Multislice scanners could presage next revolution in CT technology

GE and Toshiba show new systems; Siemens is on deck

Are you ready for the next technology wave in computed tomography? The CT industry got a glimpse of what lies ahead when GE Medical Systems and Toshiba America Medical Systems introduced new CT scanners this month that employ multislice technology that allows physicians to scan patients faster and with more anatomical detail than ever before. The new systems represent a leap in technology that could be as significant as the introduction of spiral CT in the late 1980s.

Of the two companies, GE made the bigger splash. The Milwaukee vendor introduced its new LightSpeed QX/i scanner at a press conference held Sept. 10 at the Waldorf Astoria Hotel in New York City. The event was attended not only by GEMS executives but also by GE chairman and CEO Jack Welch, who made the appearance to highlight the fact that LightSpeed is the first product whose entire design is based on the engineering principles implicit in GE’s Six Sigma quality initiative. Welch has championed Six Sigma for the past several years as a means for GE to operate more efficiently and to introduce better products more quickly.

Although Toshiba chose a more low-key introduction, its offering in the multislice CT fray is also impressive. The multislice version of the company’s new Aquilion scanner will use a four-slice detector with a half-second rotation time, allowing the system to collect eight slices of data per second.

LightSpeed and Aquilion represent the application of multislice technology to CT. With the exception of Elscint’s CT-Twin scanner, CT systems on the market operate with their detectors collecting a single slice of information for each rotation of the patient. CT-Twin was introduced in 1991 and employs a dual row of detectors to collect twice as much information as conventional scanners (SCAN 2/12/92).

There are several advantages to multislice scanning, and clinicians using a multislice system can emphasize either speed or resolution. By collecting more data in each rotation of the patient, multislice CT scanners can complete a full study in far less time than a single-slice system. Or, clinicians can set the scanner to collect thinner slices in the same amount of time, producing an image of a particular organ in much more detail than available with existing technology. Multislice scanners also put less strain on the scanner’s x-ray tube, enabling the system to scan for longer time periods with less heat loading.

In LightSpeed’s case, GE has divided the system’s detectors into 16 rows that scan as many as four adjacent slices. Like GE’s HiSpeed line, the LightSpeed detectors are based on solid-state technology. But the HiSpeed detectors are arranged in 844 channels that are 1 mm wide and 20 mm tall. The LightSpeed Matrix Detector, on the other hand, is configured in a matrix of channels that are 1 mm wide and 1.25 mm tall, resulting in a detector with 14,592 individual elements.

Combined with the system’s 0.8-second rotation time, LightSpeed is capable of producing 7.5 images per second. This enables clinicians using the scanner to conduct scans in 20 seconds that previously took three minutes, according to Vivek Paul, general manager of GE’s global CT business. The faster scanning time is especially important because it allows most exams to be conducted in less than a breath-hold, an important consideration in reducing motion artifacts.

GE didn’t stop with LightSpeed’s detector array, however. Using Six Sigma design processes, the company completely reengineered its CT platform, developing breakthroughs in design materials, software, electronics, and computers, Paul said. For example, the additional data collected with the system require more computer horsepower, so GE built a second Silicon Graphics computer into the scanner, in addition to the system’s conventional workstation. GE spent a total of $60 million on developing LightSpeed.

GE began examining multislice technology when the company realized that it was pushing the envelope of single-slice performance, Paul said. The company’s most recent upgrade to its flagship CT/i Pro single-slice scanner doubled the performance of the system (SCAN 5/13/98). Although impressive, such an increase could not realistically be considered a revolutionary boost in performance, and it is the lack of such a breakthrough technology that has caused sales in CT’s premium segment to drop off of late.

“If you look at the market, the premium segment has declined over the last year or so because it is looking for some real breakthrough technology,” Paul said.

At the same time, radiologists on the medical advisory boards that work with GE have been pushing the company to advance spiral scanning technology to the point where it is capable of conducting a single scan in the breath-hold of a sick patient, according to Paul Mirabella, vice president of Americas sales and marketing. LightSpeed represents GE’s effort to develop a system that meets both clinical requirements and the need for a new technology that revitalizes the premium CT segment.

LightSpeed has already received 510(k) clearance from the Food and Drug Administration, and GE began commercially shipping the systems with the Sept. 10 announcement. Three systems have already been installed at clinical sites in the U.S., and GE has made sales to an impressive array of luminary institutions. LightSpeed will carry a list price of about $1.25 million.

Toshiba’s Aquilion. Toshiba will offer multislice scanning on Aquilion, a new CT scanner it plans to begin selling this year. The Tustin, CA, company began examining multislice CT after determining that clinicians have been driving existing CT technology to the limit. A new design was needed to move the technology forward, according to Charles Corogenes, director of the CT business unit at TAMS.

“We looked at the way CT is going, with more and more volume and interventional studies, and increasing use in trauma and oncology. Clinicians are pushing these systems to new limits at which they’ve never been used before,” he said. “Toshiba’s position was to redesign and reengineer a whole new CT to accommodate the new advances that are coming forth, such as multislice scanning.”

Toshiba has approached multislice scanning from a slightly different angle than GE, however. Like LightSpeed, the multislice version of Aquilion will collect four slices per rotation. But its half-second rotation time is 38% faster than the GE scanner’s 0.8-second speed. As a result, Aquilion will be able to collect eight slices per second, a slight edge on the GE system. The system will also be capable of collecting slices as thin as 0.5 mm, according to Toshiba.

Aquilion’s rapid rotation speed creates 13 Gs of force on the rotating assembly, requiring the design of a gantry and components that can handle the added stress. The company also designed a special x-ray tube and generator for the scanner. Toshiba’s G-Shaft tube design passes the shaft through the anode, increasing the tube’s structural integrity, Corogenes said. Another Toshiba tube design, called PureFocus, consists of a collimator in the G-Shaft tube that eliminates off-focal electrons that can create heat in the tube and degrade image quality. As a result of PureFocus, Aquilion’s 7.5-million-heat-unit x-ray tube has an effective heat rating of 10 MHU, Corogenes said.

Meanwhile, Toshiba’s new on-board G-Generator eliminates oil, which conventional generators use as an insulating material, making G-Generator lighter. Conventional generators are too heavy to be rotated around a gantry in a half-second, according to Corogenes. Other advances had to be made in reconstruction algorithms, due to the effect of multislice scanning, according to Bill Wilson, CT product manager.

Aquilion received 510(k) clearance in August as a single-slice scanner and will begin shipping prior to this year’s Radiological Society of North America meeting. The company’s multislice package is still a work-in-progress, however, and will be introduced as an upgrade to Aquilion. The multislice upgrade will involve the exchange of some of the components in the gantry but will not require a full gantry swap, Corogenes said.

Clinical improvements. Multislice scanning should confer benefits across all CT applications, according to both GE and Toshiba executives. Patients will be more comfortable during CT exams, and it will dramatically improve throughput at radiology departments. A multislice CT study can be completed in 15 minutes, compared with 45 minutes using older scanners, according to Dr. Carl Ravin, chairman of the department of radiology at Duke Medical Center in Durham, NC. Duke is one of the first three LightSpeed installations, along with Stanford University in California and Froedert Memorial Lutheran Hospital in Milwaukee.

Other applications, such as contrast imaging and interventional CT, will also improve. The most significant advance is that multislice scanning will enable CT to move one step closer to medical imaging’s boom market: cardiac imaging. The faster scan times possible with systems like LightSpeed and Aquilion will bring improvements to cardiac scoring packages by minimizing the impact of motion artifacts produced by the beating of the heart.

GE was coy about LightSpeed’s potential as a cardiac scanner. The company in August received clearance for a coronary artery calcification scoring package for its single-slice HiSpeed line, which now can be used to scan patients for evidence of the calcifications that can be a precursor to heart disease. The vendor said it plans to introduce a cardiac package for LightSpeed, but wants to investigate the technology on the HiSpeed line first.

Toshiba also was reticent about the potential of Aquilion for cardiac scanning. The company believes that by running a multislice Aquilion in partial scanning mode, the system can collect images at 300-millisecond intervals. That’s approaching the speed of Imatron’s Ultrafast CT scanner, currently considered the gold standard for cardiac CT scanning. But CT calcium scoring still requires clinical validation, according to Corogenes.

Whether the new scanners will impact sales of Imatron scanners is unknown. GE acquired rights to sell the systems in June (SCAN 6/24/98), and GE executives said they believe that there will still be demand for a dedicated heart imaging CT scanner among cardiology practices.

“If you are a busy cardiology practice, need enormous throughput, and want a dedicated cardiology scanner, you probably will still want the Imatron scanner,” Paul said.

The rollout of multislice technology could also have a dramatic impact on other CT vendors. Those companies without multislice offerings could find themselves locked out of CT’s newly developing super-premium segment. One other vendor, Siemens Medical Systems of Iselin, NJ, has scheduled a CT product announcement for Oct. 1 that most likely will involve multislice technology. Indeed, industry observers have speculated that the curious timing of three major CT introductions in one month is being driven by the desire of CT manufacturers to avoid being upstaged by their competitors.

One limiting factor to multislice CT’s success could be its price tag, however. Some hospitals may balk at paying $1.25 million for a LightSpeed scanner, which is as much as some MRI scanners cost. Toshiba’s multislice version of Aquilion will probably sell at about $1.3 million.

“I don’t think the market will pay over $1 million for a CT scanner anymore,” said Chuck Armstrong, CT/MRI product manager at Elscint of Hackensack, NJ. “Those days are over.”

Not surprisingly, GE executives would disagree. The company rolled out a laundry list of sites that have already committed to purchasing the systems, with one site—Toronto Hospital—placing an order for three scanners. The company hopes to have 400 LightSpeed systems installed by 2000. Mirabella believes that the value of multislice scanning will justify the price, especially as hospitals strive to differentiate themselves through the use of high-end imaging technology.

“What you’re seeing in the market is that where you can substantiate value, you are not getting a lot of resistance to price,” Mirabella said. “It’s not so much a price issue as it is a value issue.”

If GE, Toshiba, and other CT vendors are successful in selling multislice CT, the modality could experience another wave of replacement purchasing that will keep CT sales healthy for years to come. The extent of the improvement depends on whether multislice CT will enable the development of new applications that will drive CT usage, according to Scott Balsters, clinical analyst for CT technology at MDB Information Network in Dallas. Until then, the market for multislice CT may be restricted to luminary sites with the cash to spend.

“Multislice CT will definitely help the CT market. But for the next few years, probably only large university teaching facilities will buy them,” Balsters said. “Mid-sized hospitals will still be buying the upper-end helical systems. We haven’t tapped into some of the new applications yet, even beyond cardiac.”