A review of patient dose and optimisation methods in adult and paediatric CT scanning

An increasing number of publications and international reports on computed tomography (CT) have addressed important issues on optimised imaging practice and patient dose. This is partially due to recent technological developments as well as to the striking rise in the number of CT scans being requested. CT imaging has extended its role to newer applications, such as cardiac CT, CT colonography, angiography and urology. The proportion of paediatric patients undergoing CT scans has also increased. The published scientific literature was reviewed to collect information regarding effective dose levels during the most common CT examinations in adults and paediatrics. Large dose variations were observed (up to 32-fold) with some individual sites exceeding the recommended dose reference levels, indicating a large potential to reduce dose. Current estimates on radiation-related cancer risks are alarming. CT doses account for about 70% of collective dose in the UK and are amongst the highest in diagnostic radiology, however the majority of physicians underestimate the risk, demonstrating a decreased level of awareness. Exposure parameters are not always adjusted appropriately to the clinical question or to patient size, especially for children. Dose reduction techniques, such as tube-current modulation, low-tube voltage protocols, prospective echocardiography-triggered coronary angiography and iterative reconstruction algorithms can substantially decrease doses. An overview of optimisation studies is provided. The justification principle is discussed along with tools that assist clinicians in the decision-making process. There is the potential to eliminate clinically non-indicated CT scans by replacing them with alternative examinations especially for children or patients receiving multiple CT scans.     

A dose comparison survey in CT departments of dedicated paediatric hospitals in Australia and Saudi Arabia

AIM: To measure and compare computed tomography (CT) radiation doses delivered to patients in public paediatric hospitals in Australia and Saudi Arabia. METHODS: Doses were measured for routine CT scans of the head, chest and abdomen/pelvis for children aged 3-6 years in all dedicated public paediatric hospitals in Australia and Saudi Arabia using a CT phantom measurement cylinder.RESULTS: CT doses, using the departments’ protocols for 3-6 year old, varied considerably between hospitals. Measured head doses varied from 137.6 to 528.0 mGy·cm, chest doses from 21.9 to 92.5 mGy·cm, and abdomen/pelvis doses from 24.9 to 118.0 mGy·cm. Mean head and abdomen/pelvis doses delivered in Saudi Arabian paediatric CT departments were significantly higher than those in their Australian equivalents. CONCLUSION: CT dose varies substantially across Australian and Saudi Arabian paediatric hospitals. Therefore, diagnostic reference levels should be established for major anatomical regions to standardise dose.     

The contribution of the internal scatter to radiation dose during CT scan of the head

Summary An acrylic head phantom was irradiated during a computed tomographic scan with four commercial scanners. Measurements of the spatial distribution of the radiation dose on the surface and internal to the phantom were performed for the scan plane and the scattered beam at various distances from the scan plane. The surface scatter dose was found to be considerably smaller than that for internal scatter. A significant increase in radiation exposure within the head phantom due to internal radiation seatter, and an asymmetrical primary beam profile for dual slice scanners were also noted.     

Image quality and dose in computed tomography

Radiation exposure to the patient during CT is relatively high, and it is therefore important to optimize the dose so that it is as low as possible but still consistent with required diagnostic image quality. There is no established method for measuring diagnostic image quality; therefore, a set of image quality criteria which must be fulfilled for optimal image quality was defined for the retroperitoneal space and the mediastinum. The use of these criteria for assessment of image quality was tested based on 113 retroperitoneal and 68 mediastinal examinations performed in seven different CT units. All the criteria, except one, were found to be usable for measuring diagnostic image quality. The fulfilment of criteria was related to the radiation dose given in the different departments. By examination of the retroperitoneal space the effective dose varied between 5.1 and 20.0 mSv (milli Sievert), and there was a slight correlation between dose and high percent of “yes” score for the image quality criteria. For examination of the mediastinum the dose range was 4.4–26.5 mSv, and there was no significant increment of image quality at high doses. The great variation of dose at different CT units was due partly to differences regarding the examination procedure, especially the number of slices and the mAs (milli ampere second), but inherent dose variation between different scanners also played a part. Received 30 August 1995; Revision received 27 December 1995; Accepted 24 January 1995     

Patient dose considerations in computed tomography examinations

Ionizing radiation is extensively used in medicine and its contribution to both diagnosis and therapy is undisputable. However, the use of ionizing radiation also involves a certain risk since it may cause damage to tissues and organs and trigger carcinogenesis. Computed tomography (CT) is currently one of the major contributors to the collective population radiation dose both because it is a relatively high dose examination and an increasing number of people are subjected to CT examinations many times during their lifetime. The evolution of CT scanner technology has greatly increased the clinical applications of CT and its availability throughout the world and made it a routine rather than a specialized examination. With the modern multislice CT scanners, fast volume scanning of the whole human body within less than 1 min is now feasible. Two dimensional images of superb quality can be reconstructed in every possible plane with respect to the patient axis (e.g. axial, sagital and coronal). Furthermore, three-dimensional images of all anatomic structures and organs can be produced with only minimal additional effort (e.g. skeleton, tracheobronchial tree, gastrointestinal system and cardiovascular system). All these applications, which are diagnostically valuable, also involve a significant radiation risk. Therefore, all medical professionals involved with CT, either as referring or examining medical doctors must be aware of the risks involved before they decide to prescribe or perform CT examinations. Ultimately, the final decision concerning justification for a prescribed CT examination lies upon the radiologist. In this paper, we summarize the basic information concerning the detrimental effects of ionizing radiation, as well as the CT dosimetry background. Furthermore, after a brief summary of the evolution of CT scanning, the current CT scanner technology and its special features with respect to patient doses are given in detail. Some numerical data is also given in order to comprehend the magnitude of the potential radiation risk involved in comparison with risk from exposure to natural background radiation levels.     

The relationship of body mass index and abdominal fat on the radiation dose received during routine computed tomographic imaging of the abdomen and pelvis

Purpose

To determine the relationship of increasing body mass index (BMI) and abdominal fat on the effective dose acquired from computed tomography (CT) abdomen and pelvis scans.

Methods

Over 6 months, dose-length product and total milliamp-seconds (mAs) from routine CT abdomen and pelvis scans of 100 patients were recorded. The scans were performed on a 64-slice CT scanner by using an automatic exposure control system. Effective dose (mSv) based on dose-length product, BMI, periumbilical fat thickness, and intra-abdominal fat were documented for each patient. BMI, periumbilical fat thickness, and intra-abdominal fat were compared with effective dose.

Results

Thirty-nine men and 61 women were included in the study (mean age, 56.3 years). The mean BMI was 26.2 kg/m². The mean effective dose was 10.3 mSv. The mean periumbilical fat thickness was 2.4 cm. Sixty-five patients had a small amount of intra-abdominal fat, and 35 had a large amount of intra-abdominal fat. The effective dose increased with increasing BMI (P < .001) and increasing amounts of intra-abdominal fat (P < .001). For every kilogram of weight, there is a 0.13 mSv increase in effective dose, which is equal to 6.5 chest radiographs per CT examination. For an increase in BMI by 5 kg/m², there is a 1.95 mSv increase in effective dose, which is equal to 97.5 chest radiographs per CT examination.

Conclusion

Increasing BMI and abdominal fat significantly increases the effective dose received from CT abdomen and pelvis scans.     

常规CT 的放射剂量最优化

目的：优化患者CT扫描参数,减少其辐射危害。方法以成人头部,胸部和腹部CT扫描为考察对象,应用CT专用16 cm直径CTDI测量模体,改变kVp和 mAs组合,测量所扫描图像的噪声,高对比分辨率,低对比分辨率等,以此为依据决定图像是否合格,并从合格影像中选出辐射剂量最小的一组kVp/mAs做为最优化结果。结果在噪声,高对比分辨率,低对比分辨率等都合格的情况下,各部位辐射剂量最小的一组kVp/mAs分别是：130/90（成人头部）,110/70（成人胸部）,130/65（成人腹部）。其辐射剂量相对设备预设条件下的辐射剂量下降百分比分别是：25．0％,12．0％和34．3％。结论体模实验证明,合理组合kVp和mAs设置可以在保证图像质量的情况下降低CT辐射剂量,从而为临床实际的CT剂量最优化提供借鉴。     

Effective radiation dose from semicoronal CT of the sacroiliac joints in comparison with axial CT and conventional radiography

The aim of this study was to evaluate the radiation dose given by semicoronal CT of the sacroiliac joints (SIJs) in comparison with axial CT and conventional radiography. The total effective radiation doses given by serial contiguous semicoronal and axial CT, using 5-mm slices, 120 kV and 330 mAs, were determined by measurement of organ doses using an anthropomorphic Rando Alderson phantom paced with thermoluminescence dosimeters. The doses given by conventional antero-posterior (AP) and oblique projections of the SIJs were determined similarly. In a female the total effective dose by semicoronal CT was found to be more than six times lower than by axial CT and 2.5 times lower than the dose use to obtain a conventional AP radiograph, the values being 102, 678, and 255 μSv, respectively. The effective dose by semicoronal CT was only a little higher than the dose given to obtain two oblique radiographs. In a male with lead protection of the gonads the dose by semicoronal CT was four times lower than by axial CT, but higher than by conventional radiography. In conclusion, the effective dose by semicoronal CT of the SIJs is lower than by axial CT, and in females a semicoronal CT implies a lower effective radiation dose that used to obtain an AP radiograph. Electronic Publication     

心脏CT辐射剂量相关研究

本文对心脏CT检查带来辐射风险,以及减少心脏CT辐射剂量的方法加以综述。对CT检查的目标人群来说,心脏冠脉图像的直接可见性的需求要超过他们对辐射剂量所带来危害的顾忌,冠脉CT利大于弊,仍为可选择的检查。     

头颈CTA中基于复合体重因子的对比剂剂量应用

目的:探讨基于复合体重因子的对比剂使用方法行头颈CTA的可行性。方法:实验组40例患者采用基于复合体重因子的对比剂使用方法在Toshiba Aquilion ONE 320容积CT上行头颈CTA,对照组26例患者采用基于体重的对比剂使用方法在同一台螺旋CT上行头颈CTA。采用独立样本t检验比较实验组和对照组的对比剂剂量、辐射剂量和主动脉弓、右颈总动脉、右颈内动脉、右椎动脉、基底动脉、大脑后动脉、大脑中动脉、大脑前动脉的CT值与其强化差值、图像信噪比、对比噪声比;采用双盲法对图像进行主观评价,并采用Mann-Whitney U检验比较两组的图像质量。结果:实验组和对照组的对比剂剂量分别为(55.4±5.9)mL/例、(62.8±7.9)mL/例,两组的对比剂剂量有显著差异(P<0.05)。实验组和对照组的辐射剂量(DLP)均值分别为(489.1±55.0)mGy·cm、(555.6±78.7)mGy·cm。实验组和对照组的辐射剂量有显著差异(P<0.05)。实验组考察的动脉CT值和动脉强化差值均高于对照组且差异具有统计学意义(P<0.05)。实验组和对照组的图像信噪比、对比噪声比无统计学差异(P>0.05)。实验组的图像主观评价好于对照组且有统计学意义(U检验,P<0.05)。结论:采用基于复合体重因子的对比剂使用方法结合低管电压技术在行头颅CTA时可以在保证图像质量、满足临床诊断需求的前提下降低对比剂用量、降低辐射剂量。     

Changing radiation dose from diagnostic computed tomography examinations in Saskatchewan

Purpose

Follow-up study to observe if provincial mean effective radiation dose for head, chest, and abdomen-pelvis (AP) computed tomographies (CTs) remained stable or changed since the initial 2006 survey.

Methods

Data were collected in July 2008 from Saskatchewan's 13 diagnostic CT scanners of 3358 CT examinations. These data included the number of scan phases and projected dose length product (DLP). Technologists compared projected DLP with 2006 reference data before scanning. Projected DLP was converted to effective dose (ED) for each head, chest, and AP CT. The total dose that the patients received with scans of multiple body parts at the same visit also was determined.

Results

The mean (± SD) provincial ED was 3.4 ± 1.6 mSv for 1023 head scans (2.7 ± 1.6 mSv in 2006), 9.6 ± 4.8 mSv for 588 chest scans (11.3 ± 8.9 mSv in 2006), and 16.1 ± 9.9 mSv for 983 AP scans (15.5 ± 10.0 mSv in 2006). Single-phase multidetector row CT ED decreased by 31% for chest scans (9.5 ± 3.9 mSv vs 13.7 ± 9.7 mSv in 2006) and 17% for AP scans (13.9 ± 6.0 mSv vs 16.8 ± 10.6 mSv in 2006) and increased by 19% for head scans (3.2 ± 1.2 mSv vs 2.7 ± 1.5 mSv in 2006). The total patient dose was highest (33.8 ± 10.1 mSv) for the 20 patients who received head, neck, chest, and AP scans during a single visit. Because of increased utilisation and the increased CT head dose, Saskatchewan per capital radiation dose from CT increased by 21% between 2006 and 2008 (1.14 vs 1.38 mSv/person per year).

Conclusion

Significant dose and variation reduction was seen for single-phase CT chest and AP examinations between 2006 and 2008, whereas CT head dose increased over the same interval. These changes, combined with increased utilisation, resulted in per capita increase in radiation dose from CT between the 2 studies.     

分化型甲状腺癌术后患者131I治疗的辐射剂量与防护

监测分化型甲状腺癌（DTC）患者术后131I治疗的辐射剂量并规范其辐射防护对DTC患者131I治疗后自身及周围人群的健康有重要意义.目前研究表明,131I治疗的DTC患者自身的辐射不良反应大多都能得到较有效地缓解和控制.只要能严格规范地遵守131I治疗DTC的辐射防护相关法规和建议,加强辐射剂量监测,并对患者、工作人员和患者家属进行适当的教育和指导,其对周围人群的辐射剂量都能达到和符合国际上的辐射防护规定.     

甲状腺癌的影像学诊断进展

目前甲状腺癌主要的影像学诊断方法是电子计算机体层摄影(CT)、磁共振成像(MRI)及超声(US)等。这些检查方法既有各自独特的优势,也有相应不足。CT对甲状腺癌内钙化的发现明显优于MRI,对肿瘤侵犯相邻结构的显示MRI优于CT;超声检查由于其操作简单、价格适宜,已成为诊断原发性甲状腺癌的首选指标;MRI诊断甲状腺癌的敏感性较高,同时MRS还可以在分子水平上反映病变。本文将甲状腺癌影像学诊断进展情况综述如下。     

131I清除分化型甲状腺癌术后残留腺体的内照射吸收剂量与疗效的分析

目的 探讨131I清除DTC术后残留甲状腺组织（简称清甲）的内照射吸收剂量与疗效的相关性.方法 前瞻性分析2009年9月至2011年9月拟行清甲的72例DTC患者[男14例,女58例,年龄16～67（41±16）岁].在患者服用3.7 GBq 131I后采用连续显像法评估残留腺体的碘代动力学,利用超声测量残留腺体的质量,按照美国核医学会医用内照射剂量学委员会提出的内照射吸收剂量计算方法,计算残留腺体的吸收剂量.清甲治疗后6～9个月,判断疗效：若刺激状态下Tg＜l μg/L及颈部超声检查提示甲状腺床区无腺体组织残留,判断为清甲成功.清甲成功与未成功者组间比较采用两样本t检验.结果 72例患者的残留腺体24h摄碘率为0.9％～6.3％, 131I有效半衰期为12.0～146.4 h,腺体质量为1.0～6.9g,吸收剂量为23～2 197 Gy,24 h吸收剂量率为0.5～8.1 Gy/h.43例清甲成功者与29例清甲未成功者残留腺体的吸收剂量分别为（363±148） Gy和（341±167） Gy,差异无统计学意义（￡=15.097,P＞0.05）;24 h吸收剂量率分别为（3.7±2.1） Gy/h和（2.9±1.6） Gy/h,差异有统计学意义（t=7.908,P＜0.05）.结论 131I清甲残留腺体的吸收剂量率影响清甲疗效.     

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.     

Measurement of the internal dose to families of outpatients treated with <Superscript>131</Superscript>I for hyperthyroidism

Objective  The aim of this study was to measure the internal dose received by family members from ingestion of radioactive contamination after outpatient therapy. Materials and methods  Advice was given to minimise transfer of radioiodine. Home visits were made approximately 2, 7 and 21 days after treatment to measure radioactivity in the thyroids of family members. A decay correction was applied to radioactivity detected assuming ingestion had occurred at the earlier contact time, either the day of treatment or the previous home visit. An effective half-life of 6 or 7 days was used depending on age. Thyroid activity was summed if activity was found at more than one visit in excess of the amount attributable to radioactive decay. Effective dose (ED) was calculated using ICRP72. Results and discussion  Fifty-three adults and 92 children, median age 12 (range 4–17) years participated. Median administered activity was 576 (range 329–690) MBq ¹³¹I. Thyroid activity ranged from 0 to 5.4 kBq in the adults with activity detected in 17. Maximum adult ED was 0.4 mSv. Thyroid activity ranged from 0 to 11.8 kBq in the children with activity detected in 26. The two highest values of 5.0 and 11.8 kBq occurred in children aged 5 and 14 years from different families. Eighty-five children had no activity or <1 kBq detected. ED was <0.2 mSv in 86 out of 92 children (93%). Previous published data showed 93% of children received an ED ≤0.8 mSv from external irradiation. Conclusion  With advice, families of outpatients receiving radioiodine should be able to comply with statutory dose limits and constraints.     

胸部CT扫描中颈部伸展体位应用价值的探讨

目的 探讨在胸部CT扫描中患者颈部伸展使甲状腺腺体上移以减少甲状腺辐射暴露的可能性。方法 对2017年3至6月北京朝阳医院进行胸部CT检查1 994例患者的图像资料进行比较分析,按颈部体位不同分为伸展组和常规组,每组997例,伸展组患者头颈部后仰成颌顶位。常规组采用常规头颅扫描头架,头部正常体位。以第一肋骨头为基准计数标志,观察两组患者甲状腺腺体暴露于扫描范围内的腺体长度及腺体全部移出扫描范围的例数。比较两组患者原发射线区域内甲状腺腺体扫描长度的差别。结果 伸展组患者甲状腺腺体暴露于扫描范围内的长度（4.69±5.68） mm,显著短于常规组（17.16±6.68） mm患者,差异有统计学意义（U=91 073.5,P<0.05）,并且伸展组患者甲状腺腺体完全脱离扫描范围内的例数519例,多于常规组32例,差异有统计学意义（U=594.8,P<0.05）。52.1%患者的甲状腺腺体完全脱离扫描范围内原发射线的辐射暴露。结论 胸部CT扫描时患者颈部伸展可以使甲状腺腺体位于扫描野内的长度缩短,有效提高甲状腺的辐射防护。