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5.1

X-ray Beam Quality

X-ray beam quality consists of:

  • Voltage and kilovoltage
  • Kilovoltage peak
  • Density and kilovoltage peak
  • Contrast and kilovoltage peak
  • Exposure time and kilovoltage peak

Wavelength determines the energy and penetrating power of radiation. X-rays with shorter wavelengths have more penetrating power. Quality is used to describe the mean energy or penetrating ability of the x-ray beam and the quality is controlled by kilovoltage.

Voltage and Kilovoltage

Voltage is the potential difference between two electrical charges. When voltage is increased, the speed of electrons is increased. The electrons strike the target with greater force and energy.

Voltage is measured in volts or kilovolts. A volt is a unit of measurement used to describe the potential that drives an electrical current through a circuit. A kilovolt equals 1000 volts.

Dental radiography requires the use of 65 to 100 kV:

  • <65 kV, inadequate penetration
  • >100 kV, overpenetration

Kilovoltage Peak (KVP)

A triangular orange high voltage warning sign with a white lightning bolt symbol in the center. Maximum or Peak Voltage

This usually refers to the peak voltage of an alternating current.

A polychromatic x-ray beam is produced as a result of varying kilovoltages in the tube current.
An orange icon of a person in a lab coat with a round head and a flask, symbolizing a scientist or chemical handling. The quality, or wavelength, and energy of the x-ray beam are controlled by the kilovolt peak.
A graph depicting an alternating voltage wave with a label indicating the peak kilovoltage (kVp) over a one-sixtieth of a second cycle, demonstrating an X-ray beam's voltage characteristics.
This graph depicts an alternating voltage wave with a label indicating the peak kilovoltage (kVp) over a one-sixtieth of a second cycle, demonstrating an X-ray beam’s voltage characteristics.
 Kilovoltage (KV) controls the quality of the x-ray beam and measures the peak voltage of the current

Density and Kilovoltage Peak

Density is the overall darkness or blackness of an image. When the kilovoltage is increased, the image will appear darker and when the kilovoltage is decreased, the image will appear lighter.

A diagnostic dental radiograph showing a detailed view of upper and lower teeth with visible dental fillings and roots. A dental X-ray image displaying upper and lower teeth, with differences in exposure likely due to an increase in kilovoltage.
A. Diagnostic Radiograph B. Increase in kilovoltage results in an image that exhibits increased density; the image appears darker.
A diagnostic dental radiograph image showing a set of teeth with fillings and details of dental structure labeled as "A" A dental radiograph labeled "B", demonstrating the effects of decreased kilovoltage, showing less contrast compared to a standard exposure.
A. Diagnostic Radiograph B. Decrease in kilovoltage results in an image that exhibits decreased density; the image appears lighter.

Contrast and Kilovoltage Peak

Contrast is how sharply dark and light areas are differentiated on an image. Low kilovoltage peak settings (65-70 kVp) create a high-contrast film. Many black and white areas, few shades of gray, and good for detection of caries. High kilovoltage peak settings (≥90 kVp) create a low-contrast image with many shades of gray and is good for the detection of periodontal or periapical disease.

Image produced with lower kilovoltage exhibits high contrast; many light and dark areas are seen, as demonstrated by the use of the stepwedge.
Image produced with lower kilovoltage exhibits high contrast; many light and dark areas are seen, as demonstrated by the use of the stepwedge.
Image produced with higher kilovoltage exhibits low contrast; many shades of gray are seen instead of black and white.
Image produced with higher kilovoltage exhibits low contrast; many shades of gray are seen instead of black and white.

Exposure Time and Kilovoltage Peak

Exposure time is the interval of time during which x-rays are produced. It is measured in impulses, which are 1/60th of a second and result from an alternating current. An adjustment in exposure time is necessary when the kilovoltage peak is increased.

Media Attributions

  • Iannucci & Howerton: Dental Radiography Principles and Techniques, 6th Edition, Chapter 5, CC BY-NC-ND

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DE 115: Dental Radiography Copyright © 2024 by verabodnarchuk; monicacoggin; alisonloach; and rbhatia2 is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.

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