Differences Between High-Frequency and Power-Frequency X-ray Machines
Release time:
2026-07-28
The use of energy-storage components greatly reduces mains-power demands; in many cases the system can run directly from a standard supply (large power-frequency units often require a dedicated feed). At the same time, the high-voltage transformer can be made much smaller, facilitating overall miniaturization of high-power generators.
High-frequency unit
- Generator switching frequency > 20 kHz.
- After rectification the high voltage is almost pure DC; ripple is < 0.1 %.
- Produces an almost mono-energetic electron beam → narrow, clean X-ray spectrum.
- Reduced scatter, 50 % lower total beam output for the same image quality, and noticeably sharper images.
Power-frequency (line-frequency) unit
- Generator frequency < 400 Hz (50/60 Hz mains).
- After rectification the high voltage still carries 100 Hz sinusoidal ripple; even after filtering the ripple remains > 10 %.
- Generates a broad X-ray spectrum with pronounced low-energy tails → more scattered radiation.
- Lower characteristic-line yield per unit time → poorer subject contrast and hazier images.
Since the 1990s all imported X-ray systems have been high-frequency; the international trend is clear and China is transitioning in the same direction.
Imported versus Domestic Molybdenum-Target X-ray Tubes
Domestic tube (custom order)
- Stationary (fixed) anode, single 0.5 mm focal spot.
- Lower heat capacity.
Imported tube
- Rotating anode, dual-focus 0.3 mm / 0.1 mm.
- Higher heat capacity.
- Routine radiography uses the 0.3 mm focus—its area is 1.5× smaller than that of the domestic tube.
- Smaller focal spot → sharper images, but manufacturing difficulty drives the cost up ~30× versus domestic tubes.
Measured performance
The domestic tube currently delivers 80 % of the spatial resolution of the imported tube, achieving 80 lp cm⁻¹—sufficient for all clinical requirements. Models B and D in our line use the imported tube and match the performance specifications of imported systems.
In terms of exposure-time accuracy, power-frequency X-ray units exhibit wide variation depending on the rectification method used, whereas high-frequency generators incorporate voltage pre-setting and closed-loop feedback, yielding far tighter control. This markedly reduces the soft-radiation component of the beam, lowers patient dose, and simultaneously improves image quality and overall X-ray output efficiency.
Structurally, high-frequency X-ray units are comparatively simple.
Because the kV and mA values are preset and regulated independently through purely electronic feedback, mechanical knobs, switches, and traditional kV-compensation or space-charge-compensation circuits are eliminated. This yields faster response, higher output accuracy, and allows kV and mA to be adjusted during the exposure itself.
The use of energy-storage components greatly reduces mains-power demands; in many cases the system can run directly from a standard supply (large power-frequency units often require a dedicated feed). At the same time, the high-voltage transformer can be made much smaller, facilitating overall miniaturization of high-power generators.
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