1 Flashcards
Anatomic landmark
Landmark, such as the xiphoid or the iliac crest, used as a reference point when planning the scout image
MTT
Mean transit time
Information technology (IT):
The study, design, development, implementation, support, or management of computer based information systems; particularly software applications and computer hardware.
Bolus injection technique
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.
Contrast-detail curve
Result of measuring and charting the relationship between object size and visibility (contrast-detail response).
Low attenuation
An x-ray beam that is nearly unimpeded by an object; typically shown as dark gray or black on an image
Beam attenuation
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.
Cupping artifacts
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.
Osmolality
Property of intravascular contrast media that refers to the number of particles in solution per unit liquid as compared with blood.
Retrospective reconstruction:
Process of using the same raw data to later generate a new image.
Embolism
The formation, development, or existence of a clot within the vascular system that detaches from its original site.
Wired
Refers to networks that are linked by a physical connection.
Time-density curves
Graphical representation that demonstrates the effect of varying contrast dose on aortic and hepatic contrast enhancement.
CT venography
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.
Lossless compression
Method of image compression in which the image that is then decompressed is an exact replica of the original.
Predetector collimators
Shape the beam and are located below the patient and above the detector array
Absorption efficiency
Number of photons absorbed by the detector; dependent on the physical properties of the detector face (e.g., thickness, material).
Radiation profile:
Variations along the length, or z axis, of the patient; also referred to as the z-axis dose distribution
Voxel
Volume element. Three-dimensional cube of data acquired in CT.
R-R interval
The distance between two R waves of a patient’s ECG that represents one complete cardiac cycle.
Cerebrovascular reserve capacity (CVRC):
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.
Wireless:
Refers to network that use radio waves to transmit data between computers.
Contrast media extravasation
The leakage of fluid from a vein into the surrounding tissue during IV contrast administration.
Sampling theorem
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.
Tube arcing
Undesired surge of electrical current (i.e., a shortcircuit) within the x-ray tube. A common cause of equipment induced artifact.
Region of interest (ROI
An area on the image defined by the operator.
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.
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.
Stroke in evolution
A time-limited event in which the
neurologic deficits occur in a progressive pattern. Also referred to as a progressive stroke.
Anaphylactoid
Life-threatening reactions; symptoms include substantial respiratory distress, unresponsiveness, convulsions, clinically manifested arrhythmias, and cardiopulmonary arrest. These reactions require prompt recognition and treatment.
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.
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
Renal failure
The inability of the kidney to filter waste from the blood that can result in the accumulation of nitrogenous wastes (or azotemia).
Molecular imaging
Any methodology that investigates events at the molecular and cellular levels.
Cone beam
The radiation emitted from the collimated x-ray source in multidetector row CT systems.
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.
Artifacts
Objects seen on the image but not present in the object scanned
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.
Z-axis dose distribution
Variations along the length, or z axis, of the patient; also referred to as the radiation profile.
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
Focal spot
Area of the anode where the electrons strike and the x-ray beam is produced.
beta-blockers
Pharmaceuticals used to reduce motion artifact on cardiac CTA images by temporarily lowering a patient’s heart rate.
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.
Imaging informatics
How information about medical images is exchanged within the radiology departments and throughout the medical enterprise.
Oblique planes:
Body planes that are slanted and lie at an angle to one of the three standard planes.
Centigray (cGy)
A centigray (cGy) equals 1 rad. There are 100 rad in 1 gray (Gy).
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.
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.
Blood-brain barrier (BBB
A semipermeable structure that protects the brain from most substances in the blood, while still allowing essential metabolic function
Ureterolithiasis
Gravel-like deposits that appear in the ureter.
Glomerular filtration rate (GFR
Describes the fl ow rate of filtered fluid through the kidney and is a measurement of kidney function.
Scanner-created MPR
Scanner protocols are programmed so that MPRs are automatically generated by the scanner software.
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.
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.
Displayed contrast
The displayed contrast of an image is dependent on the window settings used for its display
Supraorbital meatal line
Imaginary line used for positioning that connects the external acoustic meatus to the supraorbital margin. Also called the glabellomeatal line.
Health Level Seven (HL7
An organization that works to develop universal standards for clinical and administrative data throughout the healthcare arena.
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.
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.
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.
Laser light accuracy
Determination of the accuracy of the alignment of the laser light used for patient positioning.
Afterglow
A brief, persistent flash of scintillation that must be taken into account and subtracted before image reconstruction
Slice thickness accuracy
Determination of the accuracy of the slice thickness selected by the operator versus the width of the collimator opening.
Adrenal adenoma
Benign adrenal mass
Thrombosis
The formation, development, or existence of a clot within the vascular system.
Half-life
Time it takes for half of the dose of a substance to be eliminated from the body
Bow tie filters
Mechanical fi lter that removes soft, or lowenergy, x-ray beams, minimizing patient exposure and providing a more uniform beam intensity.
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.
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.
Computerized physician order-entry (CPOE
System that electronically transmits clinician orders to radiology and other departments.
Gray scale
System that assigns a certain number of Hounsfield values to each shade of gray.
Bits
binary digits
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.
Dorsal
Term used to describe movement toward the back surface of the body; also referred to as posterior.
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.
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.
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.
Image data
Once the computer has processed the raw data assigning one HU value to each pixel
Radiation absorbed dose (rad
Unit of absorbed dose
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.
Prospective reconstruction
Image reconstruction that is automatically produced during scanning.
Hybrid arrays
Detector rows that have variable widths and sizes. Also called adaptive or nonuniform arrays.
Polychromatic x-ray energy
An x-ray beam that is composed of photons with varying energies.
Segmentation errors
Errors in the reformatted image that are introduced when important vessels or other structures are inadvertently edited out of the data set.
Uniform array
Detector rows that are parallel and of equal size.
Premedication
Pretreatment, most often with steroids, to prevent reactions to contrast media
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.
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.
Sampling rate
Number of samples taken per second from the continuous signal emitted from the detector.
Table referencing
When the table position is manually set at zero by the technologist.
Compensating filters:
Filters the x-ray beam to reduce the radiation dose to the patient; help to minimize image artifact and improve image quality.
Display field of view (DFOV
The section of data selected for display on the image.
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.
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.
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.
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
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.
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.
Kinetic energy
Energy of motion
Pencil ionization chamber
A special cylindrical dosimeter used in conjunction with a CTDI phantom to assess the radiation dose in CT.
Anterior
Term used to describe movement forward (toward the face); also referred to as ventral.
Hypotensive stroke
Although rare, pressure that is too low can reduce oxygen supply to the brain enough to cause a stroke
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.
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.
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.
Archiving
Saving studies on auxiliary devices for the purpose of future viewing.
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.
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.
Incidentalomas
Unsuspected adrenal masses that are found when CT studies are ordered as a result of unrelated symptoms
Staging
The process of determining the extent and distribution of disease.
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.
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.
Write-once read-many times memory (WORM
Type of computer memory in which data can be written to once, but read from many times.
Tube current
Measured in thousandths of an ampere, or milliamperes, it controls the quantity of electrons propelled from cathode to anode.
Intracellular lipid content
The amount of fat molecules a mass contains.
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.
Wide area network (WAN
Computers that are farther apart and must be connected by telephone lines, cables, or radio waves.
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.
Clustered scans
The practice of grouping more than one scan in a single breath-hold.
Crosstalk:
Image noise resulting from the scattering of x-ray photons by adjacent detectors.
Minimum-intensity projection (MinIP
3D technique that selects voxels with the lowest value to display.
Radiopharmaceutical
Radioactive pharmaceuticals used in the field of nuclear medicine as tracers in the diagnosis and treatment of many diseases.
Multiple image display
Function that allows more than one image to be displayed in a single frame.
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.
Barium peritonitis
Barium leaking into the peritoneal cavity
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.
Hospital information systems (HIS)
Information systems that focus on administrative issues, such as patient demographic data, financial data, and patient locations within the hospital.
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.
Scannable range
Degree to which a table can move horizontally. Determines the extent a patient can be scanned without repositioning.
View
A complete set of ray sums.
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.
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.
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.
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.
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.
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.
Anode
X-ray tube design includes a cathode, which emits electrons, and an anode, which collects electrons.
Beam-hardening artifacts
Artifacts that result from lower energy photons being preferentially absorbed, leaving higher intensity photons to strike the detector array
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).
Low-contrast resolution
Ability of the system to differentiate between objects with similar densities. Also called contrast resolution or contrast detectability.
Thyroid storm
A severe, life-threatening condition resulting when thyroid hormone reaches a dangerously high level, also known as thyroid toxicosis.
Fan beam
The radiation emitted from the collimated x-ray source in single-detector row CT systems.
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).
Virtual colonoscopy
A form of volume rendering designed to reveal the inside of the colon. The technique is also called endoluminal imaging.
Negative contrast agents
A contrast agent that is of a lower density than the surrounding structure, such as air or carbon dioxide.
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.
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.
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
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.
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.
Cooling systems
Cooling mechanisms included in the gantry, such as blowers, filters, or devices that perform oil-to-air heat exchange.
Imaging planes
Imaginary planes that divide the body into sections.
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.
Adaptive array
Detector rows that have variable widths and sizes. Also called nonuniform or hybrid arrays.
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.
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.
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.
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.
Infarction
Areas of tissue death that occur because of a local lack of oxygen.
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.
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.
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.
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.
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.
Milliampere-seconds (mAs
The product of milliampere setting and scan time.
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.
Metformin therapy
An oral medication given to non–insulin dependent diabetics to lower blood sugar; also available in combination with other drugs.
Image magnification
When the displayed image is made larger. Uses only image data and does not improve resolution
RCBF
Regional cerebral blood flow.
Gray (Gy
SI unit of absorbed dose
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
Uniformity
The ability of the scanner to yield the same CT number regardless of the location of an ROI within a homogeneous object.
Topology:
The geometric arrangement of a computer system. Common topologies include bus, star, ring, and tree.
Percutaneous procedures
Interventional procedures in which access to inner organs or other tissue is done via needle puncture of the skin.
Caudal
Term used to describe movement toward the feet; synonymous with inferior.
Maximum-intensity projection (MIP
3D technique that selects voxels with the highest value to display
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.
Roentgen (R
Unit of x-ray exposure in air.
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).
Huber needle
A special noncoring hooked needle used to access an implantable port.
Reference detectors
Included in the detector array and help to calibrate data and reduce artifacts.
Isocenter
The absolute center of the gantry.
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
Standard deviation
Indicates the amount of CT number variance within the ROI.
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.
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.
Bolus shaping
Manipulating the flow rate to change the characteristics of the time-density curves.
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.
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.
Optical disc libraries
Robotic storage systems that automatically load and unload optical discs. The devices are also called optical jukeboxes, robotic drives, or autochangers.
Advanced display functions
Display functions that include multiplanar reformation and three-dimensional reformation.
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.
Luminance
Brightness
Image fidelity
Image accuracy
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.
Pixel:
Picture element. Two-dimensional square of data. When arranged in rows and columns, they make up the image matrix
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.
Off-line archiving
Storage system in which data are kept in a less accessible location, requiring manual intervention to use.
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.
Enterprise-wide distribution
Distribution channels that encompass off-site outpatient clinics or allow on-call radiologists to review studies from home.
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.
Sagittal plane
Body plane that divides the body into left and right sections.
Contrast detectability
Ability of the system to differentiate between objects with similar densities. Also called low-contrast resolution.
Region-of-interest editing
The process of selectively removing or isolating information from the data set. Also called segmentation.
Atherosclerosis
The buildup of fat and cholesterol plaque.
Delayed reactions
Reactions occurring between 1 hour and 1 week after contrast medium injection.
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.
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
Electronic health record (EHR
Generic term for a digital patient record; in general usage, EHR and EMR are used synonymously.
Gantry aperture
Opening in the gantry; range of aperture size is typically 70 to 90 cm.
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.
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.
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.
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.
Multidetector row CT (MDCT
Scanner design in which there are many parallel rows of detectors. A single rotation can produce multiple slices.
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).
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.
Focused appendiceal CT
Protocol that limits the scan area to the lower abdomen and upper pelvis.
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.
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.
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.
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.
Transverse plane
Body plane horizontal to the floor
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
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
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.
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.
Thrombolytic therapy
The use of drugs to break up or dissolve blood clots.
Window width
Mechanism that determines the quantity of Hounsfield units represented as shades of gray on a specific image.
Ischemic stroke
Category of stroke caused by a blockage in an artery.
Detector array:
Entire collection of detectors included in a CT system; detector elements are situated in an arc or a ring.
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.
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.
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.
Detector aperture:
Size of the detector opening.
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
Hemangioma:
Abnormal proliferation of blood vessels in the skin or internal organs
Reference image
Displays the slice lines in corresponding locations on the scout image.
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
Cerebrovascular accident:
Term used to describe stroke; no longer favored because it implies a random, unpredictable, or uncertain nature to the condition.
Hemorrhagic stroke
Category of stroke caused by a tear in the artery’s wall that produces bleeding in the brain
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.
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.
Nephropathy
Any condition or disease affecting the kidney; sometimes used synonymously with renal impairment.
Attenuation profile
The system accounts for the attenuation properties of each ray sum and correlates it to the position of the ray.
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.
Longitudinal resolution
Resolution in the z direction
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.
Analog-to-digital converter (ADC):
Converts the analog signal to a digital format.
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.
Prospective ECG gating
Method that uses a signal, usually derived from the R wave of the patient’s ECG, to trigger image acquisition.
Display processor
CT component that assigns a group of Hounsfield units to each shade of gray.
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).
In-plane resolution
Resolution in the x y direction
Dual source
CT design that uses two sets of x-ray tubes and two corresponding detector arrays in a single CT gantry.
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
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.
Ventral
Term used to describe movement forward (toward the face); also referred to as anterior
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.
Gantry
Ring-shaped part of the CT scanner that houses many of the components necessary to produce and detect x-rays.
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.
Renal colic
Acute, usually severe pain that accompanies the passage of renal calculi from the kidney through the urinary tract.
Optical jukebox
Robotic storage system that automatically loads and unloads optical discs. The devices are also called optical disc libraries, robotic drives, or autochangers
Image center
Specific area within the SFOV that will be displayed on the center of the image.
Convolution
Process of applying a filter function to an attenuation profile.
Renal calculi
Gravel-like deposits that appear in the kidney. Also called renal stones or kidney stones.
Reference dose values:
Values published by the ACR regarding the radiation dose that is acceptable for a variety of CT scans.
DICOM
Universally adopted standard for medical image interchange known as the Digital Imaging and Communication in Medicine.
Hand bolus
A rapid injection of contrast material delivered by hand, using syringes.
Uniphasic injection
Injection technique in which a single injection fl ow rate is used.
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.
Double contrast technique
Injection technique used for arthrography in which both iodinated contrast and air are injected into the joint space.
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.
Serum creatinine (SeCr
Laboratory test that measures creatinine level in the blood; it is a fast and inexpensive way to assess renal function.
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.
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.
Slice thickness blooming
When the slice thickness displayed on the image is wider than that selected by the operator.
High-frequency generator
Produces high voltage and transmits it to the x-ray tube.
Thrombotic stroke
Type of ischemic stroke caused from a blood clot or a fatty deposit within one of the brain’s arteries.
Virtual bronchoscopy
A form of volume rendering designed to reveal the inside of the airways. The technique is also called endoluminal imaging.
RCBV
Regional cerebral blood volume.
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.
Standard uptake value
An index of glucose metabolism. The number represents the relative uptake of radionuclides in tissue.
Serial access memory (SAM
Type of computer memory that stores data that can only be accessed sequentially (like a cassette tape).
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.
Autochangers
Robotic storage systems that automatically load and unload optical discs. The devices are also called optical disc libraries, robotic drives, or optical jukeboxes
Detector spacing
Measured from the middle of one detector to the middle of the neighboring detector; accounts for the spacing bar.
Hypertonic
Having a greater number of particles in solution per unit of liquid, as compared with blood.
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.
Table incrementation
Process of moving the table by a specified measure. Also referred to as feed, step, or index.
Clearance
The ability of the kidney to remove a substance from the blood.
Biphasic injection
Injection technique in which two flow rates are used.
Contrast-detail response
The relationship between object size and visibility.
Hyperosmolar
Having a greater number of particles in solution per unit of liquid, as compared with blood.
Window center
Mechanism that selects the center CT value of the window width. Also called window level.
Glabellomeatal line
Imaginary line used for positioning that connects the external acoustic meatus to the supraorbital margin. Also called the supraorbital meatal line.
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.
MTF graph
Charts that depict spatial frequency (object size) on the x axis and MTF along the y axis.
Hard disk
An essential component of all CT systems. It saves the thousands of bits of data acquired with each gantry rotation
360LI
A technique of interpolating helical scan data for SDCT systems using the 360° linear interpolation.
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.
Progressive stroke
A time-limited event in which the neurologic deficits occur in a progressive pattern. Also referred to as a stroke in evolution.
Back projection
Process of converting the data from the attenuation profile to a matrix.
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.
Interleukin 2:
An immunotherapy used to treat some cancers
Capture efficiency
Ability with which the detector obtains photons that have passed through the patient.
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
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).
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.
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.
Online archiving
Storage system using devices such as hard drives that are instantly accessible to the user
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.
Calcium score
The amount of calcification on cardiac CT
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.
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.
Collimators
Mechanical hardware that resembles small shutters and adjusts the opening based on the operator’s selection.
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.
Heat dissipation
Ability of the tube to rid itself of heat
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.
Prepatient collimators
Limit the x-ray beam before it passes through the patient.
Clinical information systems (CIS)
Information systems that keep track of clinical data.
Protocol:
Common set of rules and signals that computers on the network use to communicate
Near-line archiving
Storage systems in which data are readily, although not immediately, available. Examples include an optical jukebox or tape library.
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.
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.
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).
Longitudinal plane
Body plane perpendicular to the floor.
Distance measurement
The system calculates the distance between two deposited points in either centimeters or millimeters.
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
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.
High attenuation
An x-ray beam is greatly impeded by an object; typically shown as light gray or white on an image.
Thyroid toxicosis
A severe, life-threatening condition resulting when thyroid hormone reaches a dangerously high level, also known as a thyroid storm.
Bandwidth
Amount of data that can be transmitted between two points in the network in a set period of time
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.
Core servers
Server computers that are integral to the functioning of the PACS.
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.
Semiautomatic segmentation
Combines many of the benefits of manual and automatic segmentation techniques to selectively remove or isolate information from the data set.
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.
Intracranial hemorrhage (ICH
Bleeding in the brain caused by the rupture of a blood vessel.
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.
Isosmolar contrast media (IOCM
A contrast agent
(Visipaque, GE Healthcare) with an osmolality equal to that of blood.
Valsalva maneuver
Technique that requires the patient to blow the cheeks out to distend the pyriform sinuses.
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.
Nonuniform arrays
Detector rows that have variable widths and sizes. Also called adaptive or hybrid arrays
Limiting resolution
The spatial frequency possible on a given CT system at an MTF equal to 0.1.
CTDI phantoms
Phantoms used to measure the radiation dose delivered for various CT examinations. CTDI is an acronym for computed tomography dose index
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.
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.
Discrete Fourier transform (DFT)
A technique for expressing a waveform as a weighted sum of sines and cosines
Isotonic
Having nearly the same number of particles in solution per unit of liquid as compared with blood.
Scan field of view (SFOV):
The area, within the gantry, from which the raw data are acquired. Also called calibration field of view.
Kilovolt-peak (kVp)
Defines the quality (average energy) of the x-ray beam.
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.
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.
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.
Central processing unit (CPU)
Component that interprets computer program instructions and sequences tasks. It contains the microprocessor, the control unit, and the primary memory.
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.
Graves’ disease
One of the main causes of hyperthyroidism
Robotic drives
Robotic storage systems that automatically load and unload optical discs. The devices are also called optical disc libraries, optical jukeboxes, or autochangers.
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.
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.
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.
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.
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.
Peak aortic enhancement
The point after an IV injection when the contrast agent reaches the highest concentration in the aorta.
Histogram
A graphical display showing how frequently a range of CT numbers occur within an ROI.
Window level
Mechanism that selects the center CT value of the window width. Also called window center.
Informatics
The collection, classification, storage, retrieval, and dissemination of recorded information.
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.
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.
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.
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.
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.
Renal insuffiiency
Renal function is abnormal but capable of sustaining essential bodily function
Spatial frequency:
The number of line pairs visible per unit length.
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.
Heat capacity
Ability of the tube to withstand the heat
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
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.
Hydronephrosis
Obstruction resulting in dilatation, distention, and enlargement of the collection system in the kidney caused by ureteral stones.
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
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.
Multiphasic injection
Injection technique in which two or more flow rates are used.
Overlapping reconstruction
Incrementation is changed to produce overlapping images that are then used in multiplanar or 3D reformations.
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.
Aliasing
Artifacts that result from insufficient projection data; cause fine stripes that appear to be radiating from a dense structure.
Renal stones
Gravel-like deposits that appear in the kidney. Also called renal calculi or kidney stones
Ray
The path that the x-ray beam takes from the tube to the detector.
Tails
Areas of scatter radiation into the tissue of adjacent slices.
Filter functions
Applied to the scan data before back projection occurs to minimize artifacts
Multiple scan average dose (MSAD
Total dose is the central slice radiation dose, plus the scatter overlap (or tails); dose calculated from multiple scans.
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).
Z axis:
Plane that correlates to the slice thickness, or depth, of the CT slice.
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.
Bytes
Unit of information storage composed of 8 bits of data.
Image reconstruction
Use of raw data to create an image
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.
Kidney stones
Gravel-like deposits that appear in the kidney. Also called renal calculi or renal stones.
Signal-to-noise ratio (SNR)
The number of x-ray photons detected per pixel in CT.
Organ dose
The estimated radiation dose to radiosensitive organs from CT procedures. These averages are used to calculate effective dose.
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.
180LI
A technique of interpolating helical scan data for SDCT systems using 180° linear interpolation.
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.
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.
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.
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.
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.
Multiplanar reformation (MPR
Two-dimensional reformation done to show anatomy in various planes.
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.
Hepatic arterial phase
The first phase of enhancement typically occurring 15 to 25 seconds after the IV administration of a bolus of contrast material.
Beam pitch
Table movement per rotation divided by beam width.
Contiguous
Method of acquiring slices in which one slice abuts the next.
Linearity
The relationship between CT numbers and the linear attenuation values of the scanned object at a designated kVp value.
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).
Hardware
Portions of the computer that can be physically touched.
Isotropic:
Equal in all directions; a voxel that is cube-shaped
Automated injection triggering
Injection methods that individualize the scan delay. Two methods exist—the injection of a test bolus and bolus triggering.
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.
Image artifacts
Anything appearing on the image that is not present in the object scanned
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.
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
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.
RAS coordinates
Directional coordinate system—an acronym for right-left, anterior-posterior, superior-inferior—used to determine image center.
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.
Vermiform appendix
Small, tubelike structure projecting from the cecum; literally means wormlike.
Detector efficiency
Ability of the detector to capture transmitted photons and change them to electronic signals
Hounsfield units (HU
Measure of the beam attenuation capability of a specific structure. Also call pixel values, density numbers, or CT numbers.
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.
Positive contrast agents
Contrast agents that are of a higher density than the structure being imaged. Most contain barium or iodine.
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.
Detector pitch
Table movement per rotation time divided by the selected slice thickness of the detector
Computed tomography dose index (CTDI
Dose reported to the FDA; slices must be contiguous.
Inferior
Term used to describe movement toward the feet (down); synonymous with caudal.
Ray sum
The detector senses each arriving ray and senses how much of the beam was attenuated.
