The department of Medical Technology, where I have done Master thesis project, develops and researches new method and technique within areas where ultrasound can be used to obtain the image of anatomical structure, functional capabilities and to suggest required treatment.

Nowadays cardio-vascular diseases, such as infarct, atherosclerosis and ischemic syndrome, are one of the most widespread diseases in the world that’s why timely detection, identification and treatment are so important.

The Master of Science qualification report consists 3 major parts: Medico-biological part, Design and Research parts.

In Medico-biological part has been analyzed anatomical and physiological structure of the heart, current status of echocardiography with comparing with other techniques, summary of ultrasound methods with list of parameters that can be achieved is presented.

In Design part has been developed new graphical modality based on Delta-V pump model using vector based statistical analysis for identification patients with ischemia. Software algorithm for automatically determine characteristic points for state diagram written in MatLab has been developed and implemented.

In Research part in the first task using commercially available software based on Principal Component Analysis collected data from the hospital patients has been studied, results proved hypothesis concerning time variables importance; in the second task graphical module has been examined using collected data from the hospital patients both normal and with different cardio-vascular disease, and the results show good detection power of the algorithm.

At the end of the project presentation has been done and report has been published.

This project has been done in collaboration with the biggest medical institute in Sweden – Karolinska Institute - and results will be used in medical practice in Karolinska University Hospital in Huddinge and for future scientific needs.

The focus of contrast-enhanced ultrasound research has developed beyond detecting the blood pool to new areas such as perfusion imaging, drug and gene therapy, and targeted imaging. Polymer-shelled microbubbles are proposed as a new generation of ultrasound contrast agents (UCAs) which fulfil the requirements of these applications. With a shelf-life of several months and possibility to conjugate pharmacological molecules to their surface, these UCAs will allow not only to enhance the contrast of ultrasound images, but also to function as carriers of drugs to be delivered locally. In this study, the results of an experimental investigation of three types of UCAs stabilized by thick poly vinyl alcohol (PVA) shell are presented. These UCAs are synthesized from a PVA aqueous solution under varied pH values and temperature. The UCAs differ from each other in their average diameter, shell thickness and polydispersity. Knowledge of the peak negative pressure at which the solid shell fractures is paramount for a proper use of UCAs. Therefore, the dependence of this quantity on temperature and number of cycles in the incident pulse is examined. Much of the blood volume resides in the microcirculation, with capillaries playing a particularly important role in patho-physiology and drug delivery. In this sense in vitro characterization of the UCAs oscillation was moved from bulk volume to the capillary scale, where tissue-bubble interaction takes place. The main conclusion to be drawn from these results is that the shell of the UCAs begin to fracture at values of mechanical index (MI) approved for clinical applications. The fatigue, i.e. the accumulation of damage within the shell of the UCAs, is found to play an important role in fracturing the shell. Finally adhesion of the UCAs to the elastic wall is studied and correlated with estimates of the shell’s visco-elastic constants. Open questions arising from this comparison are briefly discussed.

This work examines the acoustic behavior of ultrasound contrast agents made of poly (vinyl alcohol) (PVA) shelled microbubbles manufactured at three different pH and temperature conditions. Backscattering amplitude, attenuation coefficient and phase velocity of ultrasonic waves propagating through suspensions of PVA contrast agents were measured at temperature values ranging between 24 ^oC and 37 ^oC in a frequency range from 3 MHz to 13 MHz.  A significant enhancement of the backscattering amplitude and displaying a weak dependence on temperature were observed.  Attenuation and phase velocity, on the other hand, showed higher sensitivity to temperature variations.  The dependence on system parameters such as the number of cycles, frequency, and exposure of the peak negative pressure, P_thr, at which ultrasound contrast agents fracture was also investigated.  The effects of temperature, blood, and, wherever data are available, of the dimension of the microbubbles on P_thr are also considered.  The large shell thickness notwithstanding, the results of this investigation show that at room temperature PVA contrast agents fracture at negative peak pressure values within the recommended safety limit.  Furthermore, P_thr decreases with increasing temperature, radius of the microbubbles, and number of cycles of the incident wave.  In conclusion, these results suggest that PVA-shelled microbubbles may offer a potentially viable system to be employed for both imaging and therapeutic purposes.

Polymer-shelled microbubbles have become the focus of intense research for their enhanced shelf life and demonstrated chemical versatility.  These are properties highly sought after in the ultrasonic contrast agents (UCAs) of the next generation, which will be engineered not only to enhance the contrast of ultrasound-based images, but also to function as carriers of drugs to be delivered locally.  Here, the results of an experimental investigation of three potentially new UCAs are presented.  These microbubbles are stabilized by thick poly (vinyl alcohol) shells.  These UCAs differ from each other in their dimensions and shell thickness (order of 0.5 microns).  Fundamental to their use as drug carrier is the knowledge of the pressure threshold at which the shell of these UCAs fractures.  Therefore, the dependence of this quantity on temperature, number of cycles of the incident pulse, nominal central frequency and pulse repetition frequency of the emitting transducer is examined.  The effect of using blood instead of deionized water is also considered.  The main conclusion to be drawn from these results is that their thick shell notwithstanding, these microbubbles begin to fracture at values of MI which can be acceptable in clinical applications.  This claim is supported also by images acquired by means of commercially available imaging systems.  Finally, these values of the pressure threshold are correlated with estimates of the shells’ visco-elastic constants obtained by fitting Church’s model to the frequency-dependent attenuation coefficient and phase velocity.  Open questions arising from this comparison are briefly discussed.

This paper presents the application of a method for the characterisation of the static, fully relaxed elastic properties of poroelastic materials. The approach is based on full field measurements of the 3D displacements in a number of points on the faces of the compressed material sample. These are used as targets in an inverse estimation to fit a model of the material to the experimental data. The material is modelled as an orthotropic equivalent solid, whose principal directions are not necessarily aligned with the coordinate system in which the experiments are conducted. The angles of relative orientation accounting for the potential misalignment are estimated, together with the elastic moduli of the material. In addition, the proposed model considers the region of reduced stiffness close to material discontinuities, which has been identified in previous investigations. The method is applied to a melamine foam, which is found to have its lowest stiffness in the direction parallel to the rise direction of the material.

Duct Networks (e.g. HVAC) are designed to maintain flow rates at acceptable noise levels. To accurately analyze the acoustics in a duct network in the high frequency region, the following mechanisms need to be modeled: The sound power injected into the network by sound sources (e.g. Fans), the flow noise generated in different parts in the network (e.g. junctions), and the noise reduction across different parts of the network. Traditionally only transmission of sound power with no reflection is considered in standards, e.g., ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers) or VDI (The Association of German Engineers), for analyzing noise in HVAC systems. In this paper, a more general approach is considered based on dividing the duct network into two-port elements where each element can be described by a 2x2 scattering matrix. The state variables are taken as acoustic power flow in the up/downstream directions. Junctions are described by multiports depending on the number of elements connected to the junction. A source vector is added to each element and junction to handle sound power injection by fans or other aero-acoustic sources. The advantage of this approach is that the same formalism (based on two-port network theory) can be used to analyze the low frequency range, the flow distribution and the pressure drop across each network path as well as the high frequency range. This two-port power based formulation was earlier validated against a detailed HVAC example in VDI 2081 part2. In this paper, it is validated against a real-life case study and compared with the measurements.