DIQUAD’s goal is to work with radiation protection agencies and the dental community, and assist them in improving dental image quality while minimizing patient and staff radiation dose.
It is important to minimize the radiation dose received by patients while assuring optimum quality of the radiographic images. Whenever the dose to the patients is reduced there is a similar reduction in the dose to the staff. For example, changing from D speed film to E speed film will result in a 40% reduction in radiation dose to the patients and the staff. (See below for more on today's D- and E-speed film and image quality.)
Any radiation dose, no matter how low, is believed to have the potential of causing cancer. The radiation dose from a single intraoral image is relatively low. However, it is important to assure that the radiation doses to patients (and staff) are ALARA (as low as reasonably achievable) so that any potential risk from the x-ray dose is minimized.
A single bitewing image results in a patient entrance dose of about 200 mrad* while a full mouth survey with 20 images will result in a entrance dose of 4,000 mrad, or 4 rad, similar to a CT head scan. If four bitewings are taken annually from age 10 to age 70, the patient receives a lifetime entrance dose of 48 rad, a significant radiation dose.
*The entrance dose for a chest x-ray is about 15 mrad and for head CT is about 5,000 mrad (5 rad).
Digital dental radiography uses x-rays the same as film imaging and also results in x-ray doses to your patients and staff. Digital offers the potential for significant reductions in x-ray dose. However, it has been our experience that about 25% of the offices that switch to digital dental are using doses similar to or higher than D-speed film! D-speed film usually requires a dose of about 200 mrad. Digital doses should be on the order of 50 to 75 mrad, a reduction in dose of 60 to 75%.
You should have your present doses measured, a service provided by DIQUAD, LLC via mail through the DIQUAD website image upload system. Your present exposure time should be about 25% to 45% of the exposure time you were using with D-speed film. For example, if your exposure time was 300 msec (0.3 sec) for D-speed film you should be using about 75 to 120 msec (0.075 to 0.12 sec) for digital imaging. If you were using E-speed film and an exposure time of about 200 msec (0.2 sec), your digital exposure times should also be about 75 to 120 msec (0.075 to 0.12 sec).
Today D- and E-speed films are virtually identical in image quality. When E-speed film was first introduced the image quality was somewhat inferior to D-speed film which resulted in a now undeserved reputation of grainy and low contrast images. The two films below look almost identical but with a significant difference in dose. The E-speed film (top) required a dose of 120 mrad while the D-speed film (bottom) required 200 mrad. This results in a dose reduction of approximately 40% for patients and staff.
The image quality measurements are similar to those required under the U.S. Food and Drug Administration’s Mammography Quality Standards Act (MQSA) used by about 10,000 mammography facilities throughout the U.S., plus those in Canada and Australia.
Thiosulfate, also called fixer or hypo, is a chemical used in processing photographic film. It fixes, or makes permanent, the image, hence the name fixer. However, if this chemical is not washed completely from the film the residual thiosulfate can cause problems. Stains can occur on inadequately washed film images, the image contrast is reduced significantly, and the images will fade in a relatively short period of time. Consequently, it is essential to wash the film according to the film manufacturer’s directions in fresh water. The water should be changed daily, or more often depending on the volume of films processed, in tanks with no water flow.
Properly washing film on left, stained film on right (inadequate wash)
The smell is probably from residual thiosulfate, or fixer, that is not being adequately washed out of the film. This can happen for several reasons. The flow of water through the processor may be restricted, or the wash water may be turned off. Some processors transport the film through a tank of water, with no fresh water flow. In this case the water tank should be changed frequently, at a minimum of once per day, or more often in a busy office. Fixer that remains in the film can cause problems with the images. See the question “What is residual thiosulfate and why is it important?”
Photographic development is a chemical process that is affected by the quality of the chemicals, the temperature, and the development time. Under-processing (using diluted chemicals, low development temperature, or short development time) effects the speed of the film, the overall film density, and the film contrast. Under-processing increases the radiation dose to the patient and staff, and reduces film contrast.
Twelve
Contrast is a measure of the differences in the film densities. In other words, this is a measure of whether the film is black and white, or gray all over. Image sharpness is affected by the kVp and beam filtration (high kVp or high beam filtration reduces the film contrast), processing conditions (low developer temperature, short development time, or exhausted or not properly replenished developer) or contaminated developer solution will reduce contrast. In addition, contrast varies with the type and age of film used.
Low contrast will make small details difficult to see and will also make it difficult to visualize larger structures in the image which are similar in density to the surrounding tissue, e.g., a tumor in soft tissue.
Contrast is the optical density difference between two areas on the x-ray film that have received known exposures.
Normal on left, low contrast on right.
The film manufacturer should be able to provide you with information regarding the appropriate developer temperature for the film and developer solution you are using. The development time (for manual processing) or processing speed (for automated processors) is usually provided by the developer manufacturer along with the development temperature information.
Contrast can be improved by assuring the following--
Use of the correct kVp (if adjustable) and beam filtration
Use of the appropriate film processing conditions including developer time and temperature
Replenishment of the film developer as recommended by the developer manufacturer
Avoiding contamination of the developer solution with fixer or other solutions
Selection of a dental x-ray film based on the film contrast
Use of the x-ray film by the expiration date printed on the film box
You find a lot of information on dental x-ray image quality and radiation dose on the internet. Film and equipment manufacturers provide information and manuals to help you improve image quality and minimize radiation dose. Try searching on terms such as--
If you have specific questions please call us at our toll-free number in the U.S. at 1-866-498-1662. If you are outside the U.S., e-mail us at CustomerService@DIQUAD.com, provide your phone number including country and city code and the best time to call you. Please keeping in mind that we are located in the same time zone as Chicago, Illinois. We will be pleased to help you in any way that we can!
