Consumer electronics have taken great strides forward over the past decade in terms of affordability, size and power. In contrast, medical electronics has yet to experience a similar type of innovation. However, an increasing world population, longer life expectancy and rising standards of living should become catalysts for a medical devices revolution that will help improve general wellbeing while reducing healthcare costs.
The following are some key design challenges for medical electronics designers:
1. Features differentiation – Competition is increasing within medical electronics markets, as attractive margins drive various manufacturers to deliver products with differentiating features and advanced performance to stay ahead of other contenders.
2. Power reduction - There will be a tight power budget ahead for medical devices as future medical electronics prioritise wireless operation and focus on miniaturisation. Reducing power consumption can lead to better thermal management thus reducing overall product size.
3. Development time – Medical electronic devices must pass a lengthy certification process which can significantly slow down time to market. The typical development cycle for consumer electronics products is 3 to 9 months, whereas typical medical electronics average 2-3 years. Tools and methods available to reduce development time and aid in certification will be vital.
These challenges can cause engineers to make unwanted tradeoffs between features and cost, or power and size. The design of ultrasound equipment provides a prime example.
Due to its non-invasive nature, ultrasound imaging is used across many medical applications from diagnostic investigations to therapy. High-performance ultrasound machines offering the highest resolution and state of the art 4D image viewing are still cart-based and bulky. On the other hand, portable or handheld versions have significant limitations in terms of battery life and image quality. Clearly the performance-to-size ratio still needs to be improved. One could envision a future in which personal ultrasound machines could be marketed to expectant parents. For this to happen, however, the equipment would have to reach consumer-level pricing, portability and ease of use. We may be a few years away from realisation of such product, but what are the products and platforms that can help solve the design challenges of medical designers and improve the performance/size or performance/price ratio?
For many years Field Programmable Gate Arrays (FPGAs) have been central to the enablement of medical ultrasound technology. FPGAs have a long product life cycle which can match the long time-in-market requirement for medical electronics. Performance and flexibility are two primary attributes that make FPGAs the device of choice for ultrasound imaging. By allowing algorithms and features to be updated without needing to change-out components, FPGAs enable systems to become essentially future-proof. With every technology node shrink, FPGAs provide increased performance to price ratio; for example moving from 28nm to 20nm can result in 20-50% performance improvement while also reducing power consumption. In addition, FPGA tools support an abstracted design flow, performing automated timing closure and minimising place-and-route time, leading ultimately to shorter development time. By continuing to provide such advantages, FPGAs will remain critical to the design of next-generation ultrasound equipment.
Let’s explore how to satisfy the functional requirements of a medical ultrasound system. An ultrasound imaging system can be split into three main functions: front-end, transmission, and back-end. Programmable technology such as FPGAs plays a crucial role in each of these blocks.
Figure 1: The ultrasound system data path consists of several key components that can benefit from FPGA properties
The objective of an ultrasound front end is to control transmission of ultrasonic pulses and capture the reflected sound data. Analogue-to-Digital Converters (ADCs) convert the reflected ultrasonic data into digital format. Most of the ADCs used in ultrasound imaging applications support from four to eight channels and 12-16 bits resolution at 40-60 Msamples/sec. Cart-based ultrasounds require high resolution, often with as many as 128 or even 512 channels, whereas a portable ultrasound that must meet low weight and size targets may have as few as eight channels. In order to support the high volume of data transmission, ADC outputs typically use Low Voltage Differential Signalling (LVDS). Because an FPGA has large number of input/output (IO) blocks which can be configured to support LVDS, it can aggregate data from several ADCs for pre-processing.