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Computed Tomography ARRT ( Image Production) correctly answered to pass
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Computed Tomography ARRT ( ImageProduction)
data acquisition - correct answer ✔✔the measurement of the attenuation that occurs along each path
through the patient from the x-ray tube to the detector
data reconstruction - correct answer ✔✔computerized processing of the transmission measurements
into the CT image
multidimensional image display - correct answer ✔✔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 answer ✔✔display as well as storage, both short term and
long term of images on computer workstations
scout image acquisition (localizer or scanogram) - correct answer ✔✔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 answer ✔✔the angle of the tube and detectors in relationship to the patient position
during scout acquisition
steps from x-ray to actual image - correct answer ✔✔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 answer ✔✔it is a localizer for the prescription of subsequent
cross-sectional CT acquisition(s)
what does the gantry house? - correct answer ✔✔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 answer
✔✔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 answer ✔✔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 answer ✔✔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 answer ✔✔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 answer ✔✔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 answer ✔✔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 answer ✔✔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 answer ✔✔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 answer ✔✔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 answer ✔✔oil and air cooling ,
increasing anode diameter , and conduction by tube rotation
What features must a modern multidetector CT tube have? - correct answer ✔✔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 answer ✔✔30mA-800 mA
Automatic tube current modulation (ATCM) - correct answer ✔✔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 answer ✔✔anatomic extent , detector
configuration and table speed; exposure time can be from 30-60 s in length
photon flux - correct answer ✔✔the rate at which the photon fluence passes through a unit area over
unit time
effective mAs - correct answer ✔✔the calculated mAs per acquired slice , the main controlling factor is
the table speed
pitch controls_______ - correct answer ✔✔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 answer ✔✔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 answer ✔✔70-150 kVP
ATVS -automated tube voltage selection - correct answer ✔✔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 answer ✔✔True
How does a dual energy CT system work? - correct answer ✔✔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 answer
✔✔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 answer ✔✔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 answer ✔✔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
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