Use of a flexible optical fibre bundle to interrogate a Fabry–Perot sensor for photoacoustic imaging

Abstract

Photoacoustic imaging systems based on a Fabry Perot (FP) ultrasound sensor that is read-out by scanning a free-space laser beam over its surface can provide high resolution photoacoustic images. However, this type of free-space scanning usually requires a bulky 2-axis galvanometer based scanner that is not conducive to the realization of a lightweight compact imaging head. It is also unsuitable for endoscopic applications that may require complex and flexible access. To address these limitations, the use of a flexible, coherent fibre bundle to interrogate the FP sensor has been investigated. A laboratory set-up comprising an x-y scanner, a commercially available, 1.35 mm diameter, 18,000 core flexible fibre bundle with a custom-designed telecentric optical relay at its distal end was used. Measurements of the optical and acoustic performance of the FP sensor were made and compared to that obtained using a conventional free-space FP based scanner. Spatial variations in acoustic sensitivity were greater and the SNR lower with the fibre bundle implementation but high quality photoacoustic images could still be obtained. 3D images of phantoms and ex vivo tissues with a spatial resolution and fidelity consistent with a free-space scanner were acquired. By demonstrating the feasibility of interrogating the FP sensor with a flexible fibre bundle, this study advances the realization of compact hand-held clinical scanners and flexible endoscopic devices based on the FP sensing concept.

Comparing free-space and fiber-coupled detectors for Fabry–Pérot-based all-optical photoacoustic tomography

“… 5 Experimentally, significant improvements of sensitivity by mode-filtering were shown with the use of a single-mode fiber-coupled detector (FCD). 5 , 9 Although FCDs are commonly used in the community, 10 – 12 their advantages and disadvantages to free space detectors (FSDs) were never directly compared in realistic, experimental conditions. Hence, the real functional advantage of FCDs remained unclear, since important factors such as the effective sensitivity gain as well as expected power losses in FCDs were not previously quantified.…”

Comparing free-space and fibre-coupled detectors for Fabry-Pérot based all-optical photoacoustic tomography

“…An alternative method of aberration correction is based on spatial-mode-filtering [5,9] where higher order spatial modes are removed from the beam with the use of a single-mode fibre coupled decector (FCD). Although FCDs are commonly used in the community [10,11,12] their advantages and disadvantages to free space detectors (FSD) were never directly compared in realistic, experimental conditions. Hence, the real functional advantage of FCDs remained unclear, since important factors such as the effective sensitivity gain as well as expected power losses in FCDs were not previously quantified.…”

Miniature all-optical flexible forward-viewing photoacoustic endoscopy probe for surgical guidance

“…In this Letter, we extend the concepts described in reference [ 26 ] to realize a flexible fiber bundle based endoscopic PA probe that is sufficiently small for minimally invasive use. This required designing a miniature telecentric relay system and integrating a novel excitation light fiber delivery system within the probe tip.…”

“…However, the rigid nature of the probe limits the range of applications to those where line-of-sight access is available. To address this, the use of a flexible fiber bundle to interrogate the FP sensor was investigated [ 26 ]. In that study, the acoustic SNR of a fiber bundle-interrogated FP sensor was compared with a free-space FP scanning system [ 23 ] in order to identify the additional noise sources that arise due to the non-ideal light propagation characteristics of a standard commercially available fiber bundle.…”

“…The fiber bundle (Schott Inc.) comprised 18,000 fiber-optic cores with 6.7/10.26 µm core/cladding diameters, although only the central 3,000 cores were used to readout the FP sensor. Both end faces of the fiber bundle were angle polished and wedged to minimize the Fresnel reflections, which can otherwise induce noise due to parasitic interference [ 26 ]. The diameter of the bundle was 1.35 mm and protected by a flexible plastic coating with 2.2 mm diameter.…”