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Ultrasound Trendsetting

Ultrasound Trendsetting

Figure 1. Smartphone snapshot of a demo scan of a sea sponge in Evian ...
Figure 2. A 30 mm by 30 mm portion of a natural sea sponge.

I had intended to knock off an article right after the RSNA, featuring commercial equipment first with clinical topics from the scientific sessions to follow. My original assignment was to report on ‘trends’. While I was trying to decide on practice pertinent trendiness, I got distracted by a glimmer of an issue below the radar concerning differences in trendsetting now versus the good old and/or wild west days when ultrasound imaging was still pretty new.

Before I tackle something elusive, I want to issue my own post-RSNA ‘Somascope’ Awards for commercial equipment, named for the original B-mode imaging device invented and built by Dr. Douglas Howry about 65 years ago. Incidentally, the first test object for the water immersion Reflectoscope (its original name) was a fluid-filled condom. I was looking forward to working with Dr. Howry at Massachusetts General Hospital, but he died shortly before I was to begin my diagnostic radiology residency there. I eventually started the clinical service for the hospital when I was a resident using an Aloka unit via the radar and nuclear medicine experts at the Raytheon Corporation in Waltham.

The Somascope for best full system goes to Supersonic Imagine. The Aixplorer, now in its eleventh major update, is best in class for image quality, Doppler sensitivity, and elastography. The Somascope for best portable unit goes to the Sonoscanner U-Lite for image quality, six interchangeable transducers, and a range of quantitative apps configured for subspecialty ultrasound indications. I happen to know those systems very well, because I was on the science board for Supersonic during its early years, and I have that position for Sonoscanner now. That is both a disclosure and a statement of pride that I was asked to contribute to these innovative and worthy companies.

I quite liked the SOFIA automated breast scan unit from Hitachi, which includes C-scan reconstruction, and the Delphinus SoftVue, which is now in phase III clinical trials. The SoftVue does a CT-type reconstruction of ultrasound propagation velocity. I intend to explore these units and their fundamentals subsequently. I also want to make a class Pre-Somatoscope award for the few companies who have commercial photoacoustic units ready for investigation.

LIVE Scanning
The most recent RSNA allowed live ultrasound scanning of models. I do not think that was a WISE choice (which is my own opinion and a play on the Image WISEly campaign). The big companies will demo their finest, highly tweaked, and not necessarily commercial, equipment on movie models, slender, stunning, and fit. It is not a particularly educational or edifying exercise. As much as I like watching and admire skillful demonstrators do their thing, prolonged frivolous scanning of paid models kind of trivializes the serious nature of what we do with medical imaging on real patients every day. The ALARA principle is a good one, even considering the apparent extreme biological safety of pulsed ultrasound.

Beam Former Review
The beam former is the brain and soul of a modern ultrasound device. There are two basic kinds of beam formers, passive and dynamic. The beam former is also mated specifically to transducers, so that these are actually one functional unit like a radio and its antenna, or radar and its antenna array.

This is a brief reiteration of my pre-RSNA article. Simple, passive beam formers were state of the art in the 1980s, and are now fabricated on chips in relatively small packages. There were many new commercial units at Medica 2016 in Dusseldorf that had a passive beam former between a transducer and a separate (and physically separated) display module like a smart phone or tablet. Several of these will likely appear at next year’s RSNA.

There are relatively few, complex and technically evolved dynamic beam formers which characterize “high-end” equipment. These devices have multiple transmit options, like compounding and harmonics, and quasi-holographic focusing, and they may involve plane wave insonification or other stratagems to improve on the conventional and inefficient line-by-line form of image synthesis. There are pre-beamforming stages to handle the vast amount of raw data from all of the elements of the array. There are complex algorithms that optimize the final display from real-time analysis of signal features from different parts of the insonified field. There are compressed sensing methods, injection of statistical priors, and adaptive filtering operations, which is very demanding of hardware. The results are absolutely worth it, because of the gigantic improvement in the detail, speed, and reliability of exams.

One of the ploys of large manufacturers is to use a dynamic beam former with some of its functionality removed in a smaller, cheaper version of their flagship unit, like a platform ‘yacht’, marketed at a lower cost. I’ve talked about this before. It’s pretty fishy. My own opinion is that anyone who knowingly vends a limited performance device for diagnostic medical usage is contributing to the potential for medical negligence.

The problem for the prospective buyer is figuring out what system performance really may be.

Something Old
I ambled across the massive North Exhibit Hall at McCormick place to the charming and quaint, and peripheral, French Quarter. The booths were smallish, the technology was way high, and the coffee was superb. My goal was to visit my friends at Sonoscanner. Figure 1 is the demo setup. I guess you could say that this is an example of hands-on scanning.

Typically, the higher the center frequency, the more the speckle noise, but here, noise is absent. The image is in focus throughout the field, and if you look at the vertical edges, there is no lateral resolution spread. There is a ‘parenchymal’ substructure with visible gray scale features. If Figure 1 can be magnified, have a look at the actual sponge within the beaker cup. Contrast and spatial resolution are both improved by noise reduction, like twice the bang for your center frequency and bandwidth dollar.

Something New
Excuse me for the almost bridal references. ‘Borrowed’ does not work, except maybe for trial use, and there isn’t anything blue about the U-Lite except the color Doppler display map. The new thing that I want to point out is the cable from the U-Lite to the transducer. It’s a fully flexible, weightless noodle. I do not know how it is made; I suppose it is a trade secret because there are a lot of no-loss wires for all the elements of an array. But, it is a significant and practical feature from the standpoint of the person scanning.

I am emphasizing the cable, because there has been a massive amount of hype from and about the Clarius portable unit, which is the counterpoint in this tale of two cities. A stated rationale for development for the Clarius, seems to have been an alleged need to replace a weightless wire bundle with a wireless transducer and a separate handheld display unit.

It is ironic that this ‘innovative’ development was presented at RSNA at least four years ago by Siemens as the Acuson Freestyle unit with a high capacity bluetooth transmission link from the transducers to the processor and display unit. My recollection is an excellent level of noise reduction for its three available transducers and buttons on the transducer case.

By the way, do you recall in old ultrasound systems that did line-by-line image synthesis, the tradeoff between line density and speed of imaging? There are tradeoffs between the number of elements in a transducer array, the data transmission capacity from transducer to processor, and image quality. The way to assess this, like image noise, is to view the image on a full-sized display, not a tiny screen.

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