A hospital manager argues: "A chest CT takes about a thousand projections to build…
PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Radiation physics and diagnostic imaging · Nuclear medicine, dosimetry and radiotherapy
Life at Thermal Energy, Ch Images from attenuation and from decay
Problem
A hospital manager argues: "A chest CT takes about a thousand projections to build one slice, and a full chest scan needs many slices, so the dose must simply be a thousand (or more) radiograph exposures stacked together, and the factor of 350 quoted for a chest CT against a chest radiograph (7mSv against 0.02mSv) should follow just from counting exposures."
((a)) Explain what is wrong with treating the thousand projections, or the many slices, as a thousand (or many) separate radiograph exposures.
((b)) Give the reasons the chapter gives for why a chest CT's dose is nonetheless far larger than a chest radiograph's, and say which part of the factor of 350 is a measured fact rather than something derived from counting exposures.