Scattering and Refraction as Contrast Mechanisms in X-Ray Imaging

Differentiation of various types of soft tissues is of high importance in medical imaging, because changes in soft tissue structure are often associated with pathologies, such as cancer. However, the densities of different soft tissues may be very similar, making it difficult to distinguish them in absorption images. This is especially true when the consideration of patient dose limits the available signal-to-noise ratio. Refraction is more sensitive than absorption to changes in the density, and small angle x-ray scattering on the other hand contains information about the macromolecular structure of the tissues. Both of these can be used as potential sources of contrast when soft tissues are imaged, but little is known about the visibility of the signals in realistic imaging situations. In this work the visibility of small-angle scattering and refraction in the context of medical imaging has been studied using computational methods. The work focuses on the study of analyzer based imaging, where the information about the sample is recorded in the rocking curve of the analyzer crystal. Computational phantoms based on simple geometrical shapes with differing material properties are used. The objects have realistic dimensions and attenuation properties that could be encountered in real imaging situations. The scattering properties mimic various features of measured small-angle scattering curves. Ray-tracing methods are used to calculate the refraction and attenuation of the beam, and a scattering halo is accumulated, including the effect of multiple scattering. The changes in the shape of the rocking curve are analyzed with different methods, including diffraction enhanced imaging (DEI), extended DEI (E-DEI) and multiple image radiography (MIR). A wide angle DEI, called W-DEI, is introduced and its performance is compared with that of the established methods. The results indicate that the differences in scattered intensities from healthy and malignant breast tissues are distinguishable to some extent with reasonable dose. Especially the fraction of total scattering has large enough differences that it can serve as a useful source of contrast. The peaks related to the macromolecular structure come to angles that are rather large, and have intensities that are only a small fraction of the total scattered intensity. It is found that such peaks seem to have only limited usefulness in medical imaging. It is also found that W-DEI performs rather well when most of the intensity remains in the direct beam, indicating that dark field imaging methods may produce the best results when scattering is weak. Altogether, it is found that the analysis of scattered intensity is a viable option even in medical imaging where the patient dose is the limiting factor.

Improving GPS time series for geodynamic studies

Accurate and stable time series of geodetic parameters can be used to help in understanding the dynamic Earth and its response to global change. The Global Positioning System, GPS, has proven to be invaluable in modern geodynamic studies. In Fennoscandia the first GPS networks were set up in 1993. These networks form the basis of the national reference frames in the area, but they also provide long and important time series for crustal deformation studies. These time series can be used, for example, to better constrain the ice history of the last ice age and the Earth s structure, via existing glacial isostatic adjustment models. To improve the accuracy and stability of the GPS time series, the possible nuisance parameters and error sources need to be minimized. We have analysed GPS time series to study two phenomena. First, we study the refraction in the neutral atmosphere of the GPS signal, and, second, we study the surface loading of the crust by environmental factors, namely the non-tidal Baltic Sea, atmospheric load and varying continental water reservoirs. We studied the atmospheric effects on the GPS time series by comparing the standard method to slant delays derived from a regional numerical weather model. We have presented a method for correcting the atmospheric delays at the observational level. The results show that both standard atmosphere modelling and the atmospheric delays derived from a numerical weather model by ray-tracing provide a stable solution. The advantage of the latter is that the number of unknowns used in the computation decreases and thus, the computation may become faster and more robust. The computation can also be done with any processing software that allows the atmospheric correction to be turned off. The crustal deformation due to loading was computed by convolving Green s functions with surface load data, that is to say, global hydrology models, global numerical weather models and a local model for the Baltic Sea. The result was that the loading factors can be seen in the GPS coordinate time series. Reducing the computed deformation from the vertical time series of GPS coordinates reduces the scatter of the time series; however, the long term trends are not influenced. We show that global hydrology models and the local sea surface can explain up to 30% of the GPS time series variation. On the other hand atmospheric loading admittance in the GPS time series is low, and different hydrological surface load models could not be validated in the present study. In order to be used for GPS corrections in the future, both atmospheric loading and hydrological models need further analysis and improvements.

L'ecfrasis nel Piacere di Gabriele D'Annunzio

Tutkielman aiheena on ekfrasis Gabriele D'Annunzion romaanissa Il Piacere (1889). Lähtökohtana on selvittää, millaisissa muodoissa ekfrasis esiintyy romaanissa sekä miten ekfrasis vaikuttaa teoksen tulkintatradition esille tuomaan tematiikkaan. Pyrkimyksenä on myös selkeyttää ekfrasiksen käsitettä, jonka ongelmana ovat sanaan eri aikakausina liitetyt eri merkitykset. Tärkeimpiä lähdeteoksia ovat James A.W. Heffernanin Museum of Words (1993) ja W.J.T. Mitchellin Picture Theory (1994), Marinella Cantelmon Il Piacere dei leggitori: D'Annunzio e la comunicazione letteraria (1996) sekä John Hollanderin artikkeli "The Poetics of Ekphrasis" (1988). Tutkielman avainkäsitteenä on Heffernanin määritelmä, jonka mukaan ekfrasis on sanallinen esitys kuvallisesta esityksestä. Määritelmää sovellettaessa on otettu huomioon representaatiokäsityksen avautuminen, jolloin vastaanottaja, ympäristö etc. ovat osa esitystä. Korpuksen muodostavat tapahtumaympäristöä, taideteoksia, esineistöä ja henkilöhahmoja kuvaavat ekfrastiset katkelmat. Luokittelussa toimivat alakäsitteinä Valerie Robillardin kuvaileva, attributiivinen ja assosiatiivinen ekfrasis sekä Tamar Yacobin ekfrastinen vertaus. Analyysi osoittaa, että kuvaileva ekfrasis on yleisin, mutta vain kuvitteellisten teosten yhteydessä. Katkelmissa on näkyvissä ekfrasikselle luonteenomainen kerronnallinen impulssi. Ekfrasis osallistuu tunnetun ja uuden elementin vuoropuheluun ankkuroimalla kuvitteelliset taideteokset lukijalle tuttuun ympäristöön, jolloin myös uusi tulee toden kaltaiseksi. Attributiivinen ekfrasis takaa välittömän tunnistettavuuden. Henkilöhahmot, erityisesti keskeiset naishahmot, on määritelty ekfrastisten vertausten kautta. Ekfrasis ilmentää osaltaan naishahmojen vaihdettavuuden tematiikkaa. Kyseessä on myös toiseuden haltuunotto. Kuvallisen viittaussuhteen ansiosta ekfrasis toimii tehokeinona. Tekstuaalisena strategiana ekfrasis luo siteitä tapahtumien välille ja rytmittää teoksen vaiheita. Ekfrastiset katkelmat tarjoavat myös väylän vaihtoehtoiselle tulkinnalle haastamalla tekstin totuuskäsityksen. Kuvallinen ja sanallinen esitys tuovat tekstiin omat merkityksensä, jolloin merkityskenttä laajenee. Il Piacere on intertekstuaalinen kollaasi, jossa kokonaiskuva muodostuu eri elementtien vuorovaikutuksesta. D'Annunzion mielestä kauneus on taiteen ensisijainen tarkoitus, ja ekfrasis retorisena keinona on osa pyrkimystä tavoittaa täydellinen muoto.

Death, Destruction and Commemoration : Tracing ritual activities in Finnish Late Iron Age cemeteries (AD 550-1150)

The thesis is connected with death, memory and ancestor commemoration during the Merovingian Period, the Viking Age and the beginning of the Crusade Period (AD 550-1150) in Finland. During this time, cremation was the dominant burial rite. It was not until the end of the Viking Age that inhumation became more common but both cremations and inhumations are performed even at the same sites throughout the time. Three different burial types 1) cremation cemeteries below level ground, 2) inhumation burials and 3) water burials are discussed in five articles. I consider these burial forms from three different viewpoints; collectivity-individuality, visibility-invisibility and cremation-inhumation. The thesis also discusses the topics of memory, memorialisation and monument re-use, which have been neglected subjects in Finnish archaeology until now. Both cremation cemeteries below level ground and inhumation burials have been re-used during their time of usage, and on most occasions are situated in a landscape that is overlaid by other monuments as well. The main questions of the thesis are: What kinds of ritual behaviour can we detect in the burials during the period (AD 550-1150)? How did people perceive the moraine hills that functioned as burial places? What kind of re-use can be detected in the Iron Age cemeteries? Why have ancient sites and artefacts been re-used? This thesis shows that it is possible to claim that both artefact and site re-use is a much more widespread phenomenon than has previously been thought in Finnish archaeology. It is also a conscious and deliberate behaviour that can be related to an ancestor cult and commemoration of the dead. The funerary rituals during this time period show great variation and complex, both regionally and nationally. Not only have the dead been buried using elaborate rituals, they have also been mourned and commemorated in intricate ways that proves that death was not an end product, but the start of something new.

Post-industrial Intervention : An Activity-Theoretical Expedition Tracing the Proximal Development of Forms of Conducting Interventions

Ei saatavilla

Water-ethanol mixtures by molecular dynamics and x-ray Compton scattering

Water-ethanol mixtures are commonly used in industry and house holds. However, quite surprisingly their molecular-level structure is still not completely understood. In particular, there is evidence that the local intermolecular geometries depend significantly on the concentration. The aim of this study was to gain information on the molecular-level structures of water-ethanol mixtures by two computational methods. The methods are classical molecular dynamics (MD), where the movement of molecules can be studied, and x-ray Compton scattering, in which the scattering cross section is sensitive to the electron momentum density. Firstly, the water-ethanol mixtures were studied with MD simulations, with the mixture concentration ranging from 0 to 100%. For the simulations well-established force fields were used for the water and ethanol molecules (TIP4P and OPLS-AA, respectively). Moreover, two models were used for ethanol, rigid and non-rigid. In the rigid model the intramolecular bond lengths are fixed, whereas in the non-rigid model the lengths are determined by harmonic potentials. Secondly, mixtures with three different concentrations employing both ethanol models were studied by calculating the experimentally observable x-ray quantity, the Compton profile. In the MD simulations a slight underestimation in the density was observed as compared to experiment. Furthermore, a positive excess of hydrogen bonding with water molecules and a negative one with ethanol was quantified. Also, the mixture was found more structured when the ethanol concentration was higher. Negligible differences in the results were found between the two ethanol models. In contrast, in the Compton scattering results a notable difference between the ethanol models was observed. For the rigid model the Compton profiles were similar for all the concentrations, but for the non-rigid model they were distinct. This leads to two possibilities of how the mixing occurs. Either the mixing is similar in all concentrations (as suggested by the rigid model) or the mixing changes for different concentrations (as suggested by the non-rigid model). Either way, this study shows that the choice of the force field is essential in the microscopic structure formation in the MD simulations. When the sources of uncertainty in the calculated Compton profiles were analyzed, it was found that more statistics needs to be collected to reduce the statistical uncertainty in the final results. The obtained Compton scattering results can be considered somewhat preliminary, but clearly indicative of the behaviour of the water-ethanol mixtures when the force field is modified. The next step is to collect more statistics and compare the results with experimental data to decide which ethanol model describes the mixture better. This way, valuable information on the microscopic structure of water-ethanol mixtures can be found. In addition, information on the force fields in the MD simulations and on the ability of the MD simulations to reproduce the microscopic structure of binary liquids is obtained.

TlBr raw material purification, crystal growth, annealing, detector fabrication and characterisation for gamma-ray detector applications

The research reported in this thesis dealt with single crystals of thallium bromide grown for gamma-ray detector applications. The crystals were used to fabricate room temperature gamma-ray detectors. Routinely produced TlBr detectors often are poor quality. Therefore, this study concentrated on developing the manufacturing processes for TlBr detectors and methods of characterisation that can be used for optimisation of TlBr purity and crystal quality. The processes under concern were TlBr raw material purification, crystal growth, annealing and detector fabrication. The study focused on single crystals of TlBr grown from material purified by a hydrothermal recrystallisation method. In addition, hydrothermal conditions for synthesis, recrystallisation, crystal growth and annealing of TlBr crystals were examined. The final manufacturing process presented in this thesis deals with TlBr material purified by the Bridgman method. Then, material is hydrothermally recrystallised in pure water. A travelling molten zone (TMZ) method is used for additional purification of the recrystallised product and then for the final crystal growth. Subsequent processing is similar to that described in the literature. In this thesis, literature on improving quality of TlBr material/crystal and detector performance is reviewed. Aging aspects as well as the influence of different factors (temperature, time, electrode material and so on) on detector stability are considered and examined. The results of the process development are summarised and discussed. This thesis shows the considerable improvement in the charge carrier properties of a detector due to additional purification by hydrothermal recrystallisation. As an example, a thick (4 mm) TlBr detector produced by the process was fabricated and found to operate successfully in gamma-ray detection, confirming the validity of the proposed purification and technological steps. However, for the complete improvement of detector performance, further developments in crystal growth are required. The detector manufacturing process was optimized by characterisation of material and crystals using methods such as X-ray diffraction (XRD), polarisation microscopy, high-resolution inductively coupled plasma mass (HR-ICPM), Fourier transform infrared (FTIR), ultraviolet and visual (UV-Vis) spectroscopy, field emission scanning electron microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDS), current-voltage (I-V) and capacity voltage (CV) characterisation, and photoconductivity, as well direct detector examination.

X-ray scattering and diffraction enhanced imaging studies of in vitro breast tissues

This thesis is a study of the x-ray scattering properties of tissues and tumours of the breast. Clinical radiography is based on the absorption of the x-rays when passing right through the human body and gives information about the densities of the tissues. Besides being absorbed, x-rays may change their direction within the tissues due to elastic scattering or even to refraction. The phenomenon of scattering is a nuisance to radiography in general, and to mammography in particular, because it reduces the quality of the images. However, scattered x-rays bear very useful information about the structure of the tissues at the supra-molecular level. Some pathologies, like breast cancer, produce alterations to the structures of the tissues, being especially evident in collagen-rich tissues. On the other hand, the change of direction due to refraction of the x-rays on the tissue boundaries can be mapped. The diffraction enhanced imaging (DEI) technique uses a perfect crystal to convert the angular deviations of the x-rays into intensity variations, which can be recorded as images. This technique is of especial interest in the cases were the densities of the tissues are very similar (like in mammography) and the absorption images do not offer enough contrast. This thesis explores the structural differences existing in healthy and pathological collagen in breast tissue samples by the small-angle x-ray scattering (SAXS) technique and compares these differences with the morphological information found in the DEI images and the histo-pathology of the same samples. Several breast tissue samples were studied by SAXS technique in the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Scattering patterns of the different tissues of the breast were acquired and compared with the histology of the samples. The scattering signals from adipose tissue (fat), connective tissue (collagen) and necrotic tissue were identified. Moreover, a clear distinction could be done between the scattering signals from healthy collagen and from collagen from an invasive tumour. Scattering from collagen is very characteristic. It includes several scattering peaks and scattering features that carry information about the size and the spacing of the collagen fibrils in the tissues. It was found that the collagen fibrils in invaded tumours were thinner and had a d-spacing length 0,7% longer that fibrils from healthy tumours. The scattering signals from the breast tissues were compared with the histology by building colour-coded maps across the samples. They were also imaged with the DEI technique. There was a total agreement between the scattering maps, the morphological features seen in the images and the information of the histo- pathological examination. The thesis demonstrates that the x-ray scattering signal can be used to characterize tissues and that it carries important information about the pathological state of the breast tissues, thus showing the potential of the SAXS technique as a possible diagnostic tool for breast cancer.

Patient exposure monitoring and radiation qualities in two-dimensional digital x-ray imaging

The methods for estimating patient exposure in x-ray imaging are based on the measurement of radiation incident on the patient. In digital imaging, the useful dose range of the detector is large and excessive doses may remain undetected. Therefore, real-time monitoring of radiation exposure is important. According to international recommendations, the measurement uncertainty should be lower than 7% (confidence level 95%). The kerma-area product (KAP) is a measurement quantity used for monitoring patient exposure to radiation. A field KAP meter is typically attached to an x-ray device, and it is important to recognize the effect of this measurement geometry on the response of the meter. In a tandem calibration method, introduced in this study, a field KAP meter is used in its clinical position and calibration is performed with a reference KAP meter. This method provides a practical way to calibrate field KAP meters. However, the reference KAP meters require comprehensive calibration. In the calibration laboratory it is recommended to use standard radiation qualities. These qualities do not entirely correspond to the large range of clinical radiation qualities. In this work, the energy dependence of the response of different KAP meter types was examined. According to our findings, the recommended accuracy in KAP measurements is difficult to achieve with conventional KAP meters because of their strong energy dependence. The energy dependence of the response of a novel large KAP meter was found out to be much lower than with a conventional KAP meter. The accuracy of the tandem method can be improved by using this meter type as a reference meter. A KAP meter cannot be used to determine the radiation exposure of patients in mammography, in which part of the radiation beam is always aimed directly at the detector without attenuation produced by the tissue. This work assessed whether pixel values from this detector area could be used to monitor the radiation beam incident on the patient. The results were congruent with the tube output calculation, which is the method generally used for this purpose. The recommended accuracy can be achieved with the studied method. New optimization of radiation qualities and dose level is needed when other detector types are introduced. In this work, the optimal selections were examined with one direct digital detector type. For this device, the use of radiation qualities with higher energies was recommended and appropriate image quality was achieved by increasing the low dose level of the system.

X-ray and neutron scattering studies on some nanoscale structures in molecular biology

Scattering of X-rays and neutrons has been applied to the study of nanostructures with interesting biological functions. The systems studied were the protein calmodulin and its complexes, bacterial virus bacteriophage phi6, and the photosynthetic antenna complex from green sulfur bacteria, chlorosome. Information gathered using various structure determination methods has been combined to the low resolution information obtained from solution scattering. Conformational changes in calmodulin-ligand complex were studied by combining the directional information obtained from residual dipole couplings in nuclear magnetic resonance to the size information obtained from small-angle X-ray scattering from solution. The locations of non-structural protein components in a model of bacteriophage phi6, based mainly on electron microscopy, were determined by neutron scattering, deuterium labeling and contrast variation. New data are presented on the structure of the photosynthetic antenna complex of green sulfur bacteria and filamentous anoxygenic phototrophs, also known as the chlorosome. The X-ray scattering and electron cryomicroscopy results from this system are interpreted in the context of a new structural model detailed in the third paper of this dissertation. The model is found to be consistent with the results obtained from various chlorosome containing bacteria. The effect of carotenoid synthesis on the chlorosome structure and self-assembly are studied by carotenoid extraction, biosynthesis inhibition and genetic manipulation of the enzymes involved in carotenoid biosynthesis. Carotenoid composition and content are found to have a marked effect on the structural parameters and morphology of chlorosomes.