Lääketieteellisen fysiikan ja tekniikan yhdistys (LFTY)

Finnish Society for Medical Physics and Medical Engineering

In English        



XII Finnish Medical Physics and Medical Engineering Day, 7.2.2013, University of Oulu, Oulu, Finland

The 12th Finnish Medical Physics and Medical Engineering Day was held 7th February 2013 at University of Oulu, Oulu, Finland. The annual event gathered this year 94 student and researcher participants. The traditional poster exhibition, where the best Master's theses and diploma theses finished in 2012 were awarded, had 9 participants. The award for the best theses was this year 2012 €.

From the 9 participants, three theses were reckoned to be above the others. These theses were:
These three theses were evaluated to be equally good, and therefore, all three were rewarded with a 670,67 € scholarship.

Award presentation for the best Master's theses and diploma work in 2012 (from left to right): Prof. Risto Ilmoniemi (chair of Finnish Medical Physics and Medical Engineering Society), Marja Pitkänen, Lasse Räsänen, Robert Nawfal, Tapani Koivukangas (Lewel Group Ltd), and Mika Tarvainen(secretary of Finnish Medical Physics and Medical Engineering Society).


Abstracts of the awarded theses


Research and development of a miniaturized, complete wireless EMG measuring system
Robert Nawfal, Tampere University of Technology, Tampere, Finland
Objective: According to the World Health Organization (WHO) annually 15 mil-lion people suffer a stroke. Of those, 5 million are left permanently disabled due to damage of the brain. Rehabilitation therapies restore these disabilities partially or fully, by reactivating and moving the paralyzed muscles. Electromyography (EMG) is used in rehabilitation therapies to provide information about the degree of muscle activity by capturing the electrical signals from the muscle fibres. With this infor-mation the physician can guide the patient during the treatment and occasionally the visual feedback of the degree of muscle activity is provided directly to the pa-tient. This research describes the design and implementation of a wireless EMG sensor system from the initial requirements to the first functional implementation.

Methods: First, the suitability of wireless medical device certified protocols were researched to choose the optimal protocol for an eight sensor node system, capable of transmitting 2000 samples per second per node. The Zigbee protocol based radio frequency unit (RF-unit) with an integrated microcontroller was implemented to transmit the signal to a receiver. Then an analog circuitry was designed and con-structed to condition and digitalize the electrical muscle potential. An integrated analog front end microchip with a right leg drive circuit was used to provide the signal to the microcontroller. The signal was analysed and displayed via computer display.

Results: The results acquired show that the system operates correctly with a sampling rate of 500 samples in second. The system reacts to motoric movement (Biceps curl) and shows electric potential change related to the event. The frequency spectrum of the acquired signal (10-125 Hz) is not sufficient for a high quality analysis of EMG signals, because important frequencies from 125 to 500 Hz are missing. The quantified common mode rejection ratio of 65 dB of the system is not high enough for high quality measurement since the 50 Hz powerline interference is still present with 37V amplitude.

Conclusions: The system is able to record electrical activity of muscle poten-tials and provide qualitative information about muscle contractions to guide the rehabilitation therapy. This implementation serves as a base for further develop-ment in software to enable faster data acquisition and in hardware to increase the measurement precision.


Effect of recoverin on mouse rod photoreceptor photoresponses
Marja Pitkänen, Aalto University, Espoo, Finland
Background: Absorption of a photon by a photopigment molecule rhodopsin in a retinal photoreceptor triggers phototransduction - a biochemical cascade that transforms information about the arriving light into an electrical signal. Phototransduction consists of two phases. At first the light-activated rhodopsin binds transiently to and activates a G-protein, which in turn binds to a phosphodiesterase enzyme. This G-protein-phosphodiesterase complex hydrolyzes cGMP-molecules in the cytoplasm, which eventually results in an electrical response.

The amplification of the signal is partially produced by activation of several G-proteins by a single rhodopsin before it is deactivated. Recoverin is a calcium sensor protein, which controls phototransduction gain by regulating the inactivation of the light-activated rhodopsin. The other inactivation reaction of phototransduction, inactivation of phosphodiesterase, is not known to have any calcium-dependent regulation mechanism. The objective of this Master's thesis was to study how knocking out recoverin affects the photoresponses of rod photoreceptors.

Materials and methods: The method used in this thesis was electroretinography (ERG) of isolated retina, which measures the changes in the voltage across the retina caused by the electrical light responses of the photoreceptor cells. The experiments were carried out with the retinas of recoverin knockout mice of the strain C57BL/6. For reference, similar experiments were conducted with retinas from the normal C57BL/6-strain mice. Several parameters describing the sensitivity of the rods, amplification in the activation phase of phototransduction, and the kinetics of the inactivation reactions were determined from the photoresponses.

Results: Recoverin was observed to slightly increase the sensitivity of the rods and to slow down the kinetics of response recovery . These results were consistent with previous data from single-cell recordings. As a novel result, it was found that recoverin lengthens the dominant time constant of recovery of the photoresponse that corresponds to the slower of the two inactivation reactions of phototransduction, the inactivation of phosphodiesterase.

Conclusion: The change of the dominant time constant implies that recoverin affects the lifetime of activated phosphodiesterase either directly by an unknown mechanism or indirectly through some other calcium-dependent protein by changing the calcium-buffering properties of the rod photoreceptor cells.


Implementation of collagen architecture from clinical MRI into a biomechanical model of a knee joint
Lasse Räsänen, University of Eastern Finland, Kuopio, Finland
The collagen network architecture of articular cartilage has an important role in modulating stresses and strains in the knee joint. However, the influence of the realistic, patient-specific collagen architecture of cartilage, from clinical MRI, has not been demonstrated before on knee joint mechanics. The aim of this study was to evaluate the influence of the patient-specific collagen network architecture, obtained from clinical MRI, on knee joint stress, strain and pore pressure distributions by using finite element (FE) modelling. Specifically, the aim was to assess the possible inaccuracies in the evaluation of joint mechanics caused by the imaging modality and the zonal estimation methods and the possible alterations in the knee joint mechanics caused by non-specific, literature values for the collagen architecture.

Therefore, a subject-specific collagen architecture of cartilage was obtained from T2 mapping of clinical 3.0T MRI (Osteoarthritis Initiative (OAI) database, image dataset 0.E.1, http://www.oai.ucsf.edu/), and was implemented into a 2D finite element model of a knee joint with fibril reinforced poroviscoelastic material properties for cartilage and meniscus. For comparison, we created two models with alternative collagen architectures, demonstrating the inaccuracies caused by the estimation of the collagen architecture from MRI, and two models with constant depth-dependent zone thicknesses obtained from literature. The mechanical behavior of the models was analyzed under 700 N axial impact loading and the results were compared to the patient-specific model.

The model without the tangentially oriented collagen fibrils in the superficial zone with respect to the patient-specific model showed at most 69 % decrease in maximum principal stress and fibril strain, and 38 % and 16 % increase in maximum principal strain and pore pressure, respectively, in the superficial layers of cartilage. The models with zone thickness obtained from literature demonstrated 73 % and 143 % increase in stresses and fibril strain and 25 % and 22 % decrease in strain and pore pressure, respectively, especially in the intermediate cartilage.

The results demonstrated that neglecting the patient-specific collagen architecture may lead to different stress and strain distributions. The findings also demonstrate that minor errors in the analysis of collagen architecture from MRI, e.g. due to the analysis method or MRI resolution, can lead to alterations in knee joint stresses and strains. Therefore, these results suggest that the implementation of patient-specific collagen architecture is required for accurate evaluation of joint mechanics and may improve the diagnostic potential of the present functional imaging methods.