Computed Tomography Q&A 2018 PDF

RADIOLOGIC SCIENCES FUTURE RRT REVIEWERS 2018 MEYNARD Y. CASTRO, RRT CT-MRI TECHNOLOGIST MAKATI MEDICAL CENTER INC. COM...

RADIOLOGIC SCIENCES FUTURE RRT REVIEWERS 2018 MEYNARD Y. CASTRO, RRT CT-MRI TECHNOLOGIST MAKATI MEDICAL CENTER INC. COMPUTED TOMOGRAPHY QUESTION AND ANSWER "DO YOU BEST AND GOD WILL DO THE REST" QUESTION ANSWER The number of photons absorbed by the detector and dependent Absorption Efficiency on the physical properties of the detector face Filters the x-ray beam to reduce the radiation to the patient and Compensating Filters help minimize image artifact and improve image quality Computed Tomography Dose Index Dose reported to the FDA (CTDI) Element in a CT system that collects attenuation information and measures the intensity of the transmitted x-ray radiation along a Detector beam projected from the x-ray source to that particular detector element A direct plane is one that can be obtained by positioning the Direct Axial Plane patient in a specific position A technique for expressing a waveform as a weighted sum of sines Discrete Fourier Transform (DFT) and cosines A technique of interpolating helical scan data for SDCT systems 360o Linear Interpolation using the 360° linear interpolation Process of moving the table by a specified measure Table Incrementation An acute impairment of renal function that follows the Contrast media-induced Nephropathy intravascular administration of contrast material for which (CIN) alternative causes have been excluded 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 Third-generation Design view and a detector array. It is determined how rapidly data are acquired and is controlled by gantry rotation speed, the number of detector channels in the Temporal resolution system, and the speed with which the system can record changing signals. When the table position is manually set at zero by the technologist Table Referencing The difference between the measured CT number of a given tissue System Noise and the known value for that tissue Low-voltage electrical contacts within the gantry designed to allow continuous rotation of an x-ray tube without the use of Slip Rings cables connecting internal and external components Adaptive/ Detector rows that have variable widths and sizes Nonuniform/ Hybrid Array Determines the extent a patient can be scanned without Scannable range repositioning Size of the detector opening Detector Aperture Entire collection of detectors included in a CT system Detector Array Ability of a system to resolve, as separate forms, small objects that MEYNARD Y. CASTRO, are very close together. Also call RRT high- contrast resolution or detail Spatial resolution resolution RADIOLOGIC SCIENCES FUTURE RRT REVIEWERS 2018 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 Slip Rings continuously, eliminating the need to straighten twisted system cables The leakage of fluid from a vein into the surrounding tissue during Contrast Media Extravasation IV contrast administration Process used to generate three-dimensional images that show the Shaded-surface Display (SSD) or Surface surface of a three-dimensional object Rendering Early systems, which contained only a single row of detectors in Single-detector Row CT (SDCT) the z axis, obtained data for one slice with each rotation The number of x-ray photons detected per pixel in CT Signal-to-noise Ratio (SNR) The process requires a scan acquisition, needle placement, another scan acquisition, adjustment of the needle, another scan Sequential CT acquisition, and so forth until the needle is confirmed to be in the correct location Factors that can be controlled by the operator and affect the quality of the image produced (e.g. mA, scan time, slice thickness, Scan Parameters FOV, reconstruction algorithm, and kVp) Electronic component of CT scanner that measures remnant radiation exiting the patient, converting the radiation to an analog Detector Assembly signal proportionate to the radiation intensity measured A brief, persistent flash of scintillation that must be taken into Afterglow account and subtracted before image reconstruction The disadvantage of solid state detector over xenon gas detector Afterglow Changes the digital signal from the computer memory back to an Digital-to-analog Converters (DAC) analog format so that the image can be displayed on the monitor Measured from the middle of the one detector to the middle of the Detector Spacing neighboring detector They result when wide slices are used as source images Stair-step Artifacts Instructions that tell the computer what to do and when to do it Software Ability of the detector to capture transmitted photons and change Detector Efficiency them to electronic signals Artifacts that relate to the cone-shaped beam required for MDCT Cone beam artifact helical Method of acquiring slices in which one slice abuts the next Continuous Ability of the system to differentiate between objects with similar Contrast detectability or low-contrast densities resolution Included in the detector array and help to calibrate data and reduce Reference Detectors artifacts Determines how the data are filtered in the reconstruction process Reconstruction Algorithm Table movement per rotation divided by the selected slice Detector Pitch thickness of the detector The section of data selected for display on the image Display Field of View (DFOV) Process of creating a digital image from raw data Reconstruction Processing of using the same raw data to later generate a new Retrospective Reconstruction image Output device that allows the information stored in computer Display Monitors MEYNARD Y. CASTRO, RRT RADIOLOGIC SCIENCES FUTURE RRT REVIEWERS 2018 memory to be displayed Mathematic formula designed for computers to carry out complex Algorithm calculations required for image reconstruction A designed for enhancement of soft tissue, bone, and edge Algorithm resolution 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 Response Time ready to detect another x-ray event All measurements obtained from the detector array and sitting in Raw data or scan data the computer waiting to be made into an image Type of computer memory that includes instructions that are Random Access Memory (RAM) frequently changed, such as the data used to reconstruct images Instructions for CT examination specifying slice thickness, table increments, contrast administration, scan diameter, and any other Protocol requirements specified by the radiologist CT component that assigns a group of Hounsfield units to each Display Processor shade of gray Image reconstruction that is automatically produced during Prospective Reconstruction scanning It converts the analog signal to a digital format Analog-to-digital Converter (ACD) The absolute center of the gantry Isocenter One of the oldest data storage options used to record computer Magnetic Tape data Objects seen on the image but not present in the object scanned Artifacts It is often used to graphically represent a system’s capability of Modulation Transfer Function (MTF) passing information to the observer Ratio of the maximum signal measured to the minimum signal the Dynamic Range detectors can measure The first phase of enchancement typically occurring 15-25 Hepatic Arterial Phase seconds after the IV administration of a bolus of contrast material Scanning method that includes a continually rotating x-ray tube, Helical, Spiral, Volumetric or Continuous constant x-ray output, and uninterrupted table movement Acquisition Scanning The displayed contrast of an image is dependent on the window Displayed Contrast settings used for its display More closely reflects the radiation dose for a specific CT examination and its value is affected by variances in patient Dose-length Product (DLP) anatomy Artifact that results from insufficient projection data and appears Aliasing artifact as fine stripes radiating from a dense structure Anything appearing on the image that is not present in the object Image artifacts scanned Ability of a system to resolve, as separate forms, small objects that High Contrast Resolution or are very close together. Spatial or detail resolution Arbitrary number assigned by computer to indicate relative Hounsfield Units (HU) or Pixel Values, density of a given tissue Density Numbers or CT Numbers Information that appears on images that includes facility name, patient name, identification number, date, slice number and Image Annotation thickness, pitch, table location, measurement scale, gray scale, and right and left indicators MEYNARD Y. CASTRO, RRT RADIOLOGIC SCIENCES FUTURE RRT REVIEWERS 2018 These artifacts can best be avoided by using a low pitch whenever Helical Interpolation Artifacts possible Result in subtle inaccuracies in CT numbers and can be easily Helical Interpolation Artifacts misinterpreted as disease Process by which raw data are obtained by continuous scanning Dynamic Scanning Analog image whereby each pixel in the image corresponds to a Gray-scale Image particular shade of gray System that assigns a certain number of Hounsfield values to each Gray Scale shade of gray Complex statistical methods to, in effect, take the slant and blur out of the helical image and create images that closely resemble Helical Interpolation Methods those acquired in a traditional axial mode The last phase of tissue enhancement after the IV injection of Equilibrium/ Delayed Phase contrast media The phase of renal enhancement that follows nephrogram phase that typically occurs approximately 3 minutes after the IV Excretory Phase administration of a bolus of contrast material and can last 15 minutes or longer A method to study waves of many different sorts and also to solve Fourier Transform (FT) several kinds if linear differential equations Streak artifact or shading (both light and dark) arising from irregularly shaped objects that have a pronounced difference in Edge Gradient Effect density from surrounding structures Use of volumetric CT scanning with spiral technique to acquire image data that are reconstructed into three-dimensional CT CT Angiography angiograms Distortion or error in image that is unrelated to subject being Artifacts studied The detector senses each arriving ray and senses how much of the Ray sum beam was attenuated The path that the x-ray beam takes from the tube to the detector Ray Total dose is the central slice radiation dose, plus the scatter Multiple Scan Average Dose (MSAD) overlap (or tails); dose calculated from multiple scans Postprocessing technique applied to stacks of axial image data that Multiplanar Reformation (MPR) can then be reconstructed into other orientations or imaging plane A technique of interpolating helical scan data for SDCT systems 180o Linear Interpolation using 180° linear interpolation Ancillary pieces of computer hardware designed to accept processed data from the computer (e.g. monitor, laser camera, Output Device printer, and archiving equipment (e.g. optical discs or magnetic tape) Scanner design in which there are many parallel rows of detectors Multidetector Row CT (MDCT) Preliminary image of a CT examination that is used to plan the Localizer Scans, Scout, Topogram, range of the scan depending on the vendor Scanogram or Pilot Ability of a CT scanner to demonstrate different tissue densities Contrast Resolution Amount of the x-ray beam that is scattered or absorbed per unit Linear Attenuation Coefficient (µ) thickness of the absorber Specific area within the SFOV that will be dis- played on the Image Center center of the image MEYNARD Y. CASTRO, RRT RADIOLOGIC SCIENCES FUTURE RRT REVIEWERS 2018 Image distortion caused by combination of table indexing and Image Misregistration respiration When the displayed image is made larger. Uses only image data Image Magnification and does not improve resolution Image data are used to stacked cross-sectional slices and generate Image Reformation/ an image in a plane or orientation different from the prospective Rendering image CT number assigned to measured remnant radiation intensity after Attenuation Coefficient attenuation by tissue density The resolution in the z direction Longitudinal Resolution The system accounts for the attenuation properties of each ray sum Attenuation and correlates it to the position of the ray Profile The simplest type of a mathematical method of estimating the value of an unknown function using the known value on either Linear Interpolation side of the function Process of applying a filter function to an attenuation profile Convolution Pharmaceuticals used to reduce motion artifact on cardiac CTA β-blockers images by temporarily lowering a patient's heart rate 3D technique that selects voxels with the highest value to display Maximum-intensity Projection (MIP) Mechanical hardware that resembles small shutters and adjusts the Collimator opening based on the operator's selection CT techniques that attempt to minimize cardiac motion in the study by selecting or acquiring images during cardiac segments Cardiac Gating with relatively low cardiac motion CT design that uses two sets of x-ray tubes and two corresponding Dual Source detector arrays in a single CT gantry Grid formed from the rows and columns of pixels Matrix 3D technique that selects voxels with the lowest value to display Minimum-intensity Projection (MinIP) It is often used to graphically represent a system’s capability of Modulation Transfer Function (MTF) passing information to the observer The radiation emitted from the collimated x-ray source in single- Fan Beam detector row CT systems These artifacts occur because the anatomy outside the SFOV attenuates and hardens the x-ray beam, but is ignored in the image Out-of-field artifacts reconstruction process Process by which different tissue attenuation values are averaged Partial Volume Effect to produce one less accurate pixel reading Artifact that can result when an object does not appear on all Partial Volume Artifact views Area of anatomy displayed by the cathode ray tube Field of View (FOV) This encompasses a broad range of technologies necessary for the Picture Archive and Communication storage, retrieval, distribution, and display of images System (PACS) Specialized reconstruction techniques that are applied to CT image Postprocessing Techniques to display the anatomic structures from different perspectives Applied to the scan data before back projection occurs to Filter Functions minimize artifacts Most commonly used method of describing spatial resolution Modulation Transfer Function (MTF) ability MEYNARD Y. CASTRO, RRT RADIOLOGIC SCIENCES FUTURE RRT REVIEWERS 2018 Saving studies on auxiliary devices for the purpose of future Archiving viewing Scanner configuration that uses a detector array that is fixed in a Fourth Generation Design 360o circle within the gantry Process by which computer-reconstructed transverse (or axial) image of a patient is created by an x-ray tube and detector Computed Tomography assembly rotating 360 degrees about a specified area of the body Image noise resulting from the scatting of x-ray photons by Crosstalk adjacent detectors Limit the x-ray beam before it passes through the patient Prepatient Collimators Ring-shaped part of the CT scanner that houses many of the Gantry components necessary to produce and detect x-rays Shape the beam and are located below the patient and above the Predetector Collimators detector array The most commonly used matrix size 512 x 512 Opening of the gantry through which patient passes during scan Gantry Aperture Artifacts that results from lower energy photons being Beam Hardening Artifacts preferentially absorbed, leaving higher intensity Mechanism that determines the quantity of Hounsfield units Window Width represented as shades of gray on a specific image It controls the overall gray level and affects image contrast Window Width Mechanism that selects the center CT value of the window width Window Center/Level Phenomenon by which an x-ray beam passing through a structure Beam is decrease in intensity or amount because of absorption and Attenuation interaction with matter It controls subtle gray images within a certain width range and Window Center/Level ultimately affects the brightness and overall density of an image 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, Uncoupling Effect a good image results This effect can make it difficult to identify when a dose that is Uncoupling Effect higher than necessary is used Description of significant levels of technologic development of Generation CT scanners CT technique used to visualize the arterial and venous vessels CT Angiography throughout the body Undesired surge of electrical current (e.g. a short- circuit) within Tube Arcing the x-ray tube System that assigns a certain number of Hounsfield values to each Gray Scale shade of gray Artifact that results from beam hardening Cupping Artifact A picture element or two-dimensional square of data Pixel The travel distance of the CT scan table per 360° rotation of the x- Pitch ray tube divided by the x-ray beam collimation width A measure of exposure per slice and is independent of scan length CTDIvol The preferred expression of radiation dose in CT dosimetry CTDIvol Part of detector assembly that converts analog signals to digital Data-acquisition System (DAS) signals that can be used by the CT computer MEYNARD Y. CASTRO, RRT RADIOLOGIC SCIENCES FUTURE RRT REVIEWERS 2018 Scans produced result in images that are perpendicular to the z Axial/ axis or tabletop and parallel to every other slice Step-and-Shoot Scanning It uses a large electron gun as its x-ray beam source Electron Beam Imaging Analog image whereby each pixel in the image corresponds to a Gray-scale Image particular shade of gray This adjusts for variation across the scan field of view by providing a weighted average of measurement at the center and CTDIw the peripheral slice locations (e.g. the x and y dimensions of the slice) Table movement per rotation divided by beam width Beam Pitch Unit of information storage composed of 8 bits of data Bytes Ability with which the detector obtains photons that have passed Capture through the patient Efficiency Result when the CTDI is measured using a pencil ionization chamber, a 100-mm long thin cylindrical device, which is long CTDI100 enough to span the width of 14 contiguous 7-mm CT slices Process of converting data from attenuation profile to a matrix Back Projection Phantoms used to measure the radiation dose delivered for various CTDI Phantoms CT examinations An equipment option that will make changes in tube current (mA) Automated Tube Current based on the estimated attenuation of the patient at a specific Modulation location Mechanical filter that removes soft, or low-energy x-ray beams, minimizing patient exposure and providing a more uniform beam Bow Tie Filters intensity A rapid injection of contrast material that can be delivered by hand Bolus Injection Technique (using syringes) or by a mechanical injection system Scan method in which the CT table moves to the desired location Axial/ and remains stationary while the x-ray tube rotates within the Step-and-Shoot Scanning gantry, collecting data MEYNARD Y. CASTRO, RRT CT-MRI TECHNOLOGIST MAKATI MEDICAL CENTER INC. MAY 31, 2018 MEYNARD Y. CASTRO, RRT RADIOLOGIC SCIENCES FUTURE RRT REVIEWERS 2018 MEYNARD Y. CASTRO, RRT