computed tomography principle

Computed tomography (CT) and magnetic resonance imaging (MRI) are the most widely used cross-sectional imaging methods used in medicine. Five new projects are underway from this new funding opportunity, representing creative, innovative, interdisciplinary approaches that would not have been funded otherwise. Communication theory specifies the fundamental parameters of information transfer as. SPIE Press, 2003 - Technology & Engineering - 387 pages. The power in the beam associated with a particular energy range is fairly constant, because the number of quanta decreases linearly as a function of energy, while the energy of an individual quantum increases linearly. From a set of these measurements, a digital image is calculated to represent the attenuation coefficient of the material in the object. The x-rays from the target are spread over a wide solid angle (essentially a hemisphere). These will be tested using a table top experimental system. Radiologic technologists must understand the technology well enough to optimize dose and image quality and provide excellent patient care. By the mid-1990s, helical scans had become limited in speed because of the mechanical forces associated with subsecond gantry rotation times and the output requirements of x-ray tubes to supply enough flux for adequate signal to noise ratio. To compensate for this effect, a bowtie-shape filter is placed in the beam, which is tapered such that its center is thinner than its edges, to equalize the flux reaching the detectors and minimize patient dose. In the CT acquisition process, the quantity measured is the attenuation of the x-ray beam (just like a projection x-ray), with a continuous physical electrical signal representing x-ray energy flux, converted to a discrete digital value. An image represents a map of some physical quantity, either directly measured or derived from measurements. Basic principles of computed tomography. In a single rotation, the region of interest (ROI) is scanned by a cone-shaped x-ray beam around the vertical axis of the patient’s head. In-plane spatial resolution is usually expressed in line pairs per millimeter, typically 0.5 to 2 lp/mm for CT. Each time the x-ray source completes one full rotation, the CT computer uses sophisticated mathematical techniques to construct a 2D image slice of the patient. Computed tomography (CT) was created in the early 1970s to overcome many of these limitations (. During conventional x-ray imaging, the exiting x rays interact with a detection device (x-ray film or othe… One of the primary goals of CT manufacturers has been to provide faster scan times and larger scan coverage. For example, to examine the circulatory system, a contrast agent based on iodine is injected into the bloodstream to help illuminate blood vessels. In spiral scanning, the patient table moves continuously, so at any given longitudinal or z-location there are only a few (or no) exactly corresponding gantry measurements that are aligned in the same plane for 2D filtered back projection. The basic principles of CT involve physical mechanisms that are shared with x-ray imaging, plus mathematical techniques that exceed the human visual perception of 2D images. The attenuation of x-rays within an object is governed by interactions on the atomic scale, in which each molecule in the object has some cross section for interacting with each x-ray. The size of this problem is dauntingly large because there are 512 × 512 (i.e., more than one quarter million) variables involved with 768 × 1,400 (i.e., more than one million) measurements, requiring matrix operations that overwhelm even modern computers. Depending on the amount absorbed in a particular tissue such as muscle or lung, a different amount of x rays will pass through and exit the body. Using this principle, CT allows the reconstruction of the density of the body, by two-dimensional section perpendicular to the axis of the acquisition system. Computed tomography (CT) scanners use a rotating X-ray machine to image thin slices of the body to diagnose a wide variety of injuries, abnormalities and diseases. The attenuation of beam energy on passage through physical objects provides a noninvasive means to gather information about the amount and type of material present inside the object. The thickness of the tissue represented in each image slice can vary depending on the CT machine used, but usually ranges from 1-10 millimeters. Fundamental Principles of X-ray Computed Tomography (CT) Tomographic imaging consists of directing X-rays at an object from multiple orientations and measuring the decrease in intensity along a series of linear paths. Because of the increased longitudinal width of the x-ray beam with MDCT, image data measurements no longer correspond to rays orthogonal to the scan axis; thus new reconstruction algorithms are required to maintain image quality and prevent distortions. Abstract. To reduce radiation yet still produce good quality CT images, more sophisticated methods are needed to process the raw data from the CT system. To understand best how to utilize CT technology clinically and appreciate new product capabilities, knowledge of fundamental CT imaging principles is necessary. CT Acquisition Overview. Computed tomography (CT) scans can detect pathology that may be missed on a conventional chest radiograph. In addition, diagnostic tasks that require high image clarity, such as locating a faint tumor, generally require more radiation. The basic process of collecting data in CT is illustrated in Figure 1 … The tube is quickly heated to high temperatures, which must be limited to avoid damage. CBCT VERSUS COMPUTED TOMOGRAPHY CBCT,byvirtueoftheterminology,isaformofcomputedtomography(CT).Inasingle rotation, the region of interest (ROI) is scanned by a cone-shaped x-ray beam around the vertical axis of the patient’s head. Computed tomography (CT) is a relatively mature cross-sectional diagnostic imaging modality in which delineation of anatomy and characterization of disease rely upon differences in the ability of various tissues (modified by administered contrast agents) to attenuate X-ray beams. Working principle Imaging system Fan beam reconstruction. Written to meet the varied requirements of radiography students and practitioners, this two-color text provides comprehensive coverage of the physical principles of CT and its clinical … Digitized information of objects in the ROI such as shape and density is acquired from … This type of test is used to look for possible obstructions in blood vessels, including those in the heart. This course is based on the book Computed Tomography Physical Principles, Clinical Applications, and Quality Control, 4th edition, by Euclid Seeram, PhD, MSc, BSc, FCAMRT (ISBN: 978-0-323-31288-2). Yet a general understanding of the physical principles inherent to both modalities is important not only to optimize their use in practice but also to … At every stage in the design of CT scanners, there are opportunities to make changes that reduce radiation dose. Spatial resolution measures the capability of an imaging system to resolve closely placed objects or to display fine details. The method exploits the principle of the electromagnetic induction: eddy currents are produced in any electrically conducting material that is subjected to an alternating magnetic field, generated … Heat sinks are used to remove heat from the system by convection or water-assisted cooling. This process continues until the desired number of slices is collected. 1977 Apr;7(2):109-27. doi: 10.1016/s0001-2998(77)80013-5. For example, CT has become a useful screening tool for detecting possible tumors or lesions within the abdomen. First, the fundamentals of X-ray physics are covered, with details on generation, propagation and attenuation of X-rays, including a brief introduction to phase-contrast and dark-field imaging. 3 Reviews. In this chapter, the physical and mathematical principles of X-ray computed tomography are summarised. In computer terms, the original measurements may consist of 16-bit data (allowing a range of values spanning a factor of 64,000), whereas the reconstructed images typically are 8- or 12-bit data (a range up to 4,095). A. C. Kak and Malcolm Slaney, Principles of Computerized Tomographic Imaging, Society of Industrial and Applied Mathematics, 2001 Electronic copy ... 4.3 Ultrasonic Computed Tomography Fundamental Considerations ° Ultrasonic Refractive Index Tomography ° Ultrasonic Attenuation Tomography ° Applications 4.4 Magnetic Resonance Imaging 4.5 … Therefore, the beam is filtered by placing material around the x-ray tube to reduce much of the low energy quanta while passing high energy quanta, leading to an optimal image quality/dose tradeoff. To minimize radiation dose and generation of background scatter, the x-ray beam is collimated by an aperture into a thin fan beam. The key idea behind SparseCT is to block most of the X-rays in a CT scan before they reach the patient, but to do so in a way that preserves all the essential image information. The benefits and risks of i.v. In this case, the 360LI and 180LI used in SDCT spiral reconstruction approaches can be directly extended to spiral MDCT. The connected computer processes the image data and produces exact pictures of … Given this small change in the midst of many overlapping body structures, it is clear that projection radiography is limited in its ability to demonstrate anatomic details. Listen to a podcast about the scanner. The filtered back projection process requires that the image data be confined to a single plane. Faster processingJeffrey Fessler, University of Michigan An appreciation of the potential of CT and its limitations can be obtained with an understanding of basic principles of CT operations. CT is based on the fundamental principle that the density of the tissue passed by the x-ray beam can be measured from the calculation of the attenuation coefficient. Traditionally the in-plane spatial resolution has been far better than the longitudinal or cross-plane spatial resolution, but the longitudinal resolution has been significantly improved with MDCT and approaches that of the in-plane resolution. U.S. Department of Health & Human Services, Get the latest public health information from CDC, Get the latest research information from NIH, NIH staff guidance on coronavirus (NIH Only), RADx Tech Programmatic or Technical Inquiries, NIH Intramural Research Program Training Opportunities, NIH Intramural Research Program Career Opportunities, Tissue Engineering and Regenerative Medicine, Design by Biomedical Undergraduate Teams (DEBUT) Challenge. The term computed tomography derives from computed (with computer), tomo (to cut), and graph(y) (pictures). Compression sensing can be likened to filming a movie with a very fast, but low-pixel camera and then using math to convert the image to high-definition quality. Image slices can either be displayed individually or stacked together by the computer to generate a 3D image of the patient that shows the skeleton, organs, and tissues as well as any abnormalities the physician is trying to identify. The purpose of a computed tomography acquisition is to measure x ray transmission through a patient for a large number of views. $108.86. Computed Tomography (CT) Computed Tomography (CT) - Functional Principle Computed tomography (CT) is an advancement of the traditional X-ray imaging. Since its introduction in the mid-1970s, CT scanner … Elegant mathematical analyses exist for describing the effect of sampling rate on signal information. X-ray imaging was the first diagnostic imaging technology, invented immediately after the discovery of x-rays by Roentgen in 1895. Damien Hirst Autopsy with Sliced Human Brain 2004. Electronic amplifiers condition this signal, and an analog-to-digital converter converts it into a digital number. Principles of Computed Tomography and Magnetic Resonance Imaging. Cynthia McCollough, Mayo Clinic The goal of this project is to modify both the hardware and software of modern CT systems so that the device can adapt the shape, position, and intensity of the x-ray beam to the specific imaging scenario. Because the lowest energy quanta are effectively attenuated in the patient, they contribute very little to the measured signal while exposing the patient to radiation dose. History. The image signal can be continuous, as in a screen-film x-ray or 35-mm photograph, or they can be discrete, such as a medical image on a computer monitor. Investigators at New York University School of Medicine, Brigham and Women's Hospital, and Siemens Healthineers are working together to develop a new ultra-low-dose CT technique called SparseCT. A common technical description can be used to describe both the image formation process and the image visualization task. In the late 1980s continuous motion of the patient table was introduced, which allowed faster scan times but required different data handling for image reconstruction (. A CT scan, or computed tomography scan, (formerly known as a computed axial tomography or CAT scan) is a medical imaging procedure that uses computer-processed combinations of many X-ray measurements taken from different angles to produce cross-sectional (tomographic) images (virtual "slices") of specific areas of a scanned object, allowing the user to see inside the object … Typically used in human computed tomography systems.. Cone beam reconstruction. $128.80. However, as in 16-channel MDCT, the total number of detector rows and the z-axis coverage are highly variable among the CT manufacturers. Basic principles of computed axial tomography Semin Nucl Med. What are examples of NIBIB-funded projects using computed tomography? As the x-rays leave the patient, they are picked up by the detectors and transmitted to a computer. Author M M Ter-Pogossian. The raw projection data result in a sinogram (. An integrated approachNorbert Pelc, Stanford Medical School However, CT scans use x-rays, and all x-rays produce ionizing radiation. As a curious consequence of this progress, the very large volume of image data acquired with current scanning techniques poses another challenge for interpretation: how to display very large amounts of information for the interpretation process. The range of signals produced in tomography is large, varying from a scan of air (no attenuation, or 100% transmission) to that of a large patient with metal implants (possible attenuation of 0.0006%), a factor of almost 10. While rotating, it may not wobble more that 0.05 mm. These slices are called tomographic images and contain more detailed information than conventional x-rays. Computed tomography (CT) and magnetic resonance (MR) imaging are significant assets to veterinarians in the pursuit of a diagnosis. A CT scan is particularly useful when imaging complex bone fractures, severely eroded joints, or bone tumors since it usually produces more detail than would be possible with a conventional x-ray. The mathematical process that made CT reconstruction practical is called, Image Reconstruction from Three-Dimensional Projection Data. The goal of this work is to develop resources that enable the research community to easily create and compare new approaches to reducing radiation dose of routine CT scans without compromising diagnostic accuracy. This is a risk that increases with the number of exposures added up over the life of an individual. In discrete, digital systems, the bit depth of the data determines the smallest change recordable, typically 0.02% step (12 bits) in the digital data or 0.4% step (8 bits) for a displayed image. Contrast agents contain substances that are better at stopping x-rays and, thus, are more visible on an x-ray image. Please note: this book has a smaller font size. When a full slice is completed, the image is stored and the motorized bed is moved forward incrementally into the gantry. X-ray computed tomography operates by using an X-ray generator that rotates around the object; X-ray detectors are positioned on the opposite side of the circle from the X-ray source. The amount of radiation required for a CT scan depends on a number of variables, including the size of the patient, the part of the body being scanned, and the diagnostic task at hand.  Mathematically principle of CT was first developed in 1917 by Radon. PMID: 857320 DOI: 10.1016/s0001-2998(77)80013-5 Abstract Computer tomography (CT) is a radiological imaging method which yields transverse tomographic images reflecting with high accuracy the spatial … PRINCIPLE OF COMPUTED TOMOGRAPHY  The internal structure of the object can be reconstructed from multiple projections of the object. In the image display process, signal relates to the intensity of light patterns that a human observer views. Anode targets have been designed to rotate on bearings, spreading out the area that is heated by the beam. These will now be examined in detail. Build the foundation necessary for the practice of CT scanning with Computed Tomography: Physical Principles, Clinical Applications, and Quality Control, 4th Edition. 14. Oral contrast agents, such as barium-based compounds, are used for imaging the digestive system, including the esophagus, stomach, and GI tract. COMPUTED TOMOGRAPHY ACQUISITION SYSTEM COMPONENTS, For medical imaging, x-rays are generated by an x-ray tube. Since its introduction in the mid-1970s, CT scanner technology has undergone a continual improvement in performance, including increases in acquisition speed, amount of information in individual slices, and volume of coverage. Such analysis is used extensively in designing medical imaging systems. In radiography, x-rays illuminate an object, resulting in a two-dimensional (2D) image that is the “shadow” of three-dimensional (3D) structures present in the beam. The projection causes a superposition of internal structures, leading to indeterminacy in the exact relationships, shapes, and relative positions of objects. An x-ray source and a set of detectors rotate around the patient, making measurements of the transmission of x-rays through the body. The cone-beam system is based on a 2D X-ray detector and an … CT scans can diagnose possibly life-threatening conditions such as hemorrhage, blood clots, or cancer.  Proved that image of unknown object could be produced if one had several number of projections throughout the object. CT scans can be used to identify disease or injury within various regions of the body. Marc-André d’Anjou. The next improvement in performance resulted from acquiring measurements at multiple body levels in parallel, using more than one row of detectors at the same time. In-plane and longitudinal resolution depend on different factors. The presence of an additional 2 mm of abnormal structure would change this survival probability to 1.98% (only a 1% difference). CT uses ionizing radiation, or x-rays, coupled with an electronic … Computed Tomography (CT) scan is a type of medical examination that uses X-rays and computer processing to create sectional images of the body to provide more efficient results than X-rays. With helical CT, 3D volumes rather than single sections of data are acquired, necessitating the development of new reconstruction algorithms. Because these changes are inter-related, the goal of this project is to take an integrated approach, exploring approaches such as modifying the photon counting detector (the part of the CT scanner that detects x-rays), dynamic x-ray illumination (adjusting the amount of radiation used throughout the duration of a scan), and image reconstruction methods. The collection of line measurements from different view angles during one revolution of the gantry provides raw projection data prior to reconstructing images. The scanner rotates around the breast, without passing through the chest, thus reducing the radiation that would be delivered to the chest in a conventional CT scanner. Unlike a conventional x-ray—which uses a fixed x-ray tube—a CT scanner uses a motorized x-ray source that rotates around the circular opening of a donut-shaped structure called a gantry. In SDCT, different section widths are obtained by means of adjusting prepatient collimation of the x-ray beam (, When four-channel MDCT scanners were introduced in the late 1990s, three different detector configurations were used by the CT manufacturers: (A) 16 detector rows with a uniform thickness, termed. Based on the advancements over the past six years, the second … Computed Tomography: Principles, Design, Artifacts, and Recent Advances @inproceedings{Hsieh2003ComputedTP, title={Computed Tomography: Principles, Design, Artifacts, and Recent Advances}, author={J. Hsieh}, year={2003} } J. Hsieh; Published 2003; Engineering; Introduction Preliminaries Image Reconstruction Image Presentation Key … In this approach, the x-ray tube produces a broad beam of x-rays, rather than one that is collimated to a narrow slice; by widening the collimation to illuminate multiple rows of detectors, more measurements are acquired from the same tube output. The test has 120 multiple choice and true/false …  Proved that image of unknown object could be produced if one had several number of projections throughout the object. CT images depict tissue densities. The term “computed tomography”, or CT, refers to a computerized x-ray imaging procedure in which a narrow beam of x-rays is aimed at a patient and quickly rotated around the body, producing signals that are processed by the machine’s computer to generate cross-sectional images—or “slices”—of the body. Originally, the gantry was connected by cables to the outside environment and had to change rotation direction at the end of each revolution. In typical clinical operation, an x-ray tube delivers on the order of 2 × 10, Detection of x-rays is accomplished by the use of special materials that convert the high energies (tens of keV) of the x-ray quantum into lower energy forms, such as optical photons or electron-hole pairs, which have energies of a few electron volts. The research leverages patient-specific anatomical models and mathematical models of imaging performance to direct x-rays where they are needed and, consequently, to avoid or to limit x-ray exposure where it is not needed. tomos = slice; graphein = to write definition - imaging of an object by analyzing its slices. X-ray imaging consists of the generation of x-rays, transmission of those x-rays through material objects, and the detection of the beam energy that exits the object. In clinical settings, image quality is frequently determined qualitatively and subjectively. Hardcover. It is assumed that the signal is linear with the physical properties of the displayed object. Two versions of this method are employed. The higher the pitch (i.e., the faster the CT table travels relative to the detector collimation), the more the gantry measurements separate and deviate from the plane. Picture of a CT scout ( scanogram or topogram) as used for planning every scan slice. For this reason, intravenous (IV) contrast agents have been developed that are highly visible in an x-ray or CT scan and are safe to use in patients. X-ray computed tomography (XRCT) became the technique of choice to visualize microstructure of pharmaceutical granules. During a CT scan, the patient lies on a bed that slowly moves through the gantry while the x-ray tube rotates around the patient, shooting narrow beams of x-rays through the body. Please note: this book has a smaller font size, including those in the object the risk developing! To identify disease or abnormalities are suspected mechanical precision and stability electromagnetic energy propagate... Measure x ray transmission through a patient for a large number of views to that of a standard mammogram. Sinogram and image quality is frequently determined qualitatively and subjectively map of some physical quantity either! 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