Fast controllable confocal focus photoacoustic microscopy using a synchronous zoom opto-sono objective

Design and fabrication of a focus-tunable liquid cylindrical lens based on electrowetting

In this study, a focus-tunable liquid cylindrical lens based on electrowetting was designed and fabricated. The cylindrical cavity usually used in common electrowetting zoom spherical lenses was replaced by a 20 mm × 10 mm × 8 mm cuboid cavity, in which the interface of two liquids formed a toroid owing to the electrowetting effect. The proposed liquid cylindrical lens can serve as either a converging or diverging lens with the response time under 110 ms by changing the supplied voltage. The zoom lens we fabricated worked stably under 0-110 V voltage for a long time, guaranteeing that the focal length of the liquid cylindrical lens can range within (-∞, -148.36 mm) ∪ (697.21 mm, +∞). By combining the liquid lens that we designed with a simple fixed cylindrical lens, a cylindrical lens system with an arbitrary focal length suitable for various tasks in beam manipulation can be realized.

Three dimensional confocal photoacoustic dermoscopy with an autofocusing sono-opto probe

Photoacoustic dermoscopy (PAD) is uniquely positioned for the diagnosis and assessment of dermatological conditions because of its ability to visualize optical absorption contrast in vivo in three dimensions. In this Letter, we developed a 3D confocal PAD (3D-CPAD) equipped with an autofocusing sono-opto probe to facilitate the reconstruction of high-spatial-resolution imaging of skin with multilaminate structures in depth direction. The autofocusing sono-opto probe integrated a 10-mm electrowetting-based varifocal lens to automatically control the acoustic and optical confocal length, and an annular ultrasonic detector with a mid-frequency of ~32.8 MHz is coaxially configured for receiving photoacoustic signals. Using this sono-opto probe, the acoustic and optical confocal length-shifting range from ~7 to 43 mm with high image contrast and spatial resolution in the 3D image reconstruction. Autofocusing property tests and 3D human skin in vivo imaging were carried out to demonstrate the imaging capability of the 3D-CPAD for potential clinical foreground in noninvasive biopsies of skin disease.

Multispectral photoacoustic holography of elastomers from a bright background

Photoacoustic imaging of elastomers has important biomedical value. However, a bright background, e.g., blood vessels in living tissue, brings a challenge for photoacoustic elastography. In this study, we predicted that the spectrum of photoacoustic signals from elastomers with high elasticity could appear as narrow peaks at the eigen-frequencies of elastomers, but the signals from a bright background, e.g., blood vessel, show flat broadband spectrum for their low-quality factor. Even when the two kinds of signals are mixed together, the signals from elastomers can be identified from the spectrum since they present as convex narrow peaks on a wide base. Based on this factor, we propose a multispectral photoacoustic holography to realize selective imaging of tiny elastomers. This method recovers the image only using several frequency components in photoacoustic signals, instead of the whole-band signal. Since these narrow peaks in the spectrum correspond to the eigen-vibration of elastomers, the proposed method can highlight the elastomers with high elasticity from a bright background with low elasticity. The method was validated by experiments. This study might be helpful to localize elastic anomalous areas in the tissue, such as calcification in the vascular network, microcalcification in a tumor, and implants.

Quantitative and anatomical imaging of dermal angiopathy by noninvasive photoacoustic microscopic biopsy

The ability to noninvasively acquire the fine structure of deep tissues is highly valuable but remains a challenge. Here, a photoacoustic microscopic biopsy (PAMB) combined switchable spatial-scale optical excitation with single-element depth-resolved acoustic detection mode was developed, which effectively coordinated the spatial resolution and the penetration depth for visualizations of skin delamination and chromophore structures up to reticular dermis depth, with the lateral resolution from 1.5 to 104 μm and the axial resolution from 34 to 57 μm. The PAMB obtained anatomical imaging of the pigment distribution within the epidermis and the vascular patterns of the deep dermal tissue, enabling quantification of morphological abnormalities of angiopathy without the need for exogenous contrast agents. The features of healthy skin and scar skin, and the abnormal alteration of dermal vasculature in port wine stains (PWS) skin were first precisely displayed by PAMB-shown multi-layered imaging. Moreover, the quantitative vascular parameters evaluation of PWS were carried out by the detailed clinical PAMB data on 174 patients, which reveals distinct differences among different skin types. PAMB captured the PWS changes in capillary-loop depth, diameter, and vascular volume, making it possible to perform an objective clinical evaluation on the severity of PWS. All the results demonstrated the PAMB can provide vascular biopsy and new indexes deep into the dermal skin noninvasively, which should be meaningful to timely evaluate the pathological types and treatment response of skin diseases. This opens up a new perspective for label-free and non-invasive biopsies of dermal angiopathy.

High stability liquid lens with optical path modulation function

In this paper, a high stability liquid lens with optical path modulation function is designed and fabricated. The liquid lens has an outer chamber and an inner chamber, and the inner chamber has a structure with three annular anchoring layers. This structure can limit the sliding of the three-phase contact line under electrowetting effect and anchor the position of contact angle with a limited distance. The feasibility of this structure is verified by simulation and practice. The zoom imaging, contact angle, focal length and response time of the liquid lens are analyzed. The structure with three annular anchoring layers provides six anchored precision optical path modulation gears, and the optical path difference can be changed by mechanical hydraulic control, up to 1.17 mm. Widespread applications of the proposed liquid lens are foreseeable such as microscopic imaging and a telescope system, etc.

Optical zoom imaging systems using adaptive liquid lenses

An optical zoom imaging system that can vary the magnification factor without displacing the object and the image plane has been widely used. Nonetheless, conventional optical zoom imaging systems suffer from slow response, complicated configuration, vulnerability to misalignment during zoom operation, and are incompatible with miniaturized applications. This review article focuses on state-of-the-art research on novel optical zoom imaging systems that use adaptive liquid lenses. From the aspect of the configuration, according to the number of adaptive liquid lenses, we broadly divide the current optical zoom imaging systems using adaptive liquid lenses into two configurations: multiple adaptive liquid lenses, and a single adaptive liquid lens. The principles and configurations of these optical zoom imaging systems are introduced and represented. Three different working principles of the adaptive liquid lens (liquid crystal, polymer elastic membrane, and electrowetting effect) adopted in the optical zoom imaging systems are reviewed. Some representative applications of optical zoom imaging systems using adaptive liquid lenses are introduced. The opportunities and challenges of the optical zoom imaging systems using adaptive liquid lenses are also discussed. This review aims to provide a snapshot of the current state of this research field with the aim to attract more attention to put forward the development of the next-generation optical zoom imaging systems.

An Ellipsoidal Focused Ultrasound Transducer for Extend-focus Photoacoustic Microscopy

OBJECTIVE

Limited by spherical focused ultrasound transducer (SUT) with a high acoustic numerical aperture, photoacoustic microscopy (PAM) suffers a rapidly degrading sensitivity and lateral resolution as increased depth. In this study, an ellipsoidal focused ultrasound transducer (EUT) was developed to address the above restriction via providing high sensitivity and lateral resolution over a large depth of field (DOF).

METHODS

To fabricate the EUT, the piezoelectric element was laminated onto a curved steel surface for self-focusing (the ellipsoidal continuous-focus geometry was employed instead of the spherical single-focus one). Additionally, phantoms and in vivo animal experiments were performed by an extend-focus PAM equipped with EUT to characterize its performance.

RESULTS

The EUT involved over 30 MHz center frequency and -6 dB bandwidth of 124% with a resolution-invariant focal depth of 1.39 mm, more than 3 times the DOF of the SUT.

CONCLUSION

The in vivo imaging results demonstrated that the EUT was capable of extending the focal depth to get rid of the restriction of the visual field, while the DOF of the SUT was limited by the nature of spherical geometry.

SIGNIFICANCE

The EUT markedly enhances the image quality at different imaging depths, which has great potential for promoting the biomedical development of in vivo rapid-noninvasive PAM.

In vivo volumetric monitoring of revascularization of traumatized skin using extended depth-of-field photoacoustic microscopy

Faster and better wound healing is a critical medical issue. Because the repair process of wounds is closely related to revascularization, accurate early assessment and postoperative monitoring are very important for establishing an optimal treatment plan. Herein, we present an extended depth-of-field photoacoustic microscopy system (E-DOF-PAM) that can achieve a constant spatial resolution and relatively uniform excitation efficiency over a long axial range. The superior performance of the system was verified by phantom and in vivo experiments. Furthermore, the system was applied to the imaging of normal and trauma sites of volunteers, and the experimental results accurately revealed the morphological differences between the normal and traumatized skin of the epidermis and dermis. These results demonstrated that the E-DOF-PAM is a powerful tool for observing and understanding the pathophysiology of cutaneous wound healing.