Ultrasound is often favored in biopsy guidance since it is non-ionizing, inexpensive, portable, and has a high frame rate. However, imaging probes that operate at a low frequency may not be able to differentiate between tiny targets and surrounding tissues clearly, and at a high frequency, it suffers from tissue scattering and signals attenuation, which is hard to image deeper targets such as lung tissues. In this study, we developed a biopsy needle (with a size of 18 G) integrated with a 30 MHz high-frequency ultrasound transducer (axial resolution: ~ 100 µm) for the lung nodule biopsy in vitro test. To mimic contrasting biological tissues, a melamine foam-gelatin phantom was developed. With an advancing step of 0.5 mm, the distance from the biopsy needle to the gelatin-foam boundary was estimated by the speed of sound in gelatin and the time-of-flight of the echo signal. The results showed that the 30 MHz ultrasound transducer can map the geometry of the gelatin-foam boundary, indicating the capability of distinguishing tumor and healthy lung tissue with this ultrasound-guided biopsy technique.
Among a variety of existing modalities for noninvasive brain stimulation (NIBS), low-intensity pulsed transcranial focused ultrasound (tFUS) is a promising technique to precisely stimulate deep brain structures due to its high spatial specificity and superior penetration depth. While tFUS is gaining momentum as an emerging NIBS technique, an advisable biosafety-associated combination of sonication parameters including duty cycle and power input remains to be explored. In this study, biosafety of low-intensity pulsed tFUS using various sonication parameters was evaluated by measuring acoustic intensities and temperature variations across a piece of real human skull. The results showed that ISPTA above 480 mW/cm^2 is likely to induce an excessive temperature rise for a sonication duration of 160 seconds. Also, the skull base effect and ultrasound transducer self-heating effect should be noted during the sonication. Based on the findings in this study, an initial biosafety guide was discussed for the future investigation of ultrasound-mediated NIBS.
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