In dual-focus x-ray tubes, which filament is used when imaging a patient with large body habitus to improve heat handling?

• A. Large filament
• B. Small filament
• C. Medium filament
• D. No filament

Answer: (A)

In dual-focus x-ray tubes, there are two filaments that create different focal spots. For a patient with large body habitus, you want to spread the x-ray beam over a larger area on the anode to reduce heat concentration. The large filament produces a larger focal spot, distributing the electron current over a bigger area, which increases the tube’s heat capacity and helps prevent overheating during higher exposures. While a small focal spot offers better resolution, it concentrates heat in a smaller region, making overheating more likely for large patients. The medium option isn’t the standard setup, and skipping a filament would stop x-ray production.