3T MRI made its name creating high-quality brain studies in research institutes. But today's 3T MR scanners are whole body imagers used at both academic medical centers and community-based imaging facilities, performing clinical brain, orthopedic and musculoskeletal imaging, and showing promise in areas such as breast, cardiac and molecular imaging. 3T is considered the wave of the future - but exactly when that wave will hit is still the question.
When it comes to the routine clinical utilization of 3T MRI, the imaging community is on the fence. Users of 3T are believers that their practices have much to gain from increasing field strength; not only the ability to perform imaging techniques not possible at 1.5T, but to offer patients a possible diagnosis using higher-quality digital images. They also recognize that owning and operating a 3T scanner differentiates them in the marketplace.
On the other hand, hospitals and imaging centers that do bread-and-butter MR on high-end 1.5T systems are not yet convinced the time is right for 3T; there is not enough clinical literature and immature coil and antenna technology currently limits how many clinical whole body applications can be performed at 3T - although vendors say this has improved tremendously. The convincing argument to spend the extra million on 3T is harder won.
Despite the clinical squabble, most everyone agrees the overall benefit of 3T is the doubled magnetic field strength. Higher field strength means a higher signal to noise ratio (SNR), which might be used to increase the imaging matrix, to choose thinner slices, to reduce the number of signal averages, or in some cases, to decrease the amount of contrast agent administered. Simply stated, 3T scanners produce higher resolution images and, in some cases, scan faster than their 1.5T cousins. They also perform applications better, more clearly, less invasively, with more detail or in less time than 1.5T.
Experienced, routine clinical applications at 3T include brain, musculoskeletal and orthopedic imaging. High-end brain applications include functional imaging, spectroscopy, and diffusion tensor imaging. For musculoskeletal applications, increased SNR improves image quality of bone structures, tendons, ligaments and cartilage. MR angiography (MRA) is typically better due to the signal advantages of T1 in the 3T magnet. Other applications that are SNR-starved and are sure to see benefit are breast and cardiac MR - once more surface coils become available.
"3T is terrific for the brain, spine, musculoskeletal, abdominal and pelvic imaging, vascular imaging, especially for contrast-enhanced MR angiography of carotid, renal and pulmonary arteries," says Paul Finn, MD, professor of radiology and director of cardiovascular imaging at University of Los Angeles Medical Center. "It is also excellent for the intra-cranial arteries. Still, one of its more limited applications is functional imaging of the heart. If you were going to take a 1.5T system and a 3T system and do the same patient for this specific technique, you will probably get more reliable and quality images with a 1.5T system."
"We use 3T for almost every application for which 1.5T is used including MR angiography of the renal arteries and peripheral arterial system, in addition to routine imaging of the liver and pancreas," says Bruce Distell, MD, director of body imaging at Cape Fear Valley Health Systems of Fayetteville, N.C. "However, being that our 3T is sited at an outpatient center ... and there are indications for which 3T is particularly useful, we steer certain studies to this magnet. For example, we use it for many outpatient brain studies and high resolution orthopedic work."
For almost a year, clinicians have been using GE Healthcare's Signa Excite 3T at the imaging center. The facility is the first in the region to make clinical use of a 3T magnet. Distell says both the desire to perform state-of-the-art imaging and to move into the realm of molecular imaging motivated them to adopt 3T.
"Since there is increased signal from the 3T magnet, there is the opportunity to routinely perform very high resolution imaging," says Distell. "The superb quality of the images increases the accuracy rate and the confidence level for making subtle diagnoses. The referring physicians have been very impressed with the images. For example, the orthopedic surgeons find it clinically useful when I can give them a more accurate assessment of the