Spatio-Spectral Ultrasound Characterization of Reflection and Transmission Through Bone With Temperature Dependence

Measuring sound velocity based on acoustic resonance using multiple narrow band transducers

The sound velocity in a medium is closely related to its material properties, including its composition, structure, density, pressure, and temperature. Various methods have been developed to determine the sound velocity through materials. Among them, a strategy based on ultrasound resonance frequency has been most widely used due to the simplicity. However, it requires a transducer with a wide bandwidth to cover enough resonance frequencies to perform the consequent calculations. In this paper, we develop a resonance method for measuring sound velocity, using multi-frequency narrow-band transducers breaking through the limitation of transducer bandwidth on the utilization of the resonance method. We use different transducers at different center frequencies and with different bandwidth to measure the sound velocity in 100-μm and 400-μm thick steel pieces. The measurement results of different combinations are in good agreement, verifying that the use of multi-frequency narrow-band transducer combinations. Given that most therapeutic transducers have a narrow bandwidth, this method can be used during intracranial ultrasound stimulation to optimize targeting by non-invasively measuring the sound velocity in the skull, especially at thinner locations.

Image-Guided Measurement of Radiation Force Induced by Focused Ultrasound Beams

The radiation force balance (RFB) is a widely used method for measuring acoustic power output of ultrasonic transducers. The reflecting cone target is attractive due to its simplicity and long-term stability, at a reasonable cost. However, accurate measurements using this method depend on the alignment between the ultrasound beam and cone axes, especially for highly focused beams utilized in therapeutic applications. With the advent of dual-mode ultrasound arrays (DMUAs) for imaging and therapy, image-guided measurements of acoustic output using the RFB method can be used to improve measurement accuracy. In this article, we describe an image-guided RFB measurement of focused DMUA beams using a widely used commercial instrument. DMUA imaging is used to optimize the alignment between the acoustic beam and reflecting cone axes. In addition to image-guided alignment, DMUA echo data is used to track the displacement of the cone, which provides an auxiliary measurement of acoustic power. Experimental results using a DMUA prototype with [Formula: see text] shows that 1-2 mm of misalignment can result in 5%-14% error in the measured acoustic power. In addition to the use of B-mode image guidance for improving measurement accuracy, we present preliminary results demonstrating the benefit of displacement tracking using real-time DMUA imaging during the application of (sub)therapeutic focused beams. Displacement tracking provides a direct measurement of the radiation force with high sensitivity and follows the expected dependence on changes in amplitude and duty cycle (DC) of the focused ultrasound (FUS) beam. This could lead to simpler, more reliable methods for measuring acoustic power based on the radiation force principle. Combined with appropriate computational modeling, the direct measurement of acoustic radiation force could lead to reliable dosimetry in situ in emerging applications such as transcranial FUS (tFUS) therapies.