Radiographic Quality Assurance in dentistry

Radiographic Quality Assurance

A series of procedures designed to ensure optimal and consistent operation of each component in the imaging chain.

When all components are functioning properly, the result is consistent high quality radiographs made with low exposure to patients and office personnel.

Radiographs are indispensable for patient diagnosis.

Dentist must ensure optimal exposure and film processing conditions to be maintained.

Quality assurance includes evaluation of performance of x-ray machine, manual and automatic film processing procedures image receptors and viewing conditions.

Optimization of all steps in the image chain results in the most diagnostic images and the lowest exposure for patients.

The use digital sensors can greatly simplify the tasks.

Schedule of radiographic quality assurance procedures

Daily Tasks

Weekly Tasks

Monthly Tasks

Yearly Tasks

Daily Tasks

Compare film radiographs with reference film

Use of depleted solution is common cause of poor film radiograph radiographs with reference film

Simple and effective means for constant monitoring of the quality produced in dental office is to check daily films against a reference film.

Soon after film processing unit is replaced, an image is processed and the image is kept for reference purpose for radiographs made in following weeks and days.

Sensitometer and Densitometer

Most accurate way of testing film processing solution is using sensitometer and densitometer. Sensitometer exposes film to a calibrated light pattern. Densitometer is used to measure the optical density of each step in the test pattern of the film exposed by sensitometer.  A change in the density from day to day indicates a problem in the dark room.

Enter findings in retake log

Simple and effective means of reducing number of faulty radiograph is to keep a retake log. All errors for image that must be re-exposed are recorded. This process quickly reveals the source of recurring problems.

Replenish processing solution

At beginning of every day, the levels of processing should be checked and replenished if necessary. The developer is replenished with fresh developing solution and fixer is replenished as well.

Check temperature of processing solution

At beginning of each early day, temperature of processing solution should be checked. Temperature must reach the optimal temperature before use, 20° C, for manual processing and 28° C for heated automatic processors. Proper temperature regulation is required for accurate time-temperature processing.

Weekly Tasks

Replace processing solutions

Frequency of changing the solution depends on rate of use of solution primarily as well as on size of tanks, se of cover, temperature of solution, etc... Mostly, solutions should be changed weekly or every other week.
Result of step wedge test help to determine the proper frequency.

Clean processing equipment

Regular cleaning if processing equipment is necessary for optimal operation. Solution should be cleaned when the solutions are changed. Roller of automatic film processor should be cleaned weekly and after cleaning the tanks and roller should be rinsed twice as long as the default to prevent cleaners from interfering with actions of the film processing solutions.

Clean viewboxes and review retake logs

Viewboxes should be cleaned weekly to remove any particle or defects that may interfere with film interpretation.
The retake record should be reviewed weekly to identify any recurring problems with film processing conditions or operator technique.

Monthly tasks

Photostimulable phosphor plates

Photostimulable phosphor plate (PSP) plates may become scratched in course of use. The scratches may be seen as a light streaks on processed images, so plates should be inspected monthly for such defects and removed from service when such defects are found.

Check darkroom safelighting

Films become fogged in darkroom because of inappropriate safelight filters, excessive exposure to safelights and stray lights from any other sources. These films are dark, show low contrast and have muddy gray appearance.
To check for light leaks in darkroom, all sources should be turned off and check for light leaks after accommodation of the checker’s vision. Light leaks found should be marked with chalk or masking tape and weather stripping is useful for sealing light leaks under doors.

Check intensifying screens

All intensifying screens in panoramic and cephalometric film cassettes should be cleaned monthly. Presence of scratches or debris results in recurring light areas on resultant images. The foam supporting the screens must be intact and capable of holding both screens closely against the film and if not, the image loses sharpness.

Rotate film stock

Dental x-ray should be stored in cool, dry facility away from a radiation source. Stock should be rotated when new film is received so that old film doesn't accumulate in storage. The oldest film should be use at first but never after its expiration date.

Check exposure charts

Each month, inspection should be done of exposure tables listing the proper kilovoltage (kVp) and exposure times for making radiographs of each region of oral cavity that are posted by each radiation machine. One should verify that the information is legible and accurate.
Typically, mA is fixed at its highest setting, the kVp is fixed at 70 kVp and exposure time is variable from patient to patient.

Check leaded aprons and collars

Leaded aprons and collars should be visually checked for evidence of cracking. A fluoroscopic examination can confirm any crack in lead shielding. If crack is present, then these items should be replaced as necessary. Cracking usually occurred by folding the shields when not in use.

Yearly tasks

Digital sensors

Digital sensors and PSP palates should also be checked yearly for sign of image degradation. Failing sensors may reveal loss of sensitivity, contrast resolution or spatial resolution. Phantoms are designed for test purpose of the sensors.

Calibrate X-Ray machine

A dosimeter should be used to measure the intensity and reproducibility of radiation output.
Field diameter for dental x-ray should not be more than 2.75 inch.
The kVp of the beam should be measured to ensure that the beam has sufficient energy for film exposure without excessive soft tissue dosage. KVp measurement should be within 5 kVp.
Timer should be accurate and reproducible.

The linearity of mA should be verified if 2 or more mA settings are available. The mA value for first and second exposure should be equal for undistorted images. A discrepancy implies nonlinearity in mA control or fault in timer

The tube head should be stable when placed around the patient’s head and should not drift during the exposure.
An enlarged focal spot contributes to geometric fuzziness in image. The focal spot may be enlarged due to excessive heat buildup within x-ray machine. A specialized piece of equipment is required for this test.

X Ray Darkroom fog test

This test is usually done to check for light leaks.

Equipment needed
     Stopwatch
     New Film
     Coin

·        Turn off safelights

·        In totally darkened room, remove the film from film holder and place it on counter. Place the coin on the film.

·        Turn on safe lights and let the film sit for 2 minutes. Tester should not block any light.

·        Process the film and look around the dark room for light leaks since eye has adapted to the dark.

·        Evaluate the film. If outline of the coin is visible, a fog problem exists that needed to be corrected.

Sources of fog
Crack in safelight filter. If so, then replace filter.
Bulb to work surface distance incorrect. A 15 watt bulb should be 4 feet or more from the surface.

                  Fig: Coin Test or Penny Test

Step wedge test

An aluminum step wedge is taken and image is taken in a new unexposed film with fresh solution. The produced image will be used for comparison of daily test films.

Equipment required
Step wedge

New film

Collimate to the edges of the step wedge

Make an exposure of the step wedge and process normally

Evaluation
Compare new radiograph with the comparison image. If the density are not within 1 step of comparison film, then there is no constancy.

This test is primarily used to check the quality of x ray.

Repetition of the same step to confirm the results.

If same result persists, there is a problem with the processor.

Contact to x ray and processor service engineer for corrective actions.

                                                          

Fig: Step Wedge Test

Conclusion

The given daily, weekly, monthly and yearly tasks are performed for optimized performance of radiographs and present best quality of radiographs along with minimum exposure to both patient and physician.

The ALARA concept should be well applied while doing both radiographs and processing them as well.

Patient protection is important and so is protecting ourselves. Properly assured instruments and processing can greatly help in protecting ourselves.