MRI: The Next Generation

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MRI has come a long way since its inception, and it has yet to cease evolving. New developments continue to surface, bringing with them changes in radiology practice patterns and opportunities to bolster revenues by attracting new patient populations.

The evolution of multichannel coils ranks among the most significant developments. Systems with 32 and 48 channels are considered standard; 120- and 128-channel systems, as well as wireless coils and specialty surface coils, are emerging.
Robert Lenkinski, PhD, is vice chair of radiology and director of radiology research, experimental radiology, and the 3T MR Spectroscopy Program at Beth Israel Deaconess Medical Center, Boston, Massachusetts. He says, “Multichannel coils, which bring improved signals and greater reliability, are having an enormous impact on MRI in general. They enable parallel imaging, higher-quality scans in a shorter time period (by an average of a factor of four), and broader coverage of body parts with very good signal strength.”

Reduced scan time, stemming from access to additional channels, reduces motion-related problems and increases patient compliance. This, in turn, is spurring physicians to make MRI their study choice for a wider range of patients, including pediatric, elderly, and severely debilitated individuals.

Richard Semelka, MD, says, “It is much easier now to perform MRI studies on patients who, in the past, could not or would not remain still long enough to complete the process, or presented some other kind of challenge.” Semelka is professor, director of MRI services, vice chair of clinical research, and vice chair for quality and safety of the Department of Radiology at the University of North Carolina Hospitals in Chapel Hill. He continues, “The less time patients must remain in the machine, the easier to perform MRI studies on them, and the greater the likelihood of compliance.”

Lawrence Wald, PhD, of the Department of Radiology’s Martinos Center for Biomedical Imaging at Massachusetts General Hospital (MGH) in Boston, is director of the MGH NMR core. He adds that new multichannel phased-array coil systems also permit users to execute different, more exotic imaging procedures. He notes that while such procedures were previously impractical because of the amount of time needed to encode captured images, large coil arrays and multiple channels remove that factor from the equation.

“For example, with a higher number of coils, spectroscopic imaging that once took three hours has a 16-fold acceleration, into the 10-minute range,” Wald states. “Capturing 0.75-mm isotropic, high-resolution 3D images of the brain can take 15 minutes, rather than many times that. The more channels, the more MRI will become a replacement for CT, because users are able to get patients in and out in comparable time, with heightened image sensitivity, and without compromising image quality.” See Figures 1, 2, and 3.

Diffusion Imaging Migrates

The advent of multichannel coil systems and parallel imaging, coupled with such hardware and technical advances as rapid echoplanar imaging and larger-amplitude gradient systems, has also paved the way for the use of diffusion-weighted imaging, not only for evaluating intracranial abnormalities, but for imaging other parts of the body.

imageFigure 1. A 96-channel brain-array prototype constructed at Massachusetts General Hospital in Boston; the detector uses very small loop detectors placed on a close-fitting helmet. The high density of small detectors improves image sensitivity and increases the ability of parallel-imaging techniques to decrease scan time.

Bachir Taouli, MD, director of body MRI at Mount Sinai Medical Center, New York, New York, says, “The combination of all of these factors helps to overcome many limitations that previously precluded the application of diffusion-weighted imaging to areas beyond the brain.” For example, prior to recent hardware and technical advances, inherent limitations in signal-to-noise ratio (SNR) and image resolution tended to compound artifacts when patients were evaluated in diffusion-weighted imaging mode.

imageFigure 2. Section from a T1-weighted whole-brain volume acquired with a 32-channel brain-array prototype constructed at Massachusetts General Hospital in Boston; in this case, the scan time was conventional (8 minutes), but at a voxel volume that was four times smaller. In-plane resolution is 0.4 mm and partition thickness is 1.5 mm.

Moreover, the larger