Data pipeline paves way for new generation of MR surface coils

April 1, 2005

Speed has long been radiology's drug of choice. For years, faster was undeniably better. But now, with detectors firing signals in picoseconds and computers gigaflopping this way and that, speed needs a purpose. Through its Excite High Definition (HD) MR, GE Healthcare has defined one.

Speed has long been radiology's drug of choice. For years, faster was undeniably better. But now, with detectors firing signals in picoseconds and computers gigaflopping this way and that, speed needs a purpose. Through its Excite High Definition (HD) MR, GE Healthcare has defined one.

Applications that stop motion artifact in its tracks have often had the same effect on a radiology department, dragging reconstructions out for so long that they become impractical. The latest iteration of the company's Excite data pipeline tackles that problem, with impressive results.

"My brain exams are higher resolution and faster. My abdominal exams have higher in-plane resolution and deliver thinner slices," said Dr. Lawrence Tanenbaum, section chief of MRI, CT, and neuroradiology for Edison Imaging in New Jersey. "We are getting sharper images that allow us to see smaller lesions in shorter times."

Difficult applications have been the first to benefit. Primary among them are brain scans of patients who have trouble keeping still, such as children and those with Parkinson's disease. The technique is especially suited to children because it obviates the costs and risks of sedation.

The data being processed by HDMR come from a new generation of coil technology. Sixteen-channel coils for the head and other body parts are becoming more prevalent. The increased data flow from these coils and the advanced processing capabilities of HDMR allow MR information to be gathered in novel ways. For example, the Propeller method acquires data radially rather than in conventional rectilinear fashion. Propeller is relatively insensitive to motion and therefore ideally suited for use with patients likely to move. Its radial acquisition of data "sprays" artifacts out of the volume rather than through it, according to Tanenbaum.

"Under strenuous circumstances, there is actually a mechanism built into Propeller that corrects for patient motion," he said. "So, for all intents and purposes, you can get images that are motion-free even from unsedated children and adults who can't cooperate because of tremor, as with Parkinson's."

HDMR can also be used to speed up scan times, as in the case of Vibrant (volume imaging for breast assessment). This bilateral breast imaging technique integrates fat-suppression with GE's parallel imaging technology.

"Breast MR has traditionally been very difficult to perform. It has been time-consuming, and the results have been inconsistent," Tanenbaum said. "With Vibrant, we get reliable results in a reasonable amount of time."

GE has bolstered the power of HDMR with the introduction of a next-generation 32-element peripheral vascular coil that extends below the knee and covers each foot with what looks like a ski boot.

This coil boosts the signal-to-noise ratio by a power of 15 compared with the SNR typically delivered by a body coil, said Dr. Steven D. Wolff, director of cardiovascular MRI and CT at the Cardiovascular Research Foundation in New York City. By comparison, the typical torso coil boosts SNR by a power of two or three.

The new coil, in combination with HDMR, allows dynamic imaging of blood flow. Blood vessels enhance at different phases and at different times. With this combination, Wolff and colleagues can even control for enhancement at different times in each leg.

"This has really changed the way we do runoffs," he said. "We don't even have to do a test bolus. We just inject 8 cc of contrast, turn on the coils, and image for a minute or two."

Traditionally, MR angiography and CTA are static techniques. They provide snapshots of only single points in time, whereas x-ray angiography depicts flow.

Dynamic MRA of the peripherals is possible because of the time-resolved imaging of contrast kinetics (TRICKS) data acquisition technique, which itself is made practical by HDMR. TRICKS automatically produces maximum intensity projections through each 3D volume.

"With TRICKS, we can image over time," Tanenbaum said. "This can be helpful in imaging complex vascular anatomy. We see below the knee where collateral flow and retrograde flow are common features of the pathophysiology in patients with vascular disease."

HDMR excels at handling difficult applications, but it is not so constrained. Any application might benefit from its use, he said. As a result, this technology could have a profound effect on radiology.

"We are seeing a new level of image quality where physiologic effects do not create artifacts the way they do with traditional scanning," Tanenbaum said.