Endoscopic Probe for Ultrasound-Assisted Photodynamic Therapy of Deep-Lying Tissue

Abstract

Endoscopic photodynamic therapy (PDT) has attracted much attention as a minimally invasive, minimally toxic treatment. PDT can selectively destroy cancer cells by reactive oxygen generated through chemical reaction of photosensitizers that absorb incident light with a certain wavelength. However, the efficacy of PDT is limited due to shallow light penetration mainly caused by Rayleigh scattering in biological tissue. We previously demonstrated that the air bubbles temporarily induced by ultrasound (US) act as a Mie scattering medium, thus increasing light penetration, called US-assisted light penetration increase. For endoscopic applications of the proposed method, the endoscopic probe for US-assisted PDT should be developed; it should be as small as possible while being able to deliver laser for treatment and provide high acoustic energy for air bubble generation in the laser pathway. Satisfying those requirements is very challenging. In this paper, we report a recently developed endoscopic probe for US-assisted PDT that meets the requirements. The probe consists of two 3 MHz US transducers placed side by side and tilted at an angle of 25° and an optical fiber for laser delivery. The probe size was measured at 60.5 mm × 14 mm × 14 mm suitable for endoscopic applications. In the experiment, it was shown that the probe could increase the laser intensity by 28%, compared to the laser only illumination. Even this increase is higher than the previous measurement using a commercial ring-shaped 1.1 MHz HIFU transducer with outer and inner diameters of 64 mm and 22.6 mm.

Ultrasound‐Assisted Photothermal Therapy (ULTRA‐PTT) for the Treatment of Deep‐Seated Tumors

“…g , obtained from the average cosine of the scattering angle, approaches unity in the case of Mie scattering involving large particles. [ 28 ] Ultrasound has the capacity to generate gas bubbles, often several tens of micrometers in size, within the biological medium located in front of the target lesion, [ 24 ] and these gas bubbles act as large Mie scatterers. [ 23 ] Consequently, the TMFP is significantly extended, preventing diffusion from occurring before the incident light reaches the target lesion.…”

“…The proposed method built upon our previous discovery that gas bubbles, transiently created by ultrasound in the path of light propagation, serve as optical clearing agents, consequently reducing the optical scattering within a biological medium. [23][24][25] In ULTRA-PTT, in contrast to DTT, the ultrasound focal point is positioned within the scattering medium through which the incident light travels toward the target lesion. This setup enables the irradiated light to reach the target lesion with minimal energy loss, primarily due to the presence of gas bubbles formed within the scattering medium.…”

Mechanically Rotating Intravascular Ultrasound (IVUS) Transducer: A Review

“…The signal connection in the developed catheter is equal to a parallel connection of two signal wires because the housing serves as a ground. As the parallel connection leads to a reduction in electrical impedance [ 177 ], series connection is preferred if both elements have an electrical impedance lower than a system impedance (typically 50 Ω). The developed multifrequency IVUS transducers are listed in Table 3 .…”

Activation of photosensitive proteins with radioluminescent nanoparticles and X-rays

“…For example, combining PDT and chemotherapy reduces the likelihood of tumor recurrence 35 . Other examples of treatments combined with PDT are radiotherapy 40 , ultrasound 41 , and hyperthermia 42 . However, the limited penetration depth of UV-vis light into the human body restricts the scope of photomedicine applications.…”