Photoacoustic ophthalmoscopy (PAOM) is a high-resolution in vivo imaging modality that is capable of providing specific optical absorption information for the retina. A high-frequency ultrasonic transducer is one of the key components in PAOM, which is in contact with the eyelid through coupling gel during imaging. The ultrasonic transducer plays a crucial role in determining the image quality affected by parameters such as spatial resolution, signal-to-noise ratio, and field of view. In this paper, we present the results of a systematic study on a high-frequency ultrasonic transducer design for PAOM. The design includes piezoelectric material selection, frequency selection, and the fabrication process. Transducers of various designs were successfully applied for capturing images of biological samples in vivo. The performances of these designs are compared and evaluated.
We developed optical coherence photoacoustic microscopy (OC-PAM) to demonstrate that the functions of optical coherence tomography (OCT) and photoacoustic microscopy (PAM) can be achieved simultaneously by using a single illuminating light source. We used a pulsed broadband laser centered at 580 nm and detected the absorbed photons through photoacoustic detection and the back-scattered photons with an interferometer. In OC-PAM, each laser pulse generates both one OCT A-line and one PAM A-line simultaneously; as a result, the two imaging modalities are intrinsically co-registered in the lateral directions. In vivo images of the mouse ear were acquired to demonstrate the capabilities of OC-PAM.
We combined photoacoustic ophthalmoscopy (PAOM) with autofluorescence imaging for simultaneous in vivo imaging
of dual molecular contrasts in the retina using a single light source. The dual molecular contrasts come from melanin and
lipofuscin in the retinal pigment epithelium (RPE). Melanin and lipofuscin are two types of pigments and are believed to play opposite roles (protective vs. exacerbate) in the RPE in the aging process. We successfully imaged the retina of
pigmented and albino rats at different ages. The experimental results showed that multimodal PAOM system can be a
potentially powerful tool in the study of age-related degenerative retinal diseases.
The ultimate goal of the study is to provide an imaging tool to detect the earliest signs of glaucoma before clinically
visible damage occurs to the retinal nerve fiber layer (RNFL). Studies have shown that the optical reflectance of the
damaged RNFL at short wavelength (<560nm) is reduced much more than that at long wavelength, which provides
spectral contrasts for imaging the earliest damage to the RNFL. To image the spectral contrasts we built a dual-band
spectral-domain optical coherence tomography (SD-OCT) with centered wavelength of 415nm (VIS) and 808nm (NIR),
respectively. The light at the two bands was provided by the fundamental and frequency-doubled outputs of a broadband
Ti: Sapphire laser. The depth resolutions of the VIS and NIR OCT systems are 12.2μm and 4.7μm in the air. The system
was applied to imaging the rat retina in vivo. Significantly different appearances between the OCT cross sectional
images at the two bands are observed. The experimental results showed that the dual-band OCT system is feasible for
imaging the spectral contrasts of the RNFL.
We combined photoacoustic ophthalmoscopy (PAOM) with autofluorescence imaging for simultaneous in vivo imaging of dual molecular contrasts in the retina using a single light source. The dual molecular contrasts come from melanin and lipofuscin in the retinal pigment epithelium (RPE). Melanin and lipofuscin are two types of pigments and are believed to play opposite roles (protective versus exacerbate) in the RPE in the aging process. We have successfully imaged the retina of pigmented and albino rats at different ages. The experimental results showed that multimodal PAOM system can be a potentially powerful tool in the study of age-related degenerative retinal diseases.
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