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JP2013154173

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2013154173
Abstract: PROBLEM TO BE SOLVED: To provide an apparatus and method capable of focusing on
multiple focal points while eliminating the grating lobe phenomenon when operating a high
intensity focused ultrasound (HIFU) apparatus. SOLUTION: The focus forming method for
ultrasonic treatment of the present invention comprises the steps of selecting at least one
candidate focal point position among focal point positions of a region to be irradiated with
therapeutic ultrasonic waves, the selected candidate focal point When the focal point of the
therapeutic ultrasonic wave is formed at the position of p, it is determined whether the negative
pressure increase phenomenon occurs at a position other than the selected candidate focal
position, and the phenomenon based on the determination result Determining a candidate focal
point position where does not occur as a set of focal point positions for irradiating the
therapeutic ultrasound. [Selected figure] Figure 10
Method and apparatus for forming multi-focus of ultrasonic transducer array
[0001]
The present invention relates to focusing of high intensity focused ultrasound (HIFU) devices,
and more particularly, to an apparatus and method of multi-focusing an ultrasound transducer
array.
[0002]
The present invention relates to a therapeutic apparatus using ultrasound, and more particularly,
to a therapeutic apparatus using High Intensity Focused Ultrasound (HIFU).
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[0003]
With the development of medicine, local treatment for tumors develops from Extended Radical
Surgery to Function Preserving Surgery, which in turn develops to Minimally Invasive Surgery. It
has been.
However, recently, with the revolutionary advances in technology, non-invasive surgery has been
developed and various surgical methods have emerged.
[0004]
Ultrasound is mechanical energy that has good straightness that can penetrate the body.
Such ultrasound can have a large effect and can bring about two effects through intratumoral
energy accumulation by irradiation of HIFU waves, and these two effects have a thermal effect
(hyperthermal effect) and a mechanical effect ( mechanical effect).
[0005]
The first effect, the thermal effect, is an effect that is generated by instantaneously raising the
temperature to 70 ° C. or higher while partially converting high-density ultrasonic waves into
partial heat energy, and Coagulate and kill blood vessels and blood vessels. At this time, since the
temperature rise occurs rapidly and instantaneously, heat does not diffuse to the surrounding
tissue.
[0006]
The mechanical effect of the second sound wave is a tissue destruction phenomenon due to
cavitation. When the human body is exposed to high-density ultrasound, the low pressure due to
the negative pressure of the acoustic wave causes the intracellular moisture to become a gas
phase while generating microbubbles, which causes the current state of resonance. If it becomes
large enough to cause a shock, it bursts and generates a high-pressure shock wave to destroy the
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organization.
[0007]
These two effects occur almost simultaneously, and the macroscopic change of the treatment site
by these causes clear distinction between the treatment site and the surrounding normal site,
while coagulation and nostalgia occur, 1 to 2 weeks after the ultrasonic irradiation. The border is
felt harder.
[0008]
However, when such tumors are treated, damage to normal tissue should be minimized as much
as possible.
Furthermore, for effective treatment of the tumor, the treatment time must be minimized.
Therefore, the conditions required for high intensity focused ultrasound (HIFU) devices must: 1)
minimize ultrasound treatment time and 2) create ultrasound focused area 3) ultrasound
amplification should not occur at points other than the focal region.
[0009]
The technical problem addressed by at least one embodiment of the present invention is to
provide an apparatus and a method capable of focusing on multiple focal points while
eliminating the phenomenon of grating lobes when operating the HIFU apparatus. It is to do.
Another object of the present invention is to provide a method of obtaining the output of a
transducer element for forming multi-focus while eliminating the grating lobe phenomenon.
Another object of the present invention is to provide a computer readable recording medium
having recorded thereon a program for causing a computer to execute the method. The technical
problems to be solved by the present embodiment are not limited to the technical problems as
described above, and other technical problems may exist.
[0010]
According to one aspect of the present invention, there is provided a focus forming method for
ultrasound treatment, which comprises selecting at least one candidate focus position among
focus positions of a region to be irradiated with therapeutic ultrasound, the selected candidate
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focus Determining whether the negative pressure increase phenomenon occurs at a position
other than the selected candidate focus position if the focus of the therapeutic ultrasonic wave is
formed at the position of And determining a treatment plan that indicates information about the
combination of candidate focal positions where the phenomenon does not occur.
[0011]
According to another aspect of the present invention, there is provided a computer readable
recording medium having recorded thereon a program for causing a computer to execute the
focus formation method for ultrasonic treatment.
[0012]
According to yet another aspect of the present invention, there is provided a focusing device for
ultrasound treatment comprising: When the focus of the therapeutic ultrasonic wave is formed at
the position of the selected candidate focus, it is determined whether or not a negative pressure
increase phenomenon occurs at a position other than the selected candidate focus position. And
an optimal focus determination unit that determines a treatment plan indicating information
related to a combination of the candidate focal positions where the phenomenon does not occur
based on the determination result.
[0013]
According to the present invention, during operation of the HIFU device, it is possible to
simultaneously form multiple foci to shorten the treatment time of the HIFU device while
eliminating the grating lobe phenomenon, and during the treatment, damage to the organ around
the lesion. Can be prevented.
Then, it is possible to calculate the output of the transducer element which simultaneously forms
a large number of focal points while eliminating the grating lobe phenomenon.
[0014]
It is a block diagram of the multi-focus formation apparatus by one embodiment of this invention.
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FIG. 6 illustrates the transducer array of the HIFU device and a plurality of focal regions present
in the treatment region.
FIG. 5 is a diagram illustrating a plurality of focal points present in a treatment area input from a
user according to an embodiment of the present invention. It is a figure which shows the optimal
focus set already determined by the optimal focus determination part. FIG. 3C is a view showing
the remaining focus excluding the focus belonging to the optimal focus set in the focus of FIG.
3A. FIG. 13 is a diagram in which candidate point determination units arrange candidate points in
a line in order to select or reselect a predetermined number of focal points among candidate
points. It is the figure which the case where a candidate focus determination part selected five at
random among candidate points was represented by the chromosome. It is a figure which shows
the method a candidate focus determination part produces | generates a new chromosome in the
combination of the existing chromosomes. FIG. 6 is a diagram showing a treatment area and a
non-treatment area. It is a figure which shows the structure of a focus formation confirmation
part. FIG. 5 is a diagram showing a position vector rn of a transducer element and a position
vector rm of an arbitrary focus on a three-dimensional orthogonal coordinate. It is a flowchart
which shows one embodiment of this invention.
[0015]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the attached drawings.
[0016]
FIG. 1 is a block diagram of a multi-focus forming apparatus according to an embodiment of the
present invention.
Referring to FIG. 1, the multi-focus forming apparatus according to the embodiment illustrated in
FIG. 1 includes an object point determining unit 101, a candidate focus determining unit 102, a
focus forming confirmation unit 103, an optimal focus determining unit 104, a memory 106, and
an interface. And 107, an irradiation determination unit 108 and an optimum focus storage unit
109.
[0017]
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When the user (for example, a doctor) inputs information on a plurality of focal points present in
the treatment area, the target point determination unit 101 determines the target point among
the focal points, and the candidate focal point determination unit 102 Output. Here, information
related to a plurality of focal points input by the user refers to a treatment area for the high
intensity focused ultrasound (HIFU) device to form an ultrasonic focus and treat a lesion. It
means information on the position and the number of a plurality of focal points formed in the
inside. And an object point means the point used as the object of calculation by this embodiment
among a plurality of focal points which exist in a treatment field.
[0018]
FIG. 2 is a drawing showing the transducer array of the HIFU device and a plurality of focal areas
present in the treatment area. The transducer array 201 of the HIFU device may be antenna-like,
as in FIG. This is because when the transducer array is in the form of an antenna, it is easy to
concentrate on a certain area. Ultrasound signals are focused on the treatment area 202 from the
transducer array of the HIFU device. The HIFU device applies an electrical signal to a plurality of
transducer elements to cause them to vibrate, thereby generating ultrasonic waves. Then, the
generated ultrasound is focused in the treatment area 202, but when focusing, a certain number
of focal points are determined in the treatment area, and the ultrasonic waves are simultaneously
focused on the certain number of focal points to generate heat. it can.
[0019]
FIG. 3A is a diagram showing a plurality of focal points present in a treatment area input from a
user according to an embodiment of the present invention. The plurality of focal points shown in
FIG. 3A are within the 16 mm × 16 mm wide treatment area, and each focal point is indicated by
an * mark. The number of focal points is set to 25.
[0020]
The target point determination unit 101 immediately outputs the plurality of focal points to the
candidate focal point determination unit 102 when information about a plurality of focal points
present in the treatment area is input from the user. That is, the entire focus shown in FIG. 3A is
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output to the candidate focus determination unit 102.
[0021]
The focus forming apparatus according to the present invention can determine the maximum
number of focal sets that can be formed without generating the grating lobe phenomenon by one
irradiation of ultrasonic waves. The process of determining the maximum number of focus sets
by the focus forming device will be described specifically. First, the focus forming device
determines whether a grating lobe phenomenon occurs when one focus is formed.
[0022]
A grating lobe means a phenomenon in which an ultrasonic signal is amplified at a position
different from the position of the focal point. More specifically, the ultrasonic transducer array
has a structure in which a plurality of transducers are periodically repeated with a constant
interval. If the spacing between the periodically repeated transducers is larger than λ / 2 (λ is
the wavelength of ultrasonic waves), signals generated between the transducers interfere with
each other. The phenomenon in which amplification occurs outside the desired focal area by this
interference is the grating lobe phenomenon. In that case, the degree of amplification will be
similar in magnitude to the degree of amplification at the position of the focal point. Grating
lobes are an undesirable phenomenon in HIFU devices. The reason is as follows. In order for the
HIFU device to treat the location of the lesion, an ultrasound signal is focused at the location of
the lesion to generate heat and heat is used to treat the lesion. By the way, when grating lobes
are generated, amplification lobes of the ultrasound signal may be formed by grating lobes at
points of other organ regions other than the position of the lesion. Grating lobes are an
undesirable phenomenon in HIFU devices, since the amplification of the signal can damage the
body organ cells that are not the lesion due to the heat generated by the ultrasound, and thus
removed It must be done.
[0023]
Therefore, in order to prevent the grating lobe phenomenon, the focus forming device
determines whether the grating lobe phenomenon occurs or not when one focus is formed, and
then determines that the number of focal spots is not one. The focal point set in which the
grating lobe phenomenon does not occur can be searched while incrementing by one. If it is
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assumed that the grating lobe phenomenon does not occur when the focus forming device forms
a focus on all the focal points input from the user by one irradiation of ultrasonic waves, the
focus forming device focuses on its entire focus, It can be determined that one ultrasonic
irradiation is to be performed.
[0024]
If a grating lobe phenomenon occurs when the focus forming device performs the single
irradiation of the ultrasonic wave on the entire focus, the focus forming device can sequentially
perform the irradiation of the ultrasonic wave a plurality of times. In that case, in order to obtain
the focal point formed each time the focal point forming device irradiates ultrasonic waves, while
increasing the number of focal points one by one, a focal point set in which the grating lobe
phenomenon does not occur at one irradiation of ultrasonic waves is It can be decided.
[0025]
The process of determining in this way is repeated to determine several focal sets. The focus
forming device can form the ultrasonic focus on the entire focus position shown in FIG. 3A by
sequentially irradiating the maximum number of focus sets thus determined. However, when the
focus forming device determines the focus set, it can only determine the focus set of one group in
one operation, so in order for the focus forming device to determine several focus sets, The focal
set to which the ultrasound is sequentially emitted is determined through the process of
repeating or repeating.
[0026]
In the operation repeated as described above, the target point determination unit 101 excludes
the focus set that has already been determined, and determines another focus set with the
remaining focus. Therefore, subsequently, when the object point determination unit 101
determines an object point, among the plurality of focal points as shown in FIG. 3A, the focal
points belonging to the optimal focus set stored in the optimal focus storage unit 109 Exclude
from and determine the remaining focus points as target points. The optimal focus set means a
set of focal points that can maximize the number of focal points without generating grating lobes,
and the optimal focus means a focus belonging to the optimal focus set. The optimal focus
determination unit 104 determines a set of optimal focal points among the target points
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determined by the target point determination unit 101. Of the remaining foci other than the foci
thus determined, another set of optimal foci must be determined. Therefore, the object point
determination unit 101 determines the remaining focal points excluding the set of optimal focal
points already determined as the object points.
[0027]
FIG. 3B shows the optimal focus set that has already been determined by the optimal focus
determination unit 104. Group 1 and group 2 are the optimal focus sets already determined by
the optimal focus determination unit 104, respectively. The target point determination unit 101
determines, as a target point, the remaining focal points of the plurality of focal points in FIG. 3A
determined by the optimal focus determination unit 104 except for the position of the focal point
already belonging to the optimal focus set. The position and coordinate information of the
detected point are output to the candidate focus determination unit 102. As in FIG. 3B, since the
group 1 and the group 2 are the optimal focus sets, the target point determining unit 101
excludes the focal points belonging to the group 1 and the focal points belonging to the group 2
from the target points and the rest. The focus is determined as the target point. FIG. 3C illustrates
the remaining focus excluding the focus belonging to the optimal focus set at the focus of FIG.
3A. The target point determination unit 101 determines a focus corresponding to FIG. 3C as a
target point.
[0028]
The candidate focus determination unit 102 selects, from among the target points determined by
the target point determination unit 101, the focus of the number of focal points input from the
optimum focus determination unit 104. If the number of focal points has not been input from the
optimum focal point determining unit 104, the candidate focal point determining unit 102
selects points approximately equal to the number of focal points set basically. At this time, the
number of basic focal points set in the optimum focal point determination unit 104 may be two.
Therefore, when there is no input of the number of focal points from the optimum focal point
determination unit 104, two focal points are selected from the target points and output to the
focal point formation confirmation unit 103. If the number of focal points is input from the
optimum focal point determining unit 104, the number of focal points input is selected among
the target points, and is selected and output to the focal point formation confirmation unit 103.
For example, when the number of focal points is input from the optimum focal point determining
unit 104 as four, four of the target points are selected and output to the focal point forming
confirmation unit 103. At this time, a method of selecting among the target points will be
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described in detail with reference to FIG. 4 below.
[0029]
As described above, the focus selected by the candidate focus determination unit 102 is output to
the focus formation confirmation unit 103, and the focus formation confirmation unit 103
determines that the focus selected by the candidate focus determination unit 102 is a new
optimum focus set. Calculate whether or not If there is a request from the optimum focus
determination unit 104 to reselect the focus, the candidate focus determination unit 102
reselects the focus again and outputs the focus to the focus formation confirmation unit 103. The
reason why the optimum focus determination unit 104 requests reselection is as follows. When
focusing on the focus selected by the candidate focus determination unit 102, the focus
formation confirmation unit 103 determines whether or not it is possible to simultaneously focus
without generating grating lobes. In this case, when it is determined by the focus formation
confirmation unit 103 that focusing can be performed without generating a grating lobe, the
optimum focus determination unit 104 causes the candidate focus determination unit 102 to
select one more focus. Request to increase That is, it is to calculate whether or not the optimum
focal point set can be formed even with a larger number of focal points. If the focus formation
confirmation unit 103 determines that it is not possible to focus at the same time without
generating grating lobes, the optimum focus determination unit 104 causes the candidate focus
determination unit 102 to again perform as another focus. It asks you to make a choice. That is,
since the selected focus set does not become the optimum focus set, the optimum focus
determination unit 104 requests the candidate focus determination unit 102 to select another
focus set among the target points.
[0030]
When the optimal focus determination unit 104 requests reselection, the number of focal points
selected by the candidate focus determination unit 102 is a number of focal points such as the
number of focal points selected before being requested again. For example, assuming that the
candidate focus determination unit 102 selects three focal points, the focus formation
confirmation unit 103 calculates the optimum negative pressure associated with the three focal
points, and calculates the result that grating lobes occur, the candidate focus The determination
unit 102 selects three focal points, which is the number of such focal points, according to the
reselection request, and outputs the selected focal point to the focal point formation confirmation
unit 103.
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[0031]
The candidate focus determination unit 102 receives the number of focal points from the
optimum focus determination unit 104 and receives the request for reselection, the number of
focal points input among the target points determined by the target point determination unit
101. The focal point is reselected and output to the focal point formation confirmation unit 103.
That is, if it is calculated by the focus formation confirmation unit 103 that the focus set selected
by the candidate focus determination unit 102 can be focused without generating grating lobes
before it is requested, it is optimal. The focus determination unit 104 requests the candidate
focus determination unit 102 to select again by the number of focal points obtained by adding
one to the calculated number of focal points. Although the focal point formation confirmation
unit 103 obtains the focal point set in which no grating lobe occurs, the reason for requesting the
candidate focal point determination unit 102 to select the focal point position again is one
ultrasonic wave. This is because transmission attempts to simultaneously focus as many focus as
possible. That is, when the optimal focus determination unit 104 selects three focal points, but
the focal point formation confirmation unit 103 calculates a focal point set in which no grating
lobe occurs, the next four focal points are selected. It tries to calculate whether it is possible to
match at the same time. Therefore, if the optimal focus set having three focal points is calculated,
the focus formation confirmation unit 103 requests the optimal focus determination unit 104 to
increase the number of focal points by one, and the optimal focus determination unit 104. The
number of focal points is increased from three to four, and the number of focal points and a
request for reselection are output to the candidate focal point determining unit 102.
[0032]
FIG. 4 is a diagram illustrating that the candidate focus determination unit 102 arranges the
target points in a line in order to select or reselect a predetermined number of focal points
among the target points. The focus selection process of the candidate focus determination unit
102 according to one embodiment utilizes a genetic algorithm. Genetic algorithms are heuristic
search processes that mimic natural evolution. The present invention will be described by way of
example. In the process of selecting the focus among the target points, the candidate focus
determination unit 102 does not select randomly but the candidate focus determination unit 102
randomly selects up to the first 10 After making the selection, it is to select 5 out of 10 excellent
results and combine the 5 selected results again to select a focus. That is, it is called genetic
algorithm as it is similar to natural evolution to cross superior seeds. In FIG. 4, the target point is
arranged in a line in order for the candidate focus determination unit 102 to apply a genetic
algorithm, and a set of object points arranged in a line in this way is called a chromosome. The
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display of * on the left side of FIG. 4 is the target point set of FIG. 3C. The candidate focus
determination unit 102 arranges this target point set in a row, but the focus excluded in the
middle is also excluded from the array. Therefore, in the case of FIG. 3C, when the candidate
focus determination unit 102 generates a chromosome, it has all 19 elements. Chromosome
numbers indicate selection. For example, as shown in FIG. 4, in the chromosome composed of 1
and 0, 1 indicates that the candidate focus determination unit 102 has selected a focus, and 0
indicates that the candidate focus determination unit 102 has not selected a focus Indicates that.
Therefore, since the number of chromosomes illustrated in FIG. 4 is five, it indicates that five
focal points among the nineteen target points are selected by the candidate focal point
determining unit 102.
[0033]
FIG. 5 is a diagram showing a chromosomal expression of the case where the candidate focus
determination unit 102 randomly selects five focus points among the target points. Each
chromosome shows the case where the candidate focus determination unit 102 selects five of the
target points. For example, when the candidate focus determination unit 102 generates 10
chromosomes in this way, it is possible to select five with excellent performance. In that case, the
meaning of excellent performance means that the number of grating lobes is small or the
intensity is weak when focusing on the five selected ones. Alternatively, it can be shown that the
number and intensity of grating lobes are both excellent in consideration. If the five excellent
chromosomes are selected, the candidate focus determination unit 102 generates a new
combination using the five chromosomes. In that case, the 5 chromosomes selected as superior
in performance are called parent chromosomes (chromosoma maternum) or maternal
chromosomes.
[0034]
FIG. 6 is a diagram showing how the candidate focus determination unit 102 generates a new
chromosome by combining existing chromosomes. The chromosomes 1 and 2 are existing
chromosomes, and the chromosomes 3 and 4 are chromosomes newly generated by the
candidate focus determination unit 102 using a combination of chromosome 1 and chromosome
2. . Among the chromosomes arranged in FIG. 5, the chromosomes 1 and 2 are the chromosomes
that the candidate focus determination unit 102 has calculated as being superior. When the
candidate focus determination unit 102 combines the chromosome 1 and the chromosome 2, as
shown in FIG. 6, the candidate focus determination unit 102 generates a part of the chromosome
1 and a part of the chromosome 2 by exchanging them with each other. In that case, the number
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of parts of chromosome 1 exchanged and the number of parts of chromosome 2 are equal. In
that case, the number of partials to be exchanged is also a value determined in advance by the
candidate focus determination unit 102, and the number of partials can be all exchanged from 1
to the number of whole chromosomes. Briefly, one of the chromosomes 1 and 2 starts with
exchanging one, leaving one in the chromosome 1 and all the rest, and leaving one in the
chromosome 2. It can include up to exchanging everything. In such a manner, the candidate
focus determination unit 102 combines parent chromosomes to generate a new chromosome,
and a chromosome generated in this manner is called a child chromosome. However, in such a
case, the number of selected foci of chromosomes generated by the partial replacement of
chromosome by the candidate foci determining unit 102 may be different from the number of
selected foci of the parent chromosome. There is something to do. Since the selected focal point
is expressed by the numeral 1, different numbers of numeral 1 and zero numerals are cases
where the number of selected focal points is different. The candidate focus determination unit
102 excludes, among the so-formed offspring chromosomes, the ones in which the number of the
focus chromosome and the number of the selected focus is different. That is, the candidate focus
determination unit 102 must select as many focus points as the number of focus points
determined among the target points, but does not select at random but selects using such a
genetic algorithm. As described above, when selection is made using a genetic algorithm,
excellent chromosomes are newly combined, so that the result can be calculated more efficiently
than when randomly selected. The candidate focus determination unit 102 can repeat such a
process, and can generate a new combination of chromosomes infinitely, and the new
chromosome generated as such is output to the focus formation confirmation unit 103.
[0035]
When forming a focus on the focus selected by the candidate focus determination unit 102, the
focus formation confirmation unit 103 determines whether a grating lobe phenomenon occurs.
The focus formation confirmation unit 103 outputs to the optimum focus determination unit 104
whether or not the grating lobe phenomenon occurs.
[0036]
FIG. 7 shows the treatment area 702 and the non-treatment area 703. The treatment area 702 is
an area with a lesion, and the non-treatment area 703 is an organ area surrounding the
periphery of the lesion. Then, a plurality of focal spots 701 of FIG. 3A are formed in the
treatment area 702. The HIFU device has to focus the ultrasound signal in the treatment area
702, but in the non-treatment area 703 which is not the treatment area 702, the ultrasound
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signal should not be amplified. As described above, in the non-treatment area 703, the
phenomenon in which the ultrasound signal is amplified is a grating lobe.
[0037]
In one example, when the focus belonging to group 1 in FIG. 3B is selected by the candidate
focus determination unit 102, the focus formation confirmation unit 103 detects negative
pressure at the focus position selected by the candidate focus determination unit 102. 1. At the
same time, find a solution in which the negative pressure in a part of the non-treatment area 703
is zero, and when the solution is used to form a focus, does the grating lobe phenomenon occur
in the entire non-treatment area 703? Decide whether or not. Hereinafter, a method of
determining whether or not the grating lobe phenomenon occurs will be described with
reference to the drawings.
[0038]
FIG. 8 is a view illustrating the configuration of the focus formation confirmation unit 103. As
shown in FIG. Referring to FIG. 8, the focus formation confirmation unit 103 illustrated in FIG. 1
includes an element output calculation unit 105 and a negative pressure generation
determination unit 110. The element output calculation unit 105 focuses on the candidate focus
selected by the candidate focus determination unit 102, and obtains the output of each
transducer for which the negative pressure in a part of the non-focus area is zero. Hereinafter, a
process in which the element output calculation unit 105 obtains an output for forming a focus
on a candidate focus while the negative pressure is 0 in a part of the non-focus area will be
described with reference to FIG. FIG. 9 shows the position vector of the transducer element 801
on three-dimensional orthogonal coordinates.
[0039]
And any focal point 802 position vector
[0040]
And FIG.
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Since the number of transducer elements is plural and the position of each transducer element is
different in three-dimensional space, in order to calculate the negative pressure at any focal
point, the position vector of each transducer element
[0041]
Must be defined. As in FIG. 9, a three-dimensional orthogonal coordinate system can be set
arbitrarily. A vector starting at the origin of the set rectangular coordinate system and ending at
the position of the nth transducer element is
[0042]
Defined as a vector
[0043]
The vector can be used as the position vector of the nth transducer element.
In the same three-dimensional Cartesian coordinate system, a vector starting at the origin and
ending at the position of the mth focal point
[0044]
Define the
[0045]
The vector can be used as a position vector for the mth focal point.
[0046]
The equation (1) is a basic equation for the element output calculation unit 105 to calculate the
negative pressure, and the integration region in the equation (1) is called the RayleighSommerfeld integral.
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[0047]
Equation (1) is negative pressure at the mth focal point
[0048]
Is a formula to calculate
[0049]
In equation (1), j is a complex number
[0050]
Show,
[0051]
Is a complex number, and the amplitude and phase of the signal applied from the transducer
[0052]
Is the density of air, k is the wave number, c is the speed of sound, N is the number of transducer
elements, M is the number of target points,
[0053]
Is the position vector of the mth focal point as in FIG. 9, as in FIG.
[0054]
Is the position vector of the n th transducer element,
[0055]
Means the area of the transducer element surface area.
The reason why the Rayleigh-Sommerfeld integral is expressed by the equation of summation in
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equation (1) is that, since the number of elements of the transducer is N, the total negative
pressure generated in each transducer element is actually combined. To
[0056]
This is because the result of the negative pressure generated at the position of the vector is
derived.
[0057]
Furthermore, not only the negative pressure at the mth focal point but also the negative pressure
corresponding to various focal points
[0058]
As in equation (2), to calculate with
[0059]
Can be defined.
[0060]
As in equation (2)
[0061]
In the case of defining, the negative pressure at M focal points can be expressed by a single
matrix equation, as in the following equation (3).
[0062]
In equation (3)
[0063]
Is the same as in formula (1).
[0064]
And if Formula (4), Formula (5), and Formula (6) are defined as follows in order, Formula (3) will
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be expressed like Formula (7).
[0065]
The equation (7) is the same as the equation (3), and the particular matrix in the equations (4) to
(6) is defined, and only the expression is simplified.
That is, P is the position of the focal point, as expressed by equation (6)
[0066]
Position negative pressure,
[0067]
It is represented by a matrix, and in the case of an example like FIG. 3A, M = 25.
H denotes an (M × N) matrix representing the array of equation (2) justified in equation (4),
[0068]
Denotes a (N × 1) matrix indicating the amplitudes and phases of the signals applied to the N
transducer elements.
[0069]
The element output calculation unit 105 sets the negative pressure of the focus selected by the
candidate focus determination unit 102 in the focus area 702 to 1 and the negative pressure of
the focus not selected in the focus area 702 to 0, 7) to satisfy
[0070]
Derive the value of
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On the other hand, satisfy equation (7)
[0071]
There may be more than one value of.
The reason is that the unknowns to be determined are N, which is the number of transducer
elements, and the number of simultaneous equations generated by equation (7) is M, if (N> M)
For example, the number of unknowns is greater than the number of simultaneous equations.
As a result, the focus formation confirmation unit 103 obtains a solution satisfying the condition
in which the grating lobe does not occur among the plurality of solutions satisfying the equation
(7).
The equation (7) can be expressed by the equation (8) using linear algebra.
[0072]
In the equation (8), w is an arbitrary vector, and the superscript + means a pseudo inverse matrix.
[0073]
Since the w vector is an arbitrary vector, any value can be designated, but in the non-treatment
area of FIG. 7, a value which does not generate a grating lobe is determined.
That is, a w vector that satisfies the condition that the negative pressure in the non-treatment
region is zero is determined.
However, since there are infinite points in the non-treatment area, it is not easy to express the
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condition that the negative pressure is 0 in the entire non-treatment area by equations.
For this purpose, create an equation that sets the negative pressure to zero by selecting a few
points at random in the non-treatment area, or setting the negative pressure to 0 in areas that
are weak to heat and must be protected, Find a w vector that satisfies the equation.
For example, in the embodiment in which the negative pressure in the protected area is set to 0,
assuming that the number of positions in the protected area is C, the negative pressure in the
protected area is expressed by a matrix as in equation (9). The condition that the negative
pressure value at that position is all zero is the condition that no grating lobe is generated.
[0074]
In equation (9), the p 'is marked to distinguish that the protected area is under negative pressure.
And in the protected area
[0075]
The matrix of B can be expressed as B, as in equation (10), to separate it from the focal region.
And, the superscript of H is to indicate that it is the H value in the protected area.
[0076]
Formula (11) can be obtained by using Formula (9) and Formula (10).
[0077]
Equation (11) shows the condition under which the negative pressure in the protective region
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becomes zero.
The element output calculation unit 105 simultaneously satisfies Expression (7) and Expression
(11).
[0078]
By calculating equation (7), the ultrasonic wave can be focused on the desired focal point by
equation (7), and the negative pressure in the protected area can be eliminated by equation (11).
In order to obtain a solution of equation (11), element output calculation unit 105 determines
equation (11) by equation (8).
[0079]
Substituting a value, the following equation (12) can be obtained.
[0080]
The solution of w in equation (12) is further obtained as in equation (13) by linear algebra.
What the value of w in the equation (13) means is a condition under which the negative pressure
becomes 0 in the protective region, that is, a condition under which no grating lobe occurs in the
protective region.
[0081]
The element output calculation unit 105 substitutes the value of the w vector into the equation
(8) when the value of the w vector is calculated, and is an output value of the transducer element.
[0082]
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After calculating the value, the value is stored in the memory 106 in correspondence with the
input candidate focus.
Calculated in this way
[0083]
(7) and (11) at the same time, the output value of the transducer which forms the focus on the
candidate focal point and which satisfies the negative pressure of 0 in the protected area It is.
This is the output of the transducer calculated in this way
[0084]
Are output to the negative pressure generation determination unit 110.
[0085]
The negative pressure generation determination unit 110 is an output of the transducer obtained
by the element output calculation unit 105.
[0086]
Is applied to the transducer, it is determined whether grating lobe phenomenon occurs in the
entire non-focus area.
The element output calculation unit 105 sets the condition that the negative pressure in the
protected area is 0 so that the grating lobe phenomenon does not occur particularly in the
protected area in the non-focus area.
[0087]
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I asked for.
Therefore, the output calculated by the element output calculation unit 105
[0088]
Grating lobe phenomenon does not occur in the protected area when using.
However, since the grating lobe phenomenon may occur in the entire non-focus area outside the
protected area, the negative pressure generation determination unit 110 determines whether the
grating lobe occurs in the entire non-focus area.
Furthermore, when the negative pressure generation determination unit 110 determines that the
grating lobe phenomenon occurs in the non-focus area, but the negative pressure of the
generated grating lobe is at a low level or the area is harmless to the human body. Also, it can be
judged the same as the occurrence of grating lobes.
The negative pressure generation determination unit 110 determines whether a grating lobe
phenomenon occurs and outputs the determination to the optimum focus determination unit
104.
[0089]
When the grating lobe phenomenon is input from the negative pressure generation
determination unit 110, the optimum focus determination unit 104 causes the candidate focus
determination unit 102 to output the same number of focal points, and the number of focal
points corresponding to that number is read again. Request a choice.
The focal point set reselected by the candidate focal point determination unit 102 is calculated
by the focal point formation confirmation unit 103 again whether the grating lobe phenomenon
occurs.
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In the case where the grating lobe phenomenon is maintained despite the fact that the candidate
focus determination unit 102 repeatedly performs reselection in this manner and the
predetermined number of times or more, the optimum focus determination unit 104 performs
the refocusing on the candidate focus determination unit 102. Cancel the request for selection.
That is, the optimum focus determination unit 104 determines that generation of grating lobes
can not be eliminated by the number of continuously selected focal points, and cancels the
request for reselection.
For example, even if the optimum focus determination unit 104 requests the candidate focus
determination unit 102 to continuously select seven focal spots, it is possible to exclude the
grating lobe phenomenon within 50 times. In the seven focal points, it is determined that the
occurrence of the grating lobe present can not be eliminated, and the candidate focal point
determining unit 102 does not request reselection.
[0090]
When canceling the request for reselection to the candidate focus determination unit 102, the
optimum focus determination unit 104 determines the most recent focus set stored in the
memory 106 as the optimum focus set.
In the memory 106, the number of focal points one less than the number of focal points giving
up reselection request is the set of focal points without occurrence of grating lobe and the output
of the corresponding transducer as a focal point set.
[0091]
Is stored.
That is, as in the example described above, after the optimal focus determination unit 104
determines that the occurrence of grating lobes can not be eliminated with seven focal points, a
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focal point set consisting of six focal points stored in the memory 106 Is determined as the
optimal focus set. The focal set is a focal set without occurrence of grating lobes. Thus, the
optimal focus set obtained by the optimal focus determination unit 104 is used as the optimal
focus set in the optimal focus storage unit 109,
[0092]
Is stored with the value of
[0093]
The optimum focus determination unit 104 outputs, from the focus formation confirmation unit
103, the number of focal points one more than the current number of focal points when the
result that the grating lobe phenomenon does not occur and the number of current focal points
are input. The number of outputs of the candidate focus determination unit 102 is required to be
selected.
That is, the current focus set means a set that can be focused without occurrence of the grating
lobe phenomenon. However, in order to determine whether or not the grating lobe phenomenon
occurs even if the number of focal points is further increased, the optimal focal point
determining unit 104 selects the number of focal points more than the candidate focal point
determining unit 102. Request that.
[0094]
As described above, the object point determining unit 101 excludes the optimal focus set input
from the focus formation confirmation unit 103 when determining the object points. When the
target point determination unit 101 excludes the optimal focus set among the plurality of focal
points present in the treatment area input from the user, the operation ends if there is no
remaining focus.
[0095]
The memory 106 corresponds to a focus set in which no grating lobe is generated among the
focus sets calculated by the focus formation confirmation unit 103 and a focus set calculated by
the element output calculation unit 105.
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[0096]
Remember the value of.
[0097]
The optimum focus storage unit 109 corresponds to the focus set determined by the optimum
focus determination unit 104 to be the optimum focus set and the focus set.
[0098]
Remember the value of.
[0099]
The interface 107 inputs focus information from the user to the target point determination unit
101, or corresponds to the optimum focus set and the optimum focus set from the optimum
focus storage unit 109.
[0100]
Output the value of
[0101]
The irradiation determination unit 108 determines the order or the time for irradiating the focal
point determined as the optimal focal point determination unit 104 as the optimal focal point.
There may be a plurality of sets of focal points determined by the optimal focus determination
unit 104 as the optimal focus.
Therefore, the set of focal points is sequentially irradiated, but the order in which the irradiation
is performed or the time to irradiate the set of focal points with ultrasonic waves is determined.
[0102]
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FIG. 10 shows a flow chart according to an embodiment of the present invention.
In step 901, n, which is the number of focus points determined by the candidate focus
determination unit 102, is set to one.
In operation 902, the target point determination unit 101 excludes the focal point input from the
optimal focal point determination unit 104 as the optimal focal point set among the plurality of
focal points in the treatment area input from the user, and the remaining focal points Select as
the target point.
In operation 903, the candidate focus determination unit 102 selects n candidate focus points
from the target points.
In step 904, the focus formation confirmation unit 103 calculates the optimum negative pressure
of the n focal points determined by the candidate focus determination unit 102, and proceeds to
step 906 if a grating lobe is generated, and no grating lobe is generated. Proceed to step 905.
Step 905 is a case where grating lobes are not generated, but the optimum focus determination
unit 104 repeats step 903 after adding one to n which is the number of focal points determined
by the candidate focus determination unit 102. In step 906, grating lobes are generated, but the
optimum focus determination unit 104 proceeds to step 907 when the predetermined number of
repetitions exceeds, or 903 when the predetermined number of repetitions is not exceeded. To
repeat. In step 907, the target point determination unit 101 determines whether a target point
remains or not, and ends when no target point remains, and repeats step 902 when a target point
remains.
[0103]
Meanwhile, the embodiment of the present invention described above can be implemented as a
program executed by a computer, and can be embodied as a general-purpose digital computer
that operates a program using a computer readable recording medium. Also, the structure of data
used in the above-described embodiment of the present invention is recorded on a computerreadable recording medium via various means. The computer readable recording medium
includes a magnetic recording medium such as a hard disk, a floppy disk and a magnetic tape, an
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optical medium such as a CD-ROM disk and a DVD, a magneto-optical medium such as an optical
disk, and a read only It includes hardware devices that are specifically configured to store and
execute program instructions such as memory (ROM), random access memory (RAM), flash
memory, and the like.
[0104]
The present invention has been described above centering on the preferred embodiments. Those
skilled in the art will understand that the present invention can be embodied in modified forms
without departing from the essential characteristics of the present invention. Accordingly, the
disclosed embodiments are to be considered in an illustrative rather than a restrictive sense. The
scope of the invention is indicated in the appended claims, rather than in the foregoing
description, and any difference which falls within the equivalent range is to be construed as
being included in the invention. .
[0105]
The multifocal forming method and apparatus of the ultrasonic transducer array of the present
invention can be effectively applied to, for example, the technical field related to ultrasonic
medical treatment.
[0106]
101: target point determination unit 102: candidate focus determination unit 103: focus
formation confirmation unit 104: optimum focus determination unit 105: element output
calculation unit 106: memory 107: interface 108: irradiation determination unit 109: optimum
focus storage unit 110: negative focus Pressure generation determination unit 201: transducer
array 202, 702: treatment area 701: multiple focal points 703: non-treatment area 801:
transducer elements 802: arbitrary focal point
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