Frontiers in Biophotonics for Translational Medicine

This chapter reviews the fluorescence lifetime techniques currently applied in biomedical diagnostics. Specifically the chapter focuses on time-resolved fluorescence spectroscopy (TRFS) and fluorescence lifetime imaging (FLIM) technologies for in vivo tissue characterization, with special emphasis on the translational potential of these techniques and the prospects of autofluorescence to provide intrinsic contrast for the assessment and diagnosis of human diseases. The use of these techniques in a number of medical applications, including cancer (gastrointestinal tract, lung, head and neck, brain and breast), skin and eye diseases, and atherosclerotic cardiovascular disease, are discussed and their recent developments towards translational medicine are highlighted.

Photoacoustic microscopy (PAM), combining the advantages of optical excitation and of acoustic detection, has been widely used for both structural and functional imaging with scalable resolution and penetration in biological tissues. In this chapter, we provide a detailed discussion on PAM in translational studies. We first summarize the principles and major implementations of this technology. Then we introduce the state of the art in translational PAM, including studies on burns, peripheral arterial occlusive disease, eye disease, diabetic microvascular complications, pain, melanoma, gastrointestinal tract disease, and the brain. Finally, we discuss the major challenges and future directions of translational PAM.

Optoacoustic imaging has been widely used for in vivo disease diagnosis and therapy monitoring. Acquisition hardware, analysis, and contrast agents have been subject to much innovation, creating access to an ever-growing range of biomedical applications. In this review, a broad overview of optoacoustic theory, instrumentation and data processing is provided, together with the various categories of contrast agents that have been developed. In addition, the application of these techniques and contrast agents in preclinical and clinical imaging applications will be discussed in detail, ranging from imaging of cancer and various organs like skin, brain and breast to sentinel lymph node mapping. Finally under conclusions, we highlighted future perspectives in this field, in the context of instrumentation and software development, as well as advances in clinical translation.

Raman spectroscopy is a powerful tool for measuring chemical properties of biological samples. This technique is based on inelastic scattering of light by molecules. The frequency shifts of the scattered light are related to the characteristic vibrational frequencies of the molecules, therefore the Raman spectrum is a “chemical fingerprint” of the sample. Raman spectroscopy has several features that make it attractive for translational medicine applications: (i) it requires no (or minimal) sample preparation; (ii) no labelling is required as diagnosis is based on the intrinsic chemical contrast of the sample; (iii) Raman spectroscopy uses light in the visible or near-infrared regions of the electromagnetic spectrum, where high performance microscopy and optoelectronics components have been developed during the last decades. Thus, recent advances in laser technologies, fibre optics, optical microscopes and light detectors, have brought Raman spectroscopy closer to real medical and clinical applications. This chapter reviews the main Raman spectroscopy techniques applied to translational medicine and provides an overview of various applications.

To see what is happening under our skin using light would have been a dream, as there are many strong absorbers and scatterers that act as hindrances for imaging purpose. Although light penetrates the skin a little and it is possible to image and monitor superficial blood flow using light illumination, it remains as a challenge to probe deep tissue (roughly 0.1 ~ 3.0 cm) using light alone. In this chapter, we describe the challenges and recent achievements of diffuse optical methods to probe deep tissue, running the gamut from diffuse optical spectroscopy (DOS) and diffuse optical tomography (DOT) to recently developed diffuse speckle contrast analysis (DSCA). Diffuse optics has opened up a new possibility of non-invasive diagnosis of lesions in deep tissue. In addition, the usage of light makes diffuse optics-based device compatible with other conventional medical devices such as CT and MRI as well as some implanted device such as pace maker. Moreover, diffuse optics-based device is relatively cost-effective and portable. These merits could limitlessly extend its application to primary care unit, bedside monitoring, and operation theater as an optimal modality for probing hemodynamic parameters in microvasculature in deep tissue.

Optical coherence tomography (OCT) is a low-coherence interferometry based bio-imaging technology. It has attracted extensive research interests in recent years for its non-invasive, high-speed and high-resolution properties. Numerous schemes for improving OCT resolutions have been demonstrated in literature. This chapter gives a comprehensive review of the recent developments of spectral domain (SD)-OCT systems with either high axial-resolution or lateral resolution, and then highlights the wide applications of such high-resolution OCT systems in biomedical imaging process. The influences of high-resolution OCT systems towards translational medicine are also discussed.

Photoacoustic (PA) imaging is a promising biomedical imaging modality that has emerged over the last decade. In this method, imaging is performed using pulsed far-red or near-infrared light. This light while scattering through soft tissue is absorbed at specific locations by certain molecules such as hemoglobin in blood. The absorbed energy is converted into heat; the subsequent thermoelastic expansion causes ultrasound (US) to be produced from the absorbing region. The US is measured at the surface of tissue using US detectors and the acquired signals are used to reconstruct the location and spatial details of the absorber. PA imaging thus combines the advantages of optical and US imaging, providing excellent optical spectroscopic contrast with ultrasonic resolution. While US imaging utilizes acoustic impedance mismatches in tissue for its signals to provide structural details, PA imaging extracts functional information based on optical absorption by chromophores, predominantly blood, and often exogenous contrast agents. Since PA imaging involves US detection, it can be seamlessly implemented in a commercially available US scanner to perform dual mode PA/US imaging, which is a promising translational medical diagnostic technique. These dual mode systems providing complementary contrast hold potential for myriad of clinical applications. Handheld dual mode US/PA probes use reflection mode imaging geometry, where light irradiation is done from the same side where PA signals are detected. These epi-style handheld probe-based imaging setup delivers flexibility in imaging different body parts using the same probe. This review details the fundamentals of PA/US imaging and also depicts the importance of handheld probe-based dual mode PA/US systems. Particular attention is paid to the engineering aspects of systems developed by different groups and range of clinical applications demonstrated by them.

This chapter provides an overview of plasmonic biosensor technology for the analysis of extracellular lipid vesicles that hold potential to serve as new type of biomarkers. In particular, it discusses detection of exosomes that are secreted to bodily fluids and become of increasing interest in clinical research. Plasmonic biosensor technology is pushed forward to provide new means for their sensitive and specific detection without the need of specialized laboratories. It offers a versatile optical toolbox for probing various biological species by tightly confined electromagnetic field of surface plasmons. These optical waves originate from collective oscillations of electron charge density at metallic thin films and (nano)structures. This chapter gives an introduction to surface plasmon photonics and its use in direct surface plasmon resonance and in fluorescence spectroscopy-based biosensors. It provides a brief summary of current state-of-the-art in exosome biomarker research and discusses current advances in exosome plasmonic biosensors for medical diagnostics of diseases, in particular cancer.

Endoscopy—looking deep inside the body with light—is an important part of standard medical practice, for disease detection/localization and staging and to guide treatments and monitor responses. This is especially the case in oncology applications, which is the primary focus of this chapter. However, established endoscopy techniques are unable to meet all the clinical needs and in particular fail to exploit the rich information provided by advances in molecular biology, including genomics and proteomics. Incorporating the use of nanoparticles into endoscopic technologies and procedures can significantly extend their capabilities and hence potential clinical impact. This chapter describes the endoscopic techniques that are currently in use, as well as emerging approaches using different light-tissue interactions, and how incorporating nanoparticles can enhance their information content and hence clinical sensitivity and specificity. Specific examples of current research in this field are presented in more detail to demonstrate the range of potential nanoparticle applications. Thus, surface enhanced Raman scattering nanoparticles are being developed to achieve biomarker-targeted, multiplexed imaging for tissue characterization by endoscopy, while lipid-porphyrin nanoparticles can be conjugated to targeting agents and visualized through high red/near-infrared absorption using photoacoustic methods as well as being used to enhance and spatially-localize photothermal treatment. Optimal nanoparticles for photodynamic therapy are also discussed. Challenges in the translation into clinical practice of emerging nanoparticle-enabled endoscopies are highlighted.

The development of fast, non-invasive and accurate diagnostics is of great importance in the medical field. Lasers, and optical spectroscopy and imaging techniques provide many new possibilities. Most frequently broad-band spectroscopic techniques are used for studying tissue constituents. Instead, the development of novel methods for monitoring free gas in situ using narrow-band laser spectroscopic techniques in the diagnostics of common infectious diseases and for the surveillance of pre-term infants is presented in this chapter. The gas in scattering media absorption spectroscopy (GASMAS) technique is used, relying on the fact, that the absorptive imprints of free gases are typically 10,000 times narrower than those due to the tissue itself. The work is in a translational process aiming at better diagnostics of common sinus and middle-ear infections (sinusitis and otitis) and for the management of the respiratory distress syndrome and necrotizing enterocolitis in premature infants.

Laparoscopic surgery in clinical practice has made great strides in extending novel techniques and technology in treating numerous disease conditions in recent years. It has also improved the patient’s outcome while lowering the overall cost of healthcare due mainly to the shorter duration of hospitalization. Despite the progress, the ability of a surgeon to view diseased tissue, critical structures such as blood vessels has been limited to the live video images that the surgeon views during surgery. This study looks first into the imaging needs of surgeons during laparoscopic surgery for common procedures; it then reviews the current state of the art for each imaging modality in relation to the needs of the surgeons as identified. The review concludes with a summary of the potential for some of these optical imaging methods to become mainstream techniques in laparoscopic imaging.