Lecture Notes on KVP (Kilovoltage Peak)

Introduction

• This is the third lesson in the series about prime exposure factors.
• Focus on KVP (Kilovoltage Peak).

What is KVP?

• KVP stands for kilovoltage peak.
• KVP accelerates electrons through the X-ray tube.
• During X-ray exposure:
  • Cathode: Negatively charged.
  • Anode: Positively charged.
  • Difference in charge = tube potential, measured in kilovolts.

Effects of Changing KVP

• Increasing KVP:

  • Creates a larger voltage difference.
  • Electrons move quickly, gaining more energy.
  • Produces a higher energy X-ray beam.

• Decreasing KVP:

  • Creates a smaller voltage difference.
  • Electrons move slowly, resulting in less energy.
  • Produces a lower energy X-ray beam.

Importance of KVP

• Changes in KVP significantly affect the X-ray beam:
  • Beam Intensity:
    • Increasing KVP = Increased intensity (similar to increasing mass).
  • Energy of the X-ray Beam:
    • Increasing KVP = Increased energy (quality) of X-ray beam.
• KVP is unique because it is the only prime exposure variable that can change the energy of the X-ray beam.
  • Other factors (MA, exposure time, SID) do not affect beam energy.

Mathematical Relationships

• KVP and Maximum Beam Energy:
  • KVP is mathematically equal to maximum beam energy.
  • Example: KVP set to 100 → Maximum energy photons = 100 keV.
• KVP and Beam Intensity:
  • Relationship is more complex but significant: changing KVP affects beam intensity.

Patient Dose and Receptor Exposure

• Patient Dose:

  • Increasing KVP = Increased patient dose (more X-ray photons).
  • Decreasing KVP = Decreased patient dose.

• Receptor Exposure:

  • Increasing KVP = Increased receptor exposure (more photons penetrate).
  • Decreasing KVP = Decreased receptor exposure.

• 15% Rule:

  • Increasing KVP by 15% = Doubling receptor exposure.

Image Contrast

• Effect on Image Contrast:
  • Increasing KVP = Decreased image contrast.
  • Decreasing KVP = Increased image contrast.

Summary of Relationships

• Increasing KVP:
  • Increases energy of X-ray beam.
  • Increases intensity of X-ray beam.
  • Increases patient dose.
  • Increases receptor exposure.
  • Decreases image contrast.

Practice Questions

• Question 1: Changes to which technical factors influence receptor exposure?

  • Answers: Tube current (MA), exposure time, tube potential (KVP), distance (SID).

• Question 2: Which variables influence the energy of the X-ray beam?

  • Answer: Tube potential (KVP) is the only factor that affects the energy of the X-ray beam.