估扫描方案能否达到辐射防护的要求。 方法把Toshiba Aquilion 64排和Siemens Emotion 16排CT的3980例患者数据自动传输到Radimetrics工作站,并生成患者靶组织及敏感组织辐射剂量报表,采用SPSS17.0统计学软件统计出头颅、胸部、腹部、盆腔CT检查的辐射剂量分布情况并行t检验。 结果（1）头颅、胸部、腹部、盆腔CT平扫的辐射剂量的中位值分别为2.31、4.82、3.65、4.48 mSv;增强扫描的辐射剂量的中位值分别为4.58、9.58、10.51、8.71 mSv。（2）多数患者辐射剂量在ICRP103报告书范围内,仅有80例超出范围;（3）与扫描部位越邻近的组织,受到的辐射剂量越大;（4）动脉期、静脉期的辐射剂量低于平扫;（5）64排CT辐射剂量小于16排CT。 结论Radimetrics系统可通过对CT辐射剂量分析来有效评估扫描方案的合理性。     

Imaging Quality Control in the Era of Artificial Intelligence

The advent of artificial intelligence (AI) promises to have a transformational impact on quality in medicine, including in radiology. However, experience has shown that quality tools alone are often not sufficient to bring about consistent excellent performance. Specifically, rather than assuming outcome targets are consistently met, in quality control, managers assume that wide variation is likely present unless proven otherwise with objective performance data. In this article, we discuss what we consider to be the eight essential elements required to achieve comprehensive process control, necessary to deliver consistent quality in radiology: a process control framework, performance measures, performance standards and targets, monitoring applications, prediction models, optimization models, feedback mechanisms, and accountability mechanisms. We consider these elements to be universally applicable, including in the application of AI-based models. We also discuss how the lack of specific elements of a quality control program can hinder widespread quality control efforts. We illustrate the concept using the example of a CT radiation dose optimization and process control program previously developed by one of the authors and provide several examples of how AI-based tools might be used for quality control in radiology.     

Pulmonary embolism: radiation dose with multi-detector row CT and digital angiography for diagnosis

PURPOSE: To compare radiation dose delivered at four- and 16-detector row computed tomography (CT) with a dose-modulation program and that delivered at digital angiography for evaluation of pulmonary embolism (PE). MATERIALS AND METHODS: The part of the study involving patients (seven women, four men; mean age, 62 years +/- 16 [standard deviation]; range, 41-85 years) was approved by the institutional review board. Patients gave written informed consent. Exposure was performed with an anthropomorphic phantom with thermoluminescent dosimeters for four-detector row CT without the dose-modulation program and 16-detector row CT without and with the dose-modulation program with standard protocols for pulmonary CT angiography (120 kV, 144 mAs, four and 16 detector rows with 1.00- and 0.75-mm section thickness, respectively). Digital angiograms were acquired with four standard projections at 80 kV. For digital angiography, radiation dose was calculated according to phantom measurements and adapted to acquisition and fluoroscopy times. Distribution of dose was compared for CT and digital angiography. RESULTS: During pulmonary CT angiography, mean radiation dose delivered at middle of chest was 21.5, 19.5, and 18.2 mGy for four-detector row CT and for 16-detector row CT without and with dose-modulation program, respectively. At the same level, a mean dose of 91 mGy was delivered with digital angiography. The dose adjusted to clinical conditions was 139.0 mGy for digital angiography and could be reduced after technical adjustment. Ratios of maximum dose to mean dose were 1.15 and 2.96 for CT and digital angiography, respectively. With application of the dose-modulation program at 16-detector row CT, radiation dose was reduced 15%-20% at the upper chest. CONCLUSION: Multi-detector row CT delivers a lower radiation dose, with better spatial distribution of dose, than does pulmonary CT angiography. With 16-detector row CT and a dose-modulation program, radiation dose is decreased during PE work-up.     

低剂量螺旋CT在肺结核诊断中的可行性研究

目的 探讨低剂量螺旋CT在肺结核诊断中的应用价值.方法对150例肺结核患者进行双排螺旋CT机扫描,其扫描参数为常规剂量(150 mA)及2种低剂量(15 mA,30 mA).除管电流不同外,在管电压、扫描周期、螺距及层厚方面CT扫描参数完全一致.扫描范围从肺尖至肺底,逐一记录各剂量CT扫描的影像学表现及图像质量,并将2个低剂量组与常规剂量组进行统计学比较分析.结果在肺结核的CT影像学显示率方面,低剂量30 mA的CT扫描可清晰地显示各种结核病灶,并且与常规剂量相比两者并未显示出统计学的差异(P＞0.05).但当管电流进一步降低至15 mA时,活动性和静止期肺结核的确诊率显著降低,与常规剂量和30 mA相比有统计学差异(P＜0.05).结论低剂量CT(30 mA)完全可以替代常规剂量CT 进行肺结核的诊断.     

泌尿系结石螺旋CT低辐射量扫描的临床应用

目的:探讨螺旋CT低剂量扫描在泌尿系结石诊断中的临床应用价值。方法:对75例临床怀疑泌尿系结石患者根据就诊顺序分为3组:标准剂量组、低剂量组1和低剂量组2,标准剂量组采用120kV,180mA,螺距0.938进行扫描;低剂量组1和低剂量组2分别采用管电流120mA、80mA进行扫描,其它扫描条件与标准剂量组相同。记录每次扫描的放射容积CT剂量指数(CTDIvol)、剂量长度乘积(DLP)和有效剂量(ED)。由两位具有10年以上CT工作经验的医师进行影像诊断和图像质量评估,计算标准剂量和低剂量CT检查诊断泌尿系结石的敏感度、诊断符合率和阳性预测值。对所有图像进行主观质量评分,并测量其客观噪声值。结果:两个低剂量组与标准剂量组比较,CT剂量指数分别减少29.7%和55.5%,低剂量组1、2对泌尿系结石诊断的敏感度均为93.8%,诊断符合率分别为96.0%和95.5%,阳性预测值分别88.2%和100%,与标准剂量组比较差异均无统计学意义。图像质量方面,尽管剂量降低后图像噪声有所增加,但所有图像质量仍符合诊断要求。结论:低剂量螺旋CT扫描能满足泌尿系结石的诊断要求,大大降低了受检者的辐射剂量。     

ASiR算法结合自动管电流调制技术在胸部低剂量CT中的应用研究

目的:研究自适应性统计迭代重建(ASiR)算法结合自动管电流调制技术在MSCT( GE Discovery CTHD 750HD)胸部扫描中的应用,探讨胸部低剂量扫描的可行性.方法:将100名拟行宝石CT胸部平扫的患者随机分为A、B两组,每组50名.使用自动管电流调制技术扫描,A组预设噪声指数(NI)为15HU,B组预设NI为25HU,并采用不同权重的ASiR进行图像重建.记录两组患者CT容积剂量指数(CTDIvol)、剂量长度乘积(DLP)并计算有效剂量(ED).三位放射科医师采用盲法对图像质量进行评估(5分制).结果:A组CTDIvo1为4.22 mGy,ED为2.51mSv,B组CTDIvol为1.51mGy,ED为0.89mSv,分别比A组降低了64.22％和64.54％.A、B两组的图像质量均能满足临床诊断要求.结论:使用ASiR重建算法结合自动管电流调制技术进行宝石CT胸部扫描,可以大幅降低辐射剂量,同时保证图像质量.     

CT机应用质量检测要点与分析

目的　根据甘肃省 68台CT机性能检测结果 ,分析检测与评审规范中的要点。方法　使用性能检测模型、剂量模型、剂量仪 ,按照卫生部规范对CT性能指标逐项检测分析。结果　通过检测提高了CT机应用质量 ,91.2 %的合格率说明甘肃省CT应用质量现状良好。结论　指出了提高CT应用质量的途径是加强质量控制 ,健全制度 ,培训人员 ,履行验收检测程序     

Computed tomography dose optimisation in cystic fibrosis:A review

Cystic fibrosis(CF)is the most common autosomal recessive disease of the Caucasian population worldwide,with respiratory disease remaining the most relevant source of morbidity and mortality.Computed tomography(CT)is frequently used for monitoring disease complications and progression.Over the last fifteen years there has been a six-fold increase in the use of CT,which has lead to a growing concern in relation to cumulative radiation exposure.The challenge to the medical profession is to identify dose reduction strategies that meet acceptable image quality,but fulfil the requirements of a diagnostic quality CT.Dose-optimisation,particularly in CT,is essential as it reduces the chances of patients receiving cumulative radiation doses in excess of 100 m Sv,a dose deemed significant by the United Nations Scientific Committee on the Effects of Atomic Radiation.This review article explores the current trends in imaging in CF with particular emphasis on new developments in dose optimisation.     

PET/CT中CT仿真人体模型的图像质量与辐射剂量关系的研究

目的 以仿真人体模型为实验对象,研究PET/CT中CT图像质量与辐射剂量的关系,为保证图像质量同时降低受检者的辐射剂量提供数据依据。方法 用美国GE Discovery ST型 PET/CT,对仿真人体模型（Model RS-550）进行扫描。CT采集条件：管电压120 kV,管电流30~250 mA范围内11种固定值及自动管电流,螺距（pitch）分别为0.938、1.375、1.75,模拟临床PET/CT的全身扫描方式对仿真人体模型进行扫描。对图像进行分析,计算腹部主要器官的噪声、信噪比及质量因数。结果 噪声随有效剂量的增加而降低,有效剂量<15 mSv时,噪声变化幅度较大;>15 mSv时,噪声变化缓慢。信噪比、对比信噪比随有效剂量增加而增加。相同的有效剂量时,质量因数与扫描方案相关。自动管电流模式下的所有指标,均优于固定管电流采集模式。结论在CT图像质量达到一定程度后,进一步增加有效剂量,图像质量提高有限。根据不同的临床需求在保证一定图像质量的前提下,选择适当的CT扫描方案,降低受检者的有效剂量。     

A PC program for estimating organ dose and effective dose values in computed tomography

Dose values in CT are specified by the manufacturers for all CT systems and operating conditions in phantoms. It is not trivial, however, to derive dose values in patients from this information. Therefore, we have developed a PC-based program which calculates organ dose and effective dose values for arbitrary scan parameters and anatomical ranges. Values for primary radiation are derived from measurements or manufacturer specifications; values for scattered radiation are derived from Monte Carlo calculations tabulated for standard anthropomorphic phantoms. Based on these values, organ doses can be computed by the program for arbitrary scan protocols in conventional and in spiral CT. Effective dose values are also provided, both with ICRP 26 and ICRP 60 tissue-weighting coefficients. Results for several standard CT protocols are presented in tabular form in this paper. In addition, potential for dose reduction is demonstrated, for example, in spiral CT and in quantitative CT. Providing realistic patient dose estimates for arbitrary CT protocols is relevant both for the physician and the patient, and it is particularly useful for educational and training purposes. The program, called WinDose, is now in use at the Erlangen University hospitals (Germany) as an information tool for radiologists and patients. Further extensions are planned. Received: 9 March 1998; Revision received: 4 June 1998; Accepted: 4 November 1998     

Computed tomography radiation dose optimization: scanning protocols and clinical applications of automatic exposure control

As multi-detector-row computed tomography (CT) technology evolves, manifold applications of CT scanning have been adopted in clinical practice and optimization of scanning protocols to comply with an "as low as reasonably achievable" radiation dose have become more complex. Automatic exposure control techniques, which have been recently introduced on most state-of-the-art CT equipment, aid in radiation dose optimization at a selected image quality. The present article reviews the fundamentals of automatic exposure control techniques in CT, along with the scanning protocols and associated radiation dose reduction.     

Radiation protection and quality assurance in diagnostic radiology--an IAEA coordinated research project in Asia and eastern Europe.

The International Atomic Energy Agency currently has two parallel Coordinated Research Projects (CRP) running in Asia and Eastern Europe. The main objective of the CRPs is to raise the level of awareness in participating countries about the need for radiation protection for patients undergoing diagnostic radiology procedures. This is to be achieved by first assessing the status quo in a sample of hospitals and X-ray rooms in each participating country. A program of optimization of radiation protection for patients is then introduced by means of a comprehensive quality assurance program and the implementation of appropriate dose reduction methods, taking into account clinical requirements for diagnostically acceptable images. Patient dose assessment and image quality assessment are to be performed both before and after the introduction of the quality assurance program. The CRP is divided into two phases--the first is concerned with conventional radiography, while the second involves fluoroscopy and computed tomography. The CRP is still running, restricting the scope of this paper to a discussion of the approach being taken with the project. The project will be completed in 1998, with analysis to follow.     

Quality control (QC) of CT on rail system (FOCAL Unit) with a micro-multi leaf collimator (mMLC) using new GafChromic film for stereotactic radiotherapy

PURPOSE: Recent years, CT on rail system was reported to be useful as a tool for image-guided radiotherapy (IGRT). This system was clinically developed with the aim of stereotactic irradiation (STI) for brain, lung, liver, prostate and other sites. Quality assurance and quality control (QC) is an important issue in CT on rail system to assure geometric accuracies. The purpose of this study is to estimate the geometric accuracies of our CT on rail system using a detachable micro-multi leaf collimator (mMLC) with new type radiochromic films. Carrying out our original QC program, translational errors, setup reproducibility, beam misalignment and beam characteristics were evaluated. METHODS AND MATERIALS: We have studied with CT on rail system (FOCAL unit, Toshiba Medical systems, Tokyo, Japan) and mMLC unit (Accuknife, Direx Inc., Tokyo, Japan). We have developed original alignment phantom and small steel markers (2 mm phi) were implanted on its surface at certain intervals. Firstly, we have evaluated the accuracy of self-moving CT gantry and CT resolutions for cranio-caudal directions by changing slice thickness. And then using the phantom, we have measured the accuracy and reproducibility of geometric isocenter of the linac side and the CT gantry side by scanning the phantom. We have also measured the geometric changes of the common treatment couch by weight-loaded test (up to 135 kgw). To estimate dosimetric and geometric accuracies with the mMLC unit, the misalignment of the beam axes (gantry, collimator and couch rotation axis), mMLC leaf positions, and dose distributions for the verification plan were measured with new type GafChromic films (GafChromic-RTQA, ISP Inc., USA) and cylindrical phantom. The dose characteristics of the GafChromic film were also evaluated. RESULTS: The reproducibility of the self-moving CT gantry have a good agreement within 1 mm. Weight-load test have shown a good reliability within 2 mm at the common treatment couch. The translational precision of the common treatment couch was 0.0 +/- 0.1 mm at linac side and -0.2 +/- 0.5 mm at CT gantry side. The misalignments of beam axes have been kept within 0.4 mm at maximum. Gap test have shown the accuracies of the mMLC leaf positions, which is needed to keep within 1 mm by a routine calibration. CONCLUSIONS: To practice quality control program for the FOCAL unit and the mMLC unit is essential for a regular interval to reduce systematic errors. New type radiochromic film would be useful for a verification tool as alternative to conventional film.     

A Toolkit for Pediatric CT Dose Reduction in Community Hospitals

“Eighty percent of success is just showing up.”—Woody Allen

Pediatric CT radiation dose optimization is a challenging process for pediatric-focused facilities and community hospitals alike. Ongoing experience and trial-and-error approaches to dose reduction in the large academic hospital setting may position these centers to help community hospitals that strive for CT quality improvement. We describe our hands-on approach in a pilot project to create a partnership between an academic medical center and a community hospital to develop a toolkit for implementing CT dose reduction. Our aims were to (1) assess the acceptability of an interactive educational program and electronic toolkit booklet, (2) conduct a limited test of the efficacy of the toolkit in promoting knowledge and readiness to change, and (3) assess the acceptability and practicality of a collaborative approach to implementing dose reduction protocols in community hospitals. In partnering with the community hospital, we found that they had size-specific radiation doses two to three times higher than those at our center. Survey results after a site visit with interactive educational presentations revealed an increase in knowledge, stronger opinions about the health risks of radiation from CT scans, and willingness and perceived ability to reduce pediatric CT doses.     

器官剂量调制技术对鼻窦CT图像质量和辐射剂量的影响

目的:探讨器官剂量调制(ODM)技术行鼻窦CT扫描时对图像质量和眼晶状体辐射剂量的影响。方法:应用GERevolutionevoCT对头部拟人模体进行扫描,不开启ODM为对照组,开启ODM为观察组。通过调整管电压(140、120、100 kV)、噪声指数(N17、N18)、螺距(准直宽度20 cm时0.531、0.96...     

基于品质因素评价瓦里安锥束CT成像质量与辐射剂量风险收益比

目的 分析比对不同Varian加速器平台机载千伏锥束CT（kV CBCT）系统的辐射剂量和成像质量，指导临床选用风险收益比（成像质量/辐射剂量）最高的图像引导方案。方法 利用CT剂量指数模体（CTDI模体）和CT电离室，以及Catphan604模体分别获取Edge、Truebeam、新旧两台ix加速器机载CBCT典型扫描模式的辐射剂量和成像质量参数，使用品质因素（figure of merit，FOM）值评估各图像引导方案的风险收益比。结果 不同型号的瓦里安加速器配置的kV CBCT系统的FOM不同，差异广泛分布于0.65（温和成像一圈）~48.46（温和成像半圈）区间；各扫描参数间FOM也存在较大差异，均值为22.14±13.47。结论 由于设备间和参数间存在显著差异，基于实际测量的验证评估有助于临床选择合理的影像引导方案，剂量敏感患者应优先选择加权CT剂量指数（CTDI_w）低的参数和设备；对图像质量要求高的患者应优选对比度噪声比（CNR）高的方案；而普通患者则可依据风险收益比进行选择，此时品质因素FOM可为临床决策提供有利工具。