1 Flashcards
(434 cards)
1
Q
Anatomic landmark
A
Landmark, such as the xiphoid or the iliac crest, used as a reference point when planning the scout image
2
Q
MTT
A
Mean transit time
3
Q
Information technology (IT):
A
The study, design, development, implementation, support, or management of computer based information systems; particularly software applications and computer hardware.
4
Q
Bolus injection technique
A
A rapid injection of contrast material. A volume of contrast of 50 to 200 mL is injected at a rate between 1 and 6 mL/s. The contrast bolus can be delivered by hand (using syringes) or by a mechanical injection system.
5
Q
Contrast-detail curve
A
Result of measuring and charting the relationship between object size and visibility (contrast-detail response).
6
Q
Low attenuation
A
An x-ray beam that is nearly unimpeded by an object; typically shown as dark gray or black on an image
7
Q
Beam attenuation
A
Phenomenon by which an x-ray beam passing through a structure is decreased in intensity or amount because of absorption and interaction with matter. The alteration in the beam varies with the density of the structure it passes through.
8
Q
Cupping artifacts
A
Artifact that results from beam hardening. It appears on the image as a vague area of increased density in a somewhat concentric shape around the periphery of an image, similar to the shape of a cup.
9
Q
Osmolality
A
Property of intravascular contrast media that refers to the number of particles in solution per unit liquid as compared with blood.
10
Q
Retrospective reconstruction:
A
Process of using the same raw data to later generate a new image.
11
Q
Embolism
A
The formation, development, or existence of a clot within the vascular system that detaches from its original site.
12
Q
Wired
A
Refers to networks that are linked by a physical connection.
13
Q
Time-density curves
A
Graphical representation that demonstrates the effect of varying contrast dose on aortic and hepatic contrast enhancement.
14
Q
CT venography
A
Modification of CTA that is used for the depiction of venous anatomy. Scan parameters are quite similar to CTA, except images are acquired while contrast is in the venous enhancement phase.
15
Q
Lossless compression
A
Method of image compression in which the image that is then decompressed is an exact replica of the original.
16
Q
Predetector collimators
A
Shape the beam and are located below the patient and above the detector array
17
Q
Absorption efficiency
A
Number of photons absorbed by the detector; dependent on the physical properties of the detector face (e.g., thickness, material).
18
Q
Radiation profile:
A
Variations along the length, or z axis, of the patient; also referred to as the z-axis dose distribution
19
Q
Voxel
A
Volume element. Three-dimensional cube of data acquired in CT.
20
Q
R-R interval
A
The distance between two R waves of a patient’s ECG that represents one complete cardiac cycle.
21
Q
Cerebrovascular reserve capacity (CVRC):
A
Describes how far cerebral perfusion can increase from a baseline value after undergoing stimulation. It is essentially a “stress test” for the brain. Stimulation is provided through the intravenous administration of a drug such as acetazolamide.
22
Q
Wireless:
A
Refers to network that use radio waves to transmit data between computers.
23
Q
Contrast media extravasation
A
The leakage of fluid from a vein into the surrounding tissue during IV contrast administration.
24
Q
Sampling theorem
A
Theorem that states because an object may not lie entirely within a pixel, the pixel dimension should be half the size of the object to increase the likelihood of that object being resolved.
25
Tube arcing
Undesired surge of electrical current (i.e., a shortcircuit) within the x-ray tube. A common cause of equipment induced artifact.
26
Region of interest (ROI
An area on the image defined by the operator.
27
Needle-holding devices
Devices that hold needles during a CT fluoroscopic procedure to avoid the hand of the clinician or assistant entering the CT beam.
28
Attenuation correction
Method for reducing artifacts in the PET image. In PET, loss of counts can occur because of anomalies in attenuation, scatter and random image noise, image artifacts, and image distortion. In a dedicated PET system, attenuation correction features are built into the process using a PET transmission scan. However, when PET/CT is used, data from the CT images can be used for attenuation correction of the PET emission data, eliminating the need for a separate, time consuming transmission scan.
29
Stroke in evolution
A time-limited event in which the
| neurologic deficits occur in a progressive pattern. Also referred to as a progressive stroke.
30
Anaphylactoid
Life-threatening reactions; symptoms include substantial respiratory distress, unresponsiveness, convulsions, clinically manifested arrhythmias, and cardiopulmonary arrest. These reactions require prompt recognition and treatment.
31
Homeostasis
Literally translated as “standing or staying the same,” in regards to the body, the minute-to-minute state of balance of water, electrolytes (such as sodium, potassium, chloride, and bicarbonate), and pH.
32
Edge gradient effect
Streak artifact or shading (both light and dark) arising from irregularly shaped objects that have a pronounced difference in density from surrounding structures
33
Renal failure
The inability of the kidney to filter waste from the blood that can result in the accumulation of nitrogenous wastes (or azotemia).
34
Molecular imaging
Any methodology that investigates events at the molecular and cellular levels.
35
Cone beam
The radiation emitted from the collimated x-ray source in multidetector row CT systems.
36
Pharmacokinetic factors
Pharmacokinetics includes the study of the mechanisms of absorption and distribution of an administered drug, the rate at which a drug action begins and the duration of the effect, the chemical changes of the substance in the body, and the effects and routes of excretion of the metabolites of the drug. In the context of iodinated contrast medium pharmacokinetic factors refer to contrast medium characteristics, including iodine concentration, osmolality, viscosity, volume, and fl ow rate.
37
Artifacts
Objects seen on the image but not present in the object scanned
38
Client-server network
Computers in this model are either classified as servers or clients. A server is a computer that facilitates communication between and delivers information to other computers. The server acts on requests from other networked computers (the clients), rather than from a person inputting directly into it.
39
Z-axis dose distribution
Variations along the length, or z axis, of the patient; also referred to as the radiation profile.
40
Viscosity
Physical property that may be described as the thickness or friction of the fluid as it flows. It is an important property that will influence the injectability of intravascular agents through small-bore needles and intravenous catheters
41
Focal spot
Area of the anode where the electrons strike and the x-ray beam is produced.
42
beta-blockers
Pharmaceuticals used to reduce motion artifact on cardiac CTA images by temporarily lowering a patient’s heart rate.
43
Effective slice thickness
Thickness of the slice that is actually represented on the CT image, as opposed to the size selected by the collimator opening. In traditional axial scanning, selected slice thickness is equal to effective slice thickness. However, because of the interpolation process used in helical scanning, the effective slice thickness may be wider than the selected slice thickness. Also called the slice-sensitivity profile.
44
Imaging informatics
How information about medical images is exchanged within the radiology departments and throughout the medical enterprise.
45
Oblique planes:
Body planes that are slanted and lie at an angle to one of the three standard planes.
46
Centigray (cGy)
A centigray (cGy) equals 1 rad. There are 100 rad in 1 gray (Gy).
47
Opacity value
Each voxel is assigned an opacity value based on its Hounsfield units. This opacity value determines the degree to which it will contribute, along with other voxels along the same line, to the final image.
48
Implantable ports
A single- or double-lumen reservoir attached to a catheter. The reservoir hub is implanted in the arm or chest subcutaneous tissue, and the catheter is tunneled to the accessed vein. No external device is visible. The outline of the device may be seen and felt as a small round elevation on the skin. Implanted ports are typically used for long-term intermittent access such as that required for chemotherapy.
49
Blood-brain barrier (BBB
A semipermeable structure that protects the brain from most substances in the blood, while still allowing essential metabolic function
50
Ureterolithiasis
Gravel-like deposits that appear in the ureter.
51
Glomerular filtration rate (GFR
Describes the fl ow rate of filtered fluid through the kidney and is a measurement of kidney function.
52
Scanner-created MPR
Scanner protocols are programmed so that MPRs are automatically generated by the scanner software.
53
Redundancy
Describes an arrangement in which two or more components perform the same task—if one element fails the duplication keeps the system functioning while the failed component is repaired. It can also refer to the duplication of data to provide an alternative in case of failure of one part of the process.
54
Angioplasty
Technique that is used to dilate an area of arterial blockage using a catheter with a small, inflatable, sausage-shaped balloon at its tip.
55
Displayed contrast
The displayed contrast of an image is dependent on the window settings used for its display
56
Supraorbital meatal line
Imaginary line used for positioning that connects the external acoustic meatus to the supraorbital margin. Also called the glabellomeatal line.
57
Health Level Seven (HL7
An organization that works to develop universal standards for clinical and administrative data throughout the healthcare arena.
58
Stair-step artifacts
When smooth objects, such as the aorta, appear on the reformatted image to have edges that resemble a flight of stairs. They result when wide slices are used as source images.
59
Distal
Term used in referring to extremities. Distal (away from) refers to movement toward the ends. The distal end of the forearm is the end to which the hand is attached.
60
Scan parameters
Factors that can be controlled by the
operator and affect the quality of the image produced. These factors include milliamperes, scan time, slice thickness, field of view, reconstruction algorithm, and kilovolt-peak. When using helical scan methods, the operator also has a choice of pitch.
61
Laser light accuracy
Determination of the accuracy of the alignment of the laser light used for patient positioning.
62
Afterglow
A brief, persistent flash of scintillation that must be taken into account and subtracted before image reconstruction
63
Slice thickness accuracy
Determination of the accuracy of the slice thickness selected by the operator versus the width of the collimator opening.
64
Adrenal adenoma
Benign adrenal mass
65
Thrombosis
The formation, development, or existence of a clot within the vascular system.
66
Half-life
Time it takes for half of the dose of a substance to be eliminated from the body
67
Bow tie filters
Mechanical fi lter that removes soft, or lowenergy, x-ray beams, minimizing patient exposure and providing a more uniform beam intensity.
68
Idiosyncratic reactions
Unexplained reactions that are largely unpredictable, most often occurring within 1 hour of contrast medium administration, and are not related to the dose.
69
Uncoupling effect
With digital technology, the image is not as directly linked to the dose, so even when an mA or kVp setting that is too high is used, a good image results. This effect can make it difficult to identify when a dose that is higher than necessary is used.
70
Computerized physician order-entry (CPOE
System that electronically transmits clinician orders to radiology and other departments.
71
Gray scale
System that assigns a certain number of Hounsfield values to each shade of gray.
72
Bits
binary digits
73
Volume rendering (VR
A 3D imaging technique that
creates a semitransparent representation of the imaged structure. An advantage of VR is that all voxels contribute to the image, allowing the image to display multiple tissues and show their relationship to one another.
74
Dorsal
Term used to describe movement toward the back surface of the body; also referred to as posterior.
75
Air embolism
Air that enters the bloodstream and can occur during an IV injection. Small quantities of air can be absorbed by the body; thus small air emboli may never be detected if patients are asymptomatic. However, large air emboli can cause seizures, permanent neurologic damage, or occasionally death. These large air emboli occur only as a result of human error.
76
Nephrolithiasis
Gravel-like deposits that may appear in any part of the urinary system, from the kidney to the bladder; used interchangeably with renal stones, renal calculi, kidney stones, and urolithiasis.
77
High-osmolality contrast media (HOCM
Older iodinated agents, now less commonly used for intravascular injections. The osmolality of these agents ranges from approximately 1,300 to 2,140 mOsm/kg, or about 4 to 7 times that of human blood.
78
Image data
Once the computer has processed the raw data assigning one HU value to each pixel
79
Radiation absorbed dose (rad
Unit of absorbed dose
80
Partial volume effect
Process by which different tissue
| attenuation values are averaged to produce one less accurate pixel reading. Also referred to as volume averaging.
81
Prospective reconstruction
Image reconstruction that is automatically produced during scanning.
82
Hybrid arrays
Detector rows that have variable widths and sizes. Also called adaptive or nonuniform arrays.
83
Polychromatic x-ray energy
An x-ray beam that is composed of photons with varying energies.
84
Segmentation errors
Errors in the reformatted image that are introduced when important vessels or other structures are inadvertently edited out of the data set.
85
Uniform array
Detector rows that are parallel and of equal size.
86
Premedication
Pretreatment, most often with steroids, to prevent reactions to contrast media
87
Mechanical injection systems
Method of administering iodinated contrast media, intravascularly, using a mechanical injection system that controls the fl ow rate and volume. Also known as power injection.
88
Projection displays
3D technique. Two common projection displays are the maximum-intensity projection (MIP) and the minimum-intensity projection (MinIP). The former selects voxels with the highest value to display; the latter selects voxels with the lowest value.
89
Sampling rate
Number of samples taken per second from the continuous signal emitted from the detector.
90
Table referencing
When the table position is manually set at zero by the technologist.
91
Compensating filters:
Filters the x-ray beam to reduce the radiation dose to the patient; help to minimize image artifact and improve image quality.
92
Display field of view (DFOV
The section of data selected for display on the image.
93
HRCT
High-resolution CT of the chest is a technique used for the assessment of lung parenchyma in patients with diffuse lung disease such as fibrosis and emphysema.
94
Response time
Time required for the signal from the detector to return to zero after stimulation of the detector by x-ray radiation so that it is ready to detect another x-ray event.
95
Three-dimensional reformation
Reformation that seeks to represent the entire scan volume in a single image. Unlike 2D displays, 3D techniques manipulate or combine CT values to display an image; the original CT value information is not included.
96
Fast Fourier transform (FFT
Discrete Fourier transform’s inverse. FFTs are of great importance to a wide variety of applications, including acoustical and image analysis
97
Fluorine-18 fluorodeoxyglucose
Radiotracer that has played a key role in advancing PET based on the fact that malignant tumors often favor the glycolytic pathway for metabolism.
98
Redundant array of inexpensive disks (RAID
Storage solution that capitalizes on speed and reliability that divides, or replicates, data among multiple hard drives. These drives are designed to work together and appear to the computer as a single storage device.
99
Kinetic energy
Energy of motion
100
Pencil ionization chamber
A special cylindrical dosimeter used in conjunction with a CTDI phantom to assess the radiation dose in CT.
101
Anterior
Term used to describe movement forward (toward the face); also referred to as ventral.
102
Hypotensive stroke
Although rare, pressure that is too low can reduce oxygen supply to the brain enough to cause a stroke
103
Embolic stroke
Type of ischemic stroke resulting from a traveling particle that forms elsewhere and is too large to pass through small vessels and eventually lodges in a smaller artery.
104
Nephrogram phase
The phase of renal enhancement that follows the corticomedullary phase that typically occurs approximately 100 to 120 seconds after the IV administration of a bolus of contrast material.
105
Workstation-created MPR
MPR generated directly on the workstation. This allows radiologists the flexibility and interactivity to create images that are suited to the specific clinical situation.
106
Archiving
Saving studies on auxiliary devices for the purpose of future viewing.
107
Central volume principle
Principle that states cerebral blood volume can be calculated as the product of the total cerebral blood flow and the time needed for the cerebral blood passage: CBF = CBV/MTT.
108
Coronary artery disease (CAD
A condition that results when plaque builds up in the coronary arteries. A partial or total blockage results, and the heart muscle does not get an adequate blood supply. Also referred to as ischemic heart disease.
109
Incidentalomas
Unsuspected adrenal masses that are found when CT studies are ordered as a result of unrelated symptoms
110
Staging
The process of determining the extent and distribution of disease.
111
Undersampling:
Insufficient projection data (for instance, when the helical pitch is greatly extended) that cause inaccuracies related to reproducing sharp edges and small objects and result in an artifact known as aliasing.
112
Corticomedullary phase
The phase of renal enhancement that follows the portal venous phase that typically occurs approximately 30 to 70 seconds after the IV administration of a bolus of contrast material.
113
Write-once read-many times memory (WORM
Type of computer memory in which data can be written to once, but read from many times.
114
Tube current
Measured in thousandths of an ampere, or milliamperes, it controls the quantity of electrons propelled from cathode to anode.
115
Intracellular lipid content
The amount of fat molecules a mass contains.
116
Subject contrast
Relates to the inherent properties of the object scanned. For example, the lung is said to possess high subject contrast because it is primarily air-filled. The low attenuation lungs provide a background that makes nearly any other object discernible because of its dramatic difference in density.
117
Wide area network (WAN
Computers that are farther apart and must be connected by telephone lines, cables, or radio waves.
118
Sequential CT
An imaging technique used for CT-guided interventions. The process requires a scan acquisition, needle placement, another scan acquisition, adjustment of the needle, another scan acquisition, and so forth until the needle is confirmed to be in the correct location.
119
Clustered scans
The practice of grouping more than one scan in a single breath-hold.
120
Crosstalk:
Image noise resulting from the scattering of x-ray photons by adjacent detectors.
121
Minimum-intensity projection (MinIP
3D technique that selects voxels with the lowest value to display.
122
Radiopharmaceutical
Radioactive pharmaceuticals used in the field of nuclear medicine as tracers in the diagnosis and treatment of many diseases.
123
Multiple image display
Function that allows more than one image to be displayed in a single frame.
124
Slice-sensitivity profile (SSP
Thickness of the slice that is actually represented on the CT image, as opposed to the size selected by the collimator opening. In traditional axial scanning, selected slice thickness is equal to effective slice thickness. However, because of the interpolation process used in helical scanning, the effective slice thickness may be wider than the selected slice thickness. Also called the effective slice thickness.
125
Barium peritonitis
Barium leaking into the peritoneal cavity
126
Localizer scans:
Digital image acquisitions that are created while the tube is stationary and the table moves through the scan field. Referred to by various names, depending on the manufacturer, such as scout, topogram, scanogram, and pilot.
127
Hospital information systems (HIS)
Information systems that focus on administrative issues, such as patient demographic data, financial data, and patient locations within the hospital.
128
Pulmonary circulation
The circulation pattern of blood fl ow that carries oxygen-depleted blood away from the heart to the lungs, and returns oxygenated blood back to the heart.
129
Scannable range
Degree to which a table can move horizontally. Determines the extent a patient can be scanned without repositioning.
130
View
A complete set of ray sums.
131
CT fluoroscopy (CTF
An add-on option for some scanners. Often used for CT-guided interventions. CTF allows for the near real-time capabilities of traditional fluoroscopy while maintaining the superior contrast resolution and 3D anatomic display of CT.
132
ECG-pulsed tube current modulation
Method developed to address concern about the radiation dose from retrospective ECG gating methods in CT. The tube current is automatically decreased during the systolic phase of the ECG tracing.
133
Digital-to-analog converters (DAC):
Changes the digital signal from the computer memory back to an analog format so that the image can be displayed on the monitor.
134
Nyquist sampling theorem:
Because an object may not lie entirely within a pixel, the pixel dimension should be half the size of the object to increase the likelihood of that object being resolved.
135
Milliampere (mA):
Measure of the tube current used in the production of x-ray energy. In conjunction with the scan time, it is the quantitative measure of the x-ray beam.
136
Penumbra
In the context of stroke (rather than x-ray beam physics) penumbra is surviving tissue at the margin of infarcted tissue. Without successful intervention this tissue is destined for infarction, but is not yet irreversibly injured. It is the penumbra that may be salvageable with the administration of t-PA.
137
Anode
X-ray tube design includes a cathode, which emits electrons, and an anode, which collects electrons.
138
Beam-hardening artifacts
Artifacts that result from lower energy photons being preferentially absorbed, leaving higher intensity photons to strike the detector array
139
Shaded-surface display (SSD
3D reformation method in which the voxels located on the edge of a structure are used to show the outline or outside shell of the structure; it includes only information from the surface of an object. It can be compared to taking a photograph of the surface of the structure. Also known as surface rendering (SR).
140
Low-contrast resolution
Ability of the system to differentiate between objects with similar densities. Also called contrast resolution or contrast detectability.
141
Thyroid storm
A severe, life-threatening condition resulting when thyroid hormone reaches a dangerously high level, also known as thyroid toxicosis.
142
Fan beam
The radiation emitted from the collimated x-ray source in single-detector row CT systems.
143
Windmill artifacts
Appear only on MDCT helical systems and relate to the cone-shaped beam required. They appear as either streaks or as bright and dark shading near areas of large density differences (e.g., bone and muscle).
144
Virtual colonoscopy
A form of volume rendering designed to reveal the inside of the colon. The technique is also called endoluminal imaging.
145
Negative contrast agents
A contrast agent that is of a lower density than the surrounding structure, such as air or carbon dioxide.
146
Proximal
Term used in referring to extremities. Proximal (close to) may be defined as situated near the point of attachment. For example, the proximal end of the arm is the end at which it attaches to the shoulder.
147
Sievert (Sv):
Once the quality factor has been applied to the radiation absorbed dose the new quantity is called the dose equivalent. The SI equivalent unit is the sievert (Sv). There are 100 rem in 1 Sv.
148
Image reformation
Image data are used to stacked cross
sectional slices and generate an image in a plane or orientation different from the prospective image. Also called image rendering
149
Chemotoxic reactions
Reactions that result from the physicochemical properties of the contrast media, the dose, and speed of injection. All hemodynamic (i.e., relating to blood circulation) disturbances and injuries to organs or vessels perfused by the contrast medium are included in this category. Contrast-induced nephropathy is an example of a chemotoxic reaction.
150
Slip rings
Electromechanical devices that use a brushlike apparatus to provide continuous electrical power and electronic communication across a rotating surface, permitting the gantry frame to rotate continuously, eliminating the need to straighten twisted system cables.
151
Cooling systems
Cooling mechanisms included in the gantry, such as blowers, filters, or devices that perform oil-to-air heat exchange.
152
Imaging planes
Imaginary planes that divide the body into sections.
153
Scan data
All measurements obtained from the detector array and sitting in the computer waiting to be made into an image. Also called raw data.
154
Adaptive array
Detector rows that have variable widths and sizes. Also called nonuniform or hybrid arrays.
155
Step-and-shoot scanning
Scan method in which the CT table moves to the desired location and remains stationary while the x-ray tube rotates within the gantry, collecting data; scans produced with the step-and-shoot method result in images that are perpendicular to the z axis (or tabletop) and parallel to every other slice, like slices of a sausage. Also called axial scanning.
156
Dose-length product (DLP
DLP = CTDIvol × scan length. Although the DLP more closely reflects the radiation dose for a specific CT examination, its value is affected by variances in patient anatomy.
157
Direct axial plane
A direct plane is one that can be obtained by positioning the patient in a specific position. For the foot, the direct axial plane is defined as the plane parallel to the plantar surface of the foot.
158
Basal ganglia
Part of the brain. The level of the basal ganglia contains territories supplied by the anterior (ACA), middle (MCA), and posterior cerebral arteries (PCA). Therefore, this is the level most frequently scanned for brain perfusion studies.
159
Infarction
Areas of tissue death that occur because of a local lack of oxygen.
160
Quantum mottle
Occurs when there are an insuffi cient number of photons detected. It is inversely related to the number of photons used to form the image. Hence, as the number of x-ray photons used to create an image decreases, noise increases. Also referred to as quantum noise.
161
Bolus triggering
Method of individualizing the scan delay using the contrast bolus itself to initiate the scan. It uses a series of low-radiation scans to monitor the progress of the contrast bolus. Once an adequate level of enhancement is achieved, the table moves to the starting level and scanning begins.
162
Automatic tube current modulation
An equipment option that will make changes in tube current (mA) based on the estimated attenuation of the patient at a specific location. The estimations are derived from scout views done in both the anteroposterior and lateral projections or from the previous slices. From these views, the mA will be programmed to vary by location along the length of the patient. The exact details of the option vary by manufacturer.
163
Contrast washout
An imaging characteristic regarding how quickly the iodinated contrast is washed out of the adrenal gland. It can be used to differentiate adenomas from metastases; relies on physiologic differences in perfusion.
164
Raw data
All measurements obtained from the detector array and sitting in the computer waiting to be made into an image. Also called scan data.
165
Milliampere-seconds (mAs
The product of milliampere setting and scan time.
166
CTDI100
Result when the CTDI is measured using a pencil ionization chamber. This 100-mm-long thin cylindrical device is long enough to span the width of 14 contiguous 7-mm CT slices. This provides a better estimate of MSAD for thin slices than that of the single-slice method.
167
Metformin therapy
An oral medication given to non–insulin dependent diabetics to lower blood sugar; also available in combination with other drugs.
168
Image magnification
When the displayed image is made larger. Uses only image data and does not improve resolution
169
RCBF
Regional cerebral blood flow.
170
Gray (Gy
SI unit of absorbed dose
171
Out-of-field artifacts
Inaccuracies in the image caused when parts of the patient are located outside the scan field of view. These artifacts occur because the anatomy outside the SFOV attenuates and hardens the x-ray beam, but is ignored in the image reconstruction process
172
Uniformity
The ability of the scanner to yield the same CT number regardless of the location of an ROI within a homogeneous object.
173
Topology:
The geometric arrangement of a computer system. Common topologies include bus, star, ring, and tree.
174
Percutaneous procedures
Interventional procedures in which access to inner organs or other tissue is done via needle puncture of the skin.
175
Caudal
Term used to describe movement toward the feet; synonymous with inferior.
176
Maximum-intensity projection (MIP
3D technique that selects voxels with the highest value to display
177
Subjective side effects
Side effects experienced to some degree by most patients to whom contrast is administered. These often mild effects include the feeling of heat, nausea, and mild flushing.
178
Roentgen (R
Unit of x-ray exposure in air.
179
Central venous access devices (CVAD):
A venous catheter designed to deliver medications and fluids directly into the superior vena cava (SVC), inferior vena cava (IVC), or right atrium (RA).
180
Huber needle
A special noncoring hooked needle used to access an implantable port.
181
Reference detectors
Included in the detector array and help to calibrate data and reduce artifacts.
182
Isocenter
The absolute center of the gantry.
183
Volume averaging:
Process by which different tissue attenuation values are averaged to produce one less accurate pixel reading. Also referred to as partial volume effect
184
Standard deviation
Indicates the amount of CT number variance within the ROI.
185
Picture archive and communication system (PACS
One of two key elements that form the radiology department’s information infrastructure. The term PACS encompasses a broad range of technologies necessary for the storage, retrieval, distribution, and display of images.
186
Tissue plasminogen activator (t-PA
A treatment for acute ischemic stroke. The treatment, known as tissue plasminogen activator (t-PA), was the first of its kind and revolutionized the way the medical community can respond to treating the 80% of stroke patients who experience ischemic strokes. To be effective t-PA must be administered within 3 hours of the first signs of stroke. This means that the stroke victim must be transported to the hospital, diagnosed, and administered the t-PA treatment before the 3-hour window has expired.
187
Bolus shaping
Manipulating the flow rate to change the characteristics of the time-density curves.
188
Ionicity
Refers to whether the molecules in a contrast agent will separate into charged particles (i.e., ions) when dissolved in an aqueous solution. Ionic contrast agents are composed of molecules that will dissociate into ions when in solution. The molecules contained in nonionic contrast media do not dissociate.
189
Subarachnoid hemorrhagic stroke
Stroke that occurs when there is bleeding into the subarachnoid spaces and the CSF spaces; usually caused by the rupture of an aneurysm.
190
Optical disc libraries
Robotic storage systems that automatically load and unload optical discs. The devices are also called optical jukeboxes, robotic drives, or autochangers.
191
Advanced display functions
Display functions that include multiplanar reformation and three-dimensional reformation.
192
Modulation transfer function (MTF
Most commonly used method of describing spatial resolution ability. It is often used to graphically represent a system’s capability of passing information to the observer.
193
Luminance
Brightness
194
Image fidelity
Image accuracy
195
Transient ischemic attack (TIA
Reversible episode of focal neurologic dysfunction that typically lasts anywhere from a few minutes to a few hours. Attacks are usually caused by tiny emboli that lodge in an artery and then quickly break up and dissolve, with no residual damage.
196
Pixel:
Picture element. Two-dimensional square of data. When arranged in rows and columns, they make up the image matrix
197
Spatial resolution
Ability of a system to resolve, as separate forms, small objects that are very close together. Also call high contrast resolution or detail resolution.
198
Off-line archiving
Storage system in which data are kept in a less accessible location, requiring manual intervention to use.
199
CT brain perfusion
CT method that provides a qualitative and quantitative evaluation of cerebral perfusion. CT perfusion provides this information by calculating regional blood flow (rCBF), regional blood volume (rCBV), and mean transit time (MTT). Perfusion studies are obtained by monitoring the passage of iodinated contrast through the cerebral vasculature.
200
Enterprise-wide distribution
Distribution channels that encompass off-site outpatient clinics or allow on-call radiologists to review studies from home.
201
Ring artifacts
Ring artifacts occur with third-generation scanners and appear on the image as a ring or concentric rings centered on the rotational axis. They are caused by imperfect detector elements—either faulty or simply out of calibration.
202
Sagittal plane
Body plane that divides the body into left and right sections.
203
Contrast detectability
Ability of the system to differentiate between objects with similar densities. Also called low-contrast resolution.
204
Region-of-interest editing
The process of selectively removing or isolating information from the data set. Also called segmentation.
205
Atherosclerosis
The buildup of fat and cholesterol plaque.
206
Delayed reactions
Reactions occurring between 1 hour and 1 week after contrast medium injection.
207
Drip infusion
Technique used to administer contrast material in which an IV line is initiated and contrast medium is allowed to drip in during a period of several minutes.
208
Portal venous phase
The phase of enhancement that follows the hepatic arterial phase, which typically begins at 60 to 70 seconds after the IV administration of a bolus of contrast material
209
Electronic health record (EHR
Generic term for a digital patient record; in general usage, EHR and EMR are used synonymously.
210
Gantry aperture
Opening in the gantry; range of aperture size is typically 70 to 90 cm.
211
Endoluminal imaging
A form of volume rendering designed to reveal the inside of the lumen of a structure. The technique is also called virtual endoscopy, virtual bronchoscopy, and virtual colonoscopy.
212
Manual MPR
This method requires that the operator input the criteria, such as the thickness of the MPR, the plane desired, and the number or incrementation of the resulting planar images.
213
Cardiac gating
CT techniques that attempt to minimize cardiac motion in the study by selecting (or acquiring) images during cardiac segments with relatively low cardiac motion. ECG tracings are acquired with the scan acquisition.
214
Input device
Ancillary pieces of computer hardware designed to feed data into the computer. Examples include keyboard, mouse, touch-sensitive plasma screen, and CT detector mechanisms.
215
Multidetector row CT (MDCT
Scanner design in which there are many parallel rows of detectors. A single rotation can produce multiple slices.
216
Direct digital capture:
Image acquisition from the CT scanner to the PACS in which CT data are transferred directly, which allows full spatial resolution and image manipulation capabilities (such as adjusting window width and level).
217
Single-detector row CT (SDCT):
Early systems, which contained only a single row of detectors in the z axis, obtained data for one slice with each rotation.
218
Focused appendiceal CT
Protocol that limits the scan area to the lower abdomen and upper pelvis.
219
Axial scanning
Scan method in which the CT table moves to the desired location and remains stationary while the x-ray tube rotates within the gantry, collecting data; scans produced with the step-and-shoot method result in images that are perpendicular to the z axis (or tabletop) and parallel to every other slice, like slices of a sausage. Also called step-and-shoot scanning.
220
Coronary circulation
The movement of blood through the tissues of the heart. Blood is carried to the heart by the two coronary arteries and their branches. Cardiac veins remove deoxygenated blood and waste products.
221
Fourier transform (FT
A method to study waves of many different sorts and also to solve several kinds of linear differential equations. Loosely speaking it separates a function into its frequency components.
222
Third-generation design
Scanner configuration that consists of a detector array and an x-ray tube that produces a fan-shaped beam that covers the entire field of view and a detector array. Sometimes referred to as rotate-rotate scanners.
223
Transverse plane
Body plane horizontal to the floor
224
Scan time
Time the x-ray beam is on for the collection of data for each slice. Most often it is the time required for the gantry to make a 360° rotation, although with overscanning and partial scanning options there may be some mild variation
225
Image annotation
Information that appears on images. Can include facility name, patient name, identification number, date, slice number and thickness, pitch, table location, measurement scale, gray scale, and right and left indicators
226
High-contrast resolution
Ability of a system to resolve, as separate forms, small objects that are very close together. Also call spatial resolution or detail resolution.
227
CTDIvol
The CTDIvol is a measure of exposure per slice and is independent of scan length. It is the preferred expression of radiation dose in CT dosimetry.
228
Thrombolytic therapy
The use of drugs to break up or dissolve blood clots.
229
Window width
Mechanism that determines the quantity of Hounsfield units represented as shades of gray on a specific image.
230
Ischemic stroke
Category of stroke caused by a blockage in an artery.
231
Detector array:
Entire collection of detectors included in a CT system; detector elements are situated in an arc or a ring.
232
Helical scanning
Scanning method that includes a continually rotating x-ray tube, constant x-ray output, and uninterrupted table movement Also called spiral, volumetric, or continuous acquisition scanning.
233
Intermittent fluoroscopy:
Method used to reduce the radiation dose during CT fluoroscopic procedures. Consists of alternately ceasing and beginning the radiation exposure rather than the continuous use of the fluoroscopic mode throughout the procedures.
234
Contrast media-induced nephropathy (CIN
An acute impairment of renal function that follows the intravascular administration of contrast material, for which alternative causes have been excluded.
235
Detector aperture:
Size of the detector opening.
236
Coronary stenting
Stents are made of self-expanding,
stainless-steel mesh. They are mounted on a balloon catheter in a collapsed form. When the balloon is inflated, the stent expands and pushes against the inner wall of the coronary artery
237
Hemangioma:
Abnormal proliferation of blood vessels in the skin or internal organs
238
Reference image
Displays the slice lines in corresponding locations on the scout image.
239
Lossy compression
Method that introduces compression artifacts because not all data are restored; used to transmit images that do not need to be of diagnostic quality. This is sometimes referred to as “conversational” quality
240
Cerebrovascular accident:
Term used to describe stroke; no longer favored because it implies a random, unpredictable, or uncertain nature to the condition.
241
Hemorrhagic stroke
Category of stroke caused by a tear in the artery’s wall that produces bleeding in the brain
242
Equilibrium phase
The last phase of tissue enhancement after the IV injection of contrast media. It can begin as early as 2 minutes after the bolus phase or after a drip infusion. In this phase contrast media is largely emptied from the arteries, is greatly diluted in the veins, and has soaked the organ parenchyma. In this phase, intravascular structures and interstitial concentrations of contrast material equilibrate and decline at an equal rate. Also called the delayed phase.
243
Line pairs phantom
A phantom used to measure spatial resolution. This type of phantom is made of acrylic and has closely spaced metal strips imbedded in it.
244
Nephropathy
Any condition or disease affecting the kidney; sometimes used synonymously with renal impairment.
245
Attenuation profile
The system accounts for the attenuation properties of each ray sum and correlates it to the position of the ray.
246
Continuous acquisition scanning
Scanning method that includes a continually rotating x-ray tube, constant x-ray output, and uninterrupted table movement Also called helical, spiral, or volumetric scanning.
247
Longitudinal resolution
Resolution in the z direction
248
Arteriovenous malformations
Composed of tangles of arteries and arterialized veins. In the brain there is tissue interposed between the vessels, but it is usually abnormal and often scarred from previous tiny hemorrhages; blood is shunted directly from the arterial system to the venous system. This shunting allows oxygenated blood to enter the veins. The flow is high and the pressure is elevated within the veins. The elevated pressure can cause the vessels to rupture, resulting in a hemorrhagic stroke.
249
Analog-to-digital converter (ADC):
Converts the analog signal to a digital format.
250
Reconstruction algorithm
Determines how the data are filtered in the reconstruction process. The appropriate reconstruction algorithm selection depends on which parts of the data should be enhanced or suppressed to optimize the image for diagnosis.
251
Prospective ECG gating
Method that uses a signal, usually derived from the R wave of the patient’s ECG, to trigger image acquisition.
252
Display processor
CT component that assigns a group of Hounsfield units to each shade of gray.
253
Memory
Devices that store data. The three principal types of solid-state memory are read-only memory (ROM), random access memory (RAM), and write-once read-many times memory (WORM).
254
In-plane resolution
Resolution in the x y direction
255
Dual source
CT design that uses two sets of x-ray tubes and two corresponding detector arrays in a single CT gantry.
256
Ischemic heart disease
A condition that results when plaque builds up in the coronary arteries. A partial or total blockage results, and the heart muscle does not get an adequate blood supply. Also referred to as coronary artery disease (CAD
257
Electronic medical record (EMR
Electronic health records (EHR) are often composed of electronic medical records (EMR) from a variety of sources, including radiology. However, in general usage, EHR and EMR are used synonymously.
258
Ventral
Term used to describe movement forward (toward the face); also referred to as anterior
259
Array processor
Now outdated, an array processor is a CPU design frequently used for CT image reconstruction. Also called a vector processor, this design was able to run mathematical operations on multiple data elements simultaneously. General increases in performance and processor design have made this design obsolete.
260
Gantry
Ring-shaped part of the CT scanner that houses many of the components necessary to produce and detect x-rays.
261
CT angiography
CT technique used to visualize the arterial and venous vessels throughout the body. Scans are
performed in the helical mode with a high flow rate contrast injection.
262
Renal colic
Acute, usually severe pain that accompanies the passage of renal calculi from the kidney through the urinary tract.
263
Optical jukebox
Robotic storage system that automatically loads and unloads optical discs. The devices are also called optical disc libraries, robotic drives, or autochangers
264
Image center
Specific area within the SFOV that will be displayed on the center of the image.
265
Convolution
Process of applying a filter function to an attenuation profile.
266
Renal calculi
Gravel-like deposits that appear in the kidney. Also called renal stones or kidney stones.
267
Reference dose values:
Values published by the ACR regarding the radiation dose that is acceptable for a variety of CT scans.
268
DICOM
Universally adopted standard for medical image interchange known as the Digital Imaging and Communication in Medicine.
269
Hand bolus
A rapid injection of contrast material delivered by hand, using syringes.
270
Uniphasic injection
Injection technique in which a single injection fl ow rate is used.
271
Standard precautions
Include the use of hand washing and appropriate protective equipment such as gloves, gowns, and masks whenever touching or exposure to patients’ body fluids is anticipated. They are designed to reduce the risk of transmission of microorganisms from both recognized and unrecognized sources of infection in hospitals.
272
Double contrast technique
Injection technique used for arthrography in which both iodinated contrast and air are injected into the joint space.
273
Frame grabbing
Analog method of image acquisition in which an image on the monitor is converted to a digital format, somewhat similar to a screen capture. Converting CT data in this way loses the original pixel’s metrics.
274
Serum creatinine (SeCr
Laboratory test that measures creatinine level in the blood; it is a fast and inexpensive way to assess renal function.
275
Linear interpolation
The simplest type of a mathematical method of estimating the value of an unknown function using the known value on either side of the function; frequently used in mathematics and science. Linear interpolation assumes that an unknown point falls along a straight line between two known points.
276
Acute renal failure (ARF
Rapid loss of renal function caused by damage to the kidney, resulting in retention of waste products that are normally excreted by the kidney.
277
Slice thickness blooming
When the slice thickness displayed on the image is wider than that selected by the operator.
278
High-frequency generator
Produces high voltage and transmits it to the x-ray tube.
279
Thrombotic stroke
Type of ischemic stroke caused from a blood clot or a fatty deposit within one of the brain’s arteries.
280
Virtual bronchoscopy
A form of volume rendering designed to reveal the inside of the airways. The technique is also called endoluminal imaging.
281
RCBV
Regional cerebral blood volume.
282
Temporal resolution
How rapidly data are acquired. It is controlled by gantry rotation speed, the number of detector channels in the system, and the speed with which the system can record changing signals.
283
Standard uptake value
An index of glucose metabolism. The number represents the relative uptake of radionuclides in tissue.
284
Serial access memory (SAM
Type of computer memory that stores data that can only be accessed sequentially (like a cassette tape).
285
Low-osmolality contrast media (LOCM
Contrast agents introduced in the 1980s that contain much lower osmolality, from approximately 600 to 850 mOsm/kg, or roughly 2 to 3 times the osmolality of human blood.
286
Autochangers
Robotic storage systems that automatically load and unload optical discs. The devices are also called optical disc libraries, robotic drives, or optical jukeboxes
287
Detector spacing
Measured from the middle of one detector to the middle of the neighboring detector; accounts for the spacing bar.
288
Hypertonic
Having a greater number of particles in solution per unit of liquid, as compared with blood.
289
Split bolus
Contrast injection techniques in which the total contrast dose is split, often in half. The first dose is given, and a delay of about 2 minutes is observed. This allows time for structures that are slower to enhance to be opacified. The delay is followed by a second bolus containing the remainder of the contrast; scanning is initiated soon after the second injection is complete, using this second injection to more fully opacify the vessels.
290
Table incrementation
Process of moving the table by a specified measure. Also referred to as feed, step, or index.
291
Clearance
The ability of the kidney to remove a substance from the blood.
292
Biphasic injection
Injection technique in which two flow rates are used.
293
Contrast-detail response
The relationship between object size and visibility.
294
Hyperosmolar
Having a greater number of particles in solution per unit of liquid, as compared with blood.
295
Window center
Mechanism that selects the center CT value of the window width. Also called window level.
296
Glabellomeatal line
Imaginary line used for positioning that connects the external acoustic meatus to the supraorbital margin. Also called the supraorbital meatal line.
297
Partial volume artifact
Artifact that can result when an object does not appear on all views. Inconsistencies between views cause shading artifacts on the image.
298
MTF graph
Charts that depict spatial frequency (object size) on the x axis and MTF along the y axis.
299
Hard disk
An essential component of all CT systems. It saves the thousands of bits of data acquired with each gantry rotation
300
360LI
A technique of interpolating helical scan data for SDCT systems using the 360° linear interpolation.
301
Helical interpolation artifacts
Result in subtle inaccuracies in CT numbers and can be easily misinterpreted as disease. These artifacts can best be avoided by using a low pitch whenever possible.
302
Progressive stroke
A time-limited event in which the neurologic deficits occur in a progressive pattern. Also referred to as a stroke in evolution.
303
Back projection
Process of converting the data from the attenuation profile to a matrix.
304
Retrospective ECG gating
Method that acquires helical data throughout the cardiac cycle in which images are then reconstructed in specified portions of the cardiac cycle.
305
Interleukin 2:
An immunotherapy used to treat some cancers
306
Capture efficiency
Ability with which the detector obtains photons that have passed through the patient.
307
Threshold CT values
A predetermined CT value limit set by the operator in some types of 3D reformation techniques. The
software will include or exclude the voxel depending on whether its CT number is above or below the threshold
308
CTDIw
The CTDIw adjusts for variation across the scan field of view by providing a weighted average of measurements at the center and the peripheral slice locations (i.e., the x and y dimensions of the slice).
309
Urolithiasis
Gravel-like deposits that may appear in any part of the urinary system, from the kidney to the bladder; used interchangeably with renal stones, renal calculi, nephrolithiasis, and kidney stones.
310
Neutral contrast agents:
Oral contrast agents that have an HU similar to that of water. Because they possess a lower density than the surrounding bowel, may also be referred to as a negative contrast agent.
311
Online archiving
Storage system using devices such as hard drives that are instantly accessible to the user
312
Test bolus
Method of individualizing the scan delay that consists of administering 10 to 20 mL of contrast medium by IV bolus injection and performing several trial scans to determine the length of time from injection to peak contrast enhancement in a target region, such as the aorta.
313
Calcium score
The amount of calcification on cardiac CT
314
Nonequilibrium phase
Follows the bolus phase; the contrast agent is still much brighter in the arteries than in the parenchyma of organs, but now the venous structures are also opacified. This phase begins approximately 1 minute after the start of the bolus injection and lasts only a short time. Also called the venous phase.
315
Pitch:
Relation of table speed to slice thickness. It is most commonly defined as the travel distance of the CT scan table per 360° rotation of the x-ray tube, divided by the x-ray beam collimation width.
316
Collimators
Mechanical hardware that resembles small shutters and adjusts the opening based on the operator’s selection.
317
Electron beam imaging
Also referred to as EBCT or ultrafast CT. It differs from conventional CT in a number of ways. This system uses a large electron gun as its x-ray beam source. A massive anode target is placed in a semicircular ring around the patient. Neither the x-ray beam source nor the detectors move, and the scan can be acquired in a short time.
318
Heat dissipation
Ability of the tube to rid itself of heat
319
Detector
Element in a CT system that collects attenuation information. It measures the intensity of the transmitted x-ray radiation along a beam projected from the x-ray source to that particular detector element.
320
Prepatient collimators
Limit the x-ray beam before it passes through the patient.
321
Clinical information systems (CIS)
Information systems that keep track of clinical data.
322
Protocol:
Common set of rules and signals that computers on the network use to communicate
323
Near-line archiving
Storage systems in which data are readily, although not immediately, available. Examples include an optical jukebox or tape library.
324
Power capacity
Listed in kilowatts (kW). The power capacity of the generator determines the range of exposure techniques (i.e., kV and mA settings) available on a particular system.
325
Excretory phase
The phase of renal enhancement that follows the nephrogram phase that typically occurs approximately 3 minutes after the IV administration of a bolus of contrast material and can last 15 minutes or longer.
326
Surface rendering (SR
3D reformation method in which the voxels located on the edge of a structure are used to show the outline or outside shell of the structure; it includes only information from the surface of an object. It can be compared to taking a photograph of the surface of the structure. Also known as shaded-surface display (SSD).
327
Longitudinal plane
Body plane perpendicular to the floor.
328
Distance measurement
The system calculates the distance between two deposited points in either centimeters or millimeters.
329
Algorithm
A precise set of steps to be performed in a specific order to solve a problem. Algorithms are the basis for most computer programming
330
Cone-beam artifacts
Artifacts that relate to the cone-shaped beam required for MDCT helical scans. These artifacts are more pronounced for the outer detector rows. The larger the cone beam (i.e., more detector channels), the more pronounced the effect.
331
High attenuation
An x-ray beam is greatly impeded by an object; typically shown as light gray or white on an image.
332
Thyroid toxicosis
A severe, life-threatening condition resulting when thyroid hormone reaches a dangerously high level, also known as a thyroid storm.
333
Bandwidth
Amount of data that can be transmitted between two points in the network in a set period of time
334
Balloon angioplasty
Technique that is used to dilate an area of arterial blockage using a catheter with a small, inflatable, sausage-shaped balloon at its tip.
335
Core servers
Server computers that are integral to the functioning of the PACS.
336
International System of Units (SI
International System of Units (abbreviated SI from the French Le Système International d’Unités) is a system that is used internationally, both in everyday commerce and in science.
337
Semiautomatic segmentation
Combines many of the benefits of manual and automatic segmentation techniques to selectively remove or isolate information from the data set.
338
Hyperthyroidism
condition in which thyroid hormone reaches a high level. In patients with a history of hyperthyroidism, iodinated contrast media can intensify thyroid toxicosis, and in rare cases it can precipitate a thyroid storm, which is a severe, life-threatening condition.
339
Intracranial hemorrhage (ICH
Bleeding in the brain caused by the rupture of a blood vessel.
340
Quality factor (Q):
A conversion factor that is applied to the absorbed dose that accounts for the different biologic effects produced from different types of ionizing radiation. The quality factor is 1 for the diagnostic x-rays that are used in CT. When the quality factor has been applied to the
radiation absorbed dose, the new quantity is called the dose equivalent.
341
Isosmolar contrast media (IOCM
A contrast agent
| (Visipaque, GE Healthcare) with an osmolality equal to that of blood.
342
Valsalva maneuver
Technique that requires the patient to blow the cheeks out to distend the pyriform sinuses.
343
Radiology information system (RIS
One of two key
elements that form the radiology department’s information infrastructure. The RIS is most often designed for scheduling patients, storing reports, patient tracking, protocoling examinations, and billing.
344
Nonuniform arrays
Detector rows that have variable widths and sizes. Also called adaptive or hybrid arrays
345
Limiting resolution
The spatial frequency possible on a given CT system at an MTF equal to 0.1.
346
CTDI phantoms
Phantoms used to measure the radiation dose delivered for various CT examinations. CTDI is an acronym for computed tomography dose index
347
Slice thickness
On a single-detector row system this is controlled by the width of the collimator opening. On a multidetector row system it is controlled by a combination of collimation and detector confi guration.
348
Manual segmentation
The process of selectively removing or isolating information from the data set by the manual process in which the user identifi es and selects data to be saved or removed.
349
Discrete Fourier transform (DFT)
A technique for expressing a waveform as a weighted sum of sines and cosines
350
Isotonic
Having nearly the same number of particles in solution per unit of liquid as compared with blood.
351
Scan field of view (SFOV):
The area, within the gantry, from which the raw data are acquired. Also called calibration field of view.
352
Kilovolt-peak (kVp)
Defines the quality (average energy) of the x-ray beam.
353
Systemic circulation
The circular pattern of blood flow from the left ventricle of the heart through the blood vessels to all parts of the body and back to the right atrium.
354
Tunneled catheters
Central venous catheters that are inserted into the target vein (often the subclavian) by “tunneling” under the skin. This reduces the risk of infection because bacteria from the skin surface are not able to travel directly into the vein. Examples of tunneled catheters include Hickman, Broviac, and Groshong catheters.
355
Volumetric HRCT
Volumetric HRCT protocols use a helical mode to acquire images of the entire lung, rather than representative slices. Because these helical protocols cover the entire lung, they result in a more complete assessment of the lung.
356
Central processing unit (CPU)
Component that interprets computer program instructions and sequences tasks. It contains the microprocessor, the control unit, and the primary memory.
357
Overbeaming
When x-ray penumbra falls outside the active detectors; this occurs when collimators are opened so that the same x-ray intensity reaches all of the detectors in an MDCT system.
358
Graves’ disease
One of the main causes of hyperthyroidism
359
Robotic drives
Robotic storage systems that automatically load and unload optical discs. The devices are also called optical disc libraries, optical jukeboxes, or autochangers.
360
Anatomic position
Characterized by an individual standing erect, with the palms of the hands facing forward. This position
is used internationally and guarantees uniformity in descriptions of direction.
361
Arteriovenous iodine difference
Comparison of a Hounsfield unit (HU) measurement taken within the aorta to that of a measurement taken in the inferior vena cava. Used to assess the phase of tissue enhancement after the IV injection of contrast media.
362
CT arthrography (CTA
CT procedure in which a needle is introduced into a joint and contrast media is injected, outlining the joint capsule, ligaments, and articular surfaces.
363
Helical interpolation methods
Complex statistical methods to, in effect, take the slant and blur out of the helical image and create images that closely resemble those acquired in a traditional axial mode.
364
Peak organ enhancement
The point after an IV injection when the contrast agent reaches the highest concentration in a specified organ. The peak organ enhancement for organs such as the pancreas, bowel, and bladder occurs about 5 to 15 seconds after peak aortic enhancement.
365
Peak aortic enhancement
The point after an IV injection when the contrast agent reaches the highest concentration in the aorta.
366
Histogram
A graphical display showing how frequently a range of CT numbers occur within an ROI.
367
Window level
Mechanism that selects the center CT value of the window width. Also called window center.
368
Informatics
The collection, classification, storage, retrieval, and dissemination of recorded information.
369
Image rendering
Image data are used to stacked cross
sectional slices and generate an image in a plane or orientation different from the prospective image. Also called image reformation.
370
Random access memory (RAM
Type of computer memory that includes instructions that are frequently changed, such as the data used to reconstruct images. RAM is so named because all parts of it can be reached easily at random.
371
Receiver operator characteristics
The subjectivity inherent in the method of evaluating contrast resolution that requires an observer to detect objects as distinct. Result can vary because different observers will often look at the same image and evaluate it differently.
372
Magnetic tape
One of the oldest data storage options used to record computer data; consists of a long narrow strip of plastic with a magnetizable coating, most often packaged in cartridges and cassettes.
373
Quantum noise
Occurs when there are an insuffi cient number of photons detected. It is inversely related to the number of photons used to form the image. Hence, as the number of x-ray photons used to create an image decreases, noise increases. Also referred to as quantum mottle.
374
Renal insuffiiency
Renal function is abnormal but capable of sustaining essential bodily function
375
Spatial frequency:
The number of line pairs visible per unit length.
376
Peripherally inserted central catheters (PICC
A long catheter that is inserted through the large veins of the upper arm (i.e., cephalic and basilic veins) and advanced so that its tip is located in the lower third of the SVC.
377
Heat capacity
Ability of the tube to withstand the heat
378
Output device
Ancillary pieces of computer hardware designed to accept processed data from the computer. Examples include monitor, laser camera, printer, and archiving equipment such as optical discs or magnetic tape
379
Peer-to-peer (P2P) network
Networks in which each user has the same capabilities and any party can initiate communication. P2P networks exploit the diverse connectivity and the cumulative data capacity of network participants, rather than using a centralized resource.
380
Hydronephrosis
Obstruction resulting in dilatation, distention, and enlargement of the collection system in the kidney caused by ureteral stones.
381
Linear attenuation coefficient
Amount of the x-ray beam that is scattered or absorbed per unit thickness of the absorber; is represented by the Greek letter
382
Data-acquisition system (DAS)
Measures the number of photons that strikes the detector, converts the information to a digital signal, and sends the signal to the computer.
383
Multiphasic injection
Injection technique in which two or more flow rates are used.
384
Overlapping reconstruction
Incrementation is changed to produce overlapping images that are then used in multiplanar or 3D reformations.
385
Fourth-generation design:
Scanner configuration that uses a detector array that is fixed in a 360° circle within the gantry. Sometimes referred to as rotate-only systems.
386
Aliasing
Artifacts that result from insufficient projection data; cause fine stripes that appear to be radiating from a dense structure.
387
Renal stones
Gravel-like deposits that appear in the kidney. Also called renal calculi or kidney stones
388
Ray
The path that the x-ray beam takes from the tube to the detector.
389
Tails
Areas of scatter radiation into the tissue of adjacent slices.
390
Filter functions
Applied to the scan data before back projection occurs to minimize artifacts
391
Multiple scan average dose (MSAD
Total dose is the central slice radiation dose, plus the scatter overlap (or tails); dose calculated from multiple scans.
392
Virtual endoscopy
A form of volume rendering designed to reveal the inside of the lumen of a structure. The technique is also called endoluminal imaging, virtual bronchoscopy (for airways), and virtual colonoscopy (for the colon).
393
Z axis:
Plane that correlates to the slice thickness, or depth, of the CT slice.
394
Spiral scanning
Scanning method that includes a continually rotating x-ray tube, constant x-ray output, and uninterrupted table movement. Also called helical, volumetric, or continuous acquisition scanning.
395
Bytes
Unit of information storage composed of 8 bits of data.
396
Image reconstruction
Use of raw data to create an image
397
Virtual private networks (VPN):
Distribution channel used to make the Internet a safe medium for the secure transmission of clinical data. By definition, VPNs overlay another network to provide a particular functionality.
398
Kidney stones
Gravel-like deposits that appear in the kidney. Also called renal calculi or renal stones.
399
Signal-to-noise ratio (SNR)
The number of x-ray photons detected per pixel in CT.
400
Organ dose
The estimated radiation dose to radiosensitive organs from CT procedures. These averages are used to calculate effective dose.
401
Non-tunneled catheters
Central catheters of a larger caliber than PICCs because they are designed to be inserted into a relatively large, more central vein such as the subclavian or jugular. Non-tunneled catheters usually have three ports, are open ended, and typically remain in place for a few days to 2 weeks.
402
180LI
A technique of interpolating helical scan data for SDCT systems using 180° linear interpolation.
403
Fully automated segmentation
The process of selectively removing or isolating information from the data set by a method that is fully automated by the software. Fully automatic segmentation methods are usually impractical because of image complexity and the variety of image types and clinical indications.
404
Completed stroke
Preferred medical term used to describe an acute episode of interrupted blood fl ow to the brain that lasts longer than 24 hours. Also called an established stroke.
405
ACR CT accreditation phantom
A solid phantom that contains four modules and is constructed primarily from a water equivalent material. Each module is 4 cm deep and 20 cm in diameter, with external alignment markings to allow centering of the phantom in the x, y, and z axes, and is used to measure different aspects of image quality.
406
Atrial fibrillation
A disorder of heart rate and rhythm in which the atria are stimulated to contract in a very rapid or disorganized manner rather than in an organized one.
407
Coronary artery bypass graft surgery (CABG
Commonly pronounced “cabbage,” this surgical procedure is typically recommended when there is disease of the left main coronary artery or in three or more vessels, or if nonsurgical management has failed. Arteries or veins taken from elsewhere in the patient’s body are grafted from the aorta to the coronary arteries to bypass atherosclerotic narrowings and improve the blood supply to the coronary circulation supplying the myocardium. The terms “single,” “double,” “triple,” or “quadruple bypass” refer to the number of coronary arteries bypassed in the procedure.
408
Multiplanar reformation (MPR
Two-dimensional reformation done to show anatomy in various planes.
409
Roentgen equivalents man (rem):
When the quality factor has been applied to the radiation absorbed dose, the new quantity is called the dose equivalent. The unit for dose equivalent is the rem.
410
Hepatic arterial phase
The first phase of enhancement typically occurring 15 to 25 seconds after the IV administration of a bolus of contrast material.
411
Beam pitch
Table movement per rotation divided by beam width.
412
Contiguous
Method of acquiring slices in which one slice abuts the next.
413
Linearity
The relationship between CT numbers and the linear attenuation values of the scanned object at a designated kVp value.
414
PET transmission scan
The attenuation correction feature that is built into a dedicated PET system (i.e., one that does not include a CT component).
415
Hardware
Portions of the computer that can be physically touched.
416
Isotropic:
Equal in all directions; a voxel that is cube-shaped
417
Automated injection triggering
Injection methods that individualize the scan delay. Two methods exist—the injection of a test bolus and bolus triggering.
418
Bolus phase
The initial phase that immediately follows an IV bolus injection. In the bolus phase of contrast enhancement, the arterial structures are filled with contrast medium and brightly displayed on the image. Contrast media has not yet filled the venous structures. Also called the arterial phase.
419
Image artifacts
Anything appearing on the image that is not present in the object scanned
420
Read-only memory (ROM):
Type of computer memory that is imprinted at the factory and is used to store frequently used instructions such as those required for starting the system.
421
Dynamic range
Ratio of the maximum signal measured to the minimum signal the detectors can measure. The range of x-ray intensity values to which the scanner can accurately respond
422
Real-time MPR
Refers to the feature that allows the operator to manually change (typically by moving a mouse) the image plane while the software continually updates the image. This feature permits the operator to use trial and error to obtain the ideal image plane. Also called interactive MPR.
423
RAS coordinates
Directional coordinate system—an acronym for right-left, anterior-posterior, superior-inferior—used to determine image center.
424
Fatty infiltration of the liver
The accumulation of fat in liver cells. It is also called steatosis. It is one of the most common liver abnormalities diagnosed by liver CT and can result from a variety of causes including alcoholism, obesity, diabetes, chemotherapy, corticosteroid therapy, hyperalimentation (i.e., total parental nutrition—intravenous feeding), and malnutrition.
425
Vermiform appendix
Small, tubelike structure projecting from the cecum; literally means wormlike.
426
Detector efficiency
Ability of the detector to capture transmitted photons and change them to electronic signals
427
Hounsfield units (HU
Measure of the beam attenuation capability of a specific structure. Also call pixel values, density numbers, or CT numbers.
428
Effective dose
A measurement, reported in Sv or rem, that attempts to account for the effects particular to the patient’s tissue that has absorbed the radiation dose. It extrapolates the risk of partial body exposure to patients from data obtained from whole body doses to Japanese atomic bomb survivors. Although methods to calculate the effective dose have been established, they depend on the ability to estimate the dose to radiosensitive organs from the CT procedure. Also called effective dose equivalent.
429
Positive contrast agents
Contrast agents that are of a higher density than the structure being imaged. Most contain barium or iodine.
430
Slice misregistration
Occurs when a patient breathes differently with each data acquisition. This difference in breathing places the second group of scans in an incorrect anatomic position relative to the first set of slices. Valuable information may be missed because of this effect.
431
Detector pitch
Table movement per rotation time divided by the selected slice thickness of the detector
432
Computed tomography dose index (CTDI
Dose reported to the FDA; slices must be contiguous.
433
Inferior
Term used to describe movement toward the feet (down); synonymous with caudal.
434
Ray sum
The detector senses each arriving ray and senses how much of the beam was attenuated.
