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Lääketieteellisen fysiikan ja tekniikan yhdistys (LFTY) Finnish Society for Medical Physics and Medical Engineering |
LFT-päivä 10.2.2010, Tampereen teknillinen yliopisto
Posterikilpailuun osallistuneet
1. Erik Huotari, Oulun yliopisto6–15-vuotiaiden lasten fyysisen aktiivisuuden mittaaminen ranteesta
2. Leena Jaatinen, Tampereen teknillinen yliopisto
Application of an electric impedance method to assess the viability and amount of adipose stem cells cultured in biodegradable 3-dimensional scaffolds
3. Kirsikka Kaipainen, Tampereen yliopisto
Design and implementation of web-based cognitive behavioural therapy intervention methods for management of mental wellbeing
4. Tuomas Koivumäki, Tampereen teknillinen yliopisto
Theoretical background for respiratory and cardiac gating in SPECT/CT using electrical bioimpedance method
5. Minna Lahtinen, Tampereen teknillinen yliopisto
Software phantoms for texture analysis
6. Markus Malo, Oulun yliopisto
Numerical analysis of uncertainties in dual frequency ultrasound technique
7. Narayan Puthanmadam Subramaniyam, Tampereen teknillinen yliopisto
Cortical Potential Imaging with Realistic Head Model using L-curve and GCV method
8. Anne Rajala, Tampereen teknillinen yliopisto
Sulakehruuprosessin optimointi polylaktidikuituja valmistettaessa
9. Aliina Tuomenlehti, Tampereen teknillinen yliopisto
EEG interface for portable ECG recorders
10. Mikael Turunen, Itä-Suomen yliopisto
Changes in rabbit bone composition – a comparison between infrared and raman microspectroscopy
11. Panu Vesanen, Aalto-yliopisto
Compressed Sensing in Parallel Magnetic Resonance Imaging
12. Tuomas Viren, Itä-Suomen yliopisto
Nivelensisäinen ultraäänitekniikka nivelrikon diagnostiikkaan
13. Sami Väänänen, Itä-Suomen yliopisto
Aktiivinen äänenvaimennus digitaalisella signaalinkäsittelyprosessorilla
14. Nina Yliaska, Oulun yliopisto
Vaiheherkkään ilmaisuun perustuva verenvirtausmittaus
Postereiden abstraktit
6–15-vuotiaiden lasten fyysisen aktiivisuuden mittaaminen ranteesta
Erik Huotari, Oulun yliopisto
Tutkimuksen tavoitteena oli luoda ranteesta mitattuun kiihtyvyyssignaaliin perustuva menetelmä 6–15-vuotiaiden lasten fyysisen aktiivisuuden ja energiankulutuksen arviointiin. Myös koehenkilöiden demografisten tekijöiden (ikä, pituus, paino, painoindeksi ja sukupuoli) vaikutus mitattaviin signaaleihin ja niistä laskettaviin parametreihin selvitettiin.
Tutkimukseen osallistui kaksikymmentä 6–15-vuotiasta lasta. Tutkimuksessa mitattiin yksisuuntaista kiihtyvyyssignaalia kahdessatoista eri aktiviteetissa. Samanaikaisesti mitattiin hapenkulutusta kannettavalla hengityskaasuanalysaattorilla (Viasys, Oxycon Mobile). Aktiviteetit jaettiin kolmeen luokkaan: istuma-aktiviteetit, keskeytyvä liikkuminen ja jatkuva liikkuminen. Jatkuva liikkuminen koostui kävelystä ja juoksusta, jotka molemmat suoritettiin kahdella nopeudella juoksumatolla. Kaikki mittaukset suoritettiin sisätiloissa. Kiihtyvyysanturilla kerätyn mittausdatan perusteella luotiin Matlab-ohjelmointiympäristössä käytettävä sovellus, jolla arvioitiin energiankulutusta MET-yksiköitä käyttäen. Näitä verrattiin hapenkulutuksesta laskettuihin MET-yksiköihin.
Kun vertailtavana olivat kaikkien aktiviteettien havainnot, kiihtyvyydestä arvioitujen ja hapenkulutuksesta laskettujen MET-arvojen välinen keskimääräinen poikkeama oli -0,07+0,92 ja korrelaatio 0,95. Demografisista tekijöistä muodostetuista korjausfunktioista pituuskorjaus osoittautui tehokkaimmaksi menetelmäksi tarkentaa energiankulutuksen arviointia kiihtyvyyssignaalista.
Ranteesta mitattuun kiihtyvyyssignaaliin perustuva menetelmä sopii hyvin 6–15-vuotiaiden lasten energiankulutuksen arviointiin. Kehitetty menetelmä erottelee riittävällä tarkkuudella erilaisia aktiivisuuksia. Mittaukset on suoritettu laboratorio-olosuhteissa, siksi tarvitaan vielä lisää tutkimusta käytännön olosuhteissa.
Application of an electric impedance method to assess the viability and amount of adipose stem cells cultured in biodegradable 3-dimensional scaffolds
Leena Jaatinen, Tampereen teknillinen yliopisto
At the moment, there are no non-invasive methods in general use for determing the charateristic or viability of tissue engineered scaffolds with or without implanted cells. Cell cultures are normally evaluated with histological or optical methods which either damage the material or at least are not suited for continuous monitoring of microporous scaffolds. The aim of my thesis was to utilize electric impedance to study the cell viability in cell cultures and in biomaterial structures. The measurements were made with Electrical Bioimpedance Amplifier and the measurement chamber was constructed of fertilization dish and silver electrodes attached to its cover.
The method is based on dielectric polarization and bioimpedance. Cell membranes become polarized due to the applied electrical field and at low frequencies, each cell acts like a capacitor, the capacitance of which can be measured as an increase in the capacitance of the suspension. Capacitance is proportional to the permittivity and thus the relative permittivity of a cell suspension that is proportional to the cell concentration, increases owing to the increase in cell number. Solid particles or lysed (=dead) cells do not get polarised because their cell membrane is leaking. Capacitance is part of impedance so the cell viability and increasing cell number can also be seen as an increase in impedance.
In the first part of the study, the measurements were made of human liposuction-derived adipose stem cells and the impedance was measured from several monolayer cell cultures with different cell number. In the second part rabbit adipose stem cells were seeded into the PLA-based (polylactide) scaffolds and impedance was measured from empty scaffolds and cell-containing scaffolds for three weeks. Half of the scaffolds were in control medium and half of the scaffolds were cultured in chondrogenic differentiation medium.
The empty reference scaffolds and the scaffolds with stem cells and differentiated chondrocytes were measured during three experiments. The experiments did not yet provide exact information about the cell viability but important information how to improve the measurement configuration and what is really needed from the measurement equipment. Improved measurements have been made after this thesis was published and the results have been more promising. Another important discovery of the thesis was that the electric fields and agitation of the scaffolds did not cause any detected harm to the cells.
Design and implementation of web-based cognitive behavioural therapy intervention methods for management of mental wellbeing
Kirsikka Kaipainen, Tampereen yliopisto
Aim of the study: Mental health problems, such as depression and symptoms caused by stress, affect at least one in four people at some point in their lives. Since these problems are becoming increasingly common, there are not enough resources in healthcare to provide therapist treatment early enough to everyone who needs it. Web-based interventions can provide support for those who are unable or unwilling to get help for their mental health problems through conventional channels. The purpose of this study was to design, implement and evaluate a web-based cognitive behavioural therapy intervention for management of mental wellbeing, focusing especially on issues caused by stress and insufficient recovery. The web-based intervention was a part of a larger service concept which combined technological tools with a short psychological group intervention.
Methods: A literature review of relevant background theories in psychology and persuasive design was conducted and designs of existing web-based interventions were analyzed. Theories and findings were applied in practice by a constructive implementation of a web-based intervention as a web portal. The portal was evaluated by collecting feedback and usage logs from real users (N=34) after a usage period of nine to fourteen weeks, and by expert evaluations (N=5). The evaluation data were analyzed mainly descriptively and qualitatively, focusing on usage patterns, user experiences, and issues of guidance and feedback.
Results: Feedback on the portal was received from 23/34 of the participants in the user study. Most of them utilised some of the modules in the portal, although usage activity declined over the study period. The portal was considered useful by half of the respondents and the intervention methods were considered helpful by majority of those who used them. All but one user felt they had benefited in some way as a result of participating in the study, although the influence of the portal alone could not be isolated at this point. The experts were also generally positive towards the implementation and considered it useful in independent use. However, they saw a need for clearer guidance to the user and suggested enhancing motivational factors in the design.
Conclusions: The main challenge in development of web-based interventions is the lack of therapist guidance, which emphasizes the importance of understandable instructions, automated interpretation of analyses, and motivational feedback. The results from the evaluations suggest that the design of the portal was feasible and promising in providing a novel method for self-management of mental wellbeing, but the intervention structure needs improvement and the built-in motivational strategies require further work to make the portal better suitable for independent use.
Theoretical background for respiratory and cardiac gating in SPECT/CT using electrical bioimpedance method
Tuomas Koivumäki, Tampere University of Technology
Motion due to respiration and cardiac function often produces artefacts on SPECT/CT images. Motion artefacts may lead to false diagnosis, for example, in evaluation of coronary artery disease. The effects of motion on image quality can be minimized by gating that is, the synchronization of image acquisition to a physiological function.
Respiration and cardiac function can be monitored utilising bioimpedance measurement methods. Impedance pneumography and cardiography are generally regarded as cheap, safe and reliable. The aim of the thesis was to establish foundation for bioimpedance-based simultaneous respiratory and cardiac dual-gating in SPECT/CT. The main objective was to determine an optimized electrode configuration for simultaneous measurement of respiration and cardiac function using one measurement configuration that is, a pair of current injection electrodes and a pair of voltage measurement electrodes. A further objective was to study the requirements of signal processing for the separation of both gating signals from a single bioimpedance measurement signal.
In order to determine the most sensitive electrode configuration for simultaneous detection of respiration and cardiac function, computerized finite element method (FEM) modelling was performed. FEM calculations were carried out using a simplified human upper thorax model with CT-based inhomogeneities (heart, lungs and spine) and realistic tissue conductivities. The performance of over 47 000 electrode configurations was computed utilising the complete electrode model of electrical impedance tomography (EIT). The results were analyzed in terms of sensitivity and selectivity for the anatomical regions of heart and lungs. In order to study bioimpedance measurement dynamics, forward problem was solved to simulate measurements with feasible electrode configurations. Respiration and cardiac function were imitated by the alteration of lung and heart conductivities, respectively. Finally, the separation of respiratory and cardiac gating signals from simulated measurement data was studied.
An optimized electrode configuration for simultaneous detection of respiration and cardiac function was located on the level of fourth and fifth intercostals spaces on the anterior thorax. One electrode of both electrode types is located in midway and 1/3 of the distance from sternum to axilla on left and right sides, respectively. The absolute values of sensitivity for the determined electrode configuration were 75 % and 69 % of the sensitivities of separately optimized electrode configurations for respiration and cardiac function, respectively. The forward problem simulations and signal separation analysis indicated that signals for cardiac and respiratory gating can be obtained performing only one bioimpedance measurement.
The results of this study clearly indicate that the bioimpedance method is potential for dual-gating of SPECT/CT imaging. Since only four electrodes are needed to implement the method, it is simple to apply clinically and comfortable for the patient.
The thesis study was the first phase of a research project, which strives to develop a clinically feasible bioimpedance-based dual-gating method and equipment for nuclear medicine imaging.
Software phantoms for texture analysis
Minna Lahtinen, Tampereen teknillinen yliopisto
Texture analysis (TA) is a computer-assessed method for quantitative analysis of image textures. It is a potential tool for analysis of medical images. It can be used, for example, for classification of pathological tissue or detecting changes in tissues. TA is based on algorithms that describe the relationships between the grey level values of the image pixels. Different parameters function in different situations, for instance, with different textures or in different classification tasks. However, the characteristics of the texture features are not well-known. The aim of this study was to clarify the texture parameters by describing them verbally and to observe the parameter values with different texture patterns. The analysis was performed with software phantoms i.e. grey scale matrices. In addition, the ranges of the parameter values were studied and comparison between the phantoms and clinical images was completed.
The software phantoms were implemented with Matlab program by constructing 16x16 matrices containing four different grey level values. Grey scale images were drawn from the matrices and the texture analysis was performed with MaZda software. The analysis of the clinical images was performed by analyzing regions of interest (ROI) on breast magnetic resonance (MR) images and comparing the results with the software phantoms analyses.
The results show that the values of the parameters calculated with texture analysis of the phantom matrices are consistent. Useful information concerning the magnitudes of the parameters was obtained using different patterns. However, it turned out to be impossible to construct a typical pattern for each parameter as the texture characteristics the parameters describe are not always visible for human eye.
Software phantoms were proved to be an effective method to study the parameter value distribution because of the easy construction and modification of the matrices. However, the used matrices were simple patterns that were very different from real textures, and, considerably more complex patterns should be used if software phantoms were considered, for example, as reference material to physical phantoms and clinical images.
Numerical analysis of uncertainties in dual frequency ultrasound technique
Markus Malo, Tampere University of Technology
Quantitative ultrasound (QUS) measurements have shown potential in the diagnostics of osteoporosis. However, the variation in the thickness and composition of the overlying soft tissues results in significant errors in the bone QUS parameters and diminishes the reliability of the technique in vivo. Recently, the dual frequency ultrasound (DFUS) technique was introduced to minimize the soft tissue induced errors.
In this study, the significance of soft tissue induced errors and their elimination with the DFUS technique were simulated using a finite difference time domain technique. Furthermore, we investigated the potential of the DFUS corrected integrated reflection coefficient (IRC) of bone to detect changes in the cortical bone density. The effects of alterations in the thickness of fat and lean tissue layers and the inclination of interfaces between the soft-tissues and between the soft tissue-bone layers were simulated. In addition, the errors arising from non-optimal focusing of the transducer to the soft tissue-bone interface were investigated.
The main findings of this master’s thesis were that when the angle of the soft tissue interface was zero, i.e. perpendicular to the incident ultrasound beam, the DFUS-calculated soft tissue composition correlated highly linearly with the true soft tissue composition. The inclination between the soft tissue-bone interface was found to be critical. Even a 2-degree inclination between the soft tissue and the bone surface induced an almost 18% relative error in the corrected IRC. Increasing the inclination between the soft tissue layers increased the error in the DFUS-calculated lean and fat tissue thickness. This error was especially significant at inclination angles greater than 20 degrees. The significant soft tissue induced errors in IRC values (> 300 %) could be effectively minimized (< 10 %) by means of the DFUS correction. Importantly, after the DFUS correction, physiologically relevant variation in the cortical bone density could be detected (p < 0.05). In the out-of-focus study, the average relative error in IRC values was more accurate after the attenuation correction was done with the DFUS-calculated soft tissue thicknesses, than with the actual soft tissue thickness from the simulation geometry (8.9 % vs. 28.7%).
The study showed that with the DFUS technique one can accurately determine the thickness of the soft tissues overlying the bone surface, provided that each tissue layer interface is perpendicular to the incident ultrasound wavefront and the soft tissue-bone surface is in focus. This enabled us to correct accurately the reflection arising from the soft tissue-bone interface. Even small physiologically relevant differences in the cortical bone density could be separated with DFUS-corrected IRC values. The study showed that the more the interfaces of the tissues are inclined, the greater is the error induced in the DFUS-calculated thicknesses as well as on the attenuation correction of the reflection from the soft-tissue-bone interface. The changing thickness of the soft tissue layer, which leads to non-optimal focusing, was responsible for introducing an error in the DFUS calculations, when each tissue layer interface was perpendicular to proceeding ultrasound wavefront and a fixed focal length transducer was used.
Cortical Potential Imaging with Realistic Head Model using L-curve and GCV method
Narayan Puthanmadam Subramaniyam, Tampereen teknillinen yliopisto
The electroencephalography (EEG) is a non-invasive and simple technique used to measure the electrical activity of the brain and study its function. Although, the temporal resolution of EEG is excellent, its spatial resolution is reduced mainly due to the low-conducting skull. This makes it difficult to localize the sources.
The purpose of this work was to solve the inverse EEG problem using a source imaging technique known as cortical potential imaging method using Tikhonov regularization. Two widely and frequently applied methods were used to select the regularization parameter. They are the L-curve and generalized cross validation (GCV) technique. A finite difference method (FDM) model of the visible human man (VHM) was constructed as the volume conductor model where the regions modeled, were only between the scalp and cortex. The cortex was defined as closed surface as per Gauss’s Law in electromagnetism. The EEG data that was used was the N170 component of the visually evoked potential (VEP) for three type of stimulus – fearful face, neutral face and object shaped as faces. The data for three subjects were used and the inverse solution was computed for all the three subjects.
The results obtained showed that the L-curve and GCV methods used to find the regularization parameters were successful in computing the regularization parameter. The GCV method worked well even when the data was noisy. This indicates that the solutions obtained using these parameters are meaningful and the solutions to the inverse problem obtained might be optimal. It was observed in general, that for the fearful face and the neutral face, the activity was high at the occipitotemporal area. The activation sites were mainly located at temporal gyrus and parahippocampal gyrus predominantly at the right hemisphere. For objects shaped as faces, the activity was relatively low.
Sulakehruuprosessin optimointi polylaktidikuituja valmistettaessa
Anne Rajala, Tampereen teknillinen yliopisto
Kuitujen sulakehruuprosessi perustuu materiaalin sulattamiseen ja halutunlaisten kuitujen muotoiluun ekstruusion aikana. Sulakehruuprosessissa käytettävät parametrit riippuvat suuresti siitä, minkälaisia kuituja halutaan valmistaa. Työn tarkoitus oli optimoida Biolääketieteen tekniikan laitoksella sijaitseva sulakehruu- ja vetolaitteisto. Optimoinnilla tarkoitettiin sulakehruuprosessissa esiintyvien parametrien vaikutusten tuntemista niin, että tiedettiin minkälaisilla parametriyhdistelmillä saadaan valmistettua halutunlaisia kuituja. Tavoitteena oli myös löytää optimaaliset parametrien arvot käytetylle ekstruuderille ja vetolaitteistolle, esimerkiksi kuitujen halkaisijoiden minimoimiseksi sekä lujuuden maksimoimiseksi. Näin optimoinnin avulla olisi mahdollista valmistaa kuituja, joiden ominaisuudet ovat entistä paremmat ja vastaavasti tietää kuinka voidaan vaikuttaa paremmin näiden ominaisuuksien muodostumiseen.
Sulakehruuprosessin optimoinnissa käytettiin hyväksi Taguchi-menetelmää. Menetelmän avulla oli mahdollista etsiä kokeellisesti prosessille halutut parametrit, joiden avulla voitiin samanaikaisesti pienentää mahdollista ominaisuuksien vaihtelua. Taguchi-matriisit muodostettiin käyttämällä Minitab-ohjelmaa (Minitab®, Minitab Inc., State College (PA), Yhdysvallat). Ohjelman avulla voitiin muun muassa luoda koejärjestelyjä, kun tutkittavat ohjaus- ja häiriötekijät sekä halutut tasot tunnettiin, sekä analysoida koejärjestelyn mukaisia tuloksia. Optimointi suoritettiin käyttäen kuitujen valmistusmateriaalina poly-L-laktidia (PLLA). Valmistettujen kuitujen ominaisuuksien tutkimisessa hyödynnettiin vetolaitteistoa, sisäisen viskositeetin määrittämiseen suunniteltua laitteistoa (IV-laitteisto) sekä erilaisia mikroskooppeja. Lisäksi vetokokeiden yhteydessä mitattiin kuitujen halkaisijat. Osalle kuiduista suoritettiin myös monomeerimääritys.
Ekstruusioparametrien optimointi onnistui kokonaisuudessaan hyvin. Tulokset olivat lupaavia ekstruusioparametrien optimointia seuranneen vetolaitteistoparametrien optimoinnin kannalta, sillä halkaisijat olivat jo ennen vetoa pieniä, venymät suuria ja sisäiset viskositeettiarvot hyviä. Varmistusajojen tulokset olivat yleisesti ottaen parempia kuin pelkkien koeajojen tulokset ja kaikkia laatuominaisuuksia saatiin parannettua koeajoista saatuihin tuloksiin verrattaessa. Vetolaitteistoparametrien optimoinnin aikana valmistetuilla kuiduilla oli mikroskooppitarkasteluissa havaittavissa paikoitellen pinnan epätasaisuutta sekä kuroutumia. Tällaiset ongelmat olivat yllättäviä ja varmaa esiintymissyytä epätasaisuuksille ei ollut. Kuitujen pinnalla esiintynyttä epätasaisuutta lukuun ottamatta kuitujen ominaisuudet olivat kuitenkin lupaavia. Kuitujen venymät valmistetuilla kuiduilla olivat vielä hieman suuria, joten osaa kuiduista olisi voitu orientoida enemmän, jolloin kuitujen venymää olisi saatu mahdollisesti pienennettyä. Venymän pienentyessä olisi saatu myös vetolujuutta kasvatettua. Taguchi-menetelmän avulla optimointi suoritettiin alkuoletusten mukaisesti tavallisiin optimointimenetelmiin verrattaessa vähemmällä työmäärällä, ja sen avulla päästiin työn alussa asetettuihin tavoitteisiin.
Taguchi-menetelmä soveltui melko hyvin sulakehruuprosessin optimointiin. Menetelmän huono puoli oli, että menetelmän antamat optimaaliset parametriasetukset olivat riippuvaisia menetelmän käyttäjän ennalta päättämistä tasojen arvoista. Toisin sanoen menetelmän avulla ei ollut mahdollista määrittää optimiarvoja käytettyjen tasojen ulkopuolelta. Menetelmä ei myöskään pystynyt analysoimaan kuin yhtä laatuominaisuutta kerrallaan, jolloin usean laatuominaisuuden tulosten analysoiminen oli riippuvaista menetelmän käyttäjästä. Näin ollen saadut optimiasetukset olisivat voineet olla hyvinkin erilaiset, mikäli optimointi olisi suoritettu jotain toista menetelmää hyväksikäyttäen. Optimointi kokonaisuudessaan onnistui sulakehruuprosessille kuitenkin hyvin. Optimoinnin aikana opittiin tuntemaan sulakehruuprosessin parametrien vaikutuksia valmistuvien kuitujen ominaisuuksiin ja saatiin valmistettua hyvälaatuisia kuituja. Valmistettujen kuitujen pinnalla kuitenkin havaittiin epätasaisuuksia ja kuroutumia, joita kaupallisiin tarkoituksiin valmistetuilla kuiduilla ei saisi esiintyä. Näin ollen tutkimustyötä vetolaitteistolla vedettyjen kuitujen ulkoisista laatuominaisuuksista kannattaa edelleen jatkaa, jotta saataisiin selville näiden epäkohtien aiheuttajat ja voitaisiin valmistaa täydellisiä kuituja myös kaupallisiin tarkoituksiin.
EEG interface for portable ECG recorders
Aliina Tuomenlehti, Tampere University of Technology
A number of different medical conditions can cause unconsciousness. Epilepsy and trauma are examples of such conditions. These disorders affect the normal electrical brain activity and in clinical medicine these conditions are often diagnosed using electroencephalogram (EEG). Because of the complexity of the measurement procedure, EEG is not generally used in emergency medicine. However by utilizing EEG in emergency situation, vital information could be obtained.
The purpose of this thesis was to develop an interface enabling EEG measurement in emergency medicine. In order to make the implementation as simple as possible, the interface was designed to be compatible with a monitor used in electrocardiogram (ECG). Because the characteristics of the EEG and the ECG signals differ, the designed interface should be able to adapt the EEG signal for the monitor. This constitutes the basis for the system specifications. Because the EEG signal is small-amplitude, the interface should provide adequate gain. The noise level should be kept as low as possible, because such unwanted signal can interfere or even overrun the desired signal. Small size was one of the main objectives in this project, because the size has a great effect on the usability of the system. In order to make the device portable, battery was used as a power supply. This feature and the desired 24 hour operation time, required low power consumption.
The interface is based on a microcontroller unit (MCU) thus the system can be referred as an embedded system. This thesis covers the hardware design while the software development is done separately. The system is divided into operational blocks and the prototype development for clinical evaluation testing is done based on these. The hardware design was done based on both the initial system specifications and the aim of continuing improvement. Operational tests were done with an actual ECG-monitor to ensure the comparability with the actual measurement. Physiological signals like ECG and EEG were used in order to verify the operation of the interface.
All of the before mentioned specifications were fulfilled. Test measurements made during this project showed that the developed interface acts as an adapter which compensates the differences between the EEG and ECG signals so that the usage of the ECG-monitor is possible. Tests also showed that by using the designed interface good-quality EEG signal can be measured. From this signal it is possible to distinguish variations which indicate disorders affecting the brain activity and causing unconsciousness. It is evident that this would improve the quality of the emergency care.
Changes in rabbit bone composition – a comparison between infrared and raman microspectroscopy
Mikael Turunen, Itä-Suomen yliopisto
The aim of this study was to evaluate changes in bone composition during maturation from newborn to skeletally mature rabbits. The second aim was to compare compositional parameters of bone determined with Fourier transform infrared (FTIR) and Raman microspectroscopic techniques.
The molecular composition of bone undergoes alterations during maturation. Collagen fibers orientate due to mechanical loading and hydroxyapatite (HA) crystals grow between the fibers. Moreover, the immature collagen cross-links between the collagen fibers reduce to mature cross-links and carbonate substitutes into the HA. These compositional changes can be evaluated with FTIR and Raman microspectroscopic techniques based on light absorption and scattering, respectively.
Infrared and Raman microspectroscopic techniques provide similar but complementary information of the quantity and quality of the molecular composition of the sample. Bone composition determined with FTIR or Raman microspectroscopic techniques are often compared in the literature despite using slightly different parameters. This is the first study to evaluate changes in cortical bone composition during maturation with consecutive age groups from newborn to skeletally mature rabbits (newborn, 11 days, 1, 3 and 6 months) using both Infrared and Raman microspectroscopy, as well as to systematically compare similar spectroscopic parameters obtained with FTIR and Raman microspectroscopic techniques on bone. The areas and full widths of half maximum (FWHM) were determined from the representing absorption peaks of amide I, phosphate and carbonate in FTIR and Raman spectra. Shortly, the areas of the peaks represent the content of the each molecular component and the FWHM represent the homogeneity of the component. Parameters related to mineralization, mineral-to-matrix (phosphate/amide I) and carbonate-to-amide I ratios, as well as parameters related to carbonation, carbonate-to-phosphate ratio, i.e. carbonate substitution into HA, were calculated. Collagen cross-linking from FTIR spectra and carbonate content from Raman spectra were evaluated with a second derivative peak-fitting technique.
Significant changes were found in molecular composition of bone with both techniques during maturation. A rapid increase in collagen content in young bone and a slower mineral accumulation throughout the maturation were evident. The ratio of mature-to-immature collagen cross-links, i.e. the cross-link maturity, as well as the inverse of the phosphate peak from Raman spectra, i.e. crystallinity, increased significantly throughout maturation. Total carbonate substitution was found to increase, whereas type-B carbonate substitution decreased with age. Carbonate content was determined directly from the spectra and through peak fitting from Raman spectra. The correlation in carbonate peak area determined with these two techniques was significant (r = 0.928, p < 0.01). However, only weak correlation was found in carbonate-to-phosphate ratio (r = 0.362, p < 0.05). Type-B carbonate substitution is known to be negatively proportional to the crystallinity and also in this study a negative correlation was found between these parameters (r = -0.622, p < 0.01). The mineral-to-matrix FWHM ratio decreased significantly throughout the maturation.
The rapid increase in collagen content and the slower mineral accumulation during maturation support the idea that collagen fibers are first formed and the HA crystals grow slower. Collagen cross-links were found to become more mature and HA crystals more perfect with maturation, which is supported also by earlier studies. The high variation in the mineral-to-matrix FWHM ratio in the young age groups in Raman results, which was not evident in the FTIR results, can be an indicator of the suitability of these techniques on the organic matrix of bone, supporting the use of FTIR. In contrary, the calculation and reliability of the crystallinity parameter supports the use of Raman for evaluating the inorganic matrix. However, the carbonate-to-phosphate ratio represents the total carbonate substitution in FTIR spectra, whereas in Raman spectra the same ratio represents the type-B carbonate substitution, requiring both techniques for an extensive insight into carbonation of bone. Further, the weak correlation in carbonate-to-phosphate ratio can be due to phosphate overpowering carbonate when determined directly from the Raman spectra, and thus supporting the use of second derivative peak fitting. Finally, caution is peremptory when comparing similar parameters obtained with FTIR and Raman microspectroscopic techniques on bone.
Compressed Sensing in Parallel Magnetic Resonance Imaging
Panu Vesanen, Aalto University School of Science and Technology
Introduction and objective of the work
Magnetic resonance imaging (MRI) is a non-invasive method that allows the study of interior structures of matter. MRI is based on magnetizing a sample, manipulating the magnetization, and detecting the magnetic field that the sample produces. Today, MRI is widely used in medical imaging. The goal of this work is to reduce MRI scanning times. Reductions in the measurement time are important because they correspond to, e.g., higher throughput of MRI scanners or enhanced spatial resolution of images.
Methods
It is well-known that natural images, such as MR images, are compressible. Compressed sensing (CS) is a method that exploits the compressibility of signals in order to measure and reconstruct them efficiently. Moreover, in parallel MRI (pMRI), the magnetic fields produced by the magnetized sample are measured with multiple coils simultaneously. The differing sensitivity profiles of the coils allow a faster rate of information flow compared to single-coil receiving. In this work, CS and pMRI are combined to achieve shortened measurement times.
Results
Simulations were conducted to demonstrate the performance of the method in idealistic conditions. Several different sampling patterns were attempted in the simulation. In addition, experimental measurements were performed to validate the technique in practice. Simulation results indicate that the combination of CS with pMRI reduces the measurement time by 30–50%; truly randomized sampling patterns provide a slight acceleration as well compared to Cartesian ones. Experimentally, scanning time reductions of 10–20% were obtained.
Conclusion
In this work, it is shown that the combination of CS with pMRI is feasible. Both simulation and experimental results indicate that the scanning time reduction using this technique is significant. Future work includes more advanced pulse sequences for CS implementation in pMRI as well as new, compressible, and MRI-compatible function bases for more efficient CS.
Nivelensisäinen ultraäänitekniikka nivelrikon diagnostiikkaan
Tuomas Viren, University of Eastern Finland
Nivelrikko on yksi yleisimmistä syistä nivelkipuun ja liikuntakyvyn alenemiseen. Nivelrikon tyypillisiä oireita ovat nivelrustopinnan rappeutuminen sekä rustonalaisen luun paksuuntuminen ja epämuodostumat. Nivelrikkoa ei vielä voida parantaa ja nykyään sen hoito perustuu kivun lievittämiseen. Kuitenkin, jos nivelrikko havaitaan riittävän aikaisessa vaiheessa, voidaan sen etenemistä mahdollisesti hidastaa elämäntapamuutoksilla sekä lääkehoidolla. Nykyisillä kliinisessä käytössä olevilla tekniikoilla nivelrikko voidaan havaita vasta, kun rusto on peruuttamattomasti vaurioitunut. Kirjallisuudessa on esitetty useita kokeellisia, ei vielä kliinisessä käytössä olevia, tekniikoita joilla pystytään havaitsemaan ensimmäisiä nivelrikolle tyypillisiä kudosmuutoksia. Kvantitatiivinen ultraäänikuvantaminen on yksi lupaavimmista uusista tekniikoista.
Tässä opinnäytetyössä jatkokehitetään korkeataajuista ultraäänimenetelmää nivelrikon diagnostikkaan soveltamalla ensimmäistä kertaa kliinisessä käytössä olevaa IVUS-ultraäänilaitetta nivelruston kvantitatiiviseen kuvantamiseen. Työn tavoitteina oli tutkia, voidaanko IVUS-laitteella havaita eroja keinotekoisten testikohteiden pinnankarheudessa sekä tutkia voidaanko menetelmällä erottaa mekaanisesti tai biokemiallisesti vaurioitetut rustonäytteet koskemattomista näytteistä. Tutkia menetelmän soveltuvuutta nivelensisäiseen ultraäänitutkimukseen tekemällä naudan polven niveltähystys laboratorio-olosuhteissa.
Työssä tutkittiin minimaalisesti invasiivisen ultraäänitekniikan soveltuvuutta nivelrustopinnan vaurioiden havaitsemiseen laboratorio-olosuhteissa. Terveitä (n = 13), mekaanisesti vaurioitettuja (n = 7) sekä entsymaattisesti vaurioitettuja (n = 6) naudan rustonäytteitä ja erilaisia keinotekoisia testikohteita kuvattiin korkeataajuisella (40 MHz) ultraäänilaitteella. Kaikille mitatuille rustonäytteille sekä testikohteille laskettiin ultraäänen heijastuskerroin (Reflection coefficient, R), integroitu heijastuskerroin (Integrated reflection coeffisient, IRC) sekä pinnankarheusindeksi (Ultrasound roughness index, URI). Lisäksi tutkittaessa tekniikan kliinistä soveltuvuutta yksi terve naudan polvinivel kuvattiin niveltähystystä jäljittelevissä olosuhteissa.
Testikohteiden pinnankarheuksien erot havaittiin kaikilla ultraääniparametreilla. Rustopinnasta mitatut heijastuskertoimet pienenivät merkittävästi (p < 0.05) sekä mekaanisen että entsymaattisen vaurioituksen jälkeen. Lisäksi rustopinnan karheus suureni merkittävästi (p < 0.05) mekaanisen vaurioituksen jälkeen.
Tämä tutkimus osoitti että nivelensisäisellä ultraäänitekniikalla voidaan havaita sekä mekaanisesti että entsymaattisesti aiheutettu vaurio nivelrustossa. Lisäksi tekniikan soveltaminen kliinisen niveltähystyksen yhteydessä todettiin teknisesti mahdolliseksi.
Aktiivinen äänenvaimennus digitaalisella signaalinkäsittelyprosessorilla
Sami Väänänen, Itä-Suomen yliopisto
Nykypäivänä melu koetaan ongelmaksi, koska se voi johtaa kuulovaurioihin, on epämiellyttävää ja aiheuttaa muun muassa stressiä vaikuttaen näin ihmisten terveyteen. Perinteiset passiiviset äänenvaimennusmenetelmät, kuten äänieristys, vaimentavat huonosti matalia taajuuksia. Yksi mahdollisuus matataajuuksisen melun torjuntaan on käyttää aktiivisia äänenvaimennusmenetelmiä. Aktiivinen äänenvaimennus perustuu melua vastakkaisessa vaiheessa olevan äänen tuottamiseen eli kumoavaan interferenssiin.
Työn tarkoituksena oli rakentaa toimiva aktiiviseen vastaäänisuodatukseen perustuva laitteisto ja mitata sen toimintaa ja rajoituksia. Työssä johdetaan vaimennukseen käytetty yksikanavainen FxLMS-menetelmä sekä esitellään melua vastakkaisessa vaiheessa olevan äänen laskentaan käytetyn digitaalisen signaalinkäsittelyprosessorin toimintaa niiltä osin kuin se tämän tehtävän toteuttamisen kannalta on oleellista.
Aktiivisen vastaäänen vaimennusta testattiin kolmelle erilaiselle melulle: sinisignaalille, valkoiselle kohinalle ja traktorin hytistä kuljettajan pään kohdalta mitatulle melulle. Eritaajuuksisia sinejä ja valkoisen kohinan näytteitä testattiin kahdeksan molempia ja ne valittiin väliltä 100-500 Hz 1/3-oktaavikaistan perusteella. Traktorin melusta tutkittiin kaksi eri näytettä: melu kun traktori kävi tyhjäkäynnillä ja melu kun moottorin kierrosluku oli 2200 rpm. Aktiivinen äänenvaimennus suoritettiin kaikille signaaleille puolikaiuttomassa huoneessa ja vaimennuksen määrä mitattiin virhemikrofonin sekä mittausrobotin avulla.
Päätuloksena tässä työssä saatiin, että yksikanavaisella aktiivisella vastaäänisuodatuksella ja FxLMS-algoritmilla saadaan vaimennettua laajakaistaista melua hyvin virhemikrofonin kohdalla. Kuitenkin virhemikrofonin ympärillä oleva alue, missä vaimennus toimii, on pieni. Virhemikrofonin kohdalla siniä saatiin vaimenettua enimmillään 44 dB, valkoista kohinaa 15 dB ja traktorin melua 6.4 dB.
Tulosten perusteella aktiivisen äänenvaimennuksen avulla voidaan vaimentaa ympäristön melua ja näin ollen lisätä esimerkiksi työympäristön viihtyisyyttä. Aktiivisen äänenvaimennus on siten potentiaalinen menetelmä ihmisten terveyden edistämiseksi ja stressitekijöiden vähentämiseksi.
Vaiheherkkään ilmaisuun perustuva verenvirtausmittaus
Nina Yliaska, Oulun yliopisto
Diplomityössä suunniteltiin ja toteutettiin optinen verenvirtausta mittaava laite. Laitteessa on kaksi anturia, joissa kummassakin on kaksi valoa lähettävää diodia sekä vastaanottimena PIN-valodiodi. Anturit voidaan asettaa sormeen tai varpaaseen ja mitata siten valon absorptiota, joka vaihtelee veren happipitoisuuden ja suonissa virtaavan veren määrän mukaan. Mitattujen signaalien avulla on mahdollista arvioida verisuonten jäykkyyttä.
Absorptiosignaaleilla on huono signaalikohinasuhde, joten mittalaitteelta vaadittiin hyvää suorituskykyä ja kapeakaistaista suodatusta. Toimintaperiaatteeksi valittiin vaiheherkkä ilmaisu. Vaiheherkässä ilmaisussa mitattava signaali ja siihen liittynyt kohina moduloidaan korkeammalle taajuudelle. Esivahvistuksen jälkeen signaali kerrotaan modulaatiosignaalilla, jonka jälkeen epäolennaiset korkeat taajuudet sekä kohina poistetaan alipäästösuodatuksella. Suodatuksen jälkeen jäljelle jää mitattu signaali.
Mittauksissa huomattiin, että piirilevyllä kytkeytyvien häiriöiden vuoksi esivahvistinten kohinajännite on moninkertainen laskennallisiin arvoihin verrattuna. Koska vaiheherkkä ilmaisu kuitenkin suodattaa suurimman osan esivahvistinten kohinasta, lähtöjen kohinajännitteet jäivät pieniksi.
Vaiheherkkä ilmaisu osoittautui tässä sovelluksessa toimivaksi ratkaisuksi, sillä se suodattaa kohinaa tehokkaasti ja mahdollistaa absorption mittauksen samanaikaisesti kahdella eri aallonpituudella. Mittalaite täytti sille asetetut vaatimukset eli laitteella pystyttiin mittaamaan hyvälaatuisia fotopletysmografiasignaaleja, joista pystyttiin määrittämään verisuonten jäykkyyden estimointiin tarvittava pulssin huipusta huippuun- aika.