Ct was introduced into clinical practice into 1971 with a scan of a cystic. Computerized tomography ct is one of the most commonly used tests in neurology and neurosurgery. The ct scan format consists of many cells,each assigned a no. After 30 years this is a mature technology but the accumulation of innovations over the past decades have given it extraordinary capabilities and new applications continue to emerge. May 21, 2012 a basic description of the mechanism of ct computed tomography scans for medical use in remote sensing. Both spect and pet see chapter 6 give information based on. Physics of imaging systems basic principles of magnetic resonance imaging ii. Radiology is often a neglected component of the undergraduate curriculum. Physics of imaging systems basic principles of magnetic resonance imaging ii prof. Suppose our sample slice is divided into the simple 2. 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. It is unfortunate that all the manufacturers do not use the same system. This artifact can be mitigated by using dualenergy ct and reconstructing the image as a virtual monochromatic scan. Several ctspecific dose descriptors have been developed.
Magnetism we exert a couple on the nuclear spin by placing a magnetic field across the sample. Xray computed tomography ct is a medical imaging technique that produces. Conebeam ct image production current conebeam machines scan patients in three possible positions. 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. Xray computed tomography mathematics and physics of. 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. The beam comes out of the gantry, which rotates around the patient. 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. Single photon emission computed tomography mathematics. Magnetic fields and resonance m precession spin if the particle were not spinning, it would align like a compass, but, because of the spin, it precesses instead. A simple example of reconstruction based on data from 4 angles.
T1 weighted image white matter grey matter csf t1s r1s1 4 1 0. Ct computed tomography scans a level physics youtube. Crosssections are reconstructed from measurements of attenuation coefficients of xray beams in the volume of. Computed tomography ct scanning is an extremely common imaging modality in modern medicine. Dual energy ct can simulate a monochromatic xray beam. The crosssectional images generated during a ct scan can be reformatted in. Learn the basics of ct, mri and ultrasound radiology cafe. Pt lies on a moveable treatment table and lasers are used to make sure the patient is in the proper position. Xray computed tomography university of toronto physics. Introduced in the early 1970s, ct scanning gained rapid acceptance in clinics and. Filtered back projection 2 filtered back projection 3 filtered back. Hounsfield units hu ct numbers arbitrary scale based on attenuation with water assigned a ct number of 0 one ct number hu 1 of water attenuation value 0. Simulation of dualenergy ct decomposition and reconstruction in the abdomen.
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. It uses special xray equipment to make crosssectional pictures of your body. Scan an isbn with your phone use the amazon app to scan isbns and compare prices. Ct scan basics introduced in 1974 by sir jeffrey hounsfield. Free radiology books download ebooks online textbooks. A reconstruction made from projections at neighboring scan axis positions in helical ct, the scanner never images a single slice. The more dense a tissue, the more xrays it absorbs. Ct scans are generally used for studying the chest, abdomen and. To understand best how to utilize ct technology clinically and appreciate new product capabilities, knowledge of fundamental ct imaging. Introduction to mri physics slides originally by karla miller, fmrib centre. Richard ernst chemistry high resolution pulsed ft nmr 2002. Practical physics, artifacts, and pitfalls 1st edition. A basic description of the mechanism of ct computed tomography scans for medical use in remote sensing.
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. Ct uses multiple pencil or fan beams of kilovoltage photons that pass through a desired volume from multiple angles usually over 180 degrees. 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. 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. The images reflect functional information about patients similar to that obtained with positron emission tomography pet.
Basic principles of computed tomography physics and technical considerations kyongtae t. 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. A computer program then computes the brightness of each pixel from all of these separate recordings. It commences with a chapter on a radionuclide radiologists perspective about the use of petct in his medical practice. In recent years, mri scans have become increasingly common, as costs decrease. With advancements in technology, it is rapidly replacing many diagnostic radiographic procedures. Ct uses xrays to generate crosssectional, twodimensional images. The methods of simple backprojection and filtered backprojection. The table slowly passes through the center of a large xray machine. In addition, detector resolution is poorer due to the detector physics.
Ct mri ct transmission tomography mri direct tomography xray tube. A heated cathode releases highenergy electrons, which in turn release their energy as xray radiation. In this article, we will outline the basic science behind ct scans, describe the principles of interpretation, and highlight their advantages and. Plain films are given much more importance than crosssectional imaging, and rightly so. Physics of imaging systems basic principles of magnetic. Factors that affect radiation dose from ct include the beam energy, tube currenttime product, pitch, collimation, patient. Xrays pass through tissues and hit a detector on the other side. The focus is on principles of physics, effects of scan parameters on image quality, and optimum radiation dosage. Magnetic resonance imaging mri scanning principles. Since its introduction in 1972, xray computed tomography ct has evolved into an essential diagnostic imaging tool for a continually increas ing variety of. Figure 1 summarizes the relationships among the basic ct parameters. Manual on contrast media reports that studies show the amount of contrast. During a ct scan, the patient lies on a bed that slowly moves through the gantry while the xray tube rotates around the patient, shooting narrow beams of xrays through the body. Kurt wuthrich chemistry 3d molecular structure in solution by nmr 2003.
Ct computed tomography uses xrays to obtain images. Xray ct scanners can easily resolve points less than 1 mm in size, while pet scanners cannot reliably. 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. 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. Computed tomography, more commonly known as a ct or cat scan, is a diagnostic. Xrays are passed through the subject, and a scanning device. Of all the books about computed tomography, this one is the best. Anderson cancer center pure ct information regarding attenuation correction with ct and information regarding how ct is partneredinformation regarding how ct is partnered with pet will be covered later in the workshop axial platforms. Ct revolutionized neurology and neurosurgery in the 1970s enabling visualization of intracranial structures with excellent resolution. Basic principles of ct scanning linkedin slideshare. When placed in an external magnetic field, the spins align with the external field. The skills certificate, computed tomography ct or cat scan is a professional certificate designed for those who are registered radiologic technologists rt and want to continue their education after completing an associate degree or higher in the radiologic sciences.
Since computed tomography ct has entered the industrial environment around thirty year ago, an. There are other causes of streaks and dark bands on ct images. Whiting introduction slightly more than three decades old, computed tomography ct continues to advance rapidly in both imaging performance and widening clinical applications. Written by the chief physicist at johns hopkins university hospital, this easytoread short textbook explains the physics behind multidetector ct technology, particularly newer, more complex technology. 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. Information can be provide in a simple inspection of ferromagnetic materials way. However, it is important for junior doctors to be able to identify certain important pathology on crosssectional imaging, particularly in. An appreciation of the potential of ct and its limitations can be obtained with an. Single photon emission computed tomography spect is a medical imaging technique that is based on conventional nuclear medicine imaging and tomographic reconstruction methods. 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. Rt can be delivered to the tumor from any angle by rotating. 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. Ct scanner uses a motorized xray source that rotates around the circular opening of a donutshaped structure called a gantry. A computerized tomography ct scan combines a series of xray images taken from different angles around your body and uses computer processing to create crosssectional images slices of the bones, blood vessels and soft tissues inside your body.
Sep 09, 2010 welcome to part 2 in my series of the physics of medical imaging. Therefore, quantitative imaging in computed tomography requires special attention and often additional calibrations of the ct scanners are needed. Free radiology books download ebooks online textbooks tutorials. Ct imaging has become a mainstay of medical imaging. In the medical community they simply call them ct scans, because axial, as youll find out, is unnecessary in the title. Felix bloch and edward mills purcell physics basic science of nmr phenomenon 1991. An appreciation of the potential of ct and its limitations can be obtained with an understanding of basic. 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. 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. Linac1 conformal treatment blocks placed in the head of the machine multileaf collimator that is incorporated into the head of the machine. For reconstruction, you can choose a virtual noncontrast image, a noncontrast with iodine overlay in green, or a bone subtraction.
A monochromatic scan would be an xray beam with only one energy thus no possibility of beam hardening. 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. Basic principles of computed tomography physics and technical. The quiz below is designed to help you revise what you know about ct physics and instrumentation. Ct scans allow doctors to see crosssectional ct scan images slices of your body. Visit for more stuff images, videos, lectures, downloads, articles. Introduction to ct physics image generation what is computed tomography ct. Basic principles of ct scanners and image reconstruction indico. Welcome to part 2 in my series of the physics of medical imaging.
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