The scanner emits xrays towards the patient from a variety of angles and the detectors in the scanner measure the difference between the xrays that are absorbed by the body, and xrays that are transmitted through the body. Here is a description about image acquisition and the image formation processes. Basic principles of ct scanning linkedin slideshare. Ct scans are generally used for studying the chest, abdomen and. A reconstruction made from projections at neighboring scan axis positions in helical ct, the scanner never images a single slice. As one progresses through the chapter, more detail regarding the ct technique and methodology is meet. Ct scans can be used to identify disease or injury within various regions of the body. Principles of ct diagnosis precontrast study postcontrast study change in adjacent structures. Ct scans are created using a series of xrays, which are a form of radiation on the electromagnetic spectrum. A single 360degree rotation of the tube is shaded in red. Sep 09, 2010 welcome to part 2 in my series of the physics of medical imaging. From the above it can be seen that the basic data needed for ct is the intensity. With advancements in technology, it is rapidly replacing many diagnostic radiographic procedures.
Jun, 2016 the basic principle of the ct scanner is the use of a thin, fanshaped xray beam that passes through the body to a detector array, which then measures the degree of the xray transmission. Physical principles and technology of clinical pet imaging. Basic physics of mri nuclei line up with magnetic moments either in a parallel or anti parallel configuration. The intention is to provide a foundation for understanding the application of xray ct in nuclear medicine. Basic principles of computed tomography physics and technical. Knowledge of the basic physics of ultrasound is essential as a foundation for the understanding of the nature and behaviour of ultrasound, the mechanisms by which it interacts with matter, the process of image formation, the choice of imaging parameters. The application of physics to medical imaging is a part of the field of medical physics. Xray computed tomography mathematics and physics of. The combination of pet and ct not only eliminates the requirement to perform a lengthy pet transmission scan, but also provides accurately registered anatomical and functional images.
Introduction to magnetic resonance imaging techniques. The basic principle of the ct scanner is the use of a thin, fanshaped xray beam that passes through the body to a detector array, which then measures the degree of the xray transmission. The ct scan format consists of many cells,each assigned a no. The quiz below is designed to help you revise what you know about ct physics and instrumentation. Xray ct scanners can easily resolve points less than 1 mm in size, while pet scanners cannot reliably. Introduction to mri physics slides originally by karla miller, fmrib centre. Corrections, comments and inspiring questions concerning the text and software are always appreciated.
By using sliceimaging techniques tomography, selective. 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. The physics of computed tomography university of windsor. 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. 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. Early ct scanners acquired images a single slice at a time sequential scanning. Filtered back projection 2 filtered back projection 3 filtered back. In this work, we focus on the work and analytical methods.
Slices in helical ct are reconstructed by using interpolated data from two projections 180 degrees apart. 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. Basic principles of computed tomography physics and technical considerations kyongtae t. Welcome to part 2 in my series of the physics of medical imaging. After relaxation time repeat steps 59 with different g y.
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 basic description of the mechanism of ct computed tomography scans for medical use in remote sensing. 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. A computer program then computes the brightness of each pixel from all of these separate recordings. This is an illustration of a patient moving into the bore of a ct scanner.
Ct mri ct transmission tomography mri direct tomography xray tube. Knowledge of the basic physics of ultrasound is essential as a foundation for the understanding of the nature and behaviour of ultrasound, the mechanisms by which it. This text is dedicated to the basic physics of ultrasonic imaging. Basic physics of nuclear medicinexray ct in nuclear. Aldrich, phd, fccpm t o accurately interpret ultrasound images, a basic understanding of the physical principles involved in ultrasound image generation is essential. Medical physicists work closely with medical doctors and are found in. This video presentation explains the basic principle of ct scan. For example, ct has become a useful screening tool for detecting possible tumors or lesions within the abdomen. The chapter begins with some simple, yet fundamental, concepts regarding computed tomography and the physics and mathematics at the origin of ct. Specific topics discussed are computed tomography, basic prin ciples of ct. Basic interpretation of ct scans most of the ct pictures are nonspecific ct pictures are depending on the density of the structures. And, it is more than just imaging coronary arteries. In the medical community they simply call them ct scans, because axial, as youll find out, is unnecessary in the title.
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. We begin with various scanner designs and will explore a number of computational techniques relevant to this form of imaging. History 1924 mathematical theory of tomographic image. Jul 01, 2005 learning the basic concepts required to understand magnetic resonance mr imaging is a straightforward process.
Basic principles of ct scanners and image reconstruction indico. To truly understand ct scanning, you must first learn about xrays and how they are produced. 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. 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 imaging techniques. 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. It is unfortunate that all the manufacturers do not use the same system. It is highly recommended that you download and experiment with these programs, which are available at no charge. Crosssections are reconstructed from measurements of attenuation coefficients of xray beams in the volume of the object studied. 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. 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. 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.
Magnetic resonance imaging mri basic physics can be described at many different levels, ranging from purely descriptive all the way to quantum mechanics. Here, mri physics is dealt with mostly in a descriptive manner, and simple mathematics are introduced only if necessary. In body tissues more line up in parallel creating a small additional magnetization m in. Physics of imaging systems basic principles of magnetic resonance imaging ii. Scan time with the secondgeneration ct systems using a fanshaped xray. Although often considered a simple bedside technology, these principles can be somewhat complicated.
The basic concepts of diagnostic xray physics made easy lj notes. Although the individual concepts are simple, there are many concepts to learn and retain simultaneously. Computed tomography ct scanning is an extremely common imaging modality in modern medicine. Physics of imaging systems basic principles of magnetic resonance imaging ii prof. May 21, 2012 a basic description of the mechanism of ct computed tomography scans for medical use in remote sensing. However, during the 1980s significant advancements in technology. 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. Introduced in the early 1970s, ct scanning gained rapid acceptance in clinics and. Physics of imaging systems basic principles of magnetic. Mar 18, 2019 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. Slightly more than three decades old, computed tomography ct continues to advance rapidly in both imaging performance and widening. 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. Therefore, quantitative imaging in computed tomography requires special attention and often additional calibrations of the ct scanners are needed. Jun 28, 2014 this video presentation explains the basic principle of ct scan.
This extremely small wavelength indicates that the xrays have a much higher energy than visible light. Additionally, the case explanations are easy to understand no matter your understanding of basic physics. However, pet has the ability to demonstrate abnormal metabolic activity at the molecular level in organs that as yet do not show an abnormal appearance based on morphologic criteria. 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. Figure 1 summarizes the relationships among the basic ct parameters. This chapter provides an overview of the physical aspects of xray ct scanning from a nuclear medicine perspective. When placed in an external magnetic field, the spins align with the external field. Xrays are a form of light with a wavelength in the range of 0. Whiting introduction slightly more than three decades old, computed tomography ct continues to advance rapidly in both imaging performance and widening clinical applications. Basic principles of computed tomography physics and. Ct computed tomography scans a level physics youtube. The methodological basis used for describing 2d and 3d image reconstruction was presented in detail in the work of kak and slantay and rosenfeld and kak.
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