In this work, a synchronized dual-modal imaging system is used for in-vivo, non-contact ophthalmic imaging. The apparatus is comprised of both Photoacoustic Remote Sensing (PARS) and Swept-Source Optical Coherence Tomography (SS-OCT) subsystems. The PARS utilizes a multi-wavelength excitation source to target hemoglobin absorption and an 830 nm interrogation source to detect photoacoustic signals. PARS provides the measurements for computing blood oxygen saturation (sO2) mapping in the mouse and rat eyes. Meanwhile, a 1060 nm SS-OCT is employed to obtain volumetric tissue structure. To our knowledge, this is the first report of non-contact functional photoacoustic imaging in ophthalmic applications.
Photoacoustic Remote Sensing (PARS®) is a non-contact, label-free imaging modality that provides optical absorption contrast in biological tissues. Images are formed by raster-scanning over a target. A time-domain signal is collected at each point, representing initial pressure-induced via the photoacoustic effect. Conventionally, only the amplitude of the time-domain signals is considered to estimate pixel values, disregarding the rich temporal information present in the signals. For instance, the signal shape carries information, which may be related to specific biological structures. In this work, clustering based on signal shape is explored, followed by feature extraction, enabling the virtual labeling of PARS images.
We present a new technique for improving the temporal stability of the Stimulated Raman Scattering (SRS)-based multispectral pulsed source by decreasing the temperature of the SRS medium. This technique reduces temporal fluctuations of the output SRS peaks, generates stable multiwavelength light, improves repeatability and accuracy of functional measurements. This stabilized temperature-regulated SRS-based source is combined with the wide field of view photoacoustic remote sensing microscope utilizing a telecentric scan lens as an imaging objective. In-vivo functional imaging experiments of the chorioallantois membrane of a chicken embryo (CAM) are performed for validation purposes.
A non-contact, dual-modal imaging apparatus is introduced which will be used to obtain the Metabolic Rate of Oxygen (mRO2) in the live murine eye, based on the blood flow rate and blood Oxygen Saturation (sO2) measurements. The apparatus is comprised of both Photoacoustic Remote Sensing (PARS) and Swept-Source Optical Coherence Tomography (SS-OCT) systems, operating synchronously. A phantom model will be imaged using the proposed system to validate the accuracy of the blood flow and sO2 measurements. To the best of our knowledge, this work would report for the first time, non-contact, in-vivo measurement of the mRO2 in the ophthalmic tissues.
Photoacoustic Remote Sensing (PARS™), an all-optical, non-contact, reflection-mode, label-free biomedical imaging modality, is sensitive to optical absorption in biological tissues. Images are formed by scanning across tissue, collecting time-domain signals at each point which represent the initial pressures generated through induced thermoelastic expansion. Previously, when obtaining pixel intensity, the rich temporal and spectral content of the time-domain signals has largely been ignored. In this exploratory work, meaningful features are intelligently extracted from the time-domain signals. Based on these extracted features, attributes relevant to pixel intensity can be used to form images of improved contrast and greater detail.
To assess cancer resection margins, post-operative histological diagnosis using hematoxylin and eosin (H&E) stained slides remains the gold standard due to the lack of effective intra-operative approaches. Wait times may be up to two weeks and subsequent treatments may be necessary. Therefore, we are motivated to introduce Chromophore Selective Multi-Wavelength Photoacoustic Remote Sensing, an all-optical, non-contact, reflection-mode, label-free approach to produce H&E-like images of human tissue. This work is a step towards in-situ imaging, rapid clinical assessment of tissue, and may permit future developments as a live intraoperative surgical microscope.
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