Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. Chapter 8 Dental X-Ray Image Characteristics

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 2 Dental Radiography  Questions  What factors influence film density and contrast?  What is the difference between short-scale and long-scale contrast?  What factors will influence the sharpness, magnification, and distortion of a dental x-ray image?  What x-ray beam angulation is required to minimize distortion in an x-ray image?

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 3 Dental Radiography  Chapter 8 Reading:  Iannucci & Howerton (pp )

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 4 Dental Radiography  Chapter 8 Outline  Dental X-Ray Image Characteristics  Overview of image characteristics  Visual characteristics  Geometric characteristics

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 5 Introduction  Iannucci & Howerton (p. 76)  Purpose  To describe in detail the visual image characteristics of film density and contrast  To define the geometric image characteristics of sharpness, magnification, and distortion  To discuss how influencing factors alter these image characteristics

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 6 Dental X-Ray Image Characteristics  Iannucci & Howerton (pp ) (Figs. 8-1, 8-2)  A dental radiograph appears as a black and white image or picture with varying shades of gray.  Radiolucent The portion of the processed radiograph that is dark or black The portion of the processed radiograph that is dark or black A structure that appears black on film lacks density. A structure that appears black on film lacks density.  Radiopaque The portion of the processed radiographj that appears white The portion of the processed radiographj that appears white A structure that appears white on film is dense and absorbs or resists passage of the x-ray beam. A structure that appears white on film is dense and absorbs or resists passage of the x-ray beam.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 7 Dental X-Ray Image Characteristics  In a diagnostic radiograph the images  Have proper density and contrast  Have sharp outlines  Are of the same shape and size as the object radiographed

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 8 Visual Characteristics  Iannucci & Howerton (pp )  Density  Contrast

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 9 Density  Iannucci & Howerton (pp ) (Fig. 8-3) (Table 8-1)  The overall darkness or blackness of a dental radiograph  The relative transparency depends on distribution of black silver particles in the emulsion.  Influencing factors  Milliamperage  Operating kilovoltage  Exposure time  Subject thickness

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 10 Contrast  Iannucci & Howerton (pp )  Contrast is the difference in degrees of blackness between adjacent areas.  “A film that is a compromise between low contrast and high contrast is preferred.”  The overall contrast is determined by  Film contrast The inherent qualities of the film and film processing The inherent qualities of the film and film processing  Subject contrast The characteristics of the subject that influence radiographic contrast The characteristics of the subject that influence radiographic contrast

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 11 Contrast  Iannucci & Howerton (p. 79) (Fig. 8-4) (Table 8-1)  Influencing factors  Increasing the kilovoltage affects image contrast by increasing the mean or average energy of the x-rays and by producing higher energy x-rays.  More areas of varying tissue density are recorded on the image and appear as shades of gray.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 12 Contrast  Iannucci & Howerton (p. 79) (Table 8-2)  Scales of contrast  The range of useful densities Short-scale contrast (high contrast) Short-scale contrast (high contrast)  A radiograph with only two densities, black and white  Occurs with machines functioning at low kVp Long-scale contrast (low contrast) Long-scale contrast (low contrast)  A radiograph with many densities, many shades of gray  Occurs with machines functioning at high kVp

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 13 Contrast  Iannucci & Howerton (pp ) (Figs. 8-5, 8-6)  An aluminum stepwedge can demonstrate short-scale and long-scale contrast.  The stepwedge consists of uniform layered thicknesses of an x-ray absorbing material. Different densities appear on the dental radiograph. Different densities appear on the dental radiograph.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 14 Geometric Characteristics  Iannucci & Howerton (pp )  Sharpness  Magnification  Distortion

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 15 Sharpness  Iannucci & Howerton (p. 80)  Sharpness is the capability of the x-ray receptor to reproduce the distinct outlines of an object.  A certain lack of image sharpness is present in every radiograph; it is called the penumbra.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 16 Sharpness  Iannucci & Howerton (pp ) (Figs. 8-7 through 8-10) (Table 8-3)  Influenced by three factors  Focal spot size The smaller the focal spot, the sharper the image appears. The smaller the focal spot, the sharper the image appears.  Film composition The emulsion of faster film contains larger crystals that produce less image sharpness. The emulsion of faster film contains larger crystals that produce less image sharpness.  Movement Movement causes a loss of image sharpness. Movement causes a loss of image sharpness.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 17 Magnification  Iannucci & Howerton (pp ) (Figs. 8-11, 8-12, 8-13) (Table 8-3)  Results from the divergent paths of the x-ray beam as they radiate from the focal spot  Influencing factors  Target-receptor distance A longer PID and target-receptor distance results in less image magnification. A longer PID and target-receptor distance results in less image magnification.  Object-receptor distance An increase in object-receptor distance results in an increase in image magnification. An increase in object-receptor distance results in an increase in image magnification.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 18 Distortion  Iannucci & Howerton (p. 83) (Figs. 8-14, 8-15) (Table 8-3)  A variation in the true size and shape of object being radiographed  Results from unequal magnification of different parts of the same object because of improper receptor alignment or angulation of the x-ray beam  Influencing factors  Object-film alignment The object and film must be parallel to each other or there will be distortion. The object and film must be parallel to each other or there will be distortion.  X-ray beam angulation The x-ray beam must be directed perpendicular to the tooth and film. The x-ray beam must be directed perpendicular to the tooth and film.