Pressure measurement of geometrically curved ultrasound transducer array for spatially specific stimulation of the vagus nerve

Abstract

Vagus nerve stimulators currently on the market can treat epilepsy and depression. Recent clinical trials show the potential for vagus nerve stimulation (VNS) to treat epilepsy, autoimmune disease, and traumatic brain injury. As we explore the benefits of VNS, it is expected that more possibilities for a new treatment will emerge in the future. However, existing VNS relies on electrical stimulation, whose limited selectivity (due to its poor spatial resolution) does not allow for any control over which therapeutic effect to induce. We hypothesize that by localizing the stimulation to fascicular level within the vagus nerve with focused ultrasound (US), it is possible to induce selective therapeutic effects with less side effects. A geometrically curve US transducer array that is small enough to wrap around the vagus nerve was fabricated. An experiment was conducted in water, with 48 US elements curved in a 1 mm radius and excited at 15 MHz to test the focusing capabilities of the device. The results show that the geometrical curvature focused the US to an area with a width and height of 110 µm and 550 µm. This will be equivalent to only 2.1% of the cross section of the vagus nerve, showing the potential of focused US to stimulate individual neuronal fibers within the vagus nerve selectively.

Compliant peripheral nerve interfaces

“…The fundamental mechanism through which ultrasounds interact with neural tissue is still unclear, with most theories being explored either through modelling [154] or acute experiments on exposed nerves [155,156], which have often provided conflicting results. These are typically performed using conventional US transducers, while miniaturized systems integrated within a flexible device have only recently been developed but remain to be tested in vivo [157]. Such systems could potentially provide improved spatial resolution, thereby helping to elucidate the mechanisms behind US neuromodulation [158].…”

PMUT and CMUT Devices for Biomedical Applications: A Review

“…Ultrasound neurostimulation is used non-invasively [110] for stimulating the brain, peripheral nervous system [117]- [119], [129], and retina [130]. Administering ultrasound via implantable devices is also being investigated as a means to increase the spatial selectivity in peripheral nerve neuromodulation [114], [115], [131]. On the other hand, HIFU can be administered externally or with minimal invasion, such as through body orifices, endoscopic incisions, or intravascularly via catheters [125].…”

“…In [114] and [115] a flexible CMUT array has been curved to 1 mm radius to wrap around the vagus nerve and deliver spatially specific stimulation. The CMUT array operated at 15 MHz and had a focal spot of 110 µm and 550 µm, which is only 2.1% of the cross section of the nerve [114].…”

Schlieren visualization of focused ultrasound beam steering for spatially specific stimulation of the vagus nerve

“…In our prior work, we presented a highly miniaturized US cuff device [2]. This US cuff device is made of an array of 112 MEMS US transducer elements that is curved into a 2 mm diameter half cylinder.…”

“…In our prior work, we presented a curved ultrasound (US) transducer array with a diameter of 2 mm and with 112 miniature US transducer elements, small enough to be wrapped around the vagus nerve for precise ultrasound nerve stimulation [2]. Due to the curved alignment of the US transducers with 48 of the elements simultaneously excited, the emitted US was naturally focused at the center of the curvature.…”