data acquisition correct answers the measurement of the attenuation that occurs along each path through the patient from the x-ray tube to the detector
data reconstruction correct answers computerized processing of the transmission measurements into the CT image
multidimensional image display...
Computed Tomography ARRT (Image Production)
QUESTIONS & ANSWERS 100% ACCURATE!!
data acquisition correct answers the measurement of the attenuation that occurs along each
path through the patient from the x-ray tube to the detector
data reconstruction correct answers computerized processing of the transmission
measurements into the CT image
multidimensional image display correct answers display of the reconstructed grayscale image
in two-dimensional and / or 3-D format ; representation of the attenuation that occurred
across the scanned volume of tissue
image archival and communication correct answers display as well as storage, both short term
and long term of images on computer workstations
scout image acquisition (localizer or scanogram) correct answers this survey scan is a digital
radiograph obtained by keeping the x-ray tube and detector array in a fixed position while the
patient bed is translated through the gantry
azimuth correct answers the angle of the tube and detectors in relationship to the patient
position during scout acquisition
steps from x-ray to actual image correct answers CT scans- x-rays hit detectors- attenuation
measurements get turned into digital data- data goes to computer which process info- info is
assigned a numerical value - forms image that we can see and store on PACS
why do we need a scout image? correct answers it is a localizer for the prescription of
subsequent cross-sectional CT acquisition(s)
what does the gantry house? correct answers generator, x-ray tube, assorted collimators , the
data acquisition system , slip rings, and detectors
before slip rings, what mechanism did CT machines use to rotate around the patient? correct
answers they were limited to hardwired cables , which prevented continuous rotation within
the gantry, at the end of each rotation of the x-ray tube and/or detectors, the system would
reverse course and travel in the opposite direction because the cables were of finite length
slip ring technology correct answers eliminates the need for cables by utilizing a system of
contact brushes that supply electricity to power the system and enable the passage of
transmission data to the computer; also allowed for helical scanning which is standard today
what are the technical elements of helical CT acquisition? correct answers 1) continuous
rotation of the gantry components (slip ring )
2) a powerful x-ray tube capable of long exposure output
3) continuous movement of the patient bed
4)specialized mathematical reconstruction techniques
,helical geometry allows for_________> correct answers volumetric data acquisition ; the
reconstruction of CT sections at any point along the scanned volume is possible as long as the
section width is the same
what advantage does the multidetector give in helical acquisition? correct answers enable CT
sections of varying widths to be reconstructed at any point along the acquired volume
how many filaments are in the CT gantry and what are their focal spot size? correct answers
its a dual filament system and the focal spot sizes are 0.5mm to 1.2 mm in diameter
how can focal spot size be adjusted? correct answers this depends on the vendor, in some
cases it can be adjusted through the selection of milliamperage setting or scan field of view
flying focal spot technology correct answers involves the electromagnetic steering of the
electron beam emitted from the cathode, directed toward two separate locations on the
rotation anode, resulting in two sources of x - radiation
how is oversampling accomplished? correct answers the tube rotates around the patient , so
the number of data samples is essentially doubled because of electronic switching between
two focal spots , this improves the systems temporal and spatial resolution
what features allow CT scanners to improve heat capacity? correct answers oil and air
cooling , increasing anode diameter , and conduction by tube rotation
What features must a modern multidetector CT tube have? correct answers must have a high
heat rating , must be small size/lightweight in order to rotate at a high speed and must be
stable and long lasting because it has to withstand centrifugal forces
what is the mA setting range? correct answers 30mA-800 mA
Automatic tube current modulation (ATCM) correct answers program that adjusts the mA
throughout an acquisition to reduce patient radiation dose to a minimum, it can also alter the
mA according to predetermined noise index that is acceptable for appropriate image quality
exposure time is dependent on ____________ correct answers anatomic extent , detector
configuration and table speed; exposure time can be from 30-60 s in length
photon flux correct answers the rate at which the photon fluence passes through a unit area
over unit time
effective mAs correct answers the calculated mAs per acquired slice , the main controlling
factor is the table speed
pitch controls_______ correct answers the speed at which the patient translates through the
gantry for each tube revolution
effective mAs= mAs/pitch
as pitch increases, mAs decreases
, why are high kVp setting utilized? correct answers to decrease the streak artifact that may
occur as the beam passes through very dense parts, such as those found in the posterior fossa
during head imaging
what is the kVp range used in CT? correct answers 70-150 kVP
ATVS -automated tube voltage selection correct answers an advanced feature that may be
available on some modern CT exams, it modulates the tube potential based upon the
changing patient attenuation along the scan acquisition range
True/False Dual energy CT systems are capable of applying multiple x-ray energies during a
single CT acquisition . correct answers True
How does a dual energy CT system work? correct answers transmission data is acquired from
tissue interactions with both high and low kVp radiation. Differentiation and characterization
of tissue composition are made possible by the difference in attenuation between the two x-
ray spectra
how can complex voltage-switching systems be use to achieve dual-energy CT scanning?
correct answers the single tube rotates around the patient. the applied peak kVp is switched at
an extremely high rate for each successive projection
how is a dual energy CT system constructed? correct answers has 2 completely separate x-ray
tubes and detector arrays that are 90 deg. from each other within the gantry . the two tubes
acquire data simultaneously at different kVp rates
How has dual energy CT systems expanded clinical opportunities? correct answers 1)
improved resolution of soft tissue structures during musculoskeletal studies (
ligaments/tendons)
2) the ability to visualize atherosclerotic plaque within contrast-enhanced vasculature during
cardiac CT studies
3) contrast medium subtraction techniques for the demonstration of precontrast images from a
singe scan acquired after the contrast injection
4) characterization of the biochemical composition of urinary calculi
a filtered beam that is more homogenous is less susceptible to artifacts from this process........
correct answers beam hardening
beam hardening correct answers loss of low energy photons increases the mean energy of the
beam; as the beam traverses the patient , low energy photons get absorbed first and this
increases the average intensity of the beam
how much inherent filtration does the tube have? correct answers 3.0mm of Al equivalent
filtration
Bow tie filters correct answers thicker at the ends than in the middle, help shape the beam to
reduce pt radiation exposure; reduce beam intensity at the outer margins and result in less
dose
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