Mosbys Terms 2 Flashcards
O-arm
Portable ct-fluoro unit with telescoping gantry used to acquire 3D CT images and standard fluoro during invasive or surgical purposes
Obtundation
Depressed level of consciousness characterized by dulled feelings, with slowed response to stimuli
Opacification
Increase in CT density of a structure due to filling with positive contrast material
Operating system
Main software of the CT computer, controlling utilization of the hardware resources including the available memory, central processing unit time, disk space, etc
Out of field artifact
Hyper dense streaking that occurs when a portion of the patient has been positioned outside the SFOV
Overbearing
Expansion of primary beam in an MSCT system to ensure all detectors of the array are exposed to X-rays of equal intensity
Overlapping images
Ct images produced with a reconstruction interval that is less than the section width
Overranging
Process of applying radiation dose before and after the acquisition volume to ensure sufficient data collection for the interpolation algorithms of helical CT recons
PACS
Acronym for a picture archival and communications system. Responsible for storing, retrieving, distributing and displaying CT and other medical images
Pancreatic phase
Delayed arterial enhancement phase occurring approximately 35-45sec after start of contrast, if an adequate volume has been injected at a rate of 3mL/sec of higher
Parallel processing
Ability of a computer to perform multiple functions simultaneously
Partial volume artifact
Error that occurs when a structure is only partly positioned within a voxel and the attenuation for the object is not accurately represented by a pixel value
Partial volume averaging
Inaccuracy in pixel values that occurs when the associated voxels contain attenuation coefficients for multiple tissue types. Values averaged together to yield a single pixel value that attempts to represent an assortment of different materials
Perspective volume rendering
Technique yielding a 3D model with the perspective of being within the linen of the object, similar to an endoscopic view. Also, immersive rendering
Phantom
Quality control device typically composed of a radiolucent plastic material containing specialized inserts that is used to measure specific image quality criteria
Photodiode
Device used by a solid-state ct detector to convey the light emitted by a scintillation crystal into a proportional electronic signal
Photon fluence
Quantity of X-rays photons passing through a specified area
Photon flux
Rate at which a quantity of X-ray photons/fluence passes through a unit area over a unit time
Pipelining
Form of parallel processing used by a computer to improve computation speed
Pitch
Relationship between collimation and table movement per gantry rotation
Pixel
Abbreviation of picture element. Individual boxes arranged in the matrix used to display the CT image.
Point spread function
Measure of a CT systems in-plane spatial resolution that evaluates amount of spread inherent in an orthogonal image of a thin wire
Polyenergetic
Consisting of a spectrum of differing energies; describes the X-ray beam
Portal venous phase
Period of peak hepatic parenchymal enhancement when contrast material redistributes from the blood into the extravascular spaces. 60-70sec after the initiation of contrast agent
Prospective ECG gating
Method of improving the temporal resolution of an MSCT system during exams of the heart and mediastinum. Data acquired in axial “step and shoot” mode and only during diastolic portion of the RR interval
Prospective reconstruction
Initial construction of acquired raw data into CT image data with selected display field of view, algorithm, image center, etc
Pseudoenhancement
Minimal increase in attenuation demonstrated by a structure that typically does not enhance after IV contrast. Most common during cyst evaluation
Pulmonary embolism
Condition where a thrombus breaks free from elsewhere in the venous system and migrated into a pulmonary artery. Pulmonary artery becomes blocked, causing reduced blood flow to the lung tissue
Pulmonary hypertension
Condition of increased blood pressure in the pulmonary vasculature
Pulse oximeter
Electronic device placed in a patient’s finger, toe, or earlobe to measure pulse and blood oxygen levels
Quality assurance
Measurement of scanners performance through quality testing procedures and evaluation of test results
Quality control
Implementation of corrective actions to improve any identified performance inadequacies of the CT system
Raw data
Transmission measurements obtained by the detectors used to mathematically reconstruct image
Ray
Portion of the X-ray beam transmitted through the patient and incident upon a single detector
Ray sum
The measurement of transmitted radiation made by an individual detector used to determine the attenuation occurring along a ray
Region of interest
Used-defined graphic outline that calculates the average CT number of a given anatomic area
Rendering
Use of 3D algorithms to provide a specific perspective to the construction of a 3D model
Response time
Ability of a ct detector to quickly measure X-ray and then recover before the next measurement
Retrospective ECG gating
Method of improving the temporal resolution of an MSCT system during ct exams of the heart and mediastinum. Only data acquired during diastole are used for recons, allowing for reduced motion artifact
Ring artifact
Incorrect ring density on the reconstructed CT image resulting from detector malfunction
Saddle pulmonary embolism
Condition where a large clot straddles the main trunk of the pulmonary artery as it bifurcated into the left and right pulmonary arteries
Saline flush
Injection of a volume of normal saline solution immediately after the bolus administration of an iodinated contrast agent. Flushes any contrast remaining through automated injector tubing, improving the efficiency of contrast agent utilization
Scan delay
Time between initiation of contrast agent administration and ct acquisition. Chosen time determines phase of contrast enhancement for a given ct image
SFOV
Parameter controlling diameter of the circular data acquisition field within the ct gantry as determined by the number of activated detectors along the x-y axis. Also, calibration field
Scintillation
Production of light energy by a ct detector material in response to absorbed X-ray energy
Scout image
Digital survey radiograph acquired by CT system for purpose of prescribing the cross-sectional acquisition. Produced by translating patient through gantry without tube and detector rotation. Also, topography, scanogram, survey radiograph
Section interval
Distance between center of one CT section and the center of the next adjacent section
Section width
Dimension of a reconstructed CT slice along the longitudinal direction of acquisition z-axis. Also, slice thickness
Signal
Electronic current emitted by the ct detector in response to the absorption and measurement of transmitted radiation
Signal-to-noise ratio
Quantification of the amount of noise displayed in a CT image. calculated as standard deviation in ROI measurement of a water phantom image
Single slice CT
CT system with a single row of detectors capable of acquiring only one image section for each gantry rotation
Slice sensitivity profile
Graph demonstrating the broadening of the section width that is inherent to volumetric CT acquisition
Slip-ring
Rotating assembly used to enable the passage of electrical signal during continuous rotation of the helical CT system
Spatial frequency
Waveform of a signal that represents the varied objects images by a CT system
Spatial resolution
Ability of a CT imaging system to display fine details separately. Given in units of line pairs per centimeter (lp/cm)
Step artifact
The unwanted appearance of individual sections on a MPR or 3D reformat image resulting in a loss of sharpness and detail
Stranding
Hazy increase in density of the fat surrounding an organ on CT exams that usually indicate inflammation
Stupor
Semicomatose state of consciousness where the individual is nearly unresponsive to stimuli
Surface rendering
Construction of a 3D model of a specific tissue type by limiting the displayed volumetric data on the basis of an attenuation threshold . Also, SSD
Systole
Portion of the cardiac cycle when the heart muscle is in contraction. BP reflects the force exhibited on the arterial walls during ventricular contraction.
Teleradiology
Transmission of image data across networks from the imaging facility to an off-site location for review and interpretation
Temporal resolution
Ability of a CT system to freeze motion and provide and image free of blurring
Total collimation
Combined thickness of all of the sections that are simultaneously acquired with each gantry rotation during MSCT acquisition
Triple rule out
Comprehensive MSCT exam of the chest for cardiac and no cardiac pin. Single acquisition evaluates for coronary artery disease, aortic aneurysm, and pulmonary embolism
Tube arcing
Short circuiting within the X-ray tube during data acquisition that results in severe streak artifacts in image
Uniform matrix array
Type of MSCT detector array that utilizes multiple detectors in longitudinal direction, each of the same length
Uniformity
Maintenance of relatively consistent CT values across the entire image of an object of equal density
Urticaria
Itchy, red rash commonly referred to as hives
Valsalva effect
Temporary rise in blood pressure that may occur during forceful exhalation
View
Each data sample made by the DAS during CT data acquisition
Views per rotation
Sampling rate of transmission measurements acquired during each gantry rotation
Virtual bronchography
3D fly through endobrachial views included in this exam
Volume rendering
3D model technique that utilizes the entire acquired data set but adjusts the opacity of voxels included in the 3D image according to their tissue characteristics
Voxel
Abbreviation of volume element. Volume of tissue represented by a pixel in the matrix used to display the CT image
Window
User-defined range of pixel values that will be assigned a particular shade of gray
Window level
Pixel value, in HU, at center of window width. Controls the brightness/density of the CT image
Window width
Range of pixels assigned a shade of gray in the displayed CT image. Controls contrast
Windowing
Process of gray-scale mapping of the CT image on the basis of the CT number assigned to each pixel
X-y axis
Perpendicular plane/orthogonal to the axis of data acquisition (z-axis). Parallel to the plane of the ct gantry
Z-axis
Longitudinal direction of the coordinate system used to spatially describe location of acquired CT sections. Corresponds to the axis of data acquisition
Z-filtering
Math process utilized by MSCT systems to reconstruct thin sections at any point along the acquired z-axis volume
