A number of recent developments in magnetic resonance (MR) technology can allow hospitals to improve their systems. Such improvements include increasing the number of clinical applications available, improving the image quality, adding more automation to the scanning process, or reducing the amount of time it takes to scan a patient.
Some improvements, such as increasing the MR system’s field strength or bore size, necessitate replacing the entire MR system at great expense. But many others do not – rather, they can be obtained through software upgrades, installation of new electronics, or small hardware purchases.
When possible, upgrading the system is often a better option than replacing it. The cost of upgrading, though it can still be considerable, will usually be substantially lower than the cost of a new system installation. This is because installing a new system will always require replacement of the magnet, which is the most expensive component of the system and which always entails substantial building renovation and rigging costs. Unless a facility seeks to increase the system’s field strength, it doesn’t make sense to replace the magnet, since the performance of the magnet does not degrade over time and since any additional capabilities that would be provided by replacing the magnet will usually be available through a less expensive system upgrade.
Of course, not all upgrades or options will benefit all facilities. Hospitals will have to weigh the cost of the upgrades against the actual benefit they will provide.
Here’s a look at some of the recent developments in MR technology, along with ECRI Institute’s perspectives on whether hospitals should consider investing in them.
Improvements to RF Systems, Channels, and Coils
Availability of General-Purpose Multi-element Coils
In MR imaging, coils are used to detect the radio-frequency (RF) signals emitted from the patient; the signal is then amplified and digitized by the RF channel. Each coil is made up of one or more coil elements, and is positioned as close as possible to the anatomy being imaged.
In the past, hospitals had to purchase a wide range of dedicated anatomical coils, and technologists had to select the most appropriate coil for the study they were performing. As a result, certain dedicated coils would be underutilized because their clinical applications were performed only rarely.
Today, general-purpose coils are available that contain multiple elements and that, because of this design, are flexible and can conform to almost any anatomical region. As a result, facilities need fewer coils to perform their studies, and anatomy-specific dedicated coils are no longer needed.
Another benefit of these new multi-element coils is that, unlike previous coil designs, they include microprocessors that make them more versatile, more complex, and easier to use. The increased number of coil elements allows levels of automation not possible a few years ago. It can take less time to set up the system and scan the patient because the technologist no longer has to select the appropriate coils and elements for the study or change coils during an exam.
The bottom line: For new systems, ECRI Institute recommends purchasing general-purpose multi-element coils.
For existing systems, upgrading to general-purpose multi-element coils is often an option. Such an upgrade would require major hardware changes; additionally, the new coils cost more than the older ones. However, though expensive, this upgrade would add significant benefits, particularly for hospitals looking to improve patient throughput. The higher cost of the coils can often be offset by the cost savings that would be achieved through the reduced scan time and by the fact that fewer coils will be needed.
Moving the RF Digitization Closer to
the Patient
Image quality is affected by the location of the RF digitization electronics. In the past, MR manufacturers placed most of the digitization electronics in an equipment room that was adjacent to the scanner, rather than in the same room as the scanner. This distance between the electronics and the scanner often resulted in increased signal losses and reduced image quality. To improve image quality, manufacturers have begun miniaturizing the electronics so that the RF digitizer can be embedded into the scanner or, in one case, onto a coil.
The bottom line. For most new systems, this technology is now standard; for existing systems, this technology is often available as a major system upgrade. The cost of upgrading a system in this way is likely to be on par with the cost of a new MR system, minus the facility construction or renovation costs. The improvements in clinical capability that result from this feature enhancement are unlikely to justify the cost. Therefore, this upgrade should be considered only as part of a major system refurbishment in which all or most other components on the gantry (except the magnet) are replaced.
Adding More Coil Elements and Channels
Each of the coils used to detect patient RF signals is made up of one or more coil elements. In most systems, the number of elements is limited by the number of RF channels the system has, since each coil element must be connected to a channel. Most new systems have at least 16 channels; higher-end systems have about 100.
Increasing the number of coil elements will improve the image quality, particularly for parallel imaging, which is an accelerated image acquisition technique that enables many advanced MR applications. To perform parallel imaging, a system must have at least eight channels; however, the benefits of parallel imaging at only eight channels would be limited. Regardless of the number of channels a system has, in order to improve either the image quality or the effectiveness of the system’s parallel imaging capability, the number must be increased by a factor of two.
ECRI Institute recommends that new or upgraded MR systems have a minimum of 16 channels. Although MR manufacturers are increasingly producing systems with more and more channels, ECRI does not expect that the improvements in image quality will be as significant when going above 16 channels. Also, note that there is a limit to how many coil elements can be used on a patient, depending on the size of the anatomy being scanned. The main advantage of higher-channel systems comes in exam setup: The increased number of channels means that many of the selections previously made manually by the technologist can be automated.
One manufacturer has changed the discussion by embedding the digitization electronics into each coil element; with this arrangement, the number of coil elements used is no longer limited by the number of channels. If widely adopted, this technology would make the number of channels a system has almost irrelevant as a selection factor.
The bottom line. For new system purchases, hospitals should consider at least a 16-channel system. Systems with more than 16 channels should be considered if high patient throughput and advanced applications are expected.
For existing systems, the difficulty and cost of adding more coil elements and channels will depend on the age of the system. Some more recent systems are designed to allow for easier and less expensive channel upgrades.
Efficient Scan Setup
Adding More Automation to the Scanning Process
Health care facilities are being pressured to perform more studies in less time. However, MR image acquisition is a very complex process, and the study time and quality of the final images will depend on a multitude of scan parameter selections and decisions made by the technologist. For a typical study, the technologist must first select the scan type, correctly and safely position the patient, and select and position the coils. The technologist must then select the slice location, slice orientation, slice spacing, and slice thickness, and must choose the specific coil elements.
To help speed up the process, MR manufacturers have added more automated steps and scanning parameter selections to their systems.
An automated system not only streamlines and shortens the setup process, but also produces images that are more consistent between patients. Without automation, a technologist has to align the slices in a standard plane consistently for all patients undergoing similar studies, which can take time depending on the experience of the technologist. Adding automation to this process means that radiologists do not need to spend as much time adjusting images to meet their needs.
The bottom line. These capabilities exist as software options for both new and existing systems, and the cost is similar for both. The decision to purchase these features will likely depend on the desired patient throughput, the experience level of the technologists, and feedback from radiologists. The efficiency improvement is hard to predict, though reducing the average schedule slot from 45 minutes to 35 minutes may be feasible; this would translate to three more patients per eight-hour shift. Of course, this will depend on factors such as the experience of the technologists, the types of patients being scanned, and the types of studies being performed.
This article is excerpted from a digital story posted 3/4/15 on ECRI Institute’s membership website. The full article features additional information on patient movement suppression, improving patient comfort, and software-based acoustic noise reduction. To learn more, visit www.ecri.org; call (610) 825-6000; or e-mail communications@ecri.org.
