There’s always a new kid on the block claiming to be stronger and more agile. In MRI, that new kid is 3T. As you’ll see in this month’s special section “Trends in MRI,” 3T is standing up and being noticed.
3T a decade ago was considered heresy by clinicians based on patient safety (have you hear the urban legends of people losing their memories after being near a 3T scanner?), applications and healthcare delivery policy climates. Today it is coming into its own and poised to become mainstream over the next three to four years, estimates David Weber, GE’s global manager of the high field MR business. Clinicians are supporting the suped-up horsepower and are thankful for the “signal starved” applications it now allows, as Yuri Wedmid, Ph.D., manager of ultra high field MR for Siemens explains.
Three major vendors, GE, Siemens and Philips, are marketing systems that are rivaling their 1.5T cousins in image quality and speed, or a combination of both. Higher contrast can be a benefit, but at this point albeit unpredictable. And certain kinds of contrast are amplified at 3T. GE and Siemens have opted for long-bore 3T systems like the early 1.5T units, while Philips offers a short-bore 3T unit. To date, about 30 to 60 units are estimated to be in clinical use in the U.S., which will compete with the 3,500 or so 1.5T units installed.
Like the early days of 1.5T, 3T applications are focused largely on the brain, with the heart next in the clinical sights. 3T’s benefits are as large as its strength, including improved spatial resolution generated by higher signal to noise ratios, faster scan times and new imaging protocols migrating up from the current gold standard 1.5T. MRI technology experts agree the boost in field strength is challenging based on controlling artifacts, static fields and RF energy levels that might just demand new technology altogether to be truly harnessed. But like 1.5T, these challenges will be overcome and the advantages of speed and resolution utilized as surface, extremity and R/F coils in development are optimized.
So where is 3T headed? Work is well underway to conquer protocols for the brain and neuro system, including stroke, trauma and neurodegenerative diseases with functional MR, diffusion imaging, perfusion imaging, brain activation and spectroscopy. Cardiac and angiography are the next frontier, once respiratory and cardiac motion are finessed and perfected. Right now, 3T cardiac MR is not even a toddler on the human scale, but it will soon be able to walk, Wedmid says. Other specialized exams are in the sights as well, including knees, ankles, prostate, liver and the breast. Interventional work is not yet safe nor practical.
Equipment costs are heading down their natural migration path as well, with vendors forecasting more “affordable” pricing soon. Operating costs are not an issue as budgeting for 3T is nearly identical to 1.5T. And the current larger size of 3T magnets is expected to shrink into the same “box” as a 1.5T scanner, yet still four times the weight. But that is expected to shrink as well.
So what does burgeoning 3T mean for 1.5T? Like other high-end devices, market entries, about 10 to 20 percent of scans will migrate up to 3T. 1.5T scanners will maintain value in specialty areas that are yet to be known.
And after 3T? Of course vendors are guarding their R&D cards, but some 7T units and 9-plus T units (with magnets the size of locomotives) are being sited, a couple a year into heady research facilities. And where will the technology go, the research will tell. The brain is first, but stay tuned.
Mary C. Tierney, Editor
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