Mosbys Terms Flashcards
180-degree linear interpolation (180LI)
Type of algorithm used for multi slice computed tomography image reconstruction in which data acquired from a shorter distance (180*) away from the reconstructed slice location are interpolated
360-degree linear interpolation (360LI)
Type of algorithm used for MSCT image reconstruction in which two sets of projection data acquired 360 degrees apart are used to form an image at a precise z-axis location
Absorbed dose
Amount of X-ray energy absorbed in a unit of mass and measured in grays (Gy)
Absorption efficiency
Ability of an individual ct detector to absorb and measure the transmitted X-ray intensity incident upon it. Primarily controlled by characteristics and physical makeup of the detector material
Adaptive array
Type of MSCT detector array configured with the thinnest detectors at the center, surrounded by detectors of incrementally increasing widths along the z-axis
Advanced single-slice rebinning algorithm
Cone beam correction algorithm utilized to overcome potential attenuation calculation errors from the divergent beam of MSCT
Afterglow
Tendency of a scintillation-type ct detector to continue to glow in response to X-ray after exposure source has been terminated
Agatston score
Quantification of volume and density of calcium within the coronary arteries. Calculated for a coronary artery calcification study to indicate a patient’s risk of suffering a cardiac event
ALARA
Acronym for as low as reasonably achievable, cardinal principle of radiation dose reduction for all radiologic procedures
Algorithm
Mathematical filter applied to raw data during ct image reconstruction to remove blurring artifact inherent to back-projection. Also referred to as a kernel
Aliasing
Form of streak artifact caused by insufficient number of views/data samples obtained during data acquisition
Analog to digital converter
Component of DAS responsible for converting electrical signal emitted by ct detectors into digital form
Archival
Storage of ct data in either hard film or soft digital form
Array processor
Component of ct computer system responsible for receiving raw scan data, performing all of the major processing of the ct image, and returning the reconstructed image to the storage memory of the host computer.
Arterial phase
Period of peak enhancement after the bolus IV administration of iodinated contrast material.
Artifact
Form of noise on ct image resulting from errors during the measurement of transmitted radiation by the detectors
Ataxia
Neurological sign characterized by a loss of muscular coordination
Attenuation
Reduction in intensity of a radiation beam as it passes through a substance
Attenuation coefficient
Value assigned to an object quantifying its ability to attenuate along the scan acquisition range to reduce patient radiation dose to a minimum
ATCM
Ct system software used to adjust mA throughout an acquisition to reduce patient radiation dose to a minimum
ATVS
Ct system software used to adjust tube voltage (kvp) based upon the changing patient attenuation along the scan acquisition range to reduce patient radiation dose to a minimum
Back-projection
Mathematical process of CT image reconstruction whereby ray sum data are projected back into a matrix
Beam hardening
Phenomenon whereby low-energy photons are absorbed as the X-ray beam passes through an object, resulting in an increase in average photon energy of beam
Beam pitch
Ratio of table feed per gantry rotation to the total collimation used during acquisition with an MSCT system
Beam width
Dimension of primary beam in longitudinal or z-axis as controlled by pre-patient collimator
Binning
Process of electronically combining signal from adjacent detector elements to produce a reconstructed ct image that is thicker than the individual detector width
Bit depth
Number of information bits contained within each pixel
Blood urea nitrogen
Measurement of renal function, determined as the amount of nitrogen in the blood in the form of waste product urea. Range of 7-25mg/dL
Bow-tie filter
Type of filter added to the ct X-ray tube to compensate for the cylindrical shape of most body parts. Filter is thicker at ends and helps shape beam to reduce patient radiation exposure
Cardiac cycle
Series of blood flow-related events that occur from beginning of one heartbeat to that of the next
Cerebral blood flow
Measured during perfusion studies of brain. Quantity of blood that moves through 100-g of brain tissue each minute. Range 50-60mL/100g/min
Cerebral blood volume
Measured during perfusion studies of brain. Quantity of blood contained within 100-g volume of brain tissue. Range 4-5mL/100g
Cerebral perfusion
Level of blood flow throughout brain tissue
Coma
A state of unconsciousness where the individual is completely unresponsive to stimuli
Constant mAs
Product of mA and scan time utilized for a CT acquisition
Contiguous images
Images acquired with equal section thickness and reconstruction intervals
Contrast resolution
Ability of a ct system to detect an object with a small difference in linear attenuation coefficient from the surrounding tissue. Also, low-contrast detect ability or sensitivity
Contrast-induced nephrotoxicity
Substantial decline in renal function that can occur after a patient receives IV contrast material. A marked increase in serum creatinine over a baseline measurement obtained before contrast agent administration.
Convolution
Mathematical filtration used by CT system to remove blurring artifact during back-projection method of image reconstruction
Corticomeduallry phase
Late arterial phase of renal enhancement beginning 30-40 sec after initiation of contrast agent administration. Optimal enhancement of renal cortex and renal veins occurs during this period.
Creatinine
Waste product of metabolism found in the bloodstream and measured as an indicator of renal function. Range 0.5-1.5mg/dL
CT arthrography
Evaluation of a joint after the intra-articular injection of iodinated contrast material
CT bronchoscopy
Specialized MSCT exam of the tracheobronchial tree consisting of MPR and VR-3D images reconstructed from thin, overlapping MDCT axial images through the airways
Ct colonography
Specialized ct evaluation of the large intestine used primarily for colon cancer screening. LI is extended and scanned with thin-section CT. 2D and 3D models are constructed, including virtual endoscopic fly-through views.
Ct cystography
Specialized ct exam of the bladder whereby iodinated contrast is administered directly under gravity into the bladder via foley-catheter
Ct dose index
Approximate measure of the radiation dose received in a single ct section or slice
Ct enteroclysis
Specialized ct evaluation of the small bowel whereby enteral contrast material is administered directly into the duodenum through a nasogastric catheter place under fluoro guidance
Ct enterography
Ct evaluation of the small bowel after oral administration of low-density barium (0.1%)
Ct fluoscopy
Continuous, real-time ct imaging used predominantly for ct-guided interventional procedures
Ct myelography
Evaluation of spinal cord and nerve roots after intrathecal administration of iodinated contrast material
CT number
Relative value assigned to each pixel to quantify the attenuation occurring in each voxel in comparison with the attenuation of water. Calculated value for a pixel is in HU. Also, pixel value
Ct runoff
CTA assessment of peripheral arterial tree from the renal arteries through the lower extremities
Ct simulation
Process of obtaining anatomic information with ct imaging that is used to calculate the beam arrangement for radiotherapy
Ct urogram
Comprehensive, muliphasic evaluation of urinary tract. Consists of precontrast, postcontrast, and delayed images through K,U,B. Also, CT-IVP
Cupping artifact
Error occurring in superior portion of skull, where dense bone averages with low-attenuating brain tissue. Partial volume artifact may result in abnormally dense-appearing brain parenchyma.
DAS
Electronic components of a ct system responsible for measuring transmitted X-rays absorbed by detectors
Data channel
Pathway of data transmission from detectors to the computerized components of the system’s DAS. Number of these that a CT system determines the maximum number of sections that may be acquired with each gantry rotation.
Data transfer rate
Speed at which a computerized storage drive is able to transfer data
Deconvolution
Mathematical image processing technique used to generate blood perfusion maps during ct perfusion studies of brain
Detector
Device responsible for measuring transmitted radiation and converting it into a proportionate electronic signal to be used for image reconstruction
Detector array
Ct image receptor consisting of a series of detectors arranged in varying configurations
Detector collimation
Process of determining section width in MSCT system as determined by the defined beam width and number and thickness of detectors utilized for image reconstruction
Detector configuration
Number, length, and organization of individual detector elements in an MSCT system
Detector pitch
Ratio of table feed per gantry rotation to the acquired section width. Definition used for helical single-slice ct
Diastole
Portion of cardiac cycle when heart muscle is relaxed. Blood pressure that reflects the force exhibited on arterial walls during relaxation of the heart muscle. The bottom number provided during the assessment of blood pressure
DICOM
Acronym for Digital Imaging and Communications in medicine standard for the process of recording, storing, printing, and transmitting medical image data
Display field of view
Diameter of the acquired attenuation data displayed across the image matrix. Also, zoom factor or target view
Dose length product
Measurement of dose for an entire series of ct images. Equal to the calculated dose per section multiplied by the length of a CT acquisition along the z-axis.
Dose profile
Section of the patient exposed to radiation at the gantry iso enter
Dual-energy ct
Simultaneous acquisition, by an MSCT system, of attenuation data for a single anatomic section with two X-ray beams, each having a different energy spectrum. Rapidly switch between kvp settings during data acquisition, allowing for improved contrast between substances of differing densities.
Dual-source ct
System that consists of two separate X-ray tubes and detector arrays mounted 90 degrees from each other within the gantry, allowing for dual-energy ct acquisition
Edge gradient
Streak artifact that occurs at the interface between a high-density object and the lower-attenuation material surrounding it
Effective dose
Approximation of the relative risk from exposure to ionizing radiation; calculated by assigning weighting factors to different tissues on the basis of their individual radiosensitivities. Measured in Sv
Effective mAs
Calculated mAs per acquired slice with a MSCT system
Effective section width
Slice sensitivity profile of the reconstructed CT section. Measured at full width at half maximum of the SSP for a given ct acquisition.
Electrocardiogram
Graphical representation of the electrical activity of the heart recorded over time through electrodes placed on the patient’s skin
Electron beam CT
Specialized ct design devoid of moving parts. Utilizes beam of electrons bombarding a tungsten target to produce X-rays. Capable of extremely short exposure times and are the best for cardiac imaging.
Equilibrium phase
Contrast phase of the liver when hepatic parenchymal enhancement dissipates and there is minimal attenuation difference between intravascular and extravascular spaces. 2-3min delay post injection
Excretory phase
Delayed imaging renal enhancement phase that begins approximately 3min after the initiation of contrast agent. Contrast material excreted into renal calyces, opacifying the renal pelvis and the remainder of the urinary collecting system.
Exposure
Ability of X-rays to ionize a volume of air. Measured in Roentgens
Extravasation
Escape of contrast material outside the blood vessel into the surrounding soft tissue
Fan angle
Angle of coverage by the X-ray beam as it emerges from the tube housing and exposes the detector array within the scan plane. (X and y axis)
Feldkamp-Davis-Leeds algorithm
Cone beam correction algorithm utilized to overcome potential attenuation calculation errors from divergent beam of MSCT systems
Filtered back-projection
Math process of ct image reconstruction involving convolution of the raw data before their projection back onto a matrix
Filtration
Removal of the low-energy X-ray photons emitted from the X-ray tube to improve beam quality and reduce patient radiation dose.
Flat-panel detector
Large-area detector consisting of a film of scintillating crystals bonded to a matrix of silicon photosensors. May be used in place of segmented detector rows in MDCT
Flying focal spot
Electronic switching technique whereby electron beam is electromagnetically steered toward two separate locations on the rotating anode. Results in emission of two sources of X-rays from tube and a doubling of the data samples acquired from each gantry rotation
Focus-to-detector distance
Characteristic of the ct gantry described as the distance between the X-ray source and detector array
Focus-to-Isocenter distance
Characteristic of the ct gantry described as distance from X-ray source to the center of the gantry opening, where patient should be positioned
Full width at half maximum
Midpoint of an SSP, where the effective section width for a ct acquisition is determined
Geometric efficiency
Ability of a detector array to absorb and measure transmitted X-ray intensity incident upon it. Primarily controlled by physical arrangement of detectors within the array and the amount of interspace material required between adjacent detectors
Gantry
Assembly that houses X-ray tube, detectors and additional data acquisition components of a CT system. Where patient is positioned for scan.
Glomerular filtration rate
Approximation of creatinine clearance or the rate by which creatinine is cleared through the bloodstream. Range for men 70+/-14mL/min/m^2 and range for women 60+/-10mL/min/m^2
Half value layer
Thickness of material that is capable of reducing the intensity of the X-ray beam to one-half its original value
Helical
Type of ct acquisition whereby X-ray tube and patient continuously move during scanning, yielding a data set in form of a helix. Also, spiral
Hounsefield bar
Specific type of streaking beam-hardening artifact that occurs in the posterior fossa of the brain.
Hounsefield unit
Unit of CT number scale assigned to each pixel to quantify relative attenuation
Hybrid array
Type of MSCT detector array with narrower detectors positioned midline, flanked by wider detectors
Hyper dense
Possessing attenuation values greater than the values of the surrounding tissues
Hypodense
Possessing attenuation values less than the values of the surrounding tissues
Hypoxemia
Condition of low concentration of oxygen in blood
Hypoxia
Condition of insufficient oxygenation of tissue at the cellular level
Image compression
Complex computer technique that reduces the size of digital ct image data
Image data
Reconstructed data that have been projected back onto a matrix after convolution by an algorithm and displayed on a monitor as a grayscale ct image
Insufflation
Intro of air into an organ or cavity for distant ion and improved visualization
Interpolation
Math process used for helical CT image reconstructed whereby data from tube rotations just above and just below a given slice position are used for recons
Isocenter
Center point of gantry rotation
Isodense
Possessing CT attenuation values equal of the values of the surrounding tissue
Isotopic
Having equal dimensions along x, y and a axes; describes the voxels with this property
Iterative reconstruction
Math reconstruction method that uses multiple passes/iterations to arrive at a final image with reduced noise and artifacts, leading to improved overall quality at reduced patient dose
Kerma
Quantity of energy deposited in a unit of mass and used to describe absorbed dose of radiation
Kernel
Math filter applied to raw data during CT image reconstruction to remove blurring artifact inherent to back-projection . Also, algorithm
Lethargy
Level of consciousness characterized by feelings of fatigue, drowsiness, or apathy
Linear attenuation coefficient
Value assigned to an object to quantify extent to which it attenuates X-ray
Linearity
Relative accuracy between calculated ct numbers and their respective linear attenuation coefficients
Lossless compression
Reversible process whereby the CT image is digitally compressed in size without loss of data and is identical to the original
Lossy compression
Irreversible process whereby data are lost during the compression process and the CT image does not exactly match the original
Matrix
2D grid of numbers arranged in rows and columns
Maximum intensity projection
Multiplanar reformation technique that displays only the maximum pixel value along a ray traced through the object to the viewers assumed perspective in front of viewing monitor
Mean transit time
Common measurement during CT perfusion studies of brain. Measured in seconds, and the average time needed for blood to pass through a given region of brain tissue
Minimum intensity projection
MPR technique that displays minimum pixel value along each ray to the viewer
Misregistration
Artifact that occurs when patient motion between consecutive acquisitions causes misalignment of data and the potential loss of anatomic info
Modulation transfer function
Graph of CT system’s response to a spatial frequency that serves as a measurement of the system’s in-plane spatial resolution
Monoenergetic
Consisting of uniform photon energy; used in CT to describe a beam of X-ray
Multiphase
Ct data acquisition during multiple times phases of contrast enhancement
MPR
Process of displaying CT images in a different orientation from the one used in the original recons
Multiple scan average dose
Calculation of average cumulative radiation dose to each anatomic slice within the center of a CT scan consisting of multiple slices
Multisegment recons
Method of improving the temporal resolution of a CT system whereby the data acquisition process is subdivided into separate components of smaller rotation angles
Mulidlice ct
System with a detector array capable of acquiring more than one section for each gantry rotation. Also, MDCT
Nephrographic phase
Renal enhancement phase occurring between 70-90 sec after start of injection of contrast. Enhancement between renal cortex and medulla reaches equilibrium, providing optimal sensitivity for parenchymal lesions
Noise
Grainy appearance on the CT image due to primarily an insufficient X-ray photon flux per voxel. Also, any portion of signal that contains no useful info, as evident in certain CT image artifacts
Nyquist theorem
Sampling law dictating that the data sampling frequency must be at least twice the objects spatial frequency in order for the object to be resolved by ct system
