Diasonics creates stir with transmit claims

Debate continues in the industry over how radical Diasonics' confocalimaging ultrasound technology really is--and whether it is possibleto eliminate the risk of interzone artifacts. All sides agree,however, that clinical investigation will provide the answers.

When Diasonics revealed its variable summation technology (VST)upgrade for the Spectra ultrasound system to the clinical communityin March, it claimed that confocal imaging had progressed beyondexisting multizone transmit technology.

The confocal beamforming technology concentrates the energyof an ultrasound transmission pulse so well within a focal zonethat rapid firing of subsequent pulses is possible without interzoneartifacts, the company said. Transmit focus is effectively continuous,said Omar Ishrak, Diasonics' vice president of product development.

"The key point we are trying to communicate about thetechnology is that we have enough zones necessary to effectivelymake the transmit focus continuous, which is what people say theyhave in receive," Ishrak told SCAN.

Multizone transmit focus is used by most, if not all, high-endultrasound companies, noted Eugene A. Larson, ATL executive vicepresident, in an internal company memo.

"The (ATL) Ultramark 9 HDI architecture is capable ofthe same multiple transmit zone focusing with transmit frequencyoptimization concepts as Diasonics is claiming for the Spectra2000," Larson said.

Acuson, which first developed multizone transmit technologyin 1983, also adjusts multiple parameters to concentrate and focusthe transmitted energy, said Samuel H. Maslak, president and CEO.

Depending on transducers and other variables, Diasonics hasreduced the minimum transmit zone size by a factor of five to10, obtaining a zone as small as 1 mm, Ishrak said.

"We are adjusting the focal point each time, just as (othervendors) are from one point to another in fine steps, but in finersteps," he said.

Acuson offers 5-mm spacing on transmit zones with two transducersand could reduce this further if it chose to, Maslak said.

"We internally impose a minimum interpulse period forB-mode imaging to reduce the risk of interline or interzone artifacts,"Maslak said. "We do this because we know that over-aggressiveuse of transmit multizone exposes users to diagnostic errors thatcan be caused by interzone artifacts. Interzone artifacts occurunpredictably, particularly when imaging fluid-filled or cysticstructures."

When vendors attempt to concentrate the beam energy at onedepth during transmission, they can normally depend on the bodyto attenuate interpulse sound, he said. Unfortunately, there isstill a possibility of interzone artifacts that can create theappearance of a solid rather than a fluid-filled structure. Thisstructure might be misinterpreted as malignant.

"In many instances--probably 95% of the imaging you do--youdon't notice those interzone artifacts when looking for them.That is why we worry about them so much," Maslak said.

Acuson's dynamic computed lens system does provide continuousadjustment of focus on receive, even within the period of a singlepulse, he said. A distinction should be made between dynamic receivefocus and rapid multizone transmit focus, he said.

"There is no instant in time that lasts for more than,say 100 nanoseconds, when Acuson is not updating its receive dynamiccomputed lens system," Maslak said. "The term dynamic,as typically used in ultrasound, refers to any process accomplishedduring the period when a single pulse is fired into the body andechoes are received from that single pulse. No matter how manytransmit zones you have or how they are spaced, the fact thatthese zones are connected with different transmit pulses meansthat, by definition, it is not a dynamic process but a sequentialone."

Whether confocal imaging will be considered as aggressive multizonetransmit sequencing, similar to other efforts in the past, oras a significant breakthrough in ultrasound technology, dependson how Spectra's diagnostic quality and accuracy are judged byclinical users.

"One man's evolution may be somebody else's revolution.If doctors can see things they think are useful and revolutionary,over time that is what it will be called," Ishrak said.

It is clear, however, that Diasonics has improved its own product,stirred clinical interest and restored some of its past reputationas a technological leader in ultrasound.

"Somewhere over the years, Diasonics lost its focus,"said Dr. Thomas Stavros, a radiologist with Swedish Hospital inDenver. "For the first time in about 10 years, this (theVST upgrade) puts Diasonics back in a position where it has somethingnobody else has that significantly improves the image."