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Selecting an Appropriate Digital Radiography Sensor

Size and Placement Considerations

Advancements in digital radiography have enticed every clinician with improvements in speed, clarity, and patient education opportunities. No longer are clinicians asking themselves if they want to convert their practices to implement this technology. Now the question is "when?" While the advantages of digital radiography over traditional radiographic methods are not in question, the debate over system and sensor selection, sensor positioning, and scanning processes continues.

 

Digital Systems

There are two types of digital sensors offered for use in dentistry, direct and indirect. Direct digital radiography sensors transfer digital information adroitly to the computer; the image is obtained directly from the sensor itself via a connection to the computer. Indirect sensors gather digital information that must be "translated" in an intermediary step (typically utilizing additional equipment) and then transferred to the computer.

 

Sensor Types

The two most common types of direct sensors are charged coupled devices (CCD) and complementary metal oxide semiconductors (CMOS). The CCD sensor, which tends to be relatively thick and inflexible, was the first type of sensor to be used in dentistry.1 Although disadvantages of CCD sensors are apparent, there are unquestionable advantages to their utilization (Table).

Indirect sensors are photostimulable phosphor (PSP) storage plates, which resemble traditional radiographic film. This type of sensor must be "read" by a scanner that transfers the "translated" information to the computer. The PSP plate sensors gained initial popularity due to their flexibility and ease of placement, but recent research indicates concerns about their durability.2

 

Sensor Positioning

The CCD sensors are held in explicitly designed positioning devices. The paralleling technique can be implemented, as it would be with film-based radiography. In addition to considering the size of the sensor, the clinician must also take into account the positioning of the plastic sleeve and the cord when capturing the image. The plastic sleeve may prevent optimal visualization and cause the patient to gag, while the cord may obstruct the radiation beam. When placing the sensor intraorally, it is advised to keep the plastic sleeve taut to increase visualization and to prevent interference with positioning. Excess plastic sleeve can also increase salivation that will interfere with the radiograph. To restrain the cord, some positioning devices (eg, a notch or clamp) can help direct the cord out of the visual field.

The PSP plate sensor is similar to film in size and thickness and does not require a cord. The PSP plates are more flexible and, therefore, must be carefully managed. If they become scratched, a compromised image will result. If the receptor is bent when the patient stabilizes it, elongation of the apical portion of the image will occur. A rigid biteblock can reduce this distortion.3

 

Processing

One of the greatest advantages to digital radiography is the ability to enhance and manipulate images on screen. Typical processing tools include:

  • Mirror (ie, flip and rotate command)
  • Brighten
  • Contrast Modification
  • Reverse Gray Scale (invert or inverse)
  • Filters (for noise reduction, sharpening, and smoothing)
  • Zoom
  • Colorize
  • Measure
  • Digital Subtraction

It has been stated, however, that the more the image is manipulated, the less likely it is that the image is improved. Attention to exposure factors, patient size, and projection geometry will have a greater impact on image quality than anything that can be done to the image after it is captured.3

 

Conclusion

While there is a learning curve to mastering digital radiography techniques, the advantages over film radiography make it an attractive alternative to film-base dental radiography. When determining which digital system to purchase, it is imperative that clinicians not only determine which sensors to utilize, but also survey current computer hardware configurations and consider associated costs (eg, replacement sensors and warranty coverage).


References

  1. Farman AG. Fundamentals of image acquisition and processing in the digital era. Orthod Craniofacial Res 2003;6(suppl 1):17-22.
  1. Bedard A, Davis TD, Angelopoulos C. Storage phosphor plates: How durable are they as a digital dental radiographic system? J Contemp Dent Pract 2004;5(2):57-69.
  1. Parks ET. Practical Techniques to optimize digital radiographic imaging. Pract Proced Aesthet Dent  2008;20(2):94-98.

Tables

Table 1: Comparison of Digital Receptors

 

Feature

CCD

PSP

Size Range

0,1,2

0,1,2,3,4, panoramic, and cephalometric

Image Viewing

Instantaneous

Delayed

Resolution

8-10 lp/mm

6-8 lp/mm

Durability

Reusable; 400,000 exposures*

Reusable: approximately 30-50 exposures2

Cost

Average cost of size 2 sensor is $7,000

Average cost of size 2 sensor is $25

Physical Dimension

Thicker and more ridged than traditional film

Flexible and thinner than traditional film

*Warranties differ with manufacturers.

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