With the rapid advancement of tracking technologies, the applications of tracking systems in ultrasound imaging have expanded across a wide range of fields. In this review article, we discuss the basic tracking principles, system components, performance analyses, as well as the main sources of error for popular tracking technologies that are utilized in ultrasound imaging. In light of the growing demand for object tracking, this article explores both the potential and challenges associated with different tracking technologies applied to various ultrasound imaging applications, including freehand 3D ultrasound imaging, ultrasound image fusion, ultrasound-guided intervention and treatment. Recent development in tracking technology has led to increased accuracy and intuitiveness of ultrasound imaging and navigation with less reliance on operator skills, thereby benefiting the medical diagnosis and treatment. Although commercially available tracking systems are capable of achieving sub-millimeter resolution for positional tracking and sub-degree resolution for orientational tracking, such systems are subject to a number of disadvantages, including high costs and time-consuming calibration procedures. While some emerging tracking technologies are still in the research stage, their potentials have been demonstrated in terms of the compactness, light weight, and easy integration with existing standard or portable ultrasound machines.

Smartphones today have attracted a continuous trend of pursuing narrow-bezel and full-screen displays. To allow for a more user-friendly front side fingerprint recognition in full-screen displays, it is crucial to develop an under-display type of fingerprint sensor. Among fingerprint sensing techniques, ultrasonic fingerprint sensing has been proved to be able to provide more distinctive features and give a high resistance to spoof attacks. However, until now no study about under-display ultrasonic fingerprint sensing has been reported. In this paper, for the first time, multilayer under-display ultrasonic fingerprint sensor structure using various active materials/structures were theoretically designed. Based on the theoretical analysis results, a PZT-5A based multilayer under-display ultrasonic fingerprint sensor with a resonant frequency of 20 MHz, and a -6-dB fractional bandwidth of more than 70% was fabricated. The prototyped sensor was characterized, and the fingerprint recognition capability was tested using a custom-made fingerprint-mimicking phantom. With the 1 μJ impulse driving signal, the sensor was manipulated to image a 2.0 mm × 1.0 mm section of fingerprint-mimicking phantom by mechanical scanning, obtaining an electronic image with 500 × 500 DPI. The fingerprint-mimicking phantom imaging results suggest that the 20 MHz broadband PZT based multilayer structure holds great potential for under-display ultrasonic fingerprint sensor applications.

Transcranial ultrasonic stimulation (TUS) is emerging as a non-invasive neuromodulatory technique capable of delivering millimeter-precision stimulation at whole-brain depths. Research efforts have increasingly focused on its translational potential. Promising data have been reported across several disease populations, including Parkinson's disease and stroke, paving the way for clinical applications of TUS. Clinical studies to date, however, show substantial variability in transducer fixation, targeting approaches, and acoustic parameters. This limits the interpretability and comparability of results. Existing methodological guides address human TUS in general but do not focus on applications in neurological populations. This experimental protocol presents a standardized yet adaptable framework for applying TUS to neurological cohorts such as stroke. It offers detailed guidance on: (1) essential and optional hardware components in the context of therapy-oriented TUS; (2) hardware settings and parameter selection, including strategies to minimize auditory confounds; (3) calibration and quality assurance procedures to ensure the transducer delivers waveforms as specified; (4) targeting approaches based on simulation or non-simulation methods for accurate localization of TUS focus/foci to the intended anatomical region(s); (5) methodology adaption for clinical populations; and (6) outcome measures for clinical TUS, encompassing safety assessments and surrogate outcome measures such as corticospinal excitability and motor sequence learning. This protocol is designed as a replicable, modular resource. It accommodates both novice users (seeking a practical entry point into patient-based TUS) and experienced researchers (aiming to align with emerging scientific and methodological standards). The goal is to support the growing clinical interest in TUS and to facilitate clinically translatable, reproducible, and comparable results across research groups and patient populations.

Transcranial ultrasonic stimulation (TUS) is emerging as a non-invasive neuromodulatory technique capable of delivering millimeter-precision stimulation at whole-brain depths. Research efforts have increasingly focused on its translational potential. Promising data have been reported across several disease populations, including Parkinson's disease and stroke, paving the way for clinical applications of TUS. Clinical studies to date, however, show substantial variability in transducer fixation, targeting approaches, and acoustic parameters. This limits the interpretability and comparability of results. Existing methodological guides address human TUS in general but do not focus on applications in neurological populations. This experimental protocol presents a standardized yet adaptable framework for applying TUS to neurological cohorts such as stroke. It offers detailed guidance on: (1) essential and optional hardware components in the context of therapy-oriented TUS; (2) hardware settings and parameter selection, including strategies to minimize auditory confounds; (3) calibration and quality assurance procedures to ensure the transducer delivers waveforms as specified; (4) targeting approaches based on simulation or non-simulation methods for accurate localization of TUS focus/foci to the intended anatomical region(s); (5) methodology adaption for clinical populations; and (6) outcome measures for clinical TUS, encompassing safety assessments and surrogate outcome measures such as corticospinal excitability and motor sequence learning. This protocol is designed as a replicable, modular resource. It accommodates both novice users (seeking a practical entry point into patient-based TUS) and experienced researchers (aiming to align with emerging scientific and methodological standards). The goal is to support the growing clinical interest in TUS and to facilitate clinically translatable, reproducible, and comparable results across research groups and patient populations.