U.S. patent application number 13/151543 was filed with the patent office on 2011-12-15 for photoacoustic measuring apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Yukio Furukawa, Shigeru Ichihara, Shuichi Kobayashi.
Application Number | 20110303015 13/151543 |
Document ID | / |
Family ID | 45095121 |
Filed Date | 2011-12-15 |
United States Patent
Application |
20110303015 |
Kind Code |
A1 |
Ichihara; Shigeru ; et
al. |
December 15, 2011 |
PHOTOACOUSTIC MEASURING APPARATUS
Abstract
A photoacoustic measuring apparatus includes a light source, a
movable holding unit which holds an object, a light diffusing unit
which fixes the distance between the light diffusing unit and the
holding unit and diffuses light incident from the light source, and
an acoustic wave obtaining unit which obtains an acoustic wave
generated from the object by the light emitted via the holding unit
and the light diffusing unit.
Inventors: |
Ichihara; Shigeru; (Tokyo,
JP) ; Furukawa; Yukio; (Sagamihara-shi, JP) ;
Kobayashi; Shuichi; (Yokohama-shi, JP) |
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
45095121 |
Appl. No.: |
13/151543 |
Filed: |
June 2, 2011 |
Current U.S.
Class: |
73/656 ;
73/655 |
Current CPC
Class: |
A61B 5/4312 20130101;
A61B 8/0825 20130101; G01N 2201/0634 20130101; A61B 5/708 20130101;
A61B 5/0095 20130101; G01N 21/1702 20130101; G01N 29/2418 20130101;
G01N 2021/1787 20130101; A61B 5/0091 20130101 |
Class at
Publication: |
73/656 ;
73/655 |
International
Class: |
G01H 9/00 20060101
G01H009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2010 |
JP |
2010-132860 |
Claims
1. A photoacoustic measuring apparatus comprising: a light source;
a movable holding unit which holds an object; a light diffusing
unit which fixes the distance between the light diffusing unit and
the holding unit and diffuses light incident from the light source;
and an acoustic wave obtaining unit which obtains an acoustic wave
generated from the object by the light emitted via the holding unit
and the light diffusing unit.
2. The photoacoustic measuring apparatus according to claim 1,
wherein the light diffusing unit processes the light incident side
of the holding unit to perform surface diffusion.
3. The photoacoustic measuring apparatus according to claim 1,
wherein the light diffusing unit is a holographic diffusing plate
which adheres to the holding unit.
4. The photoacoustic measuring apparatus according to claim 1,
wherein the light diffusing unit is the holding unit which includes
particles to perform volume diffusion.
5. The photoacoustic measuring apparatus according to claim 4,
wherein the light diffusing unit increases the diffusion
coefficient as the light travels from the incident side to the
object side.
6. The photoacoustic measuring apparatus according to claim 1,
further comprising a fixing member which holds the distance between
the light diffusing unit and the holding unit constant.
7. The photoacoustic measuring apparatus according to claim 1,
wherein the holding unit sandwiches and holds the object between
two plates.
8. The photoacoustic measuring apparatus according to claim 1,
wherein the holding unit presses and holds the object.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a photoacoustic measuring
apparatus. More specifically, the present invention relates to an
apparatus having a movable holding unit which holds an object.
[0003] 2. Description of the Related Art
[0004] In recent years, photoacoustic tomography which uses the
characteristic of ultrasound waves less diffusible in a living body
than light to calculate an optical characteristic value
distribution in the living body at high resolution has been
proposed. In this specification, hereinafter, photoacoustic
tomography will be described as PAT. In a measuring apparatus using
the principle of PAT, when pulsed light generated from a light
source irradiates a living body, it is propagated while diffusing
in the living body. An absorber included in a biological tissue
absorbs the energy of the propagated pulsed light to generate an
acoustic wave (the acoustic wave is also called a photoacoustic
wave, and is typically an ultrasound wave). An acoustic wave signal
obtained by detecting and signal-processing the acoustic wave is
subjected to an analyzing process, so that an optical
characteristic distribution, in particular, an optical energy
absorption density distribution, in the living body can be
obtained.
[0005] In PAT, the sound pressure (P) of the acoustic wave obtained
from the absorber in the living body by light absorption can be
expressed by the following equation (1).
P=.GAMMA..mu.a.PHI. Equation (1)
[0006] Here, .GAMMA. is a Gruneisen coefficient which is an elastic
characteristic value, and is obtained by dividing the product of
the coefficient of cubic expansion (.beta.) and the square of the
sound speed (c) by the specific heat (Cp). .mu.a is the absorption
coefficient of the absorber, and .PHI. is the light amount in a
local region (the light amount irradiating the absorber).
[0007] In recent years, breast diagnosis has been studied as the
application of PAT to living bodies. In this specification, the PAT
apparatus for breast diagnosis will be described as photoacoustic
mammography (PAM). The PAM apparatus is an apparatus which images
angiogenesis formed around a tumor at the time of forming the tumor
and a region having high absorption coefficient and including the
angiogenesis, thereby detecting the tumor position in a breast. To
diagnose the entire breast by PAM, measurement is required up to
the deep region at a depth above 4 to 5 cm below the surface of a
living body. Although the acoustic wave signal intensity is in
proportion to the light amount .PHI., a beam incident from a
biological tissue is diffused, with the result that the light
amount reaching the deep portion decreases exponentially. For this
reason, to enable depth observation, light preferably irradiates a
wide range at irradiation intensity permissible to living bodies
(MPE: maximum permissible exposure). Therefore, as the light
source, a high-output flash lamp excitation solid-state laser is
typically used.
[0008] The flash lamp excitation solid-state laser has a locally
high energy output distribution, the light amount distribution in a
beam being less uniform than a semiconductor laser and an He--Ne
laser. When a beam at locally high energy density is used, the
local region has the upper limit of irradiation intensity.
Therefore, the light amount distribution of a beam is preferably
made uniform using a light modulation member such as a diffusing
plate (see U.S. Patent Application Publication No.
2006/0184042).
SUMMARY OF THE INVENTION
[0009] In PAM having a breast holding mechanism which fixes an
observed portion according to the shape of a breast, unlike X-ray
mammography, the following problems arise. In X-ray mammography,
since X-rays travel substantially straightly in a living body, the
X-ray intensity distribution in the living body cannot be affected
by the position of the parallel plates of the breast holding
mechanism.
[0010] On the other hand, in PAM, when a light diffusing plate as a
typical optical component is installed in a beam propagation path
in order to make the light amount distribution in a beam uniform,
the outgoing beam is diverged according to the propagation
distance. For this reason, when the distance from the surface of a
living body to the diffusing plate is different at the time of
measurement of an object at plural points, the irradiation region
becomes different. As a result, the irradiation intensity at each
point is changed according to the breast fixing position to
deteriorate the photoacoustic signal.
[0011] The present invention has been made in view of the above
problems, and an object of the present invention is to provide a
photoacoustic measuring apparatus which can irradiate the surface
of a living body uniformly and efficiently.
[0012] This invention provides a photoacoustic measuring apparatus
comprising:
[0013] a light source;
[0014] a movable holding unit which holds an object;
[0015] a light diffusing unit which fixes the distance between the
light diffusing unit and the holding unit and diffuses light
incident from the light source; and
[0016] an acoustic wave obtaining unit which obtains an acoustic
wave generated from the object by the light emitted via the holding
unit and the light diffusing unit.
[0017] According to the photoacoustic measuring apparatus of the
present invention, the surface of a living body can be irradiated
uniformly and efficiently.
[0018] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic diagram of a front detection type PAT
apparatus;
[0020] FIG. 2 is a schematic diagram of a rear detection type PAT
apparatus;
[0021] FIG. 3 is a schematic diagram of a both-side irradiation
type PAT apparatus;
[0022] FIGS. 4A and 4B are diagrams each showing an irradiation
region when a living body holding mechanism including a diffusing
mechanism is provided;
[0023] FIGS. 5A and 5B are further diagrams each showing an
irradiation region when a living body holding mechanism including a
diffusing mechanism is provided;
[0024] FIGS. 6A and 6b are diagrams each showing the irradiation
region of a comparative example in which a diffusing mechanism is
fixed;
[0025] FIG. 7 is a schematic diagram of a front detection type PAT
apparatus according to a first example;
[0026] FIG. 8 is a schematic diagram of a rear detection type PAT
apparatus according to a second example; and
[0027] FIG. 9 is a schematic diagram of a both-side irradiation
type PAT apparatus performing volume diffusion according to a third
example.
DESCRIPTION OF THE EMBODIMENTS
[0028] Hereinafter, preferred embodiments of the present invention
will be described with reference to the drawings. However, the
size, material, shape, and relative arrangements of components
described below should be appropriately changed according to the
configuration of an apparatus to which the present invention is
applied and various conditions, and the scope of the present
invention is not intended to be limited to the following
description.
[0029] A photoacoustic measuring apparatus has a living body
holding mechanism which fixes the measured portion of an object. As
breast fixing methods in breast diagnosis, a method for fixing the
side surfaces of a breast using two parallel plates, a method for
entirely pressing and fixing the front surface of a breast, and a
method for arcuately fixing a portion around a breast have been
proposed. In particular, a breast holding mechanism using a
parallel plate has an advantage of being arbitrarily movable
according to the size of a breast. In addition, the breast holding
mechanism using a parallel plate is adopted to X-ray mammography,
and has another advantage that image comparison with X-ray
mammography is easy.
[0030] When a breast is fixed using a parallel plate in PAM, some
light irradiation directions and ultrasound detector arranging
directions with respect to the parallel plate can be considered.
This will be described with reference to FIGS. 1 to 3. Further, in
the description of these, two parallel plates, not shown, which
sandwich and hold a breast are present.
[0031] FIG. 1 shows a front detection type apparatus in which an
ultrasound detector 104 is arranged on the opposite side of
irradiation light 103 with respect to an object 101. The
irradiation light is emitted by diffusion in a living body, as
shown in a diffused light area 102. FIG. 2 shows a rear detection
type apparatus in which an ultrasound detector 204 is arranged on
the same side as irradiation light 203 with respect to an object
201. The irradiation light is emitted, as shown in a diffused light
area 202. FIG. 3 shows a both-side irradiation type apparatus in
which irradiation light 303b is emitted from the opposite side of
an ultrasound detector 304 with respect to an object 301, and
irradiation light 303a is emitted from the same side as the
ultrasound detector 304 with respect to the object 301. The
irradiation light is emitted, as shown in a diffused light area
302.
[0032] In the parallel plates used to sandwich and hold the object,
various movable forms of moving each of the parallel plates on the
ultrasound detector side and on the opposite side independently,
moving only either one of them, and the like can be selected. The
movable parallel plates can appropriately press and hold abreast
according to variations among individuals.
[0033] In the irradiation used in PAM, the locally high irradiation
energy density region can be removed by using a light diffusing
mechanism. Further, the irradiation intensity of the entire
irradiation region can be made uniform with uniformity according to
diffusion angle. The irradiation range of a beam which has passed
through the light diffusing mechanism is diverged according to
diffusion angle. Here, with the use of the movable parallel plates
for fixing a breast, when the light diffusing mechanism is fixed,
the distance from the light diffusing mechanism to the parallel
plate, that is, the beam propagation distance, is changed with the
movement of the plate, so that the irradiation region is
changed.
[0034] By the way, the permissible light amount in the irradiation
onto the surface of a living body is defined according to
irradiation energy or irradiation amount per unit area. For this
reason, when the irradiation region is varied to increase the
irradiation area, the light amount per unit area onto the surface
of a living body is decreased. On the other hand, when the
irradiation area is decreased, the light amount per unit area onto
the surface of a living body is increased, so that the irradiation
intensity can be equal to or larger than MPE (maximum permissible
exposure). In PAM which requires depth observation, it is preferred
that the irradiation intensity be constant within the safe
irradiation light amount range equal to or smaller than MPE and be
high so that depth observation is enabled. For this reason, the
irradiation region is required to be constant regardless of the
movement of the movable parallel plate.
[0035] A method for making the irradiation region constant in the
present invention will be described below. In FIGS. 4A and 4B,
light 402 is emitted from a light source (not shown). In the breast
holding mechanism shown in FIGS. 4A and 4B, a light diffusing
mechanism 404 is provided to a parallel plate 403 itself. FIGS. 4A
and 4B show, in the breast holding mechanism, two types of
configurations in which the interval between the parallel plates is
different. As shown in these drawings, the irradiation region
formed by the beam via the light diffusing mechanism is not
changed, and has a constant area regardless of the interval between
the parallel plates 403. Alternatively, even when the movable
parallel plate is moved to press and hold the breast, the
irradiation region cannot be changed before and after movement.
[0036] To realize the light diffusing mechanism, there is a method
for making the light amount distribution of a beam uniform by
providing a surface diffusing mechanism in which the surface shape
on the incident side is roughened like ground glass. However, when
ground glass is used, much 0-order light is included so that a beam
perpendicularly incident upon the substrate is perpendicularly
outgoing therefrom. For this reason, to increase the uniformity of
the light amount distribution, the use of a holographic diffusing
plate in which a micron-level surface structure in surface relief
hologram pattern is randomly arranged on the surface of the
substrate is effective. The uneven shape of the surface can be
pattern-formed by epoxy UV curing. The diffusion angle can be
selected according to non-periodic uneven shape, so that the beam
can be diffused at high transmissivity without depending on the
visible to infrared wavelengths.
[0037] In addition, the light diffusing mechanism can also use
volume diffusion in which particles having different refractivities
are included in the parallel plate substrate for diffusion control
in the parallel plate. In particular, volume diffusion can be done
by including titania particles in the acrylic or polycarbonate
substrate. The diffusion angle can be increased, not only by
including the particles uniformly in the substrate, but also by
increasing the amount of particles included from the incident side
to the outgoing side to increase the diffusion coefficient. When
laser light having high coherence is used, the beam can be locally
focused near the surface in the substrate due to refraction on the
surface of the substrate. The diffusion is gradually increased to
lower the possibility that such beam can be focused, so that the
light can be diffused uniformly.
[0038] In this way, the light diffusing mechanism of the parallel
plate is referred to as the light diffusing mechanism provided on
the surface of the plate or inside the plate. As a result, the
entire plate has a diffusion angle defined in a predetermined
range. When the diffusion angle is shown as full width at half
maximum, the entire light diffusing mechanism (light diffusing
unit) of the present invention has a diffusion angle of 0.5.degree.
or more. The diffusion angle is preferably 1.degree. or more, and
more preferably is 5.degree. or more. Such light diffusing
mechanism emits uniform light onto the object.
[0039] In addition, as shown in FIGS. 5A and 5B, a jig 507 which is
a fixing member which holds the interval between alight diffusing
mechanism 504 and a parallel plate 503 constant can be provided. In
this case, since the jig having the diffusing mechanism can be
moved together according to the movement of the holding mechanism,
an irradiation region 505 can be constant. For instance, even when
the state of FIG. 5A is changed to the state of FIG. 5B in which
the parallel plate is moved in the direction pressing and holding
the breast, the irradiation area on the surface of the breast is
not changed. In the configuration of FIGS. 5A and 5B, unlike the
case that the light diffusing mechanism is provided to the parallel
plate, the surface diffusing mechanism is provided on the light
outgoing side.
[0040] However, the light diffusing mechanism 504 may be a member
using a volume diffusing mechanism in addition to the member using
the surface diffusing mechanism. In addition, when the diffusing
mechanism is provided on the surface of the light diffusing
mechanism 504 installed in the space in which the light is
propagated, the diffusing surface may be the incident side or the
outgoing side. However, when laser light having large light amount
and high coherence is used, the beam can be locally focused near
the surface in the parallel plate by refraction on the surface of
the parallel plate. Therefore, in the light diffusing member using
a material with low damage resistance, the outgoing side is
preferably the diffusing surface.
[0041] FIGS. 6A and 6B show the configurations of a comparative
example with respect to the forms of FIGS. 5A and 5B. In the
configurations, the position of a light diffusing mechanism 604 is
fixed, and the distance between the light diffusing mechanism and
the plate is increased as the parallel plate is moved in the
direction pressing the object. In this case, with the movement of
the parallel plate, an irradiation region 605 of the diffused beam
is changed (enlarged) from FIG. 6A to FIG. 6B. As a result, the
irradiation intensity in the irradiation region is significantly
lower than MPE, thereby lowering the measuring efficiency.
First Example
[0042] In this example, a configuration example of a front
detection type PAT apparatus to which the present invention is
applied will be described.
[0043] As shown in FIG. 7, the front detection type PAT apparatus
having planar parallel plates 705a and 705b, an ultrasound detector
704, and a light source 707 which emits irradiation light 703 is
prepared for a biological tissue 701 as an object. The emitted
light is diffused to irradiate a diffused light area 702. In
addition, in this apparatus, the ultrasound detector scans the
surface of the plate 705a. The beam on the opposite side is moved
with the movement of the ultrasound detector to irradiate the front
surface (the left side on the drawing sheet) of the ultrasound
detector 704 at all times.
[0044] As the light source, Nd:YAG which is a pulse laser having an
oscillation wavelength of 1064 nm is used. Other than this, the
wavelength band from the visible to the infrared region of about
500 nm to 1400 nm can be used. The wavelength varying technique
using TI:sa (titanium-sapphire) and OPO (optical parametric
generation) used together with the Nd:YAG laser and an alexandrite
laser using an alexandrite crystal which oscillates in the
wavelength band of about 750 nm can also be used. As the parallel
plates 705a and 705b, polymethylpentene having a refractivity of
1.46 is used, the thickness being 10 mm.
[0045] In this example, a holographic diffusing mechanism which is
the surface diffusing mechanism is provided on the incident side of
the plate 705b on the opposite side of the plate 705a on which the
ultrasound detector 704 is arranged, that is, on the outside of the
plate not contacted with the object. For that, a sheet 706 having
the holographic diffusing mechanism adheres to the parallel plate
705b. Alternatively, the surface of the plate may be directly
processed to form the holographic diffusing mechanism. That is, the
surface diffusing mechanism may be part of the plate, or may be a
member different from the plate. The parallel plate corresponds to
the holding unit of the present invention. The sheet having the
holographic diffusing mechanism corresponds to the light diffusing
unit of the present invention.
[0046] The diffused light is absorbed into the biological tissue
701 to generate an ultrasound wave (acoustic wave) by the expansion
and contraction of the biological tissue. This is obtained by the
ultrasound detector 704. The ultrasound detector includes, e.g., a
piezoelectric device, and can convert the obtained ultrasound wave
to an electric signal which is used for image reconstruction in the
biological tissue. The ultrasound detector corresponds to the
acoustic wave obtaining unit of the present invention.
[0047] With the use of the PAT apparatus having such configuration,
one or both of the parallel plates 705a and 705b are moved
according to the size of the breast to hold the breast for
measurement, so that the distance from the light diffusing
mechanism to the object is held constant. As a result, the
variation of the irradiation region by light diffusion can be
inhibited, so that irradiation can be performed effectively.
Second Example
[0048] In this example, a configuration example of the rear
detection type PAT apparatus to which the present invention is
applied will be described.
[0049] As shown in FIG. 8, the rear detection type PAT apparatus
having parallel plates 805, an ultrasound detector 804, and
irradiation light 803 of a light source (not shown) is prepared for
a biological tissue 801. The same light source as the first example
can be used. The light emitted from the light source is diffused to
irradiate a diffused light area 802.
[0050] A film larger than the detector surface and subjected to
acoustic matching is fixed on the front surface of the ultrasound
detector. The film preferably has higher ultrasound wave
transmissivity, and requires light transmissivity. In this example,
a polycarbonate film having a thickness of 200 .mu.m is used. A
unit which integrates the ultrasound detector and the polycarbonate
film is contacted with the plate holding the breast via a solution,
such as castor oil, which becomes an acoustic matching layer which
can easily pass an ultrasound wave therethrough, and is moved in
parallel. As the light diffusing mechanism, a surface diffusing
mechanism 806 which is the holographic diffusing mechanism is
provided on the polycarbonate film. The surface diffusing mechanism
is provided on a region other than the contacted portion of the
polycarbonate film and the ultrasound detector 804, so that the
beam is incident from the region.
[0051] In measurement performed using the PAT apparatus having such
configuration, even when the parallel plate 805 is moved according
to the size of the breast to hold the breast, the distance from the
light diffusing mechanism to the object is held constant. As a
result, the variation of the irradiation region by light diffusion
can be inhibited, so that irradiation can be performed
effectively.
[0052] Although the rear detection type PAT apparatus has been
described here, the method of this example is combined with the
method of the first example to emit the light from the light source
onto the opposite side of the ultrasound detector, so that a
both-side irradiation type PAT apparatus can be realized.
[0053] In addition, the configuration of this example can also
include one plate by eliminating the plate on the opposite side of
the ultrasound detector. In that case, the breast is pressingly
fixed and held for measurement. This configuration can also inhibit
the variation of the irradiation region by diffusion, so that
irradiation can be performed effectively. In addition, when the
breast is pressingly fixed by an arc member, the present invention
is applicable.
Third Example
[0054] In this example, a configuration example in which the light
diffusing mechanism is realized by volume diffusion in place of
surface diffusion used in the above examples will be shown.
[0055] FIG. 9 shows the configuration of the PAT apparatus of this
example. Here, the polycarbonate film which provides surface
diffusion to the front surface of the ultrasound detector, as shown
in the above example, is not necessary. A biological tissue 901
such as a breast is the object, and is sandwiched and held between
parallel plates 905. Irradiation lights 903a and 903b led by an
optical system from alight source (not shown) irradiate the object
and are diffused onto a diffused light area 902. An ultrasound
detector 904 detects an acoustic wave generated from the
object.
[0056] In this example, to adjust the refractivity in the
polymethylpentene resin which is the material of the parallel
plates 905, titania particles are included. Two titania inclusion
methods in which titania particles are uniformly included in the
plates, and in which the rate of titania particles included is
increased so as to gradually increase the diffusion effect from the
incident side to the outgoing side of the beam are prepared.
[0057] Even when either of two types of plates is used, the
parallel plate 905 is moved according to the size of the breast
using the PAT apparatus having such configuration to hold the
breast for measurement, the distance from the light diffusing
mechanism to the object can be held constant. As a result, the
variation of the irradiation region by light diffusion can be
inhibited, so that irradiation can be performed effectively.
Between two types of plates, the amount of titania included is
gradually increased from the incident side, which is preferable in
that the beam is prevented from being locally focused near the
surface by refraction.
[0058] As another form of this example, a configuration example in
which the diffusing mechanism moving with the breast holding
mechanism is provided may be adopted. In this case, the interval
between the parallel plates as the breast holding mechanism is
changed depending on the size of the breast. The movable parallel
plate is coupled to the member having the diffusing mechanism to
hold the distance between the plate and the diffusing member. As in
the first example, since the beam on the opposite side is in-plane
operated with the ultrasound detector at the time of acoustic wave
signal measurement, the diffusing member has sufficiently large
vertical and horizontal sizes, so that the beam can be emitted via
the diffusing member at all times.
[0059] By such configuration, the variation of the irradiation
region by diffusion can be inhibited, so that irradiation can be
performed effectively.
[0060] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0061] This application claims the benefit of Japanese Patent
Application No. 2010-132860, filed on Jun. 10, 2010, which is
hereby incorporated by reference herein in its entirety.
* * * * *