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Physical Principles of Computed Tomography questions with verified answers
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Physical Principles of Computed Tomography questions with verified answers
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Physical Principles of ComputedTomography
Goal of CT - correct answer ✔✔Minimal superimposition, Improved image contrast, very small
differences in tissue contrast
Physical principles - correct answer ✔✔Data Acquisition, Data processing, Format of CT image, Data flow
in a CT scanner, Sequence of events, Advantages of CT, Limitations of CT
Data Acquisition - correct answer ✔✔Systematic collection of information from the patient to produce
CT image, Slice by slice data acquisition(axial), x-ray tube rotates around the patient, data is collected
from the single slice, the tube stops, patient moves to the next location
Volume data acquisition - correct answer ✔✔Volume or helical scanning, x-ray tube rotates around the
patient and traces a spiral path to scan an entire volume of tissue, relative transmission(attenuation
measurements) values are sent to the computer and stored as raw data, large number of transmission
measurements are needed to reconstruct the CT image
Radiation attenuation - correct answer ✔✔amount of attenuation in the tissues is used to reconstruct an
image, attenuation is the reduction of intensity of a beam of radiation as it passes through an object,
either through absorption or scatter, depends on electrons per gram, atomic number, tissue density, and
radiation energy used
Homogenous beam - correct answer ✔✔All photons have same energy, Also called monochromatic or
monoenergetic beam, Used in Houndsfield's first ct scanner because of Lambert-Beer law, Each section
of absorber attenuates beam by equal amounts, Quality of beam(beam energy) does not change, Start
with 80 keV, the transmitted photons all have an energy of 80keV, Takes longer to produce, Attenuation
is exponential
Heterogeneous beam - correct answer ✔✔Photons have different energy, also called, polychromatic
beam, Used in CT x-ray tubes now. As beam passes through equal thickness the, attenuation quantity
and quality changes, Mean kV of the photons increases as it passes through, material(low energy
photons are absorbed)
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