CT Glosssary Flashcards
The reformatting of cross-sectional images to produce images of the surfaces of anatomical structures
3D Surface Rendering
A mechanism of attenuation in which x-ray photons interact with the patient’s tissues and never leave the body
Absorption
A hardware component used to increase the strength of a signal
Amplifier
Information expressed in a continuous fashion
Analog
The component that converts the analog data into digital information to be temporarily stored in the raw data file
Analog-to-Digital Converter (ADCs)
The positive terminal of the CT x-ray tube and the part of the tube where the target material is located
Anode
Saving the patient’s digital images on a long-term storage device
Archiving
A specialized computer component used to reconstruct the CT images
Array Processor
Annoying anomalies which sometimes appear in CT images
Artifacts
A reduction in the number of photons in the x-ray beam as it passes through the tissues in the patient’s body
Attenuation
A calculation used for reconstructing the final CT images from the raw data by adding together the attenuation information collected from all of the projections
Back Projection
A type of oral contrast agent known for providing very good opacification of the bowel, but is slower moving through the GI tract compared to iodinated agents
Barium Sulfate Oral Contrast Agent
The increase in the average energy of the x-ray beam as it penetrates tissues
Beam Hardening
Refers to the timing immediately following an IV contrast injection defined by at least a 30 HU difference between the abdominal aorta and the inferior vena cava
Bolus Phase of Enhancement
X-rays produced as a result of an electron colliding with or passing near the nucleus of an atom in the target
Bremsstrahlung (braking radiation)
The negative terminal of the CT x-ray tube and the part of the tube where the negatively charged electrons flow into the tube from the high voltage generator
Cathode
X-rays produced as a result of an electron in the target replacing one ejected by a fast-moving incoming electron
Characteristic Radiation
Components on the CT scanner that restrict the path of the x-ray photons
Collimator
An x-ray tomographic technique which uses computers to reconstruct the images
Computed Tomography
A calculation used for reconstructing the final images from the raw data used on multi-row detector scanners with the capability of collecting more than four slices in a single rotation
Cone Beam Reconstruction
Having no gaps between adjacent slices
Contiguous
Conditions that would preclude a patient from having a CT study performed in a given manner (i.e. with contrast)
Contraindications
The ability to differentiate small differences in density on the image
Contrast
A compound, usually pharmaceutical in nature, which when administered to a patient, may improve the sensitivity and specificity of the clinical diagnosis
Contrast Agent
A study of cross-sectional images characterized by an increment of the patient table after each x-ray tube rotation
Conventional Scan
The process of applying a reconstruction filter to the raw data
Convolution
Aligned perpendicular to the axis which travels from anterior to posterior in the patient
Coronal
Sections made by cutting anything at right angles to any axis
Cross-sections
A number that correlates to the Hounsfield scale which ranks various materials by their attenuation properties
CT Number
A study which uses IV contrast media to visualize vascular structures
CT Angiography (CTA)
Indicator of radiation dose which includes the radiation located within the intended slice thickness as well as that from the penumbra
CT Dose Index (CTDI)
A CT hardware component which measures the x-rays that pass through the patient’s body
Detector
A group of detectors
Detector Array
The standard used for communicating digital medical image information, which was established to improve workflow efficiency between imaging systems in healthcare environments worldwide
Digital Imaging and Communications in Medicine (DICOM)
Information expressed in terms of discrete numbers
Digital
The components that convert the digital commands coming out of the scan controller into analog commands that can then be executed by the power-producing and mechanical components
Digital-to-Analog Converters (DACs)
A filter applied to the digital image data to further sharpen or smooth the appearance of the tissues
Display Filter
The amount of ionizing radiation absorbed by an object per unit mass
Dose
The best indicator of radiation dose reflecting the total energy from a CT scan absorbed by the patient
Dose Length Product (DLP)
A calculated sum of the absorbed dose of all of the tissues in the body, each individually multiplied by a weighting factor for that organ or region
Effective Dose
Stationary metal contacts through which electrical signals are transferred to and from the rotating slip ring
Electrical Brushes
A CT scanner that has no x-ray tube with fast scan time making it well-suited for cardiac and coronary artery imaging.
Electron Beam CT Scanner (EBCT)
Refers to the timing usually a few minutes after an IV contract injection defined by less than a 10 HU difference between the abdominal aorta and the inferior vena cava
Equilibrium Phase of Enhancement
The condition that occurs when the substance being injected misses the vein and instead goes directly into the soft tissue
Extravasation
An x-ray beam having a shape similar to an opened paper fan
Fan Beam
A structure on the cathode terminal of the CT x-ray tube from which the electron beam is released
Filament
The area on the anode target bombarded by the electron beam and a factor in determining the image resolution
Focal Spot
The comparison of two imaging modalities yielding co-registered images
Fusion Imaging
The part of a CT scanner through which the patient table is advanced and the component that contains the CT x-ray tube and the detectors
Gantry
A unit for measuring the absorbed radiation dose in which 1 Gy equals 100 rads
Gray (Gy)
A continuous spectrum of shades of the color gray used to differentiate structures on a digital image
Gray Scale
A study of cross-sectional images characterized by continuous patient table motion during x-ray tube rotation
Helical Scan
The component that creates the high voltage that enables the CT x-ray tube to produce x-ray photons
High Voltage Generator
The communications coordinator for the rest of the CT system
Host Computer
The grid of rows and columns of pixels which forms the digital image
Image Matrix
Compounds that are injected through the theca of the spinal cord into the subarachnoid space during a myelographic study of the spine
Intrathecal Contrast Agents
Compounds, typically containing iodine, that are injected into the blood stream in order to better differentiate tissues and better delineate abnormalities on CT images
Intravenous (IV) Contrast Agents
A type of oral contrast agent known for moving through the GI tract quickly compared to barium sulfate agents
Iodinated Oral Contrast Agent
A type of IV contrast agent that breaks down in the blood stream
Ionic Contrast Agent
A type of energy that can cause detrimental changes to occur in the atoms of living tissues
Ionizing Radiation
A complex cycle of correction calculations which may be applied during the CT image reconstruction process to reduce image noise, and which allows a greatly reduce dose to be used without compromising image quality
Iterative Reconstruction
The scan parameter which is the maximum energy of the x-ray photons and the parameter that controls the contrast in a CT image
kVp
A single projection scan obtained with a stationary x-ray tube and a moving patient table generating the image used to position the cross-sectional slices
Localizer Scan
The scan parameter which is the mathematical product of the tube current and the rotation time (in sec.) and which determines the number of photons the patient’s body is exposed to
mAs
The post-processing algorithm used on CTA and MRA data to allow visualization of the complete vascular tree
Maximum Intensity Projection (MIP)
Streaks that result from metal located within the scan field-of-view during a CT scan
Metal Artifact
Streaks, blurriness, or ghosting that results from motion of any structure in or on the patient’s body during a CT scan
Motion Artifact
An indicator of radiation dose which corrects the CTDI on conventional scans by factoring in gaps or overlaps between the slices as indicated by the selected table increment
Multiple Slice Average Dose (MSAD)
The reformatting of images acquired in one orientation to produce images in other orientations
Multiplanar Reconstruction
A CT scanner design that collects information from multiple anatomical slices in each rotation of the x-ray tube
Multi-row Detector CT Scanner (MDCT)
A condition in an image that refers to electronic interference and which causes the appearance to be grainy
Noise
Refers to the timing shortly after an IV contrast injection defined by a 10-30 HU difference between the abdominal aorta and the inferior vena cava
Non-equilibrium Phase of Entertainment
Type of IV contrast that does not break down in the blood stream
Non-Ionic Contrast Agent
The link between the technologist and the computerized electronic environment of the CT scanner hardware
Operator’s Console
Compounds containing iodine or barium sulfate that are swallowed or administered rectally in order to opacify the gastrointestinal tract on CT images
Oral Contrast Agents
The concentration of molecular particles in the contrast agent solution
Osmolality
Results from selecting slices that are much thicker than the anatomy and pathology which we want to visualize
Partial Volume Artifact
Results in blurring of the images and a decreased ability to visualize small structures when the slices are too thick
Partial Voluming
A thin, focused beam of x-rays
Pencil Beam
A tiny bit of energy contributing to the x-ray beam which travels at the speed of light
Photon
The distribution, viewing and storage facility for digital images across an imaging facility’s computer network
Picture Archiving and Communication System (PACS)
The extent to which the x-ray helix is stretched during a helical scan
Pitch
A single picture element formed by the intersection of a row and column of the image grid
Pixel
A restriction on unwanted x-rays entering the detector assembly from arbitrary angles
Post-patient Collimation
Conditions that would warrant a medical decision as to whether the benefits of the exam outweigh the risks posted to the patient
Precautions
A refinement of the thickness of the x-ray beam after it leaves the x-ray tube and before it enters the patient’s body
Pre-patient Collimation
A view of the anatomical cross-section along the path of the x-ray beam from only one vantage point
Projection
Position with the posterior side of the body facing up
Prone
A pre-defined set of parameters that is used to run a CT scan for a specific clinical application
Protocol
A unit for measuring the absorbed radiation dose
Rad
Radiation that extends outside of the intended slice caused by imperfect collimation of the x-ray beam
Radiation Penumbra
The measured x-ray photon information
Raw Data
The number of millimeters of information reconstructed and displayed in the final image
Reconstruction Field-of-View (FOV)
The filter applied to the raw data during image reconstruction
Reconstruction Filter
The parameter that determines where helical slices will be reconstructed and if they will be overlapped
Reconstruction Interval
A unit for measuring the radiation dose equivalent
Rem (1 rem = 1 rad)
A measurement of the smallest structure that we can visualize, or resolve, in the image
Resolution
The process of reconstructing images from the raw data using modified parameters, after the initial image reconstruction is complete
Retrospective Reconstruction
Aligned perpendicular to the axis which travels from left to right in the patient
Sagittal
The collection of anatomical information during the time the x-ray beam is on
Scan
The component responsible for the timing and correct performance of each CT system component once the scan has been started
Scan Controller
The number of millimeters of anatomy over which projection data is collected
Scan Field-of-View (FOV)
A mechanism of attenuation in which x-ray photons interact with a dense structure and change the direction of their path
Scattering
The process of determining the patient’s current condition and medical history in order to ensure eligibility for the scanning procedure
Screening
The number of millimeters of anatomy, intersected by the thickness of the x-ray beam, which is represented in the CT image
Slice Thickness
A large rotating ring on the CT scanner to which several hardware components are mounted and which eliminates the need for power and data cables
Slip Ring
Positioned with the anterior side of the body face up
Supine
The advancement, in millimeters, of the patient table between consecutive conventional slices determining the gaps or overlap between adjacent slices
Table Increment
The material in the CT tube which is bombarded with fast-moving electrons to generate x-rays
Target
Any imaging method in which the patient’s tissues are visualized by “cutting” them into sections
Tomography
Aligned perpendicular to the axis which travels from head to foot in the patient
Transverse
The parameter that determines the number of x-ray photons produced by the CT x-ray tube
Tube Current (mA)
The parameter that determines the energy level of x-ray photons produced by the CT x-ray tube
Tube Voltage (kV)
The thickness of a substance in reference to contrast media
Viscosity
The center CT number around which the window width is positioned
Window Level
The range of CT numbers that occupy the full gray scale on the image monitor
Window Width
Adjusting the brightness and contrast of the shades of gray assigned to represent the tissues in the pixels of a CT image
Windowing
The source of x-rays in a CT scanner
CT X-ray Tube
