The actual time a technology arrives, the moment when it becomes the standard against which others in its class are compared, is apparent only in retrospect. It comes not with the realization of a single metric or even several. Rather, its arrival is marked by a change in attitude, when the development of other technologies begins to revolve around it. That time may have come for 3T, at least at GE Healthcare.
“Historically, we went [up] from 1.5T to 3T,” said Baldev Ahluwalia, director of GE's MR product development. “Now we are solving for the more challenging 3T and moving down to the less challenging 1.5T.”
The argument for moving from more to less difficult is valid for current day development of these scanners, but it would have been just as valid—or more so—in previous years, when knob twisting and sequence tweaking were what 3T was all about.
Lately, the edge separating the operation of 3T and 1.5T scanners has softened, a direct result of efforts to homogenize the components built into these systems. While the components are certainly not interchangeable among GE scanners of different field strengths, they are based on the same principles.
“The technologies in the 750 and the 450 are very similar,” Ahluwalia said. “They are based on platforms that allow us to push MR and grow the capability.”
This change toward a commonality between the two field strengths has come with the building of more and more 3T scanners. Over the past several years, 3T has transitioned from research to clinical applications. Yearto- year growth has risen in double, sometimes almost triple digits, leading vendors to seek economies of scale in shared components.
Once, greater economies could be achieved through a closer relationship with technologies built for 1.5T scanners. Now 3T has come into its own. Recognized as a leadingedge clinical tool, 3T uses advances made for it that are more easily trickled down to 1.5T than pushed up to 3T.
GE's 3T and 1.5T scanners feature shared gradient technologies and rely on similar optical radiofrequency systems to acquire and manage data. Common technologies underlie their receive channels and data reconstruction, as well as hardware and software for improving workflow. These include common means for interacting with the system and managing processed data, allowing GE to automate many of the steps for acquiring and processing data. This approach has sped up scans for both 1.5T and 3T systems.
As their names imply, the MR750 and MR450 are members of the same Discovery class of products, a class recently established by GE to indicate premium products.
“Buyers of this class are looking to bring a clinical advantage to their community, as in a center of excellence or a site where they want to make a mark as being more clinically advanced than competitors,” said Chris Fitzpatrick, MR marketing programs manager for GE. “They want cuttingedge hardware, specifications, and value at 1.5T and 3T.”
Just as the technology at GE is trickling down from 3T to 1.5T, so are the clinical applications. Shared clinical applications on Discovery MR750 and MR450 include SWAN (T2 Star Weighted Angiography) for visualizing small vessels and microbleeds, assessing iron and calcium deposits, and imaging vasculature of the brain in 3D at high resolution.
A major difference between SWAN on the two products of different field strengths is the time needed to complete the scans: six minutes at 1.5T versus three minutes at 3T. The clinical results are on a par regardless of the field strengths, according to Fitzpatrick.
Stroke imaging has emerged in early luminary studies as a major use. The application has the resolution to find microbleeds in the brain, he said. Another potential is to visualize the deep brain nuclei that indicate Parkinson's disease.
Another area of applications made possible by the shared technologies among the MR750 and MR450 also addresses vascular imaging. GE's Inhance allows vascular imaging without the administration of contrast media. This is particularly applicable to examining the renal arteries in patients who may be susceptible to gadolinium-linked nephrogenic systemic fibrosis.
Variants of Inhance are designed for specific parts of the body. Inhance 3D Velocity is a phase-contrast-based sequence optimized to acquire 3D MR angiography images in the brain and abdomen. Inhance 2D Inflow is optimized to visualize straight-path blood vessels, such as femoral and tibial arteries, found when doing peripheral angiography. It can also be used to see the carotids.
Inhance 3D Velocity captures both arteries and veins. Postprocessing can be done to segment blood vessels and parts of the brain. Examinations of the abdomen, such as ones to capture the renal arteries, may be gated to control for respiratory motion. Velocity eliminates pulsatility artifacts sometimes seen in peripheral exams.
These and other packages developed for the MR750 and MR450 ultimately will find their way to GE's Signa platform. Like the migration from Discovery class 3T to 1.5T, the latest iteration of this platform, Signa HDxt, is reaping the benefits of an engineering concept that goes from more to less challenging, one that remains in alignment with a basic tenet of GE MR engineering: to maintain upgradability from early to later releases.
“We have customers with 18-year-old magnets who can upgrade to the HDxt platform or Discovery 750 or 450,” Ahluwalia said. “The continuum is still alive and well.”
