What is CT simple definition?
A computerized tomography (CT) scan combines a series of X-ray images taken from different angles around your body and uses computer processing to create cross-sectional images (slices) of the bones, blood vessels and soft tissues inside your body.
What is CT principle?
CT uses ionizing radiation, or x-rays, coupled with an electronic detector array to record a pattern of densities and create an image of a “slice” or “cut” of tissue. The x-ray beam rotates around the object within the scanner such that multiple x-ray projections pass through the object (Fig 1).
Why is it called a CT?
CT scans have nothing to do with cats, except that when people talk about them, they usually say "cat scan" instead of "CT scan." CT stands for computed tomography, so you can see why people say "CT." CT scans are a kind of X-ray that gives doctors a much better picture of what's going on inside the body.
What are the 4 types of CT?
CT Scan Brain/ CT Scan Head. CT Scan Chest (CT Scan Lung) CT Scan Neck. CT Scan Pelvis.
How is a CT image formed?
CT images are two-dimensional pictures that represent three-dimensional physical objects. The images are made by converting electrical energy (moving electrons) into X-ray photons, passing the photons through an object, and then converting the measured photons back into electrons.
What are the applications of CT?
CT Scan UsesExamine internal and bone injuries from vehicle accidents or other trauma.Diagnose spinal problems and skeletal injuries.Detect osteoporosis.Detect many different types of cancers and determine the extent (spread) of the tumors.Locate infections.More items...•
How do you read CT?
To read a CT scan, start by noting the shades of white, gray, and black. The white area signals dense tissues like bone, the gray area represents soft tissues and fluids, and the dark gray and black area shows air and fat.
What is full form of CT?
Computed Tomography ScanCT scan / Full name
Who invented CT?
Godfrey HounsfieldGodfrey Hounsfield, a biomedical engineer contributed enormously towards the diagnosis of neurological and other disorders by virtue of his invention of the computed axial tomography scan for which he was awarded the Nobel Prize in 1979.
Why is CT better than MRI?
Both MRIs and CT scans can view internal body structures. However, a CT scan is faster and can provide pictures of tissues, organs, and skeletal structure. An MRI is highly adept at capturing images that help doctors determine if there are abnormal tissues within the body. MRIs are more detailed in their images.
Are there 2 types of CT scans?
The two major types of CT are helical CT and conventional, axial, step-and-shoot CT. Helical CT is most prevalent, but conventional step-and-shoot, axial technique is used for high-resolution CT scanning of the lungs, coronary artery calcium scoring, and prospective ECG-triggered coronary CT angiography.
How many types of CT machines are there?
The commonly available slice counts include 16, 32, 64, 128, 256, and 320-slice CT scanners. When choosing a CT scanner, be sure it is suitable for the studies you want to perform. At the same time, you should have a sufficient budget and be clear on your patient flow targets.
Which detector is used in CT?
The x-ray detector is a major component of a CT scanner that is critical to image formation and has a substantial effect on image quality and radiation dose.
Why CT scan is used?
CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage. CT can also be used for a tissue or fluid biopsy.
What is CT in measurement?
The carat (ct) is a unit of mass equal to 200 mg (0.00705 oz) or 0.00643 troy oz, and is used for measuring gemstones and pearls.
How is CT number calculated?
CT number means the number used to represent the x-ray attenuation associated with each elemental area of the CT image:CTN = k(ux - uw)uwwhere:k = A constant, a normal value of 1,000 when the Houndsfield scale of CT number is used; ux = Linear attenuation coefficient of the material of interest;uw = Linear attenuation ...
What are the basic principles of CT?
The basic principles of CT involve physical mechanisms that are shared with x-ray imaging, plus mathematical techniques that exceed the human visual perception of 2D images. A common technical description can be used to describe both the image formation process and the image visualization task. These will now be examined in detail.
When was CT created?
Computed tomography (CT) was created in the early 1970s to overcome many of these limitations (13). By acquiring multiple x-ray views of an object and performing mathematical operations on digital data, a full 2D section of the object can be reconstructed with exquisite detail of the anatomy present (Fig. 1-1). During the years since its invention, CT technology has undergone continual improvement in performance through refinements in components and innovation in scanning techniques (19). As a result, scan times have dramatically improved, and volume coverage and resolution detail have increased.
What is a single detector row CT?
In single-detector row CT (SDCT), each individual detector row functions as a single unit and provides projection data for a single section per rotation. In SDCT, different section widths are obtained by means of adjusting prepatient collimation of the x-ray beam (Fig. 1-6). In MDCT, the detectors are further divided along the z-axis, allowing simultaneous acquisition of multiple sections per rotation. Thus MDCT provides larger and faster z-axis coverage per rotation with thinner section widths.
Why is the spectrum of an x-ray tube constant?
The power in the beam associated with a particular energy range is fairly constant, because the number of quanta decreases linearly as a function of energy, while the energy of an individual quantum increases linearly.
What is X-ray imaging?
X-ray imaging was the first diagnostic imaging technology , invented immediately after the discovery of x-rays by Roentgen in 1895. X-rays are a form of electromagnetic energy that propagate through space and are absorbed or scattered by interactions with atoms. The attenuation of beam energy on passage through physical objects provides a noninvasive means to gather information about the amount and type of material present inside the object. In radiography, x-rays illuminate an object, resulting in a two-dimensional (2D) image that is the “shadow” of three-dimensional (3D) structures present in the beam. The projection causes a superposition of internal structures, leading to indeterminacy in the exact relationships, shapes, and relative positions of objects. Because of this indeterminacy, radiologists require extensive training and experience to interpret 3D structures from the 2D image data. Furthermore, projection radiographs have very limited ability to differentiate low-contrast differences in tissues.
How has CT technology improved?
Since its introduction in the mid-1970s, CT scanner technology has undergone a continual improvement in performance, including increases in acquisition speed, amount of information in individual slices, and volume of coverage. A graph (Fig. 1-2) of these parameters versus time looks similar to Moore’s Law for computer price-performance, which observes that computer metrics (clock speed, cost of random access memory or magnetic storage, etc.) double every 18 months. In the case of CT technology, the doubling period is approximately 32 months, still an impressive rate. For example, scan time per slice has decreased from 300 seconds in 1972 to 0.005 seconds in 2005. Factors contributing to this remarkable advance include improvements in electronics hardware and development of innovative mechanical scanning configurations.
Why are x-rays so inefficient?
The inefficiency in conversion of electron current into x-rays has been a significant practical limitation in the operation of x-ray imaging equipment. The tube is quickly heated to high temperatures, which must be limited to avoid damage. Anode targets have been designed to rotate on bearings, spreading out the area that is heated by the beam. Heat sinks are used to remove heat from the system by convection or water-assisted cooling.
What is a helical CT?
In helical CT, a single transverse slice represents. A plane through the body perpendicular to the scan axis . A plane through the body oblique to the scan axis. A reconstruction made from projections at neighboring scan axis positions. In helical CT, the scanner never images a single slice.
Why is a retrospective CT low pitch?
Retrospective gated cardiac CT is done with very low pitch because the scanner must acquire images of the entire heart during diastole so it has to cover each point multiple times. Multiplanar reconstructions need relatively closely spaced data, so the higher the pitch the more likely for artifacts to occur.
Does increasing patient size increase or decrease CTDI?
Increasing patient size causes increased dose. Increasing patient size causes decreased dose. Increasing patient size does not change dose. Because of the bowtie filter, and to a lesser extent patient attenuation, larger patients will receive less dose than expected with the same CTDI.
What is the basic principle of computed tomography?
1. PRINCIPLE AND BASIC PHYSICS OF COMPUTED TOMOGRAPHY. 2. INTRODUCTION <ul><li>COMPUTED TOMOGRAPHY is well accepted imaging modality for evaluation of the entire body. </li></ul><ul><li>The images are obtained directly in the axial plane </li></ul><ul><li>of varying tissue thickness with the help of a </li></ul><ul><li>computer.
What is a narrow beam of X-ray scans across a patient in synchrony with a?
4. Basically, a narrow beam of X ray scans across a patient in synchrony with a radiation detector on the opposite side of the patient. The sufficient no. of transmission measurements are taken at different orientation of X ray source & detectors, the distribution of attenuation coefficients within the layer may be determined. By assigning different levels to different attenuation coefficients, an image can be reconstructed with aid of com. that represent various structures with diff attenuation properties.
What is the shadow in a CT?
In CT, the x-ray tube rotates around the “phantom” In this case the x-ray beam is attenuated by the water in the phantom, and therefore “projects” a “shadow” within the detectors…
Does CT have a Compton interaction?
Since CT scanners operate at high x-ray energies, Compton interaction is predominate. The probability of a Compton interaction depends primarily on the density of the tissue.
What is CT based on?
CT is based on the fundamental principle that the density of the tissue passed by the x-ray beam can be measured from the calculation of the attenuation coefficient. Using this principle, CT allows the reconstruction of the density of the body, by two-dimensional section perpendicular to the axis of the acquisition system.
How is an image of an object irradiated by an x-ray reconstructed?
The image of the section of the object irradiated by the x-ray is reconstructed from a large number of measurements of attenuation coefficient. It gathers together all the data coming from the elementary volumes of material through the detectors. Using the computer, it presents the elementary surfaces of the reconstructed image from a projection of the data matrix reconstruction, the tone depending on the attenuation coefficients.
What is the multiplication factor of 1000 used for CT numbers?
CT numbers based on measurements with the EMI scanner invented by Sir Godfrey Hounsfield 6, a Nobel prize winner for his work in 1979, related the linear attenuation coefficient of a localized region with the attenuation coefficient of water, the multiplication factor of 1000 is used for CT number integers.
How does a computer get tomographic images?
In order to obtain tomographic images of the patient from the data in "raw" scan, the computer uses complex mathematical algorithms for image reconstruction.
What is CAT scan?
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 x -rays to build cross-sectional images ("slices") of the body.
Does a CT scanner produce an image?
Unlike x-ray radiography, the detectors of the CT scanner do not produce an image. They measure the transmission of a thin beam (1-10 mm) of x-rays through a full scan of the body. The image of that section is taken from different angles, and this allows to retrieve the information on the depth (in the third dimension).
Is CT proportional to attenuation?
In conclusion, a measurement made by a detector CT is proportional to the sum of the attenuation coefficients.
