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: 18.10.2017
HS 2016: Seminare über Biomedizinische Photonik
Wednesday 10-12
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Mittwoch, 31.08.2016

Master's thesis presentation: Clutter reduction in a clinical combined ultrasound and optoacoustic system using Displacement-Compensation Averaging

Zeit: 10:15 Uhr
Hörsaal: A97
 
Christian Schneeberger
Institute of Applied Physics
University of Bern

The University of Bern is a member in the EU FP7 project "Fullphase" where a combined ultrasound and optoacoustic clinical imaging system is developed. As part of the projects objectives the displacement-compensated averaging (DCA) method was implemented by which clutter can be reduced in image sequences acquired while palpating the tissue with the imaging probe. In the optimisation process of this system a transparent gel pad and a palpation mount was developed. Combined ultrasound and optoacoustic images were acquired and the DCA method was applied. Solutions to integrate 2D displacement tracking are proposed to simplify application in free-hand measurements.

 
Mittwoch, 07.09.2016

Image Reconstruction in Optoacoustic Microscopy: Recovering Information from blurry Data

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

Optoacoustic Microscopy, by its nature, produces highly resolved images only in a very confined region around its plane of focus. However, the out-of focus regions can be improved in post-processing to provide better depth-assessment in images. What are the mechanics of such techniques and what are the physical limits of how much information can be recovered from out-of-focus regions?

 
Mittwoch, 14.09.2016

Sound velocity of metastable liquid water under negative pressure determined by Brillouin Light Scattering

Zeit: 10:15 Uhr
Hörsaal: A97
 
Chen Qiu
Institute of Applied Physics
University of Bern

Water is the most important and the most familiar substance on earth, but the science behind its complex behavior and anomalies are poorly understood. We explore water in low-temperature metastable region derived from synthetic fluid inclusions. We conduct sound velocity measurements on liquid water down to -20°C and down to -130 MPa by means of Brillouin light scattering. We observe the sound velocity anomalies that is inconsistent with the IAPWS equation of state. The experimental data shed light on the properties of liquid water in the low-temperature metastable region and provide clear indications to assess the trend of Line of Density Maxima (LDM) of water under negative pressure.

 
Montag, 19.09.2016

Biomedical Photoacoustic and Ultrasonic Imaging Using Advances from Seismology

Zeit: 14:15 Uhr
Hörsaal: B78
 
Jami Johnson
Physical Acoustics Lab
University of Auckland, AUS
Dr. Joost van der Neut
Applied Geophysics and Petrophysics
Delft University of Technology, NL

Biomedical photoacoustic and ultrasonic imaging have the ability to image biological tissues at centimeter depths by harnessing the low scattering and absorption properties of acoustic waves. The two techniques provide complementary information about the structure and function of tissues; however, each modality requires a different approach to image reconstruction. The aim of photoacoustics is to image the location of an embedded acoustic source generated by optical absorption, whereas the goal of reflection-mode ultrasound is to image the location that a surface-generated wavefield is scattered by acoustic heterogeneities. In this talk, we will present image reconstruction and re-datuming techniques based on the state-of-the-art in seismology tuned for biomedical applications. While the wavefields we deal with are vastly different scales, the overall imaging goals of seismologists are largely similar to those of medical imagers. Locating the epicenter of an earthquake is analogous to locating a photoacoustic source, and imaging of the subsurface of the earth is directly related to ultrasonic imaging. Furthermore, significant progress has been made to remove multiple reflections in seismic data, an effect known as "clutter" in medical images. First, we will introduce photoacoustic and (laser-)ultrasound imaging, and describe methods for reconstructing the respective images with time-reversal and reverse-time migration. Subsequently, we will discuss advanced methods for eliminating reverberation artifacts (clutter) in photoacoustic images using using the Marchenko equation via an intuitive 1D example.

 
Mittwoch, 21.09.2016

Repetitive laser pulses to reduce thermal damage during laser-tissue-soldering

Zeit: 10:15 Uhr
Hörsaal: A97
 
Annemarie Schönfeld
Institute of Applied Physics
University of Bern

Laser-tissue-soldering (LTS) is based on the thermal denaturation of proteins and a promising alternative to sutures and staples for the bonding of tissues. In vivo experiments involving pigs, where we fused an artery of the left rectus abdominis muscle to the right cranial epigastric artery, showed that the immediate mechanical strength of the anastomosis was withstanding the blow flow and no rupture or leakage was found. However, the flap did not survive the observation period of 7 days and the vessels were occluded. Hence, further optimization of the temperature during soldering is required to minimize the thermal damage during LTS. In this seminar I will discuss the temperature distribution within the vessel wall and speak about the different techniques used for the energy deposition during LTS. Additionally the influence of continuous versus pulsed energy deposition on the strength of soldered blood vessels will be presented.

 
Mittwoch, 05.10.2016

Towards clutter free clinical optoacoustic imaging using localized vibration tagging (LOVIT)

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

In epi-illumination optoacoustic (OA) imaging, strong OA transients from the tissue irradiation site reach the acoustic probe directly or after acoustic scattering. These clutter signals interfere with the signals of interest, thus reducing contrast and imaging depth. Localized vibration tagging (LOVIT) enables identifying the signals of interest within the clutter background: The high ultrasound intensity in the focus of an ultrasonic beam generates a volumetric acoustic radiation force (ARF) initiating a localized tissue displacement. By subtraction of OA images prior and immediately after the ARF push mainly signal originating from the localized displacement region is visible. We are investigating a clinically realistic setup, where the same linear array probe is used both for imaging and for ARF generation. The results demonstrate that a substantial clutter reduction down to the noise level and an increase in imaging depth by about a factor of two is possible in a clinically realistic implementation of LOVIT.

 
Mittwoch, 12.10.2016

Clinical Optoacoustic (OA) imaging: What does an OA image actually represent?

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

In order to retrieve quantitative estimates about chromophores concentrations in tissue (e.g. hemoglobin) using spectral Optoacoustic (OA) imaging, it is important to recall what OA images actually represent and what their appearance depend on. In this seminar, we will re-visit the physical mechanisms of OA signal generation and detection, which helps to gain a better understanding when interpreting clinical OA images.

 
Mittwoch, 19.10.2016

Determine aberration delay from echo phase shift: The mysterious factor 2 uncovered

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

Computed ultrasound tomography in echo mode (CUTE) generates an image of the spatial distribution of speed-of-sound inside the human body using handheld echo-ultrasound, aiming at an improved diagnosis of e.g. liver disease or cancer. CUTE is based on analysing the phase shift of local echoes when insonifying the tissue under various different angles. A year ago, I first discovered a fundamental disagreement between theoretical predictions and experimental results of how local echo phase shift relates to the spatial distribution of speed of sound. Finally, after many frustrating months of meditation, the solution is found and I would like to share my joy about the newly developed theoretical model which is now able to (more) consistently describe the experiments.

 
Mittwoch, 26.10.2016

Implementation and comparison of clutter reduction in a clinical combined ultrasound and optoacoustic system using Displacement-Compensation Averaging

Zeit: 10:15 Uhr
Hörsaal: A97
 
Christian Schneeberger
Institute of Applied Physics
University of Bern

The University of Bern is a member in the EU FP7 project "Fullphase" where a combined ultrasound and optoacoustic clinical imaging system is developed. As part of the projects objectives the displacement-compensated averaging (DCA) method was implemented by which clutter can be reduced in image sequences acquired while palpating the tissue with the imaging probe. In the optimization process of this system a transparent gel pad and a palpation mount was developed. Combined ultrasound and optoacoustic images were acquired and the DCA method was applied. The results are discussed in respect to previous DCA results.

 
Mittwoch, 02.11.2016

Considerations on the Bouguer-Lambert-Beer law

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

The attenuation of electromagnetic radiation propagating through an opaque medium can be described by an exponential decay, which is commonly referred to as the Bouguer-Lambert-Beer law, in homage to the physicists who first formulated it based on empirical observations. The apparent simplicity of this exponential decay – ubiquitous in numerous branches of physics – can be deceiving. This is perhaps best summed up in the optics textbook by Bohren and Huffman:

“ …if quantitative data are to be extracted from transmission measurements, some care must be taken. It takes little experimental ability to insert a sample into a spectrophotometer and press the scan button. Some kind of spectrum will dutifully emerge from the instrument. But it is an entirely different matter to extract from such spectra accurate numerical values...”

In this seminar, we shall discuss the applicability limits of the aforementioned law and reflect on its relevance in our research work.

 
Mittwoch, 09.11.2016

Fluorescence characteristics of the chlorin derivative photosensitizer (SerCE) in various micro-enviroment

Zeit: 10:15 Uhr
Hörsaal: A97
 
Maryam Mostafaei
Institute of Applied Physics
University of Bern

Photodynamic therapy (PDT) has been used clinically for treating various disease including malignant tumors. PDT treats a diseased tissue through energy transfer from an excited photosensitizer (PS) resulting in the formation of singlet oxygen and thus cell death. A single PS cannot be effective for treating any types of cancers. Therefore, it is important to search for new types of PS with desired properties for a range of PDT purposes. Fluorescence lifetime (FL) of a PS reflects its micro-environment and aggregate-formation, and is thus expected to provide insights into structural requirements and conditions for developing highly efficient PS-carrier systems.

This study aims to address the aggregation state of amino acid chlorine derivative PS (SerCE), as a potential PS for PDT, in different micro-environments. To this end, we measured the FL of SerCE encapsulated in polymeric based nano particles (PVP and KP188), in the form of solution, using the time-correlated-single-photon-counting technique. Preliminary results reveal reproducibility of the FL measurements within the confidence regions of the FLs. Measured FLs suggest that KP188 performs relatively better (compared to PVP) in monomerizing SerCE with longer FL for a prescribed set of SerCE, PVP and KP188 concentrations.

 
Mittwoch, 16.11.2016

Er-YAG laser through fibers and free bream propagation

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

Er-YAG laser (2.9um wavelength) has been used to perform ablation in tissues - now commercially used in dentistry or still in research because it is highly absorbed in water. As Er-YAG is also strongly absorbed in conventional silica fibers, different fiber types that have low transmission losses and high damage threshold are required for high power transmission. I have been evaluating three such fiber types for maximum possible transmission to be further used in ablation experiments. In this seminar I will discuss my setup, challenges that I faced and some results. In turn I have been working on making the free beam ablation better and will shortly talk about some new ideas.

 
Mittwoch, 30.11.2016

Ultrasound Tomography

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

Ultrasound Computed Tomography (UCT) provides images of the spatial distribution of speed of sound (SoS) inside the breast for cancer diagnosis. This technique is based on detection of ultrasound that has propagated through the tissue, providing 'projections' of SoS from various directions similar to X-ray CT. Upcoming commercial instruments typically employ a time-intensive iterative non-linear inversion of the wave equation, which is thought necessary to account for refraction and diffraction effects and reconstruct an accurate image with high spatial resolution. In my master thesis, I investigate a different approach where conventional delay-and-sum beamforming is used as a pre-processing step to the linear and thus much more efficient inverse Radon transform (IRT). My results not only show that this approach overcomes the resolution limit that was conventionally attributed to IRT-based techniques, but also that the reconstructed SoS reproduces the theoretical values up to a high contrast with surprising accuracy. A current challenge is posed by artefacts due to shadowing caused by total internal reflection.

 
Mittwoch, 07.12.2016

Polarimetric patterns as a manifestation of the optical geometric phase

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

Light diffusely reflected from scattering media contains clover- and bow-tie-like patterns when observed trough a polarization filter. These patterns are used in a current study to calibrate a polarimetric microscope aimed at tissue diagnosis. Besides this application, the study of said patterns is interesting from a theoretical perspective. They appear relatively independent of the nature of the individual scattering events and in a regime where the usual approximations to the radiative transfer equation (single scattering, diffusion) fail and current understanding is limited.

We will - after a brief review of the optical geometric phase - discuss how the patterns can be viewed as a manifestation of said effect and compare these results to Monte Carlo simulations and measurements.

 
Mittwoch, 25.01.2017

Determining the refractive index of highly scattering media by means of imaging with an ellipsometric setup

Zeit: 09:15 Uhr
Hörsaal: A97
 
Patrick Stähli
Institute of Applied Physics
University of Bern

Determining the complex refractive index of highly scattering media by means of applying Fresnel's equations can be challenging. This is attributable to three main difficulties: First, the directly specularly reflected beam needs to be distinguished from the backscattered light. Secondly, the angle between the media’s surface normal and the illumination beam's propagation direction has to be measured in a precise manner in order to achieve reasonable results. Finally, the media's surface roughness has a big impact on the kind of reflection and therefore, in order to apply Fresnel's equations, this issue needs to be taken into account. In this Master thesis, a compact and inexpensive imaging system was developed to circumvent this issues. An ellipsometry based set-up was built and optimized in order to be able to measure the refractive index of highly scattering media independent of the illumination beam's intensity and angle of incidence. The applicability thereof has been ascertained with experiments on highly concentrated colloidal latex suspensions. The real part of the refractive index was measured with a deviation from literature of only a few tenth of a percent over a wide range of particle concentrations. In a second step, the effect of surface roughness was investigated by performing Monte Carlo simulations. These simulations revealed that the developed data analysis is promising to give reliable results in real measurements.