Uniform light delivery in volumetric optoacoustic tomography

Abstract

Accurate image reconstruction in volumetric optoacoustic tomography implies the efficient generation and collection of ultrasound signals around the imaged object. Non‐uniform delivery of the excitation light is a common problem in optoacoustic imaging often leading to a diminished field of view, limited dynamic range and penetration, as well as impaired quantification abilities. Presented here is an optimized illumination concept for volumetric tomography that utilizes additive manufacturing via 3D printing in combination with custom‐made optical fiber illumination. The custom‐designed sample chamber ensures convenient access to the imaged object along with accurate positioning of the sample and a matrix array ultrasound transducer used for collection of the volumetric image data. Ray tracing is employed to optimize the positioning of the individual fibers in the chamber. Homogeneity of the generated light excitation field was confirmed in tissue‐mimicking agar spheres. Applicability of the system to image entire mouse organs ex vivo has been showcased. The new approach showed a clear advantage over conventional, single‐sided illumination strategies by eliminating the need to correct for illumination variances and resulting in enhancement of the effective field of view, greater penetration depth and significant improvements in the overall image quality.

Deep tissue volumetric optoacoustic tracking of individual circulating tumor cells in an intracardially perfused mouse model

“…Basically, the output light beam of a tunable optical parametric oscillator (OPO)-based laser was guided through a fiber bundle to illuminate an area of ∼4 mm diameter on the surface of the phantom (optical fluence <20 mJ/cm 2 ). The generated OA signals were detected with a custom-made 512-element spherical array coaxially aligned with the fiber bundle, which provides an almost isotropic resolution of ∼150 μm around the center of the sphere [26] . The volume enclosed between the phantom and the array surface was filled with agar to guarantee acoustic coupling.…”

“…The spherical array (Imasonic SaS, Voray, France) used for optoacoustic tomographic imaging of the mouse brain was previously described [26] . Briefly, it consists of 512 piezocomposite elements densely distributed on a spherical surface with 40 mm radius and 140° (1.3π solid angle) angular coverage.…”

Multifocal structured illumination optoacoustic microscopy

“…The signals detected by the array are sampled by a 512-channel data acquisition system at 40 mega-samples per second and are then transferred to the computer via a 1 Gbps Ethernet connection. Such a spherical array has been shown to provide an almost isotropic resolution of 150–250 µm for an effective FOV of 10 × 10 × 10 mm 3 by imaging an agar phantom containing sparsely distributed 50 μm diameter polyethylene-absorbing spheres 52 .…”

Concurrent fluorescence and volumetric optoacoustic tomography of nanoagent perfusion and bio-distribution in solid tumors

“…An emission filter was placed in front of an electron multiplying charged-coupled device (EMCCD)-based camera (Andor Luca R, Oxford Instruments, UK) to selectively collect the fluorescence responses transmitted through the optic guide. The ultrasound array (Imasonic SaS, France) was used to collect OA signals with 512 piezocomposite elements having ~2.5 mm diameter, 5 MHz central frequency and ~100% detection bandwidth [29].The elements are uniformly distributed on a spherical surface with 40 mm radius and 140° angular coverage (1.3π solid angle). An optical parametric oscillator (OPO)-based short-pulsed laser (Innolas Laser GmbH, Germany) was guided through the illumination bundle of the fiberscope, simultaneously exciting OA and fluorescence responses.…”