Wearable Ultrasound Device | Cardiac Imaging

It is important to be able to take pictures of the heart's functions continuously in order to monitor heart health over time, detect problems quickly, and take care of sick or surgical patients. However, current methods for taking these pictures are not easy to use and do not provide continuous measurements. Other devices that can be worn on the body can only measure signals on the skin. To address this problem, a research group from the University of California San Diego has created a new portable ultrasound device for continuous, real-time and direct assessment of cardiac function.

In addition, they've developed a deep learning model that automatically extracts the left ventricular volume from the continuous image recording, yielding waveforms of key cardiac performance indices such as stroke volume, cardiac output and ejection fraction. This technology enables dynamic wearable monitoring of cardiac performance with substantially improved accuracy in various environments.

Function and possibilities of the wearable cardiac ultrasound device

The wearable ultrasound imager uses piezoelectric transducer arrays, liquid metal composite electrodes, and triblock copolymer encapsulation. It has an orthogonal configuration and a center resonant frequency of 3 MHz for deep tissue imaging. The high-density multilayered stretchable electrodes are made of a composite of eutectic gallium–indium liquid metal and SEBS, which is highly conductive and easy to pattern. The device also has electromagnetic shielding, low dielectric loss, wide bandwidth, and high stretchability, making it suitable for maintaining intimate contact with the skin over a large area.

This innovative device was evaluated based on five crucial metrics for anatomical imaging: spatial resolutions, signal-to-noise ratio, location accuracies, dynamic range, and contrast-to-noise-ratio. The transmit beamforming strategy was compared among three different strategies: plane-wave, mono-focus and wide-beam compounding. Wide-beam compounding strategy was found to have the best quality with an expanded sonographic window. The device also used a receive beamforming strategy to further improve image quality.

The wide-beam compounding achieved a synthetic focusing effect, high acoustic intensity across the entire insonation area, and the best signal-to-noise ratio and spatial resolutions. Moreover, the location accuracies of the device in the axial and lateral directions are 96.01% and 95.90%, respectively, indicating excellent location accuracies. The dynamic range of the device was 63.2 dB and contrast-to-noise ratio of the device ranges from 0.63 to 2.07. The performance of the wearable imager is comparable with that of the commercial device.

Extensive possibilities, stability and reliability

So, the device was tested and compared to a commercial device in four primary views of echocardiography, including apical four-chamber view, apical two-chamber view, parasternal long-axis view, and parasternal short-axis view. The results of the wearable device were found to be comparable to the commercial device, and the device was able to capture important cardiac features such as contractile function of the myocardium.

The study also used a three-dimensional scanner to collect the chest curvature to compensate for element position shifts within the wearable imager and thus correct phase distortion during transmit and receive beamforming. It also used motion-mode (M-mode) images to track activities over time in a one-dimensional target region, and correlated the mechanical activities in the M-mode images with the electrical activities in the electrocardiogram.

To sum up: The portable device is able to record cardiac activities before, during, and after exercise with minimal motion artefacts. Furthermore, it is able to capture changes in the left ventricular internal diameter end systole and left ventricular internal diameter end diastole during exercise and recovery stages. The device also captured patterns of deep breathing. Plus: The device was tested on different subjects and found to be stable and reliable.