U.S. patent application number 15/824074 was filed with the patent office on 2018-03-22 for acoustic wave measuring apparatus and control method of acoustic wave measuring apparatus.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Akira Sato.
Application Number | 20180078145 15/824074 |
Document ID | / |
Family ID | 48224151 |
Filed Date | 2018-03-22 |
United States Patent
Application |
20180078145 |
Kind Code |
A1 |
Sato; Akira |
March 22, 2018 |
ACOUSTIC WAVE MEASURING APPARATUS AND CONTROL METHOD OF ACOUSTIC
WAVE MEASURING APPARATUS
Abstract
Provided is an acoustic wave measuring apparatus including: an
acoustic probe; region-of-interest setting unit for setting two or
more regions of interest for an object; priority setting unit for
setting priorities on the regions of interest; region calculating
unit for determining, for each of the set priorities, an inclusion
region including the regions of interest set with the priority;
scanning method determining unit for assigning a scanning stripe to
each of the inclusion regions so as to include all regions of
interest included in the inclusion region; scanning path
identifying unit for determining a scanning order of a plurality of
scanning stripes having a same priority so as to shorten a movement
distance of the acoustic probe; and scanning unit for scanning the
scanning stripes according to the determined scanning order, based
on the priority order, by moving the acoustic probe.
Inventors: |
Sato; Akira; (Kawasaki-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
48224151 |
Appl. No.: |
15/824074 |
Filed: |
November 28, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13649672 |
Oct 11, 2012 |
9867545 |
|
|
15824074 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/0095 20130101;
A61B 8/54 20130101; A61B 8/469 20130101; A61B 8/5292 20130101 |
International
Class: |
A61B 5/00 20060101
A61B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 2011 |
JP |
2011-242271 |
Claims
1. An acoustic wave measuring apparatus, comprising: a probe
configured to measure an acoustic wave propagated from an object; a
moving unit configured to move the probe with respect to the
object; a region designating unit configured to designate a
plurality of measurement regions for receiving the acoustic wave on
the object; and a controlling unit configured to determine a path
including the plurality of measurement regions on which the probe
is moved by the moving unit and operation of the probe on the path,
wherein the operation of the probe is determined based on
information relating to positions of the plurality of measurement
regions, and wherein the path is determined based on the
information relating to positions of the plurality of measurement
regions and the operation of the probe.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
13/649,672, filed Oct. 11, 2012, claims benefit of that application
under 35 U.S.C. .sctn. 120, and claims benefit under 35 U.S.C.
.sctn. 119 of Japanese Patent Application No. 2011-242271, filed on
Nov. 4, 2011. The entire contents of each of the mentioned prior
applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to an acoustic wave measuring
apparatus and a control method of such an acoustic wave measuring
apparatus.
Description of the Related Art
[0003] An ultrasound measuring apparatus of imaging the structure
inside a biological object by transmitting ultrasound waves to the
biological object and analyzing the reflected ultrasound waves has
been put into practical application in the medical area. When
ultrasound waves are transmitted to the biological object, the
reflection of ultrasound waves occurs at the interfaces in the
biological object having different acoustic impedances. An
ultrasound measuring apparatus images configuration information in
the biological object by analyzing the reflected waves and
detecting the interfaces.
[0004] Moreover, in recent years, technology has been devised for
analyzing the structure and condition of the surface and inside of
a biological object by irradiating a laser beam onto the biological
object and generating acoustic waves (photoacoustic waves) caused
by such laser irradiation from the inside of the biological object,
and analyzing such photoacoustic waves (U.S. Pat. No. 5,840,023).
This technology is also referred to as photoacoustic wave
measurement, and there is consideration for diverting this
technology to medical use, such as for the examination of the
inside of the human body, since examination can be performed
non-invasively.
[0005] Both of the apparatuses described above use an acoustic
probe for receiving the ultrasound waves. As the acoustic probe,
there are types which are handheld and used by being manually
pressed against the skin near the region of interest which the user
wishes to acquire information, and types which mechanically scan
the surface of the skin of the biological object by introducing a
mechanical scanning mechanism.
[0006] With existing acoustic probes, it is difficult to produce a
sensor with a large opening as with an X-ray imaging apparatus from
the perspective of production yield and cost. Thus, the generally
adopted method is to use an acoustic probe of a size that is
smaller than the region that needs to be examined and covering such
region to be examined via automatic or manual scanning.
[0007] A measuring apparatus which mechanically drives an acoustic
probe includes an input setting unit to be used by the user for
setting the region of interest. The input setting unit is
configured, for example, from devices such as a keyboard, a mouse,
or a touch pen, and is used for setting the region of interest by
inputting the detailed measurement setting, or designating the
measuring position. Among the foregoing apparatuses, there are
types which enable the user to designate, in detail, the scanning
track of the probe by using a touch pen or the like (Japanese
Patent Application Laid-Open No. 2006-000185). A measuring
apparatus performs measurement while moving the acoustic probe so
as to trace the designated scanning track. [0008] Patent Literature
1: U.S. Pat. No. 5,840,023 [0009] Patent Literature 2: Japanese
Patent Application Laid-Open No. 2006-000185
SUMMARY OF THE INVENTION
[0010] A conventional measuring apparatus has a problem in that
much time is required for measuring an object in both photoacoustic
measurement and ultrasound measurement. For example, with
mammography for examining breast cancer, the suspected site is
compressed and fixed for measurement, and the time that imposes
burden on the subject due to compression is preferably short.
[0011] In fact, the level of burden felt in response to the
compression and fixation will vary among different individuals, and
certain subjects are unable to withstand such compression and
fixation for a long period of time. Generally speaking, in
measurement using ultrasound waves and photoacoustic waves, higher
examination accuracy can be obtained as the thickness of the
suspected site is shallower. Thus, in order to ensure the required
examination accuracy, a certain level of compressive holding is
required.
[0012] Due to the foregoing circumstances, the measurement time is
desirably as short as possible. Nevertheless, when there are a
plurality of set regions of interest, the acoustic probe makes a
round by scanning all regions and, therefore, the movement distance
increases, and there is a problem in that wasted time results
depending on the scanning order.
[0013] Moreover, even in cases where the measurement is suspended
midway, data of a location of high measurement priority is
preferably acquired as much as possible. When a plurality of
regions of interest are designated, it is possible to deal with the
foregoing case by assigning a priority to each of the plurality of
regions of interest and performing scanning in that priority order.
Nevertheless, for a conventional apparatus to deal with the
foregoing problem, the user was required to personally be aware of
the foregoing circumstances and designate the scanning track in
order from the location of highest priority, and the operation was
complicated.
[0014] The present invention was devised in view of the foregoing
problems, and an object of this invention is to provide an acoustic
wave measuring apparatus capable of simplifying the setting
operation to be performed by the user, and determining a scanning
path among a plurality of regions of interest according to a
priority order.
[0015] In order to achieve the foregoing object, the present
invention provides an acoustic wave measuring apparatus,
comprising:
[0016] an acoustic probe;
[0017] a region-of-interest setting unit configured to set two or
more regions of interest for an object;
[0018] a priority setting unit configured to set priorities on the
regions of interest that have been set;
[0019] a region calculating unit configured to determine, for each
of the set priorities, an inclusion region including the regions of
interest set with the priority;
[0020] a scanning method determining unit configured to assign a
scanning stripe, which is a rectangle that is formed by moving the
acoustic probe in a scanning direction, to each of the inclusion
regions so as to include all regions of interest included in the
inclusion region;
[0021] a scanning path identifying unit configured to determine a
scanning order of a plurality of scanning stripes having a same
priority so as to shorten a movement distance of the acoustic
probe; and
[0022] a scanning unit configured to scan the scanning stripes
according to the determined scanning order, based on the priority
order, by moving the acoustic probe.
[0023] The present invention also provides a method of controlling
an acoustic wave measuring apparatus having an acoustic probe,
comprising the steps of:
[0024] receiving a designation of two or more regions of interest
for an object;
[0025] receiving a designation of priorities on the regions of
interest that have been set;
[0026] determining, for each of the designated priorities, an
inclusion region including the regions of interest;
[0027] assigning a scanning stripe, which is a rectangle that is
formed by moving the acoustic probe in a scanning direction, to
each of the inclusion regions so as to include all regions of
interest included in the inclusion region; and
[0028] determining a scanning order of a plurality of scanning
stripes having a same priority so as to shorten a movement distance
of the acoustic probe,
[0029] wherein the scanning stripes are scanned according to the
determined scanning order, based on the priority order, by moving
the acoustic probe.
[0030] According to the present invention, it is possible to
provide an acoustic wave measuring apparatus capable of simplifying
the setting operation to be performed by the user, and determining
a scanning path among a plurality of regions of interest according
to a priority order.
[0031] 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
[0032] FIG. 1 is a system configuration diagram of the
photoacoustic measuring apparatus according to an embodiment of the
present invention;
[0033] FIG. 2 is a setting screen example of the region of interest
by the region designating unit;
[0034] FIG. 3 is a processing flowchart of the controller unit
according to the first embodiment;
[0035] FIG. 4 is a schematic diagram in the case of setting a
plurality of regions of interest;
[0036] FIG. 5 is a schematic diagram of the inclusion region
relative to the region of interest according to the first
embodiment;
[0037] FIG. 6 is an example of the stripe assignment to the
inclusion region according to the first embodiment;
[0038] FIG. 7 is a schematic diagram of determining the scanning
region in the notable stripe according to the first embodiment;
[0039] FIG. 8 is a detailed explanatory diagram of the processing
flowchart of the controller unit;
[0040] FIG. 9 is a schematic diagram of data accumulation based on
the continuous scanning by the acoustic probe;
[0041] FIGS. 10A and 10B are schematic diagrams of the overlapping
region of the regions of interest and cumulative data according to
the second embodiment; and
[0042] FIG. 11A to 11D are schematic diagrams in a case where an
excess data measurement region occurs according to the third
embodiment.
DESCRIPTION OF THE EMBODIMENTS
[0043] Embodiments of the present invention are now explained in
further detail with reference to the drawings. Note that, as a
general rule, the same reference number is given to the same
constituent elements and the explanation thereof is omitted.
(System Configuration)
[0044] Foremost, the configuration of an acoustic wave measuring
apparatus to which the present invention can be applied is
explained taking a photoacoustic measuring apparatus as an example
with reference to FIG. 1, which is a system configuration diagram.
The photoacoustic measuring apparatus according to an embodiment of
the present invention is a photoacoustic imaging apparatus for
acquiring information (in particular imaging) inside the object.
The photoacoustic measuring apparatus enables the imaging of
information of a biological object as the object for the diagnosis
of malignant tumors and vascular diseases or the follow-up of
chemical treatment. Information of a biological object refers to
the generation source distribution of the acoustic waves that were
generated based on the irradiation of light, and shows the initial
sound pressure distribution in the biological object or the light
energy absorption density distribution derived therefrom.
[0045] The photoacoustic measuring apparatus according to an
embodiment of the present invention is configured, in a broad
sense, from a measuring apparatus 100 and an operating apparatus
200. The measuring apparatus 100 is an apparatus for performing
measurement using photoacoustic waves, and the operating apparatus
200 is an apparatus for operating the measuring apparatus 100. The
measuring apparatus 100 includes a laser light source 101, an
optical system 102 and a light source drive unit 106, compression
plates 103a and 103b, an acoustic probe 104 and a probe drive unit
105, an apparatus control unit 107, a camera 108, and a signal
processing unit 109. Moreover, the operating apparatus 200 includes
a region designating unit 201, an image generating unit 202, an
image display unit 203, and a system control unit 204. The object
measuring method is now explained while explaining the
configuration of the respective components.
[0046] An object (not shown) such as a biological object is fixed
by compression plates 103a, 103b for compressing and fixing the
suspected site from either side thereof. Note that, when it is not
necessary to differentiate the compression plates 103a and 103b, a
collective designation of "compression plate 103" will be used. The
laser light source 101 is means for generating a laser beam to be
irradiated onto the object, and can be moved planarly in a
two-dimensional direction by the light source drive unit 106, which
is drive means. The laser beam generated by the laser light source
101 is guided to the surface of the compression plate 103a by the
optical system 102 such as a lens, a mirror, or an optical fibre,
becomes dispersed pulsed light, and irradiated on the object.
[0047] When a part of the energy of light that propagated inside
the object is absorbed by a light absorber such as blood vessels,
acoustic waves are generated based on thermal expansion from that
light absorber. Acoustic waves are typically ultrasound waves, and
include those which are referred to as sound waves, ultrasound
waves, acoustic waves, photoacoustic waves, and light-induced
ultrasound waves. In other words, the temperature of the light
absorber increases pursuant to the absorption of the pulsed light,
volume expansion occurs due to such temperature rise, whereby
acoustic waves are generated.
[0048] This phenomenon is generally referred to as the
photoacoustic effect, and it is possible to acquire the generation
source distribution of acoustic waves that were generated based on
the irradiation of light, initial sound pressure distribution in
the object, or light energy absorption density distribution or
absorption coefficient distribution derived from the initial sound
pressure distribution, and concentration distribution of the
substance configuring the tissues. The concentration distribution
of a substance is, for example, oxygen saturation distribution and
oxygenated and deoxygenated hemoglobin concentration
distribution.
[0049] The acoustic probe 104 for detecting acoustic waves
corresponds to a detector configured from a plurality of receiving
elements which detect the acoustic waves that were generated in or
reflected from the object. A detector detects acoustic waves that
were generated in the object, and converts the acoustic waves into
an electric signal, which is an analog signal. The detection signal
acquired by the detector is referred to as a photoacoustic signal.
The acoustic probe 104 can also move planarly in a two-dimensional
direction by the probe drive unit 105, which is a drive
mechanism.
[0050] Note that, while an embodiment of the present invention
acquires information of an object by using photoacoustic waves, it
is also possible to acquire object information by internally
providing an ultrasound source in the acoustic probe 104 for
transmitting ultrasound waves to the object, and receiving the
ultrasound waves that were reflected inside the object. In the
foregoing case, the acquired object information refers to
information which reflects the difference in the acoustic
impedances of the tissues inside the object.
[0051] The signal processing unit 109 is means for acquiring
internal information of the object from the photoacoustic signal.
The photoacoustic signal acquired from the acoustic probe 104 is
amplified by a reception amplifier, and converted into a digital
signal by an A/D converter. The digital signal is communicated to
the operating apparatus 200 via a communication line, operated into
three-dimensional information based on image reconfiguration
processing, and thereafter displayed as image information on the
image display unit 203.
[0052] With an embodiment of the present invention, in addition to
the above, provided are region of interest designating means (not
shown) for the user to designate the region of interest, a camera
108 for providing an observed image of the object to be referred to
upon designating the region of interest for the object, and an
apparatus control unit 107 for controlling the operation of the
measuring apparatus 100. The laser light source 101, the optical
system 102, the compression plate 103, the acoustic probe 104, the
camera 108, and the region designating unit 201 are now explained
in further detail.
<Laser Light Source 101>
[0053] When the object is a biological object, irradiated from the
light source is light of a specific wavelength that is absorbed by
a specific component among the components configuring the
biological object. As the light source, preferably used is a pulsed
light source capable of generating pulsed light of several
nanoseconds to several hundred nanoseconds, and at least one pulse
sound source capable of generating pulsed light of 5 nanoseconds to
50 nanoseconds is provided. While laser is preferable as the light
source, a light-emitting diode or the like may also be used in
substitute for a laser. As the laser, solid-state laser, gas laser,
dye laser, semiconductor laser and other lasers may be used.
[0054] Moreover, light may also be irradiated from the acoustic
probe side, or irradiated from the side that is opposite to the
acoustic probe. In addition, light may also be irradiated from
either side of the object. Moreover, in this embodiment, while a
single light source is shown as an example, a plurality of light
sources may also be used. In the case of using a plurality of light
sources, a plurality of light sources that oscillate the same
wavelength may be used in order to increase the irradiation
intensity of the light to be irradiated on the biological object,
or a plurality of light sources having a different oscillation
wavelength may be used in order to measure the difference in the
wavelength of optical characteristic value distribution. Note that,
as the light source, if it is possible to use dyes or OPO (Optical
Parametric Oscillators) capable of converting the oscillation
wavelength, it is also possible to measure the difference in the
wavelength of optical characteristic value distribution.
[0055] Light shows electromagnetic waves including visible light
and infrared light, and specifically light of a region between 500
nm and 1300 nm, preferably light of a region of 700 nm to 1100 nm
with low absorption in the biological object, is used. However,
when obtaining the optical characteristic value distribution of the
biological object tissue which is relatively near the biological
object surface, a wavelength region that is broader than the
foregoing wavelength region; for instance, a wavelength region of
400 nm to 1600 nm may also be used. Of the light within the
foregoing range, a specific wavelength may be selected based on the
components to be measured.
[0056] Moreover, with a laser light source, the irradiation
frequency is usually determined in advance. The irradiation
frequency is preferably high as possible since the irradiation
frequency affects the number of photoacoustic measurements that can
be performed per unit time. In this embodiment, the irradiation
frequency of the laser light source is 10 Hz.
<Optical System 102>
[0057] The optical system 102 is, for example, a mirror which
reflects light, a lens which focuses, expands or changes the shape
of light, a prism which disperses, refracts and reflects light, an
optical fibre which propagates light, a diffuser panel, or the
like. Light that is irradiated from the light source can be guided
to an object by using an optical member such as a lens or a mirror,
or propagated by using an optical member such as an optical fibre.
The foregoing optical members may be of any type so as long as the
light emitted from the light source can be irradiated, in the
intended shape, onto the object.
[0058] Note that, generally speaking, rather than focusing the
light with a lens, it is more preferable to broaden the area to a
certain extent from the perspective that the diagnosis region can
be expanded. Moreover, the region where light is irradiated onto
the object (hereinafter referred to as the "irradiation region") is
preferably movable. By causing the irradiation region to be
movable, light can be irradiated to a broader range. Moreover,
preferably, the irradiation region can be moved in synch with the
acoustic probe 104. As the method of moving the irradiation region,
a method of using a movable mirror or a method of mechanically
moving the light source itself may be adopted.
<Compression Plate 103>
[0059] The compression plate 103 retains at least a part of the
shape of the object to be constant, and is provided between the
object and the acoustic probe 104. When the object is sandwiched
from either side using the compression plates, the position during
measurement is fixed, and it is thereby possible to reduce the
positional errors caused by body motion or the like. Moreover, by
compressing the object, light can efficiently reach the deep part
of the object. As the holding member, preferably used is a member
having high optical transmittance and high acoustic compatibility
with the object and the acoustic probe. In order to improve the
acoustic compatibility, an acoustic matching member such as a gel
may be interposed between the compression plate and the object, and
between the compression plate and the acoustic probe.
<Acoustic Probe 104>
[0060] The acoustic probe 104 is a device which detects acoustic
waves and converts the detected acoustic waves into an electric
signal. The photoacoustic waves generated from a biological object
are ultrasound waves of 100 kHz to 100 MHz. Thus, as the acoustic
probe 104, an ultrasound detector capable of receiving the
foregoing frequency band is used. Note that any detector may be
used so as long as it is able to detect the acoustic wave signal
and convert the acoustic wave signal into an electric signal; for
instance, a transducer that uses the piezoelectric phenomenon, a
transducer that uses the oscillation of light, or a transducer that
uses the change in capacity. Note that a detector is preferably
configured by a plurality of receiving elements being arrayed
two-dimensionally.
[0061] As a result of using such two-dimensional arrayed elements,
acoustic waves can be simultaneously detected at a plurality of
locations, and it is possible to shorten the detection time as well
as reduce the influence of vibration of the object and so on. In an
embodiment of the present invention, let it be assumed that the
receiving element pitch is a 2 mm interval, the receiving element
array is five elements in the main scanning direction (direction in
which the acoustic probe moves while performing the scan), and five
elements in the sub scanning direction (direction that is
orthogonal to the main scanning direction).
<Camera 108>
[0062] The photoacoustic measuring apparatus according to an
embodiment of the present invention includes a camera 108 for
providing images to be referred to by the user upon designing the
regions of interest to be subject to photoacoustic measurement. The
camera 108 is installed in a direction that is orthogonal to the
holding plates that compress and hold the object, and the captured
image is transmitted to the operating apparatus 200, and displayed
as the observed image. The visual field of the camera is preferably
installed at a view angle in which the photoacoustic measurable
range can be viewed. The camera is installed so that the compressed
and held object can be observed, and the user can designate the
region of interest while observing the compressed and held
object.
<Region Designating Unit 201>
[0063] The photoacoustic apparatus according to an embodiment of
the present invention includes a region designating unit 201 as
means for the user to designate the region of interest to be
imaged. The user designates the region for imaging the region of
interest by using input means such as a mouse while referring to
the observed image of the compressed and held object that is
displayed on the display device. The input means is not limited to
a mouse or a keyboard, and may also be a tablet type or a touch pad
mounted on the display device surface. In this embodiment, a
plurality of regions of interest can be designated.
[0064] In an embodiment of the present invention, in order to
associate the observed image and the scanning surface of the
acoustic probe, the camera 108 is installed so as to capture the
observed image of a surface that is parallel to the plane to be
scanned by the acoustic probe relative to the object. The user can
designate the region to be scanned with the probe by setting a
two-dimensional rectangle (measurement designated region) at a
location corresponding to the position to be measured while
referring to the observed image captured by the camera. Note that
the measurement designated region may also be a shape other than a
rectangle.
[0065] As the method of designating the measurement region,
coordinates may also be designated based on input using a keyboard.
The coordinate designating method in the foregoing case may be the
designation of central coordinates of the measurement region of a
predetermined size in order to specify the measurement region, or a
plurality of vertex coordinates may be designated on the reference
image plane so as to set the measurement designated region. In all
of the foregoing cases, it is possible to set a measurement
designated region as the two-dimensional rectangular region on the
reference image plane.
[0066] The photoacoustic measuring apparatus according to an
embodiment of the present invention converts the image coordinate
system of the camera into an apparatus coordinate system based on
the designated measurement designated region, and performs control
so as to move the probe to a corresponding position of the actual
object.
[0067] The screen image for designating the region in this
embodiment is shown in FIG. 2. In the diagram, 301 represents an
observed image from a specific direction relative to the object,
and 302 represents a measurement designated region that was
designated by the user while referring to the observed image. With
respect to the measurement designated region 302, it is possible to
designate a region of an arbitrary size through operations such as
disposing a rectangle of a pre-set size, or inputting a rectangle
using a pointing device.
[0068] Moreover, a function for designating a plurality of
measurement designated regions is also provided. For example, this
is a method where a multiple selection button is provided and, when
the measurement designated region is designated while pressing the
multiple selection button, a plurality of measurement designated
regions which were selected while the multiple selection button is
being pressed are stored. As another method, by providing a "Select
next region" menu on the menu screen and designating this menu each
time a measurement designated region is designated, the region of
interest can be designated successively. In all of the foregoing
methods, it is preferable to prepare means for cancelling a part or
all of the designations of the measurement designated region.
[0069] Moreover, in an embodiment of the present invention, after
setting a plurality of measurement designated regions, it is
possible to newly select the respective measurement designated
regions using a pointing device and individually designate the
scanning priority. In the foregoing case, the same scanning
priority may be designated in a plurality of regions, or higher
scanning priority may be set in the order that the measurement
designated region was set.
[0070] The foregoing processes are executed by the region
designating unit 201 and the system control unit 204, and
correspond to the region-of-interest setting unit and the priority
setting unit in the acoustic wave measuring apparatus to which the
present invention can be applied.
First Embodiment
[0071] The operation of the photoacoustic measuring apparatus
according to the first embodiment is now explained in detail with
reference to the drawings.
<Designation of Region of Interest>
[0072] A plurality of measurement designated regions, so called
regions of interest, are designated by a user via the region
designating unit 201. A specific example of the designation of the
measurement designated region by the user is shown in FIG. 4. In
the diagram, 406 represents a region corresponding to the observed
image, and is a planar range in which the acoustic probe can
perform scanning. 401 to 405 are measurement designated regions
that were designated by the user. 401 to 403 are regions which are
set with a high priority (let this be priority 1), and 404, 405 are
regions which are set with a low priority (let this be priority 2).
As shown in the diagram, regardless of the setting of priority, it
is also possible to designate the measurement designated regions in
a mutually overlapping state. The designated regions of interest
are stored in the system control unit 204.
[0073] Moreover, in the foregoing case, the measuring conditions of
the photoacoustic measurement can also be set. In this embodiment,
it is also possible to set the number of acquisitions (cumulative
number) of the photoacoustic data in the same coordinate position
upon measuring the measurement region. Here, let it be assumed that
the cumulative number is set to 10 times.
[0074] When the user gives instructions for starting measurement, a
measurement request message is sent from the system control unit
204 to the apparatus control unit 107. The processing contents of
the measuring apparatus 100 in this embodiment are now explained
with reference to FIG. 3, which is a processing flowchart of the
controller unit 107.
<Calculation of Scanning Speed for Measurement>
[0075] When the apparatus control unit 107 receives a measurement
request message, the apparatus control unit 107 foremost calculates
the scanning speed for measurement and the number of scans required
for obtaining the cumulative number desired by the user (S1). Let
it be assumed that the number of elements of the acoustic probe in
the main scanning direction is Enx elements, the element pitch is
Ep (mm), the cumulative number of photoacoustic measurement is Mn,
and the light-emitting frequency of the laser light source is LHz
(Hz). In order to simplify the explanation, when the cumulative
number Mn is a multiple of the number of elements Enx, the scanning
speed Vx (mm/sec) of the acoustic probe and the laser light source
in the main scanning direction and the number of scans Sn are
calculated based on Formula (1) and Formula (2), respectively. The
processing of step S1 corresponds to the moving speed acquiring
unit in the acoustic wave measuring apparatus to which the present
invention can be applied.
Vx=Ep.times.LHz (1)
Sn=Mn/Enx (2)
[0076] In the case of this embodiment, since the number of elements
of the acoustic probe 104 in the scanning direction is five
elements, estimation can be performed 5 times when the acoustic
probe 104 is to be moved on the object surface, and 10 estimations
can be performed if the acoustic probe makes one full round.
Moreover, since the element pitch is 2 mm and the light-emitting
frequency of the laser light source is 10 Hz, the scanning speed
upon measurement will be 20 mm/sec.
[0077] The foregoing calculation example of the scanning speed is
an example of a case using photoacoustic measurement. Upon applying
an acoustic wave measuring apparatus of a type which transmits
ultrasound waves to an object and receives reflected waves thereof,
the moving speed upon measurement can be similarly calculated based
on the drive frequency of the acoustic probe and the element pitch
of the acoustic probe in the main scanning direction.
[0078] The scanning speed and number of scans for measurement
obtained as described above are used for calculating the scanning
region or determining the measurement order explained later.
<Calculation of Scanning Region>
[0079] Subsequently, the apparatus control unit 107 calculates the
scanning region as the region in which the acoustic probe actually
performs scanning. Calculation of the scanning region is performed
in the scanning priority order from the measurement designated
region having a high scanning priority. Foremost, among the
plurality of measurement designated regions that were designated,
the inclusion region which includes all measurement designated
regions of the scanning priority to be focused is calculated (S2).
In other words, a region which includes all of the measurement
designated regions and which is the smallest rectangular region is
obtained as the inclusion region. The scanning priority is
hereafter simply referred to as the "priority".
[0080] FIG. 5 shows an image of the inclusion region of priority 1.
Regions 401, 402, 403 shown in FIG. 5 are the measurement
designated regions of priority 1, and a rectangle 504 is the
inclusion region that was calculated from the measurement
designated regions.
[0081] Subsequently, a scanning strip is assigned to the inside of
the inclusion region of priority 1 (S3). A scanning stripe refers
to a rectangular region capable of moving the acoustic probe and
the light source (hereinafter collectively referred to as the
"measurement system") in the main scanning direction. In this
embodiment, the width of the scanning stripe in the main scanning
direction in the scanning plane of the acoustic probe becomes the
length of scanning and measurement that were performed by the
acoustic probe, and the width in the sub scanning direction becomes
the length of all element regions of the acoustic probe in the sub
scanning direction. The scanning stripe is hereinafter simply
referred to as the "stripe".
[0082] In reality, while the region subject to photoacoustic
measurement is a three-dimensional region including the depth
direction, unless separately provided for herein, the
two-dimensional projection plane on the scanning surface of the
measurement system is indicated as a "stripe".
[0083] FIG. 6 shows an example of assigning the stripe. Stripes
601a, 601b are respectively stripes that were assigned to the
inclusion region 504 set with priority 1. In this embodiment, while
the stripes are assigned to the inclusion region 504 in order from
the top in a manner of lining the stripes, any method may be used
for assigning the stripes so as long as all measurement designated
regions can be included in the stripe.
[0084] Subsequently, the stripe to be processed (hereinafter
referred to as the "notable stripe") is divided into an actual
scanning region and a non-scanning region (S4). An actual scanning
region is a region where the acoustic probe actually performs
scanning for measuring the measurement designated region, and a
non-scanning region refers to the other regions. The actual
scanning region is a region that includes the measurement
designated region among the regions included in the stripe.
[0085] FIG. 7 shows an example where the notable stripe has been
divided. 701 is a notable stripe, and 702, 703, 704 are regions
that overlap with the notable stripe 701 among the measurement
designated regions 401, 402, 403 having priority 1. 705 and 706
including the foregoing regions are the actual scanning regions,
and the intermediate region is the non-scanning region.
[0086] Subsequently, the scanning region of the notable stripe is
determined (S5). The scanning region determination is the
processing of determining whether the divided regions in the stripe
are classified as any one of the following three types.
[0087] (1) Region (continuous scanning region) subject to
photoacoustic measurement as a result of continuously moving
(continuously scanning) the measurement system in the main scanning
direction while acquiring the acoustic waves.
[0088] (2) Region (moving region) in which the measurement system
moves but photoacoustic measurement is not performed.
[0089] (3) Region (fixed measuring region) that is measured (fixed
measuring) by stopping the measurement system.
[0090] In step S5, whether the foregoing actual scanning region is
to be measured via continuous scanning or measured via repeated
fixed measuring is determined. Moreover, with respect to the
non-scanning region, whether to move the acoustic probe without
performing measurement or perform continuous scanning is
determined. Specifically, the scanning method of the respective
regions or the moving method is determined so that the time
required for the measurement of the notable stripe and movement
processing becomes the shortest.
[0091] The processing time upon setting a region as the continuous
scanning region can be calculated by dividing the scanning distance
by the continuous scanning speed Vx. Moreover, the processing time
upon setting a region as the fixed measuring region can be
calculated by dividing the laser irradiation frequency by the
cumulative number. Moreover, the processing time of the moving
region can be calculated by dividing the movement distance by the
simple moving speed of the drive apparatus. The processing of step
S2 corresponds to the region calculating unit in the acoustic wave
measuring apparatus to which the present invention can be applied,
and the processing of steps S3 to S5 corresponds to the scanning
method determining unit.
[0092] A specific calculation example of the scanning region
determination is now explained with reference to FIG. 7. 707 is the
initial position of the acoustic probe.
[0093] With this calculation example, let it be assumed that the
element pitch of the acoustic probe is 2 mm, the element region of
the acoustic probe is a 10 mm square, the scanning speed during
measurement is 20 mm/sec, the simple moving speed is 50 mm/sec, the
light-emitting frequency of the light source is 10 Hz, and the
cumulative number is 5 times. Let it be further assumed that the
length of the notable stripe 701 in the main scanning direction is
50 mm, the actual scanning region 705 is 20 mm, and the actual
scanning region 706 is 10 mm.
[0094] Note that, when performing continuous scanning, since
measurement is performed while moving the acoustic probe, there are
cases where the movement distance of the acoustic probe becomes
slightly longer than the length of the actual scanning region
(refer to FIG. 9). In this embodiment, the scanning distance is
calculated by adding a distance (10 mm) for the amount of the
element region of the acoustic probe.
[0095] Foremost, considered is a case where, after measuring the
actual scanning region 705, the acoustic probe is moved short of
the actual scanning region 706 by passing through the non-scanning
region.
[0096] When the actual scanning region 705 is subject to continuous
scanning, the distance required for scanning 705 will be 30 mm, and
the simple movement distance of the non-scanning region will be 10
mm. Thus, the scanning time will be 30/20=1.5 sec, the moving time
will be 10/50=0.2 sec, and the required time can be calculated as
1.7 sec.
[0097] Meanwhile, when the actual scanning region 705 is subject to
fixed measuring, the simple movement of 10 mm will be performed a
total of 4 times, and the measurement requiring 0.5 sec will be
performed twice. Thus, the measurement time will be 0.5.times.2=1
sec, the moving time will be 40/50=0.8 sec, and the required time
can be calculated as 1.8 sec. Thus, it can be seen that the
measurement of the actual scanning region 705 can be performed
quicker via continuous scanning.
[0098] Next, considered is a case where, after measuring the actual
scanning region 706, the acoustic probe is moved outside the
notable stripe.
[0099] When the actual scanning region 706 is subject to continuous
scanning, the distance required for scanning 706 will be 20 mm, and
the required time can be calculated as 1 sec. Meanwhile, when the
actual scanning region 706 is subject to fixed measuring, the
simple movement of 10 mm will be performed a total of twice, and
the measurement requiring 0.5 sec will be performed once. Thus, the
measurement time will be 0.5 sec, the moving time will be 20/50=0.4
sec, and the required time can be calculated as 0.9 sec. Thus, it
can be seen that the measurement of the actual scanning region 706
can be performed quicker via fixed measuring.
[0100] In other words, it can be seen that the scanning can be
performed quickest when the actual scanning region 705 is set as a
continuous scanning region and the actual scanning region 706 is
set as a fixed measuring region. The remaining portion will be the
moving region. Note that the foregoing explanation is of a case
where scanning is performed once, but the time required for
measurement can be obtained with the same logic even in cases where
the number of scans is a plurality of times; for instance,
performing scanning twice in a full round.
[0101] The foregoing process of calculating the scanning region
(steps S4 and S5) is repeated for all stripes, and the scanning
region calculation of the overall inclusion region is
performed.
[0102] Moreover, the processing of foregoing steps S2 to S5 is
further performed in priority order, and the same scanning region
is calculated for each set priority.
[0103] <Determination of Scanning Track>
[0104] Subsequently, the apparatus control unit 107 determines the
scanning order among the actual scanning regions regarding the
respective scanning regions that were calculated for each priority
(S6). The determination criteria is to determine an order which
will shorten the total measurement time of the measurement regions
of all priorities, and shorten the displacement of the measurement
system. The processing of step S6 corresponds to the scanning path
identifying unit in the acoustic wave measuring apparatus to which
the present invention can be applied.
[0105] The processing of step S6 is explained in further detail in
the flowchart of FIG. 8. When step S6 is started, processing of the
stripe with the highest priority is started. Foremost, the actual
scanning region to be scanned is determined (S11). In the initial
processing, the actual scanning region to be scanned is the actual
scanning region that is closest to the acoustic probe.
[0106] Subsequently, information of the actual scanning region is
added to the measuring track list (S12). The measuring track list
records, at least, the measurement start coordinates, measurement
method (continuous scanning measuring or fixed measuring), and
information regarding the scanning distance. Note that, when there
are a plurality of actual scanning regions in the same stripe, all
actual scanning regions are added to the measuring track list.
[0107] When there are unprocessed regions of the same priority, the
same processing is performed with the actual scanning region of the
closest distance to the measurement end coordinates of the added
actual scanning region as the subsequent destination.
[0108] When the processing of all stripes of the same priority is
complete, the same processing is performed regarding one lower
priority. As a result of performing the foregoing processing,
information of the actual scanning region to be scanned will be
listed in the scanning execution order, and stored for each
priority.
[0109] The apparatus control unit 107 refers to the measuring track
list that was stored according to the foregoing procedure, and
executes measurement while moving between the actual scanning
regions (S7). The processing of step S7 corresponds to the scanning
unit in the acoustic wave measuring apparatus to which the present
invention can be applied.
[0110] The photoacoustic measuring apparatus according to this
embodiment calculates the region to be scanned by the measurement
system in the priority order based on the measurement designated
region and priority designated by the user, and determines the
track on which the measurement system is to move upon performing
the photoacoustic measurement. Consequently, the user is no longer
required to set the scanning track, and can concentrate on the
designation of the region of interest.
[0111] Moreover, the photoacoustic measuring apparatus according to
this embodiment comprises moving speed acquiring unit for
calculating the continuous scanning speed, region calculating unit
for determining the time required for the measurement and
determining the scanning region, and scanning path identifying unit
which uses the movement distance other than measurement as the
measuring condition. Consequently, in comparison to a case of
performing simple scanning scheduling such as subjecting all
regions to continuous scanning, it is possible to efficiently
calculate the scannable track, and thereby shorten the measurement
time.
[0112] Note that the moving speed acquiring unit (step S1) may be
omitted if the moving speed and cumulative number are defined there
is no need to calculate the same. Moreover, a part of the scanning
method determining unit (steps S4 and S5) may also be omitted if
there is no need to perform scanning region determination in the
same priority. Even with the foregoing configurations, it is
possible to scan the plurality of regions of interest in the
priority order designated by the user, and additionally yield an
effect of being able to shorten the measurement time.
[0113] Note that the receiving elements of the acoustic probe are
not limited to the grid pattern of this embodiment, and may also be
a honeycomb shape, a hound's-tooth shape, or other arrangement. The
determination of the moving speed of the probe is not limited to
the method illustrated in this embodiment, and various algorithms
may be applied for adjusting the scanning speed in dependence of
the measuring conditions or apparatus configuration. Moreover, the
scanning speed calculation function in this embodiment aims to
obtain the probe moving speed for measurement and, therefore, the
reference parameters and algorithms are not limited to those
described in this embodiment.
Second Embodiment
[0114] The second embodiment is the mode of detecting a portion
which overlaps with the regions of different priorities and
optimizing the shape of the regions in step (S4) of dividing the
scanning region shown in the first embodiment. The processing other
than step S4 and the system configuration are the same as the first
embodiment.
[0115] FIG. 9 is a diagram showing the state of data accumulation
of the region that was captured while moving the acoustic probe. In
the diagram, the observer's right-side direction is the main
scanning direction. The checkered rectangle represents the location
where the receiving elements of the acoustic probe existed upon
performing photoacoustic measurement while shifting the acoustic
probe in the main scanning direction one element at a time. In
order to perform photoacoustic measurement while shifting the
acoustic probe in the main scanning direction one element at a
time, the scanning region will be, as shown in the diagram, filled
by grids of the element size of the acoustic probe without any
space therebetween. Note that, in this embodiment, let it be
assumed that the cumulative number has been set to 5 times.
[0116] The numbers in the grid show number of times that
photoacoustic measurement was performed; that is, the cumulative
number of photoacoustic measurement, at that location. A region 801
is the actual scanning region, and a region where estimation is
performed 5 times. Since scanning and estimation are performed
while shifting the acoustic probe in the main scanning direction
one element at a time, this means that there will constantly be
four elements' worth of excess data before and after the actual
scanning region to be measured.
[0117] FIG. 10 shows an example of a case where a region of high
priority (first priority) and a region of low priority (second
priority) overlap with each other. As shown in FIG. 10A, let it be
assumed that an unmeasured region 901 of low priority is set so as
to overlap with the measured region 801 of high priority. In the
foregoing case, as described above, there will be data in which the
cumulative number is less than 5 obtained during the measurement of
the region 801.
[0118] In other words, when actual scanning regions of different
priorities overlap respectively, the actual scanning region can be
reduced by reusing the data obtained upon scanning the region of
high priority for the region of low priority. Specifically, in
addition to the regions in which estimation has been performed 5
times, the region may be further reduced in an amount of four
elements so as to achieve a region 902 shown in FIG. 10B. When
continuous scanning is performed to the region 902, since four
elements' worth of data on the right side can be similarly
acquired, it is possible to obtain a cumulative number of 5 times
for all regions. In other words, it is possible to shorten the
measurement time since there is no need to move the distance of the
reduced amount of eight elements.
[0119] In order to realize the foregoing function, in this
embodiment, the photoacoustic wave measuring apparatus according to
the first embodiment is additionally equipped with a storage region
in which the actual scanning region is further divided based on the
element pitch of the acoustic probe, and the cumulative number of
each of the divided regions is mapped.
[0120] In addition, upon performing the processing of step S4, the
scheduled cumulative number associated with the measurement is
mapped to each of the divided regions. Upon performing the
scheduling of low priority, the portion in which the predetermined
number of estimations is complete regarding the determination of
the measurement region is excluded from the actual scanning region.
Moreover, even when it is less than the predetermined number of
times, any region that is overlapping with the previously measured
region is determined to be a portion capable of reusing the
measured data, and also excluded from the actual scanning region.
In other words, the actual scanning region is reduced so as to
include only the unmeasured regions.
[0121] In normal measurement processing, any region that does not
satisfy the cumulative number set in the measuring conditions such
as the region outside the region 801; that is, excess data, is
erased. Nevertheless, in this embodiment, since all cumulative data
is stored for each coordinate until all measurement is complete, it
is possible to divert the data upon measuring the actual scanning
region of low priority, and thereby improve the measuring
efficiency.
[0122] Note that, in this embodiment, while a region that has been
estimated even once was excluded from the actual scanning region,
the determination of exclusion is not limited to the case that was
illustrated in this embodiment. For example, the reference
cumulative number or the like may also be changed according to the
cumulative number of data, probe shape, sensitivity distribution,
or the like.
[0123] Moreover, while this embodiment determined the overlap of
regions in step S4 of dividing the scanning region, this may also
be performed in other steps so as long as the processing can
exclude the overlap of regions of different priorities. For
example, it is also possible to determine the overlap of regions in
step S2 of determining the inclusion region per priority.
Third Embodiment
[0124] The third embodiment is a mode of changing the assignment
method in step (S3) of assigning the stripes to the inclusion
region. Upon assigning the stripes to the inclusion region, the
stripe arrangement position is adjusted so that measurement of
regions of all priorities is completed with the shortest possible
scanning distance. Note that the processing other than step S3 and
the system configuration are the same as the second embodiment.
[0125] With the photoacoustic measuring apparatus according to the
first and second embodiments, since the photoacoustic measurement
is performed in stripe units, excess regions will be measured when
they are smaller than the height of the actual scanning regions in
which the measurement designated regions designated by the user. If
it is possible to measure the measurement designated region, the
excess regions may be located anywhere, and the stripes may be
moved in the sub scanning direction in the amount of the width of
the excess region.
[0126] FIG. 11 is an explanatory diagram of a case where an excess
data measurement region occurs. In FIG. 11A, regions 1001 and 1002
are the actual scanning regions designated as being high priority
(priority 1), a region 1003 is the actual scanning region
designated as being low priority (priority 2). The stripes 1004 and
1005 are stripes that were assigned for measuring the actual
scanning regions designated as being priority 1. In the first and
second embodiments, the stripe arrangement will be of the
illustrated shape since the stripes are assigned, in order from the
top, to the inclusion region of each priority.
[0127] When the region 1003 of low priority is to be measured after
measuring the regions 1001, 1002, the unmeasured region will be
shown as an angular C-shape as shown in FIG. 11B. In other words,
in order to measure the entire region 1003 of low priority, it is
necessary to newly measure regions 1007 to 1009. Assuming that the
horizontal width of the regions 1007, 1009 is 25 mm and the
horizontal width of the region 1008 is 10 mm, the distance that
needs to be newly measured will be 25+10+25=60 mm.
[0128] Meanwhile, upon measuring the regions 1001, 1002, it is
possible to arrange the stripes in displacement as shown in FIG.
11C. In the foregoing case, the unmeasured region of the region
1003 will be displayed as an L-shape as shown in FIG. 11D. In other
words, in order to measure the entire region 1003, it is necessary
to newly measure regions 1010 to 1012. Based on the same
calculation as the case of FIG. 11B, the distance that needs to be
newly measured will be 10+10+25=45 mm and, therefore, in comparison
to the case of making no adjustment, the scanning distance upon
measuring the regions of low priority can be shortened by 15 mm.
Note that, upon performing continuous scanning, while the length of
the region to be measured and the scanning distance of the acoustic
probe will slightly differ, these are considered to be the same in
the present invention.
[0129] Step S3 in this embodiment disposes stripes in the inclusion
region of a predetermined priority, and thereafter determines
whether there is a region which overlaps with a region of one lower
priority. Here, if there is an overlapping region, the arranged
stripes are shifted in the sub scanning direction, and a position
which will shorten the scanning distance upon measuring the regions
of low priority is detected.
[0130] An example of shifting the stripes is now explained. In this
explanation, the main scanning direction is the x axis and the sub
scanning direction is the y axis.
[0131] In FIG. 11A, d1 is the distance of the excess portion of the
measurement region of the region 1001 of priority 1 in the sub
scanning direction. Since the region 1001 requires a height that is
worth two stripes for the scanning, when the number of elements of
the probe in the sub scanning direction is Eny and the element
pitch is Ep, the required height of the scanning stripe can be
calculated as 2.times.Eny.times.Ep.
[0132] Here, when the y coordinates of the uppermost part of the
region of priority 1 is Uy1, and the y coordinates of the lowermost
part of the region of priority 1 is Ly1, the excess range d1 of the
region 1001 in the sub scanning direction will be
(2.times.Eny.times.Ep-Uy1-Ly1). Note that, in the case of FIG. 11,
Uy1 will be the y coordinates of the uppermost part of the region
1001, and Ly1 will be they coordinates of the lowermost part of the
region 1001.
[0133] In FIG. 11A, d2 is the difference between the uppermost part
of the region of priority 2 and the uppermost part of the region of
priority 1. Here, when the y coordinates of the uppermost part of
the region of priority 2 is Uy2, d2 can be represented as Uy2-Uy1.
Thus, if d1>0 and d2>0, there will be a margin for adjusting
the stripe position at the upper part in the sub scanning
direction.
[0134] Subsequently, whether d1 and d2 correspond to any one of the
following three conditions is determined.
<Condition 1>
[0135] When d2 is a distance that is not smaller than the integral
multiple (N times) of Eny.times.Ep; that is, when
d2.gtoreq.N.times.Eny.times.Ep is satisfied, N-number of stripes
are disposed at the upper part of the measurement region of the
region 1003 of priority 2. Here, when
(d2-N.times.Eny.times.Ep).ltoreq.d1, the stripes for measuring the
regions of priority 1 are shifted upward by
(d2-N.times.Eny.times.Ep).
<Condition 2>
[0136] When d1.gtoreq.d2, the stripes for measuring the regions of
priority 1 are shifted to a position shifted upward by d2; that is,
shifted to the upper end of the region 1003 of priority 2.
<Condition 3>
[0137] When d2<Eny.times.Ep, the upper limit position of the
stripes for measuring the regions of priority 1 is shifted to the
same position as the upper limit position of the regions of
priority 1. The upper end of the stripes for measuring the regions
of priority 2 is started from the same position as the upper limit
of the regions of priority 2, and the measurement region thereof
will overlap with the regions of priority 1.
[0138] Based on the foregoing method, candidates of the
displacement position of the stripes for measuring the regions of
priority 1 are determined. When the candidates of the displacement
position are determined, the scanning distance upon measuring the
regions of low priority is calculated, and, upon determining
whether the scanning distance becomes shorter before and after
shifting the stripes, the ultimate stripe position is
determined.
[0139] Note that, when the scanning distance for measuring the
regions of low priority will be the same regardless of how the
stripes are shifted, the stripe position will remain unchanged.
[0140] As a result of performing the foregoing processing in
addition to the processing of step S3 in the second embodiment, it
is possible to reduce the scanning distance to the regions of low
priority, and reduce the time required for performing
measurement.
[0141] Note that, while this embodiment described an example of
processing the actual scanning region of the highest priority, this
embodiment may be applied to any priority so as long as there is
one lower priority. Moreover, in this embodiment, when the
overlapping with regions of one lower priority is determined and
the stripe position is adjusted, but there are still three or more
priorities, it is also possible to further determine the
overlapping with regions of even lower priority.
[0142] Moreover, the method of shifting the stripe is not limited
to the example illustrated in this embodiment. For example, there
are cases where the measurement accuracy is improved and the
scanning time is shortened based on scheduling in which the stripes
are overlapped in the sub scanning direction according to the data
accumulation, shape of probe, sensitivity distribution, and the
like. Moreover, while this embodiment adopted a mode of moving the
arrangement position after assigning the stripes, it is also
possible to calculate the optimal position before assigning the
stripes so as to directly assign the stripes.
[0143] Moreover, it is also possible to define the amount of
displacement of the stripes in advance, and perform calculations of
all patterns. For example, when the stripe adjustment margin is 5
mm, it is possible to perform 5 calculations by shifting the
stripes 1 mm at a time, and adopting the stripe in which the
scanning distance becomes shortest. Moreover, while this embodiment
adjusted the position of the stripes so as to shorten the scanning
distance upon measuring the regions of low priority, the scanning
time may also be used as the determination criteria in substitute
for the scanning distance.
[0144] The foregoing embodiments are merely an example, and the
present invention may be implemented by being changed as needed to
the extent that such change does not deviate from the gist of this
invention.
[0145] 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.
* * * * *