KR200497217Y1 - Image quality improvement device for full-field oct - Google Patents

Image quality improvement device for full-field oct Download PDF

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KR200497217Y1
KR200497217Y1 KR2020200003560U KR20200003560U KR200497217Y1 KR 200497217 Y1 KR200497217 Y1 KR 200497217Y1 KR 2020200003560 U KR2020200003560 U KR 2020200003560U KR 20200003560 U KR20200003560 U KR 20200003560U KR 200497217 Y1 KR200497217 Y1 KR 200497217Y1
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T11/00—2D [Two Dimensional] image generation
    • G06T11/003—Reconstruction from projections, e.g. tomography
    • G06T11/008—Specific post-processing after tomographic reconstruction, e.g. voxelisation, metal artifact correction
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/21—Polarisation-affecting properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N2021/178—Methods for obtaining spatial resolution of the property being measured
    • G01N2021/1785—Three dimensional
    • G01N2021/1787—Tomographic, i.e. computerised reconstruction from projective measurements
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/10—Image acquisition modality
    • G06T2207/10072—Tomographic images
    • G06T2207/10101—Optical tomography; Optical coherence tomography [OCT]

Abstract

본 발명은 신호적산법 기반의 전광역 OCT에서 발생하는 줄무늬 형태의 아티팩트를 보정하는 장치에 관한 것으로 아티팩트를 포함한 직교위상신호 쌍으로 계산된 위상을 통하여 광 경로차에 의존적인 오차를 보정하는 과정을 특징으로 한다.The present invention relates to a device for correcting stripe-shaped artifacts generated in full-field OCT based on signal integration, and is characterized by a process of correcting errors dependent on optical path differences through a phase calculated by a pair of orthogonal phase signals including artifacts. to be

Description

전광역 OCT의 이미지 품질을 향상시키는 장치{IMAGE QUALITY IMPROVEMENT DEVICE FOR FULL-FIELD OCT}Device for improving image quality of full-field OCT {IMAGE QUALITY IMPROVEMENT DEVICE FOR FULL-FIELD OCT}

본 발명은 신호적산법 기반의 전광역 OCT에서 발생하는 줄무늬 형태의 아티팩트를 보정하는 기술에 관한 것으로 후처리 장치를 통하여 전광역 OCT의 이미지 품질을 향상시키는 방법을 제시한다.The present invention relates to a technique for correcting stripe-shaped artifacts generated in full-field OCT based on signal integration, and proposes a method for improving the image quality of full-field OCT through a post-processing device.

전광역 OCT는 수 마이크론 단위의 해상도를 가지는 비침습적 단층영상기로 세포단위의 생체 이미징 혹은 디스플레이 패널 검사처럼 OCT의 비침습적 특성과 높은 해상도를 동시에 요구하는 분야에 적용할 수 있다.Full-field OCT is a non-invasive tomography imager with a resolution of several microns, and can be applied to fields that require both non-invasive characteristics and high resolution of OCT, such as cell-level bio-imaging or display panel inspection.

신호적산법은 전광역 OCT에서 단층 이미지를 연산하기 위한 알고리즘으로 간섭신호에 사인함수꼴의 위상변조를 가해주는 하드웨어가 필요하다. 그러면 야코비-앙거(Jacobi-Anger) 항등식에 의해서 네 장의 간섭패턴으로 직교위상관계를 가지는 신호 쌍을 연산할 수 있으며, 이들의 제곱합을 통해 단층 이미지를 재구성할 수 있다.The signal integration method is an algorithm for computing tomographic images in full-area OCT, and requires hardware that applies sinusoidal phase modulation to the interference signal. Then, a pair of signals having an orthogonal phase relationship can be calculated using the four interference patterns according to the Jacobi-Anger identity, and a tomographic image can be reconstructed through the sum of squares.

그러나 높은 해상도의 전광역 OCT를 구현하기 위해서 광대역 스펙트럼 광원을 사용하면 파장에 따라서 달라지는 변조진폭과 급격히 변화하는 간섭신호의 포락선으로 인해서 신호적산법의 가정을 충족하지 못하게 되어 줄무늬 모양의 아티팩트가 생성된다. 이는 시료의 형상을 왜곡하여 정확한 구조 파악에 장해를 유발한다.However, when a broadband spectral light source is used to implement high-resolution full-area OCT, the modulation amplitude that varies with wavelength and the envelope of an interference signal that rapidly changes do not meet the assumptions of the signal integration method, resulting in stripe-shaped artifacts. This distorts the shape of the sample and causes obstacles to accurate structural identification.

편광소자 기반의 단층 이미지 복원 알고리즘은 광학계에서 직교위상신호 쌍을 직접 측정하는 방식을 사용하기에 수학적으로 무한대의 결맞음 길이를 가져야 하는 신호적산법의 한계를 극복하였다. 더불어 파장의존 위상변조가 가능한 특수 편광소자를 사용하면 줄무늬 아티팩트를 효과적으로 제거할 수 있으나 편광소자는 가격이 비싸고 광학계 구성 및 정렬이 복잡해지는 단점이 존재한다.The polarizer-based tomographic image restoration algorithm overcomes the limitations of the signal integration method, which mathematically requires an infinite coherence length, because it uses a method of directly measuring the orthogonal phase signal pair in the optical system. In addition, if a special polarizing element capable of wavelength-dependent phase modulation is used, stripe artifacts can be effectively removed. However, the polarizing element is expensive and the configuration and alignment of the optical system are complicated.

본 발명은 후처리 소프트웨어를 통해 신호적산법 기반 고해상도 전광역 OCT의 직교위상신호 쌍을 보정하는 방법으로 편광소자를 활용하지 아니하고 줄무늬 아티팩트를 보정하는 것을 목적으로 한다.An object of the present invention is to correct stripe artifacts without using a polarizing element as a method of correcting a pair of orthogonal phase signals of a high-resolution full-area OCT based on a signal integration method through post-processing software.

본 발명은 광 경로차가 완벽한 결맞음에서 멀어질수록 신호적산법에 의해서 발생하는 직교위상신호 쌍의 오차가 선형적으로 증가한다는 관측 결과를 바탕으로 아티팩트를 포함한 직교위상신호 쌍으로 계산한 위상을 활용하여 아티팩트를 보정하는 단계가 특징인 위상추론부(20)와 신호보정부(30)로 구성된 컴퓨터 혹은 마이크로프로세서 기반의 후처리 장치를 제시하고자 한다.The present invention utilizes the phase calculated with the orthogonal phase signal pair including the artifact based on the observation result that the error of the orthogonal phase signal pair generated by the signal integration method increases linearly as the optical path difference moves away from perfect coherence. A computer or microprocessor-based post-processing device consisting of a phase inference unit 20 and a signal correction unit 30, which is characterized by the step of correcting , will be presented.

발명의 실시에 따라서 편광소자를 활용하지 아니하고 줄무늬 형태의 아티팩트를 보정할 수 있다.According to the practice of the present invention, it is possible to correct artifacts in the form of stripes without using a polarizer.

도 1은 본 발명이 설명하고자 하는 후처리 장치의 구조에 대한 도면이다.
도 2는 본 발명의 후처리 장치를 전산모사된 전광역 OCT에 대하여 적용한 결과이다.1 is a diagram of the structure of a post-processing device to be described in the present invention.
2 is a result of applying the post-processing device of the present invention to computer simulated full-area OCT.

본 발명이 설명하고자 하는 장치를 원활하게 기술하기 위하여,In order to smoothly describe the device to be described by the present invention,

전광역 OCT에서 얻은 간섭무늬에 대한 신호적산법의 결과인 동상신호(in-phase) I 및 직교위상신호(quadrature) Q에 대한 보정을 진행한다. 단, 후술할 전광역 OCT의 배열 검출기를 단일 화소로 제한하여 설명한다.Correction is performed for in-phase I and quadrature Q, which are the results of the signal integration method for the interference fringe obtained from the full-field OCT. However, the array detector of the full-area OCT, which will be described later, will be described by limiting it to a single pixel.

상기한 조건이 본 발명의 범위를 제한하는 것은 아니며, 동일한 과정의 반복을 통해 임의 화소의 배열 검출기에 대한 보정으로 확장이 가능하다는 사실은 자명하다.The above conditions do not limit the scope of the present invention, and it is obvious that it can be extended to correction of an array detector of arbitrary pixels through repetition of the same process.

도 1은 본 발명이 설명하고자 하는 후처리 장치의 구조를 도시한 것으로,1 shows the structure of a post-processing device to be described by the present invention,

신호적산부(10)는 전광역 OCT의 간섭무늬에서 신호적산법에 따라 직교위상신호 쌍 I,Q를 연산하고,The signal integration unit 10 calculates quadrature phase signal pairs I and Q according to the signal integration method from the interference fringes of the full-area OCT,

위상추론부(20)는 신호적산부(10)로부터 직교위상신호 쌍을 넘겨받아 수학식 1의 연산을 통해 광 경로차를 추론하며, 위상 언래핑(phase unwrapping) 연산을 통해 역탄젠트의 제한된 치역을 확장하고,The phase inference unit 20 receives the quadrature phase signal pair from the signal integration unit 10, infers the optical path difference through the operation of Equation 1, and the limited range of the inverse tangent through the phase unwrapping operation. expand,

신호보정부(30)는 신호적산부(10) 및 위상추론부(20)에서 직교위상신호 쌍과 위상 언래핑이 적용된 광 경로차와 사용자로부터 입력받은 추론계수 A,B,C,D로 수학식 2에 해당하는 행렬 연산을 통해 직교위상신호 쌍을 보정하여 단층 이미지에 발생한 줄무늬 형태의 아티팩트를 보정하며,The signal compensator 30 calculates the quadrature phase signal pair from the signal integrator 10 and the phase inference unit 20 and the optical path difference to which the phase unwrapping is applied and the inference coefficients A, B, C, and D input from the user. The quadrature phase signal pair is corrected through matrix operation corresponding to Equation 2 to correct the artifacts in the form of stripes occurring in the tomographic image,

추론계수 A,B,C,D의 물리적 의미 및 차원은 언급된 순서대로,The physical meanings and dimensions of the inference coefficients A, B, C, and D are, in the order mentioned,

광 경로차가 0으로 완벽한 결맞음이 성립하여 보정의 기준이 되는 위상(라디안),The phase (radian), which is the standard for correction when the optical path difference is zero and perfect coherence is established.

광 경로차에 대하여 동상신호 진폭의 오차가 상승하는 비율(1/라디안),The ratio of the rise of the error of the common-mode signal amplitude to the optical path difference (1/radian),

광 경로차에 대하여 직교위상신호 진폭의 오차가 상승하는 비율(1/라디안),The ratio of the rise of the error of the quadrature phase signal amplitude to the optical path difference (1/radian),

광 경로차에 대하여 직교위상신호 쌍 간의 위상 차이가 90도를 기준으로 상승하는 비율(무차원)이고,The ratio (dimensionless) that the phase difference between the quadrature phase signal pairs rises based on 90 degrees with respect to the optical path difference,

디스플레이(40)는 줄무늬 형태의 아티팩트가 보정된 단층 이미지를 출력한다.The display 40 outputs a tomographic image in which stripe-shaped artifacts are corrected.

추론계수 A,B,C,D는 디스플레이(40)에 표시된 줄무늬 형태의 아티팩트를 사용자가 직접 확인하며 조절할 수도 있고 이차원 푸리에 변환을 통해 특정한 공간 주파수를 최소화하는 추론계수를 탐색하는 수학적 최적화를 통해 줄무늬 형태의 아티팩트를 최소화하는 최적값으로 결정될 수도 있다.The inference coefficients A, B, C, and D can be directly checked and adjusted by the user for the artifacts in the form of stripes displayed on the display 40, or through mathematical optimization to search for inference coefficients that minimize specific spatial frequencies through two-dimensional Fourier transform. It may be determined as an optimal value that minimizes shape artifacts.

추론계수 A,B,C,D의 결정 방식은 기반이 되는 컴퓨터 혹은 마이크로프로세서의 가용 자원에 따라서 합리적으로 선택할 수 있으며, 수학적 최적화는 일반적으로 많은 반복계산을 요구하기 때문에 연산의 실시간성을 유지하기 위해서는 사용자가 직접 추론계수를 조절하는 방식에 비하여 높은 성능의 프로세서를 요구한다.The method of determining the inference coefficients A, B, C, and D can be reasonably selected according to the available resources of the underlying computer or microprocessor, and since mathematical optimization generally requires many iterative calculations, it is necessary to maintain real-time operation. To achieve this, a high-performance processor is required compared to the method in which the user directly adjusts the inference coefficient.

Claims (1)

신호적산법 기반의 전광역 OCT에서 광대역 스펙트럼 광원을 사용함에 따라 발생하는 줄무늬 형태의 아티팩트를 보정하는 기술에 있어서,
다음의 수학식을 이용하여 상기 OCT의 동상신호 I와 직교위상신호 Q로 계산한 위상 φ에 기반하여 직교위상신호 쌍을 보정하는 보정부를 포함하는 후처리 장치.

여기서,
A는 광 경로차가 0으로 완벽한 결맞음이 성립하여 보정의 기준이 되는 위상,
B는 광 경로차에 대하여 동상신호 진폭의 오차가 상승하는 비율,
C는 광 경로차에 대하여 직교위상신호 진폭의 오차가 상승하는 비율,
D는 광 경로차에 대하여 직교위상신호 쌍 간의 위상 차이가 90도를 기준으로 상승하는 비율,
I'는 보정된 동상신호,
Q'는 보정된 직교위상신호를 나타낸다.In the technique of correcting artifacts in the form of stripes caused by using a broadband spectral light source in full-field OCT based on the signal integration method,
A post-processing device comprising a correction unit for correcting a quadrature phase signal pair based on the phase φ calculated from the in-phase signal I and the quadrature phase signal Q of the OCT using the following equation.

here,
A is the phase that is the standard for correction when the optical path difference is zero and perfect coherence is established;
B is the rate at which the error of the common-mode signal amplitude rises with respect to the optical path difference,
C is the rate at which the error of the quadrature phase signal amplitude rises with respect to the optical path difference,
D is the rate at which the phase difference between quadrature phase signal pairs rises based on 90 degrees with respect to the optical path difference,
I' is the corrected common-mode signal,
Q' represents a corrected quadrature phase signal.
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Publication number Priority date Publication date Assignee Title
JP2013156229A (en) * 2012-01-31 2013-08-15 Nidek Co Ltd Optical tomographic imaging apparatus
JP2015131107A (en) 2013-12-13 2015-07-23 株式会社ニデック Optical coherence tomography device, and program
JP2018089055A (en) * 2016-12-01 2018-06-14 キヤノン株式会社 Image processing device, imaging device, image processing method, and program
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