Master thesis and projects

1. Intuitive ultrasound Doppler user interface by touch screen tablet

Relevant for a student summer job
The aim of this project is to develop and test user interface including real-time display during scanning on a tablet (e.g. IPad).   Target users are midwifes in rural areas of Africa, where Doppler blood flow measurements  during pregnancy can have a great impact on mortality of mother and the unborn child.  The challenge is to control the measurement position in the image to pick up the signal from the blood vessel, and to display and interpret the recorded waveforms.

Qualifications: Knowledge of C++  and Java programming, digital signal processing, image processing

Contact: Gabriel Kiss or Prof. Hans Torp

2. Fetal heart detector using tissue Doppler technique

The Doppler signal from a moving heart has a characteristic periodic signature which can be used to measure the heart rate. This is of special interest for fetal heart, where ECG is difficult to obtain. The aim of this project is to integrate fetal heart rate measurement in a standard ultrasound imaging probe for pocket size ultrasound. The work includes in vivo signal acquisition, signal analysis in Matlab, and real-time implementation in an ultrasound scanner.

Qualifications:Knowledge of C++  and Matlab programming, digital signal processing, image processing

Contact: Prof. Hans Torp

 

Why does the manipulation pulse make a difference?
Both the scattering and the sound propagation speed is pressure dependent. So applying a manipulation pressure will alter these properties and an imaging pulse travelling in a compression phase of the manipulation wave will be slightly different from a pulse travelling in the rarefaction phase. This difference can be used to extract more information about the tissue and thus enables more advanced processing schemes. For more information on the method take a look at the SURF imaging page.

A group of researchers works at the department with SURF imaging and we are looking forward to offer you a project or thesis in one of the most exciting fields of medical ultrasound imaging! 

Skills

In general students will gain knowledge in the following areas:

• Wave propagation (Ultrasound theory)
• Programming (Matlab, C, C++, Python)
• Signal processing
• Medicine
• Literature study and writing of articles
• team work
• research and development

Tailoring of topics

Below you'll find a list with available topics. They are all relevant both for master thesis as well as project work. The descriptions are kept quite general and since they anyway will be individually tailord to your interest f.ex. a focus on lab-work, programming, simulations, theoretical and algorithm development ...
Please get in contact with the corresponding supervisors! They'll help you finding the perfect topic for and with you.

Topic: Improved detection of ultrasound contrast agents

The ultrasound echo from blood is very weak compared to the echoes generated by tissue. In many situations it is desired to detect and image blood in the smallest blood vessels. To detect blood in these capillaries often an ultrasound contrast agent is injected into the blood circulation of a patient. These contrast agents are gas-bubbles with a typical diameter of 3µm which give en enhanced ultrasound echo and are transported with the blood. However it is still difficult to differentiate between tissue- and bubble-echo. This is especially important in the diagnosis and treatment of cancer where good imaging of the vessels and their structure is curcial. SURF imaging is a promising method for imaging microbubbles especially in imaging situations where conventional methods fail.

The topic will contain optimalizing, testing and verification of the method and the algorithms behind. Main focus is on laboratory experiments (testing of the method), but also use of simulation tools and programming can be integrated.

Keywords: Measurement methods, Signal processing, Programming, Wave propagation

Topic: Reverberation suppression

Image quality in ultrasound is very patient dependent. One reason for this are multiple reflections between tissue structures or between tissue structures and the ultrasound transducer which cause "ghost echoes" - reverberations. In the best case reverberations become visible as a discernable distinct copy of a tissue structure in shallow depths but more often and more serious a haze of noise is spread over the image.
This noise in the image causes problems in diagnosis in nearly all applications where ultrasound images are used for diagnostics.
The topic contains work on beamforming, simulations and phantom design (design test bodies) for better noise suppression. This comprises in most cases work with software tools and can also comprise experimental work in the ultrasound lab.

Topic: Estimation of non-linear scattering

Calcium particles are building up in the tissue in a number of medical conditions. In for example the diagnosis of breast cancer the physician is interested in calcium particles as they may indicate malignancy. Calcium is visualized very good in X-ray imaging, but not that good in ultrasound.
Improved imaging of calcium particles would directly give better diagnostics and guidance of tissue biopsies.

The topic contains experimental work in the lab, simulations, signal processing and estimation.

Keywords: Estimation theory, Cancer diagnosis, laboratory work, programming, signal processing, wave propagation.

Topic: Transducer for SURF Imaging

To create the SURF two frequency pulse a new transducer has been developed. The transducer consist of a stack of at least two piezoelectric layers, one for the low frequency pulse and one for the high frequency pulse, and layers inbetween the two for mechanical isolation and matching between the two layers. A couple of prototypes transducer arrays have been manufactured, and are succesfully used for imaging. However there are several issues to be investigated for the transducer design, amongst others; bandwidth of the passbands, internal reverberations, mechanical cross coupling, electrical matching to the scanner, non linear behaviour of the transducer.
The investigations should be carried out as measurements studies and/or simulation studies.

Supervision

The students have Bjørn Angelsen as a main or co-supervisor.

Main supervisor

Bjørn Angelsen

Co - supervisors

Rune Hansen
Tonni F. Johansen

1. Integrated anatomic and functional 4D model, based on cardiac magnetic resonance acquisitions

Introduction: Cardiac magnetic resonance (CMR) imaging techniques provide in-vivo, noninvasive evaluation of cardiac parameters. Different sequences are employed to image both anatomy (e.g. cine-MR) and function (e.g. perfusion imaging, late enhancement for myocardial infarct delineation, T2-STIR for edema localization). However, these sequences do not have the same spatial (3 up to 12 slices) or temporal resolution (one frame per heart cycle, up to 30 frames per cycle).

The computation of quantitative parameters requires a spatial and temporal correspondence between these datasets. To establish such a correspondence image registration techniques can be used successfully. Once an appropriate alignment is achieved, quantitative parameters such as end-diastolic and end-systolic volumes, wall thickening and infarct size can be derived. Furthermore by using registration methods patient movement and breathing artifacts can also be identified and corrected. 

 

Objectives:

1. generation of integrated 4D models based on different CMR acquisitions
2. computation of functional parameters based on the cardiac model
3. robust visualization of image and model
4. applicability on patients with known myocardial infarction

Skills:

- Basic knowledge of C++ and Matlab programming

Contact: Gabriel Kiss or Hans Torp

 

2. Real-time volume rendering on the GPU of multi-modal cardiac image data

Introduction:Full 3D left ventricular datasets are acquired using different imaging modalities (e.g. 3D echocardiography and cardiac magnetic resonance imaging). Once a spatial and temporal correspondence is established, fast volume rendering techniques are needed to visualize the image volumes. Furthermore a morphing of different information sources (e.g. 3D volumes, segmented models of endo- or epi-cardium and/or functional parameters) into the same scene is desirable.

 

Traditionally, all the computations required for generating a rendered image were done on the CPU. Nowadays CPU based applications have direct access to the GPU resources via high level languages such as CUDA or OpenCL and parts of a program can be executed on the GPU in parallel. This is particularly interesting for medical image visualization purposes.

Objectives:

1. extend the current volume renderer by adding support for multiple modalities
2. explore different visualization  techniques for combined functional and anatomic  renderings

Skills:

• Basic knowledge of C++ programming
• desire to learn parallel computing via OpenCL or CUDA

Contact: Gabriel Kiss or Hans Torp

 

3. Fast image registration of 3D echocardiographic acquisitions on the GPU

Introduction: 3D echocardiography is gaining popularity as a clinical tool for assessing cardiac performance, because it is non-invasive, can be carried out in real-time and it is cost effective. However, the image quality has large variations between subjects, the spatial resolution varies with depth and the tissue contrast is angle dependent. One possibility of improving image to noise ratio and to extend the field of view is to acquire multiple datasets from different angles, detect corresponding features in each view and fuse the recordings in order to generate a combined volume. Rigid image registration can be used for alignment purposes, having the advantage that it relies only on the image data. A GPU implementation of the registration process will speed up the computation times.

The aim of the project is to extend existing registration techniques for fusing multiple 3D echocardiographic acquisitions with the goal of improving signal-to-noise ratio, spatial resolution and field of view.

Objectives:

1. extend and customize the current registration methods for 3D echocardiographic data
2. improve the temporal registration between datasets
3. validate the developed methods on 3D echocardiographic data

Skills:

• knowledge of C++ programming (existing code implemented in C++)
• desire to learn parallel computing (CUDA)

Contact: Gabriel Kiss or Hans Torp

The capillaries in a tumor grow aggressively with an imperfect wall, so that these particles leak into the space between tumor cells (the interstitium), while they are maintained in the blood stream in normal tissue, which has well developed capillary walls. Encapsulating the smaller anti-cancer drug molecules into particles opens for selective pharmacological treatment of tumor tissue, while normal tissue is not exposed to the drug.

Ultrasound radiation force can increase transport of the particles deeper into the interstitium. Increase of temperature produced by ultrasound absorption will also increase diffusion of the particles into the interstitium.

Ultrasound can also be used to break the particles. This seems to be stimulated by cavitation of small gas-bubble nuclei in the tissue. It is therefore a very interesting strategy to combine small gas bubbles (diam ~ 2µm) and the drug encapsulating nano-particles with ultrasound.

There are several interesting Master and PhD topics in this field, ranging from

• multi-frequency ultrasound acoustics and transducer arrays for imaging of particles and stimulated transport and breakage of the particles
• signal processing for multi-frequency ultrasound imaging (SURF Imaging) of the particles
• combined optical imaging of particles with ultrasound mediated drug delivery
• experimental studies of ultrasound mediated transport and breakage of gas micro-bubbles and drug encapsulating nano-particles in lab models and small animal tumor models

When using the transducer to receive sound, the principles are the same. Received sound vibrations at the elements will be converted to an electric signal. Adjust the amplitude and
delays of the received signal on each element before summing, and you'll be able to receive from a chosen angular direction.

Project 1: Multi Line Transmission

A heart at rest is beating approximately one time each second. How the different parts of the heart muscle contracts and relaxes (or lack thereof) tells us whether a heart is healthy or not. Subtle changes can indicate that a cardiac disease is developing. To be able to capture this motion and analyse such subtle details we need high frame rate. This is especially important in 3D cardiac ultrasound, where the acquisition time per frame is increased significantly.

The ultimate limiting factor when increasing frame rate lies in physical properties of sound propagation, more specifically in the speed of sound. Ultrasound is all about capturing echoes from a transmitted sound pulse, and the transmitted pulse must travel to our maximum imaging depth and back (echo) before we can transmit the next pulse. A normal 2D image frame consists of approximately 100 transmits in different directions. In a 3D image frame this number is squared…. This is a major headache for the ultrasound industry and a high priority area of research!

The typical way of increasing the frame rate is by widening the beams and receiving in several directions at the same time. Another method that is less explored, is to transmit several narrow beams simultaneously in different directions (Multi Line Transmission). In this project, the student will combine these two techniques and their advantages to improve image quality at high frame rates.

Aim:

• Investigate the MLT-technique through simulations and lab experiments.
• Combine with previously developed STB technique for reducing image artifacts from multi line reception.
• Develop methods to reduce cross talk between the beams transmitted in parallel.

Qualifications:

• Interested in ultrasound medical imaging
• Signal processing.
• Matlab programming skills.

Contact persons:

• Bastien Denarie
• Hans Torp

Project 2: New beamforming techniques based on spatial coherence

Conventional ultrasound images are formed by delay-and-sum beamforming of the backscattered echoes received by the transducer elements. Such an interferential process can however be challenged in the presence of phase aberrations, acoustic reverberation clutters, strong off-axis targets or electronic noise. These phenomenons will all contribute in decreasing the spatial coherence of the received ultrasound signal across the aperture of the transducer, and will result in blurring artifacts in the delay-and-sum ultrasound image.
Modern ultrasound scanners allow for software processing of the data received by all the transducer elements. We can now test new beamforming techniques that can cope better with in-vivo acoustic perturbations, resulting therefore in a better contrast and signal-to-noise ratio. Several beamforming techniques based on the coherence of the received data have been proposed lately, promising for better ultrasound images using a non-linear beamforming scheme.
 

Aim:

• Implement and test new beamforming algorithms based on spatial coherence
• Apply them on simulated and in-vivo collected channel data, and compare with B-mode images

Qualifications:

• Interested in ultrasound medical imaging
• Signal processing
• Matlab programming skills

Contact persons:

• Bastien Denarie
• Hans Torp

Project 3: Combined acquisition of tissue Doppler and B-mode in 3D cardiac ultrasound

Tissue Doppler Imaging, TDI, is a modality for measuring the velocity of the cardiac tissue. The extracted tissue velocities can be used to identify pathological regions of the heart. However, at current time there is no good implementation of this modality in 3D due to frame rate limitations. The main problem is that this modality requires several transmit in the same direction and separate acquisitions for B-mode and TDI. Previous studies on 2D images has shown that using a special STB acquisition pattern, both the tissue Doppler velocities and B-mode image can be extracted from the same acquisition. This technique was named Single Pulse Tissue Doppler, SPTD.

Aim:

• Implement the SPTD technique in 3D.
• Compare the velocity estimate variance and bias to regular TDI.

Qualifications:

• Interested in ultrasound medical imaging
• Signal processing
• Matlab programming skills

Contact persons:

• Bastien Denarie
• Hans Torp

We focus on multi piezoelectric layer transducer for wideband applications (SURF and multipurpose transducers).

To characterize the manufactured transducers we develop new measurement techniques and procedures. The methods are either based on measurements of electrical impedance of the transducer stack, pulse echo type measurements, or measurements of transmitted acoustic field with hydrophones.

Below are sketches of two projects, which can be taylored in cooperation with the student

1. Design and test of two layer transducer
Design based on 1-dimensional and/or 3 dimensional simulation tools. Optimation for wide band operation.
Production in cooperation with the transducer workshop and testing in laboratory.

2. Study of mechanical crosstalk in dual piezoelectric layer transducer
Dual layer layer transducer transducer have possibly vibration further from the ideal rigid piston movement than the single layer ones. In this project the mechanical cross talk shall be investigated through simulations or measurements.
A simulation based study would focus on building a realistic model of the transducer, investigate its vibration and analyse the resulting transmitted field.
A measurement based study would consist of careful measurements of radiation from the arrays elements and estimate the elements' vibration patterns.

Contact: Tonni Franke Johansen

1: Simulation models for Doppler imaging based on computational fluid dynamics (patient specific models)

There is increasing interest in using advanced computational models for flow based on computation fluid dynamics (CFD) as input to ultrasound imaging simulations. This gives the possibility to develop and compare new imaging algorithms towards a realistic ground truth where all information of scatterer movement is available. We have previously developed a framework for these simulations in cooperation with the University in Ghent, Belgium. However, the simulations can take a long time to finish (~days), and it is critical to find approaches to reduce this time during development. In this project you will work with the trade-off between simulation accuracy and time for producing realistic Doppler signals from both patient specific CFD-models and a more ideal jet-flow. In addition to the simulations, a new flow imaging algorithm will be investigated based on ultrafast acquisition scheme, providing an image frame rate > 1000 fps.

Preferred qualifications:

• Programming in Matlab.

Contact: Professor Hans Torp, Researcher Lasse Løvstakken

 

2: Tracking of complex blood flow in congenital heart disease (babies)

Cardiac flow patterns may reveal several kinds of cardiovascular disease. Well known examples include the detection and quantification of leaky heart valves and poor systolic and diastolic function. Conventional flow imaging with ultrasound is however limited to only measuring the velocity component along the ultrasound beam, i.e. it is a one-dimensional and angle-dependent measurement. This discrepancy limits the usefulness of Doppler ultrasound in diagnostic settings. In this work we will focus on further developing multi-dimensional flow velocity estimators based on speckle tracking, i.e. image pattern matching techniques. The main clinical application will be pediatric cardiology, with the aim to improve the depiction of complex flow patterns such as vortex and shunt flow.

The proposed multidimensional approaches proposed are however not as robust as conventional methods. Thus, the aims of this student project will be to further develop and optimize tracking algorithms within a robust framework based on the predicted motion of flow, for example using a Kalman filter.

Aims:

• Further develop and validate robust tracking algorithms that optimally weight measurement and modelling errors
• Test the proposed methods on simplified simulations as well as in vivo data from pediatric cardiology

Qualifications: Knowledge of digital signal processing and preferably Matlab.

Contact: Researcher Lasse Løvstakken, PhD student Solveig Alnes

3: Navigated ultrasound imaging – 3-D reconstruction of (pulsatile) artery geometry and flow

Conventional ultrasound imaging of blood flow in central and peripheral arteries is today based on 2-D imaging, while pathology related to atherosclerosis is inherently three-dimensional. While real-time 3-D ultrasound is available for cardiac imaging, transducers for vascular imaging are not yet available. However, by utilizing highly accurate position sensors during scanning, it is possible to reconstruct the 3-D geometry of arteries based on multiple 2-D flow and B-mode images. In this project we will utilize recently installed navigation system based on optical and magnetic sensors to reconstruct 3-D flow in the carotid artery. This flow is highly pulsatile, and we will also incorporate information from ECG (electro-cardiogram) to also get timing information. The imaging approach will follow a recent plane-wave imaging scheme, where a high frame rate and high image quality can be achieved. Investigations will first be done using in vitro setup of known stationary and pulsatile flow. In vivo imaging in healthy volunteers will further be tries to show the potential of mapping arterial geometry and pulsatile 3-D flow patterns.

Preferred qualifications: Programming in Matalb and C++

Contact: Researcher Lasse Løvstakken, PhD student Daniel H. Iversen

4: Instrumentation for real-time ultrasound data streaming

Relevant for a summer internship

In this project you will work with real-time streaming of ultrasound data to an external client where the data can be stored and synchronized towards external sources such as invasive and noninvasive physiological measurements (pressure, flow, etc.), and position sensor information. Equipment will include the high-end GE Vingmed Vivid E9 ultrasound scanner with existing software for data streaming, a recently acquired position sensor system, and will also be used towards equipment for logging invasive pressure, flow, etc. at the Dept. Comparative Medicine (animal lab.). For the latter, a logging system has previously been developed to synchronize physiological measurements which further need to be stored and synchronized with ultrasound data.

Preferred qualifications: Programming in Matalb and C++

Contact: Researcher Lasse Løvstakken

 

 

 

Topic: Myocardial deformation

The heart is a muscle that both pushes blood out and sucks new blood in. In some cardiac diseases, the ability to suck is more reduced than the ability to push because the heart muscle is stiff, and this creates problems for the filling of the heart. The consequence is that the heart pumps less efficiently, and that the patient's exercise capacity is reduced. It is difficult to measure cardiac muscle stiffness directly, but with new ultrasound technology, we can achieve extreme time resolution (> 1000 images per second). Thus we can see mechanical phenomena we have not seen before, such as fast deformation waves.

Our hypothesis is that the velocity of these waves is related to cardiac muscle stiffness.

The task of this thesis is to develop a finite element model where the propagation of such waves can be simulated. The work will be based on FEM-models already developed at the Dept. of structural engineering.

Supervisors:
Leif Rune Hellevik
Hans Torp
Brage H Amundsen