Microwavephysics and Atmospheric Physics
Biomedizinische Photonik
FS 2018  ·  HS 2017
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Ultrafast Science and Technology
Last update: 29.03.2018
FS 2018: Seminare über Biomedizinische Photonik
Wednesday 10-12
Vorträge, die innerhalb der nächsten Tage stattfinden, sind speziell markiert.
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Mittwoch, 14.03.2018

*CANCELLED* Quantitative Comparison of Time-domain and Frequency-domain Approaches in Optoacoustic Microscopy Image Reconstruction

Zeit: 10:15 Uhr
Hörsaal: A97
 
Florentin Spadin
Institute of Applied Physics
University of Bern

Image reconstruction is important in optoacoustic microscopy as it allows the region of acceptable resolution around the plane of focus to be increased, which in turn greatly improves the usability of the technique. In this seminar, time-domain and frequency-domain reconstructions are quantitatively compared in terms of their ability to improve the true resolution of the final image.

 
Mittwoch, 28.03.2018

Clutter reduction methods in epi-optoacoustic imaging: a comparative study

Zeit: 10:15 Uhr
Hörsaal: A97
 
Tigran Petrosyan
Institute of Applied Physics
University of Bern

In epi-optoacoustic (OA) imaging, optical components are attached or directly integrated into the ultrasound probe, providing single-handed probe guidance for flexible imaging of the human body. Such a setup, however, generates clutter signals originating from optical absorption at the tissue irradiation site near the probe, reducing contrast and imaging depth. To increase imaging depth towards the noise limit, various clutter reduction techniques have been proposed: (1) Displacement compensated averaging (DCA) employs the clutter decorrelation that results from quasi-static tissue deformation when palpating the tissue with freehand probe motion. (2) Photoacoustic-guided focused ultrasound (PAFUSion) uses ultrasound pulse-echo acquisitions to mimic reflection artefacts, which can then be subtracted from the OA image for clutter reduction. (3) In localized vibration tagging (LOVIT), a focused ultrasonic pushing beam transiently displaces optical absorbers at its focus and thus leads to a phase shift of OA signal originating from this focal region inside the tissue. Subtraction of OA acquisitions before and after the push highlights OA signals from the focus but eliminates clutter from outside the pushing beam. In this study, we compare DCA, PAFUSion and LOVIT in terms of clutter reduction efficiency for different imaging depths and laser irradiation geometries, where all three techniques can be implemented in a single custom built setup.

 
Mittwoch, 04.04.2018

Understanding polarization and polarimetric patterns

Zeit: 10:15 Uhr
Hörsaal: A97
 
Arushi Jain
Institute of Applied Physics
University of Bern

Polarization is the the property of electromagnetic radiations in which the direction and magnitude of the vibrating electric field are related in a specified as opposed to unpolarized light vibrating in random direction. Though this being the encyclopedia meaning, there is more to that needs to be understood. In order to reach our goal of tissue diagnostics, it is crucial to understand what these patterns. We will discuss the analytical solutions and measurements, that were used to understand the said patterns. Further I will also briefly talk about our current work and future steps.

 
Mittwoch, 11.04.2018

Master Thesis: A novel approach to ultrasound computed tomography of the human breast

Zeit: 10:15 Uhr
Hörsaal: A97
 
Cyril Etter
Institute of Applied Physics
University of Bern

Ultrasound computed tomography (UCT) is a promising alternative to the standard X-ray mammography for breast cancer diagnosis due to its non invasive nature and non-ionizing radiation. The imaging principle is the same as in X-ray computed tomography (CT): Radiation transmitted through the breast is measured from different angles to reconstruct the spatial distribution of a physical tissue property, in case of UCT the speed of sound (SoS). But there is a fundamental difference to X-ray CT: The ultrasound wavelength is comparable to the spatial resolution of structures of interest, thus diffraction plays a role. In addition, spatial SoS variations are large enough to cause substantial refraction. To achieve a high-resolution and accurate SoS image by accounting for these effects, rather complex and computationally demanding reconstruction algorithms are typically needed. In this seminar, a computationally less demanding alternative method based on a modified filtered backprojection approach is presented. To compensate for diffraction and refraction, the measured signals are backpropagated into the tissue before time-of-flight determination. In phantom experiments using a setup based on two commercial linear array ultrasound transducers, we have shown that this fast reconstruction technique provides a diffraction-limited spatial resolution. The SoS could be accurately reconstructed in phantoms with size and SoS comparable to a human breast.

 
Mittwoch, 18.04.2018

Radiative Transfer Theory and Maxwell’s Equations

Zeit: 10:15 Uhr
Hörsaal: A97
 
Leonie Ulrich
Institute of Applied Physics
University of Bern

Since its first formulation more than a century ago, radiative transfer theory has extensively been used to describe the propagation of electromagnetic radiation in a variety of fields such as astrophysics, atmospheric physics and biomedical optics. Yet, the link between the heuristically derived radiative transfer equation and the fundamental laws of electrodynamics had remained unclear until very recently. In this seminar, we will look at the radiometric quantities commonly used in biomedical optics and examine their relation to the Poynting vector, by deriving the scalar radiative transfer equation from Maxwell’s equations. We will thereby identify the approximations inherent to the theory of radiative transfer and discuss their implications for the description of light propagation in tissue.

 
Mittwoch, 25.04.2018

 

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Mittwoch, 02.05.2018

Anthropomorphic oil/gel breast phantoms

Zeit: 10:15 Uhr
Hörsaal: A97
 
Patrick Stähli
Institute of Applied Physics
University of Bern

To examine new photoacoustic-based imaging modalities, anthropomorphic phantoms that mimic acoustic properties (speed of sound, echogenicity, attenuation), optical properties (absorption- and reduced scattering coefficient) and realistic tissue complexity are essential tools. Longevity, mechanically robustness, low manufacturing costs and non-toxicity are also important considerations. Among the available approaches, oil-in-gel emulsions provide realistic speed of sound and echogenicity where the former is determined by the oil/water ratio and the latter can be independently adapted by adding further ingredients such as cellulose or glass microspheres. To verify the phantom production process, breast phantoms based on a 2D and 3D design were produced, providing an undulated fat layer around a glandular inner core containing cylindrical inclusions. To acoustically characterize these breast phantoms, a 2D ultrasound tomography setup was used (1). In this seminar, I will give an overview on the phantoms production process and highlight the important steps to achieve acoustically realistic and stable phantoms. Further, first time of flight measurements (2), which characterize the optical properties of the phantom (absorption- and reduced scattering-coefficient) are shown.

1 T.Schweizer: Master’s Thesis (2017), C.Etter: Master’s Thesis (2018)

2 H. Günhan Akarçay et. Al: Determining the optical properties of a gelatin-TiO2 phantom at 780nm (2012)

 
Mittwoch, 09.05.2018

tba

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Maju Kuriakose
Institute of Applied Physics
University of Bern

 
Mittwoch, 16.05.2018

tba

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Michael Jaeger
Institute of Applied Physics
University of Bern

 
Mittwoch, 23.05.2018

tba

Zeit: 10:15 Uhr
Hörsaal: A97
 
tba

 
Mittwoch, 30.05.2018

tba

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Günhan Akarçay
Institute of Applied Physics
University of Bern

 
Mittwoch, 06.06.2018

Master Thesis

Zeit: 10:15 Uhr
Hörsaal: A97
 
Louis Wyss
Institute of Applied Physics
University of Bern