Multiple irradiation sensing of the optical effective attenuation coefficient for spectral correction in handheld OA imaging

Held, K. Gerrit; Jaeger, Michael; Rička, J.; Frenz, Martin; Akarçay, H. Günhan

doi:10.1016/j.pacs.2016.05.004

Cited by 32 publications

(31 citation statements)

References 35 publications

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“…When the sphere was uniformly illuminated, its entire surface became visible with the reconstructed images, accurately resembling the theoretically predicted (simulated) values. Even though it has been shown that OA images can, in principle, be corrected for nonuniform illumination and light attenuation, it was not necessary in this case . Such correction for limited‐view conditions or for a relatively low number of measuring positions can be still hampered by streak‐type artifacts associated with strong nonuniformity of the excitation light field (hot spots) .…”

Section: Discussionmentioning

confidence: 99%

“…To this end, several experimental and algorithmic strategies have been attempted in order to mitigate image artifacts related to suboptimal object illumination . Here, we introduce an optimized design for light delivery in three‐dimensional OA tomography based on the combination of a custom‐made optical fiber bundle with a 3D‐printed (fused deposition modeling (FDM)) sample chamber providing homogenous sample illumination.…”

Section: Introductionmentioning

confidence: 99%

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Uniform light delivery in volumetric optoacoustic tomography

Larney

Rebling

Chen

et al. 2019

Journal of Biophotonics

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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.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Uniform light delivery in volumetric optoacoustic tomography

Larney

Rebling

Chen

et al. 2019

Journal of Biophotonics

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“…First, the PA signal amplitude is proportional not only to absorption, but also to laser fluence (i.e., light level at a target) [7,8]. Because tissue attenuation depends on wavelength [33], the absorption spectrum estimated from a PA image can be very inaccurate (i.e., the shape can change dramatically and the wavelength of maximum absorption shift), especially deep within tissue [34,35]. This is illustrated in Figs.1a,c and clearly demonstrated in Results.…”

Section: Mainmentioning

confidence: 99%

“…Unfortunately, this requires a precise map of tissue optical properties, which cannot be measured or calculated during imaging. Several methods have attempted to estimate and compensate fluence variations [34][35][36][37][38][39][40][41][42][43], but none work well clinically where real-time or near real-time corrections are needed. In most cases, fluence is compensated using an approximate exponential function equalizing intensities.…”

Section: Mainmentioning

confidence: 99%

Real-time spectroscopic photoacoustic/ultrasound (PAUS) scanning with simultaneous fluence compensation and motion correction for quantitative molecular imaging

Jeng

Kim

et al. 2019

Preprint

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For over two decades photoacoustic (PA) imaging has been tested clinically, but successful human trials have been minimal. To enable quantitative clinical spectroscopy, the fundamental issues of wavelength-dependent fluence variations and inter-wavelength motion must be overcome. Here we propose a new real-time, spectroscopic photoacoustic/ultrasound (PAUS) imaging approach using a compact, 1-kHz rate wavelength-tunable laser. Instead of illuminating tissue over a large area, the fiber-optic delivery system surrounding an US array sequentially scans a narrow laser beam, with partial PA image reconstruction for each laser pulse. The final image is then formed by coherently summing partial images at a 50-Hz video rate. This scheme enables (i) automatic laser-fluence compensation in spectroscopic PA imaging and (ii) interwavelength motion correction using US speckle tracking, which have never been shown before in real-time systems. The 50-Hz video rate PAUS system is demonstrated in vivo using a murine model of drug delivery monitoring. AffiliationsContributions G.-S. J. assembled the experimental setup, developed and implemented the PAUS imaging protocol, integrated the optical system with a Vantage (Verasonics) US scanner, performed all experimental studies, performed PA and US image processing and reconstruction, developed and implemented motion correction algorithms for spectroscopic PA imaging, wrote the paper. M.-L. L. conducted experiments with G.-S. J., helped in image processing. M.K. conducted experiments with G.-S. J., developed and implemented laser fluence compensation routine in spectroscopic PA imaging. S.J.Y. assembled early-stage PAUS system, did preliminary measurements, helped in designing imaging protocol for the final PAUS scanner. J.J.P. Jr. participated in designing laser fluence compensation algorithms, fast acquisition and image processing in Verasonics US scanner and article illustration. D.S.L. synthesized Prussian blue nanocubes, helped in auxiliary measurements. I.P. conceived the idea of the spectroscopic fast-sweep approach, designed the project with M.O.D., supervised the project, specified the laser and fiber-optic coupling modules for the PAUS system, worked with vendors for their development, assembled the PAUS system, worked with M.K. on laser fluence compensation algorithms, participated in experimental studies, designed and wrote the paper. M.O.D. conceived the idea of moving beam illumination with I.P, designed the project, and wrote the paper.

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“…To evaluate the accuracy of the fluence distributions determined with NIROT/NIRFAST used to perform the correction, they were compared to reference fluence distributions. In phantom 1, the light fluence can be calculated by the light diffusion approximation Φ D ( r ) for a semi‐infinite, homogeneous medium :

Φ^{D} ((), r) \propto \frac{z}{d^{3}} ((), 1 - d \cdot {(3 μ_{a} μ_{s}^{'})}^{1 / 2}) e^{- d \cdot {(3 μ_{a} μ_{s}^{'})}^{1 / 2}},

where d is the distance between the OA illumination point on the phantom's surface and the position r . Phantom 1 served as a reference to (1) demonstrate the performance attainable with NIROT/NIRFAST, as the reconstructions for such a volume are expected to yield reliable results without any a priori knowledge, and to (2) experimentally establish the efficiency of quantitative OA imaging with our system.…”

Section: Experimental Tissue Modelmentioning

confidence: 99%

Spectral correction for handheld optoacoustic imaging by means of near‐infrared optical tomography in reflection mode

Ulrich

Ahnen²,

Akarçay

et al. 2018

Journal of Biophotonics

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In vivo imaging of tissue/vasculature oxygen saturation levels is of prime interest in many clinical applications. To this end, the feasibility of combining two distinct and complementary imaging modalities is investigated: optoacoustics (OA) and near-infrared optical tomography (NIROT), both operating noninvasively in reflection mode. Experiments were conducted on two optically heterogeneous phantoms mimicking tissue before and after the occurrence of a perturbation. OA imaging was used to resolve submillimetric vessel-like optical absorbers at depths up to 25 mm, but with a spectral distortion in the OA signals. NIROT measurements were utilized to image perturbations in the background and to estimate the light fluence inside the phantoms at the wavelength pair (760 nm, 830 nm). This enabled the spectral correction of the vessel-like absorbers' OA signals: the error in the ratio of the absorption coefficient at 830 nm to that at 760 nm was reduced from 60%-150% to 10%-20%. The results suggest that oxygen saturation (SO ) levels in arteries can be determined with<10% error and furthermore, that relative changes in vessels' SO can be monitored with even better accuracy. The outcome relies on a proper identification of the OA signals emanating from the studied vessels.

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Multiple irradiation sensing of the optical effective attenuation coefficient for spectral correction in handheld OA imaging

Cited by 32 publications

References 35 publications

Uniform light delivery in volumetric optoacoustic tomography

Uniform light delivery in volumetric optoacoustic tomography

Real-time spectroscopic photoacoustic/ultrasound (PAUS) scanning with simultaneous fluence compensation and motion correction for quantitative molecular imaging

Spectral correction for handheld optoacoustic imaging by means of near‐infrared optical tomography in reflection mode

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