U.S. patent application number 14/129486 was filed with the patent office on 2014-07-24 for object information acquiring apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. The applicant listed for this patent is Kenichi Nagae. Invention is credited to Kenichi Nagae.
Application Number | 20140206960 14/129486 |
Document ID | / |
Family ID | 46852340 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140206960 |
Kind Code |
A1 |
Nagae; Kenichi |
July 24, 2014 |
OBJECT INFORMATION ACQUIRING APPARATUS
Abstract
An object information acquiring apparatus is used. This
apparatus comprises: a light source configured to emit pulsed light
of a plurality of wavelengths; a wavelength controller configured
to switch the wavelength; a probe configured to receive an acoustic
wave generated and propagated in an object subjected to the pulsed
light emitted onto the object; a scan controller configured to move
the probe within a predetermined scanning range; and an information
processor configured to acquire information about the object by
using a plurality of electric signals corresponding to the
wavelengths of the pulsed light output from the probe at each
reception position in the scanning area. The wavelength controller
switches the wavelength of the pulsed light before the probe scans
the entire scanning area while receiving at each reception position
an acoustic wave corresponding to at least one of the wavelengths
of the pulsed light.
Inventors: |
Nagae; Kenichi;
(Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nagae; Kenichi |
Yokohama-shi |
|
JP |
|
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
46852340 |
Appl. No.: |
14/129486 |
Filed: |
August 15, 2012 |
PCT Filed: |
August 15, 2012 |
PCT NO: |
PCT/JP2012/071113 |
371 Date: |
December 26, 2013 |
Current U.S.
Class: |
600/310 ;
600/407 |
Current CPC
Class: |
A61B 5/0091 20130101;
A61B 5/14535 20130101; A61B 5/0062 20130101; A61B 5/145 20130101;
A61B 5/14551 20130101; A61B 5/0095 20130101; A61B 5/14532 20130101;
A61B 8/403 20130101; A61B 8/0825 20130101; A61B 8/4281
20130101 |
Class at
Publication: |
600/310 ;
600/407 |
International
Class: |
A61B 5/00 20060101
A61B005/00; A61B 5/145 20060101 A61B005/145 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2011 |
JP |
2011-183574 |
Claims
1. An object information acquiring apparatus, comprising: a
pulsed-light source, configured to emit pulsed light of a plurality
of wavelengths; a wavelength controller configured to switch the
wavelength of the pulsed light; a probe configured to receive an
acoustic wave generated in an object irradiated with the pulsed
light from said pulsed-light source; a scan controller configured
to move said probe within a predetermined scanning range; and an
information processor configured to acquire information about the
object by using a plurality of electric signals, corresponding to
the wavelengths of the pulsed light output from said the probe at
each reception position in the scanning area, wherein said
wavelength controller switches the wavelength of the pulsed light
before said probe scans the entire scanning area while receiving at
each reception position an acoustic wave corresponding to at least
one of the wavelengths of the pulsed light.
2. The object information acquiring apparatus according to claim 1,
wherein said scan controller enables said probe to receive an
acoustic wave within the scanning range by moving said probe in a
main scan direction and a sub-scan direction intersecting the main
scan direction, the main scan direction being a direction said
which the probe is moved while receiving an acoustic wave at each
reception position.
3. The object information acquiring apparatus according to claim 2,
wherein the scanning range is divided into a plurality of partial
areas in the sub-scan direction, and wherein after said probe
receives an acoustic wave corresponding to pulsed light of a first
wavelength at each reception position in at least one partial area
but before said probe receives an acoustic wave in the other
partial areas, said wavelength controller switches the wavelength
of the pulsed light to a second wavelength different from the first
wavelength.
4. The object information acquiring apparatus according to claim 3,
wherein the partial areas correspond to scanning orbits followed
when said probe is moved while receiving an acoustic wave at each
reception position in the main scan direction within the scanning
range, wherein said scan controller moves said probe a plurality of
times within the partial area, and wherein said wavelength
controller switches the wavelength of the pulsed light so that
pulsed light of a different wavelength is emitted each time said
probe is so moved.
5. The object information acquiring apparatus according to claim 3,
wherein the partial areas correspond scanning orbits followed when
said probe is moved while receiving an acoustic wave at each
reception position in the main scan direction within the scanning
range, and wherein said wavelength controller switches the
wavelength of the pulsed light while said probe moves in the main
scan direction in the partial areas.
6. The object information acquiring apparatus according to claim 5,
wherein said wavelength controller switches the wavelength of the
pulsed light each time the pulsed light is emitted.
7. The object information acquiring apparatus according to claim 1,
wherein said wavelength controller switches the wavelength of the
pulsed light between two different wavelengths.
8. The object information acquiring apparatus according to claim 1,
wherein said wavelength controller switches the wavelength of the
pulsed light between three different wavelengths.
9. The object information acquiring apparatus according to claim 1,
wherein said pulsed-light source emits the pulsed light having
wavelengths in the range of from 700 nm to 1100 nm.
10. The object information acquiring apparatus according to claim
1, wherein said information processor acquires at least any one of
initial acoustic pressure of the acoustic wave, density of light
energy absorbed, absorption coefficient, and information reflecting
the concentrations of substances.
Description
TECHNICAL FIELD
[0001] The present invention relates to an object information
acquiring apparatus.
BACKGROUND ART
[0002] Conventionally, an X-ray mammography apparatus has been
known as an image diagnostic apparatus effective in discovering or
diagnosing breast cancer. Also, in recent years, the method in
which light energy is transmitted through an object, a
photoacoustic signal generated as a result of thermal expansion
caused by the absorption of the light energy is received, and the
inside of the object is imaged based on the photoacoustic signal,
has received attention. A photoacoustic signal is an acoustic wave
such as an ultrasonic wave. In particular, this signal is also
called a photoacoustic wave.
[0003] For the reception and processing of a photoacoustic signal,
it is preferable to receive the photoacoustic signal and convert it
into an electric signal. A photoacoustic signal is generally
converted into an electric signal by using a conversion element
such as a CMUT (Capacitive Micromachined Ultrasonic Transducer)
produced using a piezoelectric element or semiconductor technology.
Actually, a probe in which more than one such conversion element is
arranged is usually used.
[0004] However, it is difficult in terms of cost and yield to
manufacture a probe of a size sufficient to simultaneously acquire
photoacoustic signals from the entire breast. In order to overcome
this problem, PTL 1, for example, describes an ultrasonic
diagnostic apparatus that automatically carries out mechanical
scanning using an ultrasonic probe to receive photoacoustic
signals, and reconstruct a three-dimensional image over a wide
examination area.
[0005] Meanwhile, the technology for calculating the ratio of
present substances of different optical absorption spectra by using
photoacoustic signals obtained by the emission of light of a
plurality of wavelengths has been studied.
[0006] For example, NPL 1 describes a method for calculating oxygen
saturation or the like in blood by using a plurality of
wavelengths, through focusing on the difference in optical
absorption spectra between oxidized hemoglobin and reduced
hemoglobin present in blood.
[0007] If absorption coefficients (.mu..sub.a.sup..lamda.1, and
.mu..sub.a.sup..lamda.2) corresponding to wavelengths .lamda.1 and
.lamda.2 are used in a certain position, oxygen saturation
(SO.sub.2) is calculated from the expression (1) given below.
[ Math . 1 ] SO 2 = [ HbO 2 ] [ HbO 2 ] + [ Hb ] = .mu. a .lamda. 2
Hb .lamda. 1 - .mu. a .lamda. 1 Hb .lamda. 2 .mu. a .lamda. 1
.DELTA. Hb .lamda. 2 - .mu. a .lamda. 2 .DELTA. Hb .lamda. 1 ( 1 )
##EQU00001##
[0008] Here, [HbO.sub.2] is the concentration of oxidized
hemoglobin and [Hb] is the concentration of reduced hemoglobin.
Symbols .epsilon..sub.Hb.sup..lamda.1 and
.epsilon..sub.Hb.sup..lamda.2 are molar absorption coefficients of
reduced hemoglobin at wavelengths .lamda.1 and .lamda.2
respectively. Symbols .DELTA..epsilon..sub.Hb.sup..lamda.1 and
.DELTA..epsilon..sub.Hb.sup..lamda.1 are values found by
subtracting the molar absorption coefficients of reduced hemoglobin
from the molar absorption coefficients of oxidized hemoglobin at
wavelengths .lamda.1 and .lamda.2 respectively.
[0009] Also, PTL 2 describes an apparatus for measuring glucose
concentration by emitting two wavelengths.
CITATION LIST
Patent Literature
[0010] PTL 1: Japanese Patent No. 4448189 [0011] PTL 2: Japanese
Patent Application Laid-Open No. 2010-139510
Non Patent Literature
[0011] [0012] NPL 1: Journal of Biomedical Optics 14(5), 054007
SUMMARY OF INVENTION
Technical Problem
[0013] However, where mechanical scanning is carried out with a
probe such that a plurality of wavelengths are emitted onto an
observation area of a certain object and photoacoustic signals
corresponding to the wavelengths are acquired, the problem may
occur that the object moves during scanning.
[0014] Imaging time (photoacoustic wave reception time) required to
acquire photoacoustic signals from an area (240 mm.times.180 mm)
equal to a panel used in general mammography is calculated in the
manner described below. As an example, it is assumed that the
element size is 2 square mms, the number of reception CHs is 500
CHs, the repetition frequency of light emission is 10 Hz, and the
average is calculated from 256 measurements in order to improve the
reception signal SN ratio. In this case, by simple arithmetic,
(240.times.180.times.256) (2.times.2.times.500.times.10)=552.96
(secs), that is, an imaging time of about 9 min is required in
order to acquire photoacoustic signals corresponding to one
wavelength.
[0015] As described above, to calculate, for example, oxygen
saturation, absorption coefficients corresponding to a plurality of
wavelengths at focused points are used. However, if there is a time
difference of about 9 mins between the point in time that a
photoacoustic signal at a focused point is acquired using
wavelength .lamda.1 and the point in time that a photoacoustic
signal at the focused point is acquired using wavelength .lamda.2,
there is a high possibility of displacement of an object,
especially, of a living biological object.
[0016] In order to calculate oxygen saturation or the like at a
certain focused point, absorption coefficients corresponding to
wavelengths .lamda.1 and .lamda.2 at the focused point have to be
used. If there is displacement due to the time difference between
the points in time that data corresponding to wavelength 71 is
acquired (the point in time that a photoacoustic wave is received)
and data corresponding to wavelength .lamda.2 is acquired (the
point in time that a photoacoustic wave is received), it means that
oxygen saturation is consequently calculated using absorption
coefficients corresponding to different positions. This leads to
error in the calculation result, and degradation in reliability and
accuracy.
[0017] The present invention has been proposed in view of the
foregoing problems. It is accordingly the object of the present
invention to provide a technology to prevent an object information
acquiring apparatus, which acquires photoacoustic signals by using
light of a plurality of wavelengths, from being affected by error
due to object movement.
Solution to Problem
[0018] The present invention provides an object information
acquiring apparatus, comprising:
[0019] a light source configured to emit pulsed light of a
plurality of wavelengths;
[0020] a wavelength controller configured to switch the wavelength
of the pulsed light;
[0021] a probe configured to receive an acoustic wave generated and
propagated in an object subjected to the pulsed light emitted onto
the object;
[0022] a scan controller configured to move the probe within a
predetermined scanning range; and
[0023] an information processor configured to acquire information
about the object by using a plurality of electric signals
corresponding to the wavelengths of the pulsed light output from
the probe at each reception position in the scanning area;
[0024] wherein the wavelength controller switches the wavelength of
the pulsed light before the probe scans the entire scanning area
while receiving at each reception position an acoustic wave
corresponding to at least one of the wavelengths of the pulsed
light.
Advantageous Effects of Invention
[0025] The present invention is able to provide a technology to
prevent an object information acquiring apparatus, which acquires
photoacoustic signals by using light of a plurality of wavelengths,
from being affected by error due to object movement.
[0026] 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 DRAWINGS
[0027] FIG. 1 is a diagram schematically showing the concept of
data acquisition using a plurality of wavelengths.
[0028] FIG. 2 is a diagram schematically showing probe movement
that does not use the present invention.
[0029] FIG. 3 is a time chart showing data acquisition that does
not use the present invention.
[0030] FIG. 4 is a diagram schematically showing probe movement
according to the present invention.
[0031] FIG. 5 is a time chart showing data acquisition according to
the present invention.
[0032] FIGS. 6A to 6C are diagrams showing the configuration of an
ultrasonic diagnostic apparatus according to the first
embodiment.
[0033] FIG. 7 is a schematic view of a system according to the
present invention.
[0034] FIGS. 8A and 8B are diagrams showing the configuration of an
ultrasonic diagnostic apparatus according to the second
embodiment.
[0035] FIG. 9 is a diagram schematically showing probe movement
according to the second embodiment.
[0036] FIG. 10 is a time chart showing data acquisition according
to the second embodiment.
[0037] FIGS. 11A and 11B are diagrams showing the configuration of
an ultrasonic diagnostic apparatus according to the third
embodiment.
[0038] FIG. 12 is a diagram schematically showing probe movement
according to the third embodiment.
[0039] FIG. 13 is a time chart showing data acquisition according
to the third embodiment.
[0040] FIG. 14 is a diagram schematically showing a data
acquisition range according to the present invention.
[0041] FIGS. 15A to 15C are time charts of data acquisition
according to the existing or present invention.
DESCRIPTION OF EMBODIMENTS
[0042] Referring to the accompanying drawings, preferred
embodiments of the present invention will be described below.
[0043] An object information acquiring apparatus is an apparatus
that uses a photoacoustic effect in which an acoustic wave
(typically ultrasonic wave) generated in an object by emitting
light (electromagnetic wave) onto the object and propagated in this
object is received and information about the object is acquired as
image data. The acoustic wave generated by photoacoustic effect is
also called a photoacoustic wave. Examples of object information
include the initial acoustic pressure of the acoustic wave, the
density of light energy absorbed, absorption coefficient,
information reflecting the concentrations of substances composing
the tissues in the object, and other information, all of which may
be derived from the reception signals of acoustic waves. The
concentrations of substances may be, for example, oxygen
saturation, oxyhemoglobin/deoxyhemoglobin concentration, or glucose
concentration. Additionally, object information may be acquired as
numerical or image data indicating distribution information at each
place (i.e., each target point) in an object. That is, object
information may be acquired as image data indicating distribution
information reflecting, for example, oxygen saturation distribution
in an object.
[0044] The outline of a photoacoustic signal acquiring operation
will now be explained with reference to FIGS. 14 and 15.
[0045] FIG. 14 is a diagram schematically showing a data
acquisition range according to the present invention. In the
present invention, "the data acquisition range" refers to a
predetermined scanning range that includes a plurality of reception
positions at which a probe receives acoustic waves, and that is
scanned in order that the probe receive a plurality of acoustic
waves. This predetermined data acquisition range may be a range
determined in advance or may be a range specified by a user every
time. While scanning within this data acquisition range, the probe
receives acoustic waves, thereby making it possible to acquire, as
image data, three-dimensional object information, such as oxygen
saturation distribution in an object. The probe 101 moves within
the data acquisition range 105 and receives photoacoustic waves. In
the description below, such photoacoustic waves detected by the
probe are called photoacoustic signals.
[0046] Here, it is assumed that photoacoustic signals corresponding
to pulsed light of two different wavelengths, .lamda.1 and
.lamda.2, is acquired over the data acquisition range 105. Where
the present invention is not used, it is assumed that the operation
is performed such that a photoacoustic signal corresponding to
pulsed light of wavelength .lamda.1 is captured over the entire
area of the data acquisition range 105, then, wavelength switching
is carried out, and a photoacoustic signal corresponding to pulsed
light of wavelength .lamda.2 is acquired over the entire data
acquisition range 105. As shown in FIG. 15A, the operation is
composed of time 501 taken to acquire a photoacoustic signal
corresponding to pulsed light of wavelength .lamda.1 and time 502
taken to acquire a photoacoustic signal corresponding to pulsed
light of wavelength .lamda.2. If the time required for the probe
101 to scan over the entire data acquisition range 105 is
represented by T, a time of 2T is required in total. Additionally,
there is an average difference of T between the times required to
acquire photoacoustic signals corresponding to the different
wavelengths.
[0047] Next will be described data acquisition where the present
invention is used. The data acquisition range 105 is divided into a
partial data acquisition range 400A and a partial data acquisition
range 400B, which are partial areas. Order of data acquisition is
shown in FIG. 15B. That is, the following procedure may be
performed: a photoacoustic signal corresponding to pulsed light of
wavelength .lamda.1 (a first wavelength) is first acquired (501A)
in the partial data acquisition range 400A, then wavelength
switching is carried out, and a photoacoustic signal corresponding
to pulsed light of wavelength .lamda.2 (a second wavelength) is
acquired (502A) in the partial data acquisition range 400A; next,
wavelength switching is again carried out, a photoacoustic signal
corresponding to pulsed light of wavelength .lamda.1 is acquired
(501B) in the partial data acquisition range 400B, then, wavelength
switching is carried out, and a photoacoustic signal corresponding
to pulsed light of wavelength .lamda.2 is acquired (502B) in the
partial data acquisition range 400B. If the time required for the
probe 101 to scan over the entire data acquisition range 105 is
represented by T, the total time required is 2T, which is the same
as the above. However, the average difference between the times
required to acquire photoacoustic signals corresponding to the
different wavelengths decreases to T/2.
[0048] That is, before a photoacoustic signal generated by emission
of pulsed light of one of two wavelengths is acquired over the
entire acquisition range 105, the wavelength is switched to the
other, and a photoacoustic signal is acquired using this
wavelength. This means that before completing a scan of the entire
data acquisition range (scanning range) while receiving a
photoacoustic wave corresponding to pulsed light of one wavelength
at each reception position, switching between the wavelengths of
the pulsed light is carried out. This makes it possible to reduce
the difference between the times required to acquire photoacoustic
signals corresponding to the different wavelengths. In this case,
wavelength switching is carried out three times.
[0049] In addition, there may be a case as shown in FIG. 15C. That
is, the following procedure may be performed: a photoacoustic
signal corresponding to pulsed light of wavelength .lamda.1 is
first acquired (501A) in a partial data acquisition range 400A,
then wavelength switching is carried out, and a photoacoustic
signal corresponding to pulsed light of wavelength .lamda.2 is
acquired (502A) in the partial data acquisition range 400A;
subsequently, a photoacoustic signal corresponding to pulsed light
of wavelength .lamda.2 is acquired (502B) in the partial data
acquisition range 400B, then, wavelength switching is carried out,
and a photoacoustic signal corresponding to pulsed light of
wavelength .lamda.1 is acquired (501B) in the partial data
acquisition range 400B. In this case also, the difference between
the times required to acquire photoacoustic signals corresponding
to the different wavelengths can be reduced just as in the above.
In this case, wavelength switching is carried out two times.
[0050] If the entire data acquisition area is divided into an M
number of partial data acquisition ranges (partial areas)
(M.gtoreq.2) in a case where photoacoustic signals are acquired
with different wavelengths of N types by using the present
invention, the minimum value for the number of wavelength switching
times is (N-1).times.M. In the preceding example, since two types
of wavelength are used and the entire data acquisition area is
divided into two partial data acquisition ranges, the minimum
number of times is (2-1).times.2=2.
[0051] Incidentally, where the present invention is not used, in
which the entire data acquisition range is scanned with one
wavelength and then the wavelength is switched to the other, the
number of wavelength switching times is (N-1).
[0052] That is, before all data (acoustic waves) are acquired at
all reception positions within a data acquisition range by the
emission of pulsed light of different wavelengths of N types, the
wavelength is switched (N-1).times.M times, thereby reducing the
difference between the times required to acquire photoacoustic
signals corresponding to the different wavelengths. That is to say,
error due to movement of an object, which accompanies the passage
of time, can be prevented.
First Embodiment
[0053] An embodiment of a biological information processing
apparatus according to the present invention will be described in
detail below with reference to the drawings.
[0054] First, the outline and operation of a system according to
the present embodiment will be explained and then a data acquiring
operation will be described.
[0055] FIG. 6 is a diagram of an ultrasonic diagnostic apparatus
according to the first embodiment of the present invention, and
shows the configuration of parts around objects. Each of FIGS. 6A
and 6B is a cross-sectional view of the apparatus as viewed from a
direction perpendicular to the direction in which the object is
compressed. FIG. 6C is a plan view of a holding plate as viewed
from a direction in which the object is compressed.
[0056] Each object (a breast in this embodiment) 104 is sandwiched
and held between two holding plates 103 (103a and 103b). A probe
101 is installed on the opposite side of the holding plate 103a to
the breast 104. A light emission unit 102 is installed at the
opposite side of the holding plate 103b to the breast 104. The
probe 101 and light emission unit 102 move in a data acquisition
range 105, as shown by a change from FIG. 6A to FIG. 6B.
[0057] The object is not a component of any part of the object
information acquiring apparatus of the present invention. However,
its explanation is as follows: if an object information acquiring
apparatus is used for diagnosis of malignant tumor, blood vessel
disease, blood sugar level, or the like in a human being or animal
or for follow-up to chemical treatment, a site other than a breast,
such as a finger, hand or foot of a human being or animal may be
assumed to be an object.
[0058] FIG. 7 is a diagram showing the outline of a system of the
present embodiment. A laser light source 204 generates pulsed light
(typically, 100 nsec or shorter) of wavelength (typically 700 nm to
approximately 1100 nm) close to near-infrared, according to a
timing control signal from a system controller 201 and a wavelength
control signal from a laser wavelength controller 210. After
transmission along an optical transmission path, these pulsed light
are transmitted through the holding plate 103 (not shown) from the
light emission unit 102 and emitted onto an object (not shown).
Consequently, a light absorber in the object absorbs the pulsed
light and generates acoustic waves. In the present invention, light
refers to electromagnetic waves including visible and infrared
rays. According to the constituent to be measured, a specific
wavelength may be selected. The laser wavelength controller serves
as a wavelength controller according to the present invention, and
the laser light source serves as a light source according to the
present invention.
[0059] The probe 101 has a plurality of conversion elements. Using
these conversion elements, the probe receives photoacoustic waves
passed through the holding plate 103 and converts them into
electric signals (reception signals). A reception circuit system
205 subjects reception signals output from the probe 101 to
sampling and amplifying processes and converts these signals into
digital signals (digitized reception signals).
[0060] Using data acquisition range information specified by the
system controller 201, a scan controller 211 controls the probe
scanning mechanism 202 and the emission system scanning mechanism
203 and moves the probe 101 and light emission unit 102. Then,
light emission and photoacoustic signal reception as described
above are carried out repeatedly.
[0061] A reconstruction block 206 performs an image reconstruction
process using information about probe position and so on input from
the system controller 201 and using digital signals input from the
reception circuit system 205. This image reconstruction is a
process for calculating initial acoustic pressure distribution p
(r) of photoacoustic waves in an object by using FBP (Filtered Back
Projection) or the like, expressed by, for example, the formula (2)
given below.
[ Math . 2 ] p ( r ) = - 1 2 .pi. .intg. S 0 .intg. S 0 r 0 2 [ t
.differential. p d ( r 0 , t ) .differential. t + 2 p d ( r 0 , t )
] t = r - r 0 / c ( 2 ) ##EQU00002##
wherein, dS.sub.0 is the size of a detector, S.sub.0 is the size of
an aperture used for reconstruction, each P.sub.d (r.sub.0, t) is a
signal received by the corresponding conversion element, r.sub.0 is
the position of the corresponding conversion element, and t is a
reception time.
[0062] For each wavelength, a reconstruction data storing unit 207
holds the initial acoustic pressure distributions reconstructed
from different wavelengths.
[0063] From this reconstruction data storing unit 207, a
multi-wavelength composing unit 208 receives initial acoustic
pressure distribution data reconstructed from the different
wavelengths, and performs computation, thereby calculating object
information such as oxygen saturation. Glucose concentration can
also be calculated by appropriately controlling a plurality of
different wavelengths. An image display unit 209 displays an image
by its being controlled by the system controller 201. Examples of
an image displayed may include, for example: an image showing the
initial acoustic distribution or absorption coefficient
distribution calculated from photoacoustic signals acquired using
one wavelength; and oxygen saturation calculated by the
multi-wavelength composing unit 208.
[0064] The process performed from the reconstruction block to the
multi-wavelength composing unit corresponds to the process
performed by the information processor according to the present
invention.
[0065] Next, the acquisition of photoacoustic signals by using a
plurality of wavelengths will be explained with reference to the
drawings.
[0066] FIG. 1 schematically shows the outline of data acquisition.
With reference to this drawing, a description is given of the
operation of acquiring photoacoustic signals by using a plurality
of wavelengths.
[0067] The probe 101 with the conversion elements moves, thereby
acquiring data (acoustic waves) at respective positions within the
data acquisition range 105. At this time, the probe moves in the
data acquisition range such that the probe 101 moves in main scan
and sub-scan directions a plurality of times. If it is assumed that
the probe moves in the manner of a Raster scan, the main scan
direction refers to the direction of movement along a scan line,
that is, the direction in which the probe moves while receiving an
acoustic signal at each reception position. The sub-scan direction
refers to the direction of movement between the scan lines, that
is, the direction intersecting (typically, orthogonal to) the main
scan direction. It is assumed that each partial data acquisition
range, which is acquired by one movement in the main scan
direction, is assigned to 110A, 110B, 110C, and 110D. In the
present embodiment, the partial data acquisition ranges are areas
into which the data acquisition range, i.e., the scanning range, is
divided in the sub-scanning direction. Additionally, each of the
partial data acquisition ranges 110A, 110B, 110C, and 110D is a
range corresponding to a scanning orbit followed by the probe
moving in the main scan direction within the data acquisition range
while receiving an acoustic wave at each reception position.
[0068] It is assumed that photoacoustic signals generated by the
emissions of pulsed light of two different wavelengths are acquired
over the data acquisition range 105. For example, where
photoacoustic signals are acquired by the emissions of two
wavelengths (.lamda.1 and .lamda.2), it is necessary to acquire
photoacoustic signals by emitting the wavelengths of the two types
to the four partial data acquisition ranges.
[0069] As a comparative example, an operation in which the present
invention is not used is explained with reference to FIG. 2.
[0070] First, a probe acquires data (acoustic waves) (indicated by
the solid-line arrow) by moving within the data acquisition range
105 while emitting pulsed light of wavelength .lamda.1. Then, the
wavelength of the pulsed light is switched to .lamda.2, and the
probe is moved (indicated by the broken-line arrow) within the data
acquisition range 105.
[0071] FIG. 3 is a time chart showing the partial data acquisition
ranges and emitted wavelengths in the cases where such movements
are carried out. The symbols A, B, C, and D (301) on the axis
represented by .lamda.1 in the drawing indicate timings of
acquisition of the respective photoacoustic signals in the partial
data acquisition ranges (110A, 110B, 110C, and 110D) within which
pulsed light of wavelength .lamda.1 has been emitted. Additionally,
A, B, C, and D (302) represent the timings of the acquisition of
the respective photoacoustic signals in the partial data
acquisition ranges (110A, 110B, 110C, and 110D) within which pulsed
light of wavelength .lamda.2 has been emitted.
[0072] In the moving method described above, by emitting one of the
two different wavelengths, all photoacoustic signals are acquired
from the data acquisition range 105.
[0073] Where such probe scanning is carried out, the acquisition
interval between the respective photoacoustic signals relating to
wavelengths .lamda.1 and .lamda.2 within the same partial data
acquisition range (e.g., 110A) is indicated by t1.
[0074] FIG. 4 illustrates a data acquiring operation in which the
present invention is used.
[0075] First, a wavelength control signal is transmitted to the
laser light source 204 from the laser wavelength controller 210 and
the wavelength is set to .lamda.1. A timing control signal for
laser emission is transmitted from the system controller 201 and
thereby the laser light source 204 generates pulsed light of
wavelength .lamda.1. In response to a control signal from the scan
controller 211, the probe 101 and light emission unit 102 are moved
in the main scan direction. In such a manner, photoacoustic signals
corresponding to pulsed light of wavelength .lamda.1 are acquired
(the solid-line arrow in 110A) within the partial data acquisition
range 110A. Subsequently, the probe 101 and light emission unit 102
are shifted to the sub-scan direction and moved within the partial
data acquisition range 101B. Then, while the probe 101 and light
emission unit 102 are moved in the main scan direction within the
partial data acquisition range 110B, light emission and data
acquisition are carried out (the solid-line arrow in 110B). Thus,
data in the partial data acquisition ranges 110A and 110B are
acquired.
[0076] Next, a wavelength control signal is transmitted to the
laser light source 204 from the laser wavelength controller 210 and
the wavelength is set to .lamda.2. Thereafter, photoacoustic
signals corresponding to pulsed light of wavelength .lamda.2 are
acquired in the partial data acquisition ranges 110A, 110B, 110C,
and 110D (broken-line arrows in 110A to 110D).
[0077] Subsequently, a wavelength control signal is again
transmitted to the laser light source 204 from the laser wavelength
controller 210, and the wavelength is set to .lamda.1. Then,
photoacoustic signals corresponding to pulsed light of wavelength
.lamda.1 are acquired within the data acquisition ranges 110C and
110D.
[0078] FIG. 5 is a time chart showing the partial data acquisition
ranges and emitted wavelengths in a case where such movements have
been performed. Each of the two dotted-lines between the axes
.lamda.1 and .lamda.2 indicates that wavelength switching has been
carried out. That is, wavelength switching has been carried out two
times. Specifically, electric signals corresponding to the
wavelengths of the pulsed light have been output from the probe at
their respective reception positions.
[0079] In probe scanning in the present embodiment, before all
photoacoustic signals are acquired from within the data acquisition
range 105 by emitting pulsed light of one of the two different
wavelengths (for example, .lamda.1), the wavelength of pulsed light
is switched. Also, at the points in time that the second and sixth
movements in the main scan direction of the movements (eight times)
in the main scan direction have been completed, the wavelength of
pulsed light generated by the laser light source 204 is
switched.
[0080] In probe scanning in the present embodiment, the acquisition
interval between the respective photoacoustic signals relating to
wavelengths .lamda.1 and .lamda.2 within the same partial data
acquisition range 110A is indicated by t2. As described above, this
acquisition interval is shorter than the case where a photoacoustic
signal corresponding to the emission of pulsed light of wavelength
.lamda.1 and subsequently a photoacoustic signal corresponding to
the emission of pulsed light of wavelength .lamda.2 are acquired
within the entire data acquisition range 105. Accordingly, in the
present embodiment, interval t2 is half of t1.
[0081] Therefore, according to the present embodiment, error due to
movement of an object, which accompanies the passage of time, can
be prevented. Accordingly, when oxygen saturation and so on are
calculated using reception signals corresponding to the two
wavelengths (.lamda.1 and .lamda.2), error resulting from
displacement is prevented, and a highly reliable, highly accurate
image can be composed. In the present embodiment, two initial
acoustic pressure distributions corresponding to the two
wavelengths are obtained in advance, and then oxygen saturation
distribution is obtained. However, without obtaining these initial
acoustic pressure distributions, oxygen saturation and so on can be
obtained using electric signals (reception signals) output from the
probe when photoacoustic waves are received.
[0082] Also, in the present embodiment, the acquisition of data
within each partial data acquisition range is completed by one
movement in the main scan direction. However, in order to obtain a
required signal SN ratio, movement in the main scan direction may
be carried out a plurality of times while pulsed light of the same
wavelength is emitted. For example, even by exerting control such
that movement in the sub-scan direction is carried out after one
forward and backward movement in the main scan direction, the same
advantageous effect of the present invention can be obtained.
Second Embodiment
[0083] FIG. 8 shows diagrams of an ultrasonic diagnostic apparatus
according to the second embodiment of the present invention, and
shows the configuration of parts around an object. FIG. 8B is a
cross-sectional view of the apparatus as viewed from a direction
perpendicular to the direction in which the object is compressed,
and FIG. 8A is a plan view of a holding plate as viewed from a
direction in which the object is compressed.
[0084] An object (a breast in the present embodiment) 104 is
sandwiched and held between two holding plates 103 (103a and 103b).
A probe 101 is installed at the opposite side of the holding plate
103a to the breast 104. Alight emission unit 102 is installed at
the opposite side of the holding plate 103b to the breast 104. The
probe 101 and light emission unit 102 are moved so as to acquire
data within a data acquisition range 105.
[0085] The probe 101 moves in a circular direction 801, as a main
scan direction, around an axis 803 in the object, and moves in a
direction 802, as a sub-scan direction, substantially perpendicular
to the main scan direction.
[0086] In order to receive acoustic waves transmitted through the
holding plates 103, a medium (e.g. water or caster oil) that
transmits ultrasonic waves is injected between the probe 101 and
holding plates 103.
[0087] Since the outline of the system and the flow of data
processing are the same as those in the first embodiment,
explanation thereof is omitted, and acquisition of photoacoustic
signals by using a plurality of wavelengths will be explained with
reference to the drawings.
[0088] FIG. 9 illustrates a data acquiring operation that is
performed in the present embodiment. The main scan direction is a
circular direction around the axis 803, as described above.
However, here, a two-dimensional drawing in which the circular
directions are developed in plane is used for ease of
explanation.
[0089] In the present embodiment, a description will be given of a
case where three wavelengths are used.
[0090] First, a wavelength is set to .lamda.1 and the probe 101 is
moved in the main scan direction, thereby acquiring a photoacoustic
signal corresponding to pulsed light of wavelength .lamda.1
(solid-line arrow) within a partial data acquisition range 110A.
Subsequently, the wavelength is switched to .lamda.2, and a
photoacoustic signal corresponding to pulsed light of wavelength
.lamda.2 is acquired (broken-line arrow) in the partial data
acquisition range 110A. Further, the wavelength is switched to
.lamda.3 and, then, a photoacoustic signal corresponding to pulsed
light of wavelength .lamda.3 is acquired (chain-line arrow) in the
partial data acquisition range 110A. Thereafter, the probe shifts
to the sub-scan direction, and acquires data within the partial
data acquisition range 110B. By repeating such an operation, data
up to a partial data acquisition range 110D may be acquired.
[0091] As described above, before shifting to the sub-scan
direction, movement in the main scan direction is carried out (at
least twice, specifically three times in the present embodiment),
and control for wavelength change is exerted at the time point in
time that one of the movements in the main scan direction has been
completed.
[0092] FIG. 10 is a time chart showing the partial data acquisition
ranges and emitted wavelengths, according to the present
embodiment. In probe scanning in the present embodiment, the
acquisition interval between the respective photoacoustic signals
relating to wavelengths .lamda.1 and .lamda.3 within the same
partial data acquisition range 110A, is indicated by t3. This
acquisition interval is notably shorter than the case where, after
photoacoustic signals corresponding to the emission of pulsed light
of wavelength .lamda.1 are acquired in the entire data acquisition
range 105, photoacoustic signals corresponding to emission of
pulsed light of the wavelength .lamda.2 and photoacoustic signals
corresponding to emission of pulsed light of the wavelength
.lamda.3 are acquired. In the present embodiment, the time
difference is reduced to 1/4 of the case in which the present
invention is not used.
[0093] According to the present embodiment, wavelength switching
and movement in the main scan direction are carried a plurality of
times before shifting to the sub-scan direction. Therefore,
acquisition intervals between the photoacoustic signals
corresponding to different wavelengths within the same partial data
acquisition range can be further shortened. That is, error due to
movement of an object, which accompanies the passage of time, can
be further reduced.
[0094] Therefore, by use of data reconstructed from photoacoustic
signals obtained from the wavelengths (.lamda.1, .lamda.2, and
.lamda.3), error resulting from displacement is further reduced
when oxygen saturation and so on are calculated in the
multi-wavelength composing unit. Accordingly, a more reliable,
highly accurate image can be composed.
[0095] In the present embodiment, the main scan direction is
specified as circular direction around the axis. However, even
where the probe is used for two-dimensional scanning as in spatial
arrangement of the first embodiment, the advantageous effects of
the present invention can be obtained.
Third Embodiment
[0096] FIG. 11 is a diagram of an ultrasonic diagnostic apparatus
according to the third embodiment of the present invention, and
shows the configuration of parts around an object. FIGS. 11A and
11B are diagrams of the object sagging, as viewed from one side and
from above respectively.
[0097] An object (a breast in the present invention) 104 is allowed
to sag. A probe 101 and a light emission unit 102 are installed in
opposite positions with the object 104 between them. The probe 101
and light emission unit 102 are moved so as to acquire data within
a data acquisition range.
[0098] The probe 101 moves in a circular direction 801, as a main
scan direction, around an axis 803 through the object, and moves in
a direction 802, as a sub-scan direction, substantially
perpendicular to the main scan direction. In the present
embodiment, the data acquisition range is a range obtained by
moving in a sub-scan direction a plane in which the probe 101 is
rotated 360.degree. around the axis 803.
[0099] In order to receive photoacoustic waves generated in the
object 104, a medium (e.g. water or caster oil) that transmits
ultrasonic waves is injected between the probe 101 and subject
104.
[0100] Since the outline of the system and the flow of data
processing are the same as those in the first embodiment,
explanation thereof is omitted, and acquisition of photoacoustic
signals by using a plurality of wavelengths will be explained with
reference to the drawings.
[0101] FIG. 12 illustrates a data acquiring operation that is
performed in the present embodiment. The main scan direction is a
circular direction around the axis 803, as described above.
However, here, a two-dimensional drawing in which circular
direction are developed in a plane is used for ease of explanation.
That is to say, the right and left ends of the data acquisition
range 105 in FIG. 12 are continuous with each other.
[0102] First, the probe 101 is rotated 360.degree. (indicated by
the hollow-line arrow in 150A) around the axis 803. During movement
in this main scan direction, wavelength switching is carried out.
In the present embodiment, wavelength is switched for each pulse.
That is, switching takes place in the following order: .lamda.1,
.lamda.2, .lamda.1, .lamda.2, and so on. In order to speedily
change the wavelength of pulsed light generated by laser light
source, two lasers may be used alternately.
[0103] Such an operation makes it possible to acquire photoacoustic
signals corresponding to pulsed light of wavelengths .lamda.1 and
.lamda.2 within the partial data acquisition range 110A. At the
time that the probe 101 has been rotated 360.degree. around the
axis 803, the probe 101 is shifted to the sub-scan direction, and
the probe 101 is again rotated 360.degree. (the hollow-line arrow
in 150B) around the axis 803, thereby acquiring data within a
partial data acquisition range 110B. Data are acquired for partial
data acquisition ranges 110C and 110D in a similar manner.
[0104] While movement in the main scan direction is carried out in
such a manner, control is exerted to switch the wavelength of
pulsed light generated by laser light source, and the data is
acquired from the data acquisition range.
[0105] FIG. 13 is a time chart showing emitted wavelengths. The
range of 160A schematically shows the period for which wavelength
switching is carried out for each pulse and each photoacoustic
signal corresponding to pulsed light of wavelength .lamda.1 and
each photoacoustic signal corresponding to pulsed light of
wavelength .lamda.2 are acquired within a partial data acquisition
range 110A. Similarly, the ranges 160B, 160C, and 160D correspond
to 110B, 110C, and 110D.
[0106] In probe scanning in the present embodiment, the acquisition
interval between photoacoustic signals corresponding to the
wavelengths .lamda.1 and .lamda.2 within the same partial data
acquisition range is indicated by t4. This acquisition interval is
notably shorter compared to that where, after photoacoustic signals
corresponding to emissions of pulsed light of wavelength .lamda.1
are acquired within the entire data acquisition range,
photoacoustic signals corresponding to emissions of pulsed light of
the wavelength .lamda.2 are acquired.
[0107] According to the present embodiment, since wavelength
switching is carried out during movement in the main scan
direction, acquisition interval between photoacoustic signals
corresponding to different wavelengths can be further shortened
within the same partial data acquisition range. That is, error due
to movement of an object, which accompanies the passage of time,
can be further reduced.
[0108] Therefore, by use of data reconstructed from photoacoustic
signals obtained from the plurality of wavelengths (.lamda.1 and
.lamda.2), error resulting from displacement is further reduced
when oxygen saturation and so on are calculated in the
multi-wavelength composing unit. Accordingly, a more reliable,
highly accurate image can be composed.
[0109] In the present embodiment, while the probe is continuously
moved in the main scan direction, wavelength switching and
acquisition of photoacoustic signals are carried out. Specifically,
in movement in the main scan direction, the probe is not stopped at
each reception position but is moved at almost constant speed.
Therefore, as shown in FIG. 13, the acquisition position (reception
position) of a photoacoustic signal when light of wavelength
.lamda.1 is emitted and that when light of wavelength .lamda.2 is
emitted do not coincide exactly. However, if the frequency of
pulsed light is sufficiently high, processing can substantially
proceed without taking differences between acquisition positions
into consideration. Additionally, even if the acquisition position
of a photoacoustic signal corresponding to each light pulse is
displaced, image data in a fixed area within each partial data
acquisition range is calculated in the reconstruction block 206.
Therefore, image reconstruction corresponding to the same position
can be achieved.
[0110] Alternatively, the probe may be stopped at one position on
an object, in which case, photoacoustic signals are received by
using light of wavelengths .lamda.1 and .lamda.2, and then the
probe may be moved in the next position. In this case,
photoacoustic signals with almost no time difference can be
acquired at the same reception position with respect to the
object.
[0111] In the present embodiment, the main scan direction is
specified as a circular direction around the axis. However, even
where the probe is used for two-dimensional scanning, as in spatial
arrangement of the first embodiment, the advantageous effects of
the present invention can be obtained.
[0112] 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.
[0113] This application claims the benefit of Japanese Patent
Application No. 2011-183574, filed on Aug. 25, 2011, which is
hereby incorporated by reference herein in its entirety.
* * * * *