Toshiba prepares to enter upper echelon of CT scanning

Aquilion 16 may hit production stride by year's end

Toshiba America Medical Systems expects to begin routine shipments of its 16-slice Aquilion CT scanner to U.S. customers in December. The company has been cleared by the FDA to market Aquilion 16 in the U.S. but will not crank up production until beta clinical testing is completed.

At present, only two 16-slice Aquilions are operating at clinical sites--one in Japan, the other in Europe. At least three more are scheduled to be installed in the U.S. by Oct. 1, according to John Zimmer, TAMS vice president of marketing. Two will be sited at Johns Hopkins Medical Institutions, with one dedicated to interventional radiology and the other to cardiology. The third will be sited at Long Beach Memorial Hospital in California.

A scaled-down version is already in operation at Johns Hopkins. The system has a full-sized 32-mm detector capable of 16 slices, but it has been outfitted with only eight data acquisition systems.

"The testing is designed to prove reliability and functionality of the system," Zimmer said.

Before going into routine production, Toshiba wants sufficient feedback from the beta sites around the world to ensure that clinical performance is as good as it should be. The company is also working out issues regarding rotational speed.

Toshiba reports that Aquilion can achieve both 500- and 400-msec rotation. According to Zimmer, millisecond measurements were chosen because of the recent flap (SCAN 5/1/02) about whether Siemens scanners were rotating at 0.4 or 0.42 second. Toshiba cannot guarantee that the production line Aquilion 16 will rotate at 400 msec, because the FDA has not yet cleared the scanner at this rotational speed. Such clearance is expected in time for the commercial rollout, however.

Toshiba's 16-slice CT will face tough competition. Both Philips and Siemens are in full production with their own 16-slicers, the Mx 8000 and Sensation 16, respectively. GE Medical Systems has been shipping its eight-slice LightSpeed Ultra since last year and could begin routine production of a 16-slice version before the end of 2002. Zimmer is confident, however, that Toshiba will do well against these other systems.

"Aquilion will really blossom in the 16-slice configuration," he said. "Fundamental differences in the design of our system compared with other scanners will create interesting dilemmas for our competitors."

Toshiba claims a 16% greater z-axis coverage and advantages in slice thickness and dose. The company's detector can produce 16 isotropic 0.5-mm voxels, Zimmer said, thanks in part to advanced conebeam algorithms.

Dose advantages with the Aquilion are achieved through software control and hardware advances, including a more efficient detector material. Quantitative measures of this dose advantage are difficult to assess, however. The quad-slice Aquilion delivers approximately 40% less dose than competing multislice scanners, according to test results cited by Toshiba. But competitors dispute these conclusions, citing contradictory results when the scanners are compared using the widely accepted CT Dose Index, which is designed to measure the amount of dose emitted by the x-ray tube. Toshiba has countered with the argument that CTDI is not related to the patient-absorbed dose, which is the basis for Toshiba's claims of lower dose delivery by Aquilion.

The discussion will only intensify now that 16-slice scanners are entering the market. Independent comparisons of performance will be stymied until enough of the scanners are available to support such testing. Even then, the debate over which tests to use will muddy the waters. The FDA on its Web site notes two different types of CTDI, weighted and volume, as well as two other measures: multiple scan average dose and the dose-length product. The agency notes only that these measures exist, refusing to explain what they are, because "it is beyond the scope of this discussion to describe these unique dose descriptors."

In the debate over dose, and the looming fight among vendors for market share on this new high ground of CT, discretion such as this will likely be the exception.