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Drawing Continuity: The Making of Bourgeois Family Trees
No full textThe project examines the crafting of family trees in the kin groups constituting the bourgeoisie of Basel in the 19th and early 20th cen., most of which descended from the old patriciate. Having long opposed struggles for democratic reform, even at the cost of the traumatic loss of the revolutionary ‘hinterland’ in 1833, these families eventually, in 1875, relinquished their political monopoly, yet retained economic and symbolic power (Sarasin 1997). Hence, there is, first, a complex constellation of continuity and discontinuity, comprising the kind of crisis-laden “triggering events” that have been identified as constituting the “matrix” of genealogical work (Jettot & Lezowski 2016, 18–22). Secondly, Basel presents us with the case of a society where a close-knit network of kin groups was a crucial ‘mover of modernity’, a modernity that has long been falsely associated with the declining importance of kinship (Sabean & Teuscher 2007). This constellation provides an ideal setting for further examining the tendency of the middle classes to adapt the genealogical enterprise of a bygone nobility for the maintenance of social hierarchies by purging it of its mythical contents (Timm 2016; Hohkamp 2018), thus constituting a historical bridgehead between ‘old’ noble and ‘new’ generalized forms of genealogy (Bouquet 1996). However, applying the overall approach of the Sinergia project, the subproject will open up additional pathways for research: Examining the actors, the work, and technologies that went into the production of bourgeois family trees, as well as the uses of the diagrams, f.e. in the context of socialization, might bring to light the conceptual productivity of bourgeois “family treeing” (Edwards 2017) beyond social mimicry and iconological continuation: What is actually produced through family trees? Relations among the living or relations between the living and the dead? How do family trees structure sociality by abstracting from relationships with those diagrammatically excluded, and how do they concretize what counts as kin? How does the very production of genealogical data and the crafting of trees itself generate relationships among those involved? This study will furthermore specifically pay attention to the gender aspect by not only analyzing how the patrilineal order is diagrammatically (re-)presented, but also by asking how the production of diagrams negotiated the (possibly contentious) gendered structure of descent and transmission. At the basis of the study are two sets of sources held by the public record office of Basel (Staatsarchiv Basel): 1) the large collection of representative family trees dating from the late 18th up to the middle of the 20th cen., and 2) the documentation of their making as preserved in family estates. The latter contain folders with transcriptions of parish registers, sketches, templates, but also diaries that shed light on how the production, presentation, and circulation of family trees were part of everyday life, on how family trees rendered relational structures in an urban society and negotiated familial and kin dynamics. Since this project examines material rich in iconographic elements, it is planned to associate the PhD position with the eikones Graduate School (where the group leader serves as faculty), and a joint supervision with an expert in visual studies or art history will be sought
SQUID-on-tip sensors for real-space magnetic imaging of a chiral magnet
Full text linkNanomagnetism is an area of research in Physics that studies magnetic properties of samples which have at least one dimension in the nanometer range. The aim of nanomagnetism is to investigate properties and applications of nano-objects, such as particles, dots, wires, or thin films or bulk samples exhibiting changes in magnetism (like magnetic domains or interfaces) at the nanoscale.
Among all the applications of nanomagnetism, the most successful one has been in the field of information storage and data communication. In the last few decades, magnetic recording has drastically improved, getting able to boost both areal density and data rate. The rapid growth of this technology was made possible only by the effort in analyzing the properties of magnetic thin films and of small magnetic particles that constitute a key part of magnetic read heads and hard disk platters. Another emerging field where magnetism plays a crucial role is spintronics, for the implementation of the next generation of nanoelectronic devices with reduced power consumption, increased memory and processing capability. Such devices are based on the interaction of magnetic materials with the spin degree of freedom of an electric current and make use of films and other magnetic structures at the nanoscale.
To investigate the electronic correlations that give rise rise to macroscopic phenomena such as magnetism, superconductivity, and topological phases, it is necessary to fully understand the micro- or nanoscopic mechanism behind them. This study often requires probes with very fine spatial resolution, capable to sense changes in magnetic field over a length scale of hundreds of nanometers or less. Not many imaging techniques can provide that, especially when the information is not accessible by optical or topographic images.
Magnetic field changes not only take place on short distances, but might as well be extremely weak to probe. This happens when the electronic properties are defined by a small fraction of electrons participating in a certain order, or when the phenomena take place in material layers that are screened by other layers above them. Furthermore, perturbation of the electrons by the sensing probe can be detrimental for the observation of some phenomena. So, in many experiments, a sensitive sensor offering high spatial resolution and low invasiveness is desired.
Among the variety of magnetic probes, the one interesting this thesis work is the Superconducting Quantum Interference Device (SQUID). SQUIDs are superconducting interferometers, defined by a loop threaded by magnetic field, and are one of the most powerful magnetometers, due to their excellent sensitivity to stray magnetic field and a negligible perturbation of the sample under investigation. A further strong point is their versatility to probe a broad range of electronic orders, due to the possibility to perform local thermometry and susceptometry measurements. The success of SQUID microscopy comes from the balance between magnetic field sensitivity and spatial resolution.
A game changer in the history of Scanning SQUID Microscopy (SSM) is represented by the innovative idea, by Finkler et al. in 2010, of fabricating a SQUID loop on the apex of a laser-pulled quartz pipette, having a sharp tip with an apex diameter of few tens of nanometers. This configuration brings three main advantages: a easier, self-aligned fabrication process, the possibility to miniaturize and tune the SQUID loop down to a nanometric size and, ultimately, a design that allows to move the SQUID loop and approach it at sample to probe distances comparable to the SQUID diameter. The consequent fine spatial resolution that can be achieved has led the SQUID-on-Tip (SOT) technique to tens of remarkable achievements over the last decade, probing magnetic fields and heat dissipation with sub-100 nm resolution.
In this thesis work, a contribution to the SOT field is brought, focused on implementing a new deposition method, that extends the range of materials that can be used to coat the quartz pipettes. Such capillaries, showing resolution below 100 nm and excellent magnetic sensitivity, were applied in a extensive investigation of magnetic phases in a bulk crystal of Cu2OSeO3. This chiral magnet is the first insulating material which was found to host a lattice of topologically non-trivial spin textures called magnetic skyrmions
The genetics of adaptation at a species’ southern range edge
Full text linkThis study investigates the factors influencing the geographic distribution and adaptive potential of Arabidopsis lyrata subsp. lyrata, a plant species with a restricted distribution in Northern America. The research addresses questions posed by ecologists and evolutionary biologists regarding the limitations of species adaptation and the drivers of geographic distribution. The study integrates ecological and evolutionary perspectives. On the one hand, by exploring the interplay of ecological constraints resulting from steep environmental gradients. On the other hand, evolutionary challenges of genetic drift, reduced genetic diversity, and trade-offs between adaptive traits. The focus is on the southern range edge, where climate change is expected to impose rapid and frequent environmental shifts.
Chapter I investigates how genetic diversity is maintained in a dynamic dune landscape, revealing signs of local adaptation through a genome-wide association study. The analyses identify outlier genes associated with reproductive development, highlighting the role of landscape features and climate in driving genetic differentiation.
Chapter II explores genetic constraints on traits of adaptation using a greenhouse stress experiment that simulates climatic conditions at the southern range edge. While phenotypic performance differences suggest synergistic effects under multi-stress conditions, genetic variance-covariance matrices reveal complex patterns with potential limitations to multivariate genetic variation. Constraints between growth traits and their divergence from selection pressure emphasize the challenges of adapting to changing environmental conditions.
Chapter III examines the genomic basis of the differences in performance using a natural selection experiment along the southern range edge in the USA. Family effects within the greenhouse experiment explain a high fraction of the observed variance, emphasizing the complexity of natural environments. Gene-level analysis reveals low overlap between treatment and common garden sites for the same trait, highlighting the intricate genetic pathways involved in trait establishment.
In conclusion, the study highlights the complexity of genetic processes shaping adaptive potential. While genetic variability is present under range edge conditions, the multi-environmental nature introduces genetic constraints. The study underscores the importance of considering landscape context and genetic complexities in understanding a species' adaptive responses to environmental changes. The speed of adaptation remains a question, demanding further experiments focusing on real-time evolution. Additionally, broader genetic analyses and microclimate studies may provide deeper insights into the traits and genes underlying adaptive potential at the southern range edge
Dissecting patient macrophage responses to Mycobacterium tuberculosis Complex strains from Tanzania and assessing T cell biomarkers for TB diagnosis and treatment monitoring
Full text linkTuberculosis (TB) has existed throughout human history, traced back to 9000 years ago to date. TB is transmitted through inhalation of infective air droplets from an infected person to the next susceptible host. This devastating disease has been a major cause of death from a single infectious agent more than HIV/AIDS and malaria combined before the COVID-19 pandemic. Caused by several genetically distinct Mycobacterium tuberculosis complex (MTBC) species, TB causes the death of a person every 22 seconds making MTBC one of the most successful human pathogen. TB is mostly curable with a specific combination of anti-TB drugs. Yet the increase of strains carrying drug-resistance mutations and the gap between people who are not diagnosed contributes to the reported TB related deaths. Ending this ongoing epidemic will require investment in biomedical, public health and socioeconomic interventions to sustain the necessary research and development of the necessary tools. Improvement of current diagnostic tests and development of new diagnostic approaches is necessary to increase case detection rates and close in the 4.2 million gap of people who are currently missed every year. In addition, genetically distinct MTBC lineages are differentially distributed globally; further understanding of the link between this diversity and MTBC pathogenesis is likely to improve management of TB patients in different epidemiological settings.
In the first part of this thesis, we hypothesized that TB disease epidemiology in Tanzania is driven by the human-MTBC genetic interactions resulting in an increased susceptibility of specific hosts to a specific circulating MTBC strain. This hypothesis was investigated in Chapter 3, where I will first give detailed introduction of the human adapted MTBC lineages, their distribution and factors contributing to their global distribution. I will then introduce current concepts of strain adaptation to local host populations driven by genetic interaction between human hosts and the circulating strains in various epidemiological settings. To test our hypothesis, we selected representative MTBC strain endemic to the Temeke District of Dar es Salaam where patients were recruited, and peripheral blood mononuclear cells cryopreserved. Patient-derived macrophages from monocytes isolated from their collected blood were infected either with a genetically related strain that had originally infected the patient (“matched infection”) or with other endemic lineages (“mismatched infection”). MTBC replication within patients’ macrophages as well as cytokine and chemokine production in response to infection were assessed. We observed that lineage-matched ex-vivo infection of macrophages derived from TB patients could not deliver sympatric associations signals. In turn, our results suggest that TB epidemiology in Tanzania is mainly driven by different MTBC strain-specific pathogenesis strategies rather than host-specific genetic traits.
In the second part of this thesis, we explored the hypothesis that bacterial load perception by the host adaptive immune system results in a measurable activation status that can be used to: i) diagnose TB infection and; ii) monitor disease resolution. This work is presented in Chapter 4 in which we investigated the diagnostic potential of two T-cell activation markers (TAM) for TB diagnosis (TAM-TB assay). The TAM-TB assay was assessed using a simplified protocol starting from 1ml of blood to comply with childhood TB diagnosis. In this chapter, I will introduce the current TB diagnostic tools, their limitations and provide reasons supporting the implementation of the TAM-TB assay in the field. I will then detail how we assessed the diagnostic performance of the TAM-TB assay for TB diagnosis starting from 1ml of blood from 479 active TB patients and 108 symptomatic controls. I will present how sample processing was done to measure expression of CD38 or CD27 by CD4 T cells producing IFN-γ and/or TNF-α in response to a synthetic peptide pool covering the sequences MTBC ESAT-6, CFP-10 and TB10.4 antigens using a 4-color FACSCalibur apparatus. The CD38-based TAM-TB assay specificity reached 93.4% for a sensitivity of 82.2% with an area under the receiver operating characteristics curve of 0.87 (95% CI 0.84-0.91). I will demonstrate how TAM-TB routine testing with a 24h turnaround time at district level in a resource-limited setting was successfully implemented. Starting from 1ml of blood and being not affected by HIV status, I will conclude that CD38-based TAM-TB assay performance appears closely compatible with the optimal target product profile accuracy criteria defined by WHO for a non-sputum confirmatory TB test.
In Chapter 5, we explored the use of the TAM-TB assay as proxy of host bacterial load and consequently, a treatment-monitoring tool. In this chapter, I will introduce why treatment monitoring is important not only for patient management but also for clinical trials evaluating new treatment regimens. I will also develop the shortcomings of current tools used to measure bacterial load and disease resolution and the need for alternative measures. In this work, we hypothesized that the phenotype of MTBC-specific T cells may be quantitatively impacted by the load of bacteria present in a given patient. To test this hypothesis, we obtained 1 ml blood from 105 active TB patients, before and after 5 months of antibiotic treatment. We evaluated the relationships between patients’ clinical characteristics of disease severity and microbiological as well as molecular proxies of bacterial load in sputum at the time of diagnosis. Reflecting the difficulty to extrapolate bacterial burden from a single end-point read-out, we observed statistically significant but weak correlations between Xpert MTB/RIF, MBLA and time to culture positivity. We demonstrated that resolution of CD38 expression by antigen-specific T cells was observed readily following 5 months of antibiotic therapy. However, the intensity of CD38-TAM signals measured at diagnosis did not significantly correlate with MTBC 16S rRNA or rpoB DNA detected in patients’ sputa. Altogether, our data support CD38-TAM as an accurate marker of infection resolution independently of sputum bacterial load. The CD38-based TAM-TB assay constitutes a promising assay to monitor treatment response.
In summary, in this thesis I dissected the influence of both human and MTBC genetic variability in the epidemiology of TB in Tanzania to an unprecedented extent matching endemic strains to infect patient’s host cells. Secondly, we addressed key aspects in the END-TB strategy to circumvent the limitations of current TB diagnostic tools showing the potential of CD38-based TAM-TB assay as a promising non-sputum diagnostic test that can be implemented in the field and routinely deliver accurate results with a 24h turnaround time
Valorization of Angolan traditional herbal preparations used against trypanosomiasis
Full text linkIn Angola, Human African Trypanosomiasis is caused by the protozoal subspecies Trypanosoma brucei gambiense and is transmitted by tsetse flies (Glossina spp.). It is endemic in seven provinces of the country, and an estimated 5.8 million people are at risk. Despite availability of an effective standard treatment and control activities, a certain number of cases are undetected and untreated, these are mainly found among hard-to reach communities, much exposed to the disease with difficult access to healthcare. In such context, the investigation of herbal remedies as a natural affordable and accessible resource is of high relevance. There is a lack of information on Angolan medicinal plants currently used against trypanosomiasis. In the presented PhD study, I have investigated the actual use of traditional herbal remedies in the management of this disease. By investigation of the access to and the use of the traditional remedies, I aimed to fill up this gap by delivering useful information regarding the usage of the medicinal plants and the antitrypanosomal potential of the reported traditional recipes.
First, I implemented and conducted an exploratory study in four northern endemic provinces of Angola. The ethnomedical and ethnobotanical analysis revealed that among the infected persons, 40% turn to folk medicine before consulting a medical doctor. Moreover, 30 plant species were mentioned in the management of the disease, of which Crossopteryx febrifuga was the most cited plant. In addition, the study highlighted the use of plants with potential toxicity risk, as for example an herbal preparation containing the roots of Aristolochia gigantea.
I further selected 9 species (of 30) for in vitro antitrypanosomal screening, according to four selection criteria: (1) the Use Report, (2) the correlation between traditional reported preparation and clinical data, (3) the quality of the narrative content, and (4) the novelty of the plant.
I pursued with the bioguided-activity screening of the 9 plant species, out of which 122 plant extracts were produced. Two crude extracts, the 80% ethanolic extract of Brasenia schreberi (leave) and the dichloromethane extract of Nymphaea lotus (leaf and petiole) displayed IC50 values < 10 µg/ml against Trypanosoma brucei rhodesiense, and were retained for bioguided-fractionation and isolation of active constituents. 7 active phenols for B. schreberi , namely gallic acid (1), methyl gallate (2), tetragalloylglucose (3), ethyl gallate (4), 1,2,3,4,6 pentagallyl-β-glucopyranoside (5), gossypetin-7-O-β-glucopyranoside (6), hypolaetin-7-O-glucoside (7), and 1 active compound for N. lotus, a resorcinol alkyl (8). Compounds (2-3, 5-6) were reported for the first time in the genus Brasenia and the presence of compound (8) was so far not described in the Nymphaeacea. The antitrypanosomal potential of the traditional preparation made of these two aquatic plants was assessed. We could evidence the presence of 3 active constituents in both decoctions: gallic acid, methyl gallate, and 1,2,3,4,6-Pentylgalloyl-β-glucopyranoside.
Taken together, this work provided primary evidence for the rational use of a traditionally used preparation made of Brasenia schreberi and Nymphaea lotus. As so, these results contributed to the scientific validation of an herbal remedy used in the management of sleeping sickness in Angola
The fine-tuning of barrier immunity by myeloid cells
No full textMyeloid cells, including conventional dendritic cells (cDCs) and macrophages, are key responders at epithelial barriers, regulating immunity to microbial pathogens and commensals. Equipped with innate receptors, DCs and macrophages sample and monitor the environment, maintaining homeostasis. Upon detection of danger signals these cells become activated, secrete inflammatory cytokines, and promote T cell activation. How dendritic cells at barrier tissues control the balance between tolerance and immunity is still unclear. Conditional Notch2 deficiency within CD11c-expressing cells (Notch2cKO) impairs the development of ESAM-expressing type 2 dendritic cells (ESAM+cDC2). These cells were previously shown to be critical to respond to infection with the enteropathogenic bacterium C. rodentium.
scRNAseq analysis of DC subsets in Notch2fl/flCD11cCre mice showed profound functional defects across all DC subsets, including the recently characterized cDC2b. We observed an expansion of proinflammatory CD26+CD16/32+Axl+ cDC2b. Further, Notch2cKO spontaneously developed increased IgG2c/IgA antibody titers around eight weeks of age, that remained high over time. Prolonged increases in serum immunoglobulin levels led to immune complex deposition in kidney, that is reminiscent of IgA nephropathy. This early onset of lowgrade inflammation was accompanied by increased intestinal immunopathology and permeability, increased fecal colony-forming unit (CFU) counts and dysbiosis, with colonization of pathogenic species. Co-housing of Notch2cKO with WT mice was sufficient to permanently transfer and establish the pathogenic species and promote increased antibody titers in immune sufficient mice. The pathogenic microbiome led to increased mortality in Notch2cKO mice and increased pathology in co-housed mice upon DSS-induced colitis. This increased pathology resulted from a dysregulation of the ratio between TH17 and Treg.
Collectively, Notch2 deficiency within the myeloid compartment was sufficient to compromise the intestinal barrier, enabling long-term colonization by pathogenic species. The resulting low-grade inflammation led to increased and chronically high antibody titers, which deposited as immune complexes in kidneys, suggesting that a pre-clinical autoimmunity can
be initiated by a mild dysbiosis
Geo-statistical modelling of malaria mortality and its relationship with anaemia in the Kisumu health and demographic surveillance system, Kenya
Full text linkMalaria remains a significant health concern globally, with Sub-Saharan Africa, particularly children under five, facing the highest burden. Western Kenya, where malaria causes over a third of outpatient visits, exemplifies this challenge. Despite a decline in malaria cases over the past two decades, progress has stagnated due to data inconsistencies, lack of precise regional estimates, and inadequate monitoring. Effective data management is crucial for informing timely and effective policy decisions.
This PhD focused on the Health and Demographic Surveillance System (HDSS) in western Kenya, a high-malaria-prevalence area, from 2007 to 2015. We investigated the spatio-temporal dynamics of malaria incidence and prevalence, adjusting for climatic, environmental, and socio-economic factors, across all age groups. We also examined the association between malaria, parasitic worms, and anaemia risk.
Our research revealed a significant decline in malaria incidence among children under five, with socio-economic status, altitude, and study area being critical factors. Slight increases in slide positivity rates (SPR) at hospitals strongly indicated higher all-cause and malaria-specific mortality, particularly in children aged 5 -14 years. High anaemia prevalence was noted, especially among the youngest and elderly, with malaria parasitaemia and clinical malaria linked to higher anaemia risk.
These findings underscore the multifaceted nature of malaria and its broader implications on mortality and anaemia, suggesting that SPR is an efficient measure of malaria transmission and impact measurement. Targeted, multi-pronged interventions are essential for combating malaria's complexities, emphasizing the need for specialized attention and effective policy formulation in regions like western Kenya
Semiconducting nanowire-based Josephson junctions for qubits
Full text linkThe goal of this thesis is to study the photon-mediated coupling between two distant Andreev pair qubits. Ch. 2 presents the theoretical concepts of Andreev bound states in semiconducting nanowire-based Josephson junctions (NWJJs), followed by the introduction to the implementation of Andreev qubits using full-shell epitaxial InAs/Al nanowires. The control and readout of Andreev qubits presented in this thesis rely on the coupling to a superconducting microwave resonator. Ch. 3 provides an overview of the qubit-resonator coupling and concludes the theory part of this thesis. Ch. 4 presents the DC electrical characterization of full-shell epitaxial InAs/Al nanowire Josephson junctions. The electrical performance of these nanowire devices is evaluated in terms of junction transparencies. The extracted high transparency parameters encourage us to further proceed to fabricate the microwave chip. Ch. 5 thoroughly discusses the design considerations for the superconducting cavity coupler for Andreev qubits. From the experimental requirements, we derive design rules for each relevant electronic component, which are checked using numerical simulation tools. We then combine the knowledge about our full-shell epitaxial InAs/Al nanowire Josephson junctions and superconducting cavity coupler. In Ch. 6, we demonstrate the operation of the cavity coupler as a microwave spectroscopy tool and qubit state detector for individual NWJJ devices. In Ch. 7, we simultaneously couple both Andreev pair qubits to the cavity and demonstrate distant, strong coupling of two Andreev pair qubits. With the demonstration of the capability of our superconducting cavity coupler to entangle two Andreev pair qubits, we close the investigation of qubits formed with epitaxial InAs/Al nanowires. In Ch. 8, we motivate the use of Ge/Si core/shell nanowire Josephson junctions and demonstrate coherent manipulation of a superconducting gatemon qubit, that manifests Josephson supercurrent in these nanowire devices. In Ch. 9, we summarize the important experimental techniques, which are the backbone of the presented thesis, helping the readers to understand and reproduce the experiments. This thesis is concluded in Ch. 10 with a brief outlook of possible future experiments
On real forms and birational transformations
Full text linkThis thesis is split into two parts: the first one, Part I, combines the first four papers that came out of my PhD, all on the topic of real forms. Two out of the four papers were written jointly with co-authors, namely one with Jérémy Blanc and Pierre-Marie Poloni, and the other one with Adrien Dubouloz. The second part, Part II, contains the fifth paper, on dynamical degrees. The introduction treats both parts together.
The papers are all available on the arXiv or can be accessed through the journals they were published in:
1. Anna Bot. Real forms on rational surfaces. Ann. Sc. Norm. Super. Pisa Cl. Sci. (5), 24(3):1301–1326, 2023. Available at doi : 10.2422/2036-2145.202105_056 or
arXiv.2103.00909.
2. Anna Bot. A smooth complex rational affine surface with uncountably many real forms, accepted for publication at Ann. Sci. Éc. Norm. Supér. Available at arXiv.2105.08044.
3. Jérémy Blanc, Anna Bot and Pierre-Marie Poloni. Real forms of some Gizatullin surfaces and Koras-Russell threefolds. Publ. Mat., 67(2):851–890, 2023. Available at doi : 10.5565/publmat6722314 or arXiv.2108.12389.
4. Anna Bot and Adrien Dubouloz. Relative forms of real algebraic varieties and examples of quasi-projective surfaces with algebraic moduli of real forms. Available at arXiv.2206.01713.
5. Anna Bot. The ordinal of dynamical degrees of birational maps of the projective plane. Comptes Rendus. Mathématique, Volume 362 (2024), pp. 117-134. doi : 10.5802/cr-math.540. Also available at arXiv.2207.04408.
All parts rely on the intimate study of birational maps; though the objectives may change from one project to another, the tools from Birational Geometry are the same. This red thread strings all of the projects together
Multi-Parametric brain tissue characterization using magnetic resonance imaging
No full textMagnetic resonance imaging (MRI) is one of the most powerful imaging modalities in clinical diagnostics and intervention to date. It employs strong static magnetic fields in combination with weaker, varying magnetic fields and radio frequency (RF) waves to produce an image of the body's interior. The longitudinal and transverse relaxation times, describing the tissue-type-dependent MR signal decay, are of fundamental importance for this. They are the guiding processes for image contrast between tissue types and the reason why MRI contrast is extremely versatile and often superior in comparison to other imaging modalities. However, this versatility also leads to one of MRI's biggest disadvantages, namely the fact that images do not obey an absolute scale like e.g. in computed tomography. MRI images show relative gray values which depend on imaging parameters, field strength and even the imaging device itself. Therefore, the desire to establish a reliable method to obtain quantitative images with an absolute scale is high and it comes as no surprise that the research field around quantitative imaging is one of the biggest in MRI. The main concern is the development of fast and reliable methods to quantitatively measure a variety of absolute tissue parameters. These provide the individual voxel values with a physical meaning which, ideally, is independent of the MR protocol and hardware, thus offering the possibility to directly compare the results from studies across multiple subjects, time-points, and imaging sites. In this thesis, we focus on various aspects of multi-parametric quantitative brain imaging with immediate connection to relaxometry, the study of and .
First, features of the balanced steady-state free precession (bSSFP) sequence are investigated. Phase-cycled bSSFP shows great potential in terms of fast, simultaneous quantification of and . However, systematic discrepancies between bSSFP quantification and other methods are observed, especially in brain tissue. One of the major suspected causes, the asymmetry of the bSSFP frequency response, is investigated here.
Furthermore, the magnetization-prepared rapid gradient echo (MP-RAGE) sequence, which serves as a powerful ally in quantitative imaging by offering fast -weighted anatomical references, is optimized for the new generation of clinical 0.55 T scanners. For this, potential sequence modifications are tested.
Staying at 0.55 T, myelin water imaging is investigated at this field strength in order to assess its advantages at lower field strengths and its viability. Myelin is the protective sheath around the axons of nerve cells. Its loss causes neurodegenerative diseases and fast, reliable imaging could help to understand the disease progression better.
Lastly, the method of bSSFP phase-cycled quantification is applied to Na. In contrast to H imaging, the field of sodium MRI is concerned even more with the topic of quantitative imaging due to the way in which images usually need to be acquired and the minor knowledge which can be gained by relative sodium contrast. Here, phase-cycled bSSFP could offer a more efficient alternative to the commonly used methods. Its viability is tested at 3 T