Overview of Intraoral Image Receptors

Intraoral radiographic images can be acquired with digital receptors or radiographic film (Figure 1). All three modalities are available for use. Digital image receptors include rigid sensors and phosphor plate receptors. Intraoral digital receptors are available in sizes comparable to traditional dental film. Rigid digital receptors are typically available in sizes 0, 1, and 2 while the plate receptors are available in sizes 0, 1, 2, 3, and 4. The range of available sizes is dependent on the specific product manufacturer. Digital receptors cannot be sterilized. Therefore, it is important to utilize proper infection control techniques to prepare and cover digital receptors for placement inside the mouth and effective barrier removal following completion of the survey. Refer to manufacturer recommendations for proper infection control procedures for digital receptors both rigid sensors and phosphor plates.

Figure 1: Rigid CCD Digital Sensor,
Digital Phosphor Plate,
F-Speed Dental Film

Rigid digital receptors are categorized as direct digital devices. These rigid receptors are usually either a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) sensors with the latter being the most common. The same receptor can be used for each projection by repositioning the receptor for the next view after each exposure. These direct digital receptors convert the x-ray beam into an electronic signal, which is then displayed as a grayscale image and stored in a computer. The direct digital image can be viewed on the computer monitor almost immediately.

Indirect digital receptors known as storage phosphor plates (SPP) or photostimulable phosphor plates (PSP) are also available. These plates have a europium-activated barium fluorohalide emulsion which stores the latent image after exposure. A separate plate is needed for each projection and the plates must be erased with white light before reuse. After the plate is exposed, the receptor is laser scanned and the image is digitized and displayed on the computer monitor. In newer scanner models, plate erasure occurs after the scanning step but before exit of the plate from the device. Phosphor plates require careful handling to avoid abrasion of the emulsion and resultant image artifacts.²

Digital images can be adjusted to view the information in different ways. Software enhancement features include changes in density, contrast, colorization, zoom or magnification of particular areas of interest, measurement, image reversal and the application of filters for noise reduction or edge sharpening. These tools allow the clinician to view the captured image in different ways. Image enhancement tends to be subjective and is dependent on the visual preferences of the clinician interpreting the image.³ There is some evidence in the literature that suggests post-processing or image enhancement applications may not necessarily improve the diagnostic utility of the image and, at times, may lead to inaccurate interpretation.^3-8

Subtraction can also be performed using digital images. This is the process used to compare an area before and subsequent to treatment to assess progress or change. The computer subtracts the two images and the image that remains represents the difference or change between pre- and post-treatment. The challenge with digital subtraction is the need to register the images prior to subtraction. The images are seldom identical in their placement or projection geometry and must be matched structurally in order to determine the actual change that occurred between the two images taken at different points in time.^2,3

After the image has been obtained, it can be viewed and stored on the computer, printed, or sent electronically in instances of referral or insurance claims. Digital radiography facilitates storage and easy access for image viewing, duplication, printing, or electronic transfer. Digital imaging is an integral part of a complete electronic record without the need for physical storage space and concern that the images will be damaged or destroyed. However, it is important to back-up patient records daily to avoid lost data. There are a variety of media that can be used for back-up storage such external hard drives, CDs, DVDs, or cloud technology.

Digital imaging like film radiography utilizes x-ray beam collimators to reduce the area of exposure at the skin surface with a preference for rectangular collimation and receptor holding devices to reduce retakes. Rectangular collimation more so than round reduces both primary and scatter radiation which not only benefits the patient by reducing exposure but also improves image quality.^3,8 Because digital receptors are more sensitive to scatter radiation than film, rectangular collimation is recommended for use with digital imaging systems. There are a number of commercially available devices that the clinician can utilize to achieve rectangular collimation and reduce exposure.^3,9 Current digital receptors offer equal or greater dose reduction than F-speed film and comparable diagnostic utility.³

The majority of technique and exposure errors can be produced with digital receptors and conventional film with a few exceptions. The greatest advantage of digital imaging is elimination of processing errors which are the most common causes of retakes in film-based radiography. In addition, digital imaging also eliminates the darkroom, processor and chemical maintenance which requires additional time and effort when done properly, and lengthy processing time. Regardless of the imaging system employed, the clinician should take all necessary steps to reduce the amount of radiation the patient receives in compliance with the ALARA Principle (As Low As Reasonably Achievable). Primary to dose reduction is the application of selection criteria in the determination of necessary radiographs.¹