Photoacoustic Reporter Gene Imaging And Optical Coherence Computed Tomography

Advances in imaging technologies have always been the major driving forces for the evolution of biomedical research. Compared with other modalities, optical imaging possesses several prominent merits. Because light interacts with tissue at the microscopic level through many distinct physical mechanisms, optical methods allow sensitive exploration of various aspects of the life down to the single-molecule level. From the technical perspective, optical systems utilize safe non-ionizing radiation, could be implemented at relatively low cost, also have the potential to be miniaturized for portable or endoscopic applications. As a result, optical imaging tools are playing an increasingly important role in both laboratorial research and clinical practice. Among them, photoacoustic imaging: PAI) and optical coherence tomography: OCT) are the two fastest growing branches. PAI measures the laser-induced acoustic wave, and produces high-resolution images of the optically absorbing features of tissue at multiple length-scales. OCT detects singly backscattered photons, and enables real-time high-resolution in vivo biopsy of tissue up to an optical transport mean-free-path. My doctoral research is focused on developing three novel optical imaging techniques based on the spirits of PAI and OCT. In the first part of this study, we established a new paradigm to visualize gene expression in vivo based on optical absorption. In the post-genomic era, we are now being challenged to develop novel molecular imaging methods to identify the functions of genes. PAI can detect specific molecules according to their characteristic absorption spectra, thus is a promising candidate for molecular imaging of gene expression. The full potential of photoacoustic molecular imaging still remains to be explored. For the first time, we demonstrated imaging gene expression by PAI in living mice and rats, using a chromogenic lacZ/X-gal reporter gene system. We demonstrated the expression of the lacZ reporter gene can be detected by PAI as deep as 5 cm inside tissue. In addition, we showcased that PAI could follow gene expression from the microscopic to the macroscopic level. This work represents one of the pioneering efforts to extend photoacoustic methods for molecular imaging. In the second part of this study, we developed a novel multimodal microscope, called the integrated photoacoustic and optical coherence microscope: iPOM), which combines PAI and OCT in a single imaging platform. PAI is predominantly sensitive to optical absorption, while OCT exploits optical scattering. By combining their naturally complementary imaging contrasts, iPOM can provide comprehensive information about biological tissue. We designed and built a reflection-mode prototype of iPOM, which fuses optical-resolution photoacoustic microscopy with spectral-domain optical coherence tomography. The potential applications of iPOM in studying cutaneous and ocular microcirculation, and tissue engineering were demonstrated. Finally, we invented a new optical tomography, named optical coherence computed tomography: optical CCT), which overcomes several major limitations of OCT. OCT relies on singly backscattered photons to obtain high-resolution images. Its image quality degrades fast with the increase of the depth, because the multiply scattered photons quickly become dominant at a penetration larger than 500 &mum. As a result, OCT can only effectively penetrate ~1 mm into highly scattering tissue like skin. In addition, OCT is mainly sensitive to optical scattering, which does not reflect the molecular content of tissue directly. Optical CCT measures both singly and multiply scattered photons using a low-coherence interferometer. We make use of both types of photons by adopting a model-based reconstruction algorithm. The light-tissue interaction model was established using the time-resolved Monte Carlo method. The optical properties of the tissue were reconstructed from measurements by solving the inverse radiative transport problem under the first Born approximation. As a result, optical CCT could image deeper than OCT, and provide extra molecule-specific contrasts, such as optical absorption. We designed and built the first optical CCT system. In experiments, absorbing inclusions of 100 &mum diameter were imaged with consistent quality through a 2.6-mm-thick: equivalent to ~3 transport mean-free-paths) tissue-mimicking phantom

Modeling key uncertainties in technology development: the case of twente photoacoustic mammoscope (PAM)

Tese de mestrado integrado em Engenharia Biomédica e Biofísica, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2013O efeito fotoacústico foi apresentado pela primeira vez por Alexander Graham Bell em 1880. Este princípio enuncia que a absorção de ondas eletromagnéticas por um certo meio provoca uma sequência de eventos que culmina na geração de ondas sonoras. Desde a sua descoberta surgiram inúmeras aplicações fotoacústicas, entre as quais aplicações de imagiologia médica. Estes sistemas fotoacústicos utilizam os componentes óticos como sondas e os componentes acústicos como recetores do sinal gerado, produzindo imagens de carácter tomográfico, daí a designação atribuída – sistemas fotoacústicos tomográficos, do inglês photoacoustic tomogragphy (PAT). A fusão dos componentes óticos e acústicos minimiza algumas desvantagens que as modalidades apresentam individualmente e apresenta algumas vantagens relativamente às imagens captadas por sistemas puramente óticos ou puramente acústicos, uma vez que permitem reduzir a elevada dispersão dos fotões nos tecidos biológicos: os sistemas óticos apresentam bom contraste, mas fraca resolução, enquanto os sistemas acústicos apresentam boa resolução e bons níveis de penetração no tecido biológico. Fruto desta combinação, os sistemas fotoacústicos permitem visualizar a angiogênese, um dos principais fenómenos biológicos associados à vascularização tumoral. Tal visualização é possível devido ao aumento da concentração da hemoglobina que apresenta excelentes níveis de contraste ótico e uma boa resolução acústica, sem o recurso a agentes de contraste, nem a radiação ionizante. Por estas razões os sistemas PAT são considerados ideias para o rastreio e diagnóstico do cancro da mama. Dentro dos equipamentos médicos PAT destacam-se aqueles que utilizam como sonda ótica a radiação próxima dos infravermelhos, do inglês Near Infrared Light (NIR), cujo intervalo de comprimento de onda se situa entre os 750 e os 1400 nm. A utilização do comprimento de onda neste intervalo representa a optimização do compromisso entre a resolução espacial e a profundidade de alcance no tecido biológico. O departamento de imagiologia fotónica médica da Universidade de Twente ( department of Biomedical Photonic Imaging, MIRA Institute for Biomedical Technology and Technical Medicine of University of Twente, Netherlands) desenvolveu um equipamento médico que utiliza todos os princípios físicos PAT e radiação NIR – mamografia fotoacústica, do inglês Photoacoustic Mammoscope (PAM). O PAM apresenta algumas vantagens próprias, uma vez que, por exemplo, ao contrário dos restantes equipamentos médicos PAT não requer uma compressão excessiva da mama entre a janela de iluminação e o detetor acústico. O PAM utiliza como fonte ótica um laser da classe Q-switched Nd:YAG que opera com comprimentos de onda de 1064 nm com pulsos de 5 ou 10 ns e a uma taxa de repetição de 10 Hz. Relativamente à composição e funcionamento do seu sistema de receção acústico o PAM apresenta um detetor plano com 590 elementos (matriz circular) disposto numa geometria de pratos paralelos, o que facilita a sua comparação direta com imagens de mamografia convencional e digital. O PAM em associação com o algoritmo de reconstrução de imagem atraso e soma, do inglês delay and sum algorithm apresenta um alcance máximo em profundidade de 15 a 60 mm relativamente à superfície de iluminação, dependente do tamanho e contraste do objeto absorvente e uma resolução espacial (lateral ou axial) de 3 a 4 mm, dependente da profundidade do objeto absorvente. Os primeiros testes piloto foram efetuados em 2007. Apesar de bem-sucedidos relativamente aos objetivos de funcionalidade, o tempo de medição foi considerado excessivo (25 min). Tendo como ponto de partida os testes piloto, iniciaram-se em Dezembro de 2010 um conjunto de testes clínicos de maior escala no Hospital de Oldenzaal (Center for Breast Care of the Medisch Spectrum Twente Hospital in Oldenzaal, Netherlands). O objetivo passa por incluir em três fases distintas 100 pacientes até 2014. Os pacientes no seu trajeto clinico normal entre os testes de radiologia convencional (raios-x e ultrassons) e a biópsia são questionados a participar no estudo. As imagens das diferentes modalidades são posteriormente comparadas entre si. A 1ª fase dos testes clínicos (Dezembro, 2010- Abril, 2011) já terminada permitiu retirar três conclusões: a performance do PAM é independente da densidade mamária; os quistos não apresentam contraste suficiente; as dimensões das lesões visualizadas no PAM são inferiores às dimensões resultantes da histopatologia. Por sua vez, a 2º fase dos testes clínicos (Abril, 2011 - Abril, 2012) procurava testar duas configurações de scan: “fixed scan” em que o feixe de luz é mantido fixo durante todo o processo de medição; “Tandem Scan” em que o feixe de luz se move ao longo da ROI. Durante esta fase foi possível concluir que a configuração “fixed scan” era mais vantajosa permitindo, entre outras vantagens, diminuir o signal-noise ratio e aumentar o contraste. A 3º fase de testes encontra-se a decorrer. As principais alterações nesta fase estão relacionadas com o número de elementos do detetor acústico ativados de cada vez, uma vez que passou de 1 para 10, resultando numa diminuição do tempo de duração de cada teste de 25 min para 10 min. Além dos testes clínicos, 3 estudos utilizando métodos de health tecnhology assessement (HTA) foram realizados. Um deles realizado por Haakma W. 2011 - “Expert Elicitation to Populate Early Health Economic Models of Medical Diagnostic Devices in Development”. Neste estudo foram utilizados modelos matemáticos para aglomerar as opiniões de 18 radiologistas com experiência em imagiologia mamária sobre a performance do PAM ao nível da sua sensibilidade e especificidade. Os resultados obtidos estão contidos no intervalo de confiança de 95%. Os testes clínicos efetuados conjuntamente com os estudos de HTA já realizados (que facultam estimativas de performance do PAM) não dão indicações sobre o custo-eficácia (do inglês cost-effectiveness) da utilização do PAM nos diferentes cenários no trajeto de rastreio e de diagnóstico do cancro da mama, bem como nos diferentes grupos de risco. Foi este contexto que estimulou a principal questão desta tese: Quais são os melhores potenciais cenários de utilização do PAM no trajeto de rastreio e de diagnóstico do cancro da mama do ponto de vista económico? Para responder a esta questão foi utilizado o método económico de análise de custo-eficácia (do inglês cost-effectiveness analysis) em diferentes potencias cenários de aplicação aglomerados em 3 grupos e em dois contextos económicos e epidemiológicos distintos (Portugal e Holanda): Grupo I, Grupo II e Grupo III. O Grupo I inclui o rastreio (efetuada pela mamografia convencional ou digital), o diagnóstico precoce (efetuado pela mamografia convencional ou digital + exame ultrassonográfico + exame clínico) e o diagnóstico tardio (Ressonância Magnética) no trajeto clínico regular em pacientes sem níveis de risco extraordinários de desenvolver cancro da mama. O Grupo II contempla os cenários de rastreio de diferentes grupos de risco avaliados conforme a probabilidade de desenvolver a doença. O Grupo III é uma réplica do Grupo I com a diferença que não procura testar o PAM com os dados de performance estimados, mas sim com dados hipotéticos em que a performance é assumida como sendo 5% melhor do que as técnicas utilizadas geralmente (Status- Quo). A análise de custo- eficácia foi realizada através da simulação de percursos de vida durante horizontes temporais pré-determinados em que cada cenário é testado através de 100.000 micro-simulações Monte Carlo. Os diferentes dados necessários para modelar e avaliar o percurso de vida, desde os custos associados às diferentes técnicas e tratamentos às performances para diferentes modalidades envolvidas foram recolhidas da literatura utilizando critério pré-definidos. Os resultados para cada cenário em cada contexto são dados em custo/ por QALY, em que o QALY (Quality -adjusted life year) equivale a um ano de vida num estado de perfeita saúde. A avaliação de cada estado/passo no modelo é feita através das utilities que avaliam cada estado/passo no modelo, permitindo obter uma total de QALY’s em cada microsimulação realizada durante um dado horizonte temporal. A ponderação da viabilidade de cada cenário em termos de custo- eficácia é sempre efetuada mediante a análise dos respectivos ICER’s (Incremental cost-effectiveness ratio) relativamente ao status quo. De uma forma geral, o estudo efetuado permitiu concluir que o PAM apresenta rácios de custo- eficácia viáveis em 2 cenários do grupo II: no grupo de indivíduos de alto risco com mamas densas com idades compreendidas entre os 40 e os 59 anos e no grupo de indivíduos de médio risco com mamas densas com idades compreendidas entre os 40 e os 49 anos. Por outro lado, os resultados obtidos com o grupo III de cenários permitiu concluir que a melhoria em 5% da performance dos equipamentos utilizados presentemente (satus-quo) com os custos do PAM permite obter rácios de custo-eficácia viáveis em todos os cenários do trajeto regular de rastreio e de diagnóstico do cancro da mama (rastreio, diagnóstico precoce e diagnóstico tardio).Breast cancer is one of the most common forms of cancer and one of the main causes of cancer death among females. The breast imaging standard procedures - X-ray mammography, MRI or ultrasound - suffer from some shortcomings such as insufficient specificity or sensitivity or carcinogenic risks (X-ray mammography) and high costs (MRI). Several alternatives have been suggested, among which photoacoustic technologies with near infrared (NIR) light are included. The medical photoacoustic devices merge the advantages of pure optic devices and of pure acoustic devices minimizing the respective disadvantages. Furthermore, the photoacoustic imaging can visualize the angiogenseis due to the associated increased hemoglobin concentration, with optical contrast and acoustic resolution, without the use of ionizing radiation or contrast agents and is therefore theoretically considered an ideal method for breast imaging. Under this principle, the department of Biomedical Photonic Imaging of University of Twente has designed an innovative device – The Twente Photoacoustic Mammoscope (PAM). The PAM optical source is a Q-switched Nd:YAG laser operating at 1064 nm with 5/ 10 ns pulses and a 10 Hz repetition rate. For acoustic signal reception PAM has a flat array ultrasound detector with 590 elements in a parallel plate geometry. The measured lateral and axial resolution is 2.3 to 3.9 mm and 2.5 to 3.3. mm respectively. The assessment of PAM is in process and can be placed at the main stream HTA – phase I: The first of 3 phases of clinical trials has started in December 2010 and so far, 3 HTA studies were conducted to assess the viability of its clinical implementation. However the cost-effectiveness of PAM is still unknown. The aim of this project is to implement and evaluate Markov models through Monte Carlo simulation in order to assess the cost-effectiveness of PAM in different scenarios. The tested scenarios were aggregated in 3 distinct groups: in the regular stages of the clinical pathway of breast cancer – screening, early diagnosis and late diagnosis – named Group I, and in the screening of multiple groups of high to moderate risk of breast cancer as suggested by the guidelines, named Group II. The last group of scenarios- Group III had the purpose of measuring the cost-effectiveness for a hypothetical technology that has sensitivities or specificities 5% higher than the standard of care and the same cost of PAM. The scenarios were tested simultaneously in 2 different epidemiological and economical contexts: Portugal and Netherlands. The obtained results for the different scenarios were analysed, specifically the CE ratio and the ICER ratio considering a willingness to pay threshold for each country. The cost-effectiveness results suggest that the clinical application of PAM is viable in high to moderate risk groups of breast cancer with dense breasts. Therefore, the future PAM design and development should continue to pursuit a constant effectiveness in dense and non dense breasts because it is one of the major competitive advantages of PAM

Ultrasound-guided Optical Techniques for Cancer Diagnosis: System and Algorithm Development

Worldwide, breast cancer is the most common cancer among women. In the United States alone, the American cancer society has estimated there will be 271,270 new breast cancer cases in 2019, and 42,260 lives will be lost to the disease. Ultrasound (US), mammography, and magnetic resonance imaging (MRI) are regularly used for breast cancer diagnosis and therapy monitoring. However, they sometimes fail to diagnose breast cancer effectively. These shortcomings have motivated researchers to explore new modalities. One of these modalities, diffuse optical tomography (DOT), utilizes near-infrared (NIR) light to reveal the optical properties of tissue. NIR-based DOT images the contrast between a suspected lesion’s location and the background tissue, caused by the higher NIR absorption of the hemoglobin which characterizes tumors. The limitation of high light scattering inside tissue is minimized by using ultrasound image to find the tumor location. This thesis focuses on developing a compact, low-cost ultrasound guided diffuse optical tomography imaging system and on improving optical image reconstruction by extracting the tumor’s location and size from co-registered ultrasound images. Several electronic components have been redesigned and optimized to save space and cost and to improve the user experience. In terms of software and algorithm development, manual extraction of tumor information from ultrasound images has been replaced by using a semi-automated ultrasound image segmentation algorithm that reduces the optical image reconstruction time and operator dependency. This system and algorithm have been validated with phantom and clinical data and have demonstrated their efficacy. An ongoing clinical trial will continue to gather more patient data to improve the robustness of the imaging algorithm. Another part of this research focuses on ovarian cancer diagnosis. Ovarian cancer is the most deadly of all gynecological cancers, with a less than 50% five-year survival rate. This cancer can evolve without any noticeable symptom, which makes it difficult to diagnose in an early stage. Although ultrasound-guided photoacoustic tomography (PAT) has demonstrated potential for early detection of ovarian cancer, clinical studies have been very limited due to the lack of robust PAT systems. In this research, we have customized a commercial ultrasound system to obtain real-time co-registered PAT and US images. This system was validated with several phantom studies before use in a clinical trial. PAT and US raw data from 30 ovarian cancer patients was used to extract spectral and statistical features for training and testing classifiers for automatic diagnosis. For some challenging cases, the region of interest selection was improved by reconstructing co-registered Doppler images. This study will be continued in order to obtain quantitative tissue properties using US-guided PAT

Novel Diagnostic Tools for Skin and Periorbital Cancer - Exploring Photoacoustic Imaging and Diffuse Reflectance Spectroscopy

The eyelids are susceptible to a number of skin cancers which are challenging to excise radically without sacrificing excessive healthy tissue. The way in which a tumor is delineated preoperatively has not changed significantly over the past century. The aims of the work presented in this thesis were to investigate two novel non-invasive techniques for diagnosing and delineating skin tumors.Extended-wavelength diffuse reflectance spectroscopy (EWDRS) was evaluated to determine its ability to differentiate between and classify different skin and tissue types in an in vivo pig model, with the aid of machine learning methods.The recordings were used to train a support vector machine, and it was possible to perform classifications with an overall accuracy of over 98%. The ability of EWDRS to identify the borders of pigmented skin lesions in an in vivo pig model was also evaluated. Using a thin probe, it was possible to detect the border with a median discrepancy of 70 μm, compared to the border found on histological examination.Photoacoustic imaging (PAI), a biomedical imaging modality that combines laser irradiation and ultrasound, was used to examine basal cell carcinomas (BCCs) and human eyelids ex vivo. Typical photoacoustic spectra were observed for BCCs as well as for the different layers of the healthy eyelid, and these structures could be visualized in three-dimensional images. A case was described in which PAI showed that the pentagonal excision of an eyelid BCC was non-radical, as was later confirmed by histological examination.In conclusion, both EWDRS and PAI are capable of differentiating between different kinds of tissue and, following further development and studies, could potentially be used to diagnose and delineate skin and eyelid tumors prior to surgical excision

Photoacoustic Microscopy and Computed Tomography: From Bench to Bedside

Photoacoustic imaging (PAI) of biological tissue has seen immense growth in the past decade, providing unprecedented spatial resolution and functional information at depths in the optical diffusive regime. PAI uniquely combines the advantages of optical excitation and those of acoustic detection. The hybrid imaging modality features high sensitivity to optical absorption and wide scalability of spatial resolution with the desired imaging depth. Here we first summarize the fundamental principles underpinning the technology, then highlight its practical implementation, and finally discuss recent advances toward clinical translation

Development and applications of novel fluorescent molecular probe strategies

Optical imaging and spectroscopy technologies offer the ability to provide structural and functional information in a fast, low-cost, ionizing radiation free, highly sensitive and high throughput fashion. The diverse contrast mechanisms and complementary imaging platforms form the foundation for the application of optical imaging in pre-clinical studies of pathophysiological development as well as direct clinical application as a tool for diagnosis and therapy. Fluorescence imaging techniques have been one of the most rapidly adopted methods in biology and biomedicine. Visualization of biological processes and pathologic conditions at the cellular and tissue levels largely relies on the use of exogenous fluorophores or their bioconjugates. Some fluorescent molecular probes provide usable contrast for disease diagnosis due to their responsiveness to interactions with other molecular species and/or immediate microenvironment. As a result, understanding exogenous fluorescent contrast mechanisms will allow the development of efficient strategies for biomedical fluorescence imaging. The present work focuses on exploring novel fluorescent molecular probe strategies for imaging cancer and cardiovascular diseases. We have developed a platform for synthesizing activatable fluorescent molecular probes using the fluorescence quenching properties of copper (II) ions. We used these activatable probes for rapid imaging of cancerous tissue in vivo in mice. While developing these molecular probes, we discovered an unexpected molecular interaction that yields stable dimeric molecules. This finding can potentially enable the development of new molecular entities for modifying the signaling properties of fluorescent dyes to minimize background fluorescence. Although planar fluorescence imaging methods using exogenous molecular probes provide rapid information about molecular processes in vivo, extraction of depth information require complex data acquisition and image analysis methods. By designing a dual emission fluorescent probe incorporating two spectrally different fluorophore systems, we developed a method to successfully estimate the depth of fluorescent inclusions from planar imaging data and demonstrated the potential of using this approach to locate a blood vessel and tumorous tissue in mouse in vivo. An important feature of fluorescence methods is the availability of various techniques that provide complementary information. Combining the fluorescence intensity and lifetime properties of a biologically targeted near infrared fluorescent probe, we demonstrate an effective way to distinguish specific from nonspecific uptake mechanisms in cancer cells, an approach that can be translated in vivo. Alternatively, dynamic fluorescence imaging technique expands the scope of applications to include detection and estimation of the size of circulating cancer cells and clusters. The approach developed in this work could allow longitudinal monitoring of these cells, which are implicated in cancer metastases. To circumvent the shallow penetration of light using optical methods, we developed multimodal imaging approaches by incorporating a radionuclide for nuclear imaging into a broad spectrum near infrared fluorescent tumor targeting agent. This molecular construct allows for noninvasive whole body nuclear imaging of tumors, followed by fluorescence image guided resection. In each of these areas, novel fluorescent molecular probes were developed, characterized and applied to solve critical biomedical problems

Photoacoustic tomography of intact human prostates and vascular texture analysis identify prostate cancer biopsy targets

Prostate cancer is poorly visualized on ultrasonography (US) so that current biopsy requires either a templated technique or guidance after fusion of US with magnetic resonance imaging. Here we determined the ability for photoacoustic tomography (PAT) and US followed by texture-based image processing to identify prostate biopsy targets. K-means clustering feature learning and testing was performed on separate datasets comprised of 1064 and 1197 nm PAT and US images of intact, ex vivo human prostates. 1197 nm PAT was found to not contribute to the feature learning, and thus, only 1064 nm PAT and US images were used for final feature testing. Biopsy targets, determined by the tumor-assigned pixels' center of mass, located 100% of the primary lesions and 67% of the secondary lesions. In conclusion, 1064 nm PAT and US texture-based feature analysis provided successful prostate biopsy targets

Intraoperative Photoacoustic Imaging of Breast Cancer

Breast cancer is one of the most common cancers to affect women, presenting a lifetime risk of 1 in 8. Treatment of stage 1 and 2 cancers usually involves breast conserving surgery (BCS). The goal of BCS is to remove the entire tumour with a surrounding envelope of healthy tissue, referred to as a negative margin. Unfortunately, up to 50% of surgeries fail to remove the whole tumour. To minimize the risk of cancer recurrence, a second surgery, must therefore be performed. Currently, there is no widely accepted intraoperative tool to significantly mitigate this problem. Employed systems are usually based on imaging, such as x-ray or ultrasonography. Unfortunately, sensitivity and specificity deficits, especially related to breast density, reduce the effectiveness of these methods. Photoacoustic tomography (PAT) is a relatively new imaging modality which uses safe near-infrared laser illumination to generate 3-D images of soft tissues to a depth of up to several cm. We used a custom designed and built intraoperative PAT system, called iPAT, to perform a 100 patient study on freshly excised breast lumpectomy specimens within the surgical setting. The system enabled the evaluation of tumour extent, shape, morphology and position within lumpectomy specimens measuring up to 11 cm in diameter. Scan results were used to compare iPAT-derived tumour size to the gold-standard pathologic examination, and when available, to x-ray, ultrasonography and DCE-MRI. Imaging results were also used to classify specimen margins as close or wide, and positive predictive values (PPV), negative predictive values (NPV), sensitivity and specificity were then calculated to estimate the effectiveness of the iPAT system at predicting lumpectomy margin status. With a close margin prevalence of 35%, the PPV, NPV, sensitivity and specificity of iPAT were found to be 71%, 83%, 69%, and 84%, respectively. Information provided by the iPAT system identified 9 out of the 12 positive specimens, potentially reducing the positive margin rate by 75%. . Contrary to expected photoacoustic contrast mechanisms, iPAT images of hemoglobin distribution correlated poorly with US and X-ray tumour imaging, while hypo-intense regions in lipid-weighted iPAT images were in excellent agreement

Photoacoustic microscopy

Photoacoustic microscopy (PAM) is a hybrid in vivo imaging technique that acoustically detects optical contrast via the photoacoustic effect. Unlike pure optical microscopic techniques, PAM takes advantage of the weak acoustic scattering in tissue and thus breaks through the optical diffusion limit (∼1 mm in soft tissue). With its excellent scalability, PAM can provide high-resolution images at desired maximum imaging depths up to a few millimeters. Compared with backscattering-based confocal microscopy and optical coherence tomography, PAM provides absorption contrast instead of scattering contrast. Furthermore, PAM can image more molecules, endogenous or exogenous, at their absorbing wavelengths than fluorescence-based methods, such as wide-field, confocal, and multi-photon microscopy. Most importantly, PAM can simultaneously image anatomical, functional, molecular, flow dynamic and metabolic contrasts in vivo. Focusing on state-of-the-art developments in PAM, this Review discusses the key features of PAM implementations and their applications in biomedical studies

Progress in Probe-Based Sensing Techniques for In Vivo Diagnosis

Advancements in robotic surgery help to improve the endoluminal diagnosis and treatment with minimally invasive or non-invasive intervention in a precise and safe manner. Miniaturized probe-based sensors can be used to obtain information about endoluminal anatomy, and they can be integrated with medical robots to augment the convenience of robotic operations. The tremendous benefit of having this physiological information during the intervention has led to the development of a variety of in vivo sensing technologies over the past decades. In this paper, we review the probe-based sensing techniques for the in vivo physical and biochemical sensing in China in recent years, especially on in vivo force sensing, temperature sensing, optical coherence tomography/photoacoustic/ultrasound imaging, chemical sensing, and biomarker sensing