Sub-category 2: Tissue Projection Errors

The second category of technical errors in panoramic radiographic imaging are tissue projection errors or those due to tissue superimposition. Two errors are possible:

Hard Tissue Projection Errors

1. Spine. The first hard tissue error can occur when the patient assumes the “head extended” position. One of the final instructions to patients before panoramic exposure is to move their feet slightly forward into the machine, a sort of “panoramic shuffle.” This has the effect of straightening the cervical spine of the patient. If the patient is not instructed to do this, they often adopt a projected head position. This occurs because the natural tendency of patient is to put their head forward into the panoramic head holding apparatus rather than physically moving their head and their body simultaneously. The positioning effect of this action places the spine into a more oblique position with respect to the x-ray beam and attenuates (absorbs) more x-rays. The most obvious anatomic feature of head projection is the superimposition of the spine on the ramus of the mandible and the production of a ghost image. The most characteristic ghost image is of the spine, and it appears as a central midline radiopacity that broadens inferiorly. In addition, because of poor contrast, the dentition may be difficult to visualize due the radiopaque superimposed ghost image.

These figures show the blocking effect of the spine on the anterior aspect of the image when the patient is in a slumped position.

Figure 53A. Panoramic Image.

Figure 53A. Panoramic Image.

Figure 53B. Panoramic Schematic.

Figure 53B. Panoramic Schematic.

These figures show the blocking effect of the spine on the anterior aspect of the image when the patient is in a slumped position.

2. Patient Movement. The second hard tissue error can occur when the patient moves during an exposure. Because the panoramic exposure is approximately 16 to 20 seconds, the possibility exists that a patient may move during the exposure. Prevention of this error can be aided by continuing to inform the patient throughout the exposure to remain still. Movement produces characteristic anatomic effects by stretching or breaking the image in the zone of movement. This may lead to the appearance of a “false” fracture. Appreciation of this artifact is important in the assessment of patients reporting with maxillofacial injury.²⁹ Additional presentations may result from double imaging or loss of segments. Another characteristic effect is the appearance of a dent in the lower border of the mandible.

These figures show the effect patient movement has on the image. Note the discontinuity of the left lower border of the mandible and distortion of the dentition and palate immediately superiorly.

Figure 54A. Panoramic Image.

Figure 54A. Panoramic Image.

Figure 54B. Panoramic Schematic.

Figure 54B. Panoramic Schematic.

These figures show the effect patient movement has on the image. Note the discontinuity of the left lower border of the mandible and distortion of the dentition and palate immediately superiorly.

The effect of patient movement on the dentition can be subtle and contribute to what could be called “motion microdontia.”

Figure 55. Panoramic Image.    Figure 56. Cropped/Zoomed Section.

Figure 55. Panoramic Image.    Figure 56. Cropped/Zoomed Section.

These figures depict the maxillary central incisor, tooth #8, as extremely narrow, suggesting that the patient may have a microdont central incisor. Further examination demonstrates that mandibular lateral incisor, tooth #26, directly below #8 also looks like a microdont. Additional clues that is a motion artifact are revealed by comparing the anatomy above and below the teeth with the opposite side. This is especially apparent in the relative width of the ala or soft tissue shadow of the nose.

Soft Tissue Projection Errors

1. Tongue Drop. The second type of tissue projection error can result from soft tissue artifacts associated with either the tongue not being placed against the palate during the exposure, or the lips not being closed. These errors occur when the patient is not instructed to place their tongue against the roof of their mouth during the entire exposure and to keep their lips closed. These gaps produce areas of relative radiolucency associated with the oropharyngeal and nasopharyngeal airspaces, which can obscure visualization. This occurs because panoramic x-ray beam exposure is designed to be sufficient to transmit through both the hard and soft tissues of the maxillofacial region. Particularly evident in underexposed panoramic images, the features of the maxilla are obscured by the radiolucency created by the incorrect position of the tongue and radiopacity of the palatal hard and the soft tissue. Prevention of this error can be aided by continuing to instruct the patient throughout the exposure, to maintain tongue contact against the roof of their mouth. Failure to do so does not produce any anatomic effects but does have some consequences with respect to the visibility of the dentition.

These figures illustrate the effect on the image from lack of placing the tongue against the roof of the mouth.

Figure 57A. Panoramic Image.

Figure 57A. Panoramic Image.

Figure 57B. Panoramic Schematic.

Figure 57B. Panoramic Schematic.

These figures illustrate the effect on the image from lack of placing the tongue against the roof of the mouth.

While failure to position the tongue properly is one of the most common technique errors, it is rarely the cause for a retake. However, the effect can be accentuated in two situations, when the patient is edentulous, and when the patient is positioned too far forward. Failure to place the tongue correctly may also create apparent “apical pathology.”

Figure 58. Improper Tongue Placement. This image demonstrates the effect relaxation in tongue position during panoramic exposure can produce. Take note of the cyst-like radiolucency in the maxillary midline which appears to expand inferiorly below the alveolar bone. Closer examination reveals that the uppermost part of this lesion is shaped in a gradual curve which represents the top of the palate. This is the telltale sign that this "faux lesion" was created by the patient’s tongue dropping down during exposure.

Figure 58. Improper Tongue Placement. This image demonstrates the effect relaxation in tongue position during panoramic exposure can produce. Take note of the cyst-like radiolucency in the maxillary midline which appears to expand inferiorly below the alveolar bone. Closer examination reveals that the uppermost part of this lesion is shaped in a gradual curve which represents the top of the palate. This is the telltale sign that this "faux lesion" was created by the patient’s tongue dropping down during exposure.

2. Lips not closed. The second soft tissue error results from the lips not being closed throughout the exposure. While there are no anatomic effects of this error, it can contribute to “burn out” of the crowns of the anterior teeth or be responsible for increased radiolucency over the maxillary anterior region that could be interpreted as anterior bone loss.

Figure 59. Panoramic Image with Open Lips. This image demonstrates the effect of open lips during exposure producing an area of increased radiodensity of the anterior teeth crowns.

Figure 59. Panoramic Image with Open Lips. This image demonstrates the effect of open lips during exposure producing an area of increased radiodensity of the anterior teeth crowns.