Radial array transducer-based photoacoustic and ultrasonic endoscopy system
A photoacoustic and ultrasonic endoscope includes an optical fiber, a light diffuser configured to radially diffuse a laser beam transmitted through the optical fiber, and an array transducer having a cylindrical shape and surrounding the light diffuser, the array transducer being configured to transmit the diffused laser beam therethrough and to generate an ultrasonic wave or detect an ultrasonic wave generated by an object to be examined.
1. A photoacoustic and ultrasonic endoscope comprising:
an optical fiber;
a light diffuser configured to diffuse a laser beam in a radial direction, the laser beam being transmitted through the optical fiber;
an array transducer that is optically transparent, has a cylindrical shape with a curved side surface, and surrounds the light diffuser completely in the radial direction,
wherein the light diffuser comprises:
a mirror located at a center of the array transducer and comprising a reflective surface capable of radially reflecting the laser beam transmitted through the optical fiber; and
a beam shaper between the mirror and the optical fiber and configured to deflect the laser beam transmitted through the optical fiber such that a traveling direction of the laser beam is changed,
wherein the array transducer is configured to transmit the laser beam from the light diffuser through the curved side surface of the array transducer and to generate an ultrasonic wave or detect an ultrasonic wave generated by an object to be examined through the curved side surface of the array transducer.
2. The photoacoustic and ultrasonic endoscope of claim 1 , wherein the laser beam diffused by the light diffuser passes through an entire area of the curved side surface of the array transducer.
3. The photoacoustic and ultrasonic endoscope of claim 1 , wherein a light emitting area on an outer surface of the array transducer and an ultrasonic sensor area on the outer surface of the array transducer overlap each other, the diffused laser beam exits the array transducer through the light emitting area, and an ultrasonic wave that the array transducer senses passes through the ultrasonic sensor area.
4. The photoacoustic and ultrasonic endoscope of claim 1 , further comprising an acoustic matching layer covering at least a portion of an outer surface of the array transducer, the acoustic matching layer comprising a light-transmissive material.
5. The photoacoustic and ultrasonic endoscope of claim 4 , wherein the acoustic matching layer further comprises polymethylpentene (TPX).
6. The photoacoustic and ultrasonic endoscope of claim 1 , wherein the beam shaper comprises an electro-optic modulator (EOM) capable of focusing the laser beam in a particular direction.
7. The photoacoustic and ultrasonic endoscope of claim 1 , wherein the mirror has a cone-like shape.
8. The photoacoustic and ultrasonic endoscope of claim 1 , wherein the light diffuser further comprises a cylindrical light scattering layer located inside the array transducer and surrounding the mirror.
9. The photoacoustic and ultrasonic endoscope of claim 8 ,
wherein a reduced scattering coefficient (μ s ′) of the light scattering layer is equal to or greater than 0.1 cm −1 , and equal to or less than 1.0 cm −1 .
10. The photoacoustic and ultrasonic endoscope of claim 1 , wherein the array transducer comprises:
a piezoelectric layer having a certain thickness;
a plurality of first electrodes arranged on a first surface of the piezoelectric layer in a form of a one-dimensional or two-dimensional array; and
a plurality of second electrodes on a second surface of the piezoelectric layer, the second surface facing the first surface, and the second electrodes being arranged parallel to the plurality of first electrodes.
11. The photoacoustic and ultrasonic endoscope of claim 10 , further comprising an optically-transparent backing layer between the light diffuser and the piezoelectric layer.
12. The photoacoustic and ultrasonic endoscope of claim 10 , wherein the first electrodes and the second electrodes are optically-transparent electrodes.
13. The photoacoustic and ultrasonic endoscope of claim 10 , wherein the plurality of first electrodes and the plurality of second electrodes comprise opaque electrodes.
14. The photoacoustic and ultrasonic endoscope of claim 13 , further comprising a light reflecting layer between one of the plurality of the second electrodes and the light diffuser.
15. The photoacoustic and ultrasonic endoscope of claim 1 , wherein the array transducer comprises:
a first array transducer layer comprising a ceramic or single crystal-based piezoelectric material; and
a second array transducer layer surrounding the first array transducer layer and comprising a polymer-based piezoelectric material.