1. 4
Producing Quality Radiographs

2. Objectives Define the key words.
Evaluate a radiographic image identifying the basic requirements of acceptability.
Differentiate between radiolucent and radiopaque areas on a dental radiograph.
Define radiographic density and contrast.
Differentiate between subject contrast and film contrast.

3. Objectives
List the factors that influence magnification and distortion.
List the geometric factors that affect image sharpness.
Summarize the factors affecting the radiographic image.
Describe how mA, kVp, and exposure time affect image density.

4. Objectives Discuss how kVp affects image contrast.
Explain target-surface, object-image receptor, and target-image receptor distances.
Demonstrate the practical use of the inverse square law.

5. Key Words Contrast Crystal Definition Density Distortion
Exposure chart
Exposure factors
Exposure time

6. Key Words Extraoral radiography Film contrast Focal spot
Geometric factors
Grid
Intensifying screen
Intraoral radiography
Inverse square law

7. Key Words Kilovoltage peak (kVp) Long-scale contrast Magnification
Milliampere (mA)
Motion
Object-image receptor distance
Penumbra

8. Key Words Position indicating device (PID) Radiographic contrast
Radiolucent
Radiopaque
Sharpness
Short-scale contrast

9. Key Words Subject contrast Target-image receptor distance
Target-object distance
Target-surface distance

10. Introduction
Each patient presents with a unique set of characteristics for which a customized approach to exposure settings is needed.
The dental radiographer has an ethical responsibility to produce the highest diagnostic quality radiographs for patients who agree to be exposed to ionizing radiation.

11. Introduction
To consistently produce diagnostic quality radiographs at the lowest possible radiation dose, the dental radiographer needs to understand the inter-relationships of the components of the dental x-ray machine.

12. Introduction
Three basic requirements for an acceptable diagnostic radiograph:
All parts of the structures recorded must be imaged as close to their natural shapes and sizes as the patient’s oral anatomy will permit. Distortion and superimposition of structures should be at a minimum.

13. Introduction
Three basic requirements for an acceptable diagnostic radiograph:
The area examined must be imaged completely, with enough surrounding tissue to distinguish between the structures.
The radiograph should be free of errors and show proper density, contrast, and definition.

14. Figure 4-1 An acceptable diagnostic radiograph.

15. Terminology Radiolucent Radiopaque Density Contrast Sharpness
Short-scale contrast
Long-scale contrast
Sharpness

16. Figure 4-2 Radiographic density
Figure Radiographic density. Radiograph (A) is underexposed and appears too light (less dense). Radiograph (B) is overexposed and appears too dark (more dense).

17. Figure Penetrometer tests demonstrate radiographically that a longer contrast scale results from the use of 100 kilovolt exposures. Dental radiographs exposed at 100 kVp have long-scale contrast. Radiographs exposed at 60 kVp have short-scale contrast.

18. Figure 4-4 Radiographic contrast
Figure Radiographic contrast. Radiograph (A) exposed at 60 kVp, has high contrast. Radiograph (B) exposed at 90 kVp, has low contrast.

19. Shadow Casting
A radiograph is a two-dimensional image of three-dimensional objects. Therefore, it is necessary to apply the rules for creating a shadow image to produce a quality radiographic image.

20. Rules for Shadow Casting
Small focal spot — to reduce the size of the penumbra (partial shadow around the objects of interest) resulting in a sharper image and slightly less magnification
Long target-object distance — to reduce the penumbra and magnification
Short object-film distance — to reduce penumbra and magnification

21. Rules for Shadow Casting
Parallel relationship between object and film — to prevent distortion of the image
Perpendicular relationship between central ray of x-ray beam and the object and film — to prevent distortion of the image

22. Factors Affecting the Radiographic Image
Radiographic contrast
Subject
kVp
Scatter radiation
Film/digital sensor type
Exposure
Processing

23. Table 4-1 Summary of Factors Influencing Radiographic Image Contrast

24. Factors Affecting the Radiographic Image
Sharpness/Definition
Focal spot size
Target-image receptor distance
Object-image receptor distance
Motion
Screen thickness
Screen-film contact
Crystal/pixel size of intraoral image receptors

25. Table 4-2 Summary of Factors Influencing Radiographic Image Sharpness

26. Figure Using a small focal spot on the target a long target-image receptor distance, and a short object-image receptor distance will result in a sharp image.

27. Figure Large focal spot on the target and long object-film distance results in more penumbra and therefore loss of image sharpness.

28. Figure 4-7 Movement of the tube head
Figure Movement of the tube head. Motion, even slight, of the tube head will effectively create a larger surface area of the focal spot, resulting in penumbra.

29. Figure Large focal spot on the target and short target-image receptor distance results in more penumbra and loss of image sharpness.

30. Figure 4-9 Blurry, unsharp image caused by movement of the patient, the film, or the tube head.

31. Figure 4-10 Screen thickness
Figure Screen thickness. X-ray A strikes a crystal far from the film and the divergent light exposes a wide area of the film resulting in unsharpness. X-ray B strikes a crystal close to the film, resulting in less divergence of the light that exposes the film and therefore a sharper image. The thicker the screen, the less sharp the image.

32. Factors Affecting the Radiographic Image
Magnification/enlargement is mostly influenced by the target-object distance and the object-image receptor distance. The target-object distance is determined by the length of the PID.

33. Factors Affecting the Radiographic Image
Distortion is the result of unequal magnification of different parts of the same object. Distortion results when the image receptor is not parallel to the object (Figure 4-13) and/or when the central ray of the x-ray beam is not perpendicular to the object and the plane of the image receptor (Figure 4-14)

34. Figure 4-11 Magnification. Comparison of 8-in. (20. 5-cm) and 16-in
Figure Magnification. Comparison of 8-in. (20.5-cm) and 16-in. (41-cm) target-object and target-image receptor distances. The image is magnified (enlarged) when these distances are shortened. (Courtesy of Dentsply Rinn)

35. Figure 4-13 Object and film are not parallel, resulting in distortion.

36. Figure Central ray of x-ray beam is not perpendicular to the objects and image receptor, resulting in distortion and over-lapping of object A and object B. Note that object A is magnified larger than object B because object A is a greater distance from the image receptor than object B.

37. Table 4-3 Effect of Varying Exposure Factors on Image Density

38. Effects of Varying the Exposure Factors
Variations in milliamperage (mA)
Variations in exposure time
Milliampere-seconds (mAs)
Variations in kilovoltage (kVp)

39. Effects of Variations in Distances
The operator must take into account several distances to produce the ideal diagnostic quality image:
The distance between the x-ray source (at the focal spot on the target) and the surface of the patient’s skin
The distance between the object to be x-rayed (usually the teeth) and the image receptor

40. Effects of Variations in Distances
The operator must take into account several distances to produce the ideal diagnostic quality image:
The distance between the x-ray source and the recording plane of the image receptor
the terms target-surface distance, object-image receptor distance, target-object distance, and target-image receptor distance are used.

41. Figure Distances. Relationship among target, skin surface, object (tooth), and image receptor distance

42. Effects of Variations in Distances
Target-surface distance
Object-image receptor distance
Target-image receptor distance

43. Figure 4-16 Object-image receptor distance
Figure Object-image receptor distance. This placement of the image receptor places the crown of the tooth closer to the receptor than the root.

44. Figure 4-17 Inverse square law
Figure Inverse square law. Relationship of distance (D) to the area covered by x-rays emitted from the x-ray tube. X-rays emerging from the tube travel in straight lines and diverge from each other. The areas covered by the x-rays at any two points are proportional to each other as the square of the distances measured from the source of radiation.

45. Inverse Square Law
Inverse square law states that the intensity of radiation varies inversely as the square of the distance from its source.
Inverse square law may be written as:

46. Inverse Square Law Where: I1 is the original intensity
I2 is the new intensity
D1 is the original distance
D2 is the new distance

47. Exposure Charts
Exposure charts, available commercially or custom made by the practice, should be posted at the x-ray unit control panel for easy reference.
These charts show at a glance how much exposure time is required for a film of any given speed or a digital sensor when used with all possible combinations of exposure time, milliamperage, and peak kilovoltage.

48. Review: Chapter Summary
An acceptable diagnostic radiograph must show the areas of interest completely and with minimum distortion and maximum sharpness.
When evaluating a radiographic image the oral health care professional should utilize appropriate scientific terminology.

49. Review: Chapter Summary
The dental radiographer must have a working knowledge of the factors that affect the radiographic image.

50. Recall: Study Questions
General
Chapter Review

51. Reflect: Case Study
You have just been hired to work in a new oral healthcare facility. Prior to providing patient services, you are asked to help develop exposure settings and equipment recommendations for the practice. The equipment and image receptor manufacturers’ suggestions are as follows:
F Speed Film; 8-in. (20.5 cm) PID; 85 kVp

52. Reflect: Case Study

53. Reflect: Case Study
You recommend that the facility replace the 8-in. (20.5 cm) PID with a 16-in. (41 cm) PID. Develop a new exposure chart for using the new 16-in. (41 cm) PID.
You recommend using a kVp setting of 70 when exposing radiographs for the purpose of detecting caries. Develop a new exposure chart for 70 kVp.

54. Reflect: Case Study
You recommend using a kVp setting of 90 when exposing radiographs for the purpose of evaluating supporting bone and periodontal disease. Develop a new exposure chart for 90 kVp.

55. Relate: Laboratory Application
Proceed to Chapter 4, Laboratory Application, to complete this activity.