Skinless Ultrasound Micro Needle Transducer for Simultaneous Localized Brain Stimulation and Optical Measurement in-vivo

Localized small animal brain stimulations with low frequency (<; 1 MHz) ultrasound transducers are quite limited due to their wide beam width. Also the size of the transducers is too large to optically monitor brain activities simultaneously. Thus, a skinless micro needle ultrasonic transducer transmitting 10 MHz with the aperture size of 500 μm was developed. The housing of the transducer was replaced by pasting an epoxy on the side wall of the transducer for minimizing the field-of-view blocks of optical microscopy. Due to the miniaturized foot print, optical brain imaging with a calcium transgenic mice could be performed while localized ultrasonic stimulation was delivered to a confined region of somatosensory cortex or visual cortex in a real time. As a result of the localized stimulations, the calcium signal level was increased two or three times higher than the responses in the other cortical area. Also, the artifact response in the auditory cortex which was reported previously could be still found with the periodically bursting stimulation, while the effect was noticeably reduced with the random sequence in bursting the stimulation signal. In conclusion, skinless micro needle transducer with the random transmit sequence could deliver localized stimulation to a small animal mouse brain.