Complete-noncontact photoacoustic microscopy by detection of initial pressures using a 3×3 coupler-based fiber-optic interferometer

Optical ultrasound sensors for photoacoustic imaging: a review

Significance

Photoacoustic (PA) imaging is an emerging biomedical imaging modality that can map optical absorption contrast in biological tissues by detecting ultrasound signal. Piezoelectric transducers are commonly used in PA imaging to detect the ultrasound signals. However, piezoelectric transducers suffer from low sensitivity when the dimensions are reduced and are easily influenced by electromagnetic interference. To avoid these limitations, various optical ultrasound sensors have been developed and shown their great potential in PA imaging.

Aim

Our study aims to summarize recent progress in optical ultrasound sensor technologies and their applications in PA imaging.

Approach

The commonly used optical ultrasound sensing techniques and their applications in PA systems are reviewed. The technical advances of different optical ultrasound sensors are summarized.

Results

Optical ultrasound sensors can provide wide bandwidth and improved sensitivity with miniatured size, which enables their applications in PA imaging.

Conclusions

The optical ultrasound sensors are promising transducers in PA imaging to provide higher-resolution images and can be used in new applications with their unique advantages.

Experimental demonstration of non-contact and quasi OPD-independent nanoscale-displacement measurement by phase-diversity optical digital coherent detection and comb filtering

We experimentally demonstrated and quantitatively evaluated a non-contact nanometer-displacement measurement using phase-diversity optical digital coherent detection implemented by a 90 ° optical hybrid and a narrow-linewidth probe laser without fine-tuning of optical path length difference (OPD). Combined with a comb filter, the system exhibits 99.99% linearity detection with a scale and resolution of approximately 7 nm and 2 nm respectively, as well as a wideband vibration of 5.85 MHz. We also experimentally analyzed the effect of noise arising from the OPD and demonstrated the detection of displacement down to 85 nm with a resolution of 24 nm at an OPD of 342 cm.

Applications of Optical Fiber in Label-Free Biosensors and Bioimaging: A Review

Biosensing and bioimaging are essential in understanding biological and pathological processes in a living system, for example, in detecting and understanding certain diseases. Optical fiber has made remarkable contributions to the biosensing and bioimaging areas due to its unique advantages of compact size, immunity to electromagnetic interference, biocompatibility, fast response, etc. This review paper will present an overview of seven common types of optical fiber biosensors and optical fiber-based ultrasound detection in photoacoustic imaging (PAI) and the applications of these technologies in biosensing and bioimaging areas. Of course, there are many types of optical fiber biosensors. Still, this paper will review the most common ones: optical fiber grating, surface plasmon resonance, Sagnac interferometer, Mach-Zehnder interferometer, Michelson interferometer, Fabry-Perot Interferometer, lossy mode resonance, and surface-enhanced Raman scattering. Furthermore, different optical fiber techniques for detecting ultrasound in PAI are summarized. Finally, the main challenges and future development direction are briefly discussed.

All-optical ultrasonic detector based on differential interference

We report on an all-optical ultrasonic detecting method based on differential interference. A linearly polarized probe beam is split into two closely separated ones with orthogonal polarization. After interacting with propagating ultrasonic waves in a coupling media, the split beams are recombined into one beam, with its polarization being changed into an elliptical one by the elastic-optical effect. The recombined beam is filtered by an analyzer and detected by a photodetector. The bandwidth and noise-equivalent pressure (NEP) of the acoustic detector are determined to be 107.4 MHz and 2.18 kPa, respectively. We also demonstrate its feasibility for photoacoustic microscopy (PAM) using agar-embedded phantoms.

Spectral interference contrast based non-contact photoacoustic microscopy realized by SDOCT

We introduce a method to extract the photoacoustic (PA) signal from a contrast reduction of the interference spectrum acquired by spectral domain optical coherence tomography (SDOCT). This all-optical detection is achieved in a noncontact manner directly on the water surface covered on the sample by using its specular reflection. During SDOCT exposure, the phase of the interference spectrum keeps shaking according to the water surface vibration induced by PA excitation. This results in an interference contrast reduction which is quantified by a fast Fourier transform (FFT) for PA imaging. A tungsten filament, asparagus fern leaf, and mouse auricle are imaged to demonstrate the method.

Optical ultrasound sensors for photoacoustic imaging: a narrative review

Optical ultrasound sensors have been increasingly employed in biomedical diagnosis and photoacoustic imaging (PAI) due to high sensitivity and resolution. PAI could visualize the distribution of ultrasound excited by laser pulses in biological tissues. The information of tissues is detected by ultrasound sensors in order to reconstruct structural images. However, traditional ultrasound transducers are made of piezoelectric films that lose sensitivity quadratically with the size reduction. In addition, the influence of electromagnetic interference limits further applications of traditional ultrasound transducers. Therefore, optical ultrasound sensors are developed to overcome these shortcomings. In this review, optical ultrasound sensors are classified into resonant and non-resonant ones in view of physical principles. The principles and basic parameters of sensors are introduced in detail. Moreover, the state of the art of optical ultrasound sensors and applications in PAI are also presented. Furthermore, the merits and drawbacks of sensors based on resonance and non-resonance are discussed in perspectives. We believe this review could provide researchers with a better understanding of the current status of optical ultrasound sensors and biomedical applications.

Optical dosimeter for selective retinal therapy based on multi-port fiber-optic interferometry

Selective retinal therapy (SRT) employs a micro-second short-pulse lasers to induce localized destruction of the targeted retinal structures with a pulse duration and power aimed at minimal damage to other healthy retinal cells. SRT has demonstrated a great promise in the treatment of retinal diseases, but pulse energy thresholds for effective SRT procedures should be determined precisely and in real time, as the thresholds could vary with disease status and patients. In this study, we present the use of a multi-port fiber-based interferometer (MFI) for highly sensitive real-time SRT monitoring. We exploit distinct phase differences among the fiber ports in the MFI to quantitatively measure localized fluctuations of complex-valued information during the SRT procedure. We evaluate several metrics that can be computed from the full complex-valued information and demonstrate that the complex contour integration is highly sensitive and most correlative to pulse energies, acoustic outputs, and cell deaths. The validity of our method was demonstrated on excised porcine retinas, with a sensitivity and specificity of 0.92 and 0.88, respectively, as compared with the results from a cell viability assay.

Another decade of photoacoustic imaging

Photoacoustic imaging - a hybrid biomedical imaging modality finding its way to clinical practices. Although the photoacoustic phenomenon was known more than a century back, only in the last two decades it has been widely researched and used for biomedical imaging applications. In this review we focus on the development and progress of the technology in the last decade (2010-2020). From becoming more and more user friendly, cheaper in cost, portable in size, photoacoustic imaging promises a wide range of applications, if translated to clinic. The growth of photoacoustic community is steady, and with several new directions researchers are exploring, it is inevitable that photoacoustic imaging will one day establish itself as a regular imaging system in the clinical practices.

Towards non-contact photoacoustic imaging [review]

Photoacoustic imaging (PAI) takes advantage of both optical and ultrasound imaging properties to visualize optical absorption with high resolution and contrast. Photoacoustic microscopy (PAM) is usually categorized with all-optical microscopy techniques such as optical coherence tomography or confocal microscopes. Despite offering high sensitivity, novel imaging contrast, and high resolution, PAM is not generally an all-optical imaging method unlike the other microscopy techniques. One of the significant limitations of photoacoustic microscopes arises from their need to be in physical contact with the sample through a coupling media. This physical contact, coupling, or immersion of the sample is undesirable or impractical for many clinical and pre-clinical applications. This also limits the flexibility of photoacoustic techniques to be integrated with other all-optical imaging microscopes for providing complementary imaging contrast. To overcome these limitations, several non-contact photoacoustic signal detection approaches have been proposed. This paper presents a brief overview of current non-contact photoacoustic detection techniques with an emphasis on all-optical detection methods and their associated physical mechanisms.

Multiscale high-speed photoacoustic microscopy based on free-space light transmission and a MEMS scanning mirror

The conventional photoacoustic microscopy (PAM) system allows trade-offs between lateral resolution and imaging depth, limiting its applications in biological imaging in vivo. Here we present an integrated optical-resolution (OR) and acoustic-resolution (AR) multiscale PAM based on free-space light transmission and fast microelectromechanical systems (MEMS) scanning. The lateral resolution for OR is 4.9 µm, and the lateral resolution for AR is 114.5 µm. The maximum imaging depth for OR is 0.7 mm, and the maximum imaging depth for AR is 4.1 mm. The imaging speed can reach 50 k Alines per second. The high signal-to-noise ratios and wavelength throughput are achieved by delivering light via free-space, and the high speed is achieved by a MEMS scanning mirror. The blood vasculature from superficial skin to the deep tissue of a mouse leg was imaged in vivo using two different resolutions to demonstrate the multiscale imaging capability.