Photoacoustic measurement apparatus and probe unit for use therewith
A photoacoustic measurement apparatus which includes a diffuser plate for diffusing laser light inputted from the upstream side of an optical system, a lens system for focusing 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 a light energy resistant structure at an end portion on the side of the lens system, and is disposed such that the laser light focused by the lens 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;
an optical fiber cable which includes an optical fiber having a core and cladding structure and a light energy resistant structure at an end portion on the side of the lens system, 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,
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.
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 not less than ½ 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 not less than ½ 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
2
≤
2.4
·
f
·
tan
(
(
ϕ
2
)
2
+
(
θ
2
)
2
)
.
(
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 optical fiber cable further comprises a covering member which covers the optical fiber such that a side surface portion of the optical fiber near the end face is exposed.
9. The photoacoustic measurement apparatus of claim 8 , wherein:
the optical fiber has the core and cladding structure in which the cladding is comparable in damage threshold energy density to the core; and
the covering member covers the optical fiber such that a side surface portion of the cladding of the optical fiber near the end face is exposed.
10. The photoacoustic measurement apparatus of claim 8 , wherein:
the optical fiber has an end cap structure in which a member formed of a material comparable in damage threshold energy density to the core is connected to the end portion; and
the covering member covers the optical fiber such that a side surface portion of the member of the optical fiber near the end face of the member is exposed.
11. The photoacoustic measurement apparatus of claim 1 , wherein:
the optical fiber cable further comprises a covering member which covers the optical fiber and is formed of a material comparable in damage threshold energy density to the core of the optical fiber or higher; and
a side surface portion of the optical fiber other than a portion near the end face and a portion of the inner circumferential surface of the covering member other than a portion near the end face are fixed by an adhesive.
12. 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.
13. The photoacoustic measurement apparatus of claim 12 , wherein the holding section also integrally holds the diffuser plate.
14. 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.
15. 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 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.
16. 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.
17. 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.
18. 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.
19. 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;
an optical fiber cable which includes an optical fiber having a core and cladding structure and a light energy resistant structure at an end portion on the side of the lens system, 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,
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.