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CT registry review 2

CT flash cards

QuestionAnswer
Patient Coordinates x: left to right y: anterior to posterior z: head to feet
Electrons are atomic particles which bear a ______ electrical charge. negative
3 possible paths a fast moving electron might take as it passes through an atom. 1. the electron may directly collide with the nucleus of the atom. Bremsstrahlung rad. 2.the incoming electron may enter the vicinity of the nucleus of the atom, but not collide with it or with any other particle of the atom. Bremsstrahlung radiation.
3.electron collides with inner shell electron inner shell electron shifts position x-ray photon is produced. Characteristic radiation
When are x-ray photons produced? When fast moving electrons collide with the target material & lose energy.
CHF inadequate contraction of the heart muscle.
Ischemic stroke vessel that supplies blood to the vein is blocked by a clot.
Lipoma noncancerous growth of fatty tissue cells.
Aneurysm bulging in the wall of an artery.
Aortic stenosis causes valve to not open fully restricting blood flow.
Leukemia cancer of the white cells.
AVM defects or tangles in the arteries & veins.
Encephalitis viral injection causing inflammation in brain.
What are 2 purposes of a filter? 1. To accurately represent the anatomy & remove star & streak artifacts. 2. Depending on the type of filter selected, certain image characteristics can be enhanced.
Sharp filter Used for defining structural edges & highlighting high resolution detail, at the expense of making the image appear more noisy.
Smooth filter Used for visualizing subtle differences in contrast, to do this, smooth filters minimize the appearance of noise in an image.
What are 3 advantages of helical scans? 1. shorter total exam times 2. minimal gaps between slices 3. minimal misregistration
Convolution The process of applying a filter to the raw data during the image reconstruction calculation.
Back Projection Technique Sums up the contributions from all of the attenuation profiles.
The filter convolved with the raw data enhances the edges of the attenuation profiles so that the resulting images are free from ______ & ______ ______. streaks & star arifacts
How is the volume data from which the multi planar reconstruction is generated, is created by what? Stacking up contiguous transverse slices.
What images from a helical scan are the most diagnostic multiplanar reconstructions? Stacked transverse images
The actual attenuation data measured by the detectors from all projections during a scan is contained where? CT raw data
How is image reconstruction performed? either by filtered back projection or by cone beam reconstruction.
On a single row detector scanner, the thickness is equal to what? The beam collimation.
On multirow detector scanners the x-ray beam is collimated across all of what? The rows of detectors.
On MDCT the reconstructed slice thickness may be equal to the detector size or to the size of what? A combination of detectors.
On MDCT scanners the slice thickness can be varied but never what? Made smaller than the detectors that collected the data.
Dynamic scanning Is a term applied to 15 or more conventional CT scans in rapid succession.
Electron beam CT finds principal application in imaging what? heart
A principal advantage to CTA compared to MRA is what? No flow artifacts
QCT stands for what? Quantitative computed tomography.
What are 2 things aided by QCT? 1. determining cystic or solid 2. measuring tissue perfusion
Successful QCT requires what? A region of interest (ROI)
QCT is principally employed to determine what? Tissue CT #
Name 2 characteristics of EBCT. 1. 100 ms imaging 2. reduced motion blur
What is the principal limitations to dynamic CT imaging? X-ray tube cooling.
Compared to conventional angiography, CTA (computed tomography angiography) what are 3 advantages? 1. allows 3 dimensional reconstruction 2. has lower patient dose 3. is less invasive
When is dynamic scanning employed? When spiral CT is not available.
QCT esp. requires what image characteristic? linearity
Linearity Describes the amount to which the CT number of a metrial is exactly proportional to the density of this material (in Hounsfield units)
Contrast resolution is improved most easily by increasing what? mA
What does the term "peaking" in a CT image refer to? The increase in CT # in the middle of a uniform test object.
Contrast resolution during projection radiography is compromised principally because of what? Scatter radiation
"Peaking" artifact in a CT image is an example of what? Poor image uniformity.
What are 4 principal characteristics of a medical image? 1. spatial resolution 2. contrast resolution 3. image noise 4. artifacts
What is the principal reason to use high kvp during CT exam? Reduced patient dose.
Name 4 characteristics of a CT imager with perfect linearity. 1. a water value of 0 2. a bone value of 1000 3. an air value of -1000 4. a straight line plot of CT # versus u
What are 2 effective ways in improving contrast resolution in CT? 1. imaging thicker slices 2. use a larger field of view (FOV)
Increasing a dynamic range of a CT image results in more shades of what? gray
During CT exam, the principal x-ray interaction is what? Comptom scattering
The value of the modulation transfer function (MTF) at low spatial frequencies is principally related to what? contrast resolution
What does Image Uniformity refer to? 1 CT # value of a given object.
Spacial resolution in CT is approx. 1 1p/cm. What is the smallest sized object that can be imaged. 5mm
What side of the heart receives blood from the body & pumps it to the lungs? Right
What side of the heart receives blood from the lungs & pumps it out to the body? Left
How many chambers does the heart have? 4
Name the 4 chambers of the heart. 1. left atrium 2. right atrium 3. left ventricle 4. right ventricle
What does the atrium's do? Chambers that fill with blood returning to the heart from the body & lungs.
What does the ventricle's do? Squirt out blood to the body & lungs.
Running down the middle of the heart is a thick wall of muscle called what? septum
What is the septum's job? To seperate the left side & the right side of the heart.
How does the atria & ventricles work as a team? The atria fill with blood, then dump it into the ventricles. Ventricles then squeeze, pumping blood out of the heart. While the ventricles are squeezing the atria refill & get ready for the next contraction.
The blood relie on what 4 special valves? 2 mitral valves, 1 aortic valve & 1 pulmonary valve.
What does the mitral valves do? They let blood flow from the atria to the ventricles.
What do the aortic & pulmonary valves do? They are in charge of controlling the flow as the blood leaves the heart.
How do the valves work together? They keep the blood flowing forward. They open to let blood move ahead & close to keep blood from flowing backwards.
What do arteries do? Carry blood away from the heart.
What do veins do? Carry blood back to the heart.
Absolute risk Incidence of malignant disease in a population each 1 year following a given dose. Expressed as number of cases/10 to the 6 power persons/rem.
Absorbed dose Energy transferred from ionizing radiation per unit mass of irradiated material. Expressed in rad (100 erg/g) or gray (1 J/Kg)
Absorber Any material that absorbs or reduces the intensity of radiation.
Absorption Transfer of energy from radiation to matter. Removal of x-rays from a beam via the photoelectric effect.
Acute Beginning suddenly & running a short but rather severe course.
Added Filtration Aluminum (or its equivalent) of appropriate thickness positioned outside an x-ray tube and in the primary beam.
Algorithm Computer-adapted mathematical calculation applied to raw data during the process of image reconstruction. Computer compatible equation.
Aliasing Effect Artifacts that appear on the CT image as fine lines. They occur when too few samples are acquired. Also called sampling artifacts.
Aluminum (Al) Metal most frequently selected as x-ray beam filter material because it effectively removes low-energy x-rays.
How is contrast resolution principally limited? By increasing image noise.
How can noise be reduced? 1. with 360 degree interpolation rather than 180 degree interpolation. 2. reduced scatter radiation 3. use of low-frequency convolution filter.
What is the principal reason to use high kvp during CT exam? Less x-ray tube heat loading.
Contrast resolution can be improved in CT by what? 1. reducing image noise. 2. increasing pixel size.
How is image CT linearity best defined? As the ability to assign the correct CT # to a given object.
What does good spatial resolution refer to? The ability to image high spatial frequency objects.
What does Cupping refer to? The decrease in CT # in the middle of a uniform test object.
How is Spatial Resolution in CT is improved by what? 1. using small detectors. 2. using small pixel size.
CT Spatial resolution can be improved by what? 1. using a high-frequency recontruction 2. increasing the # of views required per scan 3. decreasing the field of view (FOV) 4. increasing the matrix size
Name 3 things that contribute to improved spatial resolution. 1. small detector size 2. small pixel size 3. small voxel size
High-frequency convolution filter bests contributes to improve what? spatial resolution
Name 3 methods for evaluating spatial resolution. 1. point spread function 2. line spread function (LSF) 3. edge response function (ERF)
The spatial resolution of a CT imager can be improved by reducing what? pixel size
Fourier transformation (Ft) a mathematical transformation to convert distance into spatial frequency.
Image uniformity refers to what? Constant CT # of an object.
CT spatial resolution can be improved by what? 1. using a smaller pixel 2. thinner slice imaging 3. narrowing the predector collimation 4. increasing the source to isocenter distance
Cupping artifact in a CT image is and example of what? poor image uniformity
Fourier transformation (FT) is a method to what? 1. transform object size to spatial frequency 2. change distance into inverse distance
Spatial resolution for CT is usually expressed by the what? the value of the spatial frequency at a 10% modulation transfer function(MTF)
Noise on a CT image principally influences what? contrast resolution
Aluminum (Al) equivalent Thickness of a material resulting in the same attenuation as aluminum.
Scientific society of medical physicists American Association of Physicists in Medicine (AAPM)
Professional society of medical physicists American College of Medical Physicists (ACMP)
Professional society of radiologists & medical physicists. American College of Radiology (ACR)
Scientific & professional society of radiographers American Society of Radiologic Technologists (ASRT)
The SI unit of electric charge. 1A=1 c/s Ampere (A)
Analog Signal Continuous display of energy, intensity or radiation as opposed to the discrete display of a digital signal.
Anode Positive side of x-ray tube, containing the target.
Archival storage Secondary or permanent storage of digital images - usually magnetic tapes, magnetic disks, or optical disks - and film images.
Aperture Circular opening for the patient in the gantry of a CT or MRI.
Archiving Saving data on auxiliary devices, such as optical disk or digital audiotape, for the purpose of reviewing at a later date.
Area Beam X-ray beam pattern usually shaped as a square or rectangle used in conventional radiography & fluoroscopy.
Array Processor Part of a computer that accepts signal data & performs the mathematical calculations necessary to reconstruct a digital image.
Artifact Pattern on an image that does not represent anatomy & does not exist in reality. It may be caused by operator error, pt motion or equipment characteristics. Unintended optical density on a radiograph or other film-type image receptor.
Attenuation Reduction in radiation intensity when passing through matter as a result of absorption & scattering.
Attenuation Coefficient Numerical expression of the decrease in intensity with penetration into matter. Process of energy absorption described by % of radiation remaining after xrays pass through an object. The x-ray attentuation coefficient is expr in inverse length m-1cm-1
Attenuation Profile Result of the CT process that accounts for the attenuation properties of each ray sum relative to the position of the ray.
Attenuator Device or material that reduces x-ray or US intensity.
Axial Parallel to the long axis of the body.
Axial Plane Imaginary plane that divides the body into right & left or front & back sections- sagittal or coronal, respectively.
Back Projection Process of converting the data from the attenuation profile to a matrix.
Backscatter X-rays that have interacted with an object & are deflected in a backward direction.
Beam Hardening Artifact Artifact that results from lower-energy photons being preferentially absorbed, leaving higher-energy photons to strike the detector array.
Bolus Phase Phase of contrast enhancement that immediately follows an intravenous bolus injection. Characterized by an attenuation difference of 30 or more Hounsfield units between ther aorta & the inferior vena cava.
Bremsstrahlung X-rays produced by deceleration of electrons near the nucleus of a target atom; braking radiation.
Calibration Comparison of a laboratory source or instrument in daily use with a standard source or instrument to improve accuracy.
Carcinogenic Causing cancer.
Cataractogenic Causing cataracts.
Cataracts Clouding of the lens resulting in vision obstruction.
Cathode Negative side of the x-ray tube, contains the filament & focusing cup.
Cathode ray tube (CRT) Electron beam vacuum tube designed for a 2D display. A TV picture tube used to display CT image & to communicate with computer.
Center for devices & radiological health (CDRH) Agency of the US Food & Drug Administration. Responsible for a national radiation control program.
Centigray .01 Gy (1 rad)
Charged Particle. An ion. Elementary particle carrying a positive or negative electric charge.
Central Processing Unit (CPU) Primary component of a computer. The CPU takes information from the data acquisition system & manipulates it so that an image can be formed.
Characteristics x-rays X-rays produced following ionization of inner-shell electrons of the target element.
Classical Scattering Scattering of x-rays with no loss of energy. Also called coherent, Rayleigh or Thompson Scattering.
Collimation Restriction of the useful x-ray beam to the anatomical area of interest in order to reduce pt dose & improve image contrast.
Compensating Filter Material inserted between an x-ray source & a pt to shape the intensity of the x-ray beam. X-ray beam filter designed to make the remnant beam more uniform in intensity, such as a bow tie filter.
Compton Effect Interaction between an x-ray & a loosely bound outer-shell electron, resulting in ionization & x-ray scattering.
The ____ _____ ______ position is often used to differentiate the pancreatic head & the duodenum. Right lateral decubitus
The ______ ______ descends to the level of L4, where it bifurcates into the left & right common iliac arteries. Abdominal aorta
The location of the liver on the inferior portion of the image indicates that this patient is in what position? Right lateral decubitis position
Pleural effusion A build up of fluid between the layers of tissue that line the lungs & chest cavity.
Pleaural effusion, where is it commonly seen? *commonly seen in the posterior portion of the lung field on images obtained w/ the pt in a supine position.
Pleural effusion - differentiation *Differentiation between pleural effusion & pleural thickening is made when region of interest (ROI) measurements reveal fluid w/ density readings at or slightly above 0.
What can cause pleural effusions? Pleural effusion may be caused by multiple pathologic processes including: infection, neoplasm, CHF
On a single-row detector scanner, collimation does what 3 things? 1. Controls the slice thickness 2. Minimizes the x-ray dose to the patient. 3. reduces the detection of scatter radiation
When acquired directly, coronal images may be obtained in what 2 ways? 1. Patient is positioned head 1st & supine with the head hyperextended & the top of the gantry titled forward by about 20 degree.
2. Patient is positioned head 1st & prone, resting on the chin & the top of the gantry is tilted backwards by about 20 degrees.
High resolution CT Is a specialized tech. using narrow section widths & a high resolution algorithm for image reconstruction. It is used to maximize detail of high spatial frequency tissue, such as the lungs.
Steatosis Diffuse fatty infiltration of the hepatic parenchyma.
Fatty liver disease or hepatic steatosis A condition in which large quantities of fats (lipids) are retained within the liver.
What does normal liver parenchyma exhibit? Attenuation values approx. 10 HU higher than those of the spleen, the liver w/ steatosis has attenuation values at least 10 HU below those of the spleen.
Created by: dhathaway