Enhanced dual-mode imaging: Superior photoacoustic and ultrasound endoscopy in live pigs using a transparent ultrasound transducer

Abstract

Dual-mode photoacoustic/ultrasound endoscopy (ePAUS) is a promising tool for preclinical and clinical interventions. To be clinically useful, ePAUS must deliver high-performance ultrasound imaging comparable to commercial systems and maintain high photoacoustic imaging performance at long working distances. This requires a transducer with an intact physical aperture and coaxial alignment of acoustic and optical beams within the probe, a challenging integration task. We present a high-performance ePAUS probe with a miniaturized, optically transparent ultrasonic transducer (TUT) called ePAUS-TUT. The 1.8-mm-diameter probe, fitting into standard endoscopic channels, aligns acoustic and optical beams efficiently, achieving commercial-level ultrasound and high-resolution photoacoustic imaging over long distances. These imaging capabilities were validated through in vivo imaging of a rat's rectum and a pig's esophagus. The ePAUS-TUT system substantially enhances feasibility and potential for clinical applications.

Fig. 1.. Fabrication and operating characteristics of a TUT.

(A) Fabrication of the TUT. (B) Schematic of the layer structure and (inset) photograph of the TUT. (C) Simulated and (D) Experimental acoustic performances. (E) Experimental optical transmittance. CF, center frequency; BW, bandwidth; and ML, matching layer.

Fig. 2.. System schematic and performance of the TUT-based ePAUS system.

(A) Schematic of the overall ePAUS-TUT system and a photograph of the probe. (B) Optical beam shapes after each component: #1 immediately after the prism, #2 after passing the TUT, and #3 after passing through the TUT and tube. (C) PA and US transverse and axial resolutions as a function of distance. MMF, multimode fiber; SUS, steel use stainless; DAQ, data acquisition device; DGT, digitizer; PR, pulser/receiver; SW, switch; HSR, hollow-shaft slip ring; ORJ, optical rotary joint; and AMP, amplifier.

Fig. 3.. Endoscopic PA/USI of a rat’s rectum in vivo.

(A) 3D-rendered overlaid PA/US, translucent PA/US, and depth-encoded PA-only images (movie S1). (B) Cross-sectional overlaid B-mode PA/US images indicated by numbers in (A). (C) PA MAP and US MIP images. (D) Three depth-encoded PA MAP images: The entire depth, from 0- to 0.15-mm deep, and below 0.45 mm. Insets are magnified images from the boxes in (D). All scale bars, 5 mm.

Fig. 4.. Endoscopic PA/USI of a pig’s esophagus in vivo.

(A) Photograph of the ePAUS probe inserted into a commercial endoscope. (B) 3D-rendered overlaid PA/US image of a pig’s esophagus. (C) Cross-sectional PA/US image cut along the vertical direction in (B). (D) Cross-sectional PA/US images (#1 to #3) cut along the radial direction in (B). (E) PA MAP image of the pig’s esophagus. IPCL, intrapapillary capillary loops. All scale bars, 5 mm.