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. The scan therefore produces the axial images that form the basis of 3d ct scans. Helical scan technology, utilizing continuous gantry rotation and table feed, provided for longer anatomic coverage in a shorter time. Computed axial tomography ct scans or cat scans use x rays to create images of body tissues. Basic data acquisition in ct xray tube detectors ct table xray beam ct gantry gantry opening 6070 cm dia. 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.
Thereafter, it has undergone multiple improvements with an increase in the number of detectors and decrease in the scan time. Multidetector computed tomography mdct is a form of computed tomography ct technology for diagnostic imaging. Multiple detector computed tomography mdct the imaging. Physics of cardiac imaging with multiplerow detector ct. Today, millions of scans are performed worldwide every year for different clinical questions in a variety of clinical fields. Computed tomography ct understanding medical radiation. 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.
Path of the tube forms a helical pattern around the patient c. Multiple images are acquired in a sequence by a rotating xray tube. Detectors the detectors is a component of ct scan machine which collect information regarding the degree to which each anatomic structure attenuated the beam. In ct, we use detectors to collect the information. We are manufacturing those products in a clean room environment with fully automated production lines to achieve high precision and reliability repeatedly. 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. Discover how siemens, the recognized innovation leader in computed tomography, can work for you. A mdct scan allows the radiologist to see the location, or abnormalities. The amount of radiation dose a patient receives from a ct scan depends upon two key factors, the design of the scanner and also on the way that the scanner is used. High detection efficiency for xrays in ct energy range. The detectors are developed together with our other product components for optimal synchronization and compatibility. Gas ionization detectors convert the xrays directly into an electrical signal.
Coronal and 3d images demonstrate the difference in motion artifact. The purpose of this article is to describe the physics of cardiac imaging with multiplerow detector ct. Computed tomography ct donut shaped machine uses xray energy and computer generation of images. Scan types 1516 conclusion and sign off 16 appendix a contrast media reactions appendix a 111 appendix b i. Definition facts about ctdefinition facts about ct computer tomography ct, originally known as computed axial tomography cat or ct scan and body section rentenography. In recent years, there have been several notable advances in ct technology that already. Ct scan images provide moredetailed information than plain xrays do. Photoncounting computed tomography ct is a computed tomography technique currently under research and development, both within academia and by major vendors of ct systems. In conventional radiography we used a film screen system to record the attenuated information.
The components of ct detection systems, such as scintillator materials. Computed tomography, more commonly known as a ct or cat scan, is a diagnostic medical imaging test. Summary the availability of new detector array technology allowing multislice ct acquisitions has enabled new applications for ct. A ct scanner typically operates with the xray tube and detector gantry perpendicular to the long axis of the patient z direction. 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. We describe the stateoftheart of ct detection systems, their calibrations, software corrections and common performance metrics. If you have a condition like cancer, heart disease, emphysema, or liver masses, ct scans can spot it or help. That is a huge leap in coverage from the early days of 3 rd generation ct. Pdf advances in computed tomography imaging technology. Ct generations and common ct scan modes on modern ct. Notice that the xray tube and detectors rotate around the patient. The three ct components with the greatest impact on image quality are the xray source, detection system and reconstruction algorithms. 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 patient lies on a table that passes through a gantry which resembles a donut hole, containing the xray tube and multiple detectors.
Computed tomography ct images provide this kind of view, as shown in the drawing. 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. 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. However, even without using spectral information, pcd photoncounting detectors may reduce beamhardening artifacts and improve contrasttonoise ratios cnr contrasttonoise ratios due to. Instead of film, ct scanners use special digital xray detectors, which are located directly opposite the xray source.
Feasibility of dosereduced chest ct with photoncounting. Ct data acquisition calibrate detectors prior to acquiring each view. The graphs in figure 4 demonstrate the effect on the absorbed dose of a reduced zaxis. Starts improving your odds appendix b 17 appendix c news article from msnbc on radiation dose in ct nov. Mcleod cormack 1971 first commercial ct sir godfrey hounsfield. 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. Now all scanners are multislice and have 864 rows of detectors. Previously, gasfilled detectors were used, but now, all are scintillation, solid state detectors. 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. Two types of detectors currently are used in multislice ct scanners. 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. Photoncounting ct has the potential both to offer significant improvements to existing ct imaging techniques and to make possible completely novel applications.
Approximately 90% of the xrays incident on the detectors are absorbed. Ct scans can be used to identify disease or injury within various regions of the body. Computed tomography ct is an essential tool in diagnostic imaging for evaluating many clinical conditions. 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. Enabled by ultrafast kv switching, you can scan more challenging patients and reduce the effects of motion. For example, ct has become a useful screening tool for detecting possible tumors or lesions within the abdomen. 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 amount of radiation dose a patient receives from a ct scan depends upon two key. 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.
Pdf the three ct components with the greatest impact on image quality are the xray source, detection system and reconstruction algorithms. 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. Multidetector ctcta advanced medical imaging center. Narrow gaps between active elements good geometrical. The walls of the opening into the gantry are wedgeshaped, designed so that claustrophobia. 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. You will be alone in the exam room during the ct scan, however, the. 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. Spectral information of photoncounting computed tomography ct has been successfully used to separate up to three mixed contrast agents in vivo 5,6. Scintillation detectors have high detection efficiency. 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. The highly collimated beam provides excellent rejection of radiation scattered in the patient. Ct scans can detect bone and joint problems, like complex bone fractures and tumors.
The 1d projections are combined by the process of filtered. Multislice helical ct imaging systems have multiple detectors in an array up to tens of thousands. Similar to singledetector ct units, the rotation speed of the xray tube and detectors for multidetector ct units is variable. A ct scan of the heart may be ordered when various types of heart disease or abnormalities are suspected. The evolution of ct scanner detectors medwow articles. 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.
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. At a given pitch, this increase in rotation time enables acquisition of data through a longer volume area. Compared to singledetector helical ct, this technique offers three significant advantages. Multiple adjacent slices are acquired by moving the patients. 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.
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. 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. Imaging and detectors for medical physics lecture 3. Sampled region where attenuation measurements are made 50 55 cm diameter field of view fov. The crosssectional images generated during a ct scan can be reformatted in multiple planes. 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 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. Like traditional xrays, it produces multiple images or pictures of the inside of the body. The original singleslice scanners had one row of detectors. 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. 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. 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 ct computed tomography ct scanners have been available since the mid1970s and have revolutionized medical imaging. Crosssections are reconstructed from measurements of attenuation coefficients of xray beams in the volume of the object studied. 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. This ct system has different characteristics from conventional ct systems, which have only one row of ct detectors. These scanners, called multislice ct or multidetector ct, allow thinner slices to be obtained in a shorter period of time, resulting in more. 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. 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. X rays are a form of high energy radiation and are themselves, able to cause cancer.
Introduction and brief history of xray tube xray tube is a device in which energy conversion takes place i. Scintillation detectors first change the xrays into light, and then the light is. These ct scanner developments have been largely directed towards faster scanning of further lengths of the patient, using finer slices. The components of ct detection systems, such as scintillator materials, photodiodes. 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. 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. In conventional radiography we used a film screen system to record the attenuated. 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 1979 nobel prize in physiology or medicine was awarded. Thirdgeneration ct detectors have to produce the same signal for the same irradiation within a scan and between system calibrations. Basic principles of computed tomography univerzita karlova.