As use and sophistication of magnetic resonance imaging systems increases, following proper care and maintenance guidelines is more important than ever
Magnetic resonance imaging (MRI) is the diagnostic tool that currently offers a sensitive, noninvasive way to image the brain, spinal cord, and many other areas of the body. Unlike a computed tomography (CT) scan or x-ray, MRI does not use ionizing radiation, but instead measures the water content in tissue—both normal and abnormal—with the use of a powerful super-conducting magnetic field and pulsed radio frequency (RF). And while CT scans are limited to imaging harder structures, like bones, an MR image also provides information on soft tissues and organs, making it the investigative method of choice for many physicians.
MRI scanning, in widespread use since the early 1980s, is constantly evolving. New clinical features now deliver fast and robust MR solutions for neurology, trauma, pediatric, and fatty liver patients, as well as for routine fat saturation. Complementary technologies, such as ultrasound and MR elastography (which produces images indicating tissue stiffness in the abdominal area, such as in the liver or muscle) have fostered the evolution of MRI. With the advent of digital MRI, which further reduces scan times, physician diagnosis is available even faster. Today, there are even operating room MRI configurations available.
Clarity and speed, long opposing forces in MR technology, have lately come together in widely adopted digital MR architecture that offers the best of both worlds: exceptional images and remarkable speed. And thanks to digital MR, RF upgrades on this equipment are a thing of the past. These days, environmental factors related to cooling and safety are among the primary considerations. By preparing for potential events, making sure all repair personnel receive proper training, and following necessary care and maintenance practices, hospitals can help ensure their MR system remains a key part of their imaging offerings.
How MR Machines Function
An MR system works by aligning the water molecules in our bodies through a strong magnetic field produced by a superconducting magnet. When the magnetic field is released, the hydrogen atoms within the water molecules return to their normal state. In doing so, the molecules emit various levels of energy, depending on the type of body tissue from which they come. The MR system measures this energy to create an image.
The magnetic field is generated when electric current runs through conducting wire, known as coils. These coils are located within the MRI machine and are also placed around the subject to measure the radio waves. The system’s electronic components help generate and measure the RF signal and the magnetic field gradient, while the patient coils bring the area of study into focus. A workstation then processes the signals and generates images
To achieve superconduction, the magnet in an MR machine needs to be kept at a very low temperature, close to absolute zero. Helium gas is also cooled by an attached water chiller system. When the system’s power is switched on, the immediate force on the magnetic coils causes the coils to expand, resulting in a loud clicking sound. When the MR system is in active use, the electric current switches on and off rapidly. The result is a staccato-like sound, which is amplified by the enclosed space in which the patient lies.
Maintenance and Repair Best Practices
As might be expected, service plays a very important role in maintaining a system that involves a supercooled magnet and sophisticated electronic components. Confident operation of all components is required to produce high-quality images that lead to proper diagnosis and protect the life of the system. As MRI systems evolve, there are also more software applications and workflows available that require trained technical and clinical specialists with software diagnostic tools to fine-tune the system.
It is imperative when a system has an issue that a trained technician, whether in-house or affiliated with a service provider, responds to the situation. It is wise to require everyone on staff who works with or on MRI equipment to take a magnetic resonance training course. If a department uses OEM technicians, it is important that they, too, have undergone training. With MRI equipment, the actual environment can induce as many issues as the system itself, so it is necessary that someone well-versed in all areas of troubleshooting corrects the problem.
The environment around an MR machine needs careful attention. Hospitals should clearly designate safety zones near the magnetic field and put in place ferromagnetic detectors. In particular, hospitals must ensure the water chiller is capable of maintaining the temperature necessary to cool the helium and MRI coils. Older MRI systems require a temperature of 10 kelvins. Newer systems, called “zero boil-off” machines because they do not lose helium during normal operation, need an even lower temperature of 4 kelvins. (These machines are referred to as 10K or 4K systems.) The supply of chilled water must be monitored around-the-clock to ensure that any cooling issues are handled immediately. A city water bypass is recommended.
In addition, hospitals must consider how to manage their supply of helium. Since it is a limited resource produced as a byproduct of natural gas, few national suppliers can guarantee availability on demand. To ensure proper functioning of the system, it is essential to maintain and monitor helium levels within the MRI magnet, preferably using a remote-capable environment alert system that can measure cryogen levels, temperature, humidity, etc.
With expert maintenance, MRI equipment will stay online and operate at an optimal level. If the imaging department is conducting daily picture image quality tests and weekly American College of Radiology-recommended scans, then 90% of the system is already being checked. However, regularly scheduled preventive maintenance (PM) is needed to maintain standards around proper cooling of the magnet and electronic components, to test the operation of individual coils, and to conduct a comprehensive check of the system. PM procedures can start with simple things like checking for physical damage due to wear and tear, inspecting the system’s water and helium levels, verifying in-room temperature and humidity levels, and running quick scans with standard test equipment.
While most system issues are readily avoidable with proper precautions, occasionally issues do arise for which departments must be prepared. If the equipment or exam rooms exceed acceptable temperature or humidity ranges, it could result in avoidable patient burns, image quality degradation with artifacts, or premature failure of the coils or other electronic components.
Repair costs of MRI systems on a time and material basis can start from a few tens of thousands of dollars for compressors or cold heads and quickly increase for gradient repairs or RF amplifiers. Recovering from a magnet quench can run into the hundreds of thousands of dollars. To reduce these and other unforeseen expenses, a comprehensive or shared service agreement that includes a magnet maintenance package can often be the best route for supporting the complexities of an MRI system.
Expect the Unexpected
In addition to following all manufacturers’ recommended temperature and safety precautions, imaging departments should have a plan in place for extraordinary events. MR departments typically work with facility HVAC teams to maintain the proper room temperature for the MR equipment. However, should a serious natural disaster, such as a tornado or flood, cause an extended power interruption to the building, a specialized MRI engineer needs to be on-site to investigate the state of the magnet and surrounding electronics.
If the MRI system heats up and loses the supercooled helium needed to keep the magnet in its superconducting state—a situation known as a quench—representatives from several teams (including a service provider, biomed engineer, helium supplier, and member of the HVAC team) may be required to return the system to normal operation. A quench must be addressed immediately. In this scenario, the magnet vessel is open to the atmosphere. The longer it remains open, the more ice builds up in the vessel. The resulting burst disk must then be replaced by a qualified technician as soon as possible. In a worst-case scenario where the MR magnet can no longer be repaired and needs to be replaced entirely, having a magnet maintenance package with magnet insurance is helpful to avoid the very high costs associated with removing, rigging and transporting a magnet to the OEM factory.
In another unusual scenario, a ferrous object might be sucked into the magnetic field by the magnet. Depending on the object and whether it is causing injury to a person or preventing a patient from being removed from the system, a quench may have to be manually initiated by the service provider. If a quench is activated, then a technician should be called immediately to recover the quench and assess any damage caused by the object. Even if a manual quench is not required, a technician should still assess how to remove the object from the system and determine if it has caused any damage.
Occasionally, patients may have emergencies in the MR exam room unrelated to their scan. Should a patient code in the room, he or she must be removed from the room immediately. The code response should then continue outside the room. Most code equipment is not MR-compatible, and it is uncommon for code responders to be fully versed, if at all, in MR safety. It is recommended, therefore, that the hospital conduct regular drills for just such a scenario.
While it is rare for a fire to occur in or near an MR space, facilities would be wise to prepare a response plan for such an event. Remember that the MR magnet is always engaged and first responders, such as firemen, police, and EMTs, are not necessarily up to speed on MR safety. If possible, a hospital staff member should remain nearby to ensure that they do not enter the exam room with oxygen tanks, axes, or other MR-incompatible equipment. If a fire burns out of control, the magnet should be manually quenched.
What the Future Holds
MRI is likely to play an increasingly important role in medicine as researchers strive to make it easier and faster to diagnose a patient. Facilities across the United States are currently exploring new technology that combines MRI and positron emission tomography (PET) machines to diagnose cancer patients. Coupling these machines integrates treatment while reducing patient stress and the number of time-consuming tests. In addition, MRI-guided radiation therapy will soon be paired with a linear accelerator to provide gentler cancer treatments with fewer side effects and better outcomes. Researchers are also developing ways that MRI can be used to evaluate and treat brain injuries shortly after they occur. Faster tests mean faster, more targeted treatments.
On the hardware front, current population trends and increasing patient size are driving a move towards systems with a larger bore width of 70 cm in order to prolong the MR system lifecycle. The earlier 60 cm bore size remains popular with pediatric and research facilities.
Service capabilities are also evolving to create smarter MR systems that talk to each other in order to help detect anomalies and resolve issues before problems arise. Hospitals and imaging centers can choose to interact with each other and with clinical specialists from any location at any time. Field engineers equipped with the latest interactive devices can have advanced diagnostic capabilities at their fingertips, enabling more “first time right” resolutions when it comes to repairing and maintaining the equipment.
Future developments in MRI technology will continue to progress toward improved patient care at a lower cost, and will go a long way toward building a healthier future.
Todd Reinke is senior director of Customer Services Marketing at Philips. For more information, contact chief editor Jenny Lower at [email protected].
Photo caption: The Philips Ingenia MRI system with Ambient Experience, a feature that soothes patient anxiety by creating a customized lighting environment.