Photoacoustic measurement apparatus and probe unit for use therewith, and endoscope
A photoacoustic measurement apparatus which includes a diffuser plate which diffuses laser light inputted from the upstream side of an optical system, a lens system which focuses the laser light diffused by the diffuser plate, and an optical fiber cable which includes an optical fiber having a core and cladding structure and is disposed such that the laser light focused by the lens system is inputted from one end, in which the light projection unit projects the laser light guided by the optical fiber cable as the measuring light. In a photoacoustic measurement performed by guiding the measuring light using an optical fiber, high energy measuring light can be guided while inhibiting end face damage of the optical fiber.
1. A photoacoustic measurement apparatus, comprising:
a diffuser plate which diffuses measuring light inputted from the upstream side of an optical system;
a lens system which focuses the measuring light diffused by the diffuser plate and is disposed such that the measuring light diffused by the diffuser is inputted from the upstream side of the lens system;
an optical fiber cable which includes an optical fiber having a core and cladding structure and is disposed such that the measuring light focused by the lens system is inputted from one end;
a light projection unit which projects the measuring light guided by the optical fiber cable into a subject;
an electroacoustic transducer unit which detects a photoacoustic wave generated in the subject by the projection of the measuring light and converts the photoacoustic wave into an electrical signal; and
a signal measurement unit which performs a signal measurement based on the electrical signal.
2. The photoacoustic measurement apparatus of claim 1 , wherein:
the lens system focuses the measuring light such that a minimum beam diameter of the measuring light is ⅓ to ⅔ of a core diameter of the optical fiber; and
the optical fiber cable is disposed such that the measuring light is inputted with a beam diameter of the measuring light being ⅓ to ⅔ of the core diameter of the optical fiber.
3. The photoacoustic measurement apparatus of claim 2 , wherein a divergence angle φ of the measuring light when incident on the diffuser plate, a diffusion angle θ of the diffuser plate, a focal length f of the lens system, and a core diameter d of the optical fiber satisfy a formula (1) given below:
d
3
≤
2.4
·
f
·
tan
(
(
ϕ
2
)
2
+
(
θ
2
)
2
)
≤
2
d
3
.
(
1
)
4. The photoacoustic measurement apparatus of claim 1 , wherein the lens system has a focal length of 4 to 40 mm.
5. The photoacoustic measurement apparatus of claim 1 , wherein:
the diffuser plate is a holographic diffuser; and
the holographic diffuser has a diffusion angle of 0.2 to 2.0°.
6. The photoacoustic measurement apparatus of claim 1 , wherein:
the diffuser plate is a light shaping diffuser in which tiny concave lenses are arranged randomly on one surface of a substrate; and
the light shaping diffuser has a diffusion angle of 0.2 to 2.0°.
7. The photoacoustic measurement apparatus of claim 1 , wherein the optical fiber has a core diameter of 100 to 600 μm.
8. The photoacoustic measurement apparatus of claim 1 , wherein the apparatus comprises a holding section which integrally holds the lens system and the optical fiber cable.
9. The photoacoustic measurement apparatus of claim 8 , wherein the holding section also integrally holds the diffuser plate.
10. The photoacoustic measurement apparatus of claim 1 , wherein:
the apparatus comprises a branch section which branches the measuring light; and
the diffuser plate, the lens system, and the optical fiber cable are disposed with respect to each optical path of the branched measuring light portions.
11. The photoacoustic measurement apparatus of claim 1 , wherein:
the apparatus comprises a branch section which branches the measuring light;
the diffuser plate is the sole diffuser plate provided and disposed so as to diffuse at least two of the branched measuring light portions; and
the lens system and the optical fiber cable are disposed with respect to each optical path of the branched measuring light portions.
12. The photoacoustic measurement apparatus of claim 1 , wherein:
the lens system is a lens array;
the optical fiber cable is provided in plural; and
each end face of the plurality of optical fibers of the plurality of optical fiber cables on the lens array side is arranged so as to correspond to each lens section constituting the lens array.
13. The photoacoustic measurement apparatus of claim 1 , wherein:
the lens system is a micro-lens array;
the optical fiber cable is a bundle fiber cable which includes a plurality of optical fibers; and
each end face of the plurality of optical fibers of the bundle fiber cable on the micro-lens array side is arranged so as to correspond to each micro-lens constituting the micro-lens array.
14. The photoacoustic measurement apparatus of claim 1 , wherein:
the measuring light is light in a near infrared wavelength range; and
the diffuser plate, the lens system, and the optical fiber cable are of a structure capable of guiding light in the near infrared wavelength range.
15. The photoacoustic measurement apparatus of claim 1 , wherein the signal measurement unit includes an acoustic image generation unit which generates a photoacoustic image with respect to the electrical signal of the photoacoustic wave.
16. The photoacoustic measurement apparatus of claim 15 , wherein:
the electroacoustic transducer unit detects a reflected ultrasonic wave of an ultrasonic wave transmitted to the subject;
the acoustic image generation unit generates an ultrasonic image based on an ultrasonic wave signal of the reflected ultrasonic wave.
17. A probe unit for use with a photoacoustic measurement apparatus, comprising:
a diffuser plate which diffuses measuring light inputted from the upstream side of an optical system;
a lens system which focuses the measuring light diffused by the diffuser plate and is disposed such that the measuring light diffused by the diffuser is inputted from the upstream side of the lens system;
an optical fiber cable which includes an optical fiber having a core and cladding structure and is disposed such that the measuring light focused by the lens system is inputted from one end;
a light projection unit which projects the measuring light guided by the optical fiber cable into a subject;
an electroacoustic transducer unit which detects a photoacoustic wave generated in the subject by the projection of the measuring light and converts the photoacoustic wave into an electrical signal; and
a signal measurement unit which performs a signal measurement based on the electrical signal.
18. An endoscope, comprising the probe unit of claim 17 .