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Mosby's Chapter 3 CT Registry- Review of Safety in Computed Tomography Questions with Accurate Answers
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Mosby's Chapter 3 CT Registry- Review of Safety in Computed Tomography
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Mosby's Chapter 3 CT Registry- Reviewof Safety in Computed Tomography
What is the relationship between mA and patient radiation dose? - answer Directly
proportional
Define attenuation - answer defined as the reduction of intensity of a radiation beam as
it passes through a substance
Define photoelectric absorption - answer occurs when the energy of an incoming
(incident) xray photon is completely absorbed through the ionization of an inner-shell
electron of the target atom
Define Compton scattering - answerwhen incident x-ray photons interact with a target
atom's outer-shell electron, a transfer of energy may occur which ejects the outer-shell
election (ionization), resulting in a loss of energy for the incident x-ray photon and a
subsequent change in direction
What is the attenuation of the CT xray beam dependent on? - answer-beam quality
(photon energy)
-atomic density of the imaged tissue
As the distance from the xray tube to the detector decreases, the dose
(increases/decreases) - answerincreases
Define focus-to-isocenter distace - answerthe distance from the CT tube to the center of
the gantry opening
Define focus-to-detector distance - answerthe distance between the xray source (CT
tube) and the detector array
What kind of filtration is used with the CT xray tube? - answerbetween 6 and mm
aluminum or equivalent material
What is the purpose of filtration - answerto remove the unwanted low quality portion of
the xray beam that adds to the patient dose while failing to yield useful data
What is added to the xray tube to compensate for the noncylindrical nature of most body
shapes? - answerbeam-shaping or bowtie filters
, Why is positioning the patient in isocenter when a bowtie filter is employed? -
answerpositioning the patient off-center can result in unwanted variations in patient
exposure and dose
Define inherent absorption efficiency of a detector - answerdescribes the ability of the
detector to capture transmitted xray quanta and produce the appropriate response
Inefficiency in the inherent absorption can result in what? - answerthe loss of data and a
compensatory increase in patient dose
Define geometric efficiency of a detector array - answerdescribes the spatial
arrangement of detector elements, including the amount of interspace material required
between adjacent elements.
What is the importance of interspace material in MDCT? - answerthe interspace
materials absorbs transmitted radiation but yields no response. This results in a loss of
acquisition data and requires an increase in radiation dose to compensate. MDCT has a
complex arrangement of multiple row of detectors and increases the interspace
material, which reduces geometric efficiency
What is used in MDCT to expose the widened detector array equally? - answerMDCT
utilizes a cone-shaped beam instead of a fan-shaped beam traditionally used by single-
slice CT.
Define overbeaming - answerexpanding the beam even further to avoid exposing the
detectors to undesirable pnumbra
How does overbeaming affect radiation dose? - answerIt results in a radiation dose to
the patient that does not contribute to the CT image
Define overranging - answeroccurs when radiation dose is applied before and after the
acquisition volume to ensure sufficient data collection for the interpolation algorithms
inherent in spiral CT.
What is common for overranging and how does it affect dose? - answerup to half
rotation both before and after the spiral scan are common and it adds to the patient
radiation dose
What is another name for noise reduction algorithms? - answeradaptive filters
Define noise reduction algorithms/adaptive filters - answerare employed during the
reconstruction process to reduce displayed noise within the CT image.
What is the benefit of noise reduction ? - answerReduction of displayed noise allows for
lower mAs settings during data acquisition.
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