Interferometry-free noncontact photoacoustic detection method based on speckle correlation change

Photoacoustic speckle pattern interferometry for detecting cracks of different sizes

A system and method for non-destructive detection of cracks of different width and depths based on digital speckle interferometry coupled with pulsed laser excitation is introduced and tested. Based on photoacoustic effect, acoustic waves are induced onto the rear of the samples by pumping a pulsed laser beam on it. The generated mechanical wave propagates from the rear surface of the sample to the front while front surface is monitored by speckle interferometry. In order to acquire information about surface deformation, the front surface is illuminated by continuous wave laser and interference are imaged onto the camera as speckle images. After processing the produced fringe patterns, it indicates the presence and location of the cracks in qualitative way. In this study, the system and method mentioned above are validated by detecting medium density fiberboard with simulated cracks. The fringe patterns from areas with or without defects are compared and discussed. Besides, the system and method to distinguish and predict cracks sizes is proposed and validated.

Halftone spatial frequency domain imaging enables kilohertz high-speed label-free non-contact quantitative mapping of optical properties for strongly turbid media

The ability to quantify optical properties (i.e., absorption and scattering) of strongly turbid media has major implications on the characterization of biological tissues, fluid fields, and many others. However, there are few methods that can provide wide-field quantification of optical properties, and none is able to perform quantitative optical property imaging with high-speed (e.g., kilohertz) capabilities. Here we develop a new imaging modality termed halftone spatial frequency domain imaging (halftone-SFDI), which is approximately two orders of magnitude faster than the state-of-the-art, and provides kilohertz high-speed, label-free, non-contact, wide-field quantification for the optical properties of strongly turbid media. This method utilizes halftone binary patterned illumination to target the spatial frequency response of turbid media, which is then mapped to optical properties using model-based analysis. We validate the halftone-SFDI on an array of phantoms with a wide range of optical properties as well as in vivo human tissue. We demonstrate with an in vivo rat brain cortex imaging study, and show that halftone-SFDI can longitudinally monitor the absolute concentration as well as spatial distribution of functional chromophores in tissue. We also show that halftone-SFDI can spatially map dual-wavelength optical properties of a highly dynamic flow field at kilohertz speed. Together, these results highlight the potential of halftone-SFDI to enable new capabilities in fundamental research and translational studies including brain science and fluid dynamics.

Low-consumption photoacoustic method to measure liquid viscosity

Viscosity measurement is important in many areas of biomedicine and industry. Traditional viscometers are usually time-consuming and require huge sample volumes. Microfluidic viscometry may overcome the challenge of large sample consumption but suffers from a long process time and a complicated structure design and interaction. Here, we present a photoacoustic method that measures the liquid viscosity in a simple microfluidic-based tube. This new viscosity measurement method embraces fast detection speed and low fluid consumption, offering a new tool for efficient and convenient liquid viscosity measurement in a broad range of applications.

Photoacoustic-guided surgery from head to toe [Invited]

Photoacoustic imaging-the combination of optics and acoustics to visualize differences in optical absorption - has recently demonstrated strong viability as a promising method to provide critical guidance of multiple surgeries and procedures. Benefits include its potential to assist with tumor resection, identify hemorrhaged and ablated tissue, visualize metal implants (e.g., needle tips, tool tips, brachytherapy seeds), track catheter tips, and avoid accidental injury to critical subsurface anatomy (e.g., major vessels and nerves hidden by tissue during surgery). These benefits are significant because they reduce surgical error, associated surgery-related complications (e.g., cancer recurrence, paralysis, excessive bleeding), and accidental patient death in the operating room. This invited review covers multiple aspects of the use of photoacoustic imaging to guide both surgical and related non-surgical interventions. Applicable organ systems span structures within the head to contents of the toes, with an eye toward surgical and interventional translation for the benefit of patients and for use in operating rooms and interventional suites worldwide. We additionally include a critical discussion of complete systems and tools needed to maximize the success of surgical and interventional applications of photoacoustic-based technology, spanning light delivery, acoustic detection, and robotic methods. Multiple enabling hardware and software integration components are also discussed, concluding with a summary and future outlook based on the current state of technological developments, recent achievements, and possible new directions.

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.

Photoacoustic imaging of microenvironmental changes in facial cupping therapy

As a traditional medicine practice, cupping therapy has been widely used to relieve symptoms like fatigue, tension, and muscle pain. During the therapy, negative pressure is applied to the skin for a while with an intention to enhance blood circulation or induce micro-bleeding. The therapeutic effect, however, is not clear due to the lack of direct quantification. Aiming at a quantitative assessment of the treatment effect, we explore optical-resolution photoacoustic microscopy (OR-PAM) in monitoring the structural and functional changes after cupping. We find that, after 5-minutes of ∼ 20 kPa negative pressure cupping, more capillaries appear in the focus, and micro-blooding is observed from the capillaries. We quantify the images and find the blood vessel density is increased by 64%, and the total hemoglobin concentration in both the veins and the arteries exhibits 62% and 40% elevation, respectively. Oxygen saturation in the vein and artery decreased by 17% and 3% right after cupping, respectively. After two hours of recovery, the three blood-related parameters return to their original levels, indicating that the effects in the tissue last only a short period after cupping at the given pressure and time duration. Note that no significant cupping marks are induced with the treatment parameters in this study. This work proposes OR-PAM to quantitatively monitor and evaluate the effect of cupping therapy from the perspective of imaging. The method is also useful for accurate control of the therapeutic outcome.