CT Mosby Terms Flashcards
1
Q
180 Degree Linear Interpolation (180LI)
A
Type of algorithm used for MSCT image reconstruction in which data acquired from a shorter distance (180 degrees) away from the reconstructed slice location are interpolated.
2
Q
360-degree linear interpolation (360 LI)
A
type of algorithm used for MSCT image reconstruction in which two sets of projection data acquired 360 degress apart are used to form an image at a precise z-axis location
3
Q
Absorbed Dose
A
The amount of x-ray energy absorbed in a unit of mass (measured in grays Gy)
4
Q
Absorption Efficiency
A
The ability of an individual CT detector to absorb & measure the transmitted x-ray intensity incident upon it. Primarily controlled by the characteristics & physical makeup of the detector material.
5
Q
Adaptive Array
A
the type of MSCT detector array configured with the thinnest detectors at the center, surrounded by detectors of incrementally increasing widths along the z-axis.
6
Q
Advanced Single Slice Rebinning (ASSR) Algorithm
A
cone beam correction algorithm used to overcome potential attenuation calculation errors from the divergent beam of MSCT systems.
7
Q
Afterglow
A
the tendency of a scintillation-type CT detector to continue to glow in response to x-radiation after the exposure source has been terminated
8
Q
Agatston Score
A
quantification of the volume and density of calcium within the coronary arteries. As calculated a CT coronary artery calcification (CAC) examination, the Agatston score is used to indicate a patient’s risk of suffering a cardiac event.
9
Q
ALARA
A
Cardinal principle of radiation dose reduction for all radiologic procedures (as low as reasonably achievable)
10
Q
Algorithm
A
Mathematical filter applied to raw data during CT image reconstruction to remove blurring artifact inherent to back-projection (also referred to as KERNEL)
11
Q
Aliasing
A
A form of streak artifact caused by an insufficient number of views (data samples) obtained during data acquisition.
12
Q
Analog-to-Digital Converter (ADC)
A
component of the data acquisition system (DAS) responsible for converting the electronic signal emitted by the CT detectors into digital form.
13
Q
Archival
A
the storage of CT data in either hard (film) or soft (digital) form.
14
Q
Array Processor (AP)
A
Component of the 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.
15
Q
Arterial Phase
A
Period of peak arterial enhancement after the bolus IV admin of iodinated CM (for example, the hepatic arterial phase occurs approximately 25-35 seconds after the initiation of CM admin)
16
Q
Artifact
A
A form of noise on the CT image resulting from errors during the measurement of transmitted radiation by the detectors
17
Q
Ataxia
A
A neurologic sign characterized by a loss of muscular coordination
18
Q
Attenuation
A
the reduction in intensity of a radiation beam as it passes through a substance.
19
Q
Attenuation Coefficient
A
the value assigned to an object quantifying its ability to attenuate an x-ray beam
20
Q
Automatic Tube Current Modulation (ATCM)
A
CT system software used to adjust the mA throughout an acquisition to reduce patient radiation dose to a minimum
21
Q
Automatic Tube Voltage Selection (ATVS)
A
CT system software used to adjust the tube voltage (kVp) based upon the changing patient attenuation along the scan acquisition range to reduce patient radiation dose to a minimum.
22
Q
Back-Projection
A
the mathematical process of CT image reconstruction whereby ray sum data are projected back onto a matrix.
23
Q
Beam Hardening
A
The phenomenon whereby low-energy photons are absorbed as the x-ray beam passes through an object, resulting in an increase in the average photon energy of the beam.
24
Q
Beam Pitch
A
The ratio of table feed per gantry rotation to the total collimation used during acquisition with a multislice CT (MSCT) system.
25
Beam Width
The dimension of the primary beam in the longitudinal or z-axis as controlled by the pre-patient collimator.
26
Binning
the process of electronically combining signal from adjacent detector elements to produce a reconstructed CT image that is thicker than the individual detector width
27
Bit Depth
The number of information bits contained within each pixel
28
Blood Urea Nitrogen (BUN)
A measurement of renal function, determined as the amount of nitrogen in the blood in the form of the waste product urea (normal range: 7-25mg/dL)
29
Bow-tie Filter
A type of filter added to the CT x-ray tube to compensate for the cylindrical shape of most body parts. The filter is thicker at the ends & helps shape the beam to reduce patient radiation exposure
30
Cardiac Cycle
The series of blood flow-related events that occur from the beginning of one heartbeat to that of the next
31
Cerebral Blood Flow (CBF)
A common measurement during CT perfusion studies of the brain. The quantity of blood (ML) that moves through 100g of brain tissue each minute. (Normal range in gray matter is 50-60 mL/100g/min)
32
Cerebral Blood Volume (CBV)
a common measurement during CT perfusion studies of the brain. The quantity of blood (mL) contained within a 100g volume of brain tissue. (Normal range is 4 to 5 mL/100 g)
33
Cerebral Perfusion
the level of blood flow throughout brain tissue
34
Coma
A state of unconsciousness where the individual is completely unresponsive to stimuli
35
Constant mAs
the product of milliamperage (mA) and scan time (seconds) utilized for a CT acquisition.
36
Contiguous Images
CT images acquired with equal section thickness and reconstruction intervals
37
Contrast Resolution
the ability of a CT system to detect an object with a small difference in linear attenuation coefficient from the surrounding tissue. (May also be referred to as low-contrast detectability or sensitivity.)
38
Contrast-Induced Nephrotoxicity (CIN)
a substantial decline in renal function that can occur after a patient receives IV contrast material. it is usually signified by a marked increase in serum creatinine over a baseline measurement obtained prior to contrast agent administration.
39
Convolution
Mathematical filtration used by the CT system to remove blurring artifact during the back-projection method of image reconstruction.
40
Corticomedullary Phase
a late arterial phase of renal enhancement beginning 30-40 seconds after the initiation of contrast agent administration. Optimal enhancement of the renal cortex and renal veins occurs during this period.
41
Creatinine
A waste product of metabolism found in the bloodstream and measured as an indicator of renal function (normal range 0.5-1.5 mg/dL)
42
CT Arthrography
CT evaluation of a joint after the intra-articular injection of iodinated contrast material.
43
CT Bronchography
specialized MSCT examination of the tracheobronchial tree consisting of MPR and volume-rendered 3D images reconstructed from thin, overlapping MDCT axial images through the airways.
44
CT Colonography
specialized CT evaluation of the large intestine used primarily for colon cancer screening. The large intestine is extended and scanned with thin-section CT. 2D and 3D models are constructed, including virtual endoscopic "fly-through" views.
45
CT Cystography
specialized CT examination of the bladder whereby iodinated contrast material is administered directly under gravity into the bladder via Foley catheter
46
CT Dose Index (CTDI)
an approximate measure of the radiation dose received in a single CT section or slice.
47
CT Enteroclysis
specialized CT evaluation of the small bowel whereby enteral contrast material is administered directly into the duodenum through a nasogastric catheter placed under fluoroscopic guidance.
48
CT Enterography
specialized CT evaluation of the small bowel after the oral administration of low-density (0.1%) barium.
49
CT Fluoroscopy
continuous, real-time CT imagine used predominantly for CT guided interventional procedures.
50
CT Myelography
CT evaluation of the spinal cord and nerve roots after the intrathecal administration of iodonated contrast material.
51
CT Number
relative value assinged to each pixel to quantify the attenuation occurring in each voxel in comparison with the attenuation of water. Given in Hounsfield units (HU) may also be referred to as PIXEL VALUE.
52
CT Runoff
the CT angiographic assessment of the peripheral artierial tree from the renal arteries through the lower extremeties.
53
CT Simulation
the process of obtaining anatomic information with CT imaging that is used to calculate the beam arrangement for radiotherapy.
54
CT Urogram
a comprehensive, multiphasic CT evaluation of the urinary tract. Consists primarily of pre-contrast, post-contrast, and delayed CT acquisitions through the kidneys, ureters, and bladder. (Commonly referred to as a CT-IVP.)
55
Cupping Artifact
an error appearing in the superior portion of the skull, where dense bone averages with the low-attenuating brain tissue. This partial volume artifact may result in abnormally dense-appearing brain parenchyma.
56
Data Acquisition System (DAS)
The electronic components of a CT system responsible for measuring the transmitted x-radiation absorbed by the detectors.
57
Data Channel
pathway of data transmission from the detectors to the computerized components of the system's data acquisition system. The number of data channels of a CT system determines the maximum number of sections that may be acquired with each gantry rotation
58
Data Transfer Rate
The speed at which a computerized storage device is able to transfer data
59
Deconvolution
mathematical image processing technique used to generate blood perfusion maps during CT perfusion studies of the brain.
60
Detector
device responsible for measuring transmitted radiation and converting it into a proportionate electronic signal to be used for image reconstruction.
61
Detector Array
the CT image receptor, consisting of a series of detectors arranged in varying configurations.
62
Detector Collimation
the process of determining section width in the MSCT system as determined by the defined beam width and the number and thickness of detectors utilized for image reconstruction.
63
Detector Configuration
the number, length, and organization of the individual detector elements in an MSCT system
64
Detector Pitch
the ratio of table feed per gantry rotation to the acquired section width. This definition of pitch is used for helical single-slice CT (SSCT)
65
Diastole
The portion of the cardiac cycle when the heart muscle is relaxed. Reflects the force exhibited on the arterial walls during relaxation of the heart muscle. (Bottom or second number provided during try assessment of blood pressure)
66
DICOM
The process of recording, storing, printing, and transmitting medical images data (Digital Imaging and Communications in Medicine)
67
Display Field of View (DFOV)
the diameter of the acquired attenuation data displayed across the image matrix. (may also be referred to as the ZOOM FACTOR or TARGET VIEW)
68
Dose Length Product (DLP)
the measurement of dose for the entire series of CT images. Equal to the calculated dose per section mulitplied by the length of a CT acquisition along the z-axis.
69
Dose Profile
The section of the patient exposed to radiation at the gantry isocenter.
70
Dual-Energy CT
simultaneous acquisition, by and MSCT system, of attenuation data for a single anatomic section with two x-ray beams, each having a different energy spectrum.
These CT systems rapidly switch between or alternate kVp settings during data acquisition, allowing for improved contrast between substances of differing densities.
71
Dual-Source CT
CT system that consists of two seperate x-ray tubes and detector arrays mounted 90 degrees from each other within the gantry, allowing for dual-energy CT aquisition.
72
Edge Gradient
streak artifact that occurs at the interface between a high-density object and the lower-attenuation material surrounding it.
73
Effective Dose
approximation of the relative risk from exposure to ionizing radiation; is calculated by assigning weighting factors to different tissues on the basis of their individual radiosensitivities. (measured in Sieverts (Sv)
74
Effective mAs
the calculated mAs per acquired slice with a multislice CT (MSCT) system.
75
Effective Section Width
the slice sensitivity profile (SSP) of the reconstructed CT section. It is measured at the full width at half maximum (FWHM) of the SSP for a given CT acquisition.
76
Electrocardiogram (ECG)
a graphical representation of the electrical activity of the heart recorded over time through electrodes placed on the patient's skin.
77
Electron Beam CT (EBCT)
specialized CT design devoid of moving parts. Utilizes a beam of electrons bombarding a tungsten target to produce x-radiation. EBCT systems are capable of extremely short exposure times and have their greatest application in cardiac imaging
78
Equilibrium Phase
contrast phase of the liver when hepatic parenchymal ehancement dissipates and there is minimal attenuation differenes between the intravascular and extravascualr spaces. Usually occurs at 2-3 minutes after the initiation of contrast agent administration.
79
Excretory Phase
a delayed imaging renal enhancement that begins approximately 3 minutes after the initiation of contrast agent administration. Contrast material has been excreted into the renal calyces, opacifying the renal pelvis and the remainder of the urinary collecting system (ureters, bladder)
80
Exposure
The ability of x-rays to ionize a volume of air (measured in roentgens R)
81
Extravasation
escape of contrast material outside the blood vessel into the surrounding soft tissue
82
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-y axis)
83
Feldkamp-Davis-Kress (FDK) Algortihm
Cone beam correction algorithm utilized to overcome potential attenuation calculation errors from the divergent beam of MSCT systems
84
Filtered Back Projection
the mathematical process of CT image reconstruction that involves convolution of the raw data prior to their projection back onto a matrix.
85
Filtration
Removal of the low-energy x-ray photons emitted from the x-ray tube to improve beam quality and reduce patient dose
86
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 the segmented detector rows found in MDCT systems.
87
Flying Focal Spot
electronic switching technique whereby the electron beam is electromagnetically steered toward two separate locations on the rotating anode. Results in the emission of two sources of x-radiation from the CT x-ray tube.
88
Focus-to-Detector Distance
the distance between the x-ray source (CT tube) and the detector array
89
Focus-to-Isocenter Distance
the distance from the x-ray source (CT tube) to the center of the gantry opening, where the patient should be positioned
90
Full Width at Half Maximum (FWHM)
the midpoint of a slice sensitivity profile (SSP), where the effective section width for a CT acquisition is determined.
91
Gantry
The assembly that houses the x-ray tube, detectors, and additional data acquisition components of a CT system.
92
Geometric Efficiency
the ability of a detector array to absorb and measure the transmitted x-ray intensity incident upon it. Primarily controlled by the physical arrangement of detectors within the array and the amount of interspace material required between adjacent detectors.
93
Glomerular Filtration Rate (GFR)
An approx of creatinine clearance or the rate by which creatinine is filtered from the bloodstream. GFR utilized as a measure of renal function with normal ranges of:
(70 +/-14mL/min/m^2 for men)
(60+/-10mL/min/m^2 for women)
94
Half-Value Layer (HVL)
The thickness of material that is capable of reducing the intensity of the x-ray beam to one-half of its original value.
95
Helical
the type of CT acquisition whereby the x-ray tube and patient continuously move during scanning, yielding a data set in the form of a helix. (SPIRAL)
96
Hounsfield Bar
specific type of streaking beam-hardening artifact that occurs in the posterior fossa of the brain.
97
Hounsfield Unit (HU)
the unit of the CT number scale assigned to each pixel to quantify relative attenuation.
98
Hybrid Array
the type of MSCT detector array with narrower detectors positioned midline, flanked by the wider detectors.
99
Hyperdense
possessing CT attenuation values greater than the values of the surrounding tissue.
100
Hypodense
possessing CT attenuation values less than the values of the surrounding tissue.
101
Hypoxemia
Condition of low concentration of oxygen in the blood
102
Hypoxia
Condition of insufficient oxygenation of tissue at the cellular level
103
Image Data
the reconstructed data that have been projected back onto a matrix after convolution by an algorithm and displayed on a monitor as a gray-scale CT image.
104
Insufflation
Introduction of air into an organ or cavity for distention and improved visualization
105
Interpolation
mathematical process used for helical CT image reconstruction whereby data from tube rotations just above and just below a given slice position are used for image reconstruction
106
Isocenter
the center point of gantry rotation
107
Isodense
possessing CT attenuation values equal to the values of the surrounding tissue.
108
Isotropic
having equal dimensions along the x-,y-, and z-axes; in CT, describes voxels with this property.
109
Iterative Reconstruction
a mathematical CT 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
110
Kerma
quantity of energy deposited in a unit of mass. (absorbed dose of x-radiation)
111
Kernel
Mathematical filter applied to raw data during CT image reconstruction to remove the blurring artifact inherent to back-projection (ALGORITHM)
112
Lethargy
A level of consciousness characterized by feelings of fatigue, drowsiness or apathy
113
Linear Attenuation Coefficient
the value assigned to an object to quantify the extent to which it attenuates x-ray.
114
Linearity
the relative accuracy between calculated CT numbers and their respective linear attenuation coefficients
115
Lossless Compression
the reversible process whereby the CT image is digitally compressed in size without loss of data and is identical to the original
116
Lossy Compression
The irreversible process whereby data are lost during the compression process and the CT image dose not exactly match the original
117
Matrix
Two-dimensional grid of numbers arranged in rows and columns
118
Maximum Intensity Projection (MIP)
multiplanar reformation technique that displays only the maximum pixel value along a ray traced through the object to the viewer's assumed perspective in front of the viewing monitor.
119
Mean Transit Time (MTT)
a common measurement during CT perfusion studies of the brain. MTT refers to the average transit time, in seconds, needed for blood to pass through a given region of brain tissue
120
Minimum Intensity Projection (min-IP)
Multiplanar reformation technique that displays the minimum pixel value along each ray to the viewer
121
Misregistration
artifact that occurs when patient motion between consecutive acquisitions causes misalignment of data and the potential loss of anatomic information
122
Modulation Transfer Function (MTF)
A graphical representation of a CT system's response to a spatial frequency that serves as a measurement of the system's in-plane spatial resolution
123
Monoenergetic
consisting of a uniform photon energy; used in CT to describe a beam of x-radiation.
124
Multiphase
CT data acquisition during multiple timed phases of contrast enhancement
125
Multiplanar Reformation (MPR)
the process of displaying CT images in a different orientation from the one used in the original reconstruction.
126
Multisegment Reconstruction
a method of improving the temporal resolution of a CT system whereby the data acquisition process is subdivided into separate components of smaller rotation angles
127
Multislice CT (MSCT)
a CT system with a detector array capable of acquiring more than one section for each gantry rotation. (also referred to as multidetector CT (MDCT)
128
Nephrographic Phase
Renal enhancement phase occurring between 70-90 seconds after the start of injection of contrast. Enhancement between renal cortex and medulla reaches equilibrium, providing optimal sensitivity for parenchymal lesions.
129
Noise
Grainy appearance on the CT image due primarily to an insufficient x-ray photon flux per voxel. May also be described as any portion of the signal that contains no useful information, as evident in certain CT image artifacts
130
Nyquist Theorem
a sampling law dictating that the data sampling frequency must be at least twice the object's spatial frequency in order for the object to be resolved by the CT system.
131
O-Arm
portable CT-fluoroscopy unit with a telescoping gantry used to acquire 3D CT images and standard fluoroscopy during invasive or surgical procedures.
132
Obtundation
A depressed level of consciousness characterized by dulled feelings, with slowed response to stimuli.
133
Opacification
the increase in CT density of a structure due to filling with positive contrast material.
134
Operating System (OS)
the main software of the CT computer, controlling the utilization of the hardware resources including the available memory, CPU time, disk space, and so on.
135
Orthogonal
imaging planes that are perpendicular to each other.
136
Orthographic Volume Rendering
technique yielding a 3D model with the perspective of externally viewing the reconstructed object
137
Osmolality
the propensity of an iodinated contrast medium to cause fluid from outside the blood vessel to move into the bloodstream.
138
Out-of-Field Artifact
hyperdense streaking that occurs when a portion of a patient has been positioned outside the scan field of view (SFOV)
139
Overbeaming
expansion of the primary beam in an MSCT system to ensure that all detectors of the array are exposed to x-rays of equal intensity.
140
Overlapping Image
CT images produced with a reconstruction interval that is less than the section width
141
Overranging
the process of applying radiation dose before and after the acquisition volume to ensure sufficient data collection for the interpolation algorithms of helical CT reconstruction.
142
PACS
Responsible for storing, retrieving, distributing, and displaying CT and other digital medical images (picture archival and communications system)
143
Pancreatic Phase
a delayed arterial enhancement phase occuring approximately 35 to 45 seconds after the start of contrast agent administration, if an adequate volume has been injected at a rate of 3mL/sec or greater.
144
Parallel Processing
The ability of the computer to perform multiple functions simultaneously
145
Partial Volume Artifact
an 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
146
Partial Volume Averaging
inaccuracy in pixel values that occurs when the associated voxels contain attenuation coefficients for multiple tissue types. The values are averaged together to yield a single pixel value that attempts to represent an assortment of different materials.
147
Perspective Volume Rendering
technique yielding a 3D model with the perspective of being within the lumen of the object, similar to an endoscopic view. may also be referred to as (IMMERSIVE RENDERING).
148
Phantom
a quality control device typically composed of a radiolucent plastic material containing specialized inserts that is used to measure specific image quality criteria.
149
Photodiode
device used by a solid-state CT detector to convert the light emitted by a scintillation crystal into a proportional eletronic signal.
150
Photon Fluence
quantity of x-ray photons passing through a specified area
151
Photon Flux
the rate at which a quantity of x-ray photons (fluence) passes through a unit area over unit time
152
Pipelining
a form of parallel processing used by a computer to improve computation speed.
153
Pitch
The relationship between collimation and table movement per gantry rotation
154
Pixel
Refers to the individual boxes arranged in the matrix used to display the CT image (PICTURE ELEMENT)
155
Point Spread Function (PSF)
a measure of a CT system's in-plane spatial resolution that evaluates the amount of spread inherent in an orthogonal image of a thin wire.
156
Polyenergetic
consisting of a spectrum of different energies; used in CT to describe the beam of x-radiation.
157
Portal Venous Phase
period of peak hepatic parenchymal enhancement when contrast material redistributes from the blood into the extravascular spaces. Typically occurs 60-70 seconds after the initiation of contrast agent administration.
158
Prospective ECG Gating
method of improving the temporal resolution of an MSCT system during examination of the heart and mediastinum. Data are required in an axial "step-and-shoot" mode and only during the diastolic portion of the R-R interval.
159
Prospective Reconstruction
the initial construction of the acquired raw data into CT image data with selected display field-of-view, algorithm, image center, and so on.
160
Pseudoenhancement
minimal increase in attenuation demonstrated by a structure that typically does not enhance following intravenous contrast administration. Most common during MSCT evaluation of cysts.
161
Pulmonary Embolism
The condition where a thrombus (blood clot) breaks free from elsewhere in the venous system (usually the lower extremity) and migrates into a pulmonary artery. The pulmonary artery becomes blocked, causing reduced blood flow to the lung tissue
162
Pulmonary Hypotension
A condition of increased blood pressure in the pulmonary vasculature (i.e. pulmonary artery, pulmonary vein, and/or pulmonary capillaries)
163
Pulse Oximeter
an electronic device placed on a patient's finger, toe, or earlobe to measure pulse and blood oxygen levels.
164
Quality Assurance
the measurement of the scanner's performance through quality testing procedures and evaluation of the test results.
165
Quality Control
the implementation of corrective actions to improve any identified performance inadequacies of the CT system
166
Raw Data
the transmission measurements obtained by the detectors used to mathematically reconstruct the CT image.
167
Ray
The portion of the x-ray beam transmitted through the patient and incident upon a single detector
168
Ray Sum
measurement of transmitted radiation made by an individual detector used to determine the attenuation occurring along a ray
169
Region of Interest (ROI)
a user-defined graphic outline that calculates the average CT number of a given anatomic area.
170
Rendering
use of 3D algorithms to provide a specific perspective to the construction of a 3D model.
171
Retrospective ECG Gating
method of improving the temporal resolution of an MSCT system during CT examinations of the heart and mediastinum. Only data acquired during diastole are used for image reconstruction, allowing for a reduction of motion artifacts in the CT image.
172
Retrospective Reconstruction
reconstruction performed after the initial prospective reconstruction. Multiple retrospective reconstruction of raw data are possible, with changes to display field of view, algorithms, and image center
173
Ring Artifact
an incorrect ring of density on the reconstructed CT image resulting from detector malfunction.
174
Saddle Pulmonary Embolism
a condition where a large clot (thrombus) straddles the main trunk of the pulmonary artery as it bifurcates into the left and right pulmonary arteries
175
Saline Flush
injection of a volume of normal saline solution immediately following the bolus injection of a contrast agent; flushes any remaining contrast through the automated injector tubing, improving the efficiency of contrast utilization.
176
Scan Delay
the time between the initiation of contrast administration and CT data acquisition. The chosen scan delay determines the phase of contrast enhancement for a given CT acquisition
177
Response Time
The ability of a CT detector to quickly measure x-ray and then recover before the next measurement
178
Scan Field of View (SFOV)
a parameter that controls the diameter of the circular data acquisition field within the CT gantry as determined by the number of activated detectors along the x-y axes. (may also be referred to as the CALIBRATION FIELD)
179
Scintillation
the production of light energy by a CT detector material in response to absorbed x-ray energy.
180
Scout Image
digital survey radiograph acquired by the CT system for the purpose of prescribing the cross-sectional acquisition. similar to a conventional radiograph, it is produced by translating the patient through the gantry without tube and detector rotation.
181
Section Interval
the distance between the center of one CT section and the center of the next adjacent section.
182
Section Width
the dimension of a reconstructed CT slice along the longitudinal direction of acquisition (z-axis). (commonly referred to as SLICE THICKNESS)
183
Signal
Electronic current emitted by the CT detector in response to the absorption and measurement of transmitted radiation
184
Signal-to-Noise Ration (SNR)
Quantification of the amount of noise in a displayed CT image. Calculated as the standard deviation in the ROI measurement of a water phantom image
185
Single-Slice CT (SSCT)
a CT system with a single row of detectors capable of acquiring only one image section for each gantry rotation.
186
Slice Sensitivity Profile (SSP)
graph demonstrating the broadening of the section width that is inherent to volumetric (helical) CT acquisition.
187
Slip-Ring
the rotating assembly used to enable the passage of electrical signal during continuous rotation of the helical CT system.
188
Spatial Frequency
the waveform of signal that represents the varied objects imaged by a CT system.
189
Spatial Resolution
the ability of a CT imaging system to display fine details separately. given in units of line pairs per centimeter (lp/cm)
190
Step Artifact
the unwanted appearance of individual sections on a mulitplanar or 3D reformation image resulting in a loss of sharpness and detail.
191
Stranding
hazy increase in density of the fat surrounding an organ on CT exams that usually indicates an inflammatory process.
192
Stupor
A semi comatose state of consciousness where the individual is nearly unresponsive to stimuli
193
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. (may also be referred to as SHADED SURFACE DISPLAY (SSD)
194
Systole
The portion of the cardiac cycle when the heart muscle is in contraction. Reflects the force exhibited on the arterial walls during ventricular contraction. (Top or first number of blood pressure)
195
Teleradiology
The transmission of image data across networks from the imaging facility to an off-site location for review and interpretation
196
Temporal Resolution
the ability of a CT system to freeze motion and provide an image free of blurring.
197
Total Collimation
the combined thickness of all of the sections that are simultaneously acquired with each gantry rotation during MSCT acquisition.
198
Triple Rule-Out
comprehensive MSCT exam of the chest for cardiac and non-cardiac pain. The single acquisition evaluates for coronary artery disease, aortic aneurysm, and pulmonary embolism.
199
Tube Arching
short circuiting within the x-ray tube during data acquisition that results in severe streak artifacts
200
Uniform Matrix Array
the type of MSCT detector array that utilized multiple detectors in the longitudinal direction, each of the same length.
201
Uniformity
maintenance of relatively consistent CT values across the entire image of an object of equal density.
202
Urticaria
Itchy, red rash commonly referred to as HIVES
203
Valsalva Effect
temporary rise in blood pressure that may occur during forceful exhalation
204
View
Each data sample made by the DAS during CT data acquisition
205
Views Per Rotation (VPR)
the sampling rate of transmission measurements acquired during each gantry rotation.
206
Virtual Bronchography
3D fly-through endobronchial views included in a CT bronchgraphy exam
207
Volume Rendering
a 3D modeling technique that utilizes the entire acquired data set but adjusts the opacity of voxels included in the 3D image according to their tissue characteristics.
208
Voxel
abbreviation of VOLUME ELEMENT. Refers to the volume of tissue represented by a pixel in the matrix used to display the CT image
209
Window
the user-defined range of pixel values that will be assigned to a particular shade of gray.
210
Window Level (WL)
the pixel value, given in Houndsfield units (HU), at the center of the window width. controls the BRIGHTNESS (density) of the CT image.
211
Window Width (WW)
the range of pixel values assigned to a shade of gray in the displayed CT image. Controls the CONTRAST of the CT image.
212
Windowing
the process of gray-scale mapping of the CT image on the basis of the CT number (Hounsfield value) assigned to each pixel.
213
X-Y Axis
The plane perpendicular (orthogonal) to the axis of data acquisition (z-axis). The x-y axis is parallel to the plane of the CT gantry.
214
Z-Axis
longitudinal direction of the coordinate system used to spatially describe the location of acquired CT sections. Corresponds to the axis of data acquisition.
215
Z-Filtering
mathematical process utilized by MSCT systems to reconstruct thin sections at any point along the acquired z-axis volume.
216
