Towards non-contact photoacoustic imaging [review]

Abstract

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.

Recent developments in photoacoustic imaging and sensing for nondestructive testing and evaluation

“…(1) A major limitation is the penetration depth of PA technology. For biomedical imaging applications, compared with pure optical microscopy, PA imaging can break the optical diffusion limit (transparent mean free path of approximately 1 mm in the skin) and enable a high US resolution at an imaging depth of up to a few centimeters in biological tissue [ 56 ]. However, for NDT/E applications using PA technology, the samples are typically not as transparent as biological tissue.…”

“…This makes the optimized arrangement of the light illumination part, the acoustic detection part, and the acoustic coupling agents more complicated using PA technology than the US counterpart for NDT/E. As stated in NDT/E with all-optical PA wave excitation and detection section, all-optical and/or non-contact approaches have the potential to overcome the above challenges [ 53 , 56 , 57 ]. (3) Device cost is another limitation of PA technology.…”

Dual-Modal Photoacoustic Imaging and Optical Coherence Tomography [Review]

“…However, it is not suitable for several clinical and preclinical applications such as wound assessment, brain imaging, or ophthalmic imaging [176]. Various approaches have been suggested to overcome this limitation among which optical detection approaches hold the promise to provide high sensitivity over a wide frequency range [177][178][179][180]. Optical detection methods also offer the opportunity of developing miniaturized and optically transparent ultrasound detectors [181].…”

Functional and structural ophthalmic imaging using noncontact multimodal photoacoustic remote sensing microscopy and optical coherence tomography

“…Biological tissues have endogenous chromophores that can be exploited as imaging targets. For example, the absorption peak of DNA/RNA is in the ultraviolet spectral region, and hemoglobin and melanin mainly absorb light in the visible and near-infrared (NIR) spectral ranges 18 . This unique imaging ability makes PAM a favorable candidate for various functional and molecular imaging applications and measuring chromophore concentration 19 .…”

“…Over the past decades, photoacoustic ophthalmoscopy has been applied for visualizing hemoglobin and melanin content in ocular tissue 20 , quantifying ocular SO 2 21 , and measuring the metabolic rate of oxygen consumption (MRO 2 ) 22 . Despite all these advantages offered by PAM devices, a major limitation arises from their need to be in contact with the ocular tissue 18 . This physical contact may increase the risk of infection and may cause patient discomfort.…”