Abstract
A noninvasive, multimodal photoacoustic and optical coherence tomography (PAT/OCT) scanner for three-dimensional in vivo (3D) skin imaging is described. The system employs an integrated, all optical detection scheme for both modalities in backward mode utilizing a shared 2D optical scanner with a field-of-view of ~13 × 13 mm2. The photoacoustic waves were detected using a Fabry Perot polymer film ultrasound sensor placed on the surface of the skin. The sensor is transparent in the spectral range 590-1200 nm. This permits the photoacoustic excitation beam (670-680 nm) and the OCT probe beam (1050 nm) to be transmitted through the sensor head and into the underlying tissue thus providing a backward mode imaging configuration. The respective OCT and PAT axial resolutions were 8 and 20 µm and the lateral resolutions were 18 and 50-100 µm. The system provides greater penetration depth than previous combined PA/OCT devices due to the longer wavelength of the OCT beam (1050 nm rather than 829-870 nm) and by operating in the tomographic rather than the optical resolution mode of photoacoustic imaging. Three-dimensional in vivo images of the vasculature and the surrounding tissue micro-morphology in murine and human skin were acquired. These studies demonstrated the complementary contrast and tissue information provided by each modality for high-resolution 3D imaging of vascular structures to depths of up to 5 mm. Potential applications include characterizing skin conditions such as tumors, vascular lesions, soft tissue damage such as burns and wounds, inflammatory conditions such as dermatitis and other superficial tissue abnormalities.
Highlights
Photoacoustic imaging (PA) is a noninvasive biomedical imaging modality in which laser generated ultrasound waves are used to obtain 3D images of soft tissue [1]
It has been shown that the vascular anatomy of the different layers of thick mouse and human skin can be highlighted against the micro-morphology of the skin with axial and lateral resolutions of 8 μm and 18 μm respectively in the Optical coherence tomography (OCT) image and 20 μm and 50-100 μm in the photoacoustic tomography mode (PAT) image
The key technical advantages of the instrument compared to previous piezoelectric based dual mode OCT-PA systems derive from the transparent optically addressable nature of the Fabry Perot (FP) ultrasound sensor
Summary
Photoacoustic imaging (PA) is a noninvasive biomedical imaging modality in which laser generated ultrasound waves are used to obtain 3D images of soft tissue [1]. Used to image the skin of the mouse ear [23] and subsequently the retina [24], addressed these limitations to some extent In this approach, co-axial PA excitation and OCT probe beams are optically scanned across the tissue surface using an x-y galvanometer scanner and the PA signals detected on the same side of the sample using a single stationary ultrasound receiver offset from the scan area. The finite angular aperture of the receiver limits the PA field of view (FOV) and only a relatively modest 3 × 3 mm scan area has been achieved with this approach Since both of these scanners designs employed the OR-PAM rather than tomographic mode of PA imaging, the photoacoustic penetration depth for non-transparent tissues was limited to less than 1 mm.
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