KR102292170B1 - Method for improving signal-to-noise of photoacoustic signal measured with photoacoustic detector - Google Patents

Abstract

The present invention relates to a method of improving a signal-to-noise ratio of a photoacoustic signal, generated from a light absorber, measured by a photoacoustic meter when an incident beam is absorbed by the light absorber in order to grasp the position or characteristics of the light absorber. According to the present invention, when a processing device performs matched filtering processing on the photoacoustic signal in the frequency domain, the method is configured to use a chirp signal spectrum from which a DC component has been removed, thereby capable of improving the signal-to-noise ratio of the photoacoustic signal. The present invention includes a step of absorbing the chirp signal emitted through a light source by the light absorber located inside a light diffusion medium.

Description

METHOD FOR IMPROVING SIGNAL-TO-NOISE OF PHOTOACOUSTIC SIGNAL MEASURED WITH PHOTOACOUSTIC DETECTOR

The present invention provides a method for improving the signal-to-noise ratio of a photoacoustic signal generated by the light absorber and measured by a photoacoustic meter when an incident beam is absorbed by the light absorber in order to grasp the position or characteristics of the light absorber. is about

In general photoacoustic measurement, in order to grasp the position or characteristics of a light absorber (eg, blood vessel, tumor, etc.) located inside the light diffusion medium (eg, living tissue, etc.), The incident beam is emitted through a light source located in the The incident beam irradiated to the light diffusion medium is scattered inside the light diffusion medium, and accordingly, only a part of the incident beam is absorbed by the light absorber.

When the intensity of the incident beam emitted through the light source changes with time, the light absorber absorbing the incident beam physically expands and contracts repeatedly due to thermal expansion, and in this process, the photoacoustic signal ( For example, an ultrasonic signal) is generated. In the photoacoustic measurement, the photoacoustic signal generated by the optical absorber is measured with an optoacoustic measuring device located outside the optical diffusion medium, and the photoacoustic signal measured by the photoacoustic measuring device is processed through a processing device. It is used to determine the position or characteristics of the absorber.

The intensity of the photoacoustic signal generated from the light absorber is proportional to the light absorption coefficient of the light absorber and the intensity of the incident beam reaching the light absorber. However, the intensity of the incident beam emitted through the light source is limited, and since the intensity of the incident beam decreases exponentially due to scattering inside the light diffusion medium, the intensity of the photoacoustic signal generated from the light absorber is very weak. do.

In addition, in photoacoustic measurement, photoacoustic noise due to heat (ie, photoacoustic thermal noise) is always present, and the photoacoustic signal generated by the light absorber is reflected or refracted by the interface of the light diffusion medium or other light absorbers. Optoacoustic noise in the form of clutter is always present. Therefore, in the conventional photoacoustic measurement, the signal-to-noise ratio of the photoacoustic signal measured by the photoacoustic meter is very low, which becomes a great obstacle in obtaining high-resolution and ultra-sensitive photoacoustic signals and image information.

Korean Patent Publication No. 1730816 (2017.04.21)

The present invention has been devised to solve the above problems, and an object of the present invention is to provide a method for improving the signal-to-noise ratio of a photoacoustic signal measured by a photoacoustic meter.

In order to achieve the above object, in the method for improving the signal-to-noise ratio of the photoacoustic signal measured by the photoacoustic meter according to the first embodiment of the present invention, a chirped signal emitted through a light source is irradiated to an optical diffusion medium. and absorbing it into a light absorber located inside the light diffusion medium; measuring a photoacoustic signal generated from the optical absorber due to the chirped signal using a photoacoustic meter; and a processing device connected to the light source and the photoacoustic meter receives the photoacoustic signal measured by the photoacoustic meter, performs matched filtering on the photoacoustic signal in the frequency domain, and matches the filtered photoacoustic signal Calculating; including, wherein the envelope of the chirped signal emitted through the light source is constant over time, and calculating the matched-filtered optoacoustic signal includes, wherein the processing device receives the chirped signal from the chirped signal. calculating a chirp signal spectrum from which the DC component is removed by removing a direct current (DC) component of the chirp signal; and performing, by the processing device, a matched filtering process on the photoacoustic signal by using the chirp signal spectrum from which the DC component is removed.

The frequency range of the chirped signal emitted through the light source is the absolute value of the value obtained by multiplying the transfer function of the photoacoustic meter and the spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter and the shape of the light absorber. It may include a frequency that becomes

The method for improving the signal-to-noise ratio of an optoacoustic signal measured by an optoacoustic measuring device according to a second embodiment of the present invention is to irradiate a chirped signal emitted through a light source to an optical diffusion medium and position it inside the optical diffusion medium Absorbing the light absorber; measuring a photoacoustic signal generated from the optical absorber due to the chirped signal using a photoacoustic meter; and a processing device connected to the light source and the photoacoustic meter receives the photoacoustic signal measured by the photoacoustic meter, performs matched filtering on the photoacoustic signal in the frequency domain, and matches the filtered photoacoustic signal Calculating; includes, wherein the envelope of the chirped signal emitted through the light source is constant over time, and the calculating of the matched-filtered optoacoustic signal includes, by the processing device, a chirped signal using the chirped signal. calculating a spectrum; and at least one of the spatial photoacoustic spectrum determined according to the transfer function of the photoacoustic meter, the shape of the photoacoustic meter, and the shape of the light absorber, by the processing device, multiplied by the chirp signal spectrum. , performing matched filtering processing on the photoacoustic signal.

The calculating of the chirped signal spectrum may include calculating, by the processing device, the chirped signal spectrum by Fourier transforming the chirped signal.

Alternatively, the calculating of the chirped signal spectrum may include calculating, by the processing device, a chirped signal spectrum from which the DC component is removed by removing the DC component of the chirp signal from the chirp signal.

The frequency range of the chirped signal emitted through the light source is the absolute value of the value obtained by multiplying the transfer function of the photoacoustic meter and the spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter and the shape of the light absorber. It may include a frequency that becomes

In addition, in the method for improving the signal-to-noise ratio of the photoacoustic signal measured by the optoacoustic measuring device according to the third embodiment of the present invention, the optical diffusion medium is irradiated with a modulated chirped signal emitted through a light source to the optical diffusion medium. Absorbing the light absorber located therein; measuring a photoacoustic signal generated from the optical absorber due to the modulated chirp signal using a photoacoustic meter; and a processing device connected to the light source and the photoacoustic meter receives the photoacoustic signal measured by the photoacoustic meter, performs matched filtering on the photoacoustic signal in the frequency domain, and matches the filtered photoacoustic signal and calculating, wherein the modulated chirp signal emitted through the light source may have an envelope that changes with time.

Calculating the matched-filtered photoacoustic signal may include: calculating, by the processing device, a modulated chirped signal spectrum by Fourier transforming the modulated chirped signal; and performing, by the processing device, matched filtering processing on the photoacoustic signal by using the modulated chirped signal spectrum.

Alternatively, the calculating of the matched filtered optoacoustic signal may include: calculating, by the processing device, a modulated chirped signal spectrum from which the DC component is removed by removing the DC component of the modulated chirp signal from the modulated chirp signal; and performing, by the processing device, a matched filtering process on the photoacoustic signal by using the modulated chirp signal spectrum from which the DC component is removed.

Alternatively, the calculating of the matched filtered photoacoustic signal may include: calculating, by the processing device, a modulated chirped signal spectrum using the modulated chirp signal; and a value obtained by multiplying, by the processing device, at least one of a transfer function of the photoacoustic meter, a spatial photoacoustic spectrum determined according to a shape of the photoacoustic meter and a shape of the light absorber, by the modulated chirped signal spectrum. Thus, the method may include performing matched filtering processing on the photoacoustic signal.

Here, the calculating of the modulated chirp signal spectrum may include calculating, by the processing device, the modulated chirp signal spectrum by Fourier transforming the modulated chirp signal.

Alternatively, the calculating of the modulated chirp signal spectrum may include: calculating, by the processing device, a modulated chirped signal spectrum from which the DC component is removed by removing the DC component of the modulated chirp signal from the modulated chirp signal; and performing, by the processing device, a matched filtering process on the photoacoustic signal by using the modulated chirp signal spectrum from which the DC component is removed.

The frequency range of the modulated chirped signal emitted through the light source is an absolute value of a value obtained by multiplying a transfer function of the photoacoustic meter and a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter and the shape of the light absorber. The maximum frequency may be included.

According to the present invention, when the processing device performs matched filtering processing on the photoacoustic signal in the frequency domain, the chirp signal spectrum from which the DC component is removed is used, or the transfer function of the photoacoustic meter, the shape of the photoacoustic meter, and the light absorber are used. As it is configured to use a value obtained by multiplying the chirp signal spectrum by at least any one of the spatial photoacoustic spectra determined according to the shape of There is an advantage in that the signal-to-noise ratio of the measured optoacoustic signal can be improved.

In addition, according to the present invention, since the chirp signal is configured to be used as an incident beam irradiated to the light diffusion medium, a low-cost and small-sized light source that operates continuously other than the pulse type can be used, and the light diffusion medium or the light absorber It has the advantage of being able to perform fast measurements such as real-time monitoring.

의 특성을 나타낸 도면이다.
도 3은 광음향 측정기의 모양 및 광 흡수체의 모양에 따라 결정되는 공간적 광음향 스펙트럼

의 특성을 나타낸 도면이다.
도 4a 및 도 4b는 광원을 통해 방출되는 처프신호의 중심 주파수 ν_c가 3MHz이고, 대역폭 bT가 4MHz인 처프신호 I_c(t)를 예시적으로 나타낸 그래프이다.
도 5는 도 4에 나타낸 처프신호를 푸리에 변환한 결과인 처프신호 스펙트럼

를 나타낸 도면이다.
도 6은 본 발명의 제1 실시예에 따른 광음향 측정기로 측정되는 광음향 신호의 신호 대 잡음비를 향상시키는 방법을 나타낸 흐름도이다.
도 7은 도 5에 나타낸 처프신호에서 DC 성분이 제거된 처프신호 스펙트럼

를 나타낸 도면이다.
도 8은 주파수가 1MHz에서 5MHz까지 변하는 처프신호 I_c(t)가 광 흡수체에 흡수될 경우, 광음향 측정기로 측정되는 광음향 신호를 처리장치가

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다.
도 9는 선폭 T=1msec이고 주파수가 1MHz에서 5MHz까지 변하는 처프신호 I_c(t)가 광 흡수체에 흡수될 경우, 광음향 측정기로 측정되는 광음향 신호를 처리장치가

및

로 각각 정합 필터링 처리를 수행하였을 때 획득되는 노이즈가 포함된 광음향 신호 파형을 나타낸 도면이다.
도 10은 본 발명의 제2 실시예에 따른 광음향 측정기로 측정되는 광음향 신호의 신호 대 잡음비를 향상시키는 방법을 나타낸 흐름도이다.
도 11은 광음향 측정기의 전달함수

와, 광음향 측정기의 모양 및 광 흡수체의 모양에 따라 결정되는 공간적 광음향 스펙트럼

의 곱에 절대값을 취한 스펙트럼을 나타낸 도면이다.
도 12는 주파수가 1MHz에서 5MHz까지 변하는 처프신호가 광 흡수체에 흡수될 경우, 광음향 측정기로 측정되는 광음향 신호를 처리장치가

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다.
도 13은 주파수가 1MHz에서 5MHz까지 변하는 처프신호가 광 흡수체에 흡수될 경우, 광음향 측정기로 측정되는 광음향 신호를 처리장치가

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다.
도 14는 본 발명의 제3 실시예에 따른 광음향 측정기로 측정되는 광음향 신호의 신호 대 잡음비를 향상시키는 방법을 나타낸 흐름도이다.
도 15는 시간에 따라 포락선이 변하는 변조 처프신호

를 예시적으로 나타낸 그래프이다.
도 16a는 도 15에 표시된 (a)부분을 확대하여 나타낸 그래프이고, 도 16b는 도 15에 표시된 (b)부분을 확대하여 나타낸 그래프이다.
도 17은 주파수가 1MHz에서 5MHz까지 변하는 변조 처프신호가 광 흡수체에 흡수될 경우, 광음향 측정기로 측정되는 광음향 신호를 처리장치가

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다.
도 18은 주파수가 1MHz에서 5MHz까지 변하는 변조 처프신호가 광 흡수체에 흡수될 경우, 광음향 측정기로 측정되는 광음향 신호를 처리장치가

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다.
도 19는 주파수가 1MHz에서 5MHz까지 변하는 변조 처프신호가 광 흡수체에 흡수될 경우, 광음향 측정기로 측정되는 광음향 신호를 처리장치가

,

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다.
도 20은 주파수가 1.5MHz에서 4MHz까지 변하는 변조 처프신호가 광 흡수체에 흡수될 경우, 광음향 측정기로 측정되는 광음향 신호를 처리장치가

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다.
도 21은 주파수가 1.5MHz에서 4MHz까지 변하는 변조 처프신호가 광 흡수체에 흡수될 경우, 광음향 측정기로 측정되는 광음향 신호를 처리장치가

,

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다. 1 is a schematic diagram of an apparatus for realizing a method for improving a signal-to-noise ratio of an optoacoustic signal measured by an optoacoustic meter according to the present invention;
2 is a transfer function of a photoacoustic meter having a center frequency of 3 MHz;

A diagram showing the characteristics of
3 is a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter and the shape of the light absorber.

A diagram showing the characteristics of
4A and 4B are graphs exemplarily illustrating a _{chirp signal I c (t) having a center frequency ν c} of 3 MHz and a bandwidth bT of 4 MHz of a chirped signal emitted through a light source.
5 is a chirped signal spectrum that is a result of Fourier transform of the chirped signal shown in FIG.

is a diagram showing
6 is a flowchart illustrating a method of improving a signal-to-noise ratio of an optoacoustic signal measured by an optoacoustic meter according to the first embodiment of the present invention.
7 is a chirp signal spectrum from which the DC component is removed from the chirp signal shown in FIG. 5;

is a diagram showing
FIG. 8 shows that when a chirp signal I _c (t) whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.
_{9 shows that when a chirp signal I c} (t) having a line width T = 1 msec and a frequency of 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

and

It is a diagram showing a photoacoustic signal waveform including noise obtained when each matched filtering process is performed.
10 is a flowchart illustrating a method of improving a signal-to-noise ratio of an optoacoustic signal measured by an optoacoustic meter according to a second embodiment of the present invention.
11 is a transfer function of the photoacoustic meter

and spatial photoacoustic spectrum determined by the shape of the photoacoustic meter and the shape of the light absorber

It is a diagram showing the spectrum obtained by taking the absolute value of the product of .
FIG. 12 shows that when a chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.
13 shows that when a chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.
14 is a flowchart illustrating a method of improving a signal-to-noise ratio of an optoacoustic signal measured by an optoacoustic meter according to a third embodiment of the present invention.
15 is a modulated chirp signal whose envelope changes with time.

It is a graph showing by way of example.
FIG. 16A is an enlarged graph of part (a) shown in FIG. 15 , and FIG. 16B is an enlarged graph showing part (b) shown in FIG. 15 .
17 shows that when a modulated chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.
18 shows that when a modulated chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.
19 shows that when a modulated chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

,

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.
FIG. 20 shows that when a modulated chirp signal whose frequency varies from 1.5 MHz to 4 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.
FIG. 21 shows that when a modulated chirp signal whose frequency varies from 1.5 MHz to 4 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

,

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.

Hereinafter, a method of improving the signal-to-noise ratio of the photoacoustic signal measured by the photoacoustic measuring device according to the present invention will be described in detail with reference to the accompanying drawings. Detailed descriptions of well-known functions and configurations that may unnecessarily obscure the gist of the present invention will be omitted.

1 is a schematic diagram of an apparatus for realizing a method for improving a signal-to-noise ratio of an optoacoustic signal measured by an optoacoustic meter according to the present invention, wherein the apparatus includes a light source 100, a photoacoustic meter 200 and a processing device ( 300) may be included.

The light source 100 emits an incident beam, and the incident beam emitted through the light source 100 is irradiated to the light diffusion medium 10 . The incident beam emitted from the light source 100 may be a chirped signal as will be described later.

The incident beam emitted from the light source 100 and irradiated to the light diffusion medium 10 propagates and diffuses in the light diffusion medium 10 , and its intensity is determined by _{the effective scattering coefficient μ eff of the light diffusion medium 10 .} is exponentially attenuated and reaches the surface of the light absorber 20 .

When an incident beam is emitted from the light source 100 , the intensity of the incident beam changes with time. At this time, the light absorber 20 positioned inside the light diffusion medium 10 absorbs the incident beam and thermally expands. Due to the phenomenon, expansion and contraction are physically repeated, and in this process, a photoacoustic signal (eg, an ultrasonic signal) is generated from the light absorber 20 .

The photoacoustic measuring device 200 is located outside the optical diffusion medium 10 and measures the photoacoustic signal generated from the optical absorber 20 . At this time, the photoacoustic signal measured by the photoacoustic meter 200 includes an ideal photoacoustic signal generated by the light absorber 20 (here, the ideal photoacoustic signal means a photoacoustic signal that does not contain noise) and noise (that is, , optoacoustic noise values to be described later) are mixed.

로 나타난다고 가정하기로 한다. 상기 광 흡수체(20)에 흡수되는 광 에너지의 공간적 분포

에서

는 광 확산매체(10)의 임의의 원점(도 1의 ○)에서 광 흡수체(20)까지의 벡터를 나타낸다. When an incident beam having an intensity of I(t) is emitted from the light source 100 and irradiated to the light diffusion medium 10 , the light energy absorbed by the light absorber 20 positioned inside the light diffusion medium 10 . the spatial distribution of

It is assumed that it appears as Spatial distribution of light energy absorbed by the light absorber 20 .

at

denotes a vector from an arbitrary origin (circle in FIG. 1 ) of the light diffusion medium 10 to the light absorber 20 .

라고 가정하기로 한다. 상기 광음향 측정기(200)의 표면 분포 함수

에서

는 광 확산매체(10)의 임의의 원점(도 1의 ○)에서 광음향 측정기(200) 표면까지의 벡터를 나타낸다. And located outside the light diffusion medium 10, the surface distribution function of the photoacoustic meter 200 having a spherical focus

to assume that Surface distribution function of the photoacoustic meter 200

at

denotes a vector from an arbitrary origin of the light diffusion medium 10 (circle in FIG. 1 ) to the surface of the photoacoustic meter 200 .

In this case, the photoacoustic signal g(t) generated in the light absorber 20 and measured by the photoacoustic measuring device 200 is obtained as the following Equation 1 by the solution of the Green function of the Helmholtz equation. can indicate

[Equation 1]

In Equation 1, Γ is the Gruneigen constant, c _s is the speed of ultrasound, and in the following simulation, Γ is set to 0.24 and c _s to 1500 m/s in consideration of a typical living tissue (light diffusion medium). In addition, in Equation 1, d ³ r _o is an integral symbol for three-dimensional integration from an arbitrary origin (circle in FIG. 1 ) of the light diffusion medium 10 to the light absorber 20 , and d ³ r _d is the light It is an integral symbol for three-dimensional integration from the arbitrary origin of the diffusion medium 10 (circle in FIG. 1 ) to the surface of the photoacoustic meter 200 .

는 다음의 수학식 2와 같이 나타낼 수 있다.Spatial distribution of light energy absorbed by the light absorber 20 in Equation 1

can be expressed as in Equation 2 below.

[Equation 2]

는 공간적으로 분포한 광 흡수체(20)를 나타내는 함수로서, 이하의 시뮬레이션에서는 반지름이 2mm인 구형으로 가정하였다. 수학식 2에 나타낸 바와 같이, 광 흡수 분포는 생체 조직에 조사되는 입사빔이 생체 조직에 의한 산란 때문에 깊이 z에 따라 지수함수적으로 감소한다고 가정하였다.In Equation 2, μ _a is the light absorption coefficient of the light absorber 20,

is a function representing the spatially distributed light absorber 20, and in the following simulation, it is assumed to be a sphere with a radius of 2 mm. As shown in Equation 2, it is assumed that the light absorption distribution decreases exponentially with the depth z due to scattering of the incident beam irradiated to the living tissue by the living tissue.

임을 고려하면, 수학식 1은 다음의 수학식 3과 같이 나타낼 수 있다. 여기서,

는 입사빔의 세기 I(t)를 주파수 영역에서 푸리에 변환한 입사빔 스펙트럼이고, ν는 주파수를, t는 시간을 나타낸다. In Equation 1, the intensity of the incident beam

Considering that , Equation 1 can be expressed as Equation 3 below. here,

is the incident beam spectrum obtained by Fourier transforming the intensity I(t) of the incident beam in the frequency domain, ν is the frequency, and t is the time.

[Equation 3]

라 하고, 수학식 3의 광음향 신호 g(t)를 주파수 영역에서 나타내면, 다음의 수학식 4와 같은 광음향 신호의 스펙트럼(즉, 광음향 스펙트럼)

을 획득할 수 있다. The transfer function of the photoacoustic meter 200

And, if the photoacoustic signal g(t) of Equation 3 is expressed in the frequency domain, the spectrum of the photoacoustic signal as in Equation 4 (ie, the photoacoustic spectrum)

can be obtained.

[Equation 4]

가 곱해져야 한다.As shown in Equation 4, the spectrum of the photoacoustic signal measured by the photoacoustic meter 200 has a transfer function of the photoacoustic meter 200 .

should be multiplied by

는 다음의 수학식 5와 같이 정의하였다. in Equation 4

is defined as in Equation 5 below.

[Equation 5]

에서 발생하는 광음향 신호가 표면 분포 함수

를 갖는 광음향 측정기(200)에 의해 측정되는 값을 나타낸다. 한편, 수학식 5에서 k는 초음파의 파수이다(

). Equation 5 is a point of the light absorber 20

The photoacoustic signal generated from the surface distribution function

represents a value measured by the photoacoustic meter 200 having . Meanwhile, in Equation 5, k is the wave number of ultrasound (

).

에, 정합 필터링 함수

의 컨쥬케이트인

를 곱함으로써 이루어질 수 있다. 따라서, 처리장치(300)에 의해 정합 필터링 처리가 이루어진 최종적인 광음향 스펙트럼은 다음의 수학식 6과 같다. In a typical photoacoustic measurement, matched filtering processing is performed in the frequency domain on the photoacoustic signal measured by the photoacoustic meter 200 , and this matched filtering process may be performed by the processing device 300 . The matched filtering process performed by the processing device 300 is the photoacoustic spectrum measured by Equation (4)

In, the matched filtering function

a conjugate of

This can be done by multiplying Accordingly, the final photoacoustic spectrum subjected to the matched filtering process by the processing device 300 is expressed by the following Equation (6).

[Equation 6]

를 적용해왔으며, 여기서

는 입사빔 스펙트럼으로서, 이는 입사빔의 세기 I(t)를 주파수 영역에서 푸리에 변환한 것이다. For reference, in the conventional frequency domain photoacoustic measurement, the matched filtering function is used for matched filtering.

has been applied, where

is the incident beam spectrum, which is a Fourier transform of the intensity I(t) of the incident beam in the frequency domain.

은 광음향 측정기(200)의 모양 및 광 흡수체(20)의 모양에 따라 결정되는 공간적 광음향 스펙트럼을 의미하며, 이하에서는 이를

로 정의하기로 한다. In Equation 6, the square bracket part

denotes a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter 200 and the shape of the light absorber 20 , which

to be defined as

는 다음의 수학식 7과 같이 나타낼 수 있다. Ideal optoacoustic spectrum without matched filtered noise

can be expressed as in Equation 7 below.

[Equation 7]

은 다음의 수학식 8과 같이 나타낼 수 있다. On the other hand, in photoacoustic measurement, optoacoustic noise such as optoacoustic thermal noise always exists, and this matched-filtered optoacoustic noise spectrum

can be expressed as in Equation 8 below.

[Equation 8]

는 광음향 잡음 스펙트럼이며,

는 정합 필터링 함수이다. in Equation 8

is the optoacoustic noise spectrum,

is the matched filtering function.

By Equation 7 and Equation 8, the signal-to-noise ratio of the photoacoustic signal measured by the photoacoustic meter 200 can be expressed as Equation 9 below.

[Equation 9]

In Equation 9, the numerator means the maximum value of the ideal optoacoustic signal in the frequency domain, and the denominator represents the time average of the optoacoustic noise in the frequency domain (ie, dispersion of the optoacoustic noise value).

의 특성은 광음향 측정기(200)가 압전(piezo) 물질로 광음향을 측정하는 타입인 경우, KLM(KrimholtLeedom Matthaei) 모델로 잘 묘사된다고 알려져 있다. 이 KLM 모델에 의해 중심 주파수가 3MHz인 광음향 측정기(200)의 전달함수

가 도 2에 나타나 있다. 도 2에서 Re[

]는 전달함수의 실수부, Im[

]는 전달함수의 허수부이며,

는 전달함수의 크기이다. On the other hand, in Equation 7, the transfer function of the photoacoustic meter 200

It is known that when the photoacoustic meter 200 is a type that measures photoacoustic with a piezo material, it is well described by a KrimholtLeedom Matthaei (KLM) model. The transfer function of the photoacoustic meter 200 with a center frequency of 3 MHz by this KLM model

is shown in FIG. 2 . In Figure 2 Re[

] is the real part of the transfer function, Im[

] is the imaginary part of the transfer function,

is the size of the transfer function.

의 크기

와

의 실수부 Re[

]가 도 3에 나타나 있다. 도 3에 나타낸

의 실수부 Re[

]는

가 광음향 측정기(200)의 초점 거리에 해당하는 위상이 더해지므로 빠르게 진동한다는 것을 보여준다. In addition, a spherical light absorber 20 having a radius of 2 mm was measured with a photoacoustic meter 200 having a focal length of 20 mm and a spherical focus with a numerical aperture (NA) of 0.35.

size of

Wow

The real part of Re[

] is shown in FIG. 3 . shown in FIG. 3

The real part of Re[

]Is

It shows that because the phase corresponding to the focal length of the photoacoustic meter 200 is added, it vibrates rapidly.

Meanwhile, the incident beam emitted through the light source 100 and irradiated to the light diffusion medium 10 may be a chirp signal as shown in Equation 10 below.

[Equation 10]

는 처프신호의 세기, F_FD는 처프신호의 광 방사 노광량(radiant exposure), T는 처프신호의 선폭(duration), ν_c는 처프신호의 중심 주파수, b는 처프신호의 선형 주파수 증가율, t는 시간, 그리고

는 선폭이 T인 구형 함수를 나타낸다. in Equation 10

is the intensity of the chirp signal, F _FD is the radiant exposure of the chirp signal, T is the duration _{of the chirp signal, ν c} is the center frequency of the chirp signal, b is the linear frequency increase rate of the chirp signal, and t is time, and

denotes a spherical function with line width T.

4A and 4B are graphs exemplarily illustrating a _{chirp signal I c (t) having a center frequency ν c} of 3 MHz and a bandwidth bT of 4 MHz of the chirped signal emitted through the light source 100 . In FIG. 4A, the x-axis represents time, the y-axis represents frequency, and the slope represents the linear frequency increase rate b of the chirp signal. In FIG. 4B , the x-axis represents time, and the y-axis represents the intensity of the chirp signal. And in FIGS. 4A and 4B, T represents the line width of the chirp signal. 4A and 4B schematically show a chirped signal whose frequency is gradually increased and an envelope is constant during the line width T. As shown in FIG.

In Equation (10), the amount of light radiation exposure represents energy of an incident beam (eg, a chirped signal) allowed per unit area. The maximum value of such light radiation exposure is determined according to the maximum permissible exposure for human skin set by the American National Standards Institute (ANSI). For example, the maximum allowable exposure amount F _FD ^{for an incident beam having a line width between 10 -7} and 10 seconds in a wavelength range of 400 to 1400 nm is expressed by Equation 11 below.

[Equation 11]

In Equation 11, the unit of the maximum allowable exposure dose F _FD is [J/m ² ], and C _A is a constant that varies depending on the wavelength. And in Equation 11, T represents the line width of the chirp signal.

를 나타낸 도면이다. 도 5에 나타낸 처프신호 스펙트럼

는 주파수가 0인 DC 부분의 크기가 주파수가 1~5MHz인 부분의 크기에 비해 매우 크기 때문에 y축을 log₁₀ 스케일로 나타내었다. 5 is a chirped signal spectrum that is a result of Fourier transform _{of a chirp signal I c} (t) having a center frequency ν _c shown in FIG. 4 and a bandwidth bT of 4 MHz.

is a diagram showing The chirp signal spectrum shown in FIG. 5

_{shows the y-axis on a log 10} scale because the size of the DC part with frequency 0 is very large compared to the size of the part with a frequency of 1 to 5 MHz.

,

및

를 각각 도 2, 도 3 및 도 5에 나타낸 바로 정하고, 적절한 정합 필터링 함수

를 선택하면, 수학식 7 내지 수학식 9를 계산할 수 있다. 이하의 시뮬레이션에서는 수학식 7의

,

및

를 각각 도 2, 도 3 및 도 5에 나타낸 바로 정하였고, 수학식 8의

은 전체 주파수에서 일정한 백색 가우시안 잡음으로 정하였으며, 그 값을 1×10^-7으로 하였다. of Equation 7

,

and

, respectively, as shown in Figs. 2, 3 and 5, and an appropriate matched filtering function

If is selected, Equations 7 to 9 can be calculated. In the following simulation, Equation 7

,

and

was determined as the bars shown in FIGS. 2, 3 and 5, respectively, and in Equation 8

was set as a constant white Gaussian noise at all frequencies, and the value was set to 1×10 ^-7 .

,

,

및

이 위에서 정한 바와 달라지게 되면 수학식 9에서 나타낸 광음향 신호의 신호 대 잡음비의 계산값은 변할 수 있다. 하지만 이 경우에도 광음향 측정기(200)로 측정되는 광음향 신호의 신호 대 잡음비를 향상시킬 수 있는 본 발명의 기술적 사상은 그대로 적용된다.

,

,

and

If this is different from the above, the calculated value of the signal-to-noise ratio of the photoacoustic signal shown in Equation 9 may change. However, even in this case, the technical idea of the present invention capable of improving the signal-to-noise ratio of the photoacoustic signal measured by the photoacoustic meter 200 is applied as it is.

6 is a flowchart illustrating a method of improving a signal-to-noise ratio of an optoacoustic signal measured by an optoacoustic meter according to the first embodiment of the present invention.

를 광 확산매체(10)에 조사하여 상기 광 확산매체(10)의 내부에 위치하는 광 흡수체(20)에 흡수시키는 단계가 이루어진다(S110). In the method according to the first embodiment of the present invention, first, the chirp signal emitted through the light source 100 is

is irradiated to the light diffusion medium 10 and absorbed by the light absorber 20 positioned inside the light diffusion medium 10 (S110).

는 광 확산매체(10) 내에서 전파 및 확산되면서 광 흡수체(20)에 도달하게 되며, 광 흡수체(20)가 처프신호

를 흡수할 경우에는 광음향 신호를 발생시키게 된다. 여기서, 광원(100)을 통해 방출되는 처프신호

는 도 4b에 나타낸 바와 같이, 시간에 따라 포락선이 일정한 신호일 수 있다. Chirp signal emitted through the light source 100

is propagated and diffused in the light diffusion medium 10 to reach the light absorber 20, and the light absorber 20 generates a chirp signal.

When it is absorbed, a photoacoustic signal is generated. Here, the chirp signal emitted through the light source 100

may be a signal having a constant envelope over time, as shown in FIG. 4B .

Next, the photoacoustic signal generated from the optical absorber 20 due to the chirped signal is measured using the photoacoustic measuring instrument 200 (S120).

The photoacoustic signal measured by the photoacoustic meter 200 includes noise. Accordingly, the processing device 300 connected to the light source 100 and the photoacoustic meter 200 receives the photoacoustic signal measured by the photoacoustic meter 200 and matches the photoacoustic signal in the frequency domain. A matched filtered photoacoustic signal is calculated by performing a filtering process (S130). The signal-to-noise ratio of the photoacoustic signal may be improved by the matched filtering process.

에서 상기 처프신호의 DC 성분을 제거하여 DC 성분이 제거된 처프신호 스펙트럼

을 산출하는 단계(S131)를 포함한다.In the first embodiment of the present invention, in step S130 , the processing device 300 emits a chirp signal through the light source 100 .

The chirp signal spectrum from which the DC component is removed by removing the DC component of the chirp signal in

and calculating ( S131 ).

The processing device 300 is connected to the light source 100 , and accordingly, the processing device 300 can know the shape of the chirp signal emitted through the light source 100 , and furthermore, the chirp signal emitted through the light source 100 . You can also control the signal.

에서 상기 처프신호의 DC 성분을 제거하여 DC 성분이 제거된 처프신호

를 산출하고, 이후 상기 DC 성분이 제거된 처프신호

를 푸리에 변환하여 DC 성분이 제거된 처프신호 스펙트럼

를 산출할 수 있다. The processing device 300 emits a chirp signal through the light source 100 .

The chirp signal from which the DC component is removed by removing the DC component of the chirp signal in

, and then the chirp signal from which the DC component is removed

chirp signal spectrum from which the DC component has been removed by Fourier transform

can be calculated.

를 푸리에 변환하여 처프신호 스펙트럼

를 산출하고, 이후 상기 처프신호 스펙트럼

에서 처프신호

의 DC 성분을 제거하여 처프신호 스펙트럼

를 산출할 수도 있다.Alternatively, the processing device 300 emits a chirp signal through the light source 100 .

chirp signal spectrum by Fourier transform

, and then the chirped signal spectrum

chirp signal from

chirp signal spectrum by removing the DC component of

can also be calculated.

를 이용하여, 주파수 영역에서 상기 광음향 신호의 정합 필터링 처리를 수행한다(S132).After the step S131, the processing device 300 is a chirp signal spectrum from which the DC component is removed.

By using , matched filtering processing of the photoacoustic signal in the frequency domain is performed (S132).

를 통해 광음향 신호의 정합 필터링 처리를 수행함으로써,

를 통해 광음향 신호의 정합 필터링 처리를 수행하던 종래 방법에 비해, 광음향 신호의 신호 대 잡음비를 향상시킬 수 있다. The processing apparatus 300 is connected to the photoacoustic meter 200 , and accordingly, the processing apparatus 300 may obtain a photoacoustic signal measured by the photoacoustic meter 200 . The processing unit 300 is a matched filtering function

By performing matched filtering processing of the photoacoustic signal through

Compared to the conventional method of performing matched filtering of an optoacoustic signal through

를 나타낸 도면이고, 도 7은 도 5에 나타낸 처프신호에서 DC 성분이 제거된 처프신호 스펙트럼

를 나타낸 도면이다. 그리고 도 8은 주파수가 1MHz에서 5MHz까지 변하는 처프신호 I_c(t)가 광 흡수체(20)에 흡수될 경우, 광음향 측정기(200)로 측정되는 광음향 신호를 처리장치(300)가

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다. As described above, FIG. 5 is a chirped signal spectrum resulting from Fourier transform _{of a chirped signal I c (t) having a center frequency ν c} of 3 MHz and a bandwidth bT of 4 MHz.

, and FIG. 7 is a chirped signal spectrum from which the DC component is removed from the chirped signal shown in FIG.

is a diagram showing And FIG. 8 shows that when the chirp signal I _c (t) whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber 20, the processing device 300 processes the photoacoustic signal measured by the photoacoustic meter 200.

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.

는

를 통해 광음향 신호의 정합 필터링 처리를 하여 산출되는 신호 대 잡음비를 평균한 것이고, mean

는

를 통해 광음향 신호의 정합 필터링 처리를 하여 산출되는 신호 대 잡음비를 평균한 것이다. 그리고 도 8에 나타낸 광음향 신호의 신호 대 잡음비는 처리장치(300)가 도 5에 나타낸

및 도 7에 나타낸

각각을 수학식 7과 8에 적용한 뒤, 수학식 7과 8의 결과를 최종적으로 수학식 9에 적용하여 산출된 결과이다. As shown in FIG. 8, in the simulation according to the first embodiment of the present invention, the photoacoustic meter 200 is used while changing the line width of the chirped signal irradiated to the optical diffusion medium 10 within the range of 0.25 to 1.2 msec. Matched filtering of the measured photoacoustic signal was performed. mean in FIG. 8

Is

It is the average of the signal-to-noise ratio calculated by performing matched filtering of the optoacoustic signal through

Is

It is an average of the signal-to-noise ratio calculated by performing matched filtering on the optoacoustic signal. And the signal-to-noise ratio of the photoacoustic signal shown in FIG. 8 is the processing device 300 shown in FIG.

and shown in FIG.

After applying each of Equations 7 and 8, the results of Equations 7 and 8 are finally applied to Equation 9 to obtain a calculated result.

를 통해 광음향 신호의 정합 필터링 처리를 수행할 경우에는,

를 통해 광음향 신호의 정합 필터링 처리를 수행하던 종래의 경우에 비해, 광음향 신호의 신호 대 잡음비가 대폭 향상된다는 것을 확인할 수 있다. As can be seen in FIG. 8 , the processing unit 300 performs a matched filtering function

In the case of performing matched filtering processing of the photoacoustic signal through

It can be seen that the signal-to-noise ratio of the optoacoustic signal is significantly improved compared to the conventional case in which the matched filtering process of the optoacoustic signal is performed.

및

에서는 DC 부분이 0에 매우 근접하다. 따라서, 광 확산매체(10)에 조사되는 처프신호 I_c(t)의 DC 부분은 수학식 7에 나타낸 잡음이 없는 이상적인 광음향 스펙트럼

에 기여하지 않는다. 이는 곧 처프신호 I_c(t)의 DC 부분은 수학식 8의 광음향 잡음 스펙트럼

에만 주로 기여하게 되는 것을 의미하고, 이것이 광음향 측정기(200)로 측정되는 광음향 신호의 신호 대 잡음비를 저하시키는 요인이 된다. As shown in Figures 2 and 3,

and

In , the DC part is very close to zero. _{Therefore, the DC portion of the chirped signal I c} (t) irradiated to the optical diffusion medium 10 is the noise-free ideal photoacoustic spectrum shown in Equation (7).

does not contribute to This means that _{the DC part of the chirp signal I c} (t) is the photoacoustic noise spectrum of Equation 8.

This means that it mainly contributes only to the .

에만 기여하는 것을 차단하게 되어, 도 8과 같이 광음향 신호의 신호 대 잡음비가 향상되게 된다. As shown in FIG. 7, when the DC component of the chirped signal is removed in the matched filtering process of the photoacoustic signal in the frequency domain, the DC component of the chirped signal is matched filtered optoacoustic noise spectrum.

As shown in FIG. 8, the signal-to-noise ratio of the optoacoustic signal is improved.

및

로 각각 정합 필터링 처리를 수행하였을 때 획득되는 노이즈가 포함된 광음향 신호 파형을 나타낸 도면이다. 9 shows that when a chirp signal having a line width T = 1 msec and a frequency of 1 MHz to 5 MHz is absorbed by the optical absorber 20, the processing device 300 processes the photoacoustic signal measured by the photoacoustic meter 200.

and

It is a diagram showing a photoacoustic signal waveform including noise obtained when each matched filtering process is performed.

를 통해 광음향 신호의 정합 필터링 처리를 수행할 경우에는,

를 통해 광음향 신호의 정합 필터링 처리를 수행하던 종래의 경우에 비해, 광음향 신호의 신호 대 잡음비가 향상된다는 것을 확인할 수 있다. As can be seen from FIG. 9 , the processing unit 300 performs a matched filtering function

In the case of performing matched filtering processing of the photoacoustic signal through

It can be confirmed that the signal-to-noise ratio of the photoacoustic signal is improved compared to the conventional case in which the matched filtering process of the photoacoustic signal is performed.

10 is a flowchart illustrating a method of improving a signal-to-noise ratio of an optoacoustic signal measured by an optoacoustic meter according to a second embodiment of the present invention.

를 광 확산매체(10)에 조사하여 상기 광 확산매체(10)의 내부에 위치하는 광 흡수체(20)에 흡수시키는 단계가 이루어진다(S210). In the method according to the second embodiment of the present invention, first, the chirp signal emitted through the light source 100 is

is irradiated to the light diffusion medium 10 and absorbed by the light absorber 20 positioned inside the light diffusion medium 10 (S210).

는 광 확산매체(10) 내에서 전파 및 확산되면서 광 흡수체(20)에 도달하게 되며, 광 흡수체(20)가 처프신호

를 흡수할 경우에는 광음향 신호를 발생시키게 된다. 여기서, 광원(100)을 통해 방출되는 처프신호

는 도 4b에 나타낸 바와 같이, 시간에 따라 포락선이 일정한 신호일 수 있다. Chirp signal emitted through the light source 100

is propagated and diffused in the light diffusion medium 10 to reach the light absorber 20, and the light absorber 20 generates a chirp signal.

When it is absorbed, a photoacoustic signal is generated. Here, the chirp signal emitted through the light source 100

may be a signal having a constant envelope over time, as shown in FIG. 4B .

Next, the photoacoustic signal generated from the optical absorber 20 due to the chirped signal is measured using the photoacoustic meter 200 (S220).

The photoacoustic signal measured by the photoacoustic meter 200 includes noise. Accordingly, the processing device 300 connected to the light source 100 and the photoacoustic meter 200 receives the photoacoustic signal measured by the photoacoustic meter 200 and matches the photoacoustic signal in the frequency domain. A matched-filtered photoacoustic signal is calculated by performing a filtering process (S230). The signal-to-noise ratio of the photoacoustic signal may be improved by the matched filtering process.

를 이용하여 처프신호 스펙트럼을 산출하는 단계(S231)를 포함한다. In the second embodiment of the present invention, in step S230 , the processing device 300 emits a chirp signal through the light source 100 .

and calculating a chirp signal spectrum by using (S231).

를 푸리에 변환하여 처프신호 스펙트럼

를 산출할 수 있다. 상술한 바와 같이, 처리장치(300)는 광원(100)과 연결되어 있기 때문에, 처리장치(300)는 광원(100)을 통해 방출되는 처프신호의 형태를 알 수 있고, 나아가 광원(100)을 통해 방출되는 처프신호를 제어할 수도 있다. 이와 같이, 처리장치(300)가 광원(100)을 통해 방출되는 처프신호의 형태를 알 수 있기 때문에, 처리장치(300)는 처프신호

로부터 처프신호 스펙트럼

를 산출할 수 있다.In step S231 , the processing device 300 emits a chirp signal through the light source 100 .

chirp signal spectrum by Fourier transform

can be calculated. As described above, since the processing device 300 is connected to the light source 100 , the processing device 300 can know the shape of the chirp signal emitted through the light source 100 , and furthermore, the light source 100 . It is also possible to control the chirp signal emitted through the In this way, since the processing device 300 can know the shape of the chirp signal emitted through the light source 100 , the processing device 300 generates the chirp signal

chirp signal spectrum from

can be calculated.

에서 상기 처프신호의 DC 성분을 제거하여 DC 성분이 제거된 처프신호 스펙트럼

를 산출할 수도 있다.Alternatively, in step S231, the chirp signal emitted through the light source 100

The chirp signal spectrum from which the DC component is removed by removing the DC component of the chirp signal in

can also be calculated.

에서 상기 처프신호의 DC 성분을 제거하여 DC 성분이 제거된 처프신호

를 산출하고, 이후 상기 DC 성분이 제거된 처프신호

를 푸리에 변환하여 DC 성분이 제거된 처프신호 스펙트럼

를 산출할 수 있다. Since the processing device 300 can know the shape of the chirp signal emitted through the light source 100 , the processing device 300 detects the chirp signal emitted through the light source 100 .

The chirp signal from which the DC component is removed by removing the DC component of the chirp signal in

, and then the chirp signal from which the DC component is removed

chirp signal spectrum from which the DC component has been removed by Fourier transform

can be calculated.

를 푸리에 변환하여 처프신호 스펙트럼

를 산출하고, 이후 상기 처프신호 스펙트럼

에서 처프신호

의 DC 성분을 제거하여 처프신호 스펙트럼

를 산출할 수도 있다. Alternatively, the processing device 300 emits a chirp signal through the light source 100 .

chirp signal spectrum by Fourier transform

, and then the chirped signal spectrum

chirp signal from

chirp signal spectrum by removing the DC component of

can also be calculated.

와, 광음향 측정기(200)의 모양 및 광 흡수체(20)의 모양에 따라 결정되는 공간적 광음향 스펙트럼

중 적어도 어느 하나를, 상기 S231 단계에서 산출한 처프신호 스펙트럼에 곱한 값을 이용하여, 광음향 신호의 정합 필터링 처리를 수행한다(S232).After the step S231 , the processing device 300 performs the transfer function of the photoacoustic meter 200 .

and a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter 200 and the shape of the light absorber 20 .

Matched filtering of the photoacoustic signal is performed using at least one of the values multiplied by the chirp signal spectrum calculated in step S231 (S232).

와, 광음향 측정기(200)의 모양 및 광 흡수체(20)의 모양에 따라 결정되는 공간적 광음향 스펙트럼

중 적어도 어느 하나를 유추할 수 있을 경우에 적용된다. 즉, 처리장치(300) 내에는 광음향 측정기(200)의 전달함수

및 공간적 광음향 스펙트럼

중 적어도 어느 하나가 저장되어 있을 수 있다. Since the processing device 300 is connected to the photoacoustic meter 200 , it is possible to obtain a photoacoustic signal measured by the photoacoustic meter 200 . In addition, in the second embodiment of the present invention, the processing device 300 is a transfer function of the photoacoustic meter 200 .

and a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter 200 and the shape of the light absorber 20 .

It is applied when at least one of them can be inferred. That is, the transfer function of the photoacoustic meter 200 in the processing device 300 .

and spatial optoacoustic spectrum

At least one of them may be stored.

와, 광음향 측정기(200)의 모양 및 광 흡수체(20)의 모양에 따라 결정되는 공간적 광음향 스펙트럼

의 곱에 절대값을 취한 스펙트럼을 나타낸 도면이다. 보다 구체적으로, 도 11에 나타낸 스펙트럼

은 도 2에 나타낸

와 도 3에 나타낸

의 곱에 절대값을 취한 것이다. 11 is a transfer function of the photoacoustic meter 200

and a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter 200 and the shape of the light absorber 20 .

It is a diagram showing the spectrum obtained by taking the absolute value of the product of . More specifically, the spectrum shown in FIG. 11

is shown in Figure 2

and shown in Figure 3

is the absolute value of the product of

에 가까운 어떤 함수

가 있다고 가정했을 때, 종래의 정합 필터링 함수

를

와 같이 변형하고, 상기 정합 필터링 함수

를 통해 광음향 측정기(200)로 측정되는 광음향 신호의 정합 필터링 처리를 수행하면, 상기 광음향 신호의 신호 대 잡음비를 향상시킬 수 있다. 보다 구체적으로는, 이하의 시뮬레이션 결과에서 알 수 있듯이, 정합 필터링 함수

에서

가 스펙트럼

에 점점 더 가까워질수록 광음향 신호의 신호 대 잡음비는 더 향상될 수 있다. if spectrum

any function close to

Assuming that there is a conventional matched filtering function

cast

Transform as , and the matched filtering function

If the matched filtering process of the photoacoustic signal measured by the photoacoustic meter 200 is performed through , the signal-to-noise ratio of the photoacoustic signal can be improved. More specifically, as can be seen from the simulation results below, the matched filtering function

at

autumn spectrum

As it gets closer to , the signal-to-noise ratio of the optoacoustic signal may be further improved.

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다. 12 shows that when a chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber 20, the processing device 300 processes the photoacoustic signal measured by the photoacoustic meter 200.

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.

,

,

의 순서대로 스펙트럼

에 점점 더 가까워지는 것이 명백하다. 따라서, 처리장치(300)가 광음향 측정기(200)로 측정되는 광음향 신호를 주파수 영역에서 정합 필터링 처리를 수행할 경우,

,

,

의 순서대로 광음향 신호의 신호 대 잡음비를 향상시킬 수 있게 된다. 또한, 도 12에 나타낸 어떤 경우에도,

를 통해 광음향 신호의 정합 필터링 처리를 수행하던 종래의 경우에 비해, 광음향 신호의 신호 대 잡음비가 향상된다는 것을 확인할 수 있다.The spectra shown in Fig. 12 are

,

,

spectrum in the order of

It is clear that it is getting closer and closer to Therefore, when the processing device 300 performs matched filtering processing on the photoacoustic signal measured by the photoacoustic meter 200 in the frequency domain,

,

,

It is possible to improve the signal-to-noise ratio of the optoacoustic signal in the order of . In addition, in any case shown in Fig. 12,

It can be confirmed that the signal-to-noise ratio of the photoacoustic signal is improved compared to the conventional case in which the matched filtering process of the photoacoustic signal is performed.

대신

를 이용하여도 도 12와 동일한 결과가 도출된다. 이는 도 2에 나타낸 바와 같이, 광음향 측정기(200)의 전달함수

의 DC 부분이 0에 매우 근접하기 때문이다. 즉, 처리장치(300)가 광음향 측정기(200)로 측정되는 광음향 신호를 주파수 영역에서 정합 필터링 처리를 수행할 경우,

,

,

의 순서대로 광음향 신호의 신호 대 잡음비를 향상시킬 수 있게 된다. Additionally,

instead

The same result as in FIG. 12 is derived even by using . As shown in FIG. 2 , this is the transfer function of the photoacoustic meter 200 .

This is because the DC part of is very close to zero. That is, when the processing device 300 performs matched filtering processing on the photoacoustic signal measured by the photoacoustic meter 200 in the frequency domain,

,

,

It is possible to improve the signal-to-noise ratio of the optoacoustic signal in the order of .

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다. 13 shows that when a chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.

,

,

의 순서대로 스펙트럼

에 점점 더 가까워지는 것이 명백하다. 따라서, 처리장치(300)가 광음향 측정기(200)로 측정되는 광음향 신호를 주파수 영역에서 정합 필터링 처리를 수행할 경우,

,

,

의 순서대로 광음향 신호의 신호 대 잡음비를 향상시킬 수 있게 된다. 또한, 도 13에 나타낸 어떤 경우에도,

를 통해 광음향 신호의 정합 필터링 처리를 수행하던 종래의 경우에 비해, 광음향 신호의 신호 대 잡음비가 향상된다는 것을 확인할 수 있다. The spectra shown in Fig. 13 are

,

,

spectrum in the order of

It is clear that it is getting closer and closer to Therefore, when the processing device 300 performs matched filtering processing on the photoacoustic signal measured by the photoacoustic meter 200 in the frequency domain,

,

,

It is possible to improve the signal-to-noise ratio of the optoacoustic signal in the order of . In addition, in any case shown in Fig. 13,

It can be confirmed that the signal-to-noise ratio of the photoacoustic signal is improved compared to the conventional case in which the matched filtering process of the photoacoustic signal is performed.

대신

를 이용하여도 도 13과 동일한 결과가 도출된다. 이는 도 2 및 도 3에 나타낸 바와 같이, 광음향 측정기(200)의 전달함수

의 DC 부분, 그리고 공간적 광음향 스펙트럼

의 DC 부분이 0에 매우 근접하기 때문이다. 즉, 처리장치(300)가 광음향 측정기(200)로 측정되는 광음향 신호를 주파수 영역에서 정합 필터링 처리를 수행할 경우,

,

,

의 순서대로 광음향 신호의 신호 대 잡음비를 향상시킬 수 있게 된다. Additionally, in FIG. 13

instead

The same result as in FIG. 13 is derived even by using . This is the transfer function of the photoacoustic meter 200 as shown in FIGS. 2 and 3 .

The DC portion of the, and spatial optoacoustic spectrum

This is because the DC part of is very close to zero. That is, when the processing device 300 performs matched filtering processing on the photoacoustic signal measured by the photoacoustic meter 200 in the frequency domain,

,

,

It is possible to improve the signal-to-noise ratio of the optoacoustic signal in the order of .

14 is a flowchart illustrating a method of improving a signal-to-noise ratio of an optoacoustic signal measured by an optoacoustic meter according to a third embodiment of the present invention.

In the method according to the third embodiment of the present invention, first, the optical diffusion medium 10 is irradiated with a modulated chirp signal emitted through the light source 100 , and the light absorber 20 positioned inside the optical diffusion medium 10 . ) is absorbed in (S310).

Previously, in the method according to the first and second embodiments of the present invention, the envelope of the chirp signal emitted through the light source 100 was constant with time, but in the method according to the third embodiment of the present invention, in the method according to the third embodiment of the present invention, the light source The envelope of the modulated chirp signal emitted through (100) changes with time. In the third embodiment of the present invention _{, instead of the chirp signal I c} (t) whose envelope is constant with time, the modulated chirp signal I _m (t) whose envelope changes with time is emitted through the light source 100 through the light diffusion medium ( _{10), and then the modulated chirp signal I m} (t) is also used when the processing device 300 performs matched filtering processing on the photoacoustic signal measured by the photoacoustic meter 200 in the frequency domain.

에 가까운 어떤 함수

가 있다고 가정했을 때, 시간에 따라 포락선이 일정한 처프신호 I_c(t)를

를 토대로 변조시켜 광 흡수체(20)에 흡수시키고, 이후 처리장치(300)가 광음향 측정기(200)에 의해 측정되는 광음향 신호를 주파수 영역에서 정합 필터링 처리를 수행함으로써, 상기 광음향 신호의 신호 대 잡음비를 향상시킬 수 있다. spectrum

any function close to

Assuming that there is a chirp signal I _c (t) whose envelope is constant with time,

The signal of the photoacoustic signal is modulated and absorbed by the optical absorber 20 based on The noise-to-noise ratio can be improved.

를 토대로 변조시키는 일례이다.Next, the processing device 300 generates a chirp signal I _c (t) with a constant envelope over time.

This is an example of modulation based on

를 산출하고,

에

를 곱하여 다음의 수학식 12와 같은 결과를 산출한다.As a first step, a Fourier transform of a chirped signal having a constant envelope over time, for example, a chirped signal I _{c (t) according to Equation 10,}

to calculate,

to

multiplied by to yield a result as in Equation 12 below.

[Equation 12]

를 역푸리에 변환하여, 그 결과값인

를 산출한다.As step 2,

is an inverse Fourier transform, and the result is

to calculate

에

의 포락선을 더해서 다음의 수학식 13과 같은 결과를 산출한다. As step 3,

to

A result as shown in Equation 13 is calculated by adding the envelope of .

[Equation 13]

In Equation 13, i is an imaginary sign, t is time, and * denotes convolution.

의 단위 면적당 에너지를 수학식 11과 같이 미국 국립 표준 협회(ANSI)에서 정한 광 방사 노광량으로 정하기 위해, 다음의 수학식 14와 같은 계산을 통해, 시간에 따라 포락선이 변하는 변조 처프신호 I_m(t)를 산출한다. As step 4,

In order to determine the energy per unit area of , as the light radiation exposure dose determined by the American National Standards Institute (ANSI) as shown in Equation 11, the modulation chirp signal I _m (t ) is calculated.

[Equation 14]

의 형태로 나타내기로 한다. 여기서, 변조 처프신호를

의 형태로 나타내는 것은, 시간에 따라 포락선이 일정한 처프신호 I_c(t)가 스펙트럼

에 의해 포락선이 변조되었음을 강조하기 위함이다. Hereinafter, the modulated chirp signal calculated through the above steps is used instead _{of I m (t)}

to be expressed in the form of Here, the modulated chirp signal is

In the form of , the chirped signal I _c (t) with a constant envelope over time is the spectrum

This is to emphasize that the envelope has been modulated by

와, 광음향 측정기(200)의 모양 및 광 흡수체(20)의 모양에 따라 결정되는 공간적 광음향 스펙트럼

중 적어도 어느 하나 이상을 이용하여 변조시킬 수 있다. The processing device 300 transmits a chirp signal I _c (t) having a constant envelope over time, and a transfer function of the photoacoustic meter 200 .

and a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter 200 and the shape of the light absorber 20 .

It may be modulated using at least one or more of

만을 가지고 처프신호 I_c(t)를 변조시킬 경우(즉,

인 경우), 변조 처프신호는

의 형태로 나타낼 수 있다. 처리장치(300)가 공간적 광음향 스펙트럼

만을 가지고 처프신호 I_c(t)를 변조시킬 경우(즉,

인 경우), 변조 처프신호는

의 형태로 나타낼 수 있다. 또한, 처리장치(300)가 광음향 측정기(200)의 전달함수

및 공간적 광음향 스펙트럼

의 곱을 가지고 상기 처프신호 I_c(t)를 변조시킬 경우(즉,

인 경우), 변조 처프신호는

의 형태로 나타낼 수 있다. 참고로,

의 스펙트럼 크기가 일정한 함수라면

는

가 된다. The processing device 300 is a transfer function of the photoacoustic meter 200 .

When modulating the chirp signal I _c (t) with only

), the modulated chirp signal is

can be expressed in the form of The processing device 300 is a spatial photoacoustic spectrum

When modulating the chirp signal I _c (t) with only

), the modulated chirp signal is

can be expressed in the form of In addition, the processing device 300 is a transfer function of the photoacoustic meter 200 .

and spatial optoacoustic spectrum

When modulating the chirp signal I _c (t) with the product of

), the modulated chirp signal is

can be expressed in the form of Note that,

If the spectral magnitude of is a constant function

Is

becomes

를 예시적으로 나타낸 그래프이다. 도 15에 의하면, 시간에 따라 포락선이 일정한 처프신호 I_c(t)가 광음향 측정기(200)의 전달함수

및 공간적 광음향 스펙트럼

의 곱에 의해 포락선이 변조된 결과,

의 포락선은 도 11에 나타난 스펙트럼의 형태와 거의 동일함을 알 수 있다. 15 is a modulated chirp signal whose envelope changes with time.

It is a graph showing by way of example. According to FIG. 15 , a chirp signal I _c (t) having a constant envelope over time is a transfer function of the photoacoustic meter 200 .

and spatial optoacoustic spectrum

As a result of modulating the envelope by the product of

It can be seen that the envelope of is almost identical to the shape of the spectrum shown in FIG. 11 .

는 도 4b에 나타낸 처프신호와 동일하게 시간에 따라 주파수가 점점 증가하지만, 도 4b에 나타낸 처프신호와는 달리 시간에 따라 포락선이 변한다는 것을 알 수 있다. FIG. 16A is an enlarged graph of part (a) shown in FIG. 15 , and FIG. 16B is an enlarged graph showing part (b) shown in FIG. 15 . 15, 16A and 16B, the modulated chirp signal

It can be seen that although the frequency gradually increases with time in the same way as the chirp signal shown in FIG. 4B, the envelope changes with time, unlike the chirp signal shown in FIG. 4B.

가 광 확산매체(10)에 조사될 경우, 상기 광 확산매체(10)의 내부에 위치하는 광 흡수체(20)에서는 광음향 신호를 발생시키게 된다. In step S310, the modulated chirp signal emitted through the light source 100

is irradiated to the optical diffusion medium 10 , the optical absorber 20 positioned inside the optical diffusion medium 10 generates a photoacoustic signal.

로 인해 광 흡수체(20)에서 발생하는 광음향 신호를 측정한다(S320).After the step S310, the modulated chirp signal using the photoacoustic meter 200

Therefore, a photoacoustic signal generated from the light absorber 20 is measured (S320).

The photoacoustic signal measured by the photoacoustic meter 200 includes noise. Accordingly, the processing device 300 connected to the light source 100 and the photoacoustic meter 200 receives the photoacoustic signal measured by the photoacoustic meter 200 and matches the photoacoustic signal in the frequency domain. A matched filtered photoacoustic signal is calculated by performing a filtering process (S330). The signal-to-noise ratio of the photoacoustic signal may be improved by the matched filtering process.

를 푸리에 변환하여 변조 처프신호 스펙트럼

를 산출하는 단계(S331)를 포함할 수 있다. In the third embodiment of the present invention, in step S330 , the processing device 300 emits a modulated chirp signal through the light source 100 .

Modulated chirped signal spectrum by Fourier transform

It may include a step of calculating (S331).

로부터 변조 처프신호 스펙트럼

를 산출할 수 있다.Since the processing device 300 is connected to the light source 100 , the processing device 300 can know the shape of the modulated chirp signal emitted through the light source 100 , and furthermore, the modulated chirp signal emitted through the light source 100 . It is also possible to control the chirp signal. In this way, since the processing device 300 can know the shape of the modulated chirped signal, the processing device 300 generates the modulated chirp signal.

Modulated chirp signal spectrum from

can be calculated.

를 이용하여, 광음향 측정기(200)로 측정되는 광음향 신호의 정합 필터링 처리를 수행하는 단계(S332)가 이루어질 수 있다. After the step S331, the processing device 300 is the modulated chirp signal spectrum

A step ( S332 ) of performing matched filtering processing on the photoacoustic signal measured by the photoacoustic meter 200 may be performed using .

를 통해 광음향 신호의 정합 필터링 처리를 수행함으로써,

를 통해 광음향 신호의 정합 필터링 처리를 수행하던 종래 방법에 비해, 광음향 신호의 신호 대 잡음비를 향상시킬 수 있다. The processing apparatus 300 is connected to the photoacoustic meter 200 , and accordingly, the processing apparatus 300 may obtain a photoacoustic signal measured by the photoacoustic meter 200 . The processing unit 300 is a matched filtering function

By performing matched filtering processing of the photoacoustic signal through

Compared to the conventional method of performing matched filtering of an optoacoustic signal through

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다. 17 shows that when a modulated chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber 20, the processing device 300 processes the photoacoustic signal measured by the photoacoustic meter 200.

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.

가 각각

,

및

인 경우, 처리장치(300)는 정합 필터링 함수

,

및

를 통해 광음향 신호의 정합 필터링 처리를 수행할 수 있다. As shown in FIG. 17 , the modulated chirp signal emitted through the light source 100 .

are each

,

and

If , the processing unit 300 is a matched filtering function

,

and

Through this, matched filtering processing of the optoacoustic signal can be performed.

가 방출되어 광 흡수체(20)에 흡수되고, 이때 처리장치(300)가 상기 변조 처프신호

를 푸리에 변환하여 산출한 변조 처프신호 스펙트럼

를 통해 광음향 신호의 정합 필터링 처리를 수행할 경우에는,

를 통해 광음향 신호의 정합 필터링 처리를 수행하던 종래의 경우에 비해, 광음향 신호의 신호 대 잡음비가 향상된다. As can be seen from FIG. 17 , the modulated chirp signal through the light source 100

is emitted and absorbed by the light absorber 20, and at this time, the processing device 300 generates the modulated chirp signal.

Modulated chirped signal spectrum calculated by Fourier transform

In the case of performing matched filtering processing of the photoacoustic signal through

The signal-to-noise ratio of the optoacoustic signal is improved compared to the conventional case in which the matched filtering process of the optoacoustic signal is performed.

에서 상기 변조 처프신호의 DC 성분을 제거하여 DC 성분이 제거된 변조 처프신호 스펙트럼

을 산출하는 단계(S333)를 포함할 수 있다. Meanwhile, in the third embodiment of the present invention, in step S330 , the processing device 300 emits a modulated chirp signal through the light source 100 .

The modulated chirp signal spectrum from which the DC component is removed by removing the DC component of the modulated chirp signal in

It may include a step of calculating (S333).

Since the processing device 300 is connected to the light source 100 , it is possible to know the shape of the modulated chirp signal emitted through the light source 100 and further control the modulated chirp signal emitted through the light source 100 . have.

에서 상기 변조 처프신호의 DC 성분을 제거하여 DC 성분이 제거된 변조 처프신호

를 산출하고, 이후 상기 DC 성분이 제거된 변조 처프신호

를 푸리에 변환하여 DC 성분이 제거된 변조 처프신호 스펙트럼

를 산출할 수 있다. The processing device 300 is a modulated chirp signal emitted through the light source 100 .

The modulated chirp signal from which the DC component is removed by removing the DC component of the modulated chirp signal in

, and then the modulated chirp signal from which the DC component is removed.

Modulated chirped signal spectrum from which DC component is removed by Fourier transform

can be calculated.

를 푸리에 변환하여 변조 처프신호 스펙트럼

를 산출하고, 이후 상기 변조 처프신호 스펙트럼

에서 변조 처프신호

의 DC 성분을 제거하여 변조 처프신호 스펙트럼

를 산출할 수도 있다.Alternatively, the processing device 300 is a modulated chirp signal emitted through the light source 100 .

Modulated chirped signal spectrum by Fourier transform

, and then the modulated chirped signal spectrum

Modulated chirp signal from

Modulated chirped signal spectrum by removing the DC component of

can also be calculated.

를 이용하여, 광음향 측정기(200)로 측정되는 광음향 신호의 정합 필터링 처리를 수행한다(S334). After the step S333, the processing device 300 is a modulated chirped signal spectrum from which the DC component is removed.

is used to perform matched filtering of the photoacoustic signal measured by the photoacoustic meter 200 (S334).

를 통해 상기 광음향 신호의 정합 필터링 처리를 수행함으로써,

를 통해 상기 광음향 신호의 정합 필터링 처리를 수행하던 종래 방법에 비해, 상기 광음향 신호의 신호 대 잡음비를 향상시킬 수 있다. The processing apparatus 300 is connected to the photoacoustic meter 200 , and accordingly, the processing apparatus 300 may obtain a photoacoustic signal measured by the photoacoustic meter 200 . The processing unit 300 is a matched filtering function

By performing matched filtering processing of the photoacoustic signal through

Compared to the conventional method of performing matched filtering of the photoacoustic signal through

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다. 18 shows that when a modulated chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device processes the photoacoustic signal measured by the photoacoustic meter.

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.

가 각각

,

및

인 경우, 처리장치(300)는 정합 필터링 함수

,

및

를 통해 광음향 신호의 정합 필터링 처리를 수행할 수 있다. As shown in FIG. 18 , the modulated chirp signal emitted through the light source 100 .

are each

,

and

If , the processing unit 300 is a matched filtering function

,

and

Through this, matched filtering processing of the optoacoustic signal can be performed.

가 방출되어 광 흡수체(20)에 흡수되고, 이때 처리장치(300)가 상기 변조 처프신호

에서 변조 처프신호의 DC 성분을 제거하여 산출한 DC 성분이 제거된 변조 처프신호 스펙트럼

를 통해 광음향 신호의 정합 필터링 처리를 수행할 경우에는,

를 통해 광음향 신호의 정합 필터링 처리를 수행하던 종래의 경우에 비해, 광음향 신호의 신호 대 잡음비가 향상된다. As can be seen from FIG. 18 , the modulated chirp signal through the light source 100

is emitted and absorbed by the light absorber 20, and at this time, the processing device 300 generates the modulated chirp signal.

Spectrum of the modulated chirp signal from which the DC component is removed, calculated by removing the DC component of the modulated chirp signal

In the case of performing matched filtering processing of the photoacoustic signal through

The signal-to-noise ratio of the optoacoustic signal is improved compared to the conventional case in which the matched filtering process of the optoacoustic signal is performed.

를 이용하여 변조 처프신호 스펙트럼을 산출하는 단계(S335)를 포함할 수 있다. Meanwhile, in the third embodiment of the present invention, in step S330 , the processing device 300 emits a modulated chirp signal through the light source 100 .

It may include calculating a spectrum of the modulated chirp signal using (S335).

를 푸리에 변환하여 변조 처프신호 스펙트럼

를 산출할 수 있다. 상술한 바와 같이, 처리장치(300)는 광원(100)과 연결되어 있기 때문에, 처리장치(300)는 광원(100)을 통해 방출되는 변조 처프신호의 형태를 알 수 있고, 나아가 광원(100)을 통해 방출되는 변조 처프신호를 제어할 수도 있다. 이와 같이, 처리장치(300)가 광원(100)을 통해 방출되는 변조 처프신호의 형태를 알 수 있기 때문에, 처리장치(300)는 변조 처프신호

로부터 변조 처프신호 스펙트럼

를 산출할 수 있다. In step S335, the processing device 300 is a modulated chirp signal emitted through the light source 100

Modulated chirped signal spectrum by Fourier transform

can be calculated. As described above, since the processing device 300 is connected to the light source 100 , the processing device 300 can know the shape of the modulated chirp signal emitted through the light source 100 , and furthermore, the light source 100 . It is also possible to control the modulated chirp signal emitted through As such, since the processing device 300 can know the shape of the modulated chirp signal emitted through the light source 100 , the processing device 300 generates the modulated chirp signal.

Modulated chirp signal spectrum from

can be calculated.

에서 상기 변조 처프신호의 DC 성분을 제거하여 DC 성분이 제거된 변조 처프신호 스펙트럼

를 산출할 수도 있다. Alternatively, in step S335, the modulated chirp signal emitted through the light source 100

The modulated chirp signal spectrum from which the DC component is removed by removing the DC component of the modulated chirp signal in

can also be calculated.

에서 상기 변조 처프신호의 DC 성분을 제거하여 DC 성분이 제거된 변조 처프신호

를 산출하고, 이후 상기 DC 성분이 제거된 변조 처프신호

를 푸리에 변환하여 DC 성분이 제거된 처프신호 스펙트럼

를 산출할 수 있다.The processing device 300 is a modulated chirp signal emitted through the light source 100 .

The modulated chirp signal from which the DC component is removed by removing the DC component of the modulated chirp signal in

, and then the modulated chirp signal from which the DC component is removed.

chirp signal spectrum from which the DC component has been removed by Fourier transform

can be calculated.

를 푸리에 변환하여 변조 처프신호 스펙트럼

를 산출하고, 이후 상기 변조 처프신호 스펙트럼

에서 처프신호

의 DC 성분을 제거하여 변조 처프신호 스펙트럼

를 산출할 수도 있다. Alternatively, the processing device 300 is a modulated chirp signal emitted through the light source 100 .

Modulated chirped signal spectrum by Fourier transform

, and then the modulated chirped signal spectrum

chirp signal from

Modulated chirped signal spectrum by removing the DC component of

can also be calculated.

와, 광음향 측정기(200)의 모양 및 광 흡수체(20)의 모양에 따라 결정되는 공간적 광음향 스펙트럼

중 적어도 어느 하나를, 상기 S335 단계에서 산출한 변조 처프신호 스펙트럼에 곱한 값을 이용하여, 광음향 신호의 정합 필터링 처리를 수행한다(S336). After the step S335, the processing device 300 is the transfer function of the photoacoustic meter 200

and a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter 200 and the shape of the light absorber 20 .

Matched filtering of the photoacoustic signal is performed using at least one of the values multiplied by the modulated chirped signal spectrum calculated in step S335 (S336).

및 공간적 광음향 스펙트럼

중 적어도 어느 하나가 저장되어 있을 수 있다. 이에 따라, 처리장치(300)는 정합 필터링 함수

를 통해 광음향 신호의 정합 필터링 처리를 수행할 수 있다. 도 11에 관해 상술한 바와 마찬가지로, 이 경우에도 상기 정합 필터링 함수

에서

및

는 각각

의 스펙트럼에 더 가까워질수록 광음향 신호의 신호 대 잡음비는 더 향상될 수 있다. Since the processing device 300 is connected to the photoacoustic meter 200 , it is possible to obtain a photoacoustic signal measured by the photoacoustic meter 200 . In addition, in the processing device 300, the transfer function of the photoacoustic meter 200

and spatial optoacoustic spectrum

At least one of them may be stored. Accordingly, the processing device 300 is a matched filtering function

Through this, matched filtering processing of the optoacoustic signal can be performed. As described above with respect to FIG. 11 , in this case as well, the matched filtering function

at

and

are each

As it gets closer to the spectrum of the optoacoustic signal, the signal-to-noise ratio of the optoacoustic signal can be further improved.

,

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다. 도 19에서 알 수 있듯이,

및

이 각각

의 스펙트럼에 더 가까울수록 광음향 신호의 신호 대 잡음비가 향상될 수 있다. 19 shows that when a modulated chirp signal whose frequency is changed from 1 MHz to 5 MHz is absorbed by the optical absorber, the processing device 300 processes the photoacoustic signal measured by the photoacoustic meter 200.

,

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed. As can be seen in Figure 19,

and

each of these

The closer to the spectrum of , the better the signal-to-noise ratio of the optoacoustic signal.

를 통해 광음향 신호의 정합 필터링 처리를 수행함으로써,

를 통해 상기 광음향 신호의 정합 필터링 처리를 수행하던 종래 방법에 비해, 상기 광음향 신호의 신호 대 잡음비를 향상시킬 수 있다. In addition, as can be seen in FIGS. 8 and 19 , the processing unit 300 performs the matched filtering function

By performing matched filtering processing of the photoacoustic signal through

Compared to the conventional method of performing matched filtering of the photoacoustic signal through

에서

대신

를 이용하여도 도 19와 동일한 결과가 도출된다. 이는 도 2 및 도 3에 나타낸 바와 같이, 광음향 측정기(200)의 전달함수

의 DC 부분, 그리고 공간적 광음향 스펙트럼

의 DC 부분이 0에 매우 근접하기 때문이다.Additionally,

at

instead

The same result as in FIG. 19 is derived even by using . This is the transfer function of the photoacoustic meter 200 as shown in FIGS. 2 and 3 .

The DC portion of the, and spatial optoacoustic spectrum

This is because the DC part of is very close to zero.

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다. On the other hand, FIG. 20 shows that when a modulated chirp signal whose frequency varies from 1.5 MHz to 4 MHz is absorbed by the optical absorber 20 , the processing device 300 processes the photoacoustic signal measured by the photoacoustic meter 200 .

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.

The matched filtering functions shown in FIG. 20 are the same as the matched filtering functions shown in FIG. 18 . However, in FIG. 18, the modulated chirp signal whose frequency varies from 1 MHz to 5 MHz is emitted through the light source 100 and absorbed by the light absorber 20, whereas in FIG. 20, the modulated chirped signal whose frequency varies from 1.5 MHz to 4 MHz. is emitted through the light source 100 and absorbed by the light absorber 20 .

Comparing FIGS. 18 and 20 , the signal-to-noise ratio of the optoacoustic signal is compared with the case where the modulation chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber 20, the modulation chirp whose frequency varies from 1.5 MHz to 4 MHz. It can be seen that the case where the signal is absorbed by the light absorber 20 is further improved.

,

,

및

로 각각 정합 필터링 처리를 수행하였을 때 산출되는 정합 필터링된 광음향 신호의 신호 대 잡음비를 나타낸 도면이다. As another example, FIG. 21 shows that when a modulated chirp signal whose frequency varies from 1.5 MHz to 4 MHz is absorbed by the optical absorber 20, the processing device 300 processes the photoacoustic signal measured by the photoacoustic meter 200.

,

,

and

It is a diagram showing the signal-to-noise ratio of the matched-filtered optoacoustic signal calculated when each matched filtering process is performed.

The matched filtering functions shown in FIG. 21 are the same as the matched filtering functions shown in FIG. 19 . However, in FIG. 19, the modulated chirp signal whose frequency varies from 1 MHz to 5 MHz is emitted through the light source 100 and absorbed by the light absorber 20, whereas in FIG. 21, the modulated chirp signal whose frequency varies from 1.5 MHz to 4 MHz is emitted through the light source 100 and absorbed by the light absorber 20 .

19 and 21, the signal-to-noise ratio of the optoacoustic signal is compared to the case where the modulation chirp signal whose frequency varies from 1 MHz to 5 MHz is absorbed by the optical absorber 20 It can be seen that the case where the signal is absorbed by the light absorber 20 is further improved.

와, 광음향 측정기(200)의 모양 및 광 흡수체(20)의 모양에 따라 결정되는 공간적 광음향 스펙트럼

과 밀접한 관련이 있다. 즉, 도 11에 의하면, 광음향 측정기(200)의 전달함수

와 공간적 광음향 스펙트럼

를 곱한 값의 절대값이 최대가 되는 주파수는 약 2.5MHz이며, 이때 광원(100)을 통해 방출되는 변조 처프신호의 주파수 범위가 약 2.5MHz를 중심으로 해서 보다 더 협소한 범위로 설정될수록 광음향 신호의 신호 대 잡음비가 향상될 수 있게 된다. The frequency range of the modulated chirp signal absorbed by the optical absorber 20 is a transfer function of the photoacoustic meter 200 .

and a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter 200 and the shape of the light absorber 20 .

is closely related to That is, according to FIG. 11 , the transfer function of the photoacoustic meter 200 is

and spatial optoacoustic spectrum

The frequency at which the absolute value of the multiplied value becomes the maximum is about 2.5 MHz. At this time, as the frequency range of the modulated chirp signal emitted through the light source 100 is set to a narrower range centered on about 2.5 MHz, the more optoacoustic The signal-to-noise ratio of the signal can be improved.

와 공간적 광음향 스펙트럼

를 곱한 값의 절대값이 최대가 되는 주파수를 포함하지 않을 경우에는 광음향 신호의 신호 대 잡음비가 낮아지게 된다는 것을 의미한다. In other words, the frequency range of the modulated chirp signal emitted through the light source 100 is the transfer function of the photoacoustic meter 200 .

and spatial optoacoustic spectrum

If the absolute value of the multiplied value does not include the maximum frequency, it means that the signal-to-noise ratio of the photoacoustic signal is lowered.

와 공간적 광음향 스펙트럼

를 곱한 값의 절대값이 최대가 되는 주파수를 포함하는 것이 광음향 신호의 신호 대 잡음비를 향상시키는데 있어서 유리하다. Therefore, the frequency range of the modulated chirp signal emitted through the light source 100 is the transfer function of the photoacoustic meter 200 .

and spatial optoacoustic spectrum

It is advantageous in improving the signal-to-noise ratio of the optoacoustic signal to include the frequency at which the absolute value of the multiplied value is maximized.

와 공간적 광음향 스펙트럼

과 밀접한 관련이 있다. 즉, 광원(100)을 통해 방출되는 처프신호의 주파수 범위 역시 광음향 측정기(200)의 전달함수

와 공간적 광음향 스펙트럼

를 곱한 값의 절대값이 최대가 되는 주파수를 포함하는 것이 광음향 신호의 신호 대 잡음비를 향상시키는데 있어서 유리하다. 20 and 21 are not applied only to the modulated chirp signal. That is, not only the modulated chirp signal, but also the frequency range of the chirped signal having a constant envelope over time, and the transfer function of the photoacoustic meter 200 .

and spatial optoacoustic spectrum

is closely related to That is, the frequency range of the chirp signal emitted through the light source 100 is also the transfer function of the photoacoustic meter 200 .

and spatial optoacoustic spectrum

It is advantageous in improving the signal-to-noise ratio of the optoacoustic signal to include the frequency at which the absolute value of the multiplied value is maximized.

It should be understood that the embodiments described above are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the following claims rather than the above detailed description, and all changes or modifications derived from the meaning, scope, and equivalent concept of the claims should be construed as being included in the scope of the present invention.

10: light diffusion medium
20: light absorber
100: light source
200: photoacoustic meter
300: processing unit

Claims (13)

delete delete irradiating a chirp signal emitted through a light source to an optical diffusion medium and absorbing it into a light absorber positioned inside the optical diffusion medium;
measuring a photoacoustic signal generated from the optical absorber due to the chirped signal using a photoacoustic meter; and
The light source and the processing device connected to the photoacoustic meter receive the photoacoustic signal measured by the photoacoustic meter, perform matched filtering processing on the photoacoustic signal in the frequency domain, and calculate a matched filtered photoacoustic signal including;
The chirped signal emitted through the light source has a constant envelope over time,
Calculating the matched filtered photoacoustic signal comprises:
calculating, by the processing device, a chirped signal spectrum using the chirped signal; and
The processing device multiplies the chirp signal spectrum by at least any one of the transfer function of the photoacoustic meter, the spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter and the shape of the light absorber, A method of improving the signal-to-noise ratio of the photoacoustic signal measured by an optoacoustic meter comprising; performing matched filtering processing on the photoacoustic signal.
4. The method of claim 3,
Calculating the chirp signal spectrum comprises:
The method of improving the signal-to-noise ratio of the photoacoustic signal measured by the photoacoustic meter comprising the step of the processing device Fourier transforming the chirped signal to calculate the chirped signal spectrum.
4. The method of claim 3,
Calculating the chirp signal spectrum comprises:
The method of improving the signal-to-noise ratio of the photoacoustic signal measured by the photoacoustic meter comprising the step of the processing device removing the DC component of the chirp signal from the chirp signal to calculate a chirped signal spectrum from which the DC component is removed.
4. The method of claim 3,
The frequency range of the chirped signal emitted through the light source is,
A photoacoustic meter comprising a frequency at which an absolute value of a value obtained by multiplying a transfer function of the photoacoustic meter and a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter and the shape of the light absorber is maximized A method for improving the signal-to-noise ratio of an optoacoustic signal measured by
irradiating a modulated chirped signal emitted through a light source to an optical diffusion medium and absorbing it into a light absorber positioned inside the optical diffusion medium;
measuring a photoacoustic signal generated from the optical absorber due to the modulated chirp signal using a photoacoustic meter; and
The light source and the processing device connected to the photoacoustic meter receive the photoacoustic signal measured by the photoacoustic meter, perform matched filtering processing on the photoacoustic signal in the frequency domain, and calculate a matched filtered photoacoustic signal including;
The envelope of the modulated chirped signal emitted through the light source changes with time,
Calculating the matched filtered photoacoustic signal comprises:
calculating, by the processing device, a modulated chirped signal spectrum using the modulated chirped signal; and
The processing device multiplies the modulated chirped signal spectrum by at least one of the transfer function of the photoacoustic meter and the spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter and the shape of the light absorber. , performing matched filtering processing of the photoacoustic signal; Method of improving the signal-to-noise ratio of the photoacoustic signal measured by the photoacoustic meter comprising the.
delete delete delete 8. The method of claim 7,
Calculating the modulated chirped signal spectrum comprises:
The method of improving the signal-to-noise ratio of the photoacoustic signal measured by the photoacoustic meter comprising the step of the processing device Fourier transforming the modulated chirped signal to calculate the modulated chirped signal spectrum.
8. The method of claim 7,
Calculating the modulated chirped signal spectrum comprises:
The processing device removes the DC component of the modulated chir signal from the modulated chir signal to calculate a modulated chirped signal spectrum from which the DC component is removed. how to do it.
8. The method of claim 7,
The frequency range of the modulated chirp signal emitted through the light source is,
A photoacoustic meter comprising a frequency at which an absolute value of a value obtained by multiplying a transfer function of the photoacoustic meter and a spatial photoacoustic spectrum determined according to the shape of the photoacoustic meter and the shape of the light absorber is maximized A method for improving the signal-to-noise ratio of an optoacoustic signal measured by

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