ARTICLE FOCUS:

• FPGA and AFE make for dynamic duo
• How ultrasound imaging prototype was achieved
• Scalable and customizable system is end result

Reducing time-to-market while increasing the rate at which new technologies are integrated into today's medical imaging systems are presenting design challenges. A difference of even a few months in the release of a product can significantly impact the return on investment (ROI) of the project, both from missed revenue and a missed market window. Meanwhile, medical imaging system developers also are being required to integrate the latest technology to build systems with excellent analog performance, complex processing and visualization, and high data throughput resulting from higher speed analog-to-digital converters (ADCs) and increasing channel counts.

Several tools are now available to help engineers quickly prototype new designs and deliver the best performance in their systems. These tools help developers use reconfigurable field-programmable gate array (FPGA) technologies and integrated analog front-ends (AFEs) coupled with flexible integration platforms to develop prototype imaging systems faster. Developers are now able to combine modular FPGA hardware, integrated AFEs, higher-level design tools, and industry-standard platforms to create highly flexible, scalable, and customizable imaging systems.

Prototype ultrasound imaging system in just three months
A UK-based company, Diagnostic Sonar (diagnosticsonar.com) demonstrated this concept in a novel phased-array ultrasound imaging system. Designing around off-the-shelf FPGA hardware, application-specific integrated AFEs, and using higher-level design tools, it went from specifying the architecture to creating a working prototype system showing real-time ultrasound imaging in less than three months. The team was able to achieve such a short time to their first working prototype system by building the system around modular FPGA and AFE hardware. This provided significant flexibility and the ability to be customized, allowing them to focus on their domain expertise in ultrasound processing algorithms and I/O interfacing.

The PXI platform was used by Diagnostic Sonar to quickly build their prototype ultrasound imaging system.

FPGAs can enable a lot of design flexibility to try out new ideas and reduce risk earlier in the development of a system. Since FPGAs can be reconfigured through software, a designer can save development time, demonstrating hardware-based processing while being able to reprogram the FPGA to accommodate modifications that are unknown during initial specification.

One challenge of using FPGAs for prototyping is that programming a system using a traditional hardware description language like VHDL can be very time consuming, lengthening project timelines. However, recent advancements in development tools have made FPGA programming more efficient by allowing higher level graphical tools to be used for overall system design. This leverages existing VHDL IP (Xilinx CORE Generator, in-house developed, third-party, etc,) where appropriate. When used properly, these tools can enable very fast development of a prototype system so that algorithms and hardware performance can be evaluated and refined.

NI FlexRIO is an example of a product that combines a user-programmable FPGA and highly integrated Texas Instruments' AFE with customizable I/O.

The team from Diagnostic Sonar built their system around National Instruments tools such as NI FlexRIO modular FPGA hardware programmed with the LabVIEW FPGA Module, a graphical design language that can be used to design FPGA circuitry without needing to know VHDL coding. NI FlexRIO combines interchangeable, customizable I/O adapter modules with a user-programmable FPGA module in a PXI or PXI Express chassis. The Virtex series of Xilinx FPGAs are used on the board to achieve the I/O and signal processing performance required for applications like medical imaging. Diagnostic Sonar developed boards with FPGAs in the past, but NI FlexRIO was appealing to them because they could to build around known good hardware, which already included infrastructure components for I/O connectivity, PCI Express bus interfacing and DRAM communication. Developing these components in-house can consume a lot of time and can distract developers from new innovations where they add the most value.