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Lääketieteellisen fysiikan ja tekniikan yhdistys (LFTY) Finnish Society for Medical Physics and Medical Engineering |
LFT-päivä 7.2.2013, Oulun yliopisto
Posterikilpailuun osallistuneet
1. Heidi Hintsala, Oulun yliopistoDirected measures of brain connectivity
2. Juuso Honkanen, Itä-Suomen yliopisto
Nivelkierukan ja nivelruston mekaanisten ominaisuuksien karakterisointi vetomittausten avulla
3. Petteri Hyvärinen, Aalto-yliopisto
Utilization of the chirp stimulus in auditory brainstem response measurements
4. Robert Nawfal, Tampereen teknillinen yliopisto
Research and development of a miniaturized, complete wireless EMG measuring system
5. Marja Pitkänen, Aalto-yliopisto
Effect of recoverin on mouse rod photoreceptor photoresponses
6. Juha Rusanen, Oulun yliopisto
Frequency-selective transmission of graded signals in large monopolar cells of the fly compound eye
7. Lasse Räsänen, Itä-Suomen yliopisto
Implementation of collagen architecture from clinical MRI into a biomechanical model of a knee joint
8. Tiina Takalokastari, Oulun yliopisto
Langaton EKG arkiliikkujilla
9. Petri Tanska, Itä-Suomen yliopisto
Solujen käyttäytyminen kuormitettaessa nivelrikkoista rustoa - kokeellinen ja teoreettinen tarkastelu
Postereiden abstraktit
Directed measures of brain connectivityHeidi Hintsala, Oulun yliopisto
Background and the aim of the study: Neurological disorders belong to the leading global causes of years of healthy life lost, and prevalence of them is increasing. Directed functional analysis of brain signals has been proposed to be one method for early stage diagnosis of neurological disorders. It reveals not only the changes of the functional activity of the brain, but also the cause-effect phenomenon of the activity. Various new measures have recently been presented to be applied to the directed analysis of the brain signals, but so far extensive comparison between them has not been performed. Aim of the present study was to perform a comparison of commonly applied conventional and directed connectivity measures, namely cross-correlation, coherence, phase slope index (PSI), directed transfer function (DTF), partial directed coherence (PDC) and transfer entropy (TE) with simulated connectivity data.
Methods: The ability of the measures to detect the directed connectivity was evaluated with eight-and twenty-node simulation data based on real electroencephalogram source signal. Also, the effects of signal-to-noise ratio (SNR) and decimation were explored with eight-node simulation. Statistical assessment was performed by comparing the amount of detected direct causal connections (i.e. true connections in directed connectivity analysis) and the non-causal connections (i.e. false connections) for different connectivity measures with all data settings by chi-square tests.
Results: PDC detected less and coherence more false connections than the other measures with eight-node data (p<0.01). Cross-correlation, coherence, PSI, and PDC detected >80% and DTF and TE >60% of the true connections with the eight-node data. With the more complicated twenty-node data, only DTF and PDC managed satisfactory to detect the connectivity pattern. DTF and PDC tolerated low SNR better than the other measures. TE, instead, was strongly affected by the level of SNR. Decimation had no effect to cross-correlation, coherence and PSI, but it affected significantly (p<0.01) to DTF, PDC and TE.
Conclusions: To my knowledge, this is the first experimental comparison of connectivity measures in the directed connectivity analysis of the simulated data in this extend. In the present study, most measures detected directed connections well with simple eight-node simulation data, whereas only DTF and PDC performed satisfactory when more nodes were applied in the simulation. In addition, DTF and PDC had good tolerance of low SNR. However, decimation of data has to be carefully considered with these measures.
Nivelkierukan ja nivelruston mekaanisten ominaisuuksien karakterisointi vetomittausten avulla
Juuso Honkanen, Itä-Suomen yliopisto
TUTKIMUKSEN TAVOITE: Nivelrikon syntyyn liittyviä mekanismeja ei tunneta vielä tarkoin. Eräänä syynä nivelrikkoprosessin käynnistymiselle voi toimia rustopinnan mekaaninen ylikuormittuminen. Jotta nivelrikon synnystä pystyttäisiin saamaan kokonaisvaltaisempi kuva, olisi hyvin oleellista tuntea nivelruston sekä sitä ympäröivien kudosten mekaaniset ominaisuudet. Tämän Pro gradu -tutkielman tavoitteena oli tutkia vetomittausten avulla polvinivelen nivelruston ja nivelkierukan mekaanisia ominaisuuksia. Lisäksi työssä selvitettiin olivatko samasta polvesta otettujen nivelkierukka- ja nivelrustonäytteiden mekaaniset ominaisuudet riippuvia toisistaan.
MENETELMÄT: Naudan polvinivelen (n = 10) lateraalisesta nivelkierukasta ja reisiluun lateraalisen nivelnastan nivelrustosta valmistettiin mikrotomin avulla ohutleikkeet (0.30 mm × 2.97 mm). Näytteitä venytettiin 5 mm/min nopeudella hajoamiseen saakka, samalla mitaten näytteisiin kohdistuvaa voimaa ja venymää ajan ja poikkeaman alkutilanteesta funktiona. Mittausten avulla näytteille määritettiin kimmomoduulin ja jäykkyyden arvot, murtumiseen vaadittavan työn määrä sekä tämän avulla näytteiden sitkeys. Lisäksi määritettiin näytteiden maksimaalisia jännityksiä vastaavat suhteellisten venymien arvot.
TULOKSET: Nivelkierukan kimmomoduuli (p < 0.001), jäykkyys (p < 0.001), näytteen murtamiseen vaadittava työ (p < 0.001) ja sitkeys (p < 0.05) olivat merkittävästi suurempia kuin nivelrustolla. Vastaavasti nivelruston suhteellisen venymän keskiarvo oli yli kaksinkertainen (p < 0.001) nivelkierukkaan verrattuna. Samasta polvesta otettujen nivelkierukka- ja nivelrustonäytteiden mekaanisten ominaisuuksien välillä ei havaittu merkittävää riippuvuutta.
JOHTOPÄÄTÖKSET: Tulosten perusteella nivelkierukoiden ja nivelruston ollessa terveitä, ei kummankaan kudoksen ominaisuudet tai käyttäytyminen vaikuta toisen kudoksen toimintakykyyn. Kuitenkin, koska nivelkierukka vastustaa nivelrustoa enemmän vetoa sekä kykenee absorboimaan suuremman määrän energiaa ennen vaurioitumistaan, on nivelkierukoiden oikeanlainen toiminta tärkeä edellytys rustopinnan kunnossa pysymiselle. Täten nivelrikon syntyä tutkittaessa on oleellista ottaa myös nivelkierukoiden vaikutus huomioon.
Utilization of the chirp stimulus in auditory brainstem response measurements
Petteri Hyvärinen, Aalto-yliopisto
The electrical activity originating from the auditory structures of the brainstem is called the auditory brainstem response (ABR). The ABR is used widely for objective assessment of the hearing system. Whereas traditional pure tone audiometry requires the test subject to respond to probe tones in a predefined manner, the ABR can be recorded without any active participation of the subject. Recently, a new kind of stimulus has been developed for ABR measurements. This stimulus, called chirp, aims at increasing the ABR amplitude by promoting synchronous firing of the hair cells in the inner ear. 1,5-2 times higher ABR amplitudes have indeed been recorded using the chirp when compared to traditional stimuli. The aim of the thesis was to evaluate the usefulness of the chirp stimulus in clinical ABR measurements.
Traditional click and tone burst stimuli were compared to corresponding chirp variants: the broadband chirp and frequency-specific narrowband chirps. Also, the ABR results were compared to those obtained by another objective method, the auditory steady-state response (ASSR). Responses were obtained from six normal-hearing subjects and five hard-of-hearing subjects using the Eclipse platform from Interacoustics. In normal-hearing subjects, the ABR amplitudes were compared between traditional and chirp stimuli. In all subjects, ABR and ASSR thresholds were compared to the behavioural thresholds.
Results failed to show significant differences between traditional stimuli and corresponding chirp variants. Also, comparison of and ASSR thresholds could not be done reliably because of the small number of obtained thresholds.
It was concluded that the results were likely influenced by the type of the insert earphones used in this study. Previous results in favour of the chirp have been obtained using a different type of earphones. Also, it was suggested that the influence of hearing loss on chirp-elicited ABRs be investigated in the future.
Research and development of a miniaturized, complete wireless EMG measuring system
Robert Nawfal, Tampereen teknillinen yliopisto
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-yliopisto
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.
Frequency-selective transmission of graded signals in large monopolar cells of the fly compound eye
Juha Rusanen, Oulun yliopisto
Tutkimuksen tavoite: Solukalvon impedanssi määrittelee sen, kuinka signaali muuttuu edetessään solussa. Impedanssi puolestaan riippuu solukalvon passiivista ominaisuuksista ja jänniteherkistä ionikanavista. Suuret monopolaarisolut (LMC-solut) ovat toisen asteen visuaalisia neuroneita, joiden tehtävä on muun muassa yhdistää fotoreseptoreiden visuaalisia signaaleja ja siirtää signaali seuraaviin visuaalisiin systeemeihin. Varmuutta siitä, kuinka signaalin eteneminen LMC-soluissa vaikuttaa signaalin taajuussisältöön ei ole. On ehdotettu, että LMC-soluista löydetyt kahdentyyppiset jänniteherkät kaliumkanavat (Kd ja Ka) vaikuttavat signaalin eri taajuuskaistojen siirtymiseen. Tutkielman tarkoituksena oli kartoittaa jänniteherkkien kaliumkanavien vaikutus LMC-solujen virta-jännite -ominaisuuksiin ja signaaliin siirtoon.
Käytetyt metodit: LMC-solujen virta-jännite -ominaisuuksia tutkittiin intrasellulaaristen virtainjektiomittausten ja mallinnuksen avulla. Mallinnus tapahtui käyttäen NEURON(7.1)-ohjelmaa. Soluja mallinnettaessa ne jaettiin kahteen luokkaan L1/L2- ja L3-solut, joihin lisättiin solutyypille ominaisia Ka- tai Kd-kanavia. Mallien parametrien arvot johdettiin suoritettujen intrasellulaaristen mittausten sekä aikaisemmin julkaistujen tulosten pohjalta.
Tulokset ja johtopäätökset: Inrasellulaaristen mittausten ja mallin avulla suoritettujen simulaatioiden pohjalta päädyttiin siihen tulokseen, että eri LMC-soluluokille tyypillisten kaliumkanavien (Ka/Kd) ilmentäminen edesauttaa eri taajuuskaistojen siirtoa soluissa. Tämä tukee hypoteesia siitä, että eri LMC-luokat olisivat erikoistuneita siirtämään visuaalisen signaalin eri taajuuskaistoja. Lisäksi kanavien jänniteherkkyys mahdollistaa solukalvon impedanssin muuttumisen eri valaistusolosuhteissa, mikä mahdollistaa kussakin valaistusolosuhteessa tärkeän taajuuskaistan siirtämisen.
Implementation of collagen architecture from clinical MRI into a biomechanical model of a knee joint
Lasse Räsänen, Itä-Suomen yliopisto
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.
Langaton EKG arkiliikkujilla
Tiina Takalokastari, Oulun yliopisto
Tutkimuksen tavoitteena oli selvittää langattoman EKG:n äyttömahdollisuuksia liikuntasuoritusten aikaisessa sydänsähkökäyrän seurannassa.
Tutkimukseen osallistui yhteensä 36 eri-ikäistä aikuista. Kolmeltakymmeneltä henkilöltä mitattiin liikuntasuorituksen, kävelyn, pyöräilyn tai sauvakävelyn aikana sydänsähkökäyrä langattomalla mittarilla (VitalSens VS100). Samalla mitattiin myös suorituksesta aiheutuvat kiihtyvyydet (VitalSens VS100 ja DogImu. Suoritusten aikaisista tapahtumista kerätyn listan kanssa loput kuusi koehenkilöä suorittivat liikuntatehtäviä, joiden oli havaittu mahdollisesti vääristävän signaalia. Kaikki mittaukset suoritettiin sisällä, Oulun diakonissalaitoksen liikuntalääketieteen tai Oulun yliopiston EMC - laboratorion tiloissa.
Saatu EKG-aineisto jaettiin laatutasoltaan kolmeen luokkaan, hyvään (3 %), keskinkertaiseen (66 %) sekä huonoon (31 %) havaittavissa olevan QRS-kompleksin sekä häiriömäärän perusteella. Lisäksi tarkasteltiin EKG:n häiriömäärän sekä kiihtyvyyssignaalien vahvuuden suhdetta, sekä erinäisten yksittäisten liikeratojen vaikutusta signaalin todenmukaisuuteen.
Vertailtaessa aineiston laatua sekä langattomuudesta aiheutuvien positiivisten ja negatiivisten ominaisuuksien tasapainoa, todettiin langattoman EKG:n olevan vahva mahdollisuus tulevaisuuden terveydenhuollolle ja liikunnalle. Ennen todellista käyttöä on signaalin laatu saatava stabiilimmaksi sekä signaalin kantomatkaa pidennettävä. Testejä on suoritettava myös ulko-olosuhteissa, jotta voidaan havaita ulkona esiintyvien häiriötekijöiden vaikutukset signaalin laatuun.
Solujen käyttäytyminen kuormitettaessa nivelrikkoista rustoa - kokeellinen ja teoreettinen tarkastelu
Petri Tanska, Itä-Suomen yliopisto
Articular cartilage cells, i.e., chondrocytes are responsible for synthesis and assembly of the extracellular (ECM) and pericellular matrix (PCM). Biosynthesis is thought to be affected by chondrocyte volume changes. It has been observed that there are substantial differences in cell volumetric behavior between mechanically loaded normal and early osteoarthritic cartilage.
The aim of this study was to investigate if the experimentally detected altered cell volumetric behavior in early osteoarthritis (OA) can be explained by changes in the ECM and PCM composition and structure. We hypothesized that differences in the properties of the collagen fibrils and fixed charge density in the PCM of normal and degenerated cartilage results in a different cell volumetric behaviour between the groups.
Based on our own experimental tests and findings reported in the literature, the composition, structure and mechanical parameters of the ECM, PCM and cell for healthy and OA cartilage were implemented into a fibril-reinforced poroelastic swelling model. In the OA model, the fixed charge density (FCD) and collagen network modulus were reduced and the fluid fraction was increased compared to the healthy cartilage. Model simulations were compared with experimentally observed cell volume changes in mechanically loaded cartilage, obtained from anterior cruciate ligament transected (ACLT) rabbit knees. Furthermore, parametric analyses were conducted to clarify the importance of collagen fibrils, fixed charge density and fluid fraction in the ECM and PCM on cell volume changes.
The decreased extracellular and pericellular FCD, increased fluid fraction and reduced superficial collagen fibril modulus in the OA model caused a 7 % increase in cell volume following mechanical loading of the tissue. In contrast, cell volume decreased by 4 % in healthy cartilage. These findings were consistent with the experimental results. The parametric analysis suggested that the increased local transversal tissue strain due to reduced collagen fibril stiffness accompanied with reduced FCD of the PCM could increase cell volume up to 12 %.
These findings suggest that the increase in cell volume in mechanically loaded OA cartilage is primarily explained by the reduction in the pericellular FCD, while the superficial collagen fibril stiffness of the ECM is suggested to contribute secondarily to the cell volume behavior. The changes in the ECM and PCM properties in early OA may further lead to altered cell synthesis and rate of the progression of OA.