Dr. Guebert is the director of St. Louis Roentgen Associates and assistant professor, Clinical Science Division, Logan College of Chiropractic. Dr. Yochum is the director of the Rocky Mountain Chiropractic Radiological Center, adjunct professor of radiology at the Los Angeles College of Chiropractic, and an instructor, skeletal radiology, University of Colorado School of Medicine.
Chiropractors and other health care professionals who use ionizing radiation for diagnostic imaging are under mounting pressure to decrease patient dosage and simultaneously improving radiographic quality.1 Decreasing entrance skin exposure (ESE) is mandatory because states are adopting radiation reduction regulations which are often stricter than those imposed by the federal government.
Improving radiographic quality helps ensure more accurate diagnoses. A missed diagnosis on radiographs is one of the reasons chiropractors are sued for malpractice. Even in what may appear to be just a case of scoliosis, a good radiograph can confirm that some other pathology, such as a fracture, may exist in addition to the scoliotic deformity.
Patient Motion
Poor radiographic quality often stems from patient motion while the x-ray exposure is being made. Film processing problems also can affect radiograph quality. Motion is a particular problem for chiropractors, because radiographs are taken with the patient in a standing position to evaluate posture as well as pathology. The use of foam positioning aids will substantially reduce the potential for patient motion. Motion becomes even more problematic when patients are radiographed in dynamic positions. Even with the 400 speed rare earth screen/film systems frequently used today, it's not uncommon for chiropractors to repeat up to 30 percent of their exposures because motion degraded the image.
Decrease ESE Levels
The goal of every practitioner should be to simultaneously decrease ESE levels and improve quality by reducing patient motion. New high-speed screen/film systems such as the Kodak professional diagnostic imaging films, PDG and PDH, with Kodak Lanex fast screens yield system speeds of 600 and 1200, respectively, and can help achieve these goals.
The high-contrast, orthochromatic (primarily green light sensitive) films incorporate Kodak's T-Grain emulsion technology for improved image sharpness.2 They can also tolerate exposure variations such as equipment variables or technique settings.
Although it is generally true that the faster the screen/film system, the greater the loss of detail, our experience shows very little loss of detail when converting from a 400 to a 600 speed system.
The Kodak PDG film and Kodak Lanex fast screens combination (600 speed) has nearly the resolution of the 400 speed system, but because of the increased speed, exposure times can be reduced by one-third, decreasing the patient exposure and the potential for motion a corresponding amount.
We recommend Kodak Lanex fast screens and Kodak PDG film (600 speed system) for initial investigations of any body part. The film's contrast allows excellent radiographic visualization of bone detail as well as soft tissue structures. For dynamic spine images (lateral bending or flexion/extension), we suggest Kodak PDH film and Kodak Lanex fast screens (1200 speed system). This ultra-high speed, high-contrast film, when combined with Kodak Lanex fast screens, requires approximately one-half the exposure of the 600 speed system and one-third the exposure of a 400 speed system. The much shorter exposure times can eliminate most motion problems. The increased speed also means that you can obtain a quality radiograph for even the largest patients.
This 1200 speed screen/film combination may also be used to your advantage when performing a lateral lumbar spine radiograph of very large muscular or obese patients. Using Kodak PDH film and Kodak Lanex fast screens will decrease the workload on the tube by approximately one-half (compared to the 600 speed system) and will similarly reduce the patient's exposure time by one-half, thus reducing the possibility of patient motion. This technology makes it more practical to obtain sharply detailed standing lateral radiographs of the lumbar spine on larger patients.
These two screen/film systems would meet 95 percent of most chiropractic radiographic needs. And while it probably isn't necessary to switch from a 400 speed system to the new 600/1200 speed systems if your current cassettes are new and you don't have a motion problem, it is definitely something to consider when it's time to replace screens.
Switching to a faster screen/film system also is cost effective because it reduces retakes, yielding time and material savings, while reducing the load on the x-ray tube which has a replacement cost of approximately $5,000.
Testing Your Intensifying Screens
A simple test can be performed to ascertain if it's time to replace your screens. Load a film into a cassette containing old screens and a cassette containing new screens. Place the cassettes side by side so that the test object straddles the two cassettes. Make the x-ray exposure and process the film normally. A visibly lighter density on the film from the old screens indicates it's time to replace your screens.
Better Image Detail
Another advantage of the 600 speed system is that the higher speed permits the use of the 100 mA setting on many single-phase generators, and this mA setting is usually linked to a small focal spot. The smaller the focal spot, the greater the image detail. On the new high frequency machines the small focal spot can be used for almost any mA setting.
Upgrading from a single phase x-ray generator to a modern high frequency generator will provide two additional benefits. The exposure time will drop dramatically, and because of the decreased time and the greater penetrating power of the x-ray beam, the second benefit realized is a reduction in radiation exposure to the patient.
Our preferred combination is Kodak PDG film and Lanex fast screens with a high-frequency generator such as the Bennett 100 kilohertz high-frequency x-ray generator. Patient exposure and motion are reduced while yielding improved final image detail because the smaller focal spot can be used almost all of the time.
Even with the 600 speed system though, patient motion can slightly degrade the image, particularly in lumbar spine studies of large patients. Inexpensive motion restraints (compression bands) can reduce retakes by as much as 50 percent -- particularly in obese or uncooperative patients -- because patients are stabilized and abdominal tissue is compressed.
Full-Spine Radiography
The quality of full-spine studies can be remarkably improved by using sectional filters to ensure more uniform image density throughout the entire vertebral column. Some sectional filters use lightweight acrylic (30 percent lead by weight), while other systems use aluminum to selectively attenuate the x-ray beam. These filters are placed between the tube and the patient, filtering sections of the beam before it strikes the patient.3
Tests conducted by the Center for Devices and Radiological Health (CDRH) indicate that transparent lead-acrylic compensation filters and breast shields significantly reduced exposure. In some cases up to 80 percent less exposure was measured at the skin of the breast when doing AP projections, in 14" x 36" full spine and 14" x 17" sectional spine radiographs -- while providing a more uniform radiographic density.4
When a full spine is clinically indicated, we recommend an AP single exposure on the Kodak PDH film/Lanex screens 1200-speed system with compensating filtration -- not a split screen cassette. This will yield a high-quality radiograph with the lowest possible patient dose.
Changing from a 400 speed system to a 1200 speed system for full-spine radiography can result in reducing the mAs by two-thirds. We've produced high-quality, full-spine AP films on average-size patients (measuring 23 centimeters) at an mAs setting of 15 and 85 kVp at 72 inches (using Kodak's 1200 speed screen/film combination and Bennett's 100 kHz high-frequency generator). This radiographic technique is similar to that being used for lateral cervical views taken at 72 inches FFD, performed non-bucky, with a single-phase generator and a high-speed screen/film combination (200 speed, not rare earth).
Lateral full-spine studies should be done sectionally because it's too difficult to obtain a properly exposed, full-spine lateral image of diagnostic quality. There will be substantial distortion -- especially at the craniovertebral and lumbosacral junctions. Attempting to expose the lateral cervicodorsal view in a single exposure, even with heavy sectional filtration over the cervical region, typically yields an undiagnostic image.
Assuming a complete series of high-quality static films exist, the 1200 speed system also is excellent for dynamic views of the spine, cervical and lumbar lateral bending or flexion and extension. The shorter exposure times further reduce the potential for patient motion. Although the 1200 speed system may produce a "grainier" image than the 600 speed system -- too "grainy" for routine diagnosis -- the image quality is adequate to augment good static films.
Technique Adjustments for 600/1200-speed System
Switching to a 600 or 1200 speed system from a 400 speed system requires reducing the mAs, a minor technique adjustment. The accompanying chart can be used as a rough guideline for exposure adjustments; however, we suggest relying on the manufacturer of your x-ray equipment to help you generate more accurate technique charts.
It is worth noting that the typical radiographic technique chart is becoming an anachronism with the increasing affordability of automatic exposure control (AEC) devices. These devices can be calibrated to your screen/film combination, even to multiple combinations such as 600 and 1200 speed systems. The operator indicates the type of study and pre-selects the preferred kVp. When the exposure is made, the AEC measures the amount of radiation that has passed through the patient. When the level of exposure is proper to ensure a diagnostically exposed radiograph, it automatically terminates the exposure. You may want to seriously consider adding an AEC device when you upgrade your current x-ray equipment to reduce occurrences of underexposed and overexposed radiographs. You will save film and chemicals and extend the life of your x-ray tube while reducing exposure to you and your patients.
ALARA Standard
Switching from a 400 speed screen/film system and a single-phase generator to a 600 or 1200 speed system and a high-frequency generator may be necessary sooner than expected as states begin to aggressively pursue the ALARA (As Low As Reasonably Achievable) standard.5
Some state regulatory agencies have guidelines that are more restrictive than those found in the NEXT study (National Evaluation of X-ray Trends).6 When a facility is inspected and found to exceed the state guidelines, the offender is often cited for not having followed the ALARA principle.
Conclusion
It is our opinion that there will continue to be increasing pressure from the federal government to further lower allowable entrance skin exposures (ESE) in an effort to reduce the harmful effects caused by diagnostic radiation exposures. In this paper we have outlined several opportunities available to chiropractors to improve overall film quality while decreasing patient exposure
Prudent application of these techniques will keep your practice well ahead of any federal or state guidelines. Now is the time to improve the quality of your radiological services.
Note: Kodak, Lanex, T-Grain and X-Omatic are trademarks.
References
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