Xray computed tomography mathematics and physics of. Xray computed tomography ct is a medical imaging technique that produces images of transaxial planes through the human body. Crosssections are reconstructed from measurements of attenuation coefficients of xray beams in the volume of the object studied. The crosssectional images generated during a ct scan can be reformatted in multiple planes. Feb 03, 2015 introduction to the radiation physics and acquisition geometry of computed tomography ct. Note high metabolic activity within the left ventricle black arrowhead. For two objects to be seen as separate the detectors must be able to identify a gap between them. The actual ct scan only takes a couple of seconds, so if there was any pause between scans you have not received any extra radiation exposure. In the medical community they simply call them ct scans, because axial, as youll find out, is unnecessary in the title. The aapmrsna physics tutorial for residents search for isotropic resolution in ct from conventional through multiplerow detector1 mahadevappa mahesh, phd computed tomography ct is a method of acquiring and reconstructing the image of a thin cross section on the basis of measurements of attenuation. Basic principles of computed tomography physics and. There are a lot of mathematical equations and physics involved in fully understanding the process if you are interested in the details, refer to the.
The principle mathematical basis behind this technology had already been published in 1917 by j. Dense objects remove more lower energy photons from the xray beam leaving a higher average energy beam. Introduced in the early 1970s, ct scanning gained rapid acceptance in clinics and hospitals. Physics of mri yao wang polytechnic university, brooklyn, ny 11201 based on j. A basic description of the mechanism of ct computed tomography scans for medical use in remote sensing. Discuss difficulties and limitations when applying ct attenuation maps to pet acquisitions. Resolution is the measure of how far two objects must be apart before they can be seen as separate details in the image. Ct uses xrays to generate crosssectional, twodimensional images. A computer program then computes the brightness of each pixel from all of these separate recordings. 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. We can think of the different dose measurements as a stepwise algorithm, each time adding an.
Since the first ct scanner was developed in 1972 by sir godfrey hounsfield, the modality has become established as an essential radiological technique applicable in a wide range of clinical situations. We can think of the different dose measurements as a stepwise algorithm, each time adding an additional variable into the equation. Welcome to part 2 in my series of the physics of medical imaging. From the aapmrsna physics tutorial at the 2001 rsna scientific assembly. Physics of computed tomography scanning sciencedirect. Ct scans are generally used for studying the chest, abdomen and. Knowledge of the physics and imaging technology involved in the production of ct scans is vitally important for medical imaging specialists. An appreciation of the potential of ct and its limitations can be obtained with an understanding of basic.
Slices in helical ct are reconstructed by using interpolated data from two projections 180 degrees apart. As one progresses through the chapter, more detail regarding the ct technique and methodology is meet. Since the first ct scanner was developed in 1972 by sir godfrey hounsfield. Hence, this section is intended to be a culmination of the sections that precede it. Whiting introduction slightly more than three decades old, computed tomography ct continues to advance rapidly in both imaging performance and widening clinical applications. The image quality is mainly determined by 3 factors. Basic principles of computed tomography physics and technical. A reconstruction made from projections at neighboring scan axis positions in helical ct, the scanner never images a single slice. Therefore, quantitative imaging in computed tomography requires special attention and often additional calibrations of the ct scanners are needed. Basic principles of ct scanners and image reconstruction indico.
Explain the application of ct for pet image fusion and attenuation. Page 1 computed tomography notes, part 2 practical considerations in ct sampling ct the c meaning computed relies on the sampling of projection data for processing on a computer. Xray computed tomography university of toronto physics. Ibasic science 1the physics of petct scannersruth e. Ct computed tomography ct is a technique that uses an xray beam to generate images that have a very good resolution to demon strate anatomy.
The first ct scanner produced images with an 80by80 matrix of 3 mm pixel resolution and required approximately 5 min of scan time per pair of slices. For this reason, ct is sometimes called computed axial tomography cat, although the. Computerised tomography ct is a test that uses xray equipment and computer software to create detailed 2dpictures of the inside of your body. Introduction to magnetic resonance imaging techniques. Instead, the slice is reconstructed by averaging ct projections taken 180 degrees apart which are separated along the scan axis based on the value of the pitch. Frcr physics notes ct imaging this chapter focuses on the techniques of ct imaging and will cover the equipment used to acquire an image, how the image is formed and displayed, the factors affecting the quality of the image and how dose is measured.
Note that the imaged slice is perpendicular to the long axis of the body. It takes images of slices of your body 2d images and then some sophistaicated software can reassemble them into a 3d image in the latest machines. In computed tomography, it is recommended that the number of projections p must be in the same order as the number of rows of pixels in a single projection s 3. Computed tomography notes, part 2 practical considerations in ct. The presentation style, using cases and multiple choice questions, to outline key concepts in practical ct imaging, is spot on with how the abr is beginning to test residents in physics. The dose is not equal across scan plane, it is higher in. Ct uses xrays to generate crosssectional, twodimensional images of the body. 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.
The site contrasts the ct scan to xrays to show ct scans ability to take pictures of the bodys soft tissue like the brain or organs. Pet measures the two annihilation photons that are produced backtoback after positron emission from a radionuclide tagged tracer molecule, which. Even more importantly, a contrast resolution could be achieved that for the first time in radiology permitted the differentiation of soft tissue inside the highly attenuating skull. Jun 11, 2012 a basic description of the mechanism of ct computed tomography scans for medical use in remote sensing. Since computed tomography ct has entered the industrial environment around thirty year ago. It also presents some recent advances, such as 3d scans and timedependent imaging. Links, medical imaging signals and systems, and lecture notes by prince. The teaching medical physics resources are designed for teaching 1416 science using examples from medical physics. On the opposite side of the volume is a dosimeter which measures the amount of ionising radiation reaching it. Lecture notes functional magnetic resonance imaging.
There are a lot of mathematical equations and physics involved in fully understanding the process if you are interested in the details, refer to the references at the end of this presentation andor take the following classes to satisfy your curiosity. Sep 09, 2010 welcome to part 2 in my series of the physics of medical imaging. Interactive study guides, l oads of other practice content in anatomy, physics, patient care and procedures to prepare you for the ct registry exam. My background was in particle physics, so radiation and detectors were familiar concepts but in a different context. The site contrasts the ct scan to xrays to show ct scan s ability to take pictures of the bodys soft tissue like the brain or organs. Find out how computed tomography ct scans work and how they have been improved since the midseventies. In a voxel with average linear attenuation coefficient. The fi rst three sections of this text provide information on physics, patient care, and crosssectional anatomy necessary to understand and carry out ct examination protocols. The hounsfield unit hu scale is a linear transformation of the original linear attenuation coefficient measurement into one in which the radiodensity of distilled water at standard pressure and temperature is defined as zero hounsfield units hu, while the radiodensity of air at stp is defined as hu. The ct scan format consists of many cells,each assigned a no. Computed tomography ct was the first noninvasive radiological method allowing the generation of tomographic images of every part of the human body without superimposition of adjacent structures. When compared with a conventional radiograph, which is an image of many planes superimposed on each other, a ct image exhibits signi. Full content bundle includes open world practice area and full length ct registry mockpractice exams which can be taken infinite times for practice. Ct scanner uses a motorized xray source that rotates around the circular opening of a donutshaped structure called a gantry.
The specifics of ct, mri, and imaging in general were foreign to me. Since the ct scan requires so many xray exposures, the amount of radiation used to make a ct scan is typically greater that used to make a traditional xray. There are 2 kinds of sampling radial sampling along the projection in r and angular sampling q. It commences with a chapter on a radionuclide radiologists perspective about the use of petct in his medical practice. Computed tomography, more commonly known as a ct or cat scan, is a diagnostic. Tomographic imaging, ieee press, 1988 a free pdf copy is available at.
Instead of taking a single xray from a single perspective, a ct scan rotates a point source of xrays around a body to be imaged. The resources consist of six sets of presentations, worksheets and teacher notes that complement the institute of physics 2011 schools lecture from xrays to antimatter. Basic principles of computed tomography physics and technical considerations kyongtae t. Their computer systems integrate the data of the moving individual slices to generate three dimensional volumetric information 3dct scan, in turn viewable from multiple different perspectives on attached ct workstation monitors.
An understanding of the quadrant anatomy allows you to identify relevant pathology. A single 360degree rotation of the tube is shaded in red. A computerized tomography is an xray imaging procedure in which a narrow beam of xrays is aimed at a patient and quickly rotated around the body. This article explains how computed tomography ct scans have been recently developed and improved. Resolution is measured in line pairs per centimeter lpcm i. Christensens book on the physics of diagnostic radiology is, for me, a great primer on how the medical community extracts information from radiological imaging. People who get nervous in small places claustrophobic people with nonmricompatible implants people with metal pieces near. When placed in an external magnetic field, the spins align with the external field. Petct integrated pet with ct in a single unit pet ct has become an established and valued imaging modality in clinical routine. This is an important starting point because it makes a clear statement about how petct is evolving in a particular country with a view to providing a routine service.
Values are number of sections times section width millimeters. Ct uses multiple pencil or fan beams of kilovoltage photons that pass through a desired volume from multiple angles usually over 180 degrees. The other is a csi detector from a third generation scanner. The dose of a ct scan of the chest can vary quite a bit, but usually it is equivalent to between 10 and 100 chest xrays. It is highly recommended that you download and experiment with these programs, which are available at no charge. Abdominal organs can also be categorized as to whether are retroperitoneal. Compare the ct scan to xrays to show ct scans ability to take pictures of the bodys soft tissues, like the brain. Ct imaging increasingly relies on the integration of a variety of knowledge and skills. Ct cat scanningis a noninvasive medical test that helps physicians diagnose and treat medical conditions. Corrections, comments and inspiring questions concerning the text and software are always appreciated. Ct computed tomography scans a level physics teaching. Ct computed tomography scans a level physics youtube. The abdomen can be divided into four quadrants, each containing specific visceral organs.
Physics and imaging methods spect and pet yao wang polytechnic institute of nyu, brooklyn, ny 11201 based on j. Note that the sampling of the 2d fourier space is denser around the. Computed tomography scanning is essentially an extrapolation of the concept of an xray. Introduction to the radiation physics and acquisition geometry of computed tomography ct. A higher average energy of incident beam is interpreted as having passed through a structure that causes less attenuation of the beam and represented as such on the image i. Additionally, the case explanations are easy to understand no matter your understanding of basic physics. Introduction to ct physics image generation what is computed tomography ct. Introduced in the early 1970s, ct scanning gained rapid acceptance in clinics and. The chapter begins with some simple, yet fundamental, concepts regarding computed tomography and the physics and mathematics at the origin of ct. The quiz below is designed to help you revise what you know about ct physics and instrumentation. Positron emission tomography pet offers several unique advantages compared with other imaging modalities.
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