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Browsing by study line "Medical Physics and Biophysics"

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  • Petrow, Pauliina (2022)
    Acuros XB -annoslaskentamalli on Varianin Eclipse-annossuunnitteluohjelmistoon kehitetty annoslaskenta-algoritmi, joka on tarkoitettu ulkoisen sädehoidon fotoniannoslaskentaan. Sen toiminta perustuu lineaaristen Boltzmannin siirtoyhtälöiden ratkaisemiseen. Acuros XB -algoritmi laskee annoksen kudoksessa, minkä johdosta se pystyy tuottamaan tarkan laskennan myös heterogeenisessa väliaineessa. Algoritmin laskentatarkkuus on verrattavissa Monte Carlo -menetelmän tarkkuuteen, mutta tarvittava laskenta-aika on lyhyempi. Tässä tutkimuksessa konfiguroitiin ja testattiin Acuros XB -algoritmi HUS Syöpäkeskuksen sädehoito-osaston lineaarikiihdyttimille. Lisäksi tutkittiin kahden mittalaitteen, OCTAVIUS Detector 1000 SRS -ionisaatiokammiomatriisin ja SRS MapCHECK -puolijohdeilmaisimen, toimintaa pienillä säteilykentillä eli 2cm x 2cm ja tätä pienemmillä säteilykentillä. Acuros XB -algoritmi konfiguroitiin optimoimalla kolmea parametria: fokuspisteen kokoa, moniliuskarajoittimen dosimetrista aukkoa ja moniliuskarajoittimen läpäisykerrointa. Parametrien optimointi tehtiin vertailemalla mitattuja ja Acuros XB -algoritmilla laskettuja annosjakaumia ja säteilykentän keskiakseliannoksia. Konfigurointiprosessissa huomioitiin erilaiset kenttäkoot ja annossuunnittelutekniikat tutkimalla erikokoisia staattisia säteilykenttiä sekä IMRT (Intensity-Modulated Radiation Therapy)-, VMAT (Volumetric Modulated Arc Therapy)- ja SRS (Stereotactic Radiosurgery)-tekniikoilla toteutettuja kenttäjärjestelyjä. Mittalaitteita vertailtiin tutkimalla kolmen pienen staattisen kentän, kolmen dynaamisen kaarikentän ja kolmen VMAT-tekniikalla toteutetun kenttäjärjestelyn tuottamia annosjakaumia. Acuros XB -algoritmin konfiguroinnin tuloksena HUS Syöpäkeskuksen sädehoito-osaston lineaarikiihdyttimille määritettiin fotonienergiakohtaiset arvot fokuspisteen koolle, moniliuskarajoittimen dosimetriselle aukolle ja moniliuskarajoittimen läpäisykertoimelle, ja algoritmi otettiin kliiniseen käyttöön. Mittalaitteiden vertailun tuloksena havaittiin, että SRS MapCHECK -puolijohdeilmaisin toimi pienillä säteilykentillä paremmin kuin OCTAVIUS Detector 1000 SRS -ionisaatiokammiomatriisi. Mittalaitteiden annosjakaumien analysointiohjelmat kuitenkin käsittelevät mittaustulokset eri tavoin, joten lisätutkimusta voidaan tarvita yksiselitteisen tuloksen saamiseksi.
  • Halkoaho, Johannes (2022)
    MRS or magnetic resonance spectroscopy is an imagining technique which can be used to gain information about the metabolite concentration within a certain volume of interest. This can be used for example in brain imagining. The brain consists of three main types of tissue: cerebrospinal fluid, white and gray matter. It is important to know the different volume fractions of these tissues as the resolution in MRS is significantly lower than that of magnetic resonance imagining (MRI). The tissues all have different metabolite profiles and in order to get meaningful data the volume fractions need to be taken into account. This information can be gained from the segmentation of an image formed by using MRI. In this work a software tool was created to find these volume fractions with the input of a .rda file that is created by the scanner and Nifti file. The Nifti file is the image formed by using MRI and the .rda file is the manufacturers raw data format for spectroscopy data which has the relevant information about the volumes of interest. The software tool was created using Python and JavaScript programming languages and different functions of FSL. FSL is a comprehensive library of analysis tools used in brain imaging data processing. The steps for the software tool are: determining the coordinates of the volume of interest in FSL voxel coordinates, creating a mask in the correct orientation and location, removing non-brain tissue from the image using FSL’s tool tailored for that purpose (BET), segmenting the image using FSL’s segmenting tool (FAST), registering the mask on the segmented images and calculating the volume fractions. The software tool was tested on imaging data that was obtained at Meilahti Kolmiosairaala for the purpose of the testing. The testing data set included five different spectroscopy volumes from different parts of the brain and a T1 weighted image. The software tool was given the relevant information about the volume of interest in the form of a .rda file and the T1 weighted image in the form of a Nifti file. The software tool then determined the different volume fractions from all of the five volumes of interest. There is variation on the volume fraction of different brain areas within different brains and it is not possible to have an absolute reference value. The results of the test corresponded to the possible volume fractions that can be expected from the volumes in question.
  • Mikkola, Kalle (2022)
    This thesis examines the optical response of tuneable chiral plasmonic nanostructures in linear cross-polarization. Plasmonic gold-silver nanostructures composed of silver-coated gold nanorods, and dynamic DNA origami are investigated because of their optical properties of interest in the visible light wavelength region, and because of their controllable rotational asymmetry, which results in tuneable chirality in dimer structures. These plasmonic nanostructures present optical properties such as circular dichroism and optical rotatory dispersion. In this thesis we establish the relationship between perceived color, spectrometry, circular dichroism and optical rotatory dispersion of the samples, depending on the chiral geometry of the nanostructures within. The motivation is to predict perceived color from the chiral geometry of the nanostructures, which will enable visual detection for biosensing applications. Circular dichroism and optical rotatory dispersion give us detailed knowledge about the polarization state of a sample, but visible light detection and spectrometer measurements are more accessible and portable methods for characterizing the polarization state of a sample. We achieve color modulation from green to blue with the switching of chiral geometry, under cross-polarized white light. This has potential for biosensing applications, based on the perceived color change depending on the chiral geometry of the sample. The DNA origami structures react to the presence of an analyte by changing their chiral geometry. Possible applications in biosensing of analytes can be made more practical if the orientation of the DNA origami template can be determined from the perceived color or the transmission spectra, rather than from the less accessible circular dichroism or optical rotatory dispersion measurements.
  • Issakainen, Jani (2021)
    Electroencephalography (EEG) is a non-invasive neurophysiological method for evaluating brain activity by measuring electrical potential at the scalp. The electrical potentials originate mainly from postsynaptic cortical currents created by neuronal activity. It is a valuable tool for both research and clinical practice. EEG can be used e.g. to diagnose epilepsy, focal brain disorders, brain death, and coma. Intermittent photic stimulation (IPS) is an important tool in clinical EEG. Healthcare professionals use it to induce epileptic activity in patients to help diagnose their conditions. In these tests, various IPS frequencies are used with eyes-closed, eyes-open, and eye-closure conditions. IPS test is listed in clinical practice guidelines in EEG globally, and it is mainly used to diagnose photosensitive epilepsy, i.e., to detect epilepsy-related abnormal sensitivity to flickering light. Magnetoencephalography (MEG) is a non-invasive neurophysiological method in which minute magnetic fields — produced by the same postsynaptic currents as in EEG — are measured with special superconductive sensors around the head. MEG is a valuable tool for research and clinical practice with increasing world-wide utilization. The main advantages of MEG over EEG are easier source modelling and higher resolution at cortical areas. IPS has not been introduced to MEG since the IPS stimulators used in EEG are not compatible with MEG. IPS in MEG could improve the analysis of IPS and provide better tools for diagnoses. Currently, data analysis of IPS is typically limited to healthcare professionals examining the visualization of the raw data while looking for induced epileptiform activites and lateralizing them. In this thesis, an MEG-compatible IPS stimulator is introduced and alternative ways of analyzing IPS data for both MEG and EEG are showcased. Although analysis methods were applied with decent signal-to-noise ratios, further research is needed—especially to compare responses between patients with epilepsy and healthy subjects.