Medical Applications of Ultrasonic and Optoacoustic
Novel Ultrasonic and Optoacoustic Technologies in Medical Applications: Theoretical Models and Experimental Investigations
Tech Area / Field
- MED-DID/Diagnostics & Devices/Medicine
8 Project completed
Senior Project Manager
Melnikov V G
MIFI, Russia, Moscow
- Moscow State University / International Laser Center, Russia, Moscow
- Institut National de la Santé et de la Recherche Médicale / Unite de Recherche U556. Applications des Ultrasons à la Thérapie, France, Lyon
Project summaryThe main objective of this project is the development of the novel theoretical and experimental techniques in the field of optical, ultrasonic and optoacoustic medical applications. Investigations will be performed in the following actively developing research areas:
- Diagnostics of structural inhomogeneities in biological tissues by stationary and pulsed beams of polarized light
- Optoacoustic diagnostics of biological tissues applied to early breast cancer detection and high intensity focused ultrasound therapy monitoring
- Pulsed acoustic diagnostics of relaxation and resonance spectra of tissues
- Optimization of high intensity ultrasound effect on soft biological tissues.
Consider these research areas in more detail.
1. For the last twenty years there has been increased interest in researches on possibilities of biological tissue diagnostics by laser radiation [1-36]. A number of non-invasive laser methods for visualization of optical inhomogeneities and inclusions of various types in biological tissues have been proposed and approved experimentally. To obtain contrast images of inclusions in optically thick layers it is necessary to exclude the contribution of the diffusive photons from the flux scattered light. The diffusive photons propagate along strongly curved trajectories and blur the inclusion image. The rest of the photons (quasi-straightforward-propagating photons, or snake-photons [1,5-7,9,27]), deviates slightly from the straight-line trajectory and transfer the image that is little distorted by scattering through small angles. Imaging by snake-rays can be considered as an alternative to traditional utilizing harmful X-rays. Several techniques to extract the snake-photons have been proposed. The snake-photons retain their initial polarization as opposed to the diffusive photons. Therefore, polarization gating can be applied as a simple way to select photons traveling along nearly straight line and to enhance the imaging contrast. A further method to obtain of the contrast image in optically thick layers consists in tissue illumination by an ultra short pulse of light and time-resolved detection (the temporal gate is of the order of several picoseconds) of early arriving photons.
Within the framework of the project the theoretical method is planned to be developed for calculating the inclusion image in illuminating biological tissues by a polarized nonstationary beam of light. The results to be obtained will allow one to optimize the procedure of inhomogeneity imaging and to determine the main parameters of inhomogeneities from experimental data.
2. Optoacoustic (OA) tomography is a promising new method for imaging light absorbing heterogeneities in scattering medium. This method is based on the thermooptical conversion of laser light: pulsed laser radiation is absorbed in the medium, that leads to non-stationary heating of the medium and its expansion, that in turn leads to the excitation of the ultrasonic pulses – OA signals. The waveforms of these signals under certain conditions correspond to the distribution of heat release within the medium. Time-resolved detection of the OA signals allows to reconstruct the spatial distribution of heat release, light intensity and light absorption coefficient within the medium. This constitutes the problem of OA tomography. The essential difference of this method compared to optical diffusion tomography is relatively high spatial resolution, comparable to the resolution of the ultrasonic imaging methods, and the ability to detect small absorbing inclusions (less than 1 cm) at depths exceeding 3 cm. Phantom and in vitro experiments have shown the applicability and high promise of the OA tomography in the field of breast cancer detection. However, the introduction of the OA tomography into clinical practice requires thorough investigation of sound excitation mechanisms in heterogenous biological tissue, optimization of laser irradiation parameters and design of the multi-element array transducers for OA signal detection, development of OA image reconstruction algorithms. These studies are essential for further application of OA tomography in vivo for imaging different optical heterogeneities in biological tissues, such as, for example, cancerous tumors or thermal lesions resulting from HIFU therapy (see section 4).
Investigations involved in this project will include optimization of different parameters of the OA system for imaging optically absorbing inclusions in biological tissues. Imaging absorbing inclusions distribution in different scattering media and measurement of the optical properties of these media will be implemented. New algorithms of OA image reconstruction will be developed.
3. The important diagnostic information about tissue condition can be obtained by analyzing the relaxation time spectra of various internal processes in living tissue and their temporal variations. Biological media are known to possess a wide spectrum of relaxation times and in traditional spectroscopy essential efforts are required for determination of such spectra in vitro in the wide frequency range. The standard approach based on temperature-frequency analogy, when the temperature dependence, instead of the frequency dependence, is studied, turns out to be unapplicable. At the same time the methods of distant pulsed acoustic spectroscopy, developed by the authors of the project, are unique tools for studying relaxation time spectrum and its dynamics in tissues of living organism.
In this project the method for reconstruction of relaxation time spectra of biological tissues will be developed based on the techniques of pulsed acoustic diagnostics and spectroscopy.
4. Ultrasound is known to be a unique modality in medicine for both diagnostic and therapeutic applications. At low intensities, ultrasound can be used to image almost every region of the human body and this procedure has now become very commonplace. The same technology used for diagnostic purposes, but operated at a much higher acoustic intensity, can be used in tumor therapy (localized necrosis of tissue) and haemostasis (arresting of bleeding). However, the therapeutic applications of ultrasound, although proposed as early as the 1940’s, have had little commercial or clinical success. Recent advances in computing, imaging technology, and material science have many companies moving HIFU (High Intensity Focused Ultrasound) devices into clinical practice. An important aspect of HIFU is that it shows great promise as a minimally invasive therapy. Focused ultrasound can propagate through most human soft tissues without inducing a bioeffect until the small focal region, where the ultrasound intensity becomes sufficiently high to exceed a threshold level and to induce tissue necrosis and blood coagulation. An adequate understanding and control of these processes, as well as an optimization of the treatment protocol, require a comprehensive study of nonlinear acoustic propagation, cavitation, streaming, and tissue heating induced by ultrasound.
We plan to investigate the physical mechanisms involved in ultrasound propagation and interaction with tissue. Fundamental scientific studies of this project will be undertaken, but we seek also to determine those conditions that limit the engineering development, or will lead to an optimization of prototype medical devices.
The proposed project implies participation of the unique group of researchers from Moscow Engineering Physics Institute and Moscow State University that are highly experienced in the whole range of the project research directions. The development of novel theoretical approaches to solution of the formulated problems as well as their experimental verification and adaptation to medical applications will be performed
The project participants have an experience of successful joint investigations in the field of medical physics, specifically the collaboration between Acoustics Department, Faculty of Physics, MSU and Center of Industrial and Medical Ultrasound (Laboratory of Applied Physics, University of Washington, USA)
Foreign collaborators will participate in the project according to the ISTC regulations. The collaborators will provide commentaries to the technical reports of the project, implement the results inspection, participate in software testing, participate in technical inspection on project activity together with the ISTC officials, participate in joint publications.
The International Science and Technology Center (ISTC) is an intergovernmental organization connecting scientists from Kazakhstan, Armenia, Tajikistan, Kyrgyzstan, and Georgia with their peers and research organizations in the EU, Japan, Republic of Korea, Norway and the United States.
ISTC facilitates international science projects and assists the global scientific and business community to source and engage with CIS and Georgian institutes that develop or possess an excellence of scientific know-how.