Computed Tomography Image Reconstruction.

Filtered back projection was used in computed tomography (CT) but produced low-dose CT images that were noisy and included artifacts. Iterative reconstruction was introduced, which reduced noise and demonstrated dose reduction; however, reconstruction times were lengthy and noise texture appeared unnatural. Now, artificial intelligence (AI), is being applied to CT image reconstruction. These algorithms are fast and produce images comparable to those produced by iterative reconstruction. This article outlines image reconstruction techniques, including a generalized framework for deep learning. Ethics of AI in radiology also is discussed.

The use of artificial intelligence in computed tomography image reconstruction - A literature review.

BACKGROUND AND PURPOSE: The use of AI in the process of CT image reconstruction may improve image quality of resultant images and therefore facilitate low-dose CT examinations. METHODS: Articles in this review were gathered from multiple databases (Google Scholar, Ovid and Monash University Library Database). A total of 17 articles regarding AI use in CT image reconstruction was reviewed, including 1 white paper from GE Healthcare. RESULTS: DLR algorithms performed better in terms of noise reduction abilities, and image quality preservation at low doses when compared to other reconstruction techniques. CONCLUSION: Further research is required to discuss clinical application and diagnostic accuracy of DLR algorithms, but AI is a promising dose-reduction technique with future computational advances.

Computed Tomography: A Technical Review.

Computed tomography (CT) is a technical and complex diagnostic imaging modality. Radiologic technologists must understand the technology well enough to optimize dose and image quality and provide excellent patient care. This article reviews essential physical principles and technical aspects of CT, including physics related to radiation attenuation and CT numbers along with general technical concepts. In addition, the article reviews multislice CT technology.

Optimizing the Exposure Indicator as a Dose Management Strategy in Computed Radiography.

PURPOSE: To investigate a technique for optimizing radiation dose and image quality for a computed radiography system. METHODS: Entrance skin doses were measured for phantom models of the pelvis and lumbar spine imaged using the vendor's recommended exposure settings (ie, the reference doses) as well as doses above and below the vendor's recommended settings for both body parts. Images were assessed using visual grading analysis (VGA). RESULTS: The phantom dosimetry results revealed strong positive linear relationships between dose and milliampere seconds (mAs), mAs and inverse exposure indicator (EI), and dose and inverse EI for both body parts. The VGA showed that optimized values of 16 mAs/EI = 136 for the anteroposterior (AP) pelvis and 32 mAs/EI = 139 for the AP lumbar spine did not compromise image quality. DISCUSSION: Selecting optimized mAs reduced dose by 36% compared with the vendor's recommended mAs (dose) values. CONCLUSION: Optimizing the mAs and associated EIs can be an effective dose management strategy.

Computed tomography dose optimization.

Use of computed tomography (CT) as a medical diagnostic imaging tool has increased in recent decades because of its technical advances in data acquisition speed and image reconstruction technology. The increased reliance on CT was accompanied by increased patient exposure to ionizing radiation, however, and concerns among radiologic professionals and the public regarding CT dose resulted in increasing attention to dose reduction. Research and education efforts have addressed many of these concerns, and radiologic technologists play a critical role in optimizing image quality and radiation dose in CT for individual patients and for the industry in general.

The New Exposure Indicator for Digital Radiography.

This article describes the essential elements of the new standardized exposure indicator (EI) established by the International Electrotechnical Commission for digital radiography systems. First, a review of the limitations of the narrow exposure latitude of film screen radiography is presented followed by the brief description of two digital radiography systems, a computed radiography system and a flat-panel digital radiography system. These systems feature wide exposure latitude, variable speed class, and image processing to produce images that appear with the same density regardless of the exposure used and a characteristic EI displayed on images to provide the technologist with some indication of the exposure level to the digital detector. The third point described focussed on the major elements of the standardized EI of the IEC and described them with respect to standardization efforts, deviation index, and the target EI (EIT), responsibilities of both the manufacturers and users. This new standardized EI is now proportional to the detector exposure and requires the user to establish EIT values for all examinations in order to ensure optimization of the dose to the patient without compromising the image quality. The values (EI and EIT) can now be used to calculate the DI, which provides immediate feedback to the technologist as to whether the correct exposure was used for the examination. Finally, an insight into optimization research will be presented as a means of illustration of a dose-image quality optimization strategy that can be used to determine EIT values objectively.

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.

Computed Tomography: Physical Principles and Recent Technical Advances.

This Directed Reading article describes the physical principles and instrumentation of computed tomography (CT) and outlines several recent advances in CT technology. First, the history of CT is presented with emphasis on the contributions of two pioneers who earned the Nobel Prize for the development of the first clinically useful CT scanner. Second, the essential physical principles-most notably radiation attenuation, Lambert-Beer's Law-and the calculation of CT numbers using attenuation data are described. The third major topic will focus on CT technology, including a description of the major system components, the evolution of CT data acquisition systems, image reconstruction fundamentals and common digital image postprocessing operations such as windowing and three-dimensional (3D) techniques. The next section of this article addresses the elements of spiral/helical CT principles and technology. The limitations of conventional CT are first presented and provide a motivation for the development of volume CT scanners. Data acquisition, including detector technology and slip-ring technology, is reviewed, followed by a description of image reconstruction basics for multislice CT (MSCT) scanning. In particular, MSCT detector technology, pitch and various advantages are outlined, followed by a discussion of the advantages of MSCT scanning. The final section of this reading reviews the elements of MSCT applications, such as 3D imaging, virtual reality imaging and the basics of cardiac CT imaging. The article concludes with an introduction of the use of CT in other areas, such as radiation therapy and nuclear medicine.

Image Postprocessing in Digital Radiology-A Primer for Technologists.

This article deals with several image postprocessing concepts that are now commonplace in digital imaging in medicine. First, the motivation for the development of digital imaging modalities is described, followed by a rationale for understanding image postprocessing operations that have become common in radiology. Second, the image domain concept is outlined with a focus on the characteristics of a spatial location domain image including the matrix, pixels, and the bit depth. In addition, the transformation of the spatial location domain image into the spatial frequency domain is described. The third topic addresses five classes of image processing algorithms including image restoration, image analysis, image synthesis, image enhancement, and image compression. The article continues with a detailed description of point processing operations as well as local processing operations. The former is discussed in terms of the histogram, look-up table (LUT), and windowing. The latter describes spatial location filtering (convolution) and spatial frequency filtering using high- and low-pass digital filters, followed by a brief description of the unsharp masking technique. The fifth major topic presents essential features of the commercially available image postprocessing tool Photoshop, with applications in medical imaging and an emphasis on how this tool can be used by teachers and students alike in an educational environment. Finally, a technical overview of image compression is reviewed with a discussion of compression ratio and types of image compression techniques. In particular, irreversible compression is outlined briefly, and its effect on the visual quality of images is demonstrated. Furthermore, a statement from the Canadian Association of Radiologists (CAR) on the use of irreversible compression in digital radiology is provided. The article concludes with a summary of image postprocessing as an essential tool for those who work in a digital imaging environment.

Digital image compression.

The purpose of this paper is to describe the essential elements of digital image compression and its use in digital radiology. Additionally, this article is intended to increase the shared knowledge between radiologic technologists and radiologists, equipment vendors and information technology personnel.

Digital image processing.

Digital image processing is now commonplace in radiology, nuclear medicine and sonography. This article outlines underlying principles and concepts of digital image processing. After completing this article, readers should be able to: List the limitations of film-based imaging. Identify major components of a digital imaging system. Describe the history and application areas of digital image processing. Discuss image representation and the fundamentals of digital image processing. Outline digital image processing techniques and processing operations used in selected imaging modalities. Explain the basic concepts and visualization tools used in 3-D and virtual reality imaging. Recognize medical imaging informatics as a new area of specialization for radiologic technologists.

Radiation protection

There are few books on radiation protection for radiologic technologists. Several recent issues make the appearance of this text timely: (1) the Committee on Bioeffects of Ionizing Radiation (BEIR) now estimates the risk of radiation injury to the population to be greater than they had previously estimated; (2) current studies are now concerned with the bioeffects of low-level radiation, which is characteristic of diagnostic radiology; (3) based on a close examination of the radiation data on the Hiroshima and Nagasaki atom bomb survivors, the International Commission of Radiological Protection (ICRP) recently revised its recommendations on radiation protection and lowered the annual dose limit to the whole body for radiation workers from 50 mSv to 20 mSv; (4) the introduction of new imaging techniques, such as magnetic resonance imaging (MRI), requires an understanding of the bioeffects of exposure to magnetic fields and radio waves, as well as a thorough knowledge of the safety issues surrounding the use of these techniques to image the human body; and (5) quality control is an effective dose reduction tool and is now considered an essential element of radiation protection programs. Keeping these recent developments in mind, the purpose of this book is to: 1) Provide a current and thorough overview of the bioeffects of radiation. 2) Provide comprehensive coverage of the physical principles and technical aspects of radiation protection in diagnostic radiology. 3) Explore the hazards and safety considerations of MRI. 4) Explain the role of quality assurance/quality control in radiation protection. 5) Describe the recent recommendations and new developments in radiation protection for patients undergoing diagnostic X-ray examinations. 6) Summarize the results of various dose studies in X-ray imaging, including computed tomography and mammography