PC Technology Builds Better Ultrasound

Off-the-shelf PC hardware and software significantly lower cost while improving performance of ultrasound systems.

Today's hospitals and health care facilities need to reduce costs, including expenditures on medical equipment. Recognizing these needs for cost reduction, Perception Inc. was founded with a mandate to build inexpensive ultrasound systems based on the PC. By exploiting available PC technology, Perception Inc.'s ultrasound machines can be offered at a fraction of the cost of traditional systems. The price of a traditional hard-wired system ranges from $150,000 to $300,000 dollars; Perception's machine will sell for about $40,000. Coupled with these cost savings are features not available with traditional systems.
Perception's ultrasound scanner system consists of a Pentium powered computer, equipped with an imaging sub-system and Perception's own Virtual Console user interface running under Windows NT. In examining a patient, the sonographer uses a hand-held probe. The signal generated by the probe is converted to standard S-video by proprietary Perception hardware. Matrox imaging hardware digitizes the video signal, transfers the image in real time to the PC's system memory, and provides desktop display with video-in-a-window.
To control the examination procedure, the operator uses the Virtual Console user interface. Image capture, adjustments such as contrast and brightness, and any measurements or annotation to the images are performed using a mouse or touch screen. The Virtual Console was developed using Microsoft Visual Basic. Board control and image processing software were developed with the 32-bit Matrox Imaging Library (MIL-32).
Virtual sliders and buttons provide the interface to commands for image capture, processing, annotation, storage, and retrieval as well as database archiving.

The Virtual Console: a marked innovation in ultrasound system control

The Virtual Console control system represents a significant advance in the ultrasound industry, since it replaces expensive and breakable hardware-based knobs, levers, and switches with "virtual knobs" represented as software-generated icons on the computer's monitor. The console can be custom-configured, so that minor software alterations such as using sliders instead of knobs can be made. It can also be configured to operate in one of fifteen languages at the touch of a virtual button. Since different examinations require different measurements (i.e. a pregnancy exam versus a gall bladder exam), various presets, or templates, are stored in the computer. In this way, the Virtual Console streamlines the examination process, saving the operator the time it would take to reconfigure the machine manually.

The PC platform's attractive price/performance

Perception's use of mainstream PC technology is part of a growing trend as developers recognize the benefits of today's PC platform. Continual advances in PC technology have recently culminated in processors such as the Pentium, the PCI bus, and 32-bit operating systems like Windows NT. These technologies work together to give the PC the performance level required for demanding applications such as medical imaging, yet mainstream PC technology is relatively inexpensive.
The Pentium processor can easily handle the intensive computational requirements of medical imaging. Execution speed for Intel processors has increased from less than 1 MIPS for the 8086 processor (introduced in 1978) to over 100 MIPS for today's Pentium. Processors will continue to get faster; even beyond the Pentium Pro that executes over 300 MIPS. Pentium Pro systems will be widely available beginning in 1996. So the CPU has the raw power, but it cannot be fully utilized if the CPU has to wait for the image to be delivered to system RAM. A fast pipeline connecting the image capture device to the CPU is needed and the PCI bus delivers this.
PCI broke the bottleneck between the powerful CPU and the peripheral device, allowing PCI frame grabbers to transfer large amounts of image data in real time to the host system memory, giving the CPU immediate and optimal access to the data. As with processor speed, bus throughput has increased from the theoretical rate of 16.66 MB/s for ISA to PCI's current theoretical rate of 132 MB/s. Actual performance however, is dependent on such things as CPU memory caching, interaction between peripheral devices, and the quality of the bus implementation. PCI bus systems using high-performance chipsets, like Intel's Triton, offer the necessary bandwidth to ensure high-rate transfer capabilities to host RAM. When used in conjunction with a system incorporating a high-performance chipset, a PCI frame grabber such as the Matrox Pulsar can generate image data transfers of up to 60 MB/s.
To harness the power of the Pentium processor and PCI bus, Windows NT is the mainstream operating system that provides maximum performance for development and runtime applications. It is a true preemptive multitasking/multithreading 32-bit operating system. Its fully re-entrant design guarantees that multiple tasks or threads have access to the operating system resources during their time-share of the CPU. Windows NT is a proven OS that offers the crash protection, security, and networking features for many demanding medical, scientific, and industrial applications.

Perception's requirements for imaging technology

Perception was born based on the idea that PC technology was up to the task of ultrasound. Their design specifications called for off-the-shelf imaging hardware and software for the PC that could also meet their objectives of high-performance and low cost. Specifically, Perception required an integrated, single-slot imaging solution with:
  • on-board high resolution display
  • real-time transfer capabilities
  • non-destructive overlay
  • support for Microsoft Visual Basic
  • portable software tools
  • a high-level imaging library
  • software that would be easy to integrate with their Virtual Console.
As with many imaging system developers, Perception required a single-slot solution to leave PCI slots free for other components, so integrated capture and display was important. The feature rich Virtual Console environment required a high resolution display so that many controls could be displayed on the desktop along with the video-in-a-window. Real-time delivery of images to the CPU was necessary for efficient processing. Non-destructive overlay was required so that Perception could provide the functionality to annotate images while preserving the original image data as captured.
Besides the lengthy wish list for the hardware, Perception required specific software functionality and support. Support for Microsoft Visual Basic was a must since Perception was developing their Virtual Console with this environment and needed to be able to easily drop in the image capture and processing functionality. In keeping with the expandability objective, Perception also insisted on portable software to ensure an easy upgrade path to future imaging hardware. Eventually, Perception will add higher-level image processing functions such as object analysis and automated gauging, so they were looking for a higher-level library that would allow software enhancements to be built into their system later. The imaging industry offers a range of PC hardware and software but Perception ultimately selected Matrox technology because it most closely met their design specifications.

Rapid application development using PC tools

Perception saw early in the design stage that the PC platform offered more than cost savings through low-cost components. The PC offered the potential to use time-saving (and therefore, money-saving) development tools. In Perception's case, the engineers had chosen Microsoft Visual Basic. Microsoft Visual Basic is a popular development environment with over 2 million packages already sold. Visual Basic is a programming system used to build Windows applications. Microsoft supplies a rapid application development environment by providing user interface code as pre-built components. The developer writes a processing function and assigns it to a display component. For example, a generic button can be given a specific graphical appearance and associated with an event such as saving to disk or processing an image. With Visual Basic, the user interface does not have to be written from scratch. By supporting the Visual Basic environment, Matrox provided Perception with access to the high-level MIL-32 operations (i.e. hardware control, image processing). This accelerated development of the imaging functions available via the Virtual Console. Other features, such as database archiving of sessions, were implemented using various third party components. Optimized third party DLLs, VBX and OLE controls that can be used with Visual Basic are available in abundance. By using Visual Basic and third party components, Perception was able to capitalize on other companies' software expertise.

The flexibility of open architecture

Device-independent software is the driving force behind open architecture. With Windows NT's support of future processors comes easy upgrading to more power. Later this year, Pentium Pro systems will start to ship, giving developers like Perception's engineers even more performance for demanding applications.
Other tools like MIL-32 provide the portability to easily move to future imaging hardware. Perception's original design incorporated an EISA frame grabber but will now use a higher performing PCI board. The switch to the PCI board was relatively seamless thanks to the device independence of MIL-32.
Using PC tools, a developer has the freedom to build an entire product line based on different PC platforms to better fulfill the range of enduser needs. For example, Perception's system is available in portable, desktop or cart-based configurations. With a portable system, a network of clinics can share a portable ultrasound device. One NASA contractor is even evaluating the portable system for use in space.
Because a PC is at the heart of Perception's ultrasound machine, database archiving of patient and test information is part of the machine itself. PC technology promises more things to come as well. Standard PC components, such as CD-ROM drives can be added to let an operator access reference materials on-line. PC teleconferencing technology will allow professionals to discuss cases over long distances. Remote access to files and exams via networks will also prove to be a major advance. The system software will even be field upgradable via modem. New PC technology will continue to bring affordable new functionality to ultrasound systems.

The future is now

Developing using PC technology has numerous benefits and at no time in its history has this been more true. More developers are building systems based on the PC that compete with proprietary solutions and sell for much less. The availability of cutting edge, low-cost hardware tools, rapid application software development tools such as Microsoft Visual Basic and MIL-32, and a robust and secure operating environment such as Windows NT are reasons the PC is becoming the platform of choice for even more developers. Easy upgradability to the faster and less expensive PC technology of tomorrow is another. The bottom line is that using PC technology saves time and money during the development process; and lower cost, high-quality equipment is available more quickly to the markets that need it.
Original article featured in Lasers & Optronics, January 1996
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