Coronary CT angiography with low radiation dose

With the introduction of 64-slice CT and dual-source CT technology, coronary CT angiography (CCTA) has emerged as a useful diagnostic imaging modality for the noninvasive assessment of coronary heart disease. Recently, the risks associated with ionizing radiation on CT have raised serious concerns. The main concern of exposure to ionizing radiation is the potential risk of cancer. CCTA involves much higher radiation dose with the advances in the spatial and temporal resolution of cardiac CT. Currently, various dose-saving algorithms, such as ECG (electrocardiography)-based dose modulation, reduced tube voltage, and prospective ECG gating, high-pitch helical scanning are available to lower radiation exposure during cardiac CT. Therefore, careful selection of CT scanning protocols is needed to keep the radiation exposure ‘as low as reasonably achievable (ALARA)’. In this review we will discuss the radiation dose safety issues, the measurement of radiation dose and current use of dose-saving techniques in CCTA.     

Advances in deep learning for computed tomography denoising

Computed tomography (CT) has seen a rapid increase in use in recent years. Radiation from CT accounts for a significant proportion of total medical radiation. However, given the known harmful impact of radiation exposure to the human body, the excessive use of CT in medical environments raises concerns. Concerns over increasing CT use and its associated radiation burden have prompted efforts to reduce radiation dose during the procedure. Therefore, low-dose CT has attracted major attention in the radiology, since CT-associated x-ray radiation carries health risks for patients. The reduction of the CT radiation dose, however, compromises the signal-to-noise ratio, which affects image quality and diagnostic performance. Therefore, several denoising methods have been developed and applied to image processing technologies with the goal of reducing image noise. Recently, deep learning applications that improve image quality by reducing the noise and artifacts have become commercially available for diagnostic imaging. Deep learning image reconstruction shows great potential as an advanced reconstruction method to improve the quality of clinical CT images. These improvements can provide significant benefit to patients regardless of their disease, and further advances are expected in the near future.     

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.     

Radiation exposure and dose reduction measures in cardiac CT

Noninvasive visualization of the heart by CT is highly accurate and useful, but its association with ionizing radiation and the potential risk of cancer induction has raised concerns. Dose-saving algorithms, new CT scanners, and scanning techniques have been developed to effectively reduce the amount of radiation exposure without deterioration of image quality. Furthermore, additional strategies for dose reduction can be pursued in daily practice following the ALARA (as low as reasonably achievable) principle. However, there still is a high additional dose-saving potential in a consequent application of dose reduction measures, and we recommend individually adapted scan protocols to obtain cardiac CT studies with optimal diagnostic image quality and lowest possible radiation dose.     

Low Radiation Coronary CT

With the increasing use of coronary computed tomography angiography (CCTA) as a noninvasive tool to evaluate for coronary artery disease, physicians who request, perform, or interpret these studies should be aware of the associated potential risks of ionizing radiation. This article provides an overview of radiation issues in CT, the risks of diagnostic-level ionizing radiation, and strategies that can be adopted to minimize exposure to radiation of patients undergoing CCTA.     

How do radiographic techniques affect image quality and patient doses in CT?

The radiation dose received by patients who undergo CT examinations has become a subject of considerable interest. Adult effective doses for head CT examinations are of the order of 1 to 2 mSv, and for single body examinations, patient doses are typically between 4 and 6 mSv. These doses are high in comparison to most other types of radiological examinations that use ionizing radiation. Patient CT doses may also be compared with natural background (3 mSv/year), dose limits to members of the public (1 mSv/year), and the highest level of occupational exposure, which is about 5 mSv/year. The advent of multi-slice technology will serve to increase CT utilization, as well as individual doses for any given examination. Radiologists are responsible for medical radiation doses to their patients, and it is imperative that they understand the relationship between radiation dose and image quality. In this review, we address the impact that variations in radiographic techniques (ie, selected values of X-ray kVp and mAs) have on patient doses as well as the quality of the resultant CT images.     

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.     

Musings at the beginning of the hyper-CT era

In the past decade, with the introduction and acceptance of helical and multidetector computed tomography (CT), CT has gained ascendancy as the preeminent imaging examination for most abdominal conditions. However, attention must now be directed toward the implications of dose consequent to CT studies. Multidetector CT has resulted in thinner and more slices per region of interest, more extensive studies as adjacent body regions can be assessed in one breath-hold, and more pediatric examinations. Dose per slice is greater with multidetector CT than with single-slice CT, and the number of examinations nationally has risen dramatically. These factors contribute to the radiation burden given to patients and the enhancement of risks for morbidity and mortality later in life.     

Perspective on radiation risk in CT imaging

Awareness of and communication about issues related to radiation dose are beneficial for patients, clinicians, and radiology departments. Initiating and facilitating discussions of the net benefit of CT by enlisting comparisons to more familiar activities, or by conveying that the anticipated radiation dose to an exam is similar to or much less than annual background levels help resolve the concerns of many patients and providers. While radiation risk estimates at the low doses associated with CT contain considerable uncertainty, we choose to err on the side of safety by assuming a small risk exists, even though the risk at these dose levels may be zero. Thus, radiologists should individualize CT scans according to patient size and diagnostic task to ensure that maximum benefit and minimum risk is achieved. However, because the magnitude of net benefit is driven by the potential benefit of a positive exam, radiation dose should not be reduced if doing so may compromise making an accurate diagnosis. The benefits and risks of CT are also highly individualized, and require consideration of many factors by patients, clinicians, and radiologists. Radiologists can assist clinicians and patients with understanding many of these factors, including test performance, potential patient benefit, and estimates of potential risk.     

Multidetector row CT: principles and clinical applications

Multidetector row CT (MDCT) is the latest advancement in CT technology. The use of multiple detector rows allows faster scanning and thinner collimation. These improvements allow routine scans to be performed faster with higher z-axis resolution. New applications can also be developed using this new technology. To fully appreciate the potential of these new MDCT scanners, it is important for the radiologist to be familiar with the scanner design and capabilities. This article reviews the basic principles of MDCT scanners. Scanner/detector design, beam collimation/slice thickness, radiation dose, data manipulation, and display are discussed.     

Perspectives on radiation dose in abdominal imaging

Reported instances of patients’ overexposure to imaging-related radiation have spurred the radiology and medical physics communities to identify and develop methods for decreasing the amount of radiation used to achieve diagnostic-quality images. These initiatives include examining and optimizing conventional CT scanning parameters, introducing innovative scan protocols, and incorporating novel dose reduction technologies. The greatest challenge to effective dose reduction in the abdomen and pelvis remains patient size. Here, we review the state of the art in abdominopelvic CT in both adult and pediatric patients and describe some of our own efforts in dose reduction for these types of examinations.     

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.     

Paediatric magnetic resonance imaging adaptations without the use of sedation or anaesthesia: A narrative review

Magnetic Resonance Imaging (MRI) produces images with high soft tissue contrast without the use of ionising radiation, making it a valuable tool for scanning paediatrics. However, it can be difficult to scan children when they are awake, resulting often in poor image quality scans and necessitating the use of sedation and general anaesthesia (GA). The aim of sedation and anaesthesia is to reduce anxiety and movement during image acquisition, thereby improving compliance and image quality. However, there are adverse risks and costs to their use, leading to the need to consider alternative imaging adaptation methods. This research discussed potential methods of reducing anxiety and improving paediatric compliance during MRI examinations, by assessing their feasibility for use in the clinical setting. The literature suggests that adaption strategies and modification of radiographer techniques were mostly effective in reducing the requirement of sedation/GA.     

Nurses' intervention in specific risk factors in high risk employees. An economic appraisal

1. Occupational health nurses can lower employees' health risks through appropriate screening, education, and monitoring efforts at the worksite. 2. In addition to health promotion as well as benefits education, influencing the demand for health care, creating cost efficient services, and informing employees on how, when, and why to use cost efficient health care services, are the foundations for successful health care cost management. 3. To respond to growing accountability issues, nurses need to quantitatively evaluate the overall impact of their efforts on employees' health status and corporate health care costs. 4. The occupational health nurse can be an effective health care cost manager by using appropriate strategies and resources consistently.     

迭代重建技术在肺部CT的临床应用

多排CT快速发展,在常见多发的肺部疾病诊断及鉴别诊断中应用更加广泛,同时,患者所受的辐射剂量也明显增加。以往降低CT剂量主要通过优化扫描技术参数如调节管电流或管电压、增加螺距、自动曝光控制调节等,随着计算机技术的快速进步,低剂量迭代重建技术已成为肺CT领域新的研究热点,本文就滤波反投影技术与迭代重建技术的利弊及迭代重建算法目前在肺部的临床应用进行综述。     

Prediction of coronary artery plaque progression and potential rupture from 320-detector row prospectively ECG-gated single heart beat CT angiography: Lattice Boltzmann evaluation of endothelial shear stress

Advances in MDCT will extend coronary CTA beyond the morphology data provided by systems that use 64 or fewer detector rows. Newer coronary CTA technology such as prospective ECG-gating will also enable lower dose examinations. Since the current standard of care for coronary diagnoses is catheterization, CT will continue to be benchmarked against catheterization reference points, in particular temporal resolution, spatial resolution, radiation dose, and volume coverage. This article focuses on single heart beat cardiac acquisitions enabled by 320-detector row CT. Imaging with this system can now be performed with patient radiation doses comparable to catheterization. The high image quality, excellent contrast opacification, and absence of stair-step artifact provide the potential to evaluate endothelial shear stress (ESS) noninvasively with CT. Low ESS is known to lead to the development and progression of atherosclerotic plaque culminating in high-risk vulnerable plaque likely to rupture and cause an acute coronary event. The magnitude of local low ESS, in combination with the local remodeling response and the severity of systemic risk factors, determines the natural history of each plaque. This paper describes the steps required to derive an ESS map from 320-detector row CT data using the Lattice Boltzmann method to include the complex geometry of the coronary arterial tree. This approach diminishes the limitations of other computational fluid dynamics methods to properly evaluate multiple coronary arteries, including the complex geometry of coronary bifurcations where lesions tend to develop.     

Radiation dose features and solid cancer induction in pediatric computed tomography

Over the past two decades technical advances and improvements have made computed tomography (CT) a valuable and essential tool in the array of diagnostic imaging modalities. CT uses ionizing radiation (X-rays) which may damage DNA and increase the risk of carcinogenesis. This is especially pertinent in pediatric CT as children are more radiosensitive and have a longer life expectancy than adults. The purpose of this paper is to review and elucidate the potential harmful effects of ionizing radiation in terms of solid cancer induction from pediatric CT scanning. In the light of scientific and technical developments, we will also discuss the possible strategies and ongoing efforts to reduce CT radiation exposure in pediatric patients. In this context, we will not ignore the fact that a well-justified CT scan may exceed its risk and have a favorable impact.     

迭代重建联合低电压技术应用于儿童低剂量CT的进展

CT检查以其快速、简便、无创的特点在临床应用日益广泛,如何降低CT检查的辐射剂量,尤其是降低儿童CT检查的辐射剂量是热点问题。迭代重建技术（IR）可降低儿童CT扫描剂量,联合低电压技术可进一步实现降低辐射剂量。本文对IR联合低电压技术应用于儿童低剂量CT的研究进展进行综述。     

State-of-the-art imaging with 64-channel multidetector CT angiography

During the past decade, computed tomography angiography (CTA) has become a standard noninvasive imaging method for the depiction of vascular anatomy and pathology. The quality and speed of CTA examinations have increased dramatically as CT technology has evolved from single-channel spiral CT systems (circa 1990) to multichannel (4-, 8-, 10-, and 16-slice) spiral CT systems (circa 1998 through 2001). In 2004, 64-slice multichannel CT technology became available in the United States, with the first installation occurring at the Mayo Clinic College of Medicine. We describe our initial experience using this state-of-the art technology, focusing on examinations that illustrate the increased diagnostic resolution of vascular anatomy and pathology, and the effectiveness of 2-and 3-dimensional postprocessing using a 64-channel CT system. Future applications of 64-channel technology for preoperative and postoperative vascular surgery and endovascular techniques are also described.     

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.