CT industry unleashes cornucopia of 32-, 40-, and 64-slice scanners

Soft market may have forced vendors' hand

A kind of frenetic one-upmanship has gripped the CT industry. Vendors unveiled at the RSNA meeting three new premium scanners, each well beyond the performance range of the current crop and each surprisingly different.

The last time war erupted among CT manufacturers, all chose an exponential leap for their flagships from four to 16. This time, there was no consensus.

On the eve of the conference, Toshiba announced that its engineers were putting the finishing touches on a scanner capable of 32 slices. It seemed the logical next step after 16, but soon the obvious was anything but. On the day the exhibit floor opened, Philips unveiled a flagship sporting 40 slices, and Siemens countered with a claim of 64.

Not since the performance of digital ultrasound systems was rated by the number of data channels has a radiological modality been so mathematically contorted. It had been so simple. Just as ultrasound systems a decade ago were wired with discrete data channels, so were the rows of sensors in CT detectors configured to acquire a set number of slices. But the number of ultrasound channels lost its allure as a convenient indicator of power when engineers began using software to direct the flow of data, allowing manufacturers to claim the presence of channels that were not hardwired into the system. CT may be approaching a similar junction in the definition of slices.

The latest addition to the Siemens' Sensation family delivers 64 slices per rotation but not in the way the CT community has come to expect. Sensation 64 uses two focal spots that sample 32 rows of detectors virtually at the same time, creating 64 slices by multiplying 32 by a factor of two.

"This translates not so much into more volume coverage, but into more resolution for the coverage given, because it provides twice the sampling density," said Bernd Ohnesoge, vice president of Siemens CT marketing and sales.

This means the Sensation 64 captures about the same anatomic volume over a set period of time as a 32-slice system but provides resolution down to 0.4 mm, better than any competing CT, he said. Siemens' proprietary Speed4D technology makes this possible. Speed4D features a souped-up x-ray tube, called the Straton, which is designed as a kind of mini-electron-beam tomography subsystem.

"The tube makes these flying focal spots," Ohnesorge said. "Other tube technologies are not capable of doing this."

There are other benefits to Speed4D. The gantry mechanism allows the fastest rotation in the industry, 0.37 second. The design of the tube allows rapid cooling with the obvious benefits of less downtime between scans. Software has been devised to boost reconstruction and optimize x-ray dose. Siemens is now preparing its submission to the FDA to market Sensation 64 in the U.S.

Toshiba's Aquilion 32, which cleared the FDA in mid-February, is built around the company's new Quantum Detector, featuring 64 rows of 0.5-mm-wide photodiodes. They can generate 32 0.5-mm slices per 0.4-second rotation, if the x-ray beam is coned down to the 32 center 0.5-mm detector rows. Alternatively, the beam can be spread over the width of the detector, adding adjacent 0.5-mm rows to produce 32 slices, each 1-mm thick. Maximum scan is 1800 mm. An Aquilion 32 is currently running at a hospital in Japan, and a second system is due to be installed this month at Johns Hopkins Medical Institutions.

Philips' superpremium system generates 40 slices with each rotation, which can be set for either 0.42 or 0.5 second. The Brilliance 40-slice scanner will generate nearly 4000 slices in a 30-second run. Optical Slip Ring technology transfers data at 5 Gb/sec, increasing signal to noise and reducing radiation dose to the patient. The RapidView reconstruction engine generates between 20 and 40 images per second. An entire data set can be reconstructed before the patient leaves the exam room.

This explosion of CT choices came as something of a surprise to anyone not in the inner circles of CT development. Just months before the RSNA conference, industry executives were downplaying the chance that a next generation of premium CT scanner might soon be released, even though the price of flagship scanners has begun to soften. Historically, the only way to prop up prices has been to release a new technology. Vendors felt compelled to announce new premium scanners, even though the 16-slice genre had been on the market for little more than two years.

The release of these new systems, however, is not about slices but about the clinical benefit they provide, CT executives said. Each sought to drive home the potential of this new breed of CTs to support advanced clinical applications.

"Speed is everything," said Doug Ryan, director of the Toshiba CT business unit.

Aquilion 32 can cover an adult patient from the aortic arch to peripheral vasculature above the ankle in 18 seconds, he said. A high-resolution scan of the heart can be done in as little as 12 seconds. Demonstrating the benefits of speed, Philips' Brilliance has visualized side branches off the main coronary arteries.

From a technological standpoint, the new detector platforms may be near the last stepping-stone before the industry jumps to a flat-panel detector. That jump is a big one. Current flat panels lack the speed and resolution needed in high-performance CT, according to Philips CT general manager Jim Green.

"High-resolution flat-panel studies run at about 30 frames per second; the highest at eight frames per second," he said. "With CT scanning, you would need 5000 frames per second."

Philips is working on an approach that might do the trick. It would hook up detectors like the one built into the Brilliance flagship in much the same way a Lego set is assembled, one block at a time, building the width of the detector outward. Using a process patented by Philips, engineers are experimenting with a method that would draw data off the backs of the photodiode arrays, thereby overcoming a major challenge to the assembly of wide area detectors.

Toshiba is also well along in the development of CT flat-panel technology. At the RSNA meeting, the company showed a flat-panel prototype that might one day be integrated into Aquilion. The flat panel features 256 rows of detectors-the number of detector rows traditionally equated with composing a full-blown area detector.

The commercial release of a product bearing such a detector is years away, as many engineering challenges have yet to be resolved. But as the latest round of slice wars demonstrates, the next step in CT may be nearer than anyone thinks.