Light-induced resonance-based frequency-selective amplification for combined photoacoustic-ultrasound imaging

장용호,김현철 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

Photoacoustic imaging is an emerging biomedical imaging modality which offers high spatial resolution and visualization at much deeper than the depth achieved by other optical imaging modalities. However, the sensitivity of photoacoustic imaging is quite limited due to background signals produced from endogenous optical absorbers. To overcome this technical hurdle, exogenous photoacoustic contrast agents have been employed in efforts to improve sensitivity. However, photoacoustic signal usually contains a broad range of frequency components, whereas the ultrasound transducer is only capable of receiving signals within a certain frequency range. In this study, we show that the gas-cored structure of a porphyrin-phospholipid microbubble (p-MB) can act as a resonance frequency-selective amplifier for photoacoustic signals produced from the embedded porphyrin, thus improving the efficiency of the signal reception and allowing for more sensitive photoacoustic imaging.

주파수 필터링 함수에 따른 시간 및 주파수 영역 광음향 측정에 대한 노이즈-대비-신호 분석

강동열 한국광학회 2019 한국광학회지 Vol.30 No.2

We investigate the signal-to-noise ratios (SNRs) of time-domain (i.e. pulsed illumination) and frequency-domain (i.e. chirped illumination) photoacoustic signals measured by a spherically focused ultrasound transducer for spherical absorbers. The simulation results show that the time-domain photoacoustic SNR is higher than that of frequency-domain photoacoustic signals, as reported in the previous literature. We understand the reason for this SNR gap between the two measurement modes by analyzing photoacoustic-signal spectra, considering the incident beam energy controlled by the maximum permissible exposure. As the result of this approach, we find that filtering off the DC term in the chirped signal’s spectrum improves frequency-domain photoacoustic SNRs by up to approximately 5 dB. In particular, it is observed that photoacoustic SNRs are highly sensitive to an upper-frequency value of frequency filtering functions, and the optimal upper-frequency values maximizing the SNR are different in time- and frequency-domain photoacoustic measurements.

주파수 필터링 함수에 따른 시간 및 주파수 영역 광음향 측정에 대한 신호 대 잡음비 분석

강동열(DongYel Kang) 한국광학회 2019 한국광학회지 Vol.30 No.2

구면 초점 초음파 측정기에 의해 구형의 광 흡수체로부터 측정된 시간(즉, 펄스 형태 광원) 및 주파수 영역(즉, 처프 형태 광원) 광음향 신호의 신호 대 잡음비(signal-to-noise ratio)를 이론 및 시뮬레이션으로 분석하였다. 이전 문헌과 마찬가지로 시간 영역 광음향 측정에 의한 신호 대 잡음비 값이 주파수 영역 광음향 측정의 경우보다 더 높았는데 이 근본적인 이유를 최대허용노광량(maximum permissible exposure)에 따른 광원의 세기와 주파수 필터링을 통한 두 측정 모드의 광음향 스펙트럼들에 대한 분석을 통해 이해하였다. 또한, 분석의 결과로서 주파수 영역 광음향의 처프 형태 광원에 대한 정합 필터링에 더해 DC 스펙트럼 부분을 제거하니 신호 대 잡음비가 5 dB 정도 상승하는 것을 발견하였다. 특히, 주파수 필터 함수의 주파수 상한 값의 변화에 따라 신호대 잡음비 값이 급격하게 변동하였는데 신호 대 잡음비가 최대가 되는 주파수 상한 값이 두 광음향 측정 모드에서 서로 다르게 나타남을 관찰하였다. We investigate the signal-to-noise ratios (SNRs) of time-domain (i.e. pulsed illumination) and frequency-domain (i.e. chirped illumination) photoacoustic signals measured by a spherically focused ultrasound transducer for spherical absorbers. The simulation results show that the time-domain photoacoustic SNR is higher than that of frequency-domain photoacoustic signals, as reported in the previous literature. We understand the reason for this SNR gap between the two measurement modes by analyzing photoacoustic-signal spectra, considering the incident beam energy controlled by the maximum permissible exposure. As the result of this approach, we find that filtering off the DC term in the chirped signal’s spectrum improves frequency-domain photoacoustic SNRs by up to approximately 5 dB. In particular, it is observed that photoacoustic SNRs are highly sensitive to an upper-frequency value of frequency filtering functions, and the optimal upper-frequency values maximizing the SNR are different in time- and frequency-domain photoacoustic measurements.

Multifunctional theranostic contrast agent for photoacoustic- and ultrasound-based tumor diagnosis and ultrasound-stimulated local tumor ionals

Hyuncheol KIM 한국생물공학회 2016 한국생물공학회 학술대회 Vol.2016 No.4

초점 초음파 측정기로 측정한 광음향 신호의 광 흡수계수에 대한 비선형성

강동열 한국광학회 2017 한국광학회지 Vol.28 No.4

The physical shape of an ultrasound transducer has not been considered in previous studies of the photoacoustic saturationeffect, where a photoacoustic signal’s magnitude linearly increases as an absorption coefficient increases and it is finally saturated. In this paper, the effect of a spherically focused ultrasound transducer on photoacoustic nonlinearity is investigated. The focusedultrasound transducer’s spatial filtering effect on photoacoustic signals is analytically derived considering the combined conceptof a virtual point detector and Green function approach. The ultrasound transducer’s temporal response (i.e., transfer function)effect on photoacoustic signals is considered by integrating photoacoustic signal values within the absorption area covered by aspatial resolution of the ultrasound transducer. Results from the analytically derived expression show that the magnitude ofphotoacoustic signals measured by a spherical focused ultrasound transducer shows a maximum at a specific absorption coefficient,and decreases after that maximum point as an absorption coefficient is increased. The origin of this photoacoustic nonlinearityis physically understood by comparing the ultrasound transducer’s transfer functions and photoacoustic resonance spectra. Inaddition, this physical interpretation implies that the photoacoustic nonlinearity is strongly dependent on the irradiance distributioninside an absorption medium.

Photoacoustic imaging of occlusal incipient caries in the visible and near-infrared range

da Silva, Evair Josino,de Miranda, Erica Muniz,de Oliveira Mota, Claudia Cristina Brainer,Das, Avishek,Gomes, Anderson Stevens Leonidas Korean Academy of Oral and Maxillofacial Radiology 2021 Imaging Science in Dentistry Vol.51 No.2

Purpose: This study aimed to demonstrate the presence of dental caries through a photoacoustic imaging system with visible and near-infrared wavelengths, highlighting the differences between the 2 spectral regions. The depth at which carious tissue could be detected was also verified. Materials and Methods: Fifteen permanent molars were selected and classified as being sound or having incipient or advanced caries by visual inspection, radiography, and optical coherence tomography analysis prior to photoacoustic scanning. A photoacoustic imaging system operating with a nanosecond pulsed laser as the light excitation source at either 532 nm or 1064 nm and an acoustic transducer at 5 MHz was developed, characterized, and used. En-face and lateral(depth) photoacoustic signals were detected. Results: The results confirmed the potential of the photoacoustic method to detect caries. At both wavelengths, photoacoustic imaging effectively detected incipient and advanced caries. The reconstructed photoacoustic images confirmed that a higher intensity of the photoacoustic signal could be observed in regions with lesions, while sound surfaces showed much less photoacoustic signal. Photoacoustic signals at depths up to 4 mm at both 532 nm and 1064 nm were measured. Conclusion: The results presented here are promising and corroborate that photoacoustic imaging can be applied as a diagnostic tool in caries research. New studies should focus on developing a clinical model of photoacoustic imaging applications in dentistry, including soft tissues. The use of inexpensive light-emitting diodes together with a miniaturized detector will make photoacoustic imaging systems more flexible, user-friendly, and technologically viable.

Compressed Sensing With a Gaussian Scale Mixture Model for Limited View Photoacoustic Computed Tomography <i>In Vivo</i>

Meng, Jing,Liu, Chengbo,Kim, Jeesu,Kim, Chulhong,Song, Liang SAGE Publications 2018 Technology in cancer research & treatment Vol.17 No.-

<P>Photoacoustic computed tomography using an ultrasonic array is an attractive noninvasive imaging modality for many biomedical applications. However, the potentially long data acquisition time of array-based photoacoustic computed tomography—usually due to the required time-multiplexing for multiple laser pulses—decreases its applicability for rapid disease diagnoses and the successive monitoring of physiological functions. Compressed sensing is used to improve the imaging speed of photoacoustic computed tomography by decreasing the amount of acquired data; however, the imaging quality can be limited when fewer measurements are used, as traditional compressed sensing considers only the sparsity of the signals in the imaging process. In this work, an advanced compressed sensing reconstruction framework with a Wiener linear estimation-based Gaussian scale mixture model was developed for limited view photoacoustic computed tomography. In this method, the structure dependencies of signals in the wavelet domain were incorporated into the imaging framework through the Gaussian scale mixture model, and an operator based on the Wiener linear estimation was designed to filter the reconstruction artifacts. Phantom and human forearm imaging were performed to verify the developed method. The results demonstrated that compressed sensing with a Wiener linear estimation-based Gaussian scale mixture model more effectively suppressed the reconstruction artifacts of sparse-sampling photoacoustic computed tomography and recovered photoacoustic images with a higher contrast-to-noise ratio and edge resolution than the traditional compressed sensing method. This work may promote the development of low-cost photoacoustic computed tomography techniques with rapid data acquisition and enhance the performance of photoacoustic computed tomography in various biomedical studies.</P>

3D wide-field multispectral photoacoustic imaging of melanoma: a pilot study

( Chul Hwan Bang ),( Byullee Park ),( Changyeop Lee ),( Hae Eun Park ),( Hwa Jung Yook ),( Ju Hee Han ),( Wonseok Choi ),( Jeesu Kim ),( Gyeong Sin Park ),( Jong Won Rhie ),( Chulhong Kim ),( Ji Hyun 대한피부과학회 2020 대한피부과학회 학술발표대회집 Vol.72 No.1

Background: Melanoma stage is usually classified by the histopathological depth of tumor, measured as ‘the Breslow depth’, which determines surgical margin. However, it is difficult to accurately determine the actual Breslow depth before surgery using the existing ocular micrometer and biopsy technique. Objectives: The aim of this study is to evaluate the clinical use of 3D wide-field multispectral photoacoustic imaging, which can noninvasively measure depth and outline the boundary of melanomas. Methods: Six melanoma patients were examined in vivo using the 3D multispectral photoacoustic imaging system. For five cases of melanomas, spectrally unmixed photoacoustic depths were calculated and compared against histopathological depths. Results: Spectrally unmixed photoacoustic depths and histopathological depths match well within a mean absolute error of 0.36 mm. In particular, the measured minimum and maximum depths in the in situ and nodular type of melanoma were 0.6 mm and 9.1 mm, respectively. In the 3D photoacoustic image of one metastatic melanoma, feeding vessels were visualized in the melanoma, suggesting the neovascularization around the tumor. Conclusion: The 3D multispectral photoacoustic imaging not only provides well-measured depth and sizes of various types of melanomas, it also visualizes the metastatic type of melanoma. Obtaining accurate depth and boundary information of melanoma before surgery would play a useful role in the complete excision of melanoma.

관절염 진단용 광음향 이미징 시스템 개발을 위한 선행 연구

윤종인,박지원,Youn, Jong-In,Park, Ji-Won 대한물리치료학회 2010 대한물리치료학회지 Vol.22 No.4

Purpose: The goal of this study was to investigate the feasibility for the early diagnosis of inflammatory arthritis by the reconstruction of three-dimensional photoacoustic imaging with a tissue phantom. Methods: Q-switched Nd:YAG laser (l = 532 nm) was applied to a tissue phantom to generate photoacoustic waves, and the acquired photoacoustic signals at different positions around the sample were used to recombine the distribution of the optical absorption and the images were subsequently generated through a reconstruction algorithm. Results: From the acquired photoacoustic signals, the surface andinner core of the phantom was clearly distinguished. Furthermore, the back-projection algorithm was able to reconstruct two-dimensional and three-dimensional photoacoustic images that contained the optical absorption property information of the tissue phantom. Conclusion: The results indicate that the photoacoustic imaging technique has many advantages such as high optical contrast and high acoustic resolution. The acquired images can be used for the early diagnosis of inflammatory arthritis by the structural information obtained from the region of interest.

Review of Photoacoustic Imaging for Imaging-Guided Spinal Surgery

한승희 대한척추신경외과학회 2018 Neurospine Vol.15 No.4

This review introduces the current technique of photoacoustic imaging as it is applied in imaging-guided surgery (IGS), which provides the surgeon with image visualization and analysis capabilities during surgery. Numerous imaging techniques have been developed to help surgeons perform complex operations more safely and quickly. Although surgeons typically use these kinds of images to visualize targets hidden by bone and other tissues, it is nonetheless more difficult to perform surgery with static reference images (e.g., computed tomography scans and magnetic resonance images) of internal structures. Photoacoustic imaging could enable real-time visualization of regions of interest during surgery. Several researchers have shown that photoacoustic imaging has potential for the noninvasive diagnosis of various types of tissues, including bone. Previous studies of the surgical application of photoacoustic imaging have focused on cancer surgery, but photoacoustic imaging has also recently attracted interest for spinal surgery, because it could be useful for avoiding pedicle breaches and for choosing an appropriate starting point before drilling or pedicle probe insertion. This review describes the current instruments and clinical applications of photoacoustic imaging. Its primary objective is to provide a comprehensive overview of photoacoustic IGS in spinal surgery.