C H A P T E R
6
Projection Geometry
Multiple Choice
1. The capability to radiographically reproduce distinct outlines of an object is called
a. sharpness.
b. resolution.
c. distortion.
d. magnification.
2. Methods for minimizing the loss of image clarity include all EXCEPT one. Which one is
the EXCEPTION?
a. Minimize distance between object and film.
b. Use as small an effective focal spot as practical.
c. Increase distance between focal spot and object being radiographed.
d. Minimize focal spot-to-film distance; maximize object-to-film distance.
3. Which factor determines the size of the focal spot needed?
a. Frequency of machine use.
b. Number of electrons produced.
c. Effective heat dissipation of machine.
d. Type of radiographic images produced.
4. Which phenomenon is responsible for enlargement of the radiographic image?
a. Practitioner’s skill.
b. Divergent paths of photons.
c. Object-to-receptor distance.
d. Increased number of electrons produced.
5. Which cylinder BEST minimizes image magnification?
a. Long.
b. Short.
c. Pointed.
d. Rectangular.
6. To minimize distortion, which is the ideal position of the image receptor in relationship to
the object?
a. Perpendicular to the beam.
b. At right angles to the object.
c. Parallel to the long axis of the object.
d. As far from the object as structurally possible.
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7. If the object is not parallel to the film but the x-ray beam is perpendicular to the film, which
phenomenon occurs?
a. Elongation.
b. Cone-cutting.
c. Magnification.
d. Foreshortening.
8. Excessive vertical angulation is MOST evident on which teeth?
a. Mandibular molars.
b. Mandibular anteriors.
c. Maxillary molars.
d. Maxillary canines.
9. Which method of dental radiography utilizes the placement of the film as close to the teeth
as possible?
a. Periapical.
b. Panoramic.
c. Paralleling.
d. Bisecting-angle.
10. Which decreases image distortion when utilizing the bisecting-angle technique?
a. Place film as close as possible to the teeth being imaged.
b. Place film as far as possible from the teeth being imaged.
c. Direct the central ray parallel to an imaginary plane that bisects the angle between the
teeth and the film.
d. Direct the central ray perpendicular to an imaginary plane that bisects the angle between
the teeth and the film.
11. If the central ray is directed at an angle that is inclined with more negative angulation to
the bisector, the resulting image is
a. magnified.
b. elongated.
c. proportional.
d. foreshortened.
12. To achieve tooth-to-receptor parallelism, which is the usual location of the receptor?
a. Touching the teeth.
b. As close to the teeth as possible.
c. In the middle of the oral cavity, away from the teeth.
d. On the opposite side of the tongue, away from the teeth.
13. Which condition compensates for the magnification produced by placing the film in the
middle of the oral cavity, away from the teeth?
a. Use of short open-ended aiming cylinder.
b. Use of long open-ended aiming cylinder.
c. Practice of aligning central ray perpendicular to receptor.
d. Practice of aligning aiming cylinder end parallel to object.
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6—Projection Geometry
14. The right-angle technique for object localization is best for areas of interest within the
a. maxilla.
b. mandible.
c. buccal soft tissue.
d. horizontal dimension.
15. Compared to photons traveling at right angles to a surface, photons traveling through the
periphery of a curved surface are
a. straighter.
b. conservative.
c. less intense.
d. more intense.
16. Which structure does NOT demonstrate an eggshell effect when radiographed?
a. Tongue.
b. Lamina dura.
c. Sinus borders.
d. Border of nasal fossa.
17. Which is the reason that the periphery of an expansile lesion appears more radiopaque than
the interior?
a. Eggshell effect.
b. Border is thicker than interior.
c. Difference in lesion composition.
d. Lesion interior is most likely fluid.
18. If a dentist has two radiographs of a region of the dentition that were made at different
angles, which would be the point of reference for identifying changes in horizontal or vertical
angulation?
a. Not possible to determine.
b. Eggshell effect.
c. Position of “dimple” of film.
d. Relative position of osseous landmarks with respect to the teeth.
19. If the tube is shifted to a more mesial angulation to the reference object and the object in
question also moves mesially, then the object in question is located
a. distal to the tooth.
b. occlusal to the arch bone.
c. lingual to the reference object.
d. buccal to the reference object.
20. Which is an imaginary line that divides the tooth longitudinally into two equal halves?
a. Bisecting angle.
b. Long axis of the tooth.
c. Measurement of elongation.
d. Measurement of foreshortening.
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6—Projection Geometry
21. The middle portion of the primary x-ray beam is called the
a. photon.
b. focal spot.
c. central ray.
d. scatter beam.
22. If the angle formed by the film and object is bisected, then which is the relationship of the
bisector to the aiming cylinder?
a. Parallel.
b. Right angle.
c. Obtuse angle.
d. Perpendicular.
23. If the angle formed by the film and object is bisected, then which is the relationship of the
central ray to the bisector?
a. Parallel.
b. Right angle.
c. Obtuse angle.
d. Perpendicular.
24. Which components form the angle referred to in the bisecting angle technique?
a. Tooth, film.
b. Film, central ray.
c. Central ray, bisector.
d. Aiming cylinder, tooth.
25. When positioning the aiming cylinder, which plane does NOT differ between the paralleling
technique and the bisecting angle technique?
a. Vertical.
b. Horizontal.
c. Up-and-down.
d. Positive and negative degrees.
26. Disadvantages of incorrect vertical angulation include all EXCEPT one. Which one is the
EXCEPTION?
a. Augments patient comfort.
b. Results in nondiagnostic film.
c. Causes unproductive use of time.
d. Necessitates repeat patient exposure.
27. Which is the result of correct vertical angulation?
a. Foreshortening.
b. Overlapping of objects.
c. Enhancement of elongation.
d. Image the same size as the object.
28. Which image change occurs when an 8-inch aiming cylinder is used?
a. Elongation.
b. Foreshortening.
c. Increased size distortion.
d. Decreased shape magnification.
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6—Projection Geometry
29. In
a.
b.
c.
d.
the paralleling technique, the central ray is at
180 degrees to the object.
90 degrees to the imaginary bisector line.
90 degrees to the receptor and long axis of the tooth.
an acute angle to the receptor and long axis of the tooth.
Feedback
1. ANS: a
a. Correct. Sharpness is the capability to radiographically reproduce distinct outlines of an object.
b. In radiography, resolution refers to the ability to record small images placed very close
together as separate images.
c. Distortion refers to a variation in the true size and/or shape of an object.
d. Magnification of an image results in an image that appears larger than actual size.
REF: p. 84
2. ANS: d
a. Methods for minimizing the loss of image clarity include minimizing the distance
between object and film.
b. Methods for minimizing the loss of image clarity include using as small an effective focal
spot as practical.
c. Methods for minimizing the loss of image clarity include increasing the distance between
focal spot and object being radiographed.
d. Correct. Methods for minimizing the loss of image clarity do not include minimizing
focal spot-to-film distance and maximizing object-to-film distance.
REF: p. 84
3. ANS: c
a. The size of the focal spot is determined, or in direct relationship to, the effective heat
dissipation of the machine, not the frequency of machine use.
b. The size of the focal spot is determined, or in direct relationship to, the effective heat
dissipation of the machine, not the number of electrons produced.
c. Correct. The size of the focal spot is determined, or in direct relationship to, the effective
heat dissipation of the machine.
d. The size of the focal spot is determined, or in direct relationship to, the effective heat
dissipation of the machine, not the type of radiographic images produced.
REF: p. 84
4. ANS: b
a. The skill of the practitioner can serve to reduce image enlargement.
b. Correct. The divergent paths of photons are responsible for enlargement of the resulting
radiographic image.
c. The skill of the practitioner in the proper placement of the receptor in relationship to
the object being radiographed can reduce image enlargement.
d. The number of electrons produced is not related to the divergent paths of photons that
cause image enlargement.
REF: p. 84
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