Sai Zhou

Ultrasonography is widely used for fetal monitoring but it requires sonographers and is limited to snapshot evaluations at discrete intervals. Here we report a wearable ultrasound patch (UPatch) for continuous and autonomous fetal monitoring. The UPatch can acquire anatomical structures and blood flow velocities, demonstrating good agreement with a handheld clinical ultrasound device on 62 pregnancies. Real-time image segmentation allows autonomous tracking of target vessels to acquire continuous blood flow spectra during fetal and maternal movements without a sonographer. Continuous monitoring data from 52 pregnant women aligned with stratified perinatal conditions, including healthy, small for gestational age, large for gestational age, gestational diabetes, preeclampsia and gestational hypertension. With further technology development, integration with a miniaturized circuit could enable fully wireless operation and greater user mobility. The UPatch could provide continuous assessment of fetal compromise in high-risk pregnancies, expanding prenatal-care capabilities.

The rapid and complex nature of fetal development requires meticulous prenatal monitoring to ensure optimal pregnancy outcomes. Cardiotocography, which continuously records the fetal heart rate and uterine contractions, often leads to inaccurate diagnoses and unnecessary interventions. Ultrasonography is a cornerstone of fetal monitoring and diagnosis, but it is highly dependent on specialized sonographers, limiting its availability. Additionally, current ultrasound methods provide only snapshot evaluations. Even in very high-risk pregnancies, it is rare to have fetal ultrasound assessments more than once per day. Here we report a wearable ultrasound patch (UPatch) for continuous and autonomous fetal monitoring. The UPatch can acquire anatomical structures and blood flow velocities, with signal qualities comparable to those of handheld clinical ultrasound devices. Real-time image segmentation allows the autonomous tracking of target vessels and thus the acquisition of continuous blood flow spectra during fetal and maternal movements without a sonographer. We validated the UPatch accuracy on 62 pregnancies, and the continuous monitoring data on 52 pregnant women aligned with stratified perinatal conditions, including healthy, small for gestational age, large for gestational age, gestational diabetes, pre-eclampsia, and gestational hypertension. The UPatch introduces new capabilities for prenatal care and offers critical evidence for studying fetal complications in high-risk pregnancies.

Options for the continuous and non-invasive monitoring of blood pressure are limited. Cuff-based sphygmomanometers are widely available, yet provide only discrete measurements. The clinical gold-standard approach for the continuous monitoring of blood pressure requires an arterial line, which is too invasive for routine use. Wearable ultrasound for the continuous and non-invasive monitoring of blood pressure promises to elevate the quality of patient care, yet the isolated sonographic windows in the most advanced prototypes can lead to inaccurate or error-prone measurements, and the safety and performance of these devices have not been thoroughly evaluated. Here we describe validation studies, conducted during daily activities at home, in the outpatient clinic, in the cardiac catheterization laboratory and in the intensive care unit, of the safety and performance of a wearable ultrasound sensor for blood pressure monitoring. The sensor has closely connected sonographic windows and a backing layer that improves the sensor’s accuracy and reliability to meet the highest requirements of clinical standards. The validation results support the clinical use of the sensor.

Wearable electromyography devices can detect muscular activity for health monitoring and body motion tracking, but this approach is limited by weak and stochastic signals with a low spatial resolution. Alternatively, echomyography can detect muscle movement using ultrasound waves, but typically relies on complex transducer arrays, which are bulky, have high power consumption and can limit user mobility. Here we report a fully integrated wearable echomyography system that consists of a customized single transducer, a wireless circuit for data processing and an on-board battery for power. The system can be attached to the skin and provides accurate long-term wireless monitoring of muscles. To illustrate its capabilities, we use this system to detect the activity of the diaphragm, which allows the recognition of different breathing modes. We also develop a deep learning algorithm to correlate the single-transducer radio-frequency data from forearm muscles with hand gestures to accurately and continuously track 13 hand joints with a mean error of only 7.9°.

Accurate and continuous monitoring of cerebral blood flow is valuable for clinical neurocritical care and fundamental neurovascular research. Transcranial Doppler (TCD) ultrasonography is a widely used non-invasive method for evaluating cerebral blood flow¹, but the conventional rigid design severely limits the measurement accuracy of the complex three-dimensional (3D) vascular networks and the practicality for prolonged recording². Here we report a conformal ultrasound patch for hands-free volumetric imaging and continuous monitoring of cerebral blood flow. The 2 MHz ultrasound waves reduce the attenuation and phase aberration caused by the skull, and the copper mesh shielding layer provides conformal contact to the skin while improving the signal-to-noise ratio by 5 dB. Ultrafast ultrasound imaging based on diverging waves can accurately render the circle of Willis in 3D and minimize human errors during examinations. Focused ultrasound waves allow the recording of blood flow spectra at selected locations continuously. The high accuracy of the conformal ultrasound patch was confirmed in comparison with a conventional TCD probe on 36 participants, showing a mean difference and standard deviation of difference as −1.51 ± 4.34 cm s⁻¹, −0.84 ± 3.06 cm s⁻¹ and −0.50 ± 2.55 cm s⁻¹ for peak systolic velocity, mean flow velocity, and end diastolic velocity, respectively. The measurement success rate was 70.6%, compared with 75.3% for a conventional TCD probe. Furthermore, we demonstrate continuous blood flow spectra during different interventions and identify cascades of intracranial B waves during drowsiness within 4 h of recording.

Continuous imaging of cardiac functions is highly desirable for the assessment of long-term cardiovascular health, detection of acute cardiac dysfunction and clinical management of critically ill or surgical patients^1–4. However, conventional non-invasive approaches to image the cardiac function cannot provide continuous measurements owing to device bulkiness^5–11, and existing wearable cardiac devices can only capture signals on the skin^12–16. Here we report a wearable ultrasonic device for continuous, real-time and direct cardiac function assessment. We introduce innovations in device design and material fabrication that improve the mechanical coupling between the device and human skin, allowing the left ventricle to be examined from different views during motion. We also develop 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.