A miniature multi-functional photoacoustic probe

Photoacoustic technology is a promising tool to provide morphological and functional information in biomedical research. To enhance the imaging efficiency, the reported photoacoustic probes have been designed coaxially involving complicated optical/acoustic prisms to bypass the opaque piezoelectric layer of ultrasound transducers, but this has led to bulky probes and has hindered the applications in limited space. Though the emergence of transparent piezoelectric materials helps to save effort on the coaxial design, the reported transparent ultrasound transducers were still bulky. In this work, a miniature photoacoustic probe with an outer diameter of 4 mm was developed, in which an acoustic stack was made with a combination of transparent piezoelectric material and a gradient-index lens as a backing layer. The transparent ultrasound transducer exhibited a high center frequency of ~47 MHz and a −6 dB bandwidth of 29.4%, which could be easily assembled with a pigtailed ferrule of a single-mode fiber. The multi-functional capability of the probe was successfully validated through experiments of fluid flow sensing and photoacoustic imaging

Miniature intravascular photoacoustic endoscopy with coaxial excitation and detection

Recent research pointed out that the degree of inflammation in the adventitia could correlate with the severity of atherosclerotic plaques. Intravascular photoacoustic endoscopy can provide the information of arterial morphology and plaque composition, and even detecting the inflammation. However, most reported work used a non-coaxial configuration for the photoacoustic catheter design, which formed a limited light-sound overlap area for imaging so as to miss the adventitia information. Here we developed a novel 0.9 mm-diameter intravascular photoacoustic catheter with coaxial excitation and detection to resolve the aforementioned issue. A miniature hollow ultrasound transducer with a 0.18 mm-diameter orifice in the center was successfully fabricated. To show the significance and merits of our design, phantom and ex vivo imaging experiments were conducted on both coaxial and non-coaxial catheters for comparison. The results demonstrated that the coaxial catheter exhibited much better photoacoustic/ultrasound imaging performance from the intima to the adventitia

Non-invasive evaluation of endometrial microvessels via in vivo intrauterine photoacoustic endoscopy

The endometrium microvessel system, responsible for supplying oxygen and nutrients to the embryo, holds significant importance in evaluating endometrial receptivity (ER). Visualizing this system directly can significantly enhance ER evaluation. Currently, clinical methods like Narrow-band hysteroscopy and Color Doppler ultrasound are commonly used for uterine blood vessel examination, but they have limitations in depth or resolution. Endoscopic Photoacoustic Imaging (PAE) has proven effective in visualizing microvessels in the digestive tract, while its adaptation to uterine imaging faces challenges due to the uterus's unique physiological characteristics. This paper for the first time that uses high-resolution PAE in vivo to capture a comprehensive network of endometrial microvessels non-invasively. Followed by continuous observation and quantitative analysis in the endometrial injury model, we further corroborated that PAE detection of endometrial microvessels stands as a valuable indicator for evaluating ER. The PAE system showcases its promising potential for integration into reproductive health assessments

In vivo assessment of a rat rectal tumor using optical-resolution photoacoustic endoscopy

Optical-resolution photoacoustic endoscopy (OR-PAE) has been proven to realize imaging on the vascular network in the gastrointestinal (GI) tract with high sensitivity and spatial resolution, providing morphological information. Various photoacoustic endoscopic catheters were developed to improve the resolution and adaptivity of in-vivo imaging. However, this technology has not yet been validated on in-vivo GI tumors, which generally feature angiogenesis. The tumor causes thickened mucosa and neoplasia, requiring large depth-of-field (DOF) in imaging, which contradicts to high-resolution imaging. In this work, a novel catheter was developed with a high resolution of ∼27 µm, providing a matched DOF of ∼400 µm to cover the vessels up to the submucosa layer. Optical-resolution photoacoustic endoscopic imaging was first performed on in-vivo rat rectal tumors. In addition, to further characterize the vessel morphology, tumor-suspected regions and normal regions were selected for quantification and analysis of vessel dimension distribution and tortuosity. All the results suggest that the OR-PAE has great application potential in tumor diagnosis, evaluation, and monitoring of therapeutic efficacy

Supplementary document for In-vivo assessment of rat rectal tumor using optical-resolution photoacoustic endoscopy - 6877424.pdf

supplementary materia