Scan types 1516 conclusion and sign off 16 appendix a contrast media reactions appendix a 111 appendix b i. A ct image is composed of pixels, whose brightness corresponds to the absorption of xrays in a thin rectangular slab of the crosssection, which is called a voxel. Imaging and detectors for medical physics lecture 3. Multislice helical ct imaging systems have multiple detectors in an array up to tens of thousands. Sampled region where attenuation measurements are made 50 55 cm diameter field of view fov. Spectral information of photoncounting computed tomography ct has been successfully used to separate up to three mixed contrast agents in vivo 5,6. In ct, we use detectors to collect the information. 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. In recent years, there have been several notable advances in ct technology that already. Now all scanners are multislice and have 864 rows of detectors. Multidetector computed tomography mdct is a form of computed tomography ct technology for diagnostic imaging. However, even without using spectral information, pcd photoncounting detectors may reduce beamhardening artifacts and improve contrasttonoise ratios cnr contrasttonoise ratios due to. Volume spectral ct faster than the blink of an eye 2 gsi xtream extends our uncompromised revolution tm ct platform with its wide collimation and 50 cm fov to deliver the only volume spectral ct.
Computed tomography ct donut shaped machine uses xray energy and computer generation of images advantages sensitive to slight density difference cross sectional anatomy attenuation. The patient lies on a table that passes through a gantry which resembles a donut hole, containing the xray tube and multiple detectors. For example, ct has become a useful screening tool for detecting possible tumors or lesions within the abdomen. Conventional ct acquires data one slice at a time spiral ct allows data to be acquired while the table translates and the tube rotates continuously. Multiple adjacent slices are acquired by moving the patients. The amount of radiation dose a patient receives from a ct scan depends upon two key. Physics of cardiac imaging with multiplerow detector ct. Varex imaging corporation is a leading innovator, developer, and manufacturer of xray imaging component solutions, which includes xray tubes, digital flat panel detectors, software, and other key components of xray imaging systems. Because each rotation can produce 64 slices and takes less than 1 second, the total time needed for a complete ct scan is generally less than 1 minute. Scintillation detectors have high detection efficiency. Ct scans can detect bone and joint problems, like complex bone fractures and tumors. Starts improving your odds appendix b 17 appendix c news article from msnbc on radiation dose in ct nov. Crosssections are reconstructed from measurements of attenuation coefficients of xray beams in the volume of the object studied.
Dual source ct scanners moving beyond the simple adding of detector rows, somatom dual source scanners use two xray sources and two detectors at the same time. The purpose of this article is to describe the physics of cardiac imaging with multiplerow detector ct. Similar to singledetector ct units, the rotation speed of the xray tube and detectors for multidetector ct units is variable. Ct scans can be used to identify disease or injury within various regions of the body. Ct scans provide far more detailed images than conventional xray imaging, especially in the case of blood vessels and soft tissue such as internal organs and muscles. Computed tomography method for acquiring and reconstructing an image of a thin cross section of an object based on measurements of x ray attenuation through the section plane using many different projections basic data acquisition in ct xray tube detectors ct table xray beam ct gantry gantry opening. Computed axial tomography ct scans or cat scans use x rays to create images of body tissues. Ct generations and common ct scan modes on modern ct. Computed tomography ct understanding medical radiation. Introduction and brief history of xray tube xray tube is a device in which energy conversion takes place i. Photoncounting ct has the potential both to offer significant improvements to existing ct imaging techniques and to make possible completely novel applications. You will be alone in the exam room during the ct scan, however, the. Scintillation detectors first change the xrays into light, and then the light is.
The three ct components with the greatest impact on image quality are the xray source, detection system and reconstruction algorithms. Multiple images are acquired in a sequence by a rotating xray tube. Multidetector ctcta advanced medical imaging center. At a given pitch, this increase in rotation time enables acquisition of data through a longer volume area. This ct system has different characteristics from conventional ct systems, which have only one row of ct detectors.
These ct scanner developments have been largely directed towards faster scanning of further lengths of the patient, using finer slices. 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. The walls of the opening into the gantry are wedgeshaped, designed so that claustrophobia. Ct data acquisition calibrate detectors prior to acquiring each view. A ct scan of the heart may be ordered when various types of heart disease or abnormalities are suspected. Approximately 90% of the xrays incident on the detectors are absorbed. If you have a condition like cancer, heart disease, emphysema, or liver masses, ct scans can spot it or help. Fan beam, multiple detectors scan times were reduced to approximately 30 s with the use of a fan beam of xrays and a linear detector array. May 12, 2011 the ct scanner is made up of a complex combination of an xray source, detectors and computers, which produce highresolution, crosssectional images of the body.
Gas ionization detectors convert the xrays directly into an electrical signal. The 1979 nobel prize in physiology or medicine was awarded. We describe the stateoftheart of ct detection systems, their calibrations, software corrections and common performance metrics. Multiple detector computed tomography or mdct scanning is a rapid, painless diagnostic procedure that combines the use of computers and xrays. 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. Mcleod cormack 1971 first commercial ct sir godfrey hounsfield. Discover how siemens, the recognized innovation leader in computed tomography, can work for you. 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. Summary the availability of new detector array technology allowing multislice ct acquisitions has enabled new applications for ct. Two types of detectors currently are used in multislice ct scanners. The introduction of multislice scanners has focussed further attention on this issue, and it is generally believed that it will lead to higher patient doses 3. This ct scan of the whole thorax and abdomen was performed in less than 1 sec with only 20 ml of contrast media, and a radiation dose of 2. Basic principles of computed tomography univerzita karlova.
Ct scan images provide moredetailed information than plain xrays do. A ct scan can be used to visualize nearly all parts of the body and is used to diagnose disease or injury as well as to plan medical, surgical or radiation treatment. Enabled by ultrafast kv switching, you can scan more challenging patients and reduce the effects of motion. Computed tomography, more commonly known as a ct or cat scan, is a diagnostic medical imaging test. In conventional radiography we used a film screen system to record the attenuated. Pdf advances in computed tomography imaging technology.
X rays are a form of high energy radiation and are themselves, able to cause cancer. These scanners, called multislice ct or multidetector ct, allow thinner slices to be obtained in a shorter period of time, resulting in more. Ct scanner technology has advanced rapidly in recent years, moving to more efficient and stable detectors, more refined engineering and data acquisition systems and electronics, and faster computers. The scan therefore produces the axial images that form the basis of 3d ct scans.
A ct scanner typically operates with the xray tube and detector gantry perpendicular to the long axis of the patient z direction. A ct scan, or computed tomography scan is a medical imaging procedure that uses computerprocessed combinations of many xray measurements taken from different angles to produce crosssectional tomographic images virtual slices of specific areas of a scanned object, allowing the user to see inside the object without cutting. The ability to scan a given length with fewer rotations also helps to minimize head load on the xray tube, thereby allowing the scanning of longer lengths. The factors affecting temporal and spatial resolution are discussed along with scan acquisition and reconstruction methods, reconstruction algorithms, reconstruction interval, pitch, radiation dose, and geometric efficiency. The components of ct detection systems, such as scintillator materials, photodiodes. Computed tomography ct images provide this kind of view, as shown in the drawing. Like traditional xrays, it produces multiple images or pictures of the inside of the body.
The crosssectional images generated during a ct scan can be reformatted in multiple planes. Computed tomography ct computed tomography ct scanners have been available since the mid1970s and have revolutionized medical imaging. Computed tomography ct donut shaped machine uses xray energy and computer generation of images. A ct scan has many uses, but its particularly wellsuited to quickly examine people who may have internal injuries from car accidents or other types of trauma. Accurate control of the table feed speed is one of the important factors in modern ct system because scan pitch is a key factor in coronary ct angiography. Instead of film, ct scanners use special digital xray detectors, which are located directly opposite the xray source. High detection efficiency for xrays in ct energy range. Mar 05, 2017 detectors the detectors is a component of ct scan machine which collect information regarding the degree to which each anatomic structure attenuated the beam.
Ct detector o ct detector capture the radiation beam from the patient and convert it into electrical signal, which subsequently converted into binary coded information o detector characteristic o a. The length of the detector array of the ct scanners determines the number of rotations needed to cover the total scan length, and consequently, the overall scan time. Definition facts about ctdefinition facts about ct computer tomography ct, originally known as computed axial tomography cat or ct scan and body section rentenography. However, in some cases the gantry may be inclined at an angle of up to 30.
Multislice scanners projection data from multiple slice is acquired simultaneously uses multiple row of detectors in the. The multislice ct msct, or multidetectorrow ct mdct, is a ct system equipped with multiple rows of ct detectors to create images of multiple sections. Helical scan technology, utilizing continuous gantry rotation and table feed, provided for longer anatomic coverage in a shorter time. The original singleslice scanners had one row of detectors.
The 1d projections are combined by the process of filtered backprojection to form the 2d ct image, also called slice spiral helical and multislice helical ct 1. The evolution of ct scanner detectors medwow articles. Basic data acquisition in ct xray tube detectors ct table xray beam ct gantry gantry opening 6070 cm dia. Notice that the xray tube and detectors rotate around the patient. Thirdgeneration ct detectors have to produce the same signal for the same irradiation within a scan and between system calibrations.
Compared to singledetector helical ct, this technique offers three significant advantages. Computed tomography ct is an essential tool in diagnostic imaging for evaluating many clinical conditions. The ct scanner is made up of a complex combination of an xray source, detectors and computers, which produce highresolution, crosssectional images of the body. Series of 1d projections at different angles is acquired continuously by synchronously rotating the xray source and detectors through one complete revolution around the patient 2.
The 1d projections are combined by the process of filtered. The graphs in figure 4 demonstrate the effect on the absorbed dose of a reduced zaxis. Thereafter, it has undergone multiple improvements with an increase in the number of detectors and decrease in the scan time. The detectors are developed together with our other product components for optimal synchronization and compatibility.
A ct scanner is made up of 4 main components, the gantry frame houses the xray source and detectors and has a large opening in the middle patient port, the subject table which moves in and out of the patient port, the xray source and detectors, and a computer system that gathers information from the detectors and produces an image from. Multiple detector computed tomography mdct the imaging. Path of the tube forms a helical pattern around the patient c. Detectors the detectors is a component of ct scan machine which collect information regarding the degree to which each anatomic structure attenuated the beam. The ct detectors designed with a rich background of ct system development and are based on more than 40 years of development experience. That is a huge leap in coverage from the early days of 3 rd generation ct.
Now conebeam ct is the basis of modern ct scanners and it is, also called multidetector ct mdct, as there was a gradual progression of rows of ct detectors on systems from 1,2,4,16, 64, until today where stateofthe art systems can have 256 or more rows of ct detectors. Today, millions of scans are performed worldwide every year for different clinical questions in a variety of clinical fields. The components of ct detection systems, such as scintillator materials. We are manufacturing those products in a clean room environment with fully automated production lines to achieve high precision and reliability repeatedly. Narrow gaps between active elements good geometrical. Feasibility of dosereduced chest ct with photoncounting. Pdf the three ct components with the greatest impact on image quality are the xray source, detection system and reconstruction algorithms. In conventional radiography we used a film screen system to record the attenuated information.
Previously, gasfilled detectors were used, but now, all are scintillation, solid state detectors. Ct scanners were first introduced in 1971 with a single detector for brain study under the leadership of sir godfrey hounsfield, an electrical engineer at emi electric and musical industries ltd. A mdct scan allows the radiologist to see the location, or abnormalities. Coronal and 3d images demonstrate the difference in motion artifact.
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