Medical imaging demands precision in the production of high-quality diagnostic images while restricting the amount of radiation administered to patients. Proper quality assurance (QA) programs optimize the caliber of radiographic images, protect patients and personnel from unnecessary exposure to radiation and reduce the occurrence of misdiagnosis caused by failures in all phases of imaging procedures.
Although QA often is used as a description of a comprehensive overall testing program, the term may be limited to refer primarily to staff issues such as educational background requirements and licensure, peer review and maintaining competency. QC usually refers to the technical side of the equation: the design and manufacture of imaging devices followed by careful evaluation and maintenance of machines.
“Two things are of prime importance: … image quality and … radiation dose,” explains Joel E. Gray, Ph.D., vice president of business and clinical development, Lorad division, Trex Medical Corp. (Danbury, Conn.). “I put image quality first because without image quality, the radiologist will not have the information necessary to make the diagnosis. Personally, I feel if image quality is done right, the dose will fall into place and it won’t be a problem.”
George Spahn, director of imaging services at Fuji Medical Systems (Stamford, Conn.) says, “The medical benefits of X-ray far outweigh any hazards that are caused by routine X-ray images. Still, there is no clinical evidence as to the minimal dose required to enact some cellular change, so we want to be extra cautious at all times.”
The balancing act between generating a high-quality image while using the lowest dose of radiation requires careful examination throughout all segments of the imaging chain. Mike Ruthemeyer, R.T. (R)(M)(QM), QA/QC coordinator at St. Luke’s Episcopal Hospital (Houston, Texas) explains, “As a general rule, radiologists won’t know if they got a good quality exam or a bad quality exam. If we do it incorrectly, and the radiologist is under the assumption it was done correctly, you can lose detail. If he cannot see the detail in the final image that is presented to him, he can’t say if there is cancer or not.”
Richard Jacobs, M.D., M.H.A., head of medical diagnostics and medical director of medical imaging at Parexel International (Waltham, Mass.) concurs. “The worst X-ray examination is one that is falsely negative because of exposure techniques. It gives a false sense of security to the referring physician that there is nothing wrong, when actually it is just a bad image … and a tumor is missed.”
Ruthemeyer clarifies that his hospital’s QC protocols include monitoring every aspect of producing a film image. “We make sure the cassette is correct and appropriate, test the unit that creates the X-ray to make sure it’s correct and collimating correctly and that the dose output is correct, and then we check the processor. We even check the view box for the correct color of light coming out of it. Every view box is within 10 percent of all the others.”
Most imaging equipment produced today includes computerized diagnostic features. Ruthemeyer, like others, expresses concern that people will begin to rely too heavily on these properties. “One of my biggest fears is that as we become more computerized, people will say, ‘well the machine says it’s fine’.”
He compares this approach to an example of where a driver trusts a dashboard gauge that indicates a car’s oil level is adequate. The wise driver must physically check to determine whether or not there is sufficient lubricant for the engine, rather than relying solely on a dashboard gauge.
Frequency of testing depends on the imaging modality, regulations determined through state or federal mandates or accreditation standards. “We even do QC on our video monitors that our doctors use to read soft copies,” Ruthemeyer says.
Nuclear Associates’ Scooter is an 8-inch diameter, water-filled phantom containing helical scanning test objects and a unique bone correction evaluation insert.
Nuclear Associates (Carle Place, N.Y.) works with virtually every imaging equipment OEM to supply test objects, such as phantoms used to monitor the overall performance of the imaging equipment to ensure optimum quality at reduced dose to the patient. The staff works collaboratively with researchers from leading universities around the world as they develop new products and new techniques.
Quality control testing is usually performed at the time new equipment is acquired to insure that manufacturers’ specifications as to the amount of radiation being delivered is accurate, and then periodically to test any areas of equipment performance that may drift over time. The drift issue becomes particularly important when a patient is undergoing some form of treatment that requires repeat assessment of results, such as when the clinician needs to ascertain the effect of chemotherapy on tumor growth.
“Cross-time comparison is particularly important in clinical trial work where machinery drifts from one point to the next is absolutely the worst scenario…during quantitative analysis of imaging end points in clinical trials,” says Jacobs of Parexel. “You can still make a diagnosis based on imaging that has drifted from its original specifications, but to compare progression from one time to another is tantamount to have the machinery calibrated so it appears similar to its original metrics. Very subtle changes in patient and machinery can mimic each other.”
Jacobs concludes that radiology departments probably need to improve the routine inspection of their equipment and procedures. “I would encourage radiology chairmen to audit themselves, either through the ACR or some other mechanism they feel is equal, because the drift in the machinery and change in parameters can go somewhat undetected without phantom work. The phantom allows you to make sure you can recalibrate your imaging equipment to its original state at a later date.”
Departments that engage in routine QC activities will increase their efficiency of operation. Considering the overall cost of medical imaging equipment, and the relative low expense for testing equipment, the department will recognize economic benefit through effective QC programs.
“If you purchase an automobile, and don’t do the tune ups and oil changes, you know you’re going to have problems,” observes Martin J. Ratner, vice president and general manager of Nuclear Associates, an Inovision Company. “Actually [a department] may save a service call and minimize down time by doing routine testing using a test object.”
To produce high caliber images at ALARA (As Low As Reasonably Achievable) dosage, medical imaging facilities must meet standards to monitor and address problems with staff and equipment across all imaging modalities. The American College of Radiology (ACR of Reston, Va.) offers accreditation programs for several imaging modalities including mammography, stereotactic breast biopsy, ultrasound, nuclear medicine and MRI.
Mammography
All facilities that provide mammography must be certified by the FDA under the Mammography Quality Standards Act (MQSA).
“The FDA has approved five accrediting bodies: the American College of Radiology and the States of Arkansas, Iowa, Texas and California,” explains Priscilla Butler, director of breast imaging accreditation programs for ACR. “The law states that in order to legally practice mammography, you must be certified. In order to be certified, you must be accredited by a body that has been approved by the FDA.”
“We are required by the FDA to do random on-site surveys, so we can do that at any time,” Butler concludes.
“Because it is a very demanding imaging procedure, the quality of the mammographic image must be superb or the potential for missing pathology exists,” Spahn says. “All facilities that are providing mammography are following a very regimented quality control program which analyzes all of the potential areas where quality could be degraded.” These programs examine the X-ray generating machine, the processor and it’s function, the storage of X-ray films, and even the view boxes used by physicians to read the films.
“Today, a woman can have a mammogram anywhere in this country and be assured of a good level of quality,” Ratner notes. “There is consistency due to the implementation of a QC program to ensure the optimum performance of the image equipment and staff training.”
One of the most important image qualities in mammography is the level of contrast. High contrast is necessary to detect microcalcifications that may occur in a pre-stage of cancer. As the level of kVp (kilo volt peak) decreases, the contrast increases due to the attenuation coefficient differences between tumor tissue and normal soft tissue of the breast.
“Particularly in mammography, you are tempted to use a lower kVp [the energy of the photons] in order to increase contrast…” explains Carolyn, Kimme-Smith, Ph.D., professor of radiology, UCLA School of Medicine, (Los Angeles). “With a lower kVp, more radiation is retained within the body, so the dose goes up. In order to decrease the dose, you’d want to increase the kVp.”
Kimme-Smith describes the importance of accurately knowing the level of kVp being used and calibration of imaging equipment. Using monitoring equipment supplied by Frank Barker Associates Inc. (Towaco, N.J.), her department measures the effective kVp they use during mammography imaging.
Barker Associates offers the PMX-III PRO Kit QA System that provides test equipment for any X-ray room to measure kVp, with a dose detector, light detector and pre-amplifier for use with image intensifiers. This system can be used with many different radiographic and mammographic configurations.
Tom Johnson, M.D., chief medical officer of U.S. Radiology Partners Inc. (Dallas) explains that several technical procedures are required to meet accreditation standards set by ACR and FDA.
“We take phantom images, using step wedges so we have a known thickness, and then measure output,” Johnson explains. After reviewing processor parameters of temperature and chemicals, the image is examined for noise or scratches or dust particles that might have been inside the film cassette. Finally, “We use equipment that … measures throughput of light that transmits through the film to accurately measure the exact optical density of the films.”
Digital imaging
Digital X-ray imaging offers a potential dilemma. Imaging techniques require extreme accuracy to prevent administering too high a dose of radiation to the patient. With traditional film imaging, overexposure produces a black image, and underexposure results in a film that is too light. With digital imaging procedures, the ability to manipulate the image provides opportunities to clarify questionable areas like never before.
“With digital, which has an extreme dynamic range, you can expose it four times higher than normal and still obtain an image,” says medical physicist Gray. “Technologists learn they can turn up the dose a little bit and no one complains about it. So there is a tendency with digital modalities to use higher exposures than are necessary.”
Conversely, digital imaging can reduce exposure by eliminating retakes. If a mammogram revealed a suspicious dark area, film-based technology would suggest acquiring another image for clarify. “With a digital image, you have the ability to manipulate the data and make that look better so you can see what is going on there,” Gray says.
Spahn agrees, “With a digital system … each exposure gives you a lot more data. The potential for increasing accuracy of diagnosis is improved because there is that much more information captured on every single exposure compared to a film. Up to a million times more.”
The ability to post-process the image through digital technology helps to reduce the number of additional radiographic studies being performed.
“As these [digital imaging techniques] propagate, the potential benefit is to be able to have the radiologist manipulate the images to the ideal window and level so that the exposure to the patient can be minimized while the image quality is optimized in terms of review by the radiologist,” says Jacobs.
Quality control in digital radiography requires a re-evaluation of the procedural chain. “Over the years, there has been a lot of thinking into the systems that have to be checked in order to confirm the best images are being produced,” explains Spahn. “Now you need to think about the things that are important and practical in quality control in film…and you have to translate those to digital or electronic images. The goal is exactly the same. The standards should be based on the same logic that the film concepts were based on.”
“A million images per day are now being produced on computed radiography,” says Spahn, who holds primary responsibility for developing a QC program for CR so that state inspectors and medical physicists are able to test the new equipment to determine if it performs to standard. To accomplish QC tasks, the company developed a new phantom.
“From a single X-ray exposure, the phantom can provide eight important tests in the CR system,” says Spahn. “It also can evaluate the workstations that physicians use to read from, and the laser printers [used to produce any print images].
PACS reduce radiation administered to patient
Besides having equipment that is appropriately calibrated and utilizing digital systems to capture images, there are other factors that can help to eliminate the need for additional imaging procedures. With the advent of PACS, the issue of lost films has become less significant.
“One of the best ways to avoid radiation is to not lose a film,” remarks Jacobs. “The digital environment allows you to store images centrally, and distribute de-centrally and to have a permanent archive that is accessible to all simultaneously.”
Nuclear medicine
“In the case of radiation-detecting instruments such as gamma cameras in nuclear medicine, we perform exams to make sure they are sensitive and are performing optimally to produce high-quality images with as low a radiation dose as possible,” says Gary Sayed, Ph.D., associate professor and chairman of the department of diagnostic imaging at Thomas Jefferson University (Philadelphia) “In a world with no concerns, the more photons you have, the better image you get. But we don’t have that luxury because we don’t want to expose the patient to unnecessary radiation.”
Trends
Currently, the only imaging modality strictly regulated by a federal mandate is mammography. Many have raised the issue that if breast imaging deserves this type of regulation, why not the other imaging modalities that require radiation to capture an image?
Given JCAHO accreditation requirements for inpatient imaging, most radiology departments must engage in QC activities. However, outpatient imaging centers may not undergo such scrutiny. Johnson notes that several large health insurance companies in the country have begun to require accreditation before they will reimburse medical imaging procedures. This trend could have significant impact on whether or not outpatient facilities see the need for accreditation and therefore undergo stringent QC procedures.
Conclusion
Given the importance of medical imaging to the diagnostic process in serious health problems, radiology departments are charged with producing high-quality images at the lowest possible dose of radiation to the patient. QA/QC activities are critical to appropriate performance.
“Quality assurance isn’t only practiced by one person who is designated to do that,” remarks Fuji’s Spahn. “It is the responsibility of everybody in the facility to improve quality on a regular basis.”
