Ct scans are generally used for studying the chest, abdomen and. Basic principles of computed tomography physics and. Takes longer to acquire a scan than ct, more susceptible to patient motion ct mri pet. Department of radiation therapy and medical physics, hartford hospital, hartford, connecticut. The principle mathematical basis behind this technology had already been published in 1917 by j. By using sliceimaging techniques tomography, selective.
It commences with a chapter on a radionuclide radiologists perspective about the use of petct in his medical practice. First, ct forms a crosssectional image, eliminating the superimposition of structures that occurs in plane film imaging because of compression of 3d body structures onto the twodimensional. Welcome to part 2 in my series of the physics of medical imaging. This chapter focuses on the techniques of ct imaging and covers 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. 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. Ct ct computed tomography cat scan computerized axial tomography 632014 hareesha n g, dept of aero engg, dsce 14. The aapmrsna physics tutorial for residents radiographics.
A reconstruction made from projections at neighboring scan axis positions in helical ct, the scanner never images a single slice. 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. Several ctspecific dose descriptors have been developed. Figures are from the textbook except otherwise noted. However, this comes at a disadvantage as information in the gaps between helices is lost. This book has been designed as a primer which gives a practical insight into the principles and practice of computed tomography for radiology residents and technicians. Medical imaging is a collection of technologies, all having the purpose of visualization of the interior of the intact, living human body for the purpose of diagnosis.
Scanning methods digital projection ap, pa, lat or oblique projection surview, scanogram conventional ct axial startstop volumetric ct helical or spiral ct continuous acquisition. The physics of computed tomography university of windsor. The present book will try to explain the physical principle behind each of these imaging modalities, together with a description of how these are implemented. 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.
Therefore, quantitative imaging in computed tomography requires special attention and often additional calibrations of the ct scanners are needed. Computed tomography, more commonly known as a ct or cat scan, is a diagnostic medical imaging test. 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 is an illustration of a patient moving into the bore of a ct scanner. Physics of mri yao wang polytechnic university, brooklyn, ny 11201. Free radiology books download ebooks online textbooks. 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. This book addresses the aart examination content areas directly related to physics, the material that gives most students the greatest dif. A computer program then computes the brightness of each pixel from all of these separate recordings. Physics of imaging systems basic principles of magnetic. Physics of imaging systems basic principles of magnetic resonance imaging ii. Xray computed tomography university of toronto physics. Compare the ct scan to xrays to show ct scan s ability to take pictures of the bodys soft tissues, like the brain. Since its introduction in 1972, xray computed tomography ct has evolved into an essential diagnostic imaging tool for a continually increas ing variety of.
Introduction to ct physics image generation what is computed tomography ct. 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. In the medical community they simply call them ct scans, because axial, as youll find out, is unnecessary in the title. Explain the application of ct for pet image fusion and attenuation. Discuss difficulties and limitations when applying ct attenuation maps to pet acquisitions. The application of physics to medical imaging is a part of the field of medical physics. The advantage of helical ct is that it is much faster than the stepandshoot procedure since the entire scan is acquired in one fluid motion. Compared to ct and mr images, pet images appear much blurrier and or noisier, due to the relatively limited number of photons that can be collected during an imaging study. Compare the ct scan to xrays to show ct scans ability to take pictures of the bodys soft tissues, like the brain. It differs from conventional projection in two significant ways. May 21, 2012 a basic description of the mechanism of ct computed tomography scans for medical use in remote sensing. 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.
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. This extremely small wavelength indicates that the xrays have a much higher energy than visible light. Whiting introduction slightly more than three decades old, computed tomography ct continues to advance rapidly in both imaging performance and widening clinical applications. Introduced in the early 1970s, ct scanning gained rapid acceptance in clinics and hospitals. Links, medical imaging signals and systems, and lecture notes by prince. Slices in helical ct are reconstructed by using interpolated data from two projections 180 degrees apart.
Xrays are a form of light with a wavelength in the range of 0. Jan 11, 2016 tomographic reconstruction tiiln ii t0 t 0t. Ct mri ct transmission tomography mri direct tomography xray tube. History 1924 mathematical theory of tomographic image reconstructions johann radon 1930 conventional tomography a. This webinar course will provide an opportunity for medical physicists to increase their understanding of computed tomography, advanced features of scanners, and of the accreditation process. It also presents some recent advances, such as 3d scans and timedependent imaging. It goes on to cover axial versus helical imaging, multiple detector row ct, ct image contrast, slice thickness, isotropic voxels and reconstructions, cone beam. Find out how computed tomography ct scans work and how they have been improved since the midseventies. 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 scan s ability to take pictures of the bodys soft tissue like the brain or organs. A single 360degree rotation of the tube is shaded in red. The abr requires each diplomat to attain at least 75.
As one progresses through the chapter, more detail regarding the ct technique and methodology is meet. Any ctdivol values that are outside these ranges should be evaluated to determine if the exposure to the. In addition, detector resolution is poorer due to the detector physics. The aapm first addressed performance testing of ct systems with the publication of aapm report no. Factors that affect radiation dose from ct include the beam energy, tube currenttime product, pitch, collimation, patient. Xray computed tomography ct has experienced tremendous growth in recent years, in terms of both basic technology and new clinical applications. Ct imaging information sheet risks associated with diagnostic imaging using computerized tomography ct howard dickson health physics society specialists in radiation safety a ct scanalso called computerized tomography or just ctis an xray technique that produces images of your body to visualize internal structures in. It examines image display from traditional methods through the most recent. Manufacturerspecific information on scanner features will be presented. Basic principles of computed tomography physics and technical. Basic principles of computed tomography physics and technical considerations kyongtae t.
For example, ct has become a useful screening tool for detecting possible tumors or lesions within the abdomen. 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. Physics of mri yao wang polytechnic university, brooklyn, ny 11201 based on j. This article explains how computed tomography ct scans have been recently developed and improved. Physics of computed tomography scanning sciencedirect. The ct scan format consists of many cells,each assigned a no.
Ct uses xrays to generate crosssectional, twodimensional images. A basic description of the mechanism of ct computed tomography scans for medical use in remote sensing. Lothar schad 1292008 page 1 physics of imaging systems roe, ct, mri. Ct is fundamentally a method for acquiring and reconstructing an image of a thin cross section of an object, 1, 3. Annual safety training expected or typical ct dose levels. Ct computed tomography scans a level physics youtube. 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. 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. Medical physicists work closely with medical doctors and are found in.
Basic principles of ct scanners and image reconstruction indico. Since the introduction of computed tomography in the 70s, there has been tremendous changes in the way ct is performed resulting in a broad positive impact on patient management. A ct scan of the heart may be ordered when various types of heart disease or abnormalities are suspected. Xray computed tomography mathematics and physics of. Xray ct scanners can easily resolve points less than 1 mm in size, while pet scanners cannot reliably. In this paper, we study the scan and reconstruction principles of the multi.
Sep 09, 2010 welcome to part 2 in my series of the physics of medical imaging. Ct was introduced into clinical practice into 1971 with a scan of a cystic. Ct scanner uses a motorized xray source that rotates around the circular opening of a donutshaped structure called a gantry. Physics of imaging systems basic principles of magnetic resonance imaging ii prof. Additionally, the case explanations are easy to understand no matter your understanding of basic physics. Ct imaging information sheet health physics society. It also presents new challenges and new characteristics. Basic principles of ct scanning linkedin slideshare. 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. 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. 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. Mpc has developed the following table of expected ctdivol ranges, based on years of testing hundreds of ct scanners. 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. To truly understand ct scanning, you must first learn about xrays and how they are produced.
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