Transvaginal fast-scanning optical-resolution photoacoustic endoscopy
The present disclosure describes a fast-scanning optical-resolution photoacoustic (fsOR-PAE) endoscope for imaging vasculature within tissues in vivo that includes an ultrasonic transducer and a scanning mirror within a lumen of an elongate casing. The scanning mirror is configured to direct the laser pulses from the pulsed laser source to a focal spot outside the casing in a scanning pattern via an imaging window formed in the casing. The scanning mirror is further configured to direct a plurality of photoacoustic signals from the focal spot to the ultrasonic transducer via the imaging window.
1. A method of imaging a microvasculature within a tissue using a fast-scanning optical-resolution photoacoustic (fsOR-PAE) system, the method comprising:
providing an fsOR-PAE endoscope comprising a scanning mirror and an ultrasonic transducer housed within an elongate housing, a set of doublets positioned between a pulsed laser source and the scanning mirror, and the pulsed laser source, the pulsed laser source and the ultrasonic transducer coupled to the scanning mirror;
positioning the elongate housing within the tissue;
producing a plurality of laser pulses using the pulsed laser;
focusing the plurality of laser pulses using the set of doublets pulses;
directing the plurality of laser pulses through an imaging window formed within the housing to a plurality of focal spots within the tissue in a scanning pattern using the scanning mirror, wherein directing the plurality of laser pulses in a scanning pattern comprises scanning in a sweep parallel to cylindrical axis and a B-scan rate of 250 Hz over a 3 mm range;
receiving and directing a plurality of photoacoustic signals produced at the plurality of focal spots to the ultrasonic transducer via the imaging window;
detecting the plurality of photoacoustic signals using the ultrasonic transducer; and
transforming the plurality of detected photoacoustic signals into an image of the microvasculature, wherein the image comprises a lateral resolution of less than 5 μm.
2. The method of claim 1 , wherein the scanning pattern further comprises scanning the imaging window in an azimuthal scanning pattern.
3. The method of claim 1 , wherein the plurality of laser pulses are delivered at a wavelength of about 532 nm, at a pulse repetition rate of about 500 kHz, and at an optical fluence of less than about 17 mJ/cm 2 .
4. The method of claim 1 , wherein transforming the plurality of detected photoacoustic signals further comprises reconstructing the plurality of detected photoacoustic signals into the image using a reconstruction method.
5. The method of claim 4 , wherein the reconstruction method comprises a back-projection reconstruction method.