Radiation Characteristics Chapter 5 - Radiology PowerPoint PDF

Radiation Characteristics Chapter 5 Copyright © 2017, Elsevier Inc. All Rights Reserved. 1  Learning Objectives Lesson 3.1: Radiation Characteristics 1. Define the key terms associated with radiation characteristics. 2. Descri...

Radiation Characteristics Chapter 5 Copyright © 2017, Elsevier Inc. All Rights Reserved. 1  Learning Objectives Lesson 3.1: Radiation Characteristics 1. Define the key terms associated with radiation characteristics. 2. Describe the effect that the kilovoltage has on the quality of the x-ray beam and identify the range of kilovoltage required for dental imaging. 3. Describe how kilovoltage affects the density and contrast of the image. 4. Describe how milliamperage influences the quantity of the x-ray beam and identify the range of milliamperage required for dental imaging. Copyright © 2017, Elsevier Inc. All Rights Reserved. 2  Learning Objectives Lesson 3.1: Radiation Characteristics (Cont.) 5. Describe how milliamperage affects the density of the image and how exposure time and milliamperage are related. 6. Describe how kilovoltage, milliamperage, exposure time, and source-to-receptor distance influence the intensity of the x-ray beam. 7. Calculate an example of radiation intensity using the inverse square law. 8. Explain how the half-value layer determines the penetrating quality of the x-ray beam. Copyright © 2017, Elsevier Inc. All Rights Reserved. 3  Introduction  Purpose To detail the concepts of x-ray beam quality and quantity To define the concept of beam intensity To discuss how exposure factors influence these radiation characteristics Copyright © 2017, Elsevier Inc. All Rights Reserved. 4  X-Ray Beam Quality  Voltage and kilovoltage  Kilovoltage peak  Density and kilovoltage peak  Contrast and kilovoltage peak  Exposure time and kilovoltage peak Copyright © 2017, Elsevier Inc. All Rights Reserved. 5  X-Ray Beam Quality (Cont.)  Wavelength determines the energy and penetrating power of radiation. X-rays with shorter wavelength have more penetrating power.  Quality is used to describe the mean energy or penetrating ability of the x-ray beam. The quality is controlled by kilovoltage. Copyright © 2017, Elsevier Inc. All Rights Reserved. 6  Voltage and Kilovoltage  Voltage 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. Copyright © 2017, Elsevier Inc. All Rights Reserved. 7  Voltage and Kilovoltage (Cont.)  Voltage is measured in volts or kilovolts. Volt 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. 100 kV, overpenetration Copyright © 2017, Elsevier Inc. All Rights Reserved. 8  Kilovoltage Peak (kVp)  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.  The quality, or wavelength and energy of the x-ray beam, is controlled by the kilovolt peak. Copyright © 2017, Elsevier Inc. All Rights Reserved. 9  Density and Kilovoltage Peak  Density This is the overall darkness or blackness of an image.  When the kilovoltage is increased, the image will appear darker.  When the kilovoltage is decreased, the image will appear lighter. Copyright © 2017, Elsevier Inc. All Rights Reserved. 10  Contrast and Kilovoltage Peak  Contrast 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 Good for detection of caries  High kilovoltage peak settings (≥90 kVp) create a low-contrast image. Many shades of gray Good for detection of periodontal or periapical disease Copyright © 2017, Elsevier Inc. All Rights Reserved. 11 Exposure Time and Kilovoltage Peak  Exposure time This is the interval of time during which x-rays are produced. It is measured in impulses. 1/60th of a second resulting from alternating current  An adjustment in exposure time is necessary when kilovoltage peak is increased. Copyright © 2017, Elsevier Inc. All Rights Reserved. 12  X-Ray Beam Quantity  Amperage and milliamperage  Milliampere-seconds  Density and milliamperage  Exposure time and milliamperage Copyright © 2017, Elsevier Inc. All Rights Reserved. 13  Amperage and Milliamperage  Amperage Determines the amount of electrons passing through the cathode filament Increasing amperage Results in an increased number of electrons traveling from cathode to anode and production of an increased number of x-rays  The quantity of the x-rays produced is controlled by milliamperage. Copyright © 2017, Elsevier Inc. All Rights Reserved. 14 Amperage and Milliamperage (Cont.)  Ampere (A) Unit of measure used to describe the number of electrons, or current flowing through the cathode filament  Milliampere (mA) 1/1000 of an ampere  In dental radiography milliamperage ranges from 7 to 15 mA; exceeding this produces excessive heat. Copyright © 2017, Elsevier Inc. All Rights Reserved. 15 Amperage and Milliamperage (Cont.)  Milliamperage Milliamperage regulates the temperature of the cathode filament.  A higher milliampere setting increases the temperature of the cathode filament. It increases the number of electrons produced. It increases the number of x-rays emitted from the tube. Copyright © 2017, Elsevier Inc. All Rights Reserved. 16  Milliampere-Seconds (mAs)  mAs is the product of milliamperes and exposure time. When milliamperage is increased, exposure time must be decreased to maintain constant density. Copyright © 2017, Elsevier Inc. All Rights Reserved. 17  Density and Milliamperage  An increase in milliamperage Increases overall density of the image Results in a darker image Copyright © 2017, Elsevier Inc. All Rights Reserved. 18  Exposure Time and Milliamperage  An inverse relationship When milliamperage is increased, exposure time must be decreased. When milliamperage is decreased, exposure time must be increased. Copyright © 2017, Elsevier Inc. All Rights Reserved. 19  Exposure Factor Tips  All dental x-ray machines have three exposure factor settings. kV mA Time Copyright © 2017, Elsevier Inc. All Rights Reserved. 20  X-Ray Beam Intensity  Kilovoltage peak  Milliamperage  Exposure time  Distance  Inverse square law  Half-value layer Copyright © 2017, Elsevier Inc. All Rights Reserved. 21  X-Ray Beam Intensity (Cont.)  The product of the quantity (number of x-ray photons) and quality (energy of each photon) per unit of area per unit of time of exposure Copyright © 2017, Elsevier Inc. All Rights Reserved. 22  Kilovoltage Peak  Regulates the penetrating power of the x-ray beam by controlling the speed of electrons traveling between the cathode and the anode Higher kilovoltage peak settings Produce an x-ray beam with more energy and shorter wavelengths Increases intensity of the x-ray beam Copyright © 2017, Elsevier Inc. All Rights Reserved. 23  Milliamperage  Controls the penetrating power of the x-ray beam by controlling the number of electrons produced in the x-ray tube and the number of x-rays produced Higher milliamperage settings Produce an x-ray beam with more energy, increasing the intensity of the x-ray beam Copyright © 2017, Elsevier Inc. All Rights Reserved. 24  Exposure Time  Exposure time affects the number of x-rays produced. A longer exposure time Produces more x-rays and a more intense x-ray beam Copyright © 2017, Elsevier Inc. All Rights Reserved. 25  Distance  The distance traveled by the x-ray beam affects the intensity of the beam. Three distances to consider Target-surface (source to patient’s skin) Target-object (source to patient’s tooth) Target-receptor (source to receptor) Copyright © 2017, Elsevier Inc. All Rights Reserved. 26  Distance (Cont.)  As x-rays travel from their point of origin, they diverge and spread out to cover a larger surface area. The intensity of the beam lessens. Copyright © 2017, Elsevier Inc. All Rights Reserved. 27  Inverse Square Law  The intensity of radiation is inversely proportional to the square of the distance from the source of radiation. When the distance is doubled, the beam is one quarter as intense. When the distance is halved, the beam is four times more intense. Copyright © 2017, Elsevier Inc. All Rights Reserved. 28  Half-Value Layer  Aluminum filters are placed in the path of the beam inside the dental x-ray tubehead. The filters are used to remove the low-energy, less penetrating, longer wavelength x-rays. Increases mean penetrating capability of the x-ray beam while reducing the intensity  The thickness of a specified material that reduces the intensity by half is termed the half-value layer (HVL). Copyright © 2017, Elsevier Inc. All Rights Reserved. 29 Questions? Copyright © 2017, Elsevier Inc. All Rights Reserved. 30