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Equipment safety and risk management.

Because radiographers work in very busy, short-staffed imaging departments, our primary concerns involve performing good patient examinations in a timely manner. Radiographers take it for granted that someone else checks imaging equipment to ensure it's in good working order. However, checking equipment safety is a task that all radiographers should pay attention to because it relates directly to patient care and risk management.

Many agencies, both federal and state, oversee the safety and standard of care patients receive in medical imaging departments, and each agency's requirements contribute to overall safety. The U.S. Food and Drug Administration (FDA) regulates equipment used by health care organizations. States also have regulations and requirements for the installation and use of radiologic equipment. For example, the New Mexico Radiation Control Bureau is the regulatory agency for that state. In Texas, the Texas Department of Health performs similar functions. Each of these agencies has a direct impact on radiographers in the workplace.

By law, imaging departments are required to have quality assurance (QA) and quality control (QC) programs in place. QA programs involve assessing how people in the organization perform their jobs. QA also involves evaluating image quality. QC programs evaluate the radiologic and processing equipment.

This article provides an overview of the laws and agencies that enforce QA and QC standards in radiology departments. Additionally, it reviews the major components of radiologic equipment, required equipment testing and the radiographer's role in maintaining equipment safety. Except for digital fluoroscopy, digital radiographic technology is too complex to cover in this article.

JCAHO's Role

The Joint Commission on Accreditation of Healthcare Organizations (JCAHO), a nonprofit organization that inspects and accredits hospitals, should be a familiar name to hospital radiographers. JGAHO began its mission as the Joint Commission on Accreditation of Hospitals (JGAH) in 1952. (1) Before that, patient treatment fell under the purview of the American College of Surgeons (ACS). In 1917, ACS developed the Minimum Standard for Hospitals to help track patients and determine treatment effectiveness. The requirements filled only 1 page. If a treatment failed or was minimally effective, the hospital would evaluate why that treatment didn't work and change plans accordingly. ACS began inspecting hospitals a year later. In 1918, Chairman Arthur W. Allen formed the JGAH.

In 1953, JGAH assumed responsibility from ACS for inspecting hospitals. It also published the Standards for Hospital Accreditation and began offering an accreditation program for hospitals. Since then, JGAH evolved to evaluate and accredit organizations other than hospitals that deliver health care. To reflect its growing areas of responsibility and changing mission, the name changed to the Joint Commission on Accreditation of Healthcare Organizations in 1987. In addition to hospitals, JCAHO inspects and accredits clinical laboratories, ambulatory care providers, behavioral health care organizations, nursing homes, home care providers and health care networks.

Accreditation by JCAHO is voluntary. Its mission is "to continuously improve the safety and quality of care provided to the public through the provision of health care accreditation and related services that support performance improvement in health care organizations." (2) JCAHO inspects and accredits 16000 health care organizations throughout the United States. Accredited hospitals are reinspected every 3 years.

There are many benefits of becoming JCAHO accredited. One major benefit is that accredited hospitals are recognized as compliant with Medicare requirements and can participate in and receive payments from Medicare and Medicaid programs without any further inspection. Most states also recognize JGAHO-accredited hospitals as being in compliance with state regulations and license them without further inspection. The only states that do not recognize JCAHO accreditation for state hospital licensing purposes are New Jersey and Oklahoma. (3) California coinspects hospitals with JGAHO.

In the past when JCAHO evaluated a hospital, the imaging department had a specific electrical and mechanical checklist to help prepare for the inspection. Beginning in 1992, the Accreditation Manual for Hospitals changed the emphasis from functional standards of patient care to critical focus areas that measure the hospitals actual performance. Since 1995, JCAHO has traced a patient's journey through the health care system. It looks at the hospital's ability to deliver quality care while protecting patients' rights and providing a safe environment in all care service areas.

QA and QC programs are components of a continuous quality improvement (CQI) program. JCAHO introduced the CQI concept to ensure that every employee has a role in providing quality service. QA covers the administrative aspects of patient care and quality outcomes. It is used to describe and evaluate the systems and procedures that ensure quality patient care. Simply put, QA is about people. QC refers to the technical component of QA. In imaging departments, QC is designed to monitor equipment performance affecting image quality and radiation dose.

Equipment satiety directly affects patient safety. Improperly maintained equipment also can affect the outcome of the care patients receive. JCAHO addresses equipment safety in the "Management of the Environment of Care" chapter in the Accreditation Manual for Hospitals. (4) This chapter requires hospitals to have a written plan describing processes used to manage the effective, safe and reliable operation of equipment. JCAHO requires the plan to address 3 main areas. The first is equipment function. The management plan should identify whether the equipment will be used to diagnose, treat, care for or monitor patients. Secondly, the plan must identify the physical risks associated with the equipment use. Finally, any incidents in the history of that type of equipment must be taken into consideration.

Hospitals also must identify their plan for the safe and effective use and maintenance of all equipment in the inventory. The plan should specify inspection, testing and routine maintenance schedules. JGAHO also requires a management plan to include identification and monitoring of equipment recalls and hazard notices. Each x-ray, ultrasound, computed tomography and magnetic resonance imaging machine must have its own equipment maintenance log documenting maintenance history.

The History of Federal Regulations

As mandated by Congress for the protection of health, the FDA regulates almost all items and equipment used by radiographers in diagnostic imaging departments.

The regulation of medical devices in the United States evolved over many years. It began in 1872 with the Postal Fraud Statutes regulating the transportation of food and drugs. Because food and drugs were sent by mail, the U.S. Post Office enforced the statutes. The legislation provided criminal penalties for mail containing false or fraudulent representations, such as "quack" or patent medicines. However, the statutes did not specifically include medical devices, and fraudulent medical devices flourished. It wasn't until 1906, when President Theodore Roosevelt signed the Food and Drug Act, that the United States finally had a national statute to regulate food and drugs. Even so, specific legislation addressing medical devices was left out.

In 1927, the Food, Drug and Insecticide Administration was created. Four years later the name was shortened to the Food and Drug Administration. The FDA recognized the Food and Drug Act's limitations for controlling the availability of medical devices. It monitored these devices and assisted the U.S. Post Office with regulatory actions, but the FDA could not act on its own until 1938 when Congress passed the Food, Drug and Cosmetic (FD&C) Act. In addition to food and drugs, the FD&C Act allowed the FDA to regulate cosmetics and medical devices.

Medical devices as defined by the FD&C Act are "instruments, apparatus and contrivances, including their components, parts and accessories, intended (1) for use in diagnosis, cure, mitigation, treatment, or prevention of diseases in man or other animals; or (2) to affect the structure or any function of the body of man or other animals." (5) The act gave the FDA authority to take regulatory action against the adulteration or misbranding of medical devices. However, the FD&C Act still had limitations in regulating medical devices. Manufacturers determined when they had a "new" drug and were required to notify the FDA before marketing. The FDA could consider the safety of a drag only before it became available to consumers. Because medical devices are not drugs, medical device regulation was limited to challenging products that were adulterated or misbranded after they were on the market.

The revolution in biomedical technology after World War II resulted in a flood of devices on the market. The FDA had limited enforcement resources and was hard pressed to handle the number of fraudulent medical devices introduced. In 1955, a Citizen's Advisory Committee concluded that false claims for medical devices were being made frequently. The committee also concluded that the FDA needed additional resources to address the problem. Seven years later the Drug Amendments of 1962 were passed.

Political negotiations to ensure rapid passage of the legislation resulted in the dropping of provisions that addressed medical devices from the bill. Even though medical devices in particular were omitted, the Drug Amendments of 1962 became the foundation for medical device regulation. The amendments required drug manufacturers to obtain premarket approval from the FDA before introducing a new drug to consumers. Approval of a new drag now was based on its effectiveness and safety. Using the Drug Amendments of 1962, the FDA was able to successfully regulate some medical devices by defining them as drugs. However, for most medical devices, the FDA still could react to hazardous devices that injured patients only after they were on the market.

During this time, the public expressed concerns about the possibility of excess radiation exposure from color television sets, microwave ovens and other electronic products. Congress responded by passing the Radiation Control for Health and Safety Act of 1968. This law is meant to protect the public from unnecessary or unintended exposures to radiation by electronic products, whether the devices are medical or consumer products. It gives the FDA the ability to develop and enforce performance standards for diagnostic x-ray equipment, medical lasers and ultrasound therapy equipment.

In 1976, Congress finally acknowledged that treating medical devices as drugs was not effective. President Nixon authorized the Cooper Committee to study medical device safety. The committee also was charged with recommending a procedure for premarket regulation of devices and considering the need for new legislation. The committee issued a report in 1970, stating that it was "distressed by the lack of data in many areas related to the interaction of medical devices with the human body, and by seeing the unquestioning acceptance of claims for medical device safety and performance unsubstantiated or inadequately supported by scientific fact." The report documented 10000 injuries from medical devices and 731 deaths. (5) The committee decided that regulating medical devices as new drugs was unacceptable and recommended legislation that specifically addressed the safety and effectiveness of every medical device. It also recommended an inventory of all medical devices already on the market and division of medical devices into a 3-tiered classification system.

As a result of the Cooper Committee recommendations, the Department of Health and Human Services (DHHS), formerly the Department of Health, Education and Welfare, prepared legislation. The FDA, a department within DHHS, created a medical device advisory panel. An inventory of medical devices was taken and preliminary classification began. Congress passed the Medical Device Amendment in 1976. This legislation changed the FDA's regulatory authority over medical devices by empowering the FDA to require proof of the safety and effectiveness of a medical device before the device is allowed in the marketplace. The manufacturer of a medical device must demonstrate its safety and effectiveness through valid scientific evidence before receiving FDA approval to market it.

The current definition of a medical device under the FD&C Act, Title 21 USC (United States Code) is: (5) an instrument, apparatus, implement, machine, contrivance, implant, in vitro reagent, or other similar or related article, including any component, part, or accessory, which is: (1) recognized in the official National Formulary, or the U.S. Pharmacopeia, or any supplement to them, (2) intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease in man or other animals, or (3) intended to affect the structure or any function of the body of man or other animals, and which does not achieve its primary intended purposes through chemical action within or on the body of man or other animals and which is not dependent upon being metabolized for the achievement of any of its primary intended purposes.

The classification system developed by the FDA advisory panel addresses the various degrees of complexity and potential risk of medical devices. Class I devices pose the least risk and have general controls addressing good manufacturing practice, prohibiting distribution of adulterated or misbranded devices and requiring registration by manufacturers and distributors. Class II devices are subject to general controls and additional special controls to ensure the device's safety. Requirements may include patient registries, postmarket surveillance, guidance documents for device testing or other requirements to ensure device safety and effectiveness. Class III devices pose the greatest risk to patients. If the safety of a device cannot be assured using class I or class II controls, it is designated class III. Table 1 shows the classifications of some medical devices commonly used in imaging departments.

Postmarket problems with devices such as heart valves, intraocular lenses and intrauterine devices led to the passage of the Safe Medical Devices Act (SMDA) in 1990 and the Medical Device Amendments in 1992. These laws give the FDA authority to monitor medical devices after they are released to the public. The Safe Medical Devices Act provides for postmarket surveillance and tracking. The laws also require user and distributor medical device reporting. As a result, the premarket approval process takes less time so new devices are available sooner than was the case before 1990.

Medical device reporting provides a way lot the FDA and manufacturers to detect problems with devices in a timely manner. If the use of a device causes death, hospitals are required to report the incident to the FDA and the manufacturer. Hospitals also must report serious injuries resulting from the use of a medical device. Serious injury reports are scull to the manufacturer or, if the manufacturer is unknown, to the FDA. SMDA also requires a semiannual summary of all reports involving device-related death or serious injuries. (6)

The Center for Devices and Radiological Health (CDRH) is the primary arm of the FDA that oversees devices used in radiology departments. The Nuclear Regulatory Commission shares regulatory responsibility with CDRH for radiologic devices. States also have statutes regulating radiologic equipment. It's more common lot imaging departments to get the necessary permits, licenses or certificates of registration through the state department that regulates radiation safety and equipment. However, the FD&C Act prohibits state governments from creating or enforcing medical device regulations that differ from federal requirements. State and local regulations apply when there are no specific federal regulations.

State Requirements

Every state has an agency responsible for overseeing the registration and use of radiologic equipment. State regulations lot the installation and use of radiologic machines are based on federal regulations found in the Code of Federal Regulations (CFR). The names of the state agencies and the departments to which they belong vary from state to state. Management personnel should know the proper state agency and be familiar with their state's regulations.

State agencies keep an inventory of all radiologic machines in the state. Each new installation requires an application for a certificate of registration. The application must identify who owns the radiologic equipment, the physical address of its location and the model and serial number. Other information may be required, such as the specific room containing the machine, a scale drawing of the room including the lead equivalence in the walls, ceiling, floor and doors, and what type of service will be provided or the name of the company contracted to service the unit. If the facility remodels and moves an x-ray machine from one room to another, the state may require the facility to update its certificate of registration with the change of the machine's location. There is a deadline for notifying state agencies of a change or addition of radiologic equipment. For example, in Texas, the Bureau of Radiation Control requires notification within 30 days, unless the unit is being used for clinical trial evaluations or is a loaner or demonstration model. Then the hospital can use the machine for tip to 60 days before adding the machine to its certificate of registration. Likewise, if a machine is retired, written notification is required.

Before new equipment can be used it must be inspected and tested. Imaging centers must have on staff or contract with a qualified, licensed medical physicist to test equipment. The physicist tests equipment to determine whether it is operating within legal parameters. State inspectors also may be required to perform these functions, depending on state regulations. Radiologic equipment must he tested annually after the first acceptance. Some states accept the medical physicist's report tot their annual inspection requirements; other states require state inspectors to physically visit the site.

X-ray machines function for a long time, but eventually they must he replaced. When the service engineer removes an x-ray tube from service, the appropriate state agency must be notified. The service engineer must document how the tube was disabled so that it cannot be resurrected if someone tries to reconnect it to a power supply. If the unit is replaced with an upgrade and sold to another facility, this information must be included in the notification. The new owner must apply for a certificate of registration because the registration is not transferable. The hospital or imaging center is responsible for submitting to the state the documentation and request to remove a particular x-ray machine from the certificate of registration.

The Basics of Quality Control

Most state regulations require QC programs, and JGAHO only accredits facilities with an imaging department if a QA/QC program is in place. A good QC program involves the medical physicist, service engineer and a designated QC coordinator. The medical physicist must meet qualifications for state licensing. A service engineer may not need a license to repair radiologic equipment, but some states require certain education for those working on x-ray machines. In addition, most equipment vendors and service companies require their service engineers to fulfill in-house educational requirements. A QC coordinator should have the necessary continuing education to evaluate radiologic equipment and automatic processors.

A QC program consists of 3 steps. The first step is acceptance testing of new equipment. This testing should be performed before the machine is used clinically. Next, there should be a routine performance evaluation. As equipment is used, it may deteriorate or malfunction. Animal evaluation and routine maintenance based on the manufacturer's recommendations should keep radiologic equipment in good working order. Finally, a correction protocol should begin whenever any problems are detected with the equipment.

The American College of Medical Physics and the American Association of Physicists in Medicine have developed guidelines for testing radiographic equipment. Seven tests are performed on each x-ray machine in a department to ensure each complies with the guidelines. The tests are for filtration, collimation, focal-spot size, kVp calibration, exposure timer accuracy, exposure linearity and exposure reproducibility. A licensed medical physicist performs these tests when the machine is newly installed and at least once a year thereafter. If a major component of the unit is replaced or recalibrated, the machine must be tested again to confirm it is operating within acceptable parameters. When an x-ray machine passes annual testing, the medical physicist places a certificate of radiation safety label on the control panel as 1 form of documentation, lie or she also issues a written report for each machine tested.

Although a medical physicist conducts performance evaluations, the radiographer can further reduce risk of a mishap by practicing a regular safety procedure. The components of a radiographic imaging system are the generator, x-ray tube, filter, collimator and x-ray table, image receptor and film processing system. Following is an overview of these components and the tests and routine safety steps all radiographers can perform.

X-ray Equipment Components

Generator

The x-ray generator provides electrical power for the x-ray tube and other parts of the machine and performs several other functions. It allows the radiographer to select kVp, mA and exposure time (mAs), and the appropriate focal spot size for the exam. The radiographer also chooses manual or automatic exposure timing. Using the step-up transformer, the generator increases low voltage supplied by the utility, company to the high voltage (kV) required for x-ray production. The step-down transformer decreases high current from a utility company to milliamperage (mA), which determines the quantity of x-rays produced. X-ray robes require direct current, allowing electrons to flow from the cathode to the anode. Using a series of rectifiers, the generator converts the alternating current from a utility provider to direct current for the x-ray tube.

The generator has built-in safety mechanisms to protect both patients and radiographers. It safeguards the x-ray tube from any combination of kVp and mAs that could result in an electrical overload. It also is insulated to protect against electrical shock from the high voltage used to produce the x-ray beam. This prevents the x-ray tube from reaching its heat-loading capacity, particularly in examinations that require a series of exposures, such as angiography procedures. The generator has fail-safe mechanisms built into the circuitry to prevent excessive exposure due to a faulty automatic timer, and it has a service module in the system that identifies a problem with the generator itself.

There are several types of generators on the market, including single-phase, 3-phase, constant-potential and high-frequency generators. Each generator consists of the same components, but they differ in complexity, cost and efficiency in producing x-rays. Three-phase and high-frequency generators are most common in radiology departments. (7)

The medical physicist performs several tests to check the generator, including kVp accuracy, exposure timer accuracy and exposure linearity. Generators should be calibrated to correctly deliver the amount of kVp chosen. Medical physicists can select from several devices, such as filtered ion chambers or filtered photo diodes, to test kVp accuracy. Oscilloscopes or voltage diodes are more accurate, but require more time to evaluate the x-ray tube. The kVp delivered during an exposure must be within [+ or -] 5% of the selected kVp. For example, when 80 kVp is selected, the measured value must fall between 76 and 84 kVp to be within acceptable parameters. According to medical physicist Stewart Bushong, a variation of 2 to 3 kVp affects patient dose and the linage optical density. (8)

The accuracy of the exposure timer must be tested annually. The length of exposure time is under the radiographer's direct control. He or she can set the exposure time manually or use the phototimer. Patient dose is directly related to exposure time, so this test is very important. If a timer problem is suspected, the radiographer can perform the spinning top test for single-phase generators. For 3-phase or high-frequency generators, the synchronous spinning top is used. Medical physicists use more sophisticated equipment that measures exposure time based on radiation acquisition by an ion chamber or photodiode assembly. Accuracy should be within [+ or -] 5% for exposure times greater than 10 milliseconds. For exposures less than 10 milliseconds, an accuracy of [+ or -] 20% is acceptable.

Phototimers are designed to provide a constant image density regardless of the thickness of the body part. They are evaluated using various thicknesses of aluminum or acrylic between the x-ray beam and image receptor. The resulting images should have the same optical density, reading regardless of the absolute exposure time. The backup phototimer also must be tested in case the principal phototimer fails. Testing involves inserting a lead filter and making an exposure. The backup timer should stop the exposure at 6 seconds or 600 mAs, whichever happens first.

Exposure linearity is a term used for the radiographic unit's ability to produce a constant radiation output for the same mAs using different combinations of mA and time. A radiation dosimeter is used to measure radiation intensity. The linearity should be within [+ or -] 10%.

Exposure reproducibility is another required annual test. When the radiographer selects a particular combination of kVp, mA and exposure time, the image density and contrast should be constant every time. The test consists of making a minimum of 3 exposures using the same technique factors, with the medical physicist changing the factors between exposures. The test results should be within [+ or -] 5% of each other.

X-ray Tube

Another important component in radiographic imaging systems is x-ray tubes. (See Fig. 1.) These comprise the cathode assembly, anode assembly, rotor, tube envelope and tube housing. The cathode assembly is a tungsten filament positioned in a metal focusing cup. Tungsten has a melting point of 3410[degrees] C, and an atomic number of 74. The filament circuit heats the filament with 3 to 6 amps, "boiling off" electrons by thermionic emission. Over time, tungsten can vaporize and cause a buildup inside the tube envelope. This buildup eventually causes the electrical balance in the robe to shift, resulting in arcing. Tungsten vaporization is the most common cause of tube failure. To help prevent this and prolong tube life, a layer of thorium coating is applied to the tungsten filament, increasing the efficiency of thermionic emission. Another factor in x-ray tube design to help prevent arcing is the choice of material for the envelope. Glass was used originally, but it is susceptible to tungsten buildup. A combination of glass and metal or full metal envelopes have replaced glass.

[FIGURE 1 OMITTED]

Most x-ray tubes have 2 filaments in the focusing cup. The large filament is used for exams that require high output intensity for a short time, such as abdomen and chest radiographs. The small filament is used when detail on the image is important. The focusing cup is negatively charged and focuses the electrons on the focal spot on the anode. The flow of electrons from the negative cathode to file positive anode is the mA or tube current. The x-ray beam is directly proportional to the mA. When mA is doubled, the quantity of photons increases by a factor of 2. Patient dose also increases by a factor of 2 when the mA is doubled. Radiographers can choose between 50 mA to 1000 mA for exams. Fluoroscopic mA is approximately 0.1 mA to 3.0 mA.

The anode can be stationary or rotating, and is angled from 5[degrees] to 15[degrees] to produce a small effective focal spot and a large area for heat. This is called the line focus principle. As the angle is increased, the size of file image field increases. The focal spot on the anode is the area where the electrons from the cathode strike. There is a large and a small focal spot. The small focal spot is used when better detail in the image is important. The large focal spot can tolerate higher exposure factors and has higher heat capacity. For example, high mA and short exposure time can be used with the large focal spot. A stationary anode has a limited capacity for heat loading and x-ray output. The rotating anode overcomes these limitations.

Anodes formerly were made from pure tungsten. In today's state-of-the-art x-ray tubes, the anode is a compound disk: Two or more metals form the base body. The electrons strike a coating layer added to the base. A typical compound anode has a molybdenum, graphite or combination molybdenum and graphite base coated with 90% tungsten and 10% rhenium. This anode is referred to as a rhenium-tungsten-molybdenum (RTM) disk. Compound disks are lighter, have greater heat storage capacity and allow the use of higher technique factors.

The tube envelope supports the cathode and anode. It maintains a vacuum so the filament does not oxidize and cause tube failure. The x-ray beam leaves the tube through an exit window. The window is thinner than the rest of the envelope and provides inherent filtration for the beam. The tube housing surrounds the envelope, providing support and insulation. Oil is used between the housing and envelope for electrical insulation and heat dissipation. Lead sheets line the interior of the housing to prevent radiation leaks. High-voltage cables from the generator connect to 2 receptacles in the housing.

Testing of the focal spot consists of measuring the focal spot size. Tiffs lest is performed when the equipment is new or when an x-ray tube is replaced and then annually thereafter. A qualified QC radiographer or medical physicist can perform the test. Measurements are taken using the pinhole camera, the star pattern or the slit camera, which is the tool of choice. The focal spot size can vary up to 50% of the manufacturer's stated size. If the variance is greater, then the tube should be replaced.

Misuse of the x-ray tube can reduce its life. When deciding on technique factors, the radiographer can take the following steps to prolong the life of the tube:

* Avoid using a single excessive exposure. This can overheat the anode, causing it to melt or pit. Extremely high temperatures can cause tungsten to vaporize, which in turn could cause the tube to arc, and the anode could crack. If the x-ray tube has not been used for 45 minutes, a tube warm-up procedure can reduce the likelihood of tube failure.

* Avoid using long exposure times (ie, 1 to 3 seconds). This also causes the anode to overheat, damaging the anode and the bearings in a rotating anode assembly.

* Avoid ruing high mA. Over time high mA techniques vaporize the tungsten filament, leaving deposits and possibly causing arcing. The filament becomes thinner and breaks. X-ray tube manufacturers provide a tube rating chart and cooling curves. This chart should be posted in or near the operator's booth. Consulting a tube rating chart mad cooling curves helps prevent the radiographer from choosing techniques that overheat the x-ray tube. Using technique charts also prevents excessive exposures.

If problems occur while making all exposure, the radiographer should write down the error message gone appears on the console screen. The error message tells the service engineer where in the system the problem may be. If no error message is displayed, the radiographer can help the service engineer by documenting exactly what happened when the problem occurred.

Filtration

Filtration for an x-ray beam is the most important factor in protecting patients from excessive radiation. Metal filters are built into the path of the primary beam to filter out low-energy x-rays that would be absorbed lay superficial tissues rather than passing through the patient to the film. Federal regulations require the use of filters in general purpose radiographic units, and the National Council on Radiation Protection (NCRP) defines the guidelines for the amount of filtration. To meet the minimum total filtration of 2.5 millimeters aluminum equivalent, additional filtration is added to the x-ray tube. To evaluate the filtration, the half-value layer (HVL) is measured. The value of the HVL changes depending on the operating kVp used. For example, the HVL for:

* 50 kVp is 1.2 mm aluminum.

* 70 kVp is 1.5 mm aluminum.

* 90 kVp is 2.5 mm aluminum.

The filtration is tested annually.

Collimation

Collimation restricts the size of the x-ray beam by moving pairs of lead leaves. The collimator gives the radiographer the ability, to choose the correct field size for the exposure. By restricting the field size to the image receptor size or smaller, scatter radiation is reduced and, therefore, the radiation dose to the patient also is reduced. The size of the field can be set manually using the markings on the front of the collimator. Collimation is adjusted according to the source-to-image distance (SID), and collimators can be automatic or manually controlled.

Automatic collimators work in a manner similar to manual collimators. The automatic collimator also is referred to as positive beam limiting device (PBLD). The PBLD is used in conjunction with a Bucky tray. The shutters are controlled by electric motors rather than manually. The cassette tray uses electronic devices that sense the size of the cassette when it is latched in place. The electronic sensing device then is activated and automatically adjusts the shutters to the size of the film. Automatic collimators are accurate to within 2% to 3%. (9)

The beam-centering device on the collimator plays a significant role in preventing image distortion. The centering device is the most vulnerable part of the collimator because it allows the radiographer to accurately place the beam over the center of the patient's anatomy. A light housed ill the collimator allows beam centering. The light is reflected by a mirror mounted at a 45[degrees] angle in the center of the collimator. Light rays striking the mirror are reflected through the shutters and represent the borders of the beam.

The beam alignment test shows whether the alignment of the light duplicates the alignment of the primary beam. Bushong(8) recommends testing collimation semiannually. Several tools are available tot testing the collimation, or it can be performed using a 14 x 17-inch cassette and metal markers. The light beam is opened to allow a 2-inch unexposed border around the edge of the cassette. The corners of the light beam are marked with metal markers placed on the cassette. The very, center of the light beam, indicated lay the crossbar in the collimator, is marked on the cassette using a right or left marker. The cassette then is exposed using 2.5 mAs and 55 kVp.

The radiographer determines from the metal markers on the test radiograph if the light beam is identical to the primary beam. If the collimator beam is off alignment by more than [+ or -] 2% of the source-to-image receptor distance (SID), additional anatomy is exposed with resulting overexposure of the patient. Service engineers are qualified to properly adjust the collimator.

Fluoroscopy Unit Components

General radiographic units produce stationary images. Fluoroscopy is a dynamic exam used to evaluate the function and structure of organs. The highest radiation doses result from fluoroscopic exams. The average entrance skin dose is .03 to .05 Gy (3 to 5 rad) per minute, and up to a total of .1 Gy (10 rad) per exam is common. Properly maintaining fluoroscopic equipment can keep patient doses within legal limits. In a conventional fluoroscopic unit the main components are the x-ray tube, image intensifier, closed-circuit television and an image-recording device.

The x-ray tube in a conventional fluoroscopy refit produces x-rays continuously for viewing real-time images. Some units use pulsed fluoroscopy instead. In pulsed fluoroscopy, x-rays are produced in short bursts. Pulsed systems can reduce patient dose lay 90% when they deliver fewer than 10 pulses per second.

The image intensifier tube converts x-ray photons from the patient into light photons and transmits the image to a closed-circuit television system for viewing. An image distributor is coupled with the intensifier to distribute the light photons between the television camera or charge-coupled device (CCD) and the photospot film camera. In portable fluoroscopic systems, fiber optics are used to couple the image intensifier with the television camera or CCD. Fiber optics are compact and allow easy handling of the image intensifier in mobile situations.

The closed-circuit television comprises a television camera or CCD, a coaxial cable, a signal electronics unit and a television monitor. In modern fluoroscopic units, the television camera has been replaced with a solid-state CCD. The advantages of the CCD are uniform resolution over the entire image and low readout noise. Both the television camera and the CCD convert the light photons from the image intensifier into a video signal. The coaxial cable connects the CCD to the television monitor. The television monitor converts the video signal into a fluoroscopic image viewed by the radiologist.

To record a particular image, the system has either a spot-film device or a photo-spot camera. The radiographer manually loads the spot-film device with a cassette. The radiologist records the image using a variety of formats by collimating the beam. Spot-film devices record the best image quality of all the image-recording modes, but use the most radiation. Another disadvantage of the spot-film device is that it increases the length of the exam due to the time required to change cassettes. Using the photo-spot camera eliminates this problem.

The photo-spot camera uses film sizes from 90 to 105 mm. The exam time is shorter because it is not necessary to load and unload cassettes. The x-ray tube experiences less heat loading because low mA and high kVp are used. The radiation dose is about 2 to 3 times less than images taken with a cassette spot-film device.

All fluoroscopic image systems have an automatic brightness control (ABC). ABC controls the mA and kVp to maintain a constant brightness on the TV monitor. ABC has a sensor placed in the intensifier. The sensor connects to the generator, allowing adjustment of the technique factors when the x-ray beam moves from thicker anatomy to thinner anatomy. As a result, the dose rate to the patient is reduced.

Digital fluoroscopy uses a computer to process the video signal from the TV camera or CCD. Digital fluoroscopy systems have an x-ray tube and generator, image intensifier, CCD camera or TV camera tube, an analog-to-digital converter, a computer system, an operator's console and a laser camera or printer.

The x-ray tube in digital fluoroscopy produces x-rays in rapid pulses. Higher mA values are used than in conventional fluoroscopy tubes. Three-phase or high frequency generators are necessary to produce the rapid pulsing, which can be as short as 1 millisecond. The rate at which images are recorded can be 1 per second to 10 per second. The TV camera or CCD unit must be able to produce a high signal-to-noise ratio, meaning low noise. The analog-to-digital converter (ADC) is positioned between the TV camera tube or CCD and the computer. The ADC takes the video signal and converts it into digital data for the computer. The computer is a minicomputer system able to perform complex calculations rapidly. It processes the digital data from the ADC to produce a digital fluoroscopic linage viewable on the TV monitor: The image can be stored on optical disks or printed on film using a laser camera. The laser camera, also known as a laser film printer or laser imager, writes the data from the computer onto single-emulsion film. The control console allows the radiographer to perform image processing operations using alphanumeric keys. The images are viewed on a monitor on the console.

Fluoroscopy systems are tested annually. The medical physicist performs many tests including filtration, focal spot size, kVp accuracy, mA linearity, exposure reproducibility, grid uniformity and alignment, automatic brightness control, maximum exposure rates, resolution (spatial and contrast) and television monitor performance. Federal law mandates that the entrance skin dose rate cannot exceed 10 R per minute under normal operating conditions. Tiffs test should be performed semiannually. The physicist also must test the cassette spot-film device or the photo-spot camera for entrance skin dose rate. The ABS is tested using phantoms of various thicknesses to ensure that the maximum rate is not exceeded. The television monitor resolution is determined using a copper mesh test pattern. For a 23 cm (9 inch) intensifier coupled with a standard TV system, 20 to 24 mesh holes per inch must be visible in the middle of the display and 20 at the edge.

Although most radiographers do not perform the above tests on fluoroscopy units, they should visually inspect the unit at least every 6 months. Radiographers should inspect the fluoroscopic tower, table locks, protective lead curtain, exposure switch, compression device, collimator shutters, table angulation and motion, Bucky slot cover and fluoroscopic cumulative timer. By law, the cumulative timer cannot exceed 5 minutes. When 5 minutes is reached, an audible alarm sounds until the timer is reset.

Other Common Devices

Portable Equipment

Other common medical devices radiographers use are portable x-ray machines and portable fluoroscopy units. The general requirements for a portable x-ray machine are:

* Small size.

* Wheels for maneuverability.

* Brakes allowing the radiographer to immobilize the machine.

* Power outlets providing 120-volt, 15-ampere power to charge batteries.

* Radiation output sufficient to image the entire body.

* Constant, ripple-free voltage to the x-ray tube from a generator.

* Rotating anode allowing higher mA and short exposure times.

* Central column providing support and counterbalance for the x-ray tube. It should allow enough movement to position the x-ray tube however necessary.

* Control console allowing the radiographer to turn the machine on and off, check the battery charge, set technique factors and make an exposure.

* Exposure switch with a coiled cord allowing the radiographer to stand 6 feet away. The switch is a "dead man's" switch requiring constant pressure to make an exposure.

Portable x-ray machines are powered by nickel-cadmium batteries, which should be plugged in when not in use to keep them charged. Some slates have regulations mandating that there be a battery charge indicator on the control panel so the radiographer can check the battery charge visually.

Mobile fluoroscopy units have a C-arm supporting the x-ray tube and intensifier. The C-arm is designed so the patient Call be placed between the x-ray tube and intensifier. It has a wide range of movement, allowing the radiographer to position the machine vertically, horizontally, at all angle, or panning as needed during the exam. Like a stationary fluoroscopy unit, the mobile unit bas a closed-circuit TV chain that includes a CCD camera, coaxial cable, TV control electronics and TV monitor. Usually there are 2 TV monitors, one for recording the current image and a second to store the previous image. Images can be permanently recorded by either using a cassette attached to the intensifier or with a multiformat camera. Mobile fluoroscopy units have automatic brightness control systems to adjust the mA and kVp, compensating for different body part thicknesses.

Radiographers should routinely inspect portable x-ray and fluoroscopy machines, checking for the integrity of locks, brakes, front safety brake, electrical cord and plug. The medical physicist performs the same annual tests on mobile units as on stationary radiographic equipment.

Processors

The processor is an integral part of every imaging department. Excellent radiographic films can be ruined if the processor is not maintained. Four activities make up the processor QC program: chemistry, cleaning, maintenance and monitoring. The correct pH, replenishment rate, temperature, processing time and specific gravity contribute to good film quality. Cleaning crossover racks daily and the rack weekly helps to eliminate processing artifacts on films. A processor preventive maintenance program optimizes performance. A charted daily densitometry measurement will give an early warning for processor problems. (See Table 2.)

Other equipment common to imaging departments includes the automatic contrast injector, manual or electronic blood pressure cuff, defibrillator and stretchers. Routine maintenance recommended by the manufacturer and provided by a service engineer or biomedical engineer should be followed and documented.

Equipment Labeling Requirements

DHHS requires that various labels be placed on all radiographic equipment, and the manufacturer is required to affix a label stating that the equipment complies with 21 CFR Subchapter J regulations in effect at the time of manufacture. The labels list the date of manufacture, company name and address, model number and serial number of the equipment. Labels are permanently attached to each component of radiographic units. They can be found on the front of the control panel, the generator, the x-ray tube housing and the power supply cabinet. A warning label stating "the x-ray unit may be dangerous unless sale exposure factors and operating instructions are observed" must be on the front of each control panel. In addition, the medical physicist fills out and affixes a certificate of radiation safety label with the testing date confirming that the equipment passed the required tests. These labels should be checked periodically for legibility.

Use and Care of Screens and Cassettes

In a busy radiology department that uses film, cassettes are the primary tool, after the x-ray unit, for producing quality images. Cassettes are used over and over and are subject to considerable abuse. How the cassettes and the intensifying screens inside are maintained contributes to how much radiation a patient receives and the quality of radiographic images.

The cassette is the holder that protects the intensifying screen and the film. Because less than 1% of the x-ray beam contributes to the latent image on film, intensifying screens are placed in the cassette to increase efficiency by converting the x-ray beam to visible light. As a result, approximately 30% of the x-ray beam striking the screen produces visible light to create a latent image on the film. Intensifying screens' ability to amplify the radiation reaching the film means that the dose to the patient is less than when cassettes without intensifying screens are used.

Two types of screens are used in cassettes. The most common is the rare-earth screen, introduced in the 1970s. Less common now are calcium tungstate screens. Intensifying screens are manufactured in the same sizes as film, and they resemble flexible sheets of plastic. Screens are composed of 4 layers: the base, the reflective layer, the phosphor layer and the protective coating.

The base is the furthest layer from the film. It serves as a mechanical support for the phosphor layer and is constructed of flexible, high-grade polyester or cardboard. The base must not discolor with age, be susceptible to radiation damage or contain impurities that could appear on the image.

Calcium tungstate screens require a reflective layer to produce a good latent image on the film. The reflective layer is between the base and the phosphor layer. It is made of either magnesium oxide or titanium dioxide and is shiny. When x-rays strike the phosphor layer, light is emitted in all directions. Less than half of this light reaches the film. The reflective layer intercepts and redirects the light toward the film. Because of the reflective layer, the amount of light reaching the film doubles, resulting in increased efficiency. Rare-earth screens emit light much more efficiently and do not need a reflective layer.

The phosphor layer is the active layer in the intensifying screen. When x-rays stimulate the phosphor layer, it converts the x-rays' energy to visible light. Calcium tungstate was the phosphor of choice until rare-earth screens became widely available. The rare-earth phosphors are gadolinium, lanthanum and yttrium. The term "rare earth" refers to the fact that they are difficult to refine, not that they are rarely found on earth.

Rare-earth screens replaced calcium tungstate screens because they convert x-rays to light more quickly and efficiently. Although it is possible to manufacture high-speed calcium tungstate screens, the sharpness of the image deteriorates as the screen's speed increases. Rare-earth screens, on the other band, are so efficient in converting x-rays to light that there is little or no loss in image sharpness. Because less exposure is needed to produce a latent image on the film, radiation exposure to the patient is reduced.

The protective coating is a cellulose layer applied to protect the phosphor layer. It also reduces static electricity caused by the movement of the film across the screen. It provides a surface that can be cleaned without damaging the phosphor layer.

To continue producing high-quality radiographs, screens must be cared for properly. Intensifying screens need the maximum amount of care during handling. Reasonable precautions must be taken so artifacts are not introduced onto the screen, thereby degrading image quality. When loading a cassette, avoid sliding the film across the screen. The film may scratch the screen, creating an artifact. When removing the film, avoid using your fingernails to dig the film out. Instead, rock the cassette on the hinged edge and let the film fall to your fingers. Digging the film out can leave a kink mark on the film or can scratch the film or screen. Leave the cassette open only lung enough to unload the exposed film and reload. Dust and fumes from darkroom chemicals can cause screens to deteriorate. Leaving cassettes open for long periods of time allows dust or other particles to settle on the screens, creating artifacts.

Screens should be touched only when they are cleaned. How often screens should be cleaned depends on the frequency of their use and the amount of dust in the environment. Mammographers must clean screens at least once a week. General radiology departments should set a cleaning schedule based on how busy they are. At a minimum, screens should be cleaned once a month. Clean screens carefully, following the manufacturer's directions. Use only cleaning products recommended by the manufacturer. A cleaning product with antistatic compounds helps reduce static artifacts on radiographs.

Cassettes are made to withstand heavy, use. But however sturdy they seem, cassettes are precision pieces of equipment and should be treated accordingly. Over time, abusing cassettes with rough handling decreases their useful life and results in lower quality radiographs. Loose, bent or broken hinges or latches can cause poor film- screen contact, as can a cracked or sprung cassette frame. Other causes of poor film-screen contact are warped screens due to excessive moisture and warped cassette fronts. Poor film-screen contact can cause repeat films or, if the image quality is compromised enough, misdiagnosis.

Radiographers can check film-screen contact using a wire mesh device. Place the wire mesh on the cassette and expose the cassette at 50 kVp at 5 mAs and an SID of 100 cm. Stand 2 to 3 meters away from the viewbox to optimally view the radiograph. If blurred or cloudy areas are visible, the film-screen contact is compromised and the cassette should be replaced or repaired.

Properly maintained intensifying screens last indefinitely. The phosphor layer does not wear out. Mishandling and improper maintenance are the principal reasons screens require replacement. The radiographer's job is producing high-quality radiographs with minimum patient exposure; maintaining screens and handling cassettes as precision equipment go far in achieving those goals. Legal requirements for patient safety in imaging departments also are met.

Care and Testing Of Radiation Protection Devices

Other pieces of equipment radiographers may take for granted are lead aprons. Proper handling of lead aprons protects radiologists, radiographers and patients. Aprons allowed to crumple on the floor or left folded in half develop cracks in the lead. These cracks allow radiation to leak through to the person wearing the apron, resulting in an unwanted radiation dose. Lead aprons, gloves, gonad and thyroid shields must be tested annually.

The best method for testing the integrity of lead protective devices is to x-ray them to check for leaks. Lead shields or aprons must be visually inspected for cracks, tears or holes. If a lead apron or shield is found to be detective, it must be repaired or replaced. A log documenting annual testing of all lead protective devices must be kept. JCAHO or state inspectors may ask to see this log to confirm the integrity of lead protective devices and that the imaging department is maintaining the required level of radiation safety.

Maintaining Hallways and Rooms

Another safety area imaging departments should address is hallway and room clutter. Stretchers and wheelchairs should be stored in a designated storage area, not in a hallway used to bring patients into the department. Boxes of supplies should be put away as soon as possible to keep hallways and rooms clear. Old and retired equipment should be disposed of properly and not left in a corner. Hallways used as storage areas are a safety violation. The local fire marshal inspecting a facility will write up obstructions to possible evacuation routes.

JCAHO inspectors look at the ingress and egress of the imaging department with patient safety as the primary consideration. If a hallway is cluttered, maneuvering a stretcher or wheelchair with a patient into an x-ray room is a safety issue.

The first thing a radiographer can do at the beginning of each shift is visually inspect the x-ray machine. When turning the machine on, check to make sure the circuit breaker for that room is on. If the machine does not turn on, the circuit breaker may have been deliberately turned off or tripped. Look to see if the cables are in good condition. Move the x-ray tube along its track to see if the movement is unobstructed. Check the x-ray table and Bucky tray to make sure they are clean and in good working order. The radiographer should confirm that the footrest on the table is locked into place before standing a patient upright. Other equipment such as cassette holders used for cross-table laterals and handholds for tables, if available, also should be inspected routinely to ensure they are safe to use.

In addition to inspecting the equipment, rooms should be inspected lot potential hazards. If the footrest is taken off the table, it should have a safe stop age place, out of the traffic pattern. Other equipment such as grid caps, positioning sponges, cassette holders and hand-held compression devices used during fluoroscopy exams need to be clean and stored in their proper place. If these accessory devices aren't stored properly, they could be damaged. Damaged equipment could contribute to repeat films or even endanger a patient. Also, a cluttered radiographic room looks unprofessional.

Conclusion

Many federal and state laws regulate the use of radiographic equipment. The radiographer's familiarity with radiographic equipment is the first line of defense in radiographic safety. At a minimum, diagnostic imaging departments must maintain the following information for each x-ray machine:

* Maximum rating of technique factors.

* Model numbers of all certifiable components.

* Aluminum equivalent filtration of the useful beam, including any routine variation.

* Tube rating chart and cooling curves.

* A record of surveys, calibrations, maintenance and modifications performed on the machine.

A qualified medical physicist must test all radiographic equipment annually. Testing the physics of the equipments' major components may not be within radiographers' expertise, but they can do much to help ensure the equipment is safe and reliable. The radiographer's role in equipment safety is to routinely inspect all equipment for physical defects and functionality and report any problems. By using a tube-rating chart and avoiding excessive exposure techniques, he or she prolongs the life of the radiographic unit. Properly maintaining intensifying screens reduces the chance of repeat films and possible misdiagnosis due to poor-quality films. Processor QC is a very important link in producing good radiographs and must not be overlooked. Patient safety is addressed when hallways and rooms are free of clutter, ensuring safe ingress and egress as well as preventing trips.

Taken holistically, all of the above help to ensure patient safety, regulatory compliance, equipment longevity and a smoother functioning imaging department.

This article is a Directed Reading. See the quiz at conclusion.

Reprint request may be sent to the American Society of Radiologic Technologists, Communications Department, 15000 Central Ave. SE, Albuquerque, NM 87123-3917.
Table 1
Example of Device Classifications

Class I

Radiographic film
Radiographic grid
Radiographic intensifying screen
Lead shield

Class II

Automatic contrast medium injector
Radiographic collimator
Barium enema retention catheter with bag
Digital image storage device
Imaging systems
Catheter guidewires
Diagnostic intravascular catheters
Transluminal peripheral angioplasty catheter
Automatic film processor

Class III

Carotid atherectomy system
Laser angioplasty device, peripheral or coronary
Transluminal coronary angioplasty catheter
Balloon for cerebrovascular occlusion
Cardiovascular stent
Full-field digital system for mammography


Table 2
Steps for Processor QC

Activity      Procedure                              Frequency

Clean         Crossover racks                        Daily
              Entire rack assembly and tanks         Weekly

Maintenance   Visually check belts, pulleys, gears   Weekly
              Lubrication                            Weekly or Monthly

Monitor       Developer temperature                  Daily
              Wash water temperature                 Daily
              Replenishment tanks for level          Daily
              Sensitometry and densitometry          Daily
              Scheduled parts replacement            Regularly


Glossary

ABC     automatic brightness control

ACS     American College of
        Surgeons

ADC     analog-to-digital converter

CCD     charge coupled device

CFR     Code of Federal Regulations

CQI     continuous quality
        improvement

DHHS    Department of Health and
        Human Services

FDA     Food and Drug
        Administration

FD&C    Food, Drug and Cosmetic

Act     Act of 1938

HVL     half-value layer

JCAH    Joint Commission on
        Accreditation of Hospitals

JCAHO   Joint Commission on
        Accreditation of Healthcare
        Organizations

NCRP    National Council on
        Radiation Protection

PBLD    positive beam limiting
        device

SID     source-to-image distance

SMDA    Safe Medical Devices Act of
        1990


References

(1.) Joint Commission on Accreditation of Healthcare Organizations. A journey through the history of the Joint Commission. Available at: www.jcaho.org/about+us/history/index.htm. Accessed September 16, 2003.

(2.) Joint Commission on Accreditation of Healthcare Organizations. Home page. Available at: www.jcaho.org. Accessed September 16, 2003.

(3.) Joint Commission on Accreditation of Healthcare Organizations. State recognition activity. Available at: www.jcaho.org/about+us/government+relations/staterecognition+activity.htm. Accessed September 16, 2003.

(4.) Joint Commission on Accreditation of Healthcare Organizations. 2004 Hospital Standards. Pre-publication edition available at: www.jcaho.org/accredited+organizations/hospitals/standards/new+standards /hospital.pdf. Accessed September 16, 2003.

(5.) Monsein LH. Primer on medical device regulation part I. History and background. Radiology. 1997; 205:4

(6.) U.S. Food and Drug Administration. Medical device reporting (MDR)--general information. Available at: www.fda.gov/edrh/devadive/351.html. Accessed August 20, 2003.

(7.) Seeram E. Rad Tech's Guide to Equipment Operation and Maintenance. Malden, Mass: Blackwell Science Inc; 2001:40.

(8.) Bushong SC. Radiologic Science for Technologists. St. Louis, Mo: Mosby-Year Book Inc; 1997:410.

(9.) Burns EF. Radiographic Imaging: A Guide for Producing Quality Radiographs. Philadelphia, Pa: W.B. Saunders Co; 1992:145

Paula Price has 26 years' experience as a radiographer, angiographer and mammographer. She has taught a special procedures course at Tacoma Community College in Tacoma, Wash, and currently works as a traveling radiographer and freelance writer.
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Title Annotation:Directed Reading
Author:Price, Paula
Publication:Radiologic Technology
Date:Jan 1, 2004
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