3T MRI has found a sweet spot in musculoskeletal, neurological and breast imaging. Clinicians are reaping the benefits of high-resolution, high-quality images acquired at a higher field strength—and more referrals.
Open bore, quality images
3T MR addresses some of the musculoskeletal imaging challenges found with 1.5T, says John A. Carrino, MD, MPH, associate professor of radiology and orthopedic surgery at Johns Hopkins University School of Medicine in Baltimore and section chief, musculoskeletal radiology at the Russell H. Morgan department of radiology and radiological science. “We are imaging smaller joints with isotropic pulse sequences better than with 1.5T,” he says. The facility installed a Magnetom Verio 3T MR system from Siemens Healthcare in late 2007. We are “still doing the same kind of scans—just doing them a lot better.”
The two biggest challenges with 3T have been minimizing artifacts from metal, and monitoring increased specific absorption rate (SAR) generated by the pulse sequences. Compared to a 1.5T system, potential SAR can increase by a factor of four. However, measures can be taken to try and compensate for the increase—such as splitting the acquisition volume over multiple scans or using parallel imaging, Carrino adds.
The Verio, which has a 70 cm open bore and Total imaging matrix (Tim) technology, provides increased signal-to-noise ratios, which can be used to scan patients faster or improve spatial resolution. “Specifically, because of the true form design and the homogeneity of the cylindrical ‘sweet spot’ of the magnet, we can do off-isocenter imaging much better than a 1.5T or a traditional 3T,” adds Carrino.
Verio’s large bore also allows imaging of large or claustrophobic. For people in either or both categories, there is a healthcare disparity that in the past relegated them to a sub-quality open MR, and the potential of a missed diagnosis. This is no longer true with high-field, open-bore MRI.
“The benefits for orthopedics are getting better image quality with potentially reducing the invasiveness of the examination by eliminating contrast enhanced techniques [intravenous and intra-articular routes of administration]. However, this needs to be confirmed with research studies looking at the diagnostic performance of 3T compared with a reference standard such as surgery, arthroscopy or a validated imaging technique such as MR arthrography or DGEMRIC [Delayed Gadolinium Enhanced MRI of Cartilage],” Carrino notes.
Breast imaging & beyond
The nuclear medicine department at William Beaumont Hospitals in Troy and Royal Oak, Mich., is no stranger to the benefits of 3T MR. The 1,061-bed hospital, which has an annual imaging volume of close to 800,000, installed a GE Signa MR 750 in December 2007 at the Troy campus and a second scanner at the Royal Oak campus in April 2008. Hospital administration installed a new 3T in a suite contiguous with the breast radiology women’s centers at both campuses, according to Conrad Nagle, MD, corporate chief, nuclear medicine, previously corporate chief, diagnostic imaging, William Beaumont Hospitals.
The hospitals wanted to be able to offer both communities access to the same services at more than one site in the hospital system, Nagle says. While a rising need within breast imaging might have been the justification for the dual-install, it quickly became apparent that the systems were highly useful for non-breast imaging evaluations, too. The capability to depict smaller anatomic structures at improved resolution at almost 30 to 50 percent faster scan speeds made orthopedic clinicians at William Beaumont order 3T images more often for musculoskeletal imaging.
“For musculoskeletal, brain, neurology and radiology studies, the signal-to-noise ratios are improved,” Nagle says. “I believe that the detail with 3T is allowing them to make better clinical decisions.”
He notes that sequencing is taking more time on the 3T, estimating that some studies that normally took 40 minutes now take 60 minutes. This is not necessarily due to the equipment, but to the staff’s learning curve as they learn to adjust sequences or protocols. Additionally, with 3T, since SAR tends to occur more easily, more diligence is required to ensure it does not exceed the heating limits, he adds.
Ramping up to 3T
While many facilities and practices have realized the benefits, others may still not be ready for 3T MR, perhaps due to cost or space constraints. For those who are still on the fence, a rampable 1.5T magnet offers a time- and cost-friendly option.
Instead of making the jump directly to 3T, MetroHealth Medical Center in Cleveland, Ohio, installed the Achieva XR convertible 1.5T/3T MRI system from Philips Healthcare in October 2007 to transition from 1.5T to 3T as seamlessly as possible. The XR offered the level I trauma center, which had no previous 3T experience, the ability to start out at 1.5T, get familiar with the workings of the system and then ramp it up to 3T when staff had been adequately trained. In November 2007, the facility made the jump to 3T.
Pedro Diaz, PhD, vice chair of imaging and informatics systems for MetroHealth, says that, at first, he was not enamored with the idea of a rampable magnet, but that quickly faded. “Rather than take the entire 1.5T system out and put a 3T in and deal with the additional construction for that, within four days we completed all the work we needed to do to get from 1.5T to 3T,” he says.
The hospital started planning for the install in January 2007; facilities planning started later that summer. Two or three months before the install, MR technologists were sent to a basic training course at Philips to get familiar with scanner’s user interface and sequences. It took about three months for staff to get comfortable with the scanner at 1.5T and 3T, Diaz says. What made the process significantly easier? Having the same user interface, sequence families and surface coils at both field strengths.
To run at full 3T capability, MetroHealth replaced a few of the 1.5T sequences with the recommended 3T sequences, especially those relying on T1 relaxation at 1.5T. “The T1-weighted scans are not typically feasible at 3T because T1 is very long,” he says.
“As you start doing the more advanced applications, a new set of referrals opens up to take advantage of,” Diaz notes, adding that referring physicians have been impressed by what they are able to visualize at 3T for neurological and musculoskeletal applications. In some instances, the advantage has been shorter scan times. Some exams which previously took 30 minutes at 1.5T, now take approximately 15 to 20 minutes at 3T due to increased SNRs.
MetroHealth uses 3T both to obtain high-resolution images as well as to shorten scan time. “Being able to perform higher resolution and/or shorten scan time for others greatly enhances our ability to perform ‘bread and butter’ imaging,” Diaz says. The medical center is now moving into more advanced applications such as spectroscopy, diffusion tensor, and improved and faster diffusion and perfusion imaging.
With increased contrast-enhancement sensitivity, a stronger gradient and a reduced contrast dose added to the mix, it is not surprising that many facilities are making the jump to 3T for musculoskeletal imaging, to produce images with much higher spatial resolution in less time.