What is the function of the aluminium filter?

• A. To remove harmful low energy soft x-rays
• B. To focus the beam
• C. To increase image sharpness
• D. To cool the tube

Answer: (A)

Filtration of the X-ray beam removes the soft, low-energy photons before they reach the patient. The aluminium filter absorbs these photons, which would be readily absorbed by superficial tissues and contribute to patient dose without helping form the image. By trimming these low-energy components, the beam becomes harder (higher mean energy), which reduces skin dose and tends to improve image contrast because the remaining photons provide more useful penetration differences between tissues. This is the primary role of the aluminium filter.

It doesn’t serve to focus the beam, nor does it directly increase image sharpness. It also doesn’t cool the tube.