An acute abdomen series is completed with three exposures acquired at 80 kVp and 30 mAs using a three-phase six-pulse machine. What is the total number of accumulated heat units (HU) for the series?

• A. 7,200 HU
• B. 9,720 HU
• C. 12,000 HU
• D. 15,000 HU

Answer: (B)

Heat units reflect the amount of heat produced in the x-ray tube during exposure. For multi‑phase generators, you multiply kVp, mA·s (the exposure quantity), and a waveform factor that accounts for the voltage waveform. For a three‑phase six‑pulse machine, that factor is 1.35.

Each exposure is 80 kVp and 30 mAs. So the heat units per exposure are 80 × 30 × 1.35 = 3,240 HU. With three exposures, the total HU = 3,240 × 3 = 9,720 HU.

Note that with a single‑phase unit you’d use a factor of 1.0, giving 7,200 HU for three exposures (80 × 30 × 3). The three‑phase six‑pulse result of 9,720 HU reflects the higher heat output due to the waveform.