3T Defines A Role in Clinical Imaging

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The marketplace for high-field MRI, specifically 3-tesla, is transitioning from research institutes to a more clinically centered customer base at the community and specialty facility level. Originally dedicated to head imaging, developments in magnet and surface coil technology have morphed these systems into whole-body imagers - covering applications in neuro imaging, spectroscopy, body imaging and cardiovascular imaging. Coupled with its increased signal-to-noise ratio and ability to scan faster or with distinctly higher resolution, 3T magnets are clearly gaining attraction.

For years, 3T MRI has been used as a research tool for brain imaging. In 2002, 3T systems were welcomed into the spectrum of clinical MR when the U.S. Food and Drug Administration approved some 3T scanners for brain and whole body imaging. Expanded applications and the availability of more radiofrequency (RF) surface coils paved the way for 3T's inception in the clinical arena. While academic medical centers are the dominant users, 3T vendors forecast a future change in end-user demographics to large to medium-size hospitals.

Philips Medical Systems, Siemens Medical Solutions and GE Healthcare are the leaders in 3T technology. Similar in size and user interface to their 1.5T cousins, what differentiates the two is price - approximately $1 million extra a tesla - and increased signal to noise ratio (SNR). Users practically double their SNR when they go to 3T. "When you go to 3T, it gives you extra SNR and how you choose SNR is really up to you as a physician," says Gregory Sorensen, MD, a neuroradiologist at Massachusetts General Hospital. "You can use it to go faster or you can use it for higher resolution."

Buying SNR means buying flexibility on how it's spent. Increased signal to noise can be used for images that require higher spatial resolution or at times when a faster scanning time is needed, which is beneficial for patients who do not like to be scanned or are frail.

Physicians at MGH use both Siemens' Magnetom Trio 3T whole body scanner and Siemens' Magnetom Allegra 3T scanner, which is dedicated to advanced neuro studies. Siemens holds the position as the only major vendor that has two 3T scanners in its product portfolio. MGH clinicians utilize high-field in the investigation of conditions such as dementia, drug addiction, migraines, and other disorders. Sorensen says they are also studying Alzheimer's and schizophrenia patients on the 3T system and "the tools we are developing to diagnose these illnesses are clearly going to work better at 3T than 1.5T."

From the beginning, it's been clear that 3T benefits the neurosciences, particularly functional MR (fMRI), diffusion imaging, perfusion imaging and spectroscopy. "We routinely use spectroscopy for evaluating patients with brain tumors and multiple sclerosis," says Michael Lipton, MD, medical director of MRI services at Montefiore Medical Center and Albert Einstein College of Medicine in New York. Lipton adds that both MR angiography and perfusion imaging, especially arterial spin labeling techniques (ASLT), also benefit from higher field strength.

Philips' Intera 3T (the forerunner to the company's newest system released at RSNA 2003, the Intera Achieva 3T) has been used at Montefiore for more than two months. The department is learning more about its clinical applications as more RF coils are released. "The main thing that you need to get used to is that there are many more possibilities that you can do at 3T than at 1.5T," poses Lipton.


Using an older generation, long-bore 3T MRI system, physicians at Michigan State University (MSU) College of Human Medicine have performed more than 12,000 clinical exams since July 2002. About 60 percent of exams are neuro and 40 percent are musculoskeletal, says Mark Delano, MD, physician director of MRI and director of Radiology Research at the facility.

Delano believes there is an amazing capacity to improve image quality in musculoskeletal imaging with 3T MR. "What we are seeing is that there is no compromise as far as contrast features in the musculoskeletal system," he says. The facility routinely performs soft-tissue neck, abdomen, pelvis, hip, long-bone extremity, knees, ankles, feet and shoulder exams at 3T.

Makers of 3T systems have invested quite a bit into creating a comprehensive imaging platform that permitted both brain and whole body scanning. While fMRI and spectroscopy are clearly advantageous at 3T, not every