GE enhances LightSpeed VCT at RSNA meeting

Software upgrades introduced by GE Healthcare this week for the company's LightSpeed VCT scanner promise to cut patient x-ray dose for coronary CT angiography by 70% or more and double the area covered during dynamic angiography and perfusion.

Both upgrades, SnapShot Pulse for the heart and Volume Shuttle for other organs, change the scanner mode from a conventional helical acquisition to step-and-shoot mode, turning the x-ray beam off between axial acquisitions following each step of the patient through the gantry.

With each gantry rotation, SnapShot Pulse acquires data on a section of the heart the width of the 64-slice detector, then steps the patient ahead that distance, about 3.5 cm, in preparation for the next scan. Prospective ECG gating ensures that data are obtained at the same phase in the cardiac cycle.

This step-and-shoot method cuts dose during a coronary CT angiogram to as little as - or even less than - 1 mSv from 20 mSv or more using helical scanning. The size of the patient and the heart rate dictate how much the dose can be cut.

One patient scanned by GE luminary Dr. James Earls weighed 155 pounds and had a heart rate of between 34 and 38 beats per minute; the patient required just 0.932 mSv. Large patients with a quick pulse require more dose. What they get with SnapShot Pulse, however, is a lot less than they would otherwise.

"This opens the door to a lot of things that we felt we couldn't do because of the radiation dose issue," Earls said. "In the past we have done cardiac CT as a one-shot test to see where patients are in regard to cardiovascular disease. Now, with this low dose, in cases of bypass grafts or coronary stents we are in a position to image them routinely in a sequential manner over a period of years without worrying about cumulative radiation doses."

The other software upgrade introduced at the RSNA meeting, Volume Shuttle, scans one axial section of the brain, for example, then, with the x-ray beam off, steps the patient forward to scan the next section. Rather than continuing to advance, as would happen with SnapShot Pulse, however, Volume Shuttle steps the patient back to the beginning position, covering old ground. It then retraces its step forward. In this way, the table shuttles back and forth, doubling coverage of the anatomy, while minimizing dose, as the x-ray beam is turned off between rotations.

"By doing the shuttle, we have enough volume coverage so that with one contrast injection the vessels light up and perfusion of the surrounding tissue can be assessed," said Brian J. Duchinsky, global general manager for GE Healthcare's CT business. "This is most important for the assessment of tissue surrounding an occlusion, aneurysm, or some event."

The two techniques are variations of works-in-progress described earlier this year (DI SCAN 5/28/06, GE engineers integrate future technologies with LightSpeed VCT).

The software, augmented by an improved data acquisition system, the Volara XT, and a more powerful computing platform, Xtream XT, will begin shipping onboard rebranded LightSpeed VCT XTs by the end of this year. The installed base of some 1200 LightSpeed VCTs may be upgradeable to run both techniques with nothing more than the addition of software, but GE is still deciding whether to add the advanced data acquisition and computing hardware to speed the process.

Current VCT owners might be given the option of installing just the software, according to Gene Saragnese, GE's global vice president of molecular imaging and CT.

"We want to be as responsible as we can and get the upgrades out as cost-effectively as possible, he said.

Whatever their final forms, the upgrades should be available by midyear, he said.