A department currently uses a flat-panel detector with a quantum efficiency (the…
PHYSICS · Multi-part · Fermi University Physics · Nuclear Physics · Biophysics & Medical Physics · Radiation interactions, detection and dosimetry
Life at Thermal Energy, Ch Images from attenuation and from decay
Problem
A department currently uses a flat-panel detector with a quantum efficiency (the fraction of photons reaching the detector that are absorbed and counted) of ηold=0.70. A sales engineer claims: "Our new panel is twice as efficient. Fit it and you can halve the patient's entrance dose and still get the same image noise."
((a)) Write the number of photons absorbed over a detail of area A in terms of the entrance fluence Φ and the quantum efficiency η, and state what fixes the noise for that detail.
((b)) Find the greatest possible reduction in dose, at fixed noise, that any improvement in η starting from ηold=0.70 could deliver, and say what is wrong with the engineer's claim.