Photoacoustic wave measurement device

A photoacoustic wave measurement device according to the present invention includes: an optical fiber that outputs pulsed light; an external spacer that is disposed between a pulsed-light output end of the optical fiber and a measurement object, and which is adapted to allow the pulsed light to pass therethrough; a piezoelectric element that receives a photoacoustic wave generated by the pulsed light from the measurement object and converts the photoacoustic wave into an electric signal; and a spacer that is disposed between the external spacer and the piezoelectric element, and which is adapted to allow the photoacoustic wave to pass therethrough. The piezoelectric element is farther from the measurement object than the pulsed-light output end. A part of the optical fiber is disposed within the spacer.

FIELD OF THE INVENTION

The present invention relates to photoacoustic sensors.

BACKGROUND ART

Photoacoustic sensors are conventionally known to measure a photoacoustic signal generated by irradiating an object to be measured (for example, biological object) with pulsed light (see, for example, Patent Document 1 (Japanese Unexamined Patent Publication No. 2011-229660)).

SUMMARY OF THE INVENTION

However, the photoacoustic signal obtained by the photoacoustic sensor may include noise.

Accordingly, it is an object of the present invention to reduce noise included in a photoacoustic signal obtained by a photoacoustic wave measurement device.

According to the present invention, a photoacoustic wave measurement device, includes: a light outputting portion that outputs light therefrom; an arrangement member that is disposed between a light output end of the light outputting portion and a measurement object, and which is adapted to allow the light to pass therethrough; a photoacoustic wave detector that receives a photoacoustic wave generated by the light from the measurement object and converts the photoacoustic wave into an electric signal; and a photoacoustic wave transmission member that is disposed between the arrangement member and the photoacoustic wave detector, and which is adapted to allow the photoacoustic wave to pass therethrough, wherein the photoacoustic wave detector is farther from the measurement object than the light output end, and a part of the light outputting portion is disposed within the photoacoustic wave transmission member.

According to the thus constructed photoacoustic wave measurement device, a light outputting portion outputs light therefrom. An arrangement member is disposed between a light output end of the light outputting portion and a measurement object, and is adapted to allow the light to pass therethrough. A photoacoustic wave detector receives a photoacoustic wave generated by the light from the measurement object and converts the photoacoustic wave into an electric signal. A photoacoustic wave transmission member is disposed between the arrangement member and the photoacoustic wave detector, and is adapted to allow the photoacoustic wave to pass therethrough. The photoacoustic wave detector is farther from the measurement object than the light output end. A part of the light outputting portion is disposed within the photoacoustic wave transmission member.

According to the photoacoustic wave measurement device of the present invention, the light outputting portion may penetrate the photoacoustic wave transmission member.

According to the photoacoustic wave measurement device of the present invention, the light outputting portion may be an optical fiber.

According to the photoacoustic wave measurement device of the present invention, the photoacoustic wave detector may be a piezoelectric element.

DETAILED DESCRIPTION OF THE DISCLOSURE

In the following, preferred embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1is a cross-sectional view of a photoacoustic wave measurement device1according to an embodiment of the present invention. The photoacoustic wave measurement device1includes a case10, a backing member12, a piezoelectric element (photoacoustic wave detector)14, an electrode16, a spacer (photoacoustic wave transmission member)18, an optical fiber (light outputting portion)20, and an external spacer (arrangement member)34.

The case10is a case for accommodating therein the backing member12, the piezoelectric element14, the electrode16, and the spacer18. The spacer18is in contact with the bottom surface of the case10, and the electrode16is mounted on the spacer18. The piezoelectric element14is mounted on the electrode16, and the backing member12is mounted on the piezoelectric element14.

The backing member12serves as a backing material made of epoxy resin. The piezoelectric element (photoacoustic wave detector)14receives a pressure caused by compression waves or the like and converts the pressure into voltage. The electrode16receives the voltage from the piezoelectric element14and supplies the voltage to an external measurement device, not shown (for example, an oscilloscope). The electrode16is, for example, a gold electrode.

The spacer (photoacoustic wave transmission member)18is a transparent spacer that allows a compression wave (photoacoustic wave W) to pass therethrough, and which is made of, for example, acryl, epoxy, a fused quartz, or the like. The spacer18is disposed between the arrangement member34and the piezoelectric element (photoacoustic wave detector)14. The spacer18is separately formed from the arrangement member34. Note that the spacer18allows light and the photoacoustic wave to pass therethrough, and serves as a matching layer that matches an acoustic impedance of a measurement object2to that of the piezoelectric element14.

The optical fiber (light outputting portion)20outputs light (for example, pulsed light P) from a pulsed-light output end20a. The optical fiber20is connected to a pulsed light source (not shown) outside the photoacoustic wave measurement device1.

The optical fiber20penetrates the case10, the backing member12, the piezoelectric element14, and the electrode16. Further, a part of the optical fiber20is disposed within the spacer (photoacoustic wave transmission member)18. As shown inFIG. 1, the optical fiber20may penetrate the spacer18.

The external spacer (arrangement member)34is disposed between the pulsed-light output end20aand the measurement object2so as to allow the pulsed light P to pass therethrough. The external spacer34is in contact with the case10and the pulsed-light output end20a, and also in contact with the measurement object2. The external spacer34is a transparent spacer made of, for example, acryl, epoxy, a fused quartz, or the like.

The measurement object2is, for example, a ball of a finger of a human body. The measurement object2includes blood2ain a blood vessel. When receiving the pulsed light P, the blood2ain the blood vessel generates a photoacoustic wave W. The piezoelectric element14receives the photoacoustic wave W and converts the wave W into an electric signal (for example, in the form of voltage). The piezoelectric element14is farther from the measurement object2than the pulsed-light output end20a.

Next, the operation of the one embodiment in the present invention will be described by comparing with a comparative example.

First, the pulsed light P emitted from the external pulsed light source (not shown) passes through the optical fiber20, and then is output from the pulsed-light output end20a. The pulsed light P is applied to the measurement object2through the external spacer34.

The pulsed light P reaches the blood2ain the blood vessel of the measurement object2. Then, the blood2ain the blood vessel absorbs the pulsed light P and is warmed and is then adiabatically expanded. Thus, the compression wave (photoacoustic wave W) is output from the blood2ain the blood vessel.

The photoacoustic wave W reaches the piezoelectric element14through the measurement object2, the external spacer34, the spacer18, and the electrode16. The piezoelectric element14converts the pressure produced by the photoacoustic wave W into an electric signal (for example, in the form of a voltage). The voltage is taken out to the outside via the electrode16, and then fed to the oscilloscope or the like.

FIG. 2is a cross-sectional view of another photoacoustic wave measurement device1according to a comparative example.

In the comparative example, in the photoacoustic wave measurement device1shown inFIG. 2, the optical fiber20is not inserted into the spacer18at all. In the comparative example, the pulsed-light output end20ais in contact with the spacer18.

FIGS. 3(a) and 3(b)show conceptually graphs of a waveform detected by the photoacoustic wave measurement device1(seeFIG. 2) in the comparative example (seeFIG. 3(a)), as well as a waveform detected by the photoacoustic wave measurement device1(seeFIG. 1) in the embodiment of the present invention (seeFIG. 3(b)).

The comparative example (seeFIG. 3(a)) and the embodiment of the present invention (seeFIG. 3(b)) do not differ so much in near-end reflection noise A generated directly after the pulsed light P starts to be output from the pulsed-light output end20a.

In contrast, noise C generated between the near-end reflection noise A and a target signal B to be measured is large in the comparative example (seeFIG. 3(a)), but small in the embodiment of the present invention (seeFIG. 3(b)). This is the effect obtained by inserting the optical fiber20into the spacer18(particularly, by causing the optical fiber to penetrate the spacer).

In the comparative example (seeFIG. 2), the pulsed-light output end20ais located so close to the piezoelectric element14and the electrode16that the photoacoustic wave (noise C) generated in the vicinity of the pulsed-light output end20aand reaching the piezoelectric element14becomes large. In contrast, in the embodiment of the present invention (seeFIG. 1), the pulsed-light output end20ais located so far from the piezoelectric element14and the electrode16that the photoacoustic wave (noise C) generated in the vicinity of the pulsed-light output end20aand reaching the piezoelectric element14becomes small.

In the photoacoustic wave measurement device1of the embodiment of the present invention, the optical fiber20is inserted into (particularly, penetrates) the spacer18, which can reduce noise included in the photoacoustic signal obtained by the photoacoustic wave measurement device1.

Although the spacer18is a separate member from the arrangement member34as mentioned above, the spacer18and the arrangement member34may be integrally formed together.