Dual-Mode Photoacoustic and Ultrasound Endoscope for Internal Organ Imaging

This dual-mode endoscopic probe integrates photoacoustic and ultrasound imaging in a single 3.8 mm diameter package for simultaneous, spatially co-registered functional and anatomical imaging of internal organs. The probe uses a 36 MHz LiNbO₃ single-crystal transducer with a central hole for optical fiber delivery, and a rotating mirror for circumferential scanning. Photoacoustic imaging provides optical absorption contrast—enabling visualization of blood vessels, hemoglobin concentration, and oxygen saturation (sO₂)—while ultrasound provides acoustic reflectance contrast for tissue morphology. In vivo imaging of rabbit esophagus and rat colon demonstrates transesophageal lung and trachea imaging, colon wall vasculature, and contrast-enhanced lymph node mapping with Evans blue dye. Lymph vessels as small as 1 mm are resolved.

Parameter	Value
Probe Outer Diameter	3.8 mm
Rigid Distal Length	38 mm
Transducer Material	LiNbO₃ single crystal
Center Frequency	36 MHz
Fractional Bandwidth	65%
Transducer Aperture	2.6 mm
Central Hole Diameter	0.5 mm
Scanning Method	Rotating mirror (~4 Hz)
Angular FOV	270° (360° with reinsertion)
Pullback Speed	~200 μm/s
Imaging Modes	Photoacoustic (PA), Ultrasound (US), Dual‑wavelength PA
PA Wavelengths Demonstrated	562 nm, 584 nm, 523 nm, 640 nm
Functional Contrast	Total hemoglobin, sO₂, exogenous dye (Evans blue)
Minimum Resolved Lymph Vessel	~1 mm
In Vivo Targets	Rabbit esophagus, lung, trachea; rat colon, lymph nodes