Optical microscopy has been a fundamental tool of biological discovery for more than three centuries, but its in vivo tissue imaging ability has been restricted by light scattering to superficial ...investigations, even when confocal or multiphoton methods are used. Recent advances in optical and optoacoustic (photoacoustic) imaging now allow imaging at depths and resolutions unprecedented for optical methods. These abilities are increasingly important to understand the dynamic interactions of cellular processes at different systems levels, a major challenge of postgenome biology. This Review discusses promising photonic methods that have the ability to visualize cellular and subcellular components in tissues across different penetration scales. The methods are classified into microscopic, mesoscopic and macroscopic approaches, according to the tissue depth at which they operate. Key characteristics associated with different imaging implementations are described and the potential of these technologies in biological applications is discussed.
Fuelled by innovation, optical microscopy plays a critical role in the life sciences and medicine, from basic discovery to clinical diagnostics. However, optical microscopy is limited by typical ...penetration depths of a few hundred micrometres for in vivo interrogations in the visible spectrum. Optoacoustic microscopy complements optical microscopy by imaging the absorption of light, but it is similarly limited by penetration depth. In this Review, we summarize progress in the development and applicability of optoacoustic mesoscopy (OPAM); that is, optoacoustic imaging with acoustic resolution and wide-bandwidth ultrasound detection. OPAM extends the capabilities of optical imaging beyond the depths accessible to optical and optoacoustic microscopy, and thus enables new applications. We explain the operational principles of OPAM, its placement as a bridge between optoacoustic microscopy and optoacoustic macroscopy, and its performance in the label-free visualization of tissue pathophysiology, such as inflammation, oxygenation, vascularization and angiogenesis. We also review emerging applications of OPAM in clinical and biological imaging.
The emerging clinical use of targeted fluorescent agents heralds a shift in intraoperative imaging practices that overcome the limitations of human vision. However, in contrast to established ...radiological methods, no appropriate performance specifications and standards have been established in fluorescence molecular imaging. Moreover, the dependence of fluorescence signals on many experimental parameters and the use of wavelengths ranging from the visible to short-wave infrared (400–1,700 nm) complicate quality control in fluorescence molecular imaging. Here, we discuss the experimental parameters that critically affect fluorescence molecular imaging accuracy, and introduce the concept of high-fidelity fluorescence imaging as a means for ensuring reliable reproduction of fluorescence biodistribution in tissue.
Ultrasonography1 and photoacoustic2,3 (optoacoustic) tomography have recently seen great advances in hardware and algorithms. However, current high-end systems still use a matrix of piezoelectric ...sensor elements, and new applications require sensors with high sensitivity, broadband detection, small size and scalability to a fine-pitch matrix. This work demonstrates an ultrasound sensor in silicon photonic technology with extreme sensitivity owing to an innovative optomechanical waveguide. This waveguide has a tiny 15 nm air gap between two movable parts, which we fabricated using new CMOS-compatible processing. The 20 μm small sensor has a noise equivalent pressure below 1.3 mPa Hz−1/2 in the measured range of 3–30 MHz, dominated by acoustomechanical noise. This is two orders of magnitude better than for piezoelectric elements of an identical size4. The demonstrated sensor matrix with on-chip photonic multiplexing5–7 offers the prospect of miniaturized catheters that have sensor matrices interrogated using just a few optical fibres, unlike piezoelectric sensors that typically use an electrical connection for each element.An optical ultrasound sensor based on a CMOS-compatible split-rib waveguide is demonstrated, offering high sensitivity, broadband detection (measured 3–30 MHz), small size (20 μm) and scalability to a fine-pitch matrix.
A key feature of optoacoustic imaging is the ability to illuminate tissue at multiple wavelengths and therefore record images with a spectral dimension. While optoacoustic images at single ...wavelengths reveal morphological features, in analogy to ultrasound imaging or X-ray imaging, spectral imaging concedes sensing of intrinsic chromophores and externally administered agents that can reveal physiological, cellular and subcellular functions. Nevertheless, identification of spectral moieties within images obtained at multiple wavelengths requires spectral unmixing techniques, which present a unique mathematical problem given the three-dimensional nature of the optoacoustic images. Herein we discuss progress with spectral unmixing techniques developed for multispectral optoacoustic tomography. We explain how different techniques are required for accurate sensing of intrinsic tissue chromophores such as oxygenated and deoxygenated haemoglobin versus extrinsically administered photo-absorbing agents and nanoparticles. Finally, we review recent developments that allow accurate quantification of blood oxygen saturation (sO2) by transforming and solving the sO2 estimation problem from the spatial to the spectral domain.
This article is part of the themed issue ‘Challenges for chemistry in molecular imaging’.
In a pilot study, we introduce fast handheld multispectral optoacoustic tomography (MSOT) of the breast at 28 wavelengths, aiming to identify high-resolution optoacoustic (photoacoustic) patterns of ...breast cancer and noncancerous breast tissue.
We imaged 10 female patients ages 48-81 years with malignant nonspecific breast cancer or invasive lobular carcinoma. Three healthy volunteers ages 31-36 years were also imaged. Fast-MSOT was based on unique single-frame-per-pulse (SFPP) image acquisition employed to improve the accuracy of spectral differentiation over using a small number of wavelengths. Breast tissue was illuminated at the 700-970 nm spectral range over 0.56 seconds total scan time. MSOT data were guided by ultrasonography and X-ray mammography or MRI.
The extended spectral range allowed the computation of oxygenated hemoglobin (HBO
), deoxygenated hemoglobin (HB), total blood volume (TBV), lipid, and water contributions, allowing first insights into
high-resolution breast tissue MSOT cancer patterns. TBV and Hb/HBO
images resolved marked differences between cancer and control tissue, manifested as a vessel-rich tumor periphery with highly heterogeneous spatial appearance compared with healthy tissue. We observe significant TBV variations between different tumors and between tumors over healthy tissues. Water and fat lipid layers appear disrupted in cancer versus healthy tissue; however, offer weaker contrast compared with TBV images.
In contrast to optical methods, MSOT resolves physiologic cancer features with high resolution and revealed patterns not offered by other radiologic modalities. The new features relate to personalized and precision medicine potential.
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Advances in genetic engineering have enabled the use of bacterial outer membrane vesicles (OMVs) to deliver vaccines, drugs and immunotherapy agents, as a strategy to circumvent biocompatibility and ...large-scale production issues associated with synthetic nanomaterials. We investigate bioengineered OMVs for contrast enhancement in optoacoustic (photoacoustic) imaging. We produce OMVs encapsulating biopolymer-melanin (OMV
) using a bacterial strain expressing a tyrosinase transgene. Our results show that upon near-infrared light irradiation, OMV
generates strong optoacoustic signals appropriate for imaging applications. In addition, we show that OMV
builds up intense heat from the absorbed laser energy and mediates photothermal effects both in vitro and in vivo. Using multispectral optoacoustic tomography, we noninvasively monitor the spatio-temporal, tumour-associated OMV
distribution in vivo. This work points to the use of bioengineered vesicles as potent alternatives to synthetic particles more commonly employed for optoacoustic imaging, with the potential to enable both image enhancement and photothermal applications.
There is a wealth of new fluorescent reporter technologies for tagging of many cellular and subcellular processes in vivo. This imposed contrast is now captured with an increasing number of available ...imaging methods that offer new ways to visualize and quantify fluorescent markers distributed in tissues. This is an evolving field of imaging sciences that has already achieved major advances but is also facing important challenges. It is nevertheless well poised to significantly impact the ways of biological research, drug discovery, and clinical practice in the years to come. Herein, the most pertinent technologies associated with in vivo noninvasive or minimally invasive fluorescence imaging of tissues are summarized. Focus is given to small-animal imaging. However, while a broad spectrum of fluorescence reporter technologies and imaging methods are outlined, as necessary for biomedical research, and clinical translation as well.
Multi-Spectral Optoacoustic Tomography (MSOT) merges the power of high-resolution imaging at tissue depths of several millimeters to centimeters with the advantages of optical imaging, in large part ...by exploiting spectral detection of endogenous molecules in tissue or exogenous photoabsorbing probes. Current advances in fast-tuning laser technology, image reconstruction and spectral detection schemes have yielded real-time optoacoustic (photoacoustic) imaging spanning applications from microscopy to human imaging. This progress has generated an unprecedented need for imaging probes and reporter gene approaches optimized for optoacoustic signal generation. New classes of probes are emerging and create new opportunities for visualizing morphological and pathophysiological features in vivo, in a non-invasive manner. Here we review recent progress in optoacoustic probes and discuss applications and challenges for biological imaging as well as prospects for clinical translation.
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