However, conventional MIT including thermotherapy (radiofrequency ablation 13, laser ablation 14) and cryotherapy (cryoablation 15) are intended to realize large-volume efficient therapy with over 4 mm in diameter and 5 mm in depth 3, 16, which limits the applications that require localized accurate therapy.Īlthough ultrasound-based MIT offers the opportunity for localized accurate therapy, the essential point is how to emit powerful ultrasound at the needle tip to increase the therapy efficiency. MIT possesses superior advantages for tumor therapeutics 11, 12 in liver, kidney, prostate, etc. MIT can limit the size of required incisions, localize the therapeutic region, and shorten the wound healing time, associated pain and risk of infection 9, 10. Alternatively, minimally invasive energy-based treatments (MIT) can be a promising candidate, it inserts the thin needle directly to the lesion to deliver different types of energy for treatments. Such relatively large dimensions make HIFU transducers lose certain accuracy in localized therapy for deep tissues 5, 6 and some bioeffects including side burnings (by thermal-based therapies) and significant hemorrhage (by mechanical-based therapies) 7, 8 may be potentially induced. The cigar-shaped focal dimensions are usually in the order of 1–3 mm in the transverse direction and 8–15 mm in the beam axis direction. In typical ultrasound therapeutics, High Intensity Focused Ultrasound (HIFU) treatments with the frequency of 0.75 to 3 MHz and the focal intensity of over 1 kW/cm 2 are utilized to noninvasively destruct the diseased tissue by acoustic focusing from the outside of human body. Among the medical equipment, ultrasound based medical devices have been universally recognized as the low-cost and human/environmental-friendly tool for diagnostics and therapeutics, applications mainly cover from finding the source of diseases (imaging of internal body structures) 1, 2 to treatments (tissue destruction, drug delivery, gene therapy, etc.) 3, 4. Health of human beings is always the dominant concern in the modern society, which is continuously arousing further investments and development for medical devices. Since the high-power ability at high frequencies, our waveguide will also open up new research fields in medical, bio, physics and so on. This fundamental work serves as a milestone for future biomedical applications, from therapeutics to diagnostics. High-energy-density ultrasound with around 20 times amplification by two parabolic reflectors propagates through the thin waveguide between 1 to 2 MHz, and wideband large mechanical vibration at the waveguide tip from 1 kHz to 2.5 MHz accelerates the therapeutics. Here, we invent double-parabolic-reflectors acoustic waveguides, where high-power ultrasound emission and large mechanical vibration enhance the therapeutic efficiency. Although acoustic waveguides are commonly inserted into tissue for localized therapy, powerful ultrasound delivery is difficult. However, ultrasound penetration depth is shallowed with increasing frequency which limits the therapeutic accuracy for deep tissues. High intensity focused ultrasound therapeutics are widely used to noninvasively treat various types of primary tumors and metastasis.
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