A patient asks: "Why not just do a lower-resolution CT of my skeleton instead of a…
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 patient asks: "Why not just do a lower-resolution CT of my skeleton instead of a bone scan? Surely a CT could show the same thing, just blurrier?" A bone scan uses a technetium-99m-labelled bisphosphonate, with a typical effective dose of about 4mSv, and resolves detail down to several millimetres, set by the gamma camera's collimator; a CT scanner reconstructs μ on a 512×512 grid over a 40cm field of view, giving a pixel of 40cm/512≈0.78mm.
((a)) State what physical quantity each image is a map of.
((b)) Explain why a bone scan is not simply a blurrier CT of the same information, even though its spatial resolution (several millimetres) is coarser than the CT's (≈0.8mm).