3T MRI Flexing Its Muscle

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  Siemens Verio 3T MRI system

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