Dose estimation with CTDI100, air in computed tomography

Although the principal dosimetric quantity in computed tomography (CT) can be assessed using a pencil ionization chamber with an active length of 100 mm, standard CT dosimetry phantoms of polymethylmethacrylate (PMMA) , and plates of aluminum, most facilities do not possess the requisites. We present a practical method of estimating CTDI(100, c), CTDI(100, p) and the half-value layer (HVL) from CTDI(100, air), which is measured parallel with the axis of rotation of the scanner to free-in-air. The three data chosen for this method of estimation were as follows: 1) the relation of HVL to CTDI(100, air) per radiographic exposure (mAs); 2) the relation of HVL to CTDI(100, c) per CTDI(100, air); 3) the relation of HVL to CTDI(100, p) per CTDI(100, air). The data were based on the measured values of six CT scanners, so as to avoid dependence on the technical characteristics of a specific manufacturer. The estimated value has a possible maximum uncertainty of 20%, although this method of estimation is practical for dose assessment.     

Radiation doses from CT in the Sultanate of Oman

The computed tomography dose index (CTDI), dose-length product (DLP) and the effective dose were determined for a range of CT examinations in the Sultanate of Oman. There was a wide variation in CTDI. This shows that there is a variation in both scanner design and the exposure settings used by hospitals. There was also a wide variation in DLP and effective dose, suggesting that in some cases too many slices are taken. Therefore, standard protocols should be designed and adhered to in order that radiation doses may be reduced in the future.     

苏州市数字X射线摄影和CT医疗照射所致公众剂量负担的研究

目的 估算2017年苏州市医用数字X射线摄影（DR）和CT所致全市公众有效剂量负担。方法 利用分层随机抽样方法,通过医学影像存档与通信系统（PACS）和放射科信息系统（RIS）,采集苏州市27家医疗机构2017年DR和CT诊疗频度数据。对于DR,使用剂量面积乘积测量仪测量受检者常见投照部位的剂量面积乘积（DAP）,估算出有效剂量;对于CT,测量头部、胸部和腹部扫描时的加权CT剂量指数（CTDI_w）,结合扫描参数,估算出有效剂量。根据各部位的扫描人次和有效剂量,估算苏州市DR和CT医疗照射所致公众剂量负担。结果 DR检查中,腹部前后位、骨盆前后位、头颅侧位和后前位、胸部侧位和后前位、胸椎侧位和后前位、腰椎侧位和后前位一次检查所致受检者有效剂量分别为0.565、0.280、0.016、0.012、0.111、0.060、0.100、0.102、0.307和0.152 mSv。CT检查中,头部、胸部、腹部一次检查所致受检者有效剂量分别为1.33、5.75和7.31 mSv。2017年苏州市DR和CT医疗照射所致公众剂量为9 593.07人·Sv,人均年有效剂量为0.898 mSv。结论 CT医疗照射对公众剂量的贡献量远大于DR照射的贡献量。苏州市DR和CT医疗照射所致公众剂量负担处于高水平,需要引起相关卫生行政部门的重视。     

Strategies for reducing radiation exposure in multi-detector row CT

Many tools and strategies exist to enable the reduction of radiation exposure from computed tomography (CT). The common CT metrics of x-ray output, CTDI(vol) and DLP, are explained and serve as the basis for monitoring radiation exposure from CT scans. Many strategies to dose optimize CT protocols are explored that, in combination with available hardware and software tools, allow robust diagnostic quality CT scans to be performed with a radiation exposure appropriate for the clinical scenario and the size of the patients. Specific emergency department example protocols are used to demonstrate these techniques.     

Multi-detector row CT: radiation dose characteristics

PURPOSE: To determine the dose characteristics of multi-detector row computed tomography (CT) and to provide tabulated dose values and rules of thumb that assist in minimizing the radiation dose at multi-detector row CT. MATERIALS AND METHODS: Weighted CT dose index (CTDI100w) values were obtained from three multi-detector row CT scanners (LightSpeed; GE Medical Systems, Milwaukee, Wis) for both head and body CT modes by using standard CT-dose phantoms. The CTDI100w was determined as a function of x-ray tube voltage (80, 100, 120, 140 kVp), tube current (range, 50-380 mA), tube rotation time (0.5-4.0 seconds), radiation profile width (RPW) (5, 10, 15, 20 mm), and acquisition mode (helical high-quality and high-speed modes and axial one-, two-, and four-section modes). Statistical regression was performed to characterize the relationships between CTDI100w and various technique factors. RESULTS: The CTDI100w (milligray) increased linearly with tube current: in head mode, CTDI100w = (0.391 mGy/mA +/- 0.004) x tube current (milliampere) (r2 = 0.999); in body mode, CTDI100w = (0.162 mGy/mA +/- 0.002) x tube current (milliampere) (r2 = 0.999). The CTDI100w increased linearly with rotation time: in head mode, CTDI100w = (34.7 mGy/sec +/- 0.2) x rotation time (seconds) (r2 = 1.0); in body mode, CTDI100w = (13.957 mGy/sec +/- 0.005) x rotation time (seconds) (r2 = 1.0). The relationship of normalized CTDI100w (milligrays per 100 mAs) with tube voltage followed a power law: in head mode, CTDI100w = (0.00016 mGy/100 mAs. kVp +/- 0.00007) x (tube voltage)(2.5+/-0.1) (r2 = 0.997); in body mode, CTDI100w = (0.000012 mGy/100 mAs. kVp +/- 0.000007) x (tube voltage)(2.8+/-0.1) (r2 = 0.996). In all scanning modes, CTDI100w decreased when RPW increased. CTDI100w was 10% higher in head mode and 13% lower in body mode compared with the value suggested by the manufacturer, which is displayed at the scanner console. When deposited power exceeded 24 kW, CTDI100w increased by 10% as a result of use of the large focal spot. CONCLUSION: The authors provide a set of tables of radiation dose as a function of imaging protocol to facilitate implementation of radiation dose-efficient studies.     

Report on the 89th Scientific Assembly and Annual Meeting of the Radiological Society of North America--analysis of radiation dose by a change of a scan parameter of multi-slice computed tomography by a film method

PURPOSE: It is for a purpose of this study to measure radiation dose by analyzing a dose profile of multi-slice computed tomography varying with helical pitch and a row slice thickness difference complicatedly. MATERIALS AND METHODS: We used multi-slice computed tomography, and helical pitch and row slice thickness change and scanned the helical scan. I used CTDI phantom of a diameter of 25 cm and I inserted roentgen diagnosis use film UR-2(new) which I put between my own phantom in center and 1 cm away from the outer surface and scanned it. And the provided level profile was converted into a dose profile with the dose-density curve which I made beforehand. I analyzed radiation dose than the dose profile. RESULT: In multi-slice computed tomography, radiation dose varied with assembly of row slice thickness and helical pitch. The change of a dose profile changed in a phantom surface part complicatedly. The maximum dose by the measurement of this time was 29 mGy in row slice thickness 0.5 mm, assembly of helical pitch 2.5. In addition, the minimum dose was 6.8 mGy in row slice thickness 3.0 mm, assembly of helical pitch 5.5. And, as for the difference of maximum dose in the same dose profile and the smallest dose, there were about 20 % in row slice thickness 1.0 mm, assembly of helical pitch 5.5. CONCLUSION: The dosimetry of multi-slice computed tomography by a film method enabled it to measure a change of a dose profile by a difference of a scan parameter by high interest solution ability. In addition, it is a method more superior in dosimetry of multi-slice computed tomography spreading through a Z-axis direction broadly than determination by computed tomography use ionization chamber dosimeter. Because radiation dose increases by a scan in thin row slice thickness and small helical pitch, care is necessary.     

Late radiation-induced necrosis of the brain--a follow-up study using computerized tomography

One case of cerebral tumor is presented in order to describe the radiogenic alterations demonstrated by computed tomography of the brain. The possible radiogenic alterations of the brain substance, the time interval between radiotherapy and first manifestation, and the influence of radiation dose and fractionation are discussed. In order to distinguish between radiogenic alterations and tumor recurrences when performing a checkup examination by computed tomography, the knowledge of irradiation scheme, focal dose, and distribution of isodoses is necessary.     

双源CT前瞻性心电门控技术在婴幼儿先天性心脏病的成像研究

目的通过对选用前瞻性心电门控扫描技术与回顾性心电门控扫描技术所得到的图像质量和放射剂量的对照研究,探讨双源CT（DSCT）前瞻性心电门控低剂量技术应用于婴幼儿先天性心脏病成像的可行性。方法连续搜集90例临床拟行双源CT胸部大血管检查的婴幼儿患者。随机分为两组,A组（45例）选用前瞻性心电门控扫描模式扫描。B组（45例）采用回顾性心电门控扫描模式扫描。由2名高年资的诊断医师以双盲法分别对A、B组图像进行图像质量评价,两组间图像质量差异用两独立样本Wilcoxon秩和检验进行分析。两组图像图像噪声、辐射剂量参数CTDI、DLP和ED差异用两独立样本均数f检验进行比较。结果A、B两组图像质量差异无统计学意义（H=O．098,P〉0．05）;A、13两组噪声值分别为（13．25±1．27）HU,（13．51±1．41）HU,两组间噪声值差异无统计学意义（t=0．925,P〉0．05）;A、B两组CTDI、DLP、ED分别为（2．70±0．75）mGy、（29．55±10．17）mGy／cm、（0．41±0．14）mSv;（3．81±1．03）mGy、（51．57±14．81）mGy／cm、（O．72±0．20）mSv;A组CTDI、DLP、ED明显低于B组,2组差异有统计学意义（t=5．36,8．13,8．13,P=0．001）。结论双源CT婴幼儿先天性心脏病成像时使用前瞻性心电门控扫描可以有效地减少受检者接受的x射线剂量,同时可以保证图像质量。     

Conversion factor for CT dosimetry to assess patient dose using a 256-slice CT scanner

Recent rapid progress in CT technology has yielded equipment with large numbers of detector rows and standard computed tomography dose index (CTDI) is therefore no longer an adequate integration range. An integration range of 300 mm is necessary to accurately measure dose under a nominal beam width of 128 mm due to scattered radiation. However, such a long phantom is inconvenient to use routinely in cone-beam CT patient dose checking. To assess patient dose accurately with standard dosimetry methods, we determined a conversion factor (CF) which was calculated from the weighted dose profile integral (DPI(w)) for the 300 mm integration range with a 300 mm long CTDI phantom using a 300 mm long ionization chamber divided by that for the 100 mm integration range with a standard CTDI phantom (140 mm long) with a 100 mm long chamber. CF values increase with increasing nominal beam width and effective energy in the range from 1.5 to 2.0. CF values can also be adapted for use with other CT systems as their dose profiles are thought to be analogous to those for the 300 mm phantom and are useful in any hospital situation to assess accurate patient doses using standard dosimetry methods.     

Validation of a Monte Carlo tool for patient-specific dose simulations in multi-slice computed tomography

Estimating the dose delivered to the patient in X-ray computed tomography (CT) examinations is not a trivial task. Monte Carlo (MC) methods appear to be the method of choice to assess the 3D dose distribution. The purpose of this work was to extend an existing MC-based tool to account for arbitrary scanners and scan protocols such as multi-slice CT (MSCT) scanners and to validate the tool in homogeneous and heterogeneous phantoms. The tool was validated by measurements on MSCT scanners for different scan protocols under known conditions. Quantitative CT Dose Index (CTDI) measurements were performed in cylindrical CTDI phantoms and in anthropomorphic thorax phantoms of various sizes; dose profiles were measured with thermoluminescent dosimeters (TLD) in the CTDI phantoms and compared with the computed dose profiles. The in-plane dose distributions were simulated and compared with TLD measurements in an Alderson-Rando phantom. The calculated dose values were generally within 10% of measurements for all phantoms and all investigated conditions. Three-dimensional dose distributions can be accurately calculated with the MC tool for arbitrary scanners and protocols including tube current modulation schemes. The use of the tool has meanwhile also been extended to further scanners and to flat-detector CT.     

Erfassung und Monitoring der radiologischen Strahlenexposition

Strategies for reducing radiation exposure are an important part of optimizing medical imaging and therefore a relevant quality factor in radiology. Regarding the medical radiation exposure, computed tomography has a special relevance. The use of the integrating the healthcare enterprise (IHE) radiation exposure monitoring (REM) profile is the upcoming standard for organizing and collecting exposure data in radiology. Currently most installed base devices do not support this profile generating the required digital imaging and communication in medicine (DICOM) dose structured reporting (SR). For this reason different solutions had been developed to register dose exposure measurements without having the dose SR object. Registration and analysis of dose-related parameters is required for constantly optimizing examination protocols, especially computed tomography (CT) examinations based on the latest research results in order to minimize the individual radiation dose exposure from medical imaging according to the principle as low as reasonably achievable (ALARA).     

Radiation, thoracic imaging, and children: radiation safety

The chest is the most frequently evaluated region of the body in children. The majority of thoracic diagnostic imaging, namely "conventional" radiography (film screen, computed radiography and direct/digital radiography), fluoroscopy and angiography, and computed tomography, depends on ionizing radiation. Since errors, oversights, and inattention to radiation exposure continue to be extremely visible issue for radiology in the public eye it is incumbent on the imaging community to maximize the yield and minimize both the real and potential radiation risks with diagnostic imaging. Technical (e.g. equipment and technique) strategies can reduce exposure risk and improve study quality, but these must be matched with efforts to optimize appropriate utilization for safe and effective healthcare in thoracic imaging in children. To these ends, material in this chapter will review practice patterns, dose measures and modality doses, radiation biology and risks, and radiation risk reduction strategies for thoracic imaging in children.     

Effective doses in standard protocols for multi-slice CT scanning

The purpose of this study was to assess the radiation exposure of patients in several standard protocols in multi-slice CT (MSCT). Scanning protocols for neck, chest, abdomen, and spine were examined on a Somatom Plus 4 Volume Zoom MSCT (Siemens, Erlangen, Germany) with changing slice collimation (4×1, 4×2.5, and 4×5 mm), and pitch factors (1, 1.5, and 2). Effective doses were calculated from LiF–TLD measurements at several organ sites using an Alderson-Rando phantom and compared with calculations using the weighted CTDI. Effective dose for MSCT of the neck was 2.8 mSv. For different protocols for MSCT of the chest, 7.5–12.9 mSv were found. In abdominal MSCT protocols, effective dose varied between 12.4 and 16.1 mSv. The MSCT of the spine may lead to 12 mSv. An excellent correlation between the effective dose as determined by LiF–TLD and the calculated effective dose using the weighted CTDI could be demonstrated; however, a difference of up to 30% (mean 14.3%) was noted. Standard protocols for MSCT as measured in this study showed effective doses of up to16 mSv. Phantom measurement data show a good correlation to estimations using the weighted CTDI. Electronic Publication     

Spiral CT and radiation dose

Recent studies in the USA and Europe state that computed tomography (CT) scans compromise only 3-5% of all radiological exams, but they contribute 35-45% of total radiation dose to the patient population. These studies lead to concern by several public authorities. Basis of CT-dose measurements is the computed tomography dose index (CTDI), which was established 1981. Nowadays there are several modifications of the CTDI values, which may lead to confusion. It is suggested to use the standardized CTDI-100 w. value together with the dose length product in all CT-examinations. These values should be printed on all CT-images and allows an evaluation of the individualized patient dose. Nowadays, radiologist's aim must be to work at the lowest maximal diagnostic acceptable signal to noise ratio. To decrease radiation dose radiologist should use low kV and mA, but high pitches. Newly developed CT-dose-reduction soft-wares and filters should be installed in all CT-machines. We should critically compare the average dose used for a specific examination with the reference dose used in this country and/or Europe. Greater differences should caution the radiologist. Finally, we as radiologists must check very carefully all indications and recommend alternative imaging methods. But we have also to teach our customers-patients and medical doctors who are non-radiologists-that a 'good' image is not that which show all possible information, but that which visualize 'only' the diagnostic necessary information.     

Computed tomography and patient risk: Facts,perceptions and uncertainties

Since its introduction in the 1970s, computed tomography (CT) has revolutionized diagnostic decision-making. One of the major concerns associated with the widespread use of CT is the associated increased radiation exposure incurred by patients. The link between ionizing radiation and the subsequent development of neoplasia has been largely based on extrapolating data from studies of survivors of the atomic bombs dropped in Japan in 1945 and on assessments of the increased relative risk of neoplasia in those occupationally exposed to radiation within the nuclear industry. However, the association between exposure to low-dose radiation from diagnostic imaging examinations and oncogenesis remains unclear. With improved technology, significant advances have already been achieved with regards to radiation dose reduction. There are several dose optimization strategies available that may be readily employed including omitting unnecessary images at the ends of acquired series, minimizing the number of phases acquired, and the use of automated exposure control as opposed to fixed tube current techniques. In addition, new image reconstruction techniques that reduce radiation dose have been developed in recent years with promising results. These techniques use iterative reconstruction algorithms to attain diagnostic quality images with reduced image noise at lower radiation doses.