Radiation Dose Minimization and Image Optimization for Traditional Imaging Modalities

Intraoral Image Receptors

Digital receptors for intraoral and extraoral radiographic imaging, including the charge-coupled device (CCD), complementary metal oxide semiconductor (CMOS) or photostimulable phosphor plate detectors, should be used in place of film to reduce radiation dose to patients. If film is used for intraoral radiographic imaging, F speed film should be used to achieve greater dose reduction and D speed should no longer be used.^24,28 When using intraoral radiographic imaging, receptor holders with x-ray beam guides should be used whenever possible (Figure 2). Film-based panoramic or cephalometric extraoral radiographic imaging should utilize rare-earth intensifying screens with matching high-speed film of 400 or greater.²⁴

X-ray Beam Collimation

The x-ray beam should be collimated to the receptor size and shape whenever possible to limit the amount of primary and scatter radiation delivered to the patient during intraoral imaging. Rectangular collimation is preferred over round collimation because it reduces radiation dose to the patient significantly, approximately fivefold.^24,39 Rectangular collimation has the added benefits of improving image geometry and reducing scatter radiation which degrades the resultant image.⁴⁰ This impacts intraoral digital receptors because they are more sensitive to scatter radiation than film.⁴⁰ Receptor holding devices have beam guide insets to facilitate rectangular collimation alignment. Several commercial devices are available to convert round to rectangular collimation.

Source-to-Skin Distance

The distance from the x-ray focal spot or radiation source and the skin surface should be as long as possible but not exceed 20 cm (Figure 4). The use of long position-indicating devices serves to maximize the distance between the source and skin surface which limits divergence of the x-ray beam and the area of exposure.

Kilovoltage Range

The optimal operating kilovoltage (kV) range for intraoral x-ray machines is 60-80 kV but not to exceed 80 kV.²⁴ (Figure 5) Consult the manufacturer’s operating manual to determine the appropriate exposure time for each area of the mouth per the type of receptor being used to image the patient. Technique charts should be used to indicate proper exposure settings for intraoral and extraoral radiographic imaging systems with adjustable settings.¹ The clinician should make appropriate exposure adjustments when imaging children versus adult patients. X-ray machines should be evaluated regularly at intervals mandated by state regulation.

Handheld Intraoral X-ray Devices

Intraoral x-ray imaging systems include devices held by the operator during imaging procedures. Handheld devices are advantageous in certain situations and environments in which access to a traditionally wall-mounted unit is difficult or inaccessible.²⁴ Handheld devices must be FDA cleared (meet federal safety and design standards), used according to manufacturer’s instructions, restricted for use only by authorized personnel with proper training, and stored securely out of public reach when not in use.^2,24 These devices can present radiation safety and technique challenges for the operator and patient.²⁴ As such, specific training in proper device holding, imaging technique, and x-ray beam alignment is necessary to produce diagnostic images without patient re-exposures and to maximize operator protection from the backscatter shield.^2,24