867 research outputs found
Prediction and near-field observation of skull-guided acoustic waves
Ultrasound waves propagating in water or soft biological tissue are strongly
reflected when encountering the skull, which limits the use of ultrasound-based
techniques in transcranial imaging and therapeutic applications. Current
knowledge on the acoustic properties of the cranial bone is restricted to
far-field observations, leaving its near-field properties unexplored. We report
on the existence of skull-guided acoustic waves, which was herein confirmed by
near-field measurements of optoacoustically-induced responses in ex-vivo murine
skulls immersed in water. Dispersion of the guided waves was found to
reasonably agree with the prediction of a multilayered flat plate model. It is
generally anticipated that our findings may facilitate and broaden the
application of ultrasound-mediated techniques in brain diagnostics and therapy.Comment: 7 pages, 5 figures, appendix with 2 figure
Simultaneous control of volumetric light distribution through turbid media using real-time three-dimensional optoacoustic feedback
Focusing light through turbid media presents a highly fascinating challenge
in modern biophotonics. The unique capability of optoacoustics for high
resolution imaging of light absorption contrast in deep tissues can provide a
natural and efficient feedback to control light delivery in scattering medium.
While basic feasibility of using optoacoustic readings as a feedback mechanism
for wavefront shaping has been recently reported, the suggested approaches may
require long acquisition times making them challenging to be translated into
realistic tissue environments. In an attempt to significantly accelerate
dynamic wavefront shaping capabilities, we present here a feedback-based
approach using real-time three-dimensional optoacoustic imaging assisted with
genetic-algorithm-based optimization. The new technique offers robust
performance in the presence of noisy measurements and can simultaneously
control the scattered wave field in an entire volumetric region.Comment: 4 pages, 3 figure
Visual Quality Enhancement in Optoacoustic Tomography using Active Contour Segmentation Priors
Segmentation of biomedical images is essential for studying and
characterizing anatomical structures, detection and evaluation of pathological
tissues. Segmentation has been further shown to enhance the reconstruction
performance in many tomographic imaging modalities by accounting for
heterogeneities of the excitation field and tissue properties in the imaged
region. This is particularly relevant in optoacoustic tomography, where
discontinuities in the optical and acoustic tissue properties, if not properly
accounted for, may result in deterioration of the imaging performance.
Efficient segmentation of optoacoustic images is often hampered by the
relatively low intrinsic contrast of large anatomical structures, which is
further impaired by the limited angular coverage of some commonly employed
tomographic imaging configurations. Herein, we analyze the performance of
active contour models for boundary segmentation in cross-sectional optoacoustic
tomography. The segmented mask is employed to construct a two compartment model
for the acoustic and optical parameters of the imaged tissues, which is
subsequently used to improve accuracy of the image reconstruction routines. The
performance of the suggested segmentation and modeling approach are showcased
in tissue-mimicking phantoms and small animal imaging experiments.Comment: Accepted for publication in IEEE Transactions on Medical Imagin
Influence of the absorber dimensions on wavefront shaping based on volumetric optoacoustic feedback
The recently demonstrated control over light distribution through turbid
media based on real-time three-dimensional optoacoustic feedback has offered
promising prospects to interferometrically focus light within scattering
objects. Nevertheless, the focusing capacity of the feedback-based approach is
strongly conditioned by the number of effectively resolvable optical modes
(speckles). In this letter, we experimentally tested the light intensity
enhancement achieved with optoacoustic feedback measurements from different
sizes of absorbing microparticles. The importance of the obtained results is
discussed in the context of potential signal enhancement at deep locations
within a scattering medium where the effective speckle sizes approach the
minimum values dictated by optical diffraction
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