Knowing the Enemy: Health Care Provider Knowledge of Computed Tomography Radiation Dose and Associated Risks

BackgroundThere is ionizing radiation and associated risk from many medical imaging examinations, especially computed tomography (CT). Unfortunately, health care providers often have limited knowledge regarding radiation dose levels and potential risk.Research objectivesTo assess knowledge of dose levels and risk among referring physicians, imaging technologists, and radiologists in Saskatoon, Saskatchewan, and to identify potential differences between and within those groups.Materials and methodsA survey was designed and administered to health care professionals.ResultsA total of 308 of 328 surveys were completed (91% response rate). Overall 73% of physicians, 97% of radiologists, and 76% of technologists correctly believed that there is a risk for cancer from an abdomen–pelvic CT scan. Although only 18% of physicians, 28% of radiologists, and 22% of technologists selected the most appropriate estimate of abdominal–pelvic CT dose in terms of chest x-ray equivalents, this is similar to other reported studies. Physicians and technologists who use CT were more likely to select the correct dose than those who do not. Most respondents (91% of physicians, 100% of radiologists, and 100% of technologists) felt that pregnant patients should always be informed about radiation dose as a risk. Although frequency of discussing risk decreased with increasing patient age, technologists were more likely to discuss risk at any age. A total of 93% of respondents expressed interest in receiving dose feedback from medical imaging procedures.ConclusionsRadiologists and technologists generally showed better knowledge than referring physicians. Among physicians and technologists, knowledge was better in those who use CT than those who do not.     

Review of radiation issues for computed tomography.

Over the past three decades, computed tomography (CT) has proven to be central in imaging evaluation. Multidetector technology continues to drive practice patterns by combining fast scanning with high quality data sets. This has resulted in new applications as well as improved use in traditional applications. With this recognition has also come the realization that there are potential costs of CT. One major cost is the radiation dose. Therefore, in order to begin to assess benefits (which are relatively familiar to radiologists) versus costs (which are less familiar), the issues related to CT radiation need to be addressed. Familiarity with measures of CT radiation and the actual doses delivered by CT are important issues as they provide a basis for understanding the potential cancer risks from CT radiation. Moreover, these justify development of strategies to minimize radiation dose. Strategies include obtaining only necessary CT examinations and adjusting the examinations based on scan indication, region examined, and patient size. These strategies must also be combined with efforts by manufacturers in development and implementation of technology aimed at radiation dose management, as well as efforts in research, education, and CT standards and regulation. This article reviews the subject of radiation dose with multidetector CT technology, including measures of CT radiation, the dose that can result from CT examinations, the risks of this amount of radiation, and strategies for minimizing CT radiation dose.     

Model-based Iterative Reconstruction: A Promising Algorithm for Today's Computed Tomography Imaging

Because of its fast image acquisition and the rich diagnostic information it provides, computed tomography (CT) has gradually become a popular imaging modality among clinicians. Because CT scanners emit x-rays, the increased use of CT in clinical applications inevitably leads to increased medical radiation dose to the population. Because of the well-known cancer-inducing effects of high dose x-ray radiation, this increased dose has caused concerns among policy makers and general public that CT patients may be at a higher risk of developing cancer. Over the years, CT manufacturers have developed a variety of strategies to address this issue, the latest being a model-based iterative reconstruction (MBIR) algorithm. MBIR is an advanced CT algorithm that incorporates modeling of several key parameters that were omitted in earlier algorithms to reduce computational requirement and speed up scans. This review article examines the latest literature in the clinical CT field and discusses the general principles of MBIR, its dose and noise reduction potentials, its imaging characteristics, and its limitations. MBIR algorithm and its application in today's CT imaging will greatly reduce the radiation dose to patients and improve image quality for clinicians.     

Incidental findings detection using low tube potential for CT pulmonary angiography

While lowering the radiation dose using a reduced tube potential (kVp) strategy for CT pulmonary angiography (CTPA) maintains accuracy for pulmonary embolism detection, there is no data regarding the effect of increased noise from lower kVp on both the accuracy of lung and mediastinum lesion detection in the same patient cohort. This study compares the accuracy and diagnostic confidence of lung nodules and enlarged mediastinal lymph nodes detection between low and standard kVp CTPA. The study cohort included 272 CTPA studies acquired at low kVp and 274 studies at standard kVp. Each patient had a routine chest CT acquired within 60 days of the CTPA that served as a reference standard for lung and mediastinum lesions. In additional to the evaluation of image quality, two radiologists independently interpreted lung nodules and mediastinal lymph nodes on CTPA and recorded confidence level for each interpretation. Multivariate models assessed effect of kVp settings on diagnostic accuracy and confidence level in interpretation. Low kVp CTPAs had higher image noise. A significant decrease in the confidence levels for evaluation of mediastinal lymph nodes was observed at low kVp by one of two readers, although there was no significant correlation between accuracy of interpretation and kVp settings for lung and mediastinum lesion detection (adjusted odds ratios = 0.67–1.22, p values >0.2). While increased image noise may decrease the diagnostic confidence of the radiologist, the detection of lung nodules and enlarged mediastinal lymph nodes was not compromised. Referring clinicians can expect that lower radiation dose CTPA answers questions related to lungs and mediastinum.     

体型特异性剂量估计的最新概念及临床应用

CT检查时设置扫描参数的原则是在得到临床诊断可接受的图像质量的前提下,尽可能降低辐射剂量。而患者所接受的辐射剂量,不仅与CT设备的输出剂量有关,也与患者本身体型相关。现有的CT设备提供的辐射剂量信息,如容积CT剂量指数（CTDI_vol）,是基于固定大小聚甲基丙烯酸甲酯模型测量所得,并未考虑到患者的不同体型信息。美国医学物理师学会（AAPM）在204和220报告中提出了一种新的患者辐射剂量估算方法——体型特异性剂量估计（SSDE）,综合考虑了CT辐射输出量和患者体型信息,能准确评估患者辐射剂量。本文对SSDE的最新概念和临床应用进展进行综述。     

Maximizing dose reductions with cardiac CT

Multidetector computed tomography has come a long way in a short time, quickly becoming a standard tool in the cardiac imaging armamentarium. The promise of plaque imaging, combined with both anatomical visualization and stenosis detection, has made this a preferred first line test of many cardiologists and radiologists. This test is well suited to rule out coronary artery disease (obstruction) and still diagnosing subclinical plaque, with may be a good target for anti-atherosclerotic therapies. There has been recent criticism against CT imaging, and cardiac CT specifically, due to the high radiation doses that being employed. New advances have allowed for dramatic dose reductions. These include more routinely performed methods such as dose modulation, and newer methods such as prospective gating or minimizing the field of view. This paper will review the different applications to reduce cardiac CT radiation doses to nominal levels, potentially expanding the applications of cardiac CT by removing one of the biggest barriers.     

Maximizing dose reductions with cardiac CT

Multidetector computed tomography has come a long way in a short time, quickly becoming a standard tool in the cardiac imaging armamentarium. The promise of plaque imaging, combined with both anatomical visualization and stenosis detection, has made this a preferred first line test of many cardiologists and radiologists. This test is well suited to rule out coronary artery disease (obstruction) and still diagnosing subclinical plaque, with may be a good target for anti-atherosclerotic therapies. There has been recent criticism against CT imaging, and cardiac CT specifically, due to the high radiation doses that being employed. New advances have allowed for dramatic dose reductions. These include more routinely performed methods such as dose modulation, and newer methods such as prospective gating or minimizing the field of view. This paper will review the different applications to reduce cardiac CT radiation doses to nominal levels, potentially expanding the applications of cardiac CT by removing one of the biggest barriers.     

The reliability of CT numbers as absolute values for diagnostic scanning,dental imaging,and radiation therapy simulation: A narrative review

Background and purposeThe purpose of this review was to examine the reported factors that affect the reliability of Computed Tomography (CT) numbers and their impact on clinical applications in diagnostic scanning, dental imaging, and radiation therapy dose calculation.MethodsA comprehensive search of the literature was conducted using Medline (PubMed), Google Scholar, and Ovid databases which were searched using the keywords CT number variability, CT number accuracy and uniformity, tube voltage, patient positioning, patient off-centring, and size dependence. A narrative summary was used to compile the findings under the overarching theme.DiscussionA total of 47 articles were identified to address the aim of this review. There is clear evidence that CT numbers are highly dependent on the energy level applied based on the effective atomic number of the scanned tissue. Furthermore, body size and anatomical location have also indicated an influence on measured CT numbers, especially for high-density materials such as bone tissue and dental implants. Patient off-centring was reported during CT imaging, affecting dose and CT number reliability, which was demonstrated to be dependent on the shaping filter size.ConclusionCT number accuracy for all energy levels, body sizes, anatomical locations, and degrees of patient off-centring is observed to be a variable under certain common conditions. This has significant implications for several clinical applications. It is crucial for those involved in CT imaging to understand the limitations of their CT system to ensure radiologists and operators avoid potential pitfalls associated with using CT numbers as absolute values for diagnostic scanning, dental imaging, and radiation therapy dose calculation.     

Reducing Radiation Exposure from Cardiovascular Imaging Through Implementation of Appropriate Use Criteria

Cardiac imaging is a key instrument in the evaluation of patients with known or suspected coronary artery disease. Although clear benefits accompany the use of nuclear cardiology and cardiac CT techniques, is well-documented in the medical literature, there is growing concern about the risk related to exposure to ionizing radiation. Although the true impact of low-level ionizing radiation is often poorly characterized, clinicians and medical organizations encourage minimization of exposure, with a focus on a balance between benefits and risks of cardiac imaging procedures. The appropriate use criteria (AUC), developed by the American College of Cardiology Foundation, American Heart Association, and multiple other societies, provide guidance regarding test utilization and assist in optimizing an approach involving the right test for the right patient at the right time. By reducing inappropriate use of cardiac CT and radionuclide imaging, exposure to unnecessary ionizing radiation may be minimized. Evaluation of appropriateness allows for practitioners to monitor their performance and serves to provide focus for educational efforts related to inappropriate test indications. Several key areas, including test layering and the use of serial imaging in asymptomatic patients likely contribute to inappropriate use and increased radiation exposure. Therefore, the use of AUC, in conjunction with other radiation dose reduction efforts, promotes significant improvement in patient safety.     

Drug-Assisted Intubation in the Prehospital Setting (Resource Document to NAEMSP Position Statement)

We report an emergency medical services (EMS) case of self-limited torsade de pointes after administration of droperidol for nausea andvomiting in a patient with potential predisposing factors for the development of prolonged QT interval. Despite the reported association with torsade de pointes, many clinicians still consider droperidol to be a safe medication. Rare cardiac side effects may be avoided by reviewing risk factors for prolonged QT interval in individual patients prior to administering droperidol     

Prevention of radiation damage in interventional radiology (IVR)

With the development of interventional radiology, radiation protection has become increasingly important for both patients and medical staff in interventional radiology. Sometimes, long fluoroscopy times and repeated angiography lead to higher radiation doses, limited to a small area of the patient's skin surface. This becomes the potential for deterministic effects of the skin and also may lead to an increased risk of stochastic effects. The entrance skin dose and effective dose can be deduced from the dose area product. It should be noted that minimizing patient dose leads to reduction of staff dose. Here we briefly explain radiation protection in interventional radiology.     

Techniques and parameters for estimating radiation exposure and dose in cardiac computed tomography

With increasing clinical use of cardiac CT imaging it is important that all health care providers referring for or administering such examinations are familiar with the concepts and values of radiation dosimetry in CT as well as with the basic principles of radiation protection. There are important technical differences pertinent to radiation dose between the CT scanner types that are currently being used for imaging of the heart and coronary arteries. As a result of these differences, the radiation dose typically is higher when a cardiac examination is performed with multidetector-row CT (MDCT) than when it is performed with electron beam CT. Several techniques have been described to reduce radiation dose of MDCT imaging by varying the X-ray tube current during a CT examination. The volume computed tomographic dose index (CTDI_vol), the dose length product (DLP), and the effective dose (E) are the most useful parameters to describe and compare radiation doses received from cardiac CT examinations. When comparing radiation doses between scanning protocols and scanner types, the degree of image noise must be considered. Diagnostic, rather than aesthetic, quality of images should be the most important factor guiding the development of scanning protocols for cardiac CT imaging. Cardiac CT examinations should be ordered only by qualified health care providers, and the ordering clinicians should be aware of their responsibility of weighing risks of the radiation exposure against the expected benefits.     

Coronary CT angiography in emergency department patients with acute chest pain: triple rule-out protocol versus dedicated coronary CT angiography

Immediate coronary catheterization is mandatory for high risk patients with typical chest pain in the emergency department (ED). In contrast, in ED patients with acute chest pain but low to intermediate risk, traditional management protocol includes serial ECG, cardiac troponins and radionuclide perfusion imaging. However, this protocol is time-consuming and expensive, and definite treatment of unstable angina is often delayed. Due to advances of multi-detector CT (MDCT) technology, dedicated coronary CT angiography provides the potential to rapidly and reliably diagnose or exclude acute coronary syndrome in ED patients with acute chest pain. Moreover, major life-threatening causes of ED chest pain (i.e., acute aortic syndrome and pulmonary embolism as well as acute coronary syndrome) can simultaneously be assessed by the so-called “triple rule-out” protocol with a single scan. In ED patients with atypical chest pain and low to intermediate risk, the triple rule-out protocol may be preferred, especially in older patients who have relatively lower risk of lifelong radiation-induced cancer. However, the increased radiation dose resulting from the extended volume coverage with this protocol should be fully considered prior to performing this protocol. Therefore, in ED patients who have a low clinical suspicion of pulmonary embolism and acute aortic syndrome, especially younger patients, dedicated coronary CT angiography accompanied by modifications to reduce radiation dose is recommended.     

Cumulative ionizing radiation exposure in patients with end stage kidney disease: a 6-year retrospective analysis

Objective

To quantify cumulative exposure to ionizing radiation in patients with end stage kidney disease (ESKD). To investigate factors which may be independently associated with risk of high cumulative effective dose (CED).

Materials and methods

The study had local institutional review board ethical approval. We conducted a retrospective study of 394 period prevalent ESKD patients attending a single tertiary referral centre between 2004 and 2009. Patient demographics were obtained from case records. Details of radiological investigations were obtained from the institutional radiology computerized database. CED was calculated using standard procedure specific radiation levels. High exposure was defined as CED?>?50?mSv, an exposure which has been reported to increase cancer mortality by 5%. Data were compared using Pearson χ² and Mann–Whitney U test or Kruskal–Wallis tests.

Results

394 patients were followed for a median of 4?years (1518 patient years follow-up). Of these 63% were male. Seventeen percent of patients had a CED of >50?mSv. Computed tomography (CT) accounted for 9% of total radiological studies/procedures while contributing 61.4% of total study dose. Median cumulative dose and median dose per patient year were significantly higher in the hemodialysis (HD) group (15.13 and 5.79?mSv, respectively) compared to the post-transplant group (2.9 and 0.52?mSv, respectively) (P?Conclusion ESKD patients are at risk of cumulative exposure to significant levels of diagnostic radiation. The majority of this exposure is imparted as a result of CT examinations to patients in the HD group.     

Medical and occupational radiation exposure: present situation and countermeasures

This paper describes the present status and countermeasures for patient dose and occupational exposure in Japan. The patient radiation dose resulting from a large number of diagnostic radiological procedures presents no substantial risk(deterministic and stochastic effects). Nevertheless, some procedures (e.g., interventional radiology: IVR) carry a risk of deterministic effects, such as skin injury. The regulatory dose limit of the occupational dose for most medical workers was not exceeded. Nevertheless, radiation injuries, such as cataracts, to physicians performing IVR have been reported recently, although not many cases. When radiation protection/optimization issues are addressed adequately, medical exposure will decrease without decreasing the diagnostic benefit to the patient. Consequently, decreasing the patient dose will also decrease occupational exposure.     

Dose reduction methods for CT colonography

Patients, referring physicians, the media, and government agencies have all expressed concern over the risks of medical radiation, particularly as it relates to CT. This concern is particularly paramount when associated with a screening examination such as CT colonography. These theoretical risks must be weighed realistically against the substantial benefits of colon cancer screening as well as against the risks inherent in the major alternative screening option, optical colonoscopy. When put into perspective, the risk–benefit ratio is highly in favor of the performance of CT colonography. Nevertheless, in following the ALARA principle, there is an ever increasing armamentarium of options that can be employed in the pursuit of CT radiation dose reduction, all of which can be used in many synergistic combinations allowing for dose reduction while simultaneously preserving image quality and minimizing image noise. After a brief tutorial on estimating radiation dose, various strategies will be discussed including reductions in tube current and tube voltage as well as the use of automatic dose modulation and iterative reconstruction. Other practical considerations will also be reviewed including proper patient isocentering, optimization of colonic insufflation to minimize additional decubitus scans, proper choice of scan volumes to avoid overranging, and variation of slice thickness and window width to minimize perceived image noise. Finally, a strategy for how to incrementally introduce these methods as well as a way to compare dose reduction efforts across institutions throughout the country will be offered.     

Eye Lens Radiation Doses to Miscentering Patients and Health-Care Staff From Head Computed Tomography

The purposes of this study were to assess the effect of patient vertical miscentering on eye lens radiation doses in patients who have undergone head computed tomography (CT) and to measure the absorbed dose to the eye lens in health-care staff who remain in the CT room during the procedure. All measurements were performed in phantoms. Nanodot™ optically stimulated luminescence dosimeters were used to measure radiation doses. For the assessment of the effect of patient vertical miscentering, CT scans were obtained at six different table heights. The radiation doses in the eye lens of health-care staff received when working at three different locations in the CT room were measured. Correction coefficients were applied to determine equivalent dose, Hp(3), in the eye lens. The results revealed that the positioning of patients off the CT scan isocenter during head CT may result in a significantly increased eye lens dose. The phantom eye lens doses can be increased by 43.7% (70 mGy), and image noise increased when the table was 5 cm below the isocenter due to the effect of the bow tie filter and eyes being irradiated directly by the primary beam for a greater proportion of the tube rotation. An estimated eye lens dose of ≤0.1-0.2 mSv was found in phantoms simulating health-care staff, with the dose depending on positioning of the phantom. Health-care staff in the room during CT scans are at risk of a significant eye lens dose, particularly if positioned posterior to the gantry.     

Blunt trauma to the carotid arteries

Carotid artery dissection is a rare occurrence in the trauma patient. Two cases of blunt trauma resulting in carotid artery dissection are reported. Initial recognition by clinicians is often difficult because of the diverse clinical manifestations, the delay in presentation, and the associated multi-organ system injuries that accompany carotid artery dissection. Because the diagnosis of carotid injury is rarely suspected in patients with neurological deficits, the first diagnostic test performed is usually computed tomography (CT) of the head. Angiography should be strongly considered when the following occur: (a) Neurologic deficits are incompatible with CT findings; (b) there is monoparesis or hemiparesis with a normal mental status examination; (c) there is severe cervical trauma with an abnormal neurological exam; or (d) a basilar skull fracture is present in a patient with an abnormal mental status exam. Once diagnosed, the management of carotid artery dissection is complex and no generalized guidelines have been established.     

Low kVp imaging for dose reduction in dual-source cardiac CT

With the widespread application of cardiac CT has come increasing concern over the effects of radiation dose associated with this exam. Dual source CT provides a number of methods for dose reduction in helical ECG-gated cardiac CT studies. This article discusses several of these methods, with a particular emphasis on low kVp scanning, which can be applied in a large percentage of patients.