Overview of X-ray Circuit Characteristics

Phase

• Definition: Refers to the number of wave cycles in a circuit.

• Single Phase:

  • Basic form of alternating current power.

  • Consists of one distinct waveform.

  • Voltage fluctuates from maximum to zero between pulses.

  • Single Phase Half Wave Rectification:

  • Original X-ray tubes were designed this way.

  • Voltage drops to zero, creating gaps between voltage pulses.

  • Results in a pulsated X-ray beam with intermittent gaps in production.

Voltage Characteristics of Single Phase

• Voltage fluctuates from peak (maximum) to zero volts.

• Disadvantages:

  • Voltage Ripple: The change in voltage with each pulse characterized as 100% ripple (the voltage fluctuates all the way from maximum to zero, affecting beam energy and intensity).

  • Lower voltages result in:

  • Reduced energy.

  • Fewer photons.

  • Less penetration of X-rays through the patient.

• Analogy: Compares to a water supply where pressure fluctuates rapidly between maximum and zero, which is undesirable.

Three Phase Alternating Current

• Definition: A type of power supply that consists of three different waveforms generating current within the circuit.

• Three Phase Full Wave Rectified:

  • Also known as Three Phase Six Pulse.

  • Contains six pulses per wave cycle.

• Voltage Ripple Reduction:

  • Voltage ripple is significantly smaller, with fluctuations never decreasing by more than 14%.

  • Positive impact on beam quality when one pulse is replaced by another immediately.

  • Analogy: Additional water lines supplying water together results in consistent water pressure and less pulsation.

Types of Three Phase Systems

• Three Phase 12 Pulse:

  • More pulses per cycle than three phase six pulse.

  • Higher frequency leads to even smaller voltage ripple (approximately 4%).

High Frequency Generators

• Definition: Modern X-ray machines that utilize very high frequencies.

• Characteristics:

  • Thousands of pulses per wave cycle.

  • Minimal voltage loss with a voltage ripple as low as 1%.

• Enhances the quality of the X-ray output.

Summary of Key Concepts

• Phase: Analogy with water lines; refers to the number of distinct wave cycles.

• Pulse: Indicates the number of voltage pulses per cycle; can be likened to fluctuations in water pressure.

• Frequency: Represents the number of pulses; high frequency corresponds to more pulses being produced.

Effects of Increasing Phase

• Transition from single phase to three phase results in:

  • Increased number of voltage pulses.

  • Higher frequency of pulses.

  • Decreased voltage ripple.

  • Enhanced average X-ray energy.

  • Increased X-ray intensity, leading to more total X-ray photons being generated.