In a lower leg radiograph, which adjustment helps balance density when the knee is underexposed and the ankle overexposed?

In a lower leg radiograph, which adjustment helps balance density when the knee is underexposed and the ankle overexposed?

• A. Distal joint at the cathode end of the beam
• B. Proximal joint at the cathode end of the beam
• C. Proximal joint at the center of the beam
• D. Distal joint at the center of the beam

Answer: (B)

The key idea is the anode heel effect, where the x-ray beam is slightly more intense toward the cathode end and less intense toward the anode end. For a long exposure like a lower leg, this creates a natural density gradient along the beam. To balance densities when the knee (proximal part) is underexposed and the ankle (distal part) is overexposed, you place the knee toward the cathode end where the beam is stronger. That increases exposure at the knee and helps even out the overall image, while the ankle ends up in the less intense part of the beam.

The key idea is the anode heel effect, where the x-ray beam is slightly more intense toward the cathode end and less intense toward the anode end. For a long exposure like a lower leg, this creates a natural density gradient along the beam. To balance densities when the knee (proximal part) is underexposed and the ankle (distal part) is overexposed, you place the knee toward the cathode end where the beam is stronger. That increases exposure at the knee and helps even out the overall image, while the ankle ends up in the less intense part of the beam.