Ct imaging system moves around the body part at a fixed location attenuation information obtained in multiple planes reconstruct of this attenuation information into a simple grid. On the basis of both recent literature and our professional experience, we present a set of principles. Computed tomography ct and magnetic resonance imaging mri are the most widely used crosssectional imaging methods used in medicine. The basics of ct ct imaging chain system components acquisition methods image quality applications 632014 hareesha n g, dept of aero engg, dsce 2 3. A ct scan, or computed tomography scan is a medical imaging procedure that uses computerprocessed combinations of many xray measurements taken from different angles to produce crosssectional tomographic images virtual slices of specific areas of a scanned object, allowing the user to see inside the object without cutting. Computerised tomography, ct, is an ideal form of tomography yielding sequence images of thin consecutive slices of the patient and providing the opportunity to localise in three dimensions. Ct images are more detailed than conventional xray images. In this article, we will outline the basic science behind ct scans, describe the principles of interpretation, and highlight their advantages and drawbacks compared to other. Background and terminology the main advantages of ct over conventional radiography are in the elimination of superimposed structures, the ability to differentiate small differences in density of anatomic structures and abnormalities, and the superior quality of the images. An introduction to pet ct imaging1 vibhu kapoor, md barry m. A combination of positron emission tomography pet with 18 flabeled fluoro2deoxyglucose 18 ffdg and computed tomography 18 ffdgpet ct has increasingly become a widely used imaging modality for the diagnosis and management of head and neck cancer.
In medical, it is used to detect the injury in the human brain it is used to detect inner wounds. Inside view of modern ct system, the xray tube is on the top at the 1 oclock position and the arcshaped ct detector is on the bottom at the 7 oclock position. When placed in an external magnetic field, the spins align with the external field. Ideally, the three materials should be sufficiently different as to create a triangle in this plot. This allows extraction of accurate information from pet images. Basic principles and applications of 18ffdgpetct in. The first experimental setup of hounsfield in 1970 worked with the socalled translationrotation principle. A divergent pyrami dal or coneshaped source of ionizing radiation is directed through the middle of the area of interest onto an area xray detector on the opposite side.
The integration of ct scanners in multi modality imaging applications, for example by integration of a ct scanner with a pet scanner or a spect scanner. Computed tomography ct scan is a type of medical examination that uses xrays and computer processing to create sectional images of the body to provide more efficient results than xrays. In addition, positron emitting isotopes that are used in medical imaging c11, n, o15, f18, etc. Ct is based on the fundamental principle that the density of the tissue passed by the xray beam can be measured from the calculation of the attenuation coefficient.
Image slices that ct scans produce can be 2 or 3 dimensional and can reveal abnormal structures or help the physician plan and monitor. A beam of xrays is aimed at the patient and rotated around the body to generate individual slices, which are called tomographic images. Basic principle of mri the hydrogen 1h atom inside body possess spin in the absence of external magnetic field, the spin directions of all atoms are random and cancel each other. Magnetic resonance imaging mri is arguably the most sophisticated imaging method used in clinical medicine. Basic principles of ct scanning ct scanner information. Conventional and spiral ct conventional ct acquires data one slice at a time spiral ct allows data to be acquired while the table translates and the tube rotates continuously. Nov 25, 2014 pet ct has proven useful in the detection of second primary tumors in patients previously treated for hnscc and being watched for recurrence. Feb 26, 2019 computed tomography ct is a noninvasive imaging tool that provides 3dimensional 3d images of the internal organs. Computed tomography ct donut shaped machine uses xray energy and computer generation of images advantages sensitive to slight density difference cross sectional anatomy attenuation. The invention of ct scanner in 1970 was made possible by a previously established insight and development of the dedicated minicomputers. In conclusion, a measurement made by a detector ct is proportional to the sum of. Jul 24, 2018 ct scans produce 2dimensional images of a slice or section of the body, but the data can also be used to construct 3dimensional images.
The xray scanner is contained within the gantry, and rotates out of sight during the procedure. Basic principles of ct scanning linkedin slideshare. With advancements in technology, it is rapidly replacing many diagnostic radiographic procedures. I also hope that this book will bene%t those with no or limited pet ct experience, helping them to start to develop their understanding of the %eld. Computed tomography, more commonly known as a ct or cat scan, is a diagnostic medical imaging test. Todays scanners can image the entire abdomen and pelvis of most adults, making a total of 80 ct images, in less than 30 seconds. This device introduced several innovations now standard in ct table movement through the gantry, gantry angulation, and a laser indicator to position slices as well as a. A ct scan of the heart may be ordered when various types of heart disease or abnormalities are suspected. This information is not meant for those of you who havent still forgotten your high school chemistry and biology. Nucleus spin relative sensitivity gyromagnetic ratio. Alternatively the values may be graphically displayed.
Nibibs 60 seconds of science explains how ct scans work. Mar 27, 2017 how ct scans work using only basic high school mathematics. Thus, there is net magnetization in the direction of externally applied magnetic field. This first article covers the fundamental principles of ct, including the basic geometry of the ct scan process, the nature of the measurements made by ct detectors, a qualitative explanation of the image reconstruction process, the evolution of ct technology the 4 generations of ct from the emi firstgeneration scanner through modern slip.
Basic principles of magnetic resonance 1 introduction the primary purpose of this lecture is to provide an overview of the basic principles involved in the process of obtaining a nuclear magnetic resonance signal. Ct uses multiple pencil or fan beams of kilovoltage photons that pass through a desired volume from multiple angles usually over 180 degrees. Mar 07, 2017 ct images are more detailed than conventional xray images. Multislice scanners projection data from multiple slice is acquired. On the opposite side of the volume is a dosimeter which measures the amount of ionising radiation reaching it. In the medical community they simply call them ct scans, because axial, as youll find out, is unnecessary in the title. Path of the tube forms a helical pattern around the patient c. Basic working principle of magnetic resonance imaging mri. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Unlike conventional, classical tomography, computerised tomography does not suffer from interference from struc. Ct scanner block diagram, working, operation, construction. A ct scan can be compared to looking at one slice of. The working principle of mri by passing an electric current through the wire loops a strong magnetic field is created and protons in the body tend to align themselves along the magnetic field parallel or antiparallel. Basic principles of ct ct imaging system moves around the body part at a fixed location attenuation information obtained in multiple planes.
The ct scanner is the abbreviation of computer tomography scanner. Crosssections are reconstructed from measurements of attenuation coefficients of xray beams in the volume of the object studied. Using this principle, ct allows the reconstruction of the density of the body, by twodimensional section perpendicular to the axis of the acquisition system. Computed tomography ct scanning, also known as, especially in the older literature and textbooks, computerized axial tomography cat scanning, is a diagnostic imaging procedure that uses xrays to build crosssectional images slices of the body. It is hoped that this pet ct book will serve as an invaluable educational tool for all professionals working in pet ct departments and that it will contribute to the quality of their daily work. Linefocus principle the effective focal spot is the beam projected onto the patient. How ct scans work using only basic high school mathematics. The advanced model of ct scanner create image at an angle other than 90 by tilting the gantry.
The amount of detail in the image has increased sixfold since 1970. Basic principles of computed tomography physics and. The principle of this technique is illustrated in figure 3, where the typical ct numbers of three materials of known density are plotted on a graph where the y axis is the ct number at 140 kv and the x axis is the ct number at 80 kv. Xray computed tomography ct has experienced tremendous growth in recent years, in terms of both basic technology and new clinical applications. The crosssectional images generated during a ct scan can be reformatted in multiple planes. An introduction to petct imaging1 vibhu kapoor, md barry m. Magnetic resonance imaging mri scanning principles. In this article, we will outline the basic principles behind mri scans, how to orientate and interpret a scan, and address some of their advantages and. After this, ct was immediately welcomed by the medical community and.
Gantry with rotating tube and detector patient couch or bed. Referral forms and ct scan reports were obtained for 460 mhi patients from a sample of 497 patients, calculated by using the equation for estimating a single proportion from a large. Computed tomography ct scan is a type of medical examination that uses xrays and computer processing to create sectional images of the body to. Basic principles and applications of 18ffdgpetct in oral. A computed tomography ct or cat scan allows doctors to see inside your body. Rf coils gradient coils magnet how these work together will be explained later patient is required to lay as still as. Image slices that ct scans produce can be 2 or 3 dimensional and can reveal.
Basic principles of computed tomography physics and technical. Ct simulator international centre for theoretical physics. As shown in the table, the technology of ct scanners has improved dramatically since the first scanner was introduced. Basic principles of computed tomography physics and technical considerations kyongtae t. Ct is given in the dimensionless unit hounsfield, h named after the nobel prize winner of 1979 godfrey n. To understand the basic principles of ct, one may begin with the operation of this original emi mark i firstgeneration ct scanner. An appreciation of the potential of ct and its limitations can be obtained with an. History 1924 mathematical theory of tomographic image. Ct offers very good contrast of bone to soft tissue and thus can have novel.
It is quite possible to acquire images with an mr scanner without understanding the principles behind it, but choosing the best parameters and methods, and interpreting images and artifacts, requires understanding. Early scanning with pet ct has low sensitivity and specificity because there may be residual viable tumor cells. As the anode angle decreases, the effective focal spot decreases. Ct scans produce 2dimensional images of a slice or section of the body, but the data can also be used to construct 3dimensional images. By passing an electric current through the wire loops a strong magnetic field is created and protons in the body tend to align themselves along the magnetic field parallel or antiparallel. Filtered back projection 2 filtered back projection 3 filtered back projection 4 rebinning fan beam data. The image by the ct scanner is a digital image and consists of a square matrix of elements pixel, each of which represents a voxel volume element of the tissue of the patient. Welcome to part 2 in my series of the physics of medical imaging.
Pet offers quantitative analyses, allowing relative changes over time to be monitored as a disease process evolves or in response to a specific stimulus. The ct number scale has two fixed values independent of photon energy. Computed tomography ct scanning is an extremely common imaging modality in modern medicine. To familiarize the student with ct scanning principles, acquisition and reconstruction. What is the working principle of a current transformer.
The frame holding the xray tube and detector rotate around the patient as the data is gathered. Computed tomography ct is a noninvasive imaging tool that provides 3dimensional 3d images of the internal organs. Definition facts about ctdefinition facts about ct computer tomography ct, originally known as computed axial tomography cat or ct scan and body section rentenography. Only minute amounts of imaging substrate need to be injected tracer principle because of the high sensitivity of pet.
Ct scanner xray modality used to the body in cross section used to determine extent of trauma location and type of tumors status of blood vessels pre surgical planning 632014 hareesha n g, dept of aero engg, dsce 5. The term computed tomography, or ct, refers to a computerized xray imaging procedure in which a narrow beam of xrays is aimed at a patient and quickly rotated around the body, producing signals that are processed by the machines computer to generate crosssectional imagesor slicesof the body. The first waterless fullbody ct scanner was developed and installed by ledley et al. Complex clinical decisions about treatment of oncologic patients are largely guided by imaging. Conebeam ct image production current conebeam machines scan patients in three possible positions. Ct scans are computerized xray imaging procedures used to generate crosssectional images of the body. Therefore, quantitative imaging in computed tomography requires special attention and often additional calibrations of the ct scanners are needed. Introduction to magnetic resonance imaging techniques. This book provides an overview of the evolution of ct, the mathematical and physical aspects of the technology, and the fundamentals of image reconstruction using algorithms. It uses a combination of xrays and a computer to create pictures of your organs, bones, and other tissues. By using sliceimaging techniques tomography, selective. The basic principles of computed tomography and magnetic. Computed tomography ct scan is a medical imaging procedure that uses computerprocessed xrays to produce tomographic images or slices of specific areas o slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising.
The ct scanner computed tomography is an imaging technique that produces crosssectional images, representing in each pixel the local xray attenuation properties of the body. The following lectures will discuss how this signal can be used to generate images that carry information about brain function. Torok, md cancer is one of the leading causes of morbidity and mortality in developed countries such as the united states. Ct scans provide a better image of the lungs and organs in the chest cavity between the lungs. By applying an rotating magnetic field in the direction. In this article, we will outline the basic principles behind mri scans, how to orientate and interpret a scan, and address some of their advantages and disadvantages compared to. Positron emission tomography pet is a technique that measures physiological function by looking at blood flow, metabolism, neurotransmitters, and radiolabelled drugs. Ct uses ionizing radiation, or xrays, coupled with an electronic detector array to record a pattern. Basic principles of ct scanners and image reconstruction. Block diagram of ct scanner operations of ct scanner. Broken bones and vertebrae are more clearly visible on a ct scan. In recent years, mri scans have become increasingly common, as costs decrease. Whiting introduction slightly more than three decades old, computed tomography ct continues to advance rapidly in both imaging performance and widening clinical applications. The term computed tomography derives from computed with computer, tomo to cut, and graphy pictures.