Radiology - Technology Information PortalSaturday, 10 December 2016


 'CT Scanner' 
Result : Searchterm 'CT Scanner' found in 1 term [] and 18 definitions [], (+ 4 Boolean[] results
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CT Scanner
A computed tomography (CT) scanner is used to create cross-sectional slices of different objects. The medical version of CT system scans the human body for tumors or other abnormalities, other versions are used for non-destructive testing in the industry.
The CT imaging system includes the moveable gantry and patient table or couch. The gantry is a frame that contains the x-ray source, collimators, filters, detectors, a data acquisition system (DAS), rotational components including slip ring systems and all associated electronics. The x-ray tube and detector system are mounted opposite each other, allowing a rapid and synchronous rotation around the patient table.
In older CT scanners a small generator supplied power to the x-ray tube and the rotational components via cables for operation. Up to the 4th generation the CT tube and detectors rotate together around the patient for each slice. CT systems with slip ring technology (the x-ray tube rotates around a stationary ring of detectors) operate without cables and provides continuous rotation of the gantry components without interference of cables. Spiral CT scanners work with a continuous table movement while the x-ray tube is rotating around the patient.

Overview about CT scanner generations:
point 1st generation has a pencil beam and one detector;
point 2nd generation has a narrow fan beam and multiple detectors;
point 3rd generation has a wide fan beam;
point 4th generation is equipped with a detector ring;
point 5th generation is the electron beam tomography CT
point 6th generation is the helical (or spiral) CT scanner;
point 7th generation is the multi-detector row CT.

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X-ray CT(.ppt)Open this link in a new window
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Hounsfield Unit
(HU) [CT scanner display unit] The arbitrary scale is defined by air, which has a CT number of -1000 HU, and water, with a CT number of 0 HU. It is named after Sir Godfrey Hounsfield, who developed the first clinical CT scanner.

See also Hounsfield Scale.

  Further Reading:
Hounsfield scaleOpen this link in a new window
'The Hounsfield unit (HU) scale is a linear transformation of the original linear attenuation coefficient measurement in one in ...'
Contrast Enhancement of Chest CT imagesOpen this link in a new window
'In modalities such as computed tomography (CT), chest radiography and mammography, images from the acquisition system usually ...'
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CT Guided Biopsy
CAT/CT guided biopsies and other minimally invasive interventions are well established medical procedures. Since the beginning of computed tomography, conventional CAT/CT imaging studies has been used to guide an interventional procedure such as a tissue biopsy of a suspected tumor or metastases.
Advanced interventional CT scanners provide fluoroscopic techniques allowing additionally the guidance of minimally invasive surgery or micro-therapy. Fluoro CT allows the continuous monitoring of the needle trajectory or inserted surgical instrument. A wide gantry opening, external tilting laser for needle guidance and special software ease the intervention.
CT images are also used to plan radiotherapy cancer treatment and determine how the disease is responding to the treatment.

  Further Reading:
Interventional Radiology in Cancer PatientsOpen this link in a new window
'Procedures performed by an interventional radiology specialist are becoming increasingly important in the management of patients ...'
Saturday, 1 July 2000 by    
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Computed Tomography
(CT or CAT scan) Computed tomography is a diagnostic imaging technique, previously also known as computerized axial tomography (CAT), computer-assisted tomography (CAT), computerized tomographic imaging, and reconstructive tomography (RT).
A CT scan is based on the measurement of the amount of energy that a tissue absorbs as a beam of radiation passes through it from a source to a detector. As the patient table moves through the CT scanner, the CT tube rotates within the circular opening and the set of x-ray detectors rotate in synchrony. The narrow, fan-shaped x-ray beam has widths ranging from 1 to 20 mm. The large number of accurate measurements with precisely controlled geometry is transformed by mathematical procedures to image data. Corresponding to CT slices of a certain thickness, a series of two-dimensional cross-sectional images is created.
A CT is acquired in the axial plane, while coronal and sagittal images can be rendered by computer reconstruction. Although a conventional radiography provides higher resolution for bone x-rays, CT can generate much more detailed images of the soft tissues. Contrast agents are often used for enhanced delineation of anatomy and allow additional 3D reconstructions of arteries and veins.
CT scans use a relatively high amount of ionizing radiation compared to conventional x-ray imaging procedures. Due to widespread use of CT imaging in medicine, the exposure to radiation from CT scans is an important issue. To put this into perspective, the FDA considers the risk of absorbed x-rays from CT scans to be very small. Even so, the FDA recommends avoiding unnecessary exposure to radiation during diagnostic imaging procedures, especially for children.
CT is also used in other than medical fields, such as nondestructive testing of materials including rock, bone, ceramic, metal and soft tissue.
See also Contrast Enhanced Computed Tomography.

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Computed Tomography ? An Increasing Source of Radiation ExposureOpen this link in a new window
'The advent of computed tomography (CT) has revolutionized diagnostic radiology. Since the inception of CT in the 1970s, its use ...'
Thursday, 29 November 2007 by    
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Computed Tomography Dose Index
(CTDI) The computed tomography dose index is most commonly used dose descriptor, which represents the dose to a location (e.g., depth) in a scanned volume.
This index describes the dose from a single rotation of a CT scanner. CTDI must be corrected for pitch or couch increment to receive the dose for a series of slices. The CTDI100 is measured using a 100 mm long ionization chamber. The CTDIair is the value of CTDI determined free-in-air.
Different definitions of CTDI exist and are used in different applications.

  Further Reading:
Principles of CT: Radiation Dose and Image Quality(.pdf)Open this link in a new window
'This article discusses CT radiation dose, the measurement of CT dose, and CT image quality. The most commonly used dose ...'
Thursday, 15 November 2007 by    
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