In 1942, the Austrian TDussik used the Type A ultrasound imaging system to penetrate the skull and obtain ultrasound images of the head in 1949, which marked the entry of ultrasound systems into the medical field. Until today, ultrasound systems have been widely used in the medical field as a non-invasive visualization technique for the inside of the human body. A recent report states that the market size of China's medical ultrasound diagnostic instruments industry is expected to reach $1.58 billion by 2022, maintaining a CAGR of around 6%. High-performance analog signal chain front-end is a key component of ultrasound equipment, and as a major provider of high-performance analog technology ADI has made the healthcare sector one of its strategic markets. To ensure the sustainable development of ultrasound technology, ADI provides highly integrated solutions for the key signal chain functional modules of ultrasound systems, driving the implementation of best-in-class clinical imaging devices.
Ultrasound systems work by emitting acoustic energy into the body and then receiving and processing the echoes to produce images of internal organs and structures, map blood flow and tissue movement, and provide highly accurate information on blood flow velocity. Ultrasound scanning uses acoustic pulses in the frequency range of 1 MHz to 18 MHz, which scan the body's internal tissues and reflect them in echoes of varying intensity. These echoes are then captured in real time and displayed as ultrasound scans, which may contain different types of information such as acoustic impedance, blood flow, the activity of the tissue over time or its stiffness.
Achieving optimal medical imaging, data acquisition simulation front-end performance is critical
So it's easy to see that to improve the picture quality of an ultrasound system, the performance of its front-end, which is hidden deep inside the complex machine, is critical. The key functional module of a medical ultrasound front-end consists of an integrated multi-channel analog front-end (AFE), which includes a low-noise amplifier, variable gain amplifier, anti-alias filter (AAF), ADC and demodulator. One of the most important requirements for the AFE is dynamic range. Depending on the imaging modality, this requirement may need to be 70 dB to 160 dB in order to distinguish the blood signal from the background noise generated by the probe and body tissue motion. Therefore, the ADC must have high resolution, high sampling rate and low total harmonic distortion (THD) to maintain the dynamic fidelity of the ultrasound signal. In this regard, ADI offers an integrated AFE AD9671 for medical ultrasound devices to achieve the best image quality.
The AD9671 features a 14-bit ADC with sampling rates up to 125 MSPS and 75 dB SNR performance for better ultrasound imaging quality. Each channel is optimized for high dynamic performance of 160 dBFS/√Hz in continuous wave mode and low power of 62.5 mW. It has a built-in 8-channel variable gain amplifier (VGA), low-noise preamplifier (LNA), CW harmonic rejection I/Q demodulator with programmable phase rotation, anti-alias filter (AAF), analog-to-digital converter (ADC), and digital demodulator and extractor for data processing and bandwidth reduction. Each channel features a maximum gain of 52 dB, a fully differential signal path, and active input preamplifier termination, all optimized for high dynamic range and low power consumption.
The LNAs have single-ended to differential gain and can be selected via SPI. Assuming a noise bandwidth (NBW) of 15 MHz and an LNA gain of 21.6 dB, the LNA input signal-to-noise ratio (SNR) is 94 dB. In CW Doppler mode, each LNA output drives an I/Q demodulator. Each demodulator has independently programmable phase rotation and 16 phase settings.
From cart to portable, how to achieve size reduction without performance loss?
With the development of intelligent technology, portable medical devices are gradually becoming one of the mainstream development trends. In the past, the implementation of ultrasound imaging systems required a large number of high-performance transmitter and receiver circuits, resulting in large and expensive cart-based systems. Today, however, system designers are able to use the AD9671 to achieve a smaller, lower cost, more portable imaging solution with performance close to that of a cart-based system.
By integrating a 5Gb JESD204B interface, the AD9671 reduces I/O data routing for ultrasound systems by up to 80% compared to other data interface standards. The reduced routing meets the needs of manufacturers designing small, high-performance ultrasound systems that simplify ultrasound device board design while better meeting industry requirements for higher data rates, more channels, and better image resolution.
In addition, the AD9671 receiver is capable of conditioning 8 channels of RF to baseband frequency data, reducing the system FPGA (Field Programmable Gate Array) processing burden by at least 50% compared to other devices. And each channel can be individually entered into a power-saving mode, thereby extending the battery life of portable applications. Using standby mode then allows for quick power-up for power-on restart. When operating in CW Doppler mode, VGA, AAF and ADC all enter power saving mode. In addition, the ADC has built-in functional features such as programmable clock, data alignment, and generation of programmable digital test codes to optimize device flexibility and minimize system cost. The 8-channel integrated receiver front-end, AD9671, is designed for mid- to high-end portable and cart-based ultrasound systems.
Conclusion
Ultrasound systems face additional challenges in the current trend toward miniaturization, including: beamformer complexity, which requires a large number of beamforming channels to achieve high graphics quality; high complexity, which in turn leads to high power consumption and requires more imaging space to implement, and heat dissipation, which becomes important as devices move toward miniaturization, especially when the goal is to improve image quality. The AD9671 presented in this article is just one of ADI's medical ultrasound system solutions, there is a wide range of front-end, amplifier, data conversion, signal processing and power management solutions for users to choose from, including SNR performance improvements in harmonic imaging (HI) with significant advantages of linear emission solutions, etc., can make cart and portable ultrasound equipment achieve the best image quality and reduce power consumption and cost.
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