GE's Signa MR750 brings new power, simplicity to 3T

Advanced gradients and parallel imaging, along with ergonomic features, combine to boost productivityA new 3T scanner unveiled last month by GE Healthcare delivers unprecedented speed and resolution in some of the toughest areas of the body to image. Combining advanced parallel imaging software with powerful gradients and an optical radiofrequency transmit system, the MR750 can complete high-resolution liver exams in 15 minutes, according to the company.

Routine functional MRI and complete breast exams are possible in two sequences, a GE executives said."The feedback we've gotten in MR has been that the complexity of systems is constraining the use of MR across many clinical applications today," said Jim Davis, GE vice president and general manager of global MR business. "This next generation, the MR750, is going to be much simpler and more intuitive, to speed up exams and make the scanner easier to use and, thus, enable the scanner to be used more broadly."

Slated to begin commercial shipments in late summer, the Signa MR750 will allow up to five times better imaging performance than previous generations. The product, which cleared the FDA days before its debut May 5 at the International Society for Magnetic Resonance in Medicine meeting, simplifies and speeds MR studies with accelerated scan and reconstruction times, improved image uniformity, better resolution, and extended anatomical coverage. Its gradients and scalable architecture will enable a new set of applications in the near and long term."The platform has a lot of runway left," Davis said.

Its whole-body gradient system, composed of the newly developed eXtreme gradient module and gradient driver, delivers 50 mT/m amplitude and 200 T/m/sec slew rate-a notch above the gradients onboard the current Signa HDx 3.0T, which produce 45 mT/m amplitude and a 150 T/m/sec slew. The net effect is a 60% increase in resolution, according to Dave Handler, GE general manager for MR strategic global marketing. The 48-cm field-of-view provides a similar boost in an­atomical coverage.

Parallel imaging algorithms, dubbed ARC (autocalibrating reconstruction for Cartesian), are coupled with high-definition coils to accelerate data acquisition. An optical RF system cuts noise and boosts signals, increasing the signal-to-noise ratio by 27%. Further SNR improvement comes from mounting the optical RF receivers on the side of the scanner, thereby isolating them from external sources of noise.

The receive electronics are packaged in 16-channel modules mounted on the side of the MR750. The system can accommodate eight such modules, totaling 128 channels. A new thermal management system optimizes specific absorption rate (SAR), increasing scan efficiency 17%, according to GE estimates.

GE is framing ARC as the means to reduce scan time and help keep SAR in check during abdominal imaging, as well as to handle the magnetic susceptibility effects that often come from single-shot fast spin-echo sequences. Transitioning fMRI to routine clinical use, particularly in neurosurgical planning, requires maximum fidelity and stability, a key design point in the Signa MR750's new gradient subsystem and optical RF chain.

"When we say fidelity and stability, we mean accuracy and precision," said Chris Fitzpatrick, GE's marketing programs manager for MR. "The system does precisely what it is told to do over a long period of time."

The MR750 also leverages ARC to run Lava-Ideal, a dual-echo application that acquires and outputs four image contrasts from a single scan: in-phase, opposed-phase, water-only, and fat-only. This reduces the number of scans per exam, allowing complete acquisition in a single breath-hold.

"Over 300 images are acquired in one breath-hold at very high resolution and with no misregistration of the information," said Adrian Knowles, GE's MR clinical development leader.

An enhanced version of Propeller HD accompanies the MR750. The application was introduced some five years ago to reduce artifacts due to metal implants and patient motion as can happen due to patient movement, tremor, and the flow of blood and cerebrospinal fluid.

Propeller 2.0, the enhanced version onboard GE's new 3T system, is optimized for brain imaging. Its "No Phase Wrap" technique virtually eliminates motion artifact in the sagittal, coronal, axial, and oblique planes, according to GE executives. A "split blade" technique reduces distortions such as eddy current artifacts, while a "center-out" view cuts down shading artifacts.

The new 3T scanner also runs a combination of GE's Vibrant and Ideal sequences to synthesize water and fat images when doing breast imaging. Data are captured using ultrashort in- and out-of-phase echoes, keeping scan times comparable to single-echo acquisitions despite acquiring about double the quantity of data.

Vibrant-Ideal allows for fat-free visualization of breast tissue, separating fat from water without using a suppression pulse. This eliminates the need for a separate nonfat scan yet visualizes breast structures that help rule pathology in or out, according to GE executives.

Ergonomic features built into the MR750 will boost productivityfurther. These include a detachable patient table that allows patients to be wheeled in and out of the scan room, in-table sockets for connecting coils, tableside controls to run the scan from either side of the patient, and an in-room monitor mounted atop the bore. A streamlined user interface cuts the number of steps by as much as 68%. Along with other time-saving features, these ergonomic enhancements reduce setup time in the scan room by up to 71%, according to GE.

Data collection and processing is aided by the MR750's Volume Reconstruction Engine, which GE migrated from its predecessor Signa HDx platform. The computing engine, introduced in 2006, features a 64-bit processor. The version onboard the MR750 is a new acquisition-to-disk feature that conserves memory space by loading data only when the system is ready to reconstruct images. Time-saving features built into the software, such as one that links multiple sequences, make the most of the computing horsepower.

"Once a sequence is saved, it propagates to any linked sequence, allowing all of them to autoscan," said Jessica

Buzek, a GE specialist in MR advanced applications. "Without the linking feature, the tech would have to open each of those sequences, set up slices, change parameters, save them, and scan."

The advanced clinical capabilities and ergonomic features are optimized for GE's latest 3T platform. But, over time, they and the technologies that make them possible will migrate to 1.5T, Handler said.

"This platform will proliferate the use of MR," he said.

-By Greg Freiherr