How can the average photon energy of the CT x-ray beam be increased?

The average photon energy of the CT x-ray beam can be increased by using a higher kilovolt peak (kVp) setting. When the kVp is raised, the maximum energy of the x-ray photons produced also increases. This happens because kVp relates directly to the potential difference applied across the x-ray tube; a higher voltage means the electrons are accelerated more strongly towards the anode, resulting in more energetic x-ray photons upon their interaction with the target material.

An increase in filtration, while it can improve beam quality by removing lower-energy photons from the beam, does not increase the average energy of the photons produced. Filtration essentially shapes the beam by removing less useful, low-energy photons that contribute to patient dose but add little to image quality. The key factor in raising the average photon energy remains the kVp setting, as this defines the energy spectrum of the x-rays produced.

While exposure time influences the number of photons generated and ultimately contributes to the overall image quality, it does not affect the energy of the individual photons. Decreasing the tube voltage would lower the energy of the produced photons, further emphasizing that the correct approach to increasing average photon energy is indeed through increasing the kVp.