Whether it is for patient comfort or more specific clinical purposes, open MRI continues to make its mark in the medical imaging and MRI markets. Claustrophobic patients and enhanced access for healthcare practitioners have helped drive open MRI sales upward in recent years.
Physicians expectedly have embraced the open MRI design to calm skittish patients and to enhance their clinical capabilities and patient volume in their respective practices.
John F. Feller, M.D., is medical director of Desert Medical Imaging, The P.E.T. Center (DMI of Indian Wells, Calif.) and MRI consulting radiologist for Desert Orthopedic Center (Rancho Mirage, Calif.). Since 1991, he also has served as assistant clinical professor in the department of radiology at Stanford (Calif.) University. Feller has co-authored numerous peer-reviewed journal articles and is an editor of the textbook Shoulder Magnetic Resonance Imaging. His medical career includes four years as chief of MRI at David Grant USAF Medical Center (Travis Air Force Base, Calif.).
DMI is a multi-modality medical imaging center, with three affiliate MRI centers in Indian Wells, Indio and Palm Springs, Calif. Services include high-field and open MRI, spiral CT, ultrasound and positron emission tomography (PET) imaging.
DMI handles approximately 20,000 exams per year, with between 4,000 and 5,000 of those exams coming from open MRI.
The centers also use a combination of software and hardware virtual private networks (VPNs) to transfer images to subspecialists, which interpret the images on DMI’s picture archiving and communications system (PACS). Physicians also have access to images and reports on a secure Internet connection with streaming technology.
DMI also provides product support and development for several vendors, including Toshiba America Medical Systems (Tustin, Calif.) and the company’s Ultra open MRI system, which was installed at DMI in September 2002.
Feller spoke with Medical Imaging about the current uses, future applications and the healthy market for open MRI technology.
How has DMI Employed Open MRI in its Clinical Practice?
When we first got into open MR technology, we used it for claustrophobic patients and patients who exceeded the weight or size limits for our closed-bore scanners. With the development of newer technology, such as the gradient system that is on the Ultra scanner, more and more we are able to do all the different types of studies that we used to perform on our high-field scanner.
Instead of having to triage patients and send some to the open MR system and some to the closed MR system, we find now that we can accomplish most of our exams on any of the scanners. Then it comes down to patient preference, in terms of what type of scanner they want to get into and the location of the scanner so there is easy access for the patient.
What Types of Imaging Exams have the Open MRI Configuration and Advanced Technology Added to DMI’s Capabilities?
With the open scanners we had before, we could not do diffusion weighted imaging in the brain routinely. We are located in a retirement community, so the probability of vascular disease is very high when someone comes in with neurologic symptoms. In other words, there is a high likelihood of ischemia, stroke and TIAs (transient ischemic attacks) as the cause of the problems. Routinely, we have run diffusion-weighted imaging of the brain on our high-field scanner for the last four years.
Today, Toshiba’s Ultra has these high-performance gradients that allow us to do single-shot echo planar diffusion-weighted imaging (EPI). It is so fast that we are able to use it routinely on every brain MR we do. Previously, we couldn’t do that on a low-field MR scanner.
Another example would be gadolinium bolus MR angiography (MRA). Previously, we couldn’t do it at all on a low-field MR scanner, because it didn’t have the temporal resolution to accomplish the study that high performance gradients permit.
Another example would be breath-held imaging of the abdomen. That was something we could only do on our high-field scanners, but now the increased temporal resolution and increased speed from the high-performance gradients allows us to do breath-held abdominal imaging.
Another area where there has been a huge improvement is intracranial MR angiography of the brain. Previously, if a patient came in with a headache and they were worried about a cerebral aneurysm, I would always send them to our high-field scanner, because the image quality just wasn’t there. Now, the gradient performance has reduced turbulent de-phasing type artifacts and improved flow compensation techniques on the MRAs of the brain.
The image quality is so good now that my reports might say there is no cerebral aneurysm or there is no severe stenosis or branch occlusion. The detail is much better, so I can exclude many of these other entities reliably.
That is very helpful to us, because instead of imaging the brain on our open scanner and sending patients to the high-field scanner for the brain angio, we can do the whole study – including the diffusion weighted imaging – on the Ultra system.
Another area of great improvement is with steady-state free precession, or True FISP. For spine imaging, it allows you to do very fast imaging with very good myelographic effect. It is particularly helpful for axial cervical spine imaging where it previously took nine to ten minutes and the axial spine images were relatively poor. Now we can do a 3D steady-state free precession acquisition in five to six minutes and contiguous, three-millimeter axial slices through the cervical spine that are very diagnostic.
To what degree does open MRI technology reduce patient scan times, depending on the type of exam?
One of the things you can trade in gradient performance for is increased patient throughput. There is about a 15 percent improvement in the efficiency of the pulse sequences.
We are a development center, so we do a lot of extra pulse sequences. However, we have not traded that in for increased patient throughput, because we are trying to test so many different pulse sequences. If there is a site interested in improving patient throughput, they can use the higher gradient performance to do that.
What are some design and technological changes that may be in the offing for open MRI?
In terms of where things will go from here, I think improvements in MRI coil technology will continue. The main source of noise in low- and mid-field MRI scanners is the coil. Implementation of parallel imaging on low-field scanners down the road also will help reduce scan times and improve efficiency.
Creeping into the market as well are these high-field open scanners, which until now have had a fair bit of problem with vibration and ghosting artifact related to vibration from the gradient. With the Ultra, that hasn’t been a problem, because it has a four-post design, which is very stable.
What kinds of new clinical applications do you see coming to open MRI with these technological advances?
We are just realizing those now. The example I gave you of the routine diffusion-weighted imaging of the brain using single-shot EPI techniques is just being realized, as is gadolinium bolus MRAs. Breath-held imaging of the abdomen is just becoming a reality for low-field scanners. I think these areas are where we are seeing the biggest leaps.
Further down the road, the potential will be there for cardiac imaging, especially using steady-state free precession techniques and EKG (electrocardiogram) gating, which will become more feasible on low-field scanning.
How does the role of contrast agents play into open MRI technology?
There are some technical issues that one must be cognizant of in terms of the weighting differences between high field and low field. Basically, the same tenets apply in terms of patterns of contrast enhancement.
Previously, we were not able to do breath-held imaging to allow us to do gadolinium-enhanced bolus MR angiography, gadolinium bolus breath-held imaging of the liver or multi-phase gadolinium bolus imaging of the breast, because we could not scan fast enough. All of those applications will become more mainstream with low-field magnets as gradient performance improves and allows us to go at these higher speeds.
So, I think the utility of MRI contrast agents will expand on low-field scanners, as they become faster and more efficient.
Has the patient perspective on open MRI scanners changed much?
If you ask all comers, 40 percent of patients will choose an open MR scanner over a typical closed-bore system. In terms of claustrophobia, open MR reduces that problem significantly.
For us, we have the benefit of several types of scanners and several different types of platforms. Sometimes, patients will prefer to be in our short-bore, high-field scanner, because their heads are outside of the scanner — for example, when their knees are imaged — rather than being between the poles of an open scanner.
Overall, patients who have comfort and claustrophobia issues definitely prefer the open scanners.
About 10 percent of patients have claustrophobia issues and a lot of people don’t know it until they get in [a MR scanner]. It depends greatly on how you approach the patient. Many patients have some discomfort; the noise is generally loud and the rooms are generally cold. Having a MR technologist with a soft voice, warm hand and caring personality is very important.
How do you see the open MRI market in general progressing in the coming years?
I think the growth in open MR sales has leveled off some. You’re seeing 1.5 Tesla systems worldwide still have a very significant market share. I think as open MR performance continues to improve that you will see some encroachment on [the 1.5 Tesla MRI market], but the bottom line is that there are some field strength differences that can be difficult to overcome. Then, it will be interesting to see if there really is a marketplace for these high-field open scanners that are 1 Tesla and have an open platform with high-performance gradients — and that remains to be seen.
I say that because the cost to make those kinds of scanners is very high. The magnets, in particular, for these high-field scanners are very expensive. By the time you pay for one, you could have owned a 1.5 Tesla system. Good ol’ business principles will come into play there.
On low-field open scanners, there is a strong financial incentive, because the overhead is significantly less. The magnets are much less expensive than 1.5 Tesla systems, so the scan break-even point is lower.
So, it will be a combination of technical improvements that allow us to do more and more with low-field scanners that will drive market share. However, unless vendors find ways to decrease costs — particularly for high-field open scanners — it will not become reality in the marketplace, because buyers will just get a 1.5T system for the same price. High field 3.0 T MRI units are also likely to grab significant market share globally in the next three years. This will begin in university and research sites spreading to community based centers following validation of this relatively new technology.
