Microwavephysics and Atmospheric Physics
Biomedizinische Photonik
HS 2017  ·  FS 2017
HS 2016  ·  FS 2016
HS 2015  ·  FS 2015
HS 2014  ·  FS 2014
HS 2013  ·  FS 2013
HS 2012  ·  FS 2012
HS 2011  ·  FS 2011
Ultrafast Science and Technology
Last update: 13.09.2017
FS 2017: Seminare über Biomedizinische Photonik
Wednesday 10-12
Vorträge, die innerhalb der nächsten Tage stattfinden, sind speziell markiert.
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Mittwoch, 01.03.2017

Polarimetric imaging to characterize isotropic,anisotropic/birefringent and optically active matter

Zeit: 10:15 Uhr
Hörsaal: A97
 
Linda Geisser
Institute of Applied Physics
University of Bern

In this talk, I will give a quick overview of the work I have carried out as part of my Bachelor Thesis in the Biomedical Photonics (BP) Group. I have performed a calibration study and preliminary experiments on the polarimetric microscope built in BP-Lab. The aim here was to assess whether different type of biological structures can be differentiated, based on the backscattered intensity patterns recorded with the microscope, as the latter can potentially serve as a valuable diagnostics tool.

 
Mittwoch, 08.03.2017

Image reconstruction of transmission tomography

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

In this talk, I will give a quick overview of the work I have carried out as part of my Bachelor Thesis in the Biomedical Photonics (BP) Group. I have changed the actual set-up and programmed an image reconstruction for transmission tomography to reconstruct the spatial distribution of the slowness of ultrasound. The aim was to program an image reconstruction which explicitly takes into account the missing data regions which occur due to the setup. It can be shown that the new image reconstruction needs less data and has also less artefacts than the reconstruction based on the inverse Radon transform.

 
Mittwoch, 15.03.2017

Optoacoustic Imaging with a handheld multi-wavelength probe

Zeit: 10:15 Uhr
Hörsaal: A97
 
Janos Metzger
Institute of Applied Physics
University of Bern

In this seminar I will give an overview of the work I have done in the Biomedical Photonics (BP) Group for my bachelor thesis in optoacoustics. The goal of my thesis was to gather experience with the optoacoustic (OA) probe that was developed within the European project "fullphase". This probe features miniaturized multi-wavelength diode laser sources that are integrated together with the ultrasound detector inside a handpiece. In comparison to conventional OA systems that, this prope features a small laser pulse energy but a higher pulse repetition rate. As a basis for further studies, I investigated the imaging depth of this probe as a function of the number of signal averaging and gathered first experience in spectral OA imaging of blood-vessel mimicking tissue phantoms.

 
Mittwoch, 22.03.2017

Propagation and Detection of Acoustic Waves in Optoacoustic Microscopy Setups

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

We explore how acoustic waves propagate inside the glass prism assembly commonly used in optoacoustic microscopy setups. We also look at how acoustic pressure waves can be detected and how the above two processes influence and change the design of such setups.

 
Mittwoch, 29.03.2017

Clutter reduction for clinical optoacoustic imaging using comb LOVIT with fast scanning field-of-view

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 acoustic probe providing flexible single-handed clinical diagnosis of human body. Such setup, however, generates strong clutter signals originated from tissue irradiation site, which interfere with signals of interest and substantially reduce OA imaging depth. With the goal to allow efficient clutter reduction, localized vibration tagging (LOVIT) has previously been developed. A long-pulsed (few 100 microseconds) focused ultrasonic beam generates acoustic radiation force (ARF) that induces localized tissue displacement at its focus. In the basic single-focus approach, two OA images are acquired, one without and one with a preceding single-focus ARF push. Subtraction of the two images resulted in a LOVIT image that highlights true OA signal in the focus but strongly reduces the clutter signals that originate from outside the focal regions where the displacement is comparably small or even zero. The performance of single-focus LOVIT was successfully demonstrated in a clinically realistic setup where the same linear array probe was used for both, imaging and ARF generation. In this study, we propose a novel approach of LOVIT where multiple horizontally aligned foci are created simultaneously, forming grid-shaped ARF patterns (comb approach). A substantially faster scanning time within field-of-view by a factor of two times the number of foci created simultaneously with the comb approach makes it more clinically applicable compared to single-focus approach. Additionally, the comb approach demonstrates a further reduction in residual echo clutter down towards the noise level resulting in further increase in signal-to-background ratio compared to single-focus approach.

 
Mittwoch, 12.04.2017

Towards blood oxygenation saturation level measurements using MIS-OA imaging

Zeit: 10:15 Uhr
Hörsaal: A97
 
Kai-Gerrit Held
Institute of Applied Physics
University of Bern

As part of our research on quantitative deep optoacoustic (OA) imaging – of e.g. blood oxygen saturation – we focus on the spectral correction of the measured OA signals. In a proof-of-principle study we demonstrated that the spectral distortion caused by the wavelength-dependent optical attenuation can be corrected on a broad spectral range, based solely on multiple-irradiation sensing OA (MIS-OA) imaging. As a natural continuation of the aforementioned study and as a precursor to in-vivo applications, we investigated the performance of MIS-OA in heterogeneous, solid phantoms, where boundaries are strongly influential. We quantify the influence of geometric irregularities on the accuracy of the achieved spectral correction and provide insight into the limitations of the proposed technique, thereby assessing its practical value for clinical quantitative OA imaging.

 
Mittwoch, 19.04.2017

Dense assemblies of fibroblast cells in suspensions

Zeit: 10:15 Uhr
Hörsaal: A97
 
Arbnor Zenuni
Department of Physics, University of Fribourg

The properties of dense particle suspensions in food, paint and pharmaceuticals has been studied for decades. The physical behavior of living cells in suspensions is, however, a relatively new topic. In this work the structure and the dynamics of suspensions of NIH 3T3 fibroblast cells over time is investigated. With two-photon microscopy we obtain three dimensional (3D) images from which the structural and dynamical data can be extracted in two- and three dimensions. In addition, the global behavior can be analyzed by time-lapse measurements of cell sedimentation. Since cell adhesion is a non-equilibrium living process the interplay can be influenced by addition of chemicals interfering with cell-cell interactions.

 
Mittwoch, 03.05.2017

Er-YAG laser fiber delivery and bone ablation

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

Er-YAG laser (2.9 um wavelength) is used for tissue ablation – both commercially and in research – because it is highly absorbed in water. As Er-YAG is also strongly absorbed in conventional silica fibers hence different fibers are used to have low transmission losses and low damage threshold. I have been using one such fiber (Germanium oxide) for maximum possible transmission for ablation experiments. I will discuss my setup, the methodological approach, results and some challenges that I faced during this study.

 
Mittwoch, 10.05.2017

Interpretation of the spatial backscattering Perrin Müller matrix of colloidal suspensions

Zeit: 10:15 Uhr
Hörsaal: A97
 
Manes Hornung
Institute of Applied Physics
University of Bern

With its long history of success in fields such as remote sensing and astronomy, polarimetry is emerging as a new diagnostics tool for tissue assessment. However, any polarimetric experiment faces two key challenges: The correct use of conventions and the interpretation of the measurement results, usually encoded in a Perrin Müller matrix. The talk will focus on the latter problem. As of yet, the interpretation of a general depolarizing Perrin Müller matrix in terms of elementary polarization altering properties such as birefringence and depolarization, remains an unsolved problem and has to be done on a case by case basis. We will discuss how the spatially resolved backscattering Perrin Mueller matrix of colloidal suspensions can be quantitatively understood in terms of its effect on incident light polarization modeled by a Stokes vector.

 
Mittwoch, 17.05.2017

Diffraction-limited straight ray speed of sound tomography using delay and sum pre-processing

Zeit: 10:15 Uhr
Hörsaal: A97
 
Tobias Schweizer
Institute of Applied Physics
University of Bern

Transmission speed of sound (SoS) tomography is an emerging non-invasive alternative to mammography in detecting and characterising breast cancer. Its conceptual similarity to X-ray computed tomography suggests the application of linear reconstruction algorithms based on the inverse Radon transform. However, due to refraction and diffraction effects, the necessary straight-ray approximation does not hold for ultrasound tomography. This leads to low spatial resolution and distortions in the reconstructed SoS values. Therefore, computationally expensive full-wave inversion algorithms are used in current research. In my masters thesis, I implemented a signal pre-processing technique to strongly reduce the influence of refraction and diffraction. I will show that with this, the inverse Radon transform delivers accurate reconstructions of SoS distributions with diffraction limited spatial resolution. I will also discuss the challenges that arise from a limited acquisition aperture and difficulties in determining the arrival time of transmitted ultrasound pulses.

 
Mittwoch, 24.05.2017

The results of our recent CUTE liver imaging study

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

Computed ultrasound tomography in echo-mode (CUTE) is a novel ultrasound-based imaging modality that aims at complementing handheld diagnostic pulse-echo ultrasound (US), by displaying the spatial distribution of speed of sound (SoS). SoS varies significantly between different soft tissues, and can reveal pathological changes in tissue composition. Together with the Bern University Hospital, we investigate the potential of CUTE in aiding an US based diagnosis of fatty liver disease, liver fibrosis and cirrhosis. In a preliminary internal study including 12 volunteers, we aimed at gaining first experience with the diagnostic procedure and with inter-patient variability of the imaging outcome. The same volunteers were tested with the fibroscan, a gold standard for quantifying fibrosis. In my seminar, I will give a short recap of how the method works, analyse the results of the volunteer study, and discuss correlations between CUTE and the fibroscan.

 
Mittwoch, 31.05.2017

Speed of Sound and photoacoustic imaging with an optical camera based ultrasound detection system

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Robert Nuster
Department of Physics, Karl-Franzens-University Graz, Austria

CCD camera based optical ultrasound detection is a promising alternative approach for high resolution 3D photoacoustic imaging (PAI). To fully exploit its potential and to achieve an image resolution smaller than 50 um, it is necessary to incorporate variations of the speed of sound (SOS) in the image reconstruction algorithm. Hence, in the proposed work the idea and a first implementation are shown how speed of sound imaging can be added to a previously developed camera based PAI setup. The obtained dual-modality setup provides highly resolved and perfectly co-registered 3D photoacoustic and SOS images.

 
Mittwoch, 05.07.2017

Statistical analysis of speckle patterns originating from coagulating human blood samples.

Zeit: 10:15 Uhr
Hörsaal: A97
 
René Iseli
Institute of Applied Physics
University of Bern

In this Seminar, I will give you an overview of the research I have carried out within the Biomedical Photonics Group, as part of my Bachelor's thesis. I will present you the "speckle microscope" I have built, together with recordings obtained with human blood samples. The statistical analysis of the recorded intensity distributions reveals interesting features of blood coagulation: indeed, disruptions over time lead to repeated and abrupt rearrangement of the speckle patterns.