Measurement and analysis of partial lightning currents in a head phantom

Direct lightning strikes to the human head can lead to various effects, ranging from burnings to death. The biological and physical mechanisms of a direct lightning strike in the human head are not well understood. The aim of this paper is to design an experimental setup to measure the spatial and temporal current distribution during a direct lightning strike to physical head phantoms to establish normative values for personal lightning protection equipment design and testing. We created head phantoms made of agarose, replicating the geometric and dielectric properties of scalp, skull, and intracranial volume. The bases of the three compartments were galvanically contacted via copper electrodes to measure the current per compartment. We used pulse generators to apply aperiodic voltage and current signals that modelled lightning components. Our experiments indicated that the scalp compartment was exposed to the current with a fraction of 80–90%. The brain and skull compartments were exposed between 6–13% and 3–6% of the total measured current respectively. In case of a flashover, most of the current (98–99%) flowed through the discharge channel. Unlike previous theoretical estimates and measurements in technical setups, we observed considerably longer times for the flashover to build up. In our experiments, the time to build up a fully formed flashover varied from approximately 30–700 μs. The observed current patterns in cases without and with flashover provided information on regions of possible damage in the human head. Consequently, we identified the phenomenon of a flashover as a potential mechanism for humans to survive a lightning strike. Our measured current distributions and amplitudes formed the base for normative values, which can be used in later experimental investigations regarding the possibilities of individual lightning protection equipment for humans

Investigating Forward Flight Multirotor Wind Tunnel Testing in a 3-by 4-foot Wind Tunnel

Investigation of complex multirotor aerodynamic phenomena via wind tunnel experimentation is becoming extremely important with the rapid progress in advanced distributed propulsion VTOL concepts. Much of this experimentation is being performed in large, highly advanced tunnels. However, the proliferation of this class of vehicles extends to small aircraft used by small businesses, universities, and hobbyists without ready access to this level of test facility. Therefore, there is a need to investigate whether multirotor vehicles can be adequately tested in smaller wind tunnel facilities. A test rig for a 2.82-pound quadcopter was developed to perform powered testing in the Cal Poly Aerospace Department’s Low Speed Wind Tunnel, equipped with a 3-foot tall by 4-foot wide test section. The results were compared to data from similar tests performed in the U.S. Army 7-by 10-ft Wind Tunnel at NASA Ames. The two data sets did not show close agreement in absolute terms but demonstrated similar trends. Due to measurement uncertainties, the contribution of wind tunnel interference effects to this discrepancy in measurements was not able to be properly quantified, but is likely a major contributor. Flow visualization results demonstrated that tunnel interference effects can likely be minimized by testing at high tunnel speeds with the vehicle pitched 10-degrees or more downward. Suggestions towards avoiding the pitfalls inherent to multirotor wind tunnel testing are provided. Additionally, a modified form of the conventional lift-to-drag ratio is presented as a metric of electric multirotor aerodynamic efficiency

An Engineering Approach to Computational Prediction of Breakdown in Air With Surface Charging Effects

This paper presents a dielectric simulation approach for predicting withstand voltage of air insulated power devices. The paper gives an overview of typical evaluation procedures for the basic discharge stages including inception, streamer propagation and leader transition. For selected test arrangements, we compare the results of lightning impulse tests with simulations. The simulations utilize a new approach that combines the well-established empirical procedure with numerical computations for arbitrary geometries. We introduce a new formulation for evaluation of saturation charge density, which enables a revision of the streamer inception conditions due to surface charging and an estimation of the leader transition characteristics including the surface capacitance.acceptedVersio

The dynamics of starting gas-particle jets: a volcanic scenario

Explosive volcanic eruptions are a threat for a large part of global population and infrastructures. Explosive eruptions are the results of energetic magma fragmentation, where only gas exsolved in the magma drive the eruption, or of the interaction with external water. The mechanisms of fragmentation are complex and various, but despite that at explosive eruption onset the potential energy stored in gas bubbles in the magma always transforms into kinetic energy via gas expansion and produce the ejection of pyroclasts and/or non-juvenile material in the atmosphere. Particle ejection rate, velocity and trajectory differ depending on source conditions, e.g. magma composition, gas overpressure, conduit length, vent geometry, etc. Field observations, when possible, can help to characterize an ejection from which then the source conditions are indirectly retrieved. High-speed and infrared videos of volcanic ejections, seismic and acoustic measurements, as well as petrographycal and geochemical analysis on the pyroclasts ejected offer insight on the eruptive event. Nevertheless, to link observations and source parameters is not trivial and it still requires a certain number of assumptions. Therefore, the knowledge of source conditions stays uncertain. On the other hand, empirical studies can help linking observations and input parameters, since the latter are chosen experimental conditions. In general, laboratory experiments are far less complex than natural eruptions. However, the simplifications imposed benefit the investigation of single processes as well as the understanding of the effects of boundary conditions on such observed dynamics. The goal, at the end, is to learn the patterns of certain dynamics and possibly, to recognize certain characteristics of volcanic eruptions and be able to associate them to source conditions. Additionally, empirical results provide input parameters for numerical modelling and thus hazard assessment. I perform rapid decompression experiments of gas-particle mixtures generating starting jets. I use two different experimental apparatus, the first is the “fragmentation bomb” at the LMU facility and the second the “jet buster” at INGV Rome. With the two setups, it is possible to characterize the effect of boundary conditions such as: 1) vent geometry, 2) tube length, 3) particle load and size, 4) temperature, and 5) overpressure in the reservoir on the dynamics of the ejection of natural particles of different initial size distribution (from 0.125 to 4 mm). In particular, I focus the analysis on particle velocity and trajectory. Observations on particle fragmentation, mass ejection rate and lightning generation are also possible on experiments from the “fragmentation bomb”. The experiments are recorded with a high-speed camera, which provides visual observation of the dynamics. On the “jet buster” experiments, the video recordings are coupled with piezoelectric sensors providing microseismic signals of the related propagation dynamics. The two apparatus are different and complementary. The “fragmentation bomb”, a shock-tube made of metal, is 24 cm long, allows high overpressures (here 150 bar) and temperatures (here 500°C), gas and particles are pressurized in the same chamber and the observations are made at vent exit. The “jet buster”, on the other hand, with its 3 m of transparent PMMA tube allows the observation of the whole propagation and dynamics inside the pipe as well at vent exit. The overpressure threshold is in the order of few bar (here 2 bar), and the gas reservoir is separated and below the sample chamber. In the “fragmentation bomb” experiments, maximum particle velocity shows, in order of importance, 1) negative correlation with tube length; 2) positive correlation with particle load; 3) positive correlation with flaring vent walls, with peaks for funnel 15; 4) positive correlation with temperature, and 5) negative correlation with particle size. The evolution of particle velocity with time in non-linear and is mostly affected by particle load and tube length. Gas maximum initial spreading angle shows, in order of importance: 1) negative correlation with flaring vent walls; 2) negative correlation with experimental temperature; 3) positive correlation with tube length; 4) positive correlation with particle size, and 5) negative correlation with particle load. The gas spreading angle evolution with time shows a bell shape pattern and it is especially appreciable in setup 1 experiments, due to the particles later arrival. This is the main affecting parameter. The particle initial spreading angle shows: 1) positive correlation with particle load, 2) negative correlation with particle size; 3) negative correlation with vent geometry; 4) positive correlation with tube length, and 5) negative correlation with temperature. The particle spreading angle evolution with time shows patterns varying in particular with particle load and tube length. Estimations of the mass ejection rate (MER) and instantaneous mass or particle concentration show peaks of 26kg/s for setup 2 experiments, 7 kg/s for setup 3 and 4.6 kg/s for setup 1. The evolution of the MER with time reflects the evolution of particle velocity with time. Finally, mm to cm electrical discharges, i.e. lightning, are observed. Their appearance is positively correlated with particle load, and negatively correlated with tube length, temperature, particle size, and flaring of vent walls. In the “jet buster”, I perform both gas only and gas-particle mixture experiments. This to compare the elastic response of the system and jets’ dynamics. The gas only experiments includes a pinch of kaolin powder in order to make the flow front propagation visible in the camera. The gas flow front shows an initial fast propagation (up to 500m/s) in the pipe accompanied by an abrupt deceleration (to 150 m/s) at vent exit were it generates a vortex ring. On the other hand, particles show maximum velocities between 40 to 100 cm in the pipe in respect to initial sample position. In addition, in this case, maximum particle velocity shows negative correlation with particle size and the evolution of particle velocity displays a non-linear trend. Good correlation between microseismic signals and process occurring in the pipe is observed. The comparison of the experimental results with natural data collected on Stromboli volcano, Italy, is far from trivial. As mentioned above, volcanic eruptions are characterized by the interaction of several processes, thus making them far more complex. Nevertheless, I think the data set present here provides a promising link for both field volcanology (visual observations and quantitative monitoring) as well as numerical modelling in order to advance our understanding of explosive volcanic eruptions and assess the related hazard

Multiple Discharges Before Leader Inception in Long Air Gaps Under Positive Switching Impulses

There are multiple corona bursts before leader inception when the rising rate of the applied voltage or electric field is not sufficiently high enough in long positive sparks. In existing studies, no attention has been paid to whether these corona bursts occur in the same location, and they are mostly considered directly as belonging to the same discharge. However, this paper presents that in a typical rod-plate long air gap, the multiple corona bursts before leader inception are distributed in at least two different locations, and the highest probability of three discharges occurs. Also, the discharge occurs with the highest probability in the time sequence ‘tip-tip-side-tip-other side’ of the electrode in the first five corona bursts. For each discharge, the first corona current is a single, double exponential pulse, while the following corona currents are mostly a superposition of multiple pulses. The above findings are mainly based on experiments in a 1.4 m air gap under positive switching impulses, in which the voltage, current, and high-speed images were recorded simultaneously. Finally, based on the experimental results, this paper discusses the effects brought by ignoring the multiple discharges on key parameters of leader inception and makes some suggestions to optimise long spark experiments

Multiple Discharges Before Leader Inception in Long Air Gaps Under Positive Switching Impulses

There are multiple corona bursts before leader inception when the rising rate of the applied voltage or electric field is not sufficiently high enough in long positive sparks. In existing studies, no attention has been paid to whether these corona bursts occur in the same location, and they are mostly considered directly as belonging to the same discharge. However, this paper presents that in a typical rod-plate long air gap, the multiple corona bursts before leader inception are distributed in at least two different locations, and the highest probability of three discharges occurs. Also, the discharge occurs with the highest probability in the time sequence ‘tip-tip-side-tip-other side’ of the electrode in the first five corona bursts. For each discharge, the first corona current is a single, double exponential pulse, while the following corona currents are mostly a superposition of multiple pulses. The above findings are mainly based on experiments in a 1.4 m air gap under positive switching impulses, in which the voltage, current, and high-speed images were recorded simultaneously. Finally, based on the experimental results, this paper discusses the effects brought by ignoring the multiple discharges on key parameters of leader inception and makes some suggestions to optimise long spark experiments

Langley aerospace test highlights, 1985

The role of the Langley Research Center is to perform basic and applied research necessary for the advancement of aeronautics and space flight, to generate new and advanced concepts for the accomplishment of related national goals, and to provide research advice, technological support, and assistance to other NASA installations, other government agencies, and industry. Significant tests which were performed during calendar year 1985 in Langley test facilities, are highlighted. Both the broad range of the research and technology activities at the Langley Research Center and the contributions of this work toward maintaining United States leadership in aeronautics and space research, are illustrated. Other highlights of Langley research and technology for 1985 are described in Research and Technology-1985 Annual Report of the Langley Research Center

The effect of jewellery and the human hand on SAR and antenna performance

This thesis investigates the effect of the human hand and metallic jewellery items worn on the human head and hand on SAR and on the antenna radiation patterns at 900 and 1900 MHz. The field excitation is provided by means of a A./4 monopole antenna on top of a metal box to emulate a simple handset. A planar inverted 'F' antenna (PIFA) is also used for comparison with the monopole. This thesis presents a detailed parametric study utilizing computer simulations via the Transmission Line Matrix (TLM) method and measurements from the DASY 4 SAR measurement system. Two different head and hand geometries are considered. Firstly a homogenous spherical head and block-hand were used in the simpler simulation, while the more realistic head and hand models were employed for the detailed study. The hand models include fingers which allow the metallic jewellery rings to be examined. The human hand has a significant effect on Specific Absorption Rate (SAR) and on the antenna pattern due to energy absorption and possible reflection at the hand dielectric boundary. In addition, the effects of different sizes, orientation, and distance of the metallic loop-like jewellery items relative to the antenna have been investigated. The metallic rings worn on the hand tend to reduce the SAR and could also alter the antenna radiation performance. The wrist worn bangle has very little effect on the results at the frequencies tested due to its position that is relatively far away from the handset antenna. The earrings could significantly influence the SAR and the radiation patterns, but the effects varied depending on the earring's diameter, its position relative to the head, the frequency and the type of antenna in use. The effect of the combination of the hand, the earring and the finger ring only show minor difference on the SAR values and on the antenna radiation patterns. Measurements of the effects of the hand and metallic jewellery items on SAR were performed inside a Standard anthropomorphic model (SAM) head phantom. A novel liquid hand phantom with realistic fingers has been manufactured, which allow the effect of metallic ring to be further investigated. Measurement results support the simulation results

Technical Feasibility of MR-Integrated Proton Therapy: Beam Deflection and Image Quality

Es wird erwartet, dass die Integration der Magnetresonanztomografie (MRT) in die Protonentherapie die Treffgenauigkeit bei der Strahlentherapie für Krebserkrankungen deutlich verbessern wird. Besonders für Tumoren in beweglichen Organen des Thorax oder des Abdomens könnte die MRT-integrierte Protonentherapie (MRiPT) eine Synchronisierung der Bestrahlung mit der Tumorposition ermöglichen, was zu einer verminderten Normalgewebsdosis und weniger Nebenwirkungen führen könnte. Bis heute ist solch eine Integration jedoch aufgrund fehlender Studien zu potenziellen gegenseitigen Störeinflüssen dieser beiden Systeme nicht vollzogen worden. Diese Arbeit widmete sich zwei solcher Störeinflüsse, und zwar der Ablenkung des Protonenstrahls im Magnetfeld des MRT- Scanners, und umgekehrt, dem Einfluss der elekromagnetischen Felder der Protonentherapieanlage und des Protonenstrahls selbst auf die MRT-Bilder. Obwohl vorangegangene Studien den derzeitigen Konsens aufgezeigt haben, dass die Trajektorie eines abgebremsten Protonenstrahls im homogenen Phantom in einem transversalen Magnetfeld vorhersagbar ist, zeigte sich im quantitativen Vergleich der publizierten Modelle, der im ersten Teil dieser Arbeit vorgestellt wurde, dass die Vorhersagen dieser Modelle nur für eine begrenzte Anzahl von Kombinationen aus Magnetfeldstärke und Protonenenergie übereinstimmen. Die Schwächen bestehender analytischer Modelle wurden deshalb analysiert und quantifiziert. Kritische Annahmen und die mangelnde Anwendbarkeit auf realistische, d.h. inhomogene Magnetfeldstärken und Patientengeometrien wurden als Hauptprobleme identifiziert. Um diese zu überwinden, wurde ein neues semianalytisches Modell namens RAMDIM entwickelt. Es wurde gezeigt, dass dieses auf realistischere Fälle anwendbar und genauer ist als existierende analytische Modelle und dabei schneller als Monte-Carlo-basierte Teilchenspursimulationen. Es wird erwartet, dass dieses Modell in der MRiPT Anwendung findet zur schnellen und genauen Ablenkungsberechnung, zur Betrahlungsplanoptimierung und bei der MRT-geführten Strahlnachführung. In einem zweiten Schritt wurde die magnetfeldinduzierte Protonenstrahlablenkung in einem gewebeähnlichen Material durch Filmdosimetrie erstmalig gemessen und mit Monte-Carlo-Simulationen verglichen. In einem transversalen Magnetfeld einer Flussdichte von 0,95 T wurde experimentell gezeigt, dass die laterale Versetzung des Bragg-Peaks für Protonenenergien zwischen 80 und 180 MeV in PMMA zwischen 1 und 10 mm liegt. Die Retraktion des Bragg-Peaks war ≤ 0,5 mm. Es wurde gezeigt, dass die gemessene Versetzung des Bragg-Peaks innerhalb von 0,8 mm mit Monte-Carlo-basierten Vorhersagen übereinstimmt. Diese Ergebnisse weisen darauf hin, dass die Protonenstrahlablenkung durch Monte-Carlo-Simulationen genau vorhersagbar ist und damit der Realisierbarkeit der MRiPT nicht im Wege steht. Im zweiten Teil dieser Arbeit wurde erstmalig ein MRT-Scanner in eine Protonenstrahlführung integriert. Hierfür wurde ein offener Niederfeld-MRT-Scanner am Ende einer statischen Forschungsstrahlführung einer Protonentherapieanlage platziert. Die durch das statische Magnetfeld des MRT-Scanners hervorgerufene Strahlablenkung wurde bei der Ausrichtung des MRT-Scanners berücksichtigt. Die sequenzabhängigen, veränderlichen Gradientenfelder hatten keinen messbaren Einfluss auf das transversale Strahlprofil hinter dem MRT-Scanner. Die Magnetfeldhomogenität des Scanners lag innerhalb der Herstellervorgaben und zeigte keinen relevanten Einfluss von Rotationen der Protonengantry im benachbarten Bestrahlungsraum. Eine magnetische Abschirmung war zum gleichzeitigen Betrieb des MRT-Scanners und der Protonentherapieanlage nicht notwendig. Dies beweist die Machbarkeit gleichzeitiger Bestrahlung und Bildgebung in einem ersten MRiPT Aufbau. Die MRT-Bildqualität des Aufbaus wurde darauffolgend anhand eines angepassten Standardprotokolls aus Spin-Echo- und Gradienten-Echo-Sequenzen quantifiziert und es wurde gezeigt, dass die Bildqualität sowohl ohne als auch mit gleichzeitiger Bestrahlung hinreichend ist. Alle bestimmten geometrischen Parameter stimmten mit den physikalischen Abmessungen des verwendeten Phantoms innerhalb eines Bildpixels überein. Wie es für Niederfeld-MRT-Scanner üblich ist, war das Signal-Rausch-Verhältnis (SNR) der MRT-Bilder gering, was im Vergleich zu den Standardkriterien zu einer geringen Bildhomogenität und zu einem hohen Geisterbildanteil im Bild führte. Außerdem wurde aufgrund von Unsicherheiten in der Hochfrequenzkalibrierung des MRT-Scanners eine starke Schwankung der vertikalen Phantomposition mit einem Interquartilabstand von bis zu 1,5 mm beobachtet. T2*-gewichtete Gradientenechosequenzen zeigten zudem aufgrund von Magnetfeldinho- mogenitäten relevante ortsabhängige Bildverzerrungen. Es wurde gezeigt, dass die meisten Bildqualitätsparameter mit und ohne gleichzeitige Betrahlung äquivalent sind. Es wurde jedoch ein signifikanter Betrahlungseinfluss in Form von einer vertikalen Bildverschiebung und einer Verminderung des SNR beobachtet, die durch eine Änderung im Magnetfeld des MRT-Scanners erklärt werden können, welche durch zu diesem Feld parallel ausgerichtete Komponenten im Fernfeld der Strahlführungsmagneten hervorgerufen wird. Während das verminderte SNR vermutlich irrelevant ist (Dif- ferenz im Median ≤ 1,5), ist die sequenzabhängige Bildverschiebung (Differenz im Median bis zu 0,7 mm) nicht immer vernachlässigbar. Diese Ergebisse zeigen, dass die MRT-Bilder durch gleichzeitige Bildgebung nicht schwerwiegend verfälscht werden, dass aber eine dedizierte Optimierung der Hochfrequenzkalibrierung und der MRT-Bildsequenzen notwendig ist. Im letzten Teil der Arbeit wurde gezeigt, dass ein stromabhängiger Einfluss des Protonenstrahls auf MRT-Bilder eines Wasserphantoms durch zwei verschiedene MRT-Sequenzen messbar gemacht und zur Reichweiteverifikation genutzt werden kann. Der Effekt war in verschiedenen Flüssigkeiten, jedoch nicht in viskosen und festen Materialen, nachweisbar und wurde auf Hitzekonvektion zurückgeführt. Es wird erwartet, dass diese Methode in der MRiPT für Konstanztests der Protonenreichweite bei der Maschinenqualitätssicherung nützlich sein wird. Zusammenfassend hat diese Arbeit die Genauigkeit der Vorhersage der Strahlablenkung quantifiziert und verbessert, sowie Potenzial und Realisierbarkeit einer gleichzeitigen MRT-Bildgebung und Protonenbestrahlung gezeigt. Die weitere Entwicklung eines ersten MRiPT-Prototyps ist demnach gerechtfertigt.:List of Figures v List of Tables vii 1 General Introduction 1 2 State of the Art: Proton Therapy and Magnetic Resonance Imaging 3 2.1 Proton Therapy 4 2.1.1 Physical Principle 4 2.1.2 Beam Delivery 7 2.1.3 Motion Management and the Role of Image Guidance 10 2.2 Magnetic Resonance Imaging 14 2.2.1 Physical Principle 14 2.2.2 Image Generation by Pulse Sequences 18 2.2.3 Image Quality 21 2.3 MR-Guided Radiotherapy 24 2.3.1 Offline MR Guidance 24 2.3.2 On-line MR Guidance 25 2.4 MR-Integrated Proton Therapy 28 2.4.1 Aims of this Thesis 32 3 Magnetic Field-Induced Beam Deflection and Bragg Peak Displacement 35 3.1 Analytical Description 36 3.1.1 Review of Analytical Models 36 3.1.2 New Model Formulation 41 3.1.3 Evaluation of Analytical and Numerical Models 44 3.1.4 Discussion 51 3.2 Monte Carlo Simulation and Experimental Verification 54 3.2.1 Verification Setup 54 3.2.2 Monte Carlo Simulation 56 3.2.3 Experimental Verification 60 3.2.4 Discussion 61 3.3 Summary 63 4 Integrated In-Beam MR System: Proof of Concept 65 4.1 Integration of a Low-Field MR Scanner and a Static Research Beamline 65 4.1.1 Proton Therapy System 66 4.1.2 MR Scanner 66 4.1.3 Potential Sources of Interference 67 4.1.4 Integration of Both Systems 68 4.2 Beam and Image Quality in the Integrated Setup 70 4.2.1 Beam Profile 70 4.2.2 MR Magnetic Field Homogeneity 72 4.2.3 MR Image Quality - Qualitative In Vivo and Ex Vivo Test 74 4.2.4 MR Image Quality - Quantitative Phantom Tests 77 4.3 Feasibility of MRI-based Range Verification 86 4.3.1 MR Sequences 86 4.3.2 Proton Beam Parameters 88 4.3.3 Target Material Dependence 91 4.3.4 Discussion 92 4.4 Summary 96 5 Discussion and Future Perspectives 99 6 Summary/Zusammenfassung 105 6.1 Summary 105 6.2 Zusammenfassung 108 Bibliography I Supplementary Information XXIX A Beam Deflection: Experimental Measurements XXIX A.1 Setup XXIX A.2 Film Handling and Evaluation XXX A.3 Uncertainty Estimation XXX B Beam Deflection: Monte Carlo Simulations XXXIII B.1 Magnetic Field Model XXXIII B.2 Uncertainty Estimation XXXIV C Integrated MRiPT Setup XXXVI C.1 Magnetic Field Map XXXVI C.2 Sequence Parameters XXXVI C.3 Image Quality Parameters XLII C.4 Range Verification Sequences XLIIThe integration of magnetic resonance imaging (MRI) into proton therapy is expected to strongly increase the targeting accuracy in radiation therapy for cancerous diseases. Especially for tumours situated in mobile organs in the thorax and abdomen, MR-integrated proton therapy (MRiPT) could enable the synchronisation of irradiation to the tumour position, resulting in less dose to normal tissue and reduced side effects. However, such an integration has been hindered so far by a lack of scientific studies on the potential mutual interference between the two components. This thesis was dedicated to two of these sources of interference, namely the deflection of the proton beam by the magnetic field of the MR scanner and, vice versa, alterations of the MR image induced by the electromagnetic fields of the proton therapy facility and by the beam itself. Although previous work has indicated that there is general consensus that the trajectory of a slowing down proton beam in a homogeneous phantom inside a transverse magnetic field is predictable, a quantitative comparison of the published methods, as presented in the first part of this thesis, has shown that predictions of different models only agree for certain proton beam energies and magnetic flux densities. Therefore, shortcomings of previously published analytical methods have been analysed and quantified. The inclusion of critical assumptions and the lack of applicability to realistic, i.e. non-uniform, magnetic flux densities and patient anatomies have been identified as main problems. To overcome these deficiencies, a new semi-analytical model called RAMDIM has been developed. It was shown that this model is both applicable to more realistic setups and less assumptive than existing analytical approaches, and faster than Monte Carlo based particle tracking simulations. This model is expected to be useful in MRiPT for fast and accurate deflection estimations, treatment plan optimisation, and MR-guided beam tracking. In a second step, the magnetic field-induced proton beam deflection has been measured for the first time in a tissue-mimicking medium by film dosimetry and has been compared against Monte Carlo simulations. In a transverse magnetic field of 0.95 T, it was experimentally shown that the lateral Bragg peak displacement ranges between 1 mm and 10 mm for proton energies between 80 and 180 MeV in PMMA. Range retraction was found to be ≤ 0.5 mm. The measured Bragg peak displacement was shown to agree within 0.8 mm with Monte Carlo simulations. These results indicate that proton beam deflection in a homogeneous medium is accurately predictable for intermediate proton beam energies and magnetic flux densities by Monte Carlo simulations and therefore not impeding the feasibility of MRiPT. In the second part of this thesis, an MR scanner has been integrated into a proton beam line for the first time. For this purpose, an open low-field MR scanner has been placed at the end of a fixed horizontal proton research beam line in a proton therapy facility. The beam deflection induced by the static magnetic field of the scanner was taken into account for alignment of the beam and the FOV of the scanner. The pulse sequence-dependent dynamic gradient fields did not measurably affect the transverse beam profile behind the MR scanner. The MR magnetic field homogeneity was within the vendor’s specifications and not relevantly influenced by the rotation of the proton gantry in the neighbouring treatment room. No magnetic field compensation system was required for simultaneous operation of the MR scanner and the proton therapy system. These results proof that simultaneous irradiation and imaging is feasible in an in-beam MR setup. The MR image quality of the in-beam MR scanner was then quantified by an adapted standard protocol comprising spin and gradient echo imaging and shown to be acceptable both with and without simultaneous proton beam irradiation. All geometrical parameters agreed with the mechanical dimensions of the used phantom within one pixel width. As common for low-field MR scanners, the signal-to-noise ratio (SNR) of the MR images was low, which resulted in a low image uniformity and a high ghosting ratio in comparison to the standardised test criteria. Furthermore, a strong fluctuation of the vertical phantom position due to uncertainties in the pre-scan frequency calibration was observed, with an interquartile range of up to 1.5 mm. T2*-weighted gradient echo images showed relevant nonuniform deformations due to magnetic field inhomogeneities. Most image quality parameters were shown to be equivalent with and without simultaneous proton beam irradiation. However, a significant influence of simultaneous irradiation was observed as a shift of the vertical phantom position and a decrease in the SNR, both of which can be explained by a change in the B0 field of the MR scanner induced by components of the fringe field of the beam line magnets directed parallel to B0 . While the decrease in SNR is not expected to be relevant (median differences were within 1.5 ), the sequence-dependent phantom shift (median differences of up to 0.7 mm) can become non-negligible. These results show that the MR images are not severely distorted by simultaneous irradiation, but a dedicated optimisation of the pre-scan RF calibration and the MR sequences is required for MRiPT. Lastly, a current-dependent influence of the proton beam on the MR image was shown to be measurable in water in two different MR sequences, which allowed for range verification measurements. The effect was observed in different liquids but not in highly viscose and solid materials, and most probably induced by heat convection. This method is expected to be useful in MRiPT for consistency tests of the proton range during machine-specific quality assurance. In conclusion, this work has improved and quantified the accuracy of beam deflection predictions and shown the feasibility and potential of in-beam MR imaging, justifying further research towards a first MRiPT prototype.:List of Figures v List of Tables vii 1 General Introduction 1 2 State of the Art: Proton Therapy and Magnetic Resonance Imaging 3 2.1 Proton Therapy 4 2.1.1 Physical Principle 4 2.1.2 Beam Delivery 7 2.1.3 Motion Management and the Role of Image Guidance 10 2.2 Magnetic Resonance Imaging 14 2.2.1 Physical Principle 14 2.2.2 Image Generation by Pulse Sequences 18 2.2.3 Image Quality 21 2.3 MR-Guided Radiotherapy 24 2.3.1 Offline MR Guidance 24 2.3.2 On-line MR Guidance 25 2.4 MR-Integrated Proton Therapy 28 2.4.1 Aims of this Thesis 32 3 Magnetic Field-Induced Beam Deflection and Bragg Peak Displacement 35 3.1 Analytical Description 36 3.1.1 Review of Analytical Models 36 3.1.2 New Model Formulation 41 3.1.3 Evaluation of Analytical and Numerical Models 44 3.1.4 Discussion 51 3.2 Monte Carlo Simulation and Experimental Verification 54 3.2.1 Verification Setup 54 3.2.2 Monte Carlo Simulation 56 3.2.3 Experimental Verification 60 3.2.4 Discussion 61 3.3 Summary 63 4 Integrated In-Beam MR System: Proof of Concept 65 4.1 Integration of a Low-Field MR Scanner and a Static Research Beamline 65 4.1.1 Proton Therapy System 66 4.1.2 MR Scanner 66 4.1.3 Potential Sources of Interference 67 4.1.4 Integration of Both Systems 68 4.2 Beam and Image Quality in the Integrated Setup 70 4.2.1 Beam Profile 70 4.2.2 MR Magnetic Field Homogeneity 72 4.2.3 MR Image Quality - Qualitative In Vivo and Ex Vivo Test 74 4.2.4 MR Image Quality - Quantitative Phantom Tests 77 4.3 Feasibility of MRI-based Range Verification 86 4.3.1 MR Sequences 86 4.3.2 Proton Beam Parameters 88 4.3.3 Target Material Dependence 91 4.3.4 Discussion 92 4.4 Summary 96 5 Discussion and Future Perspectives 99 6 Summary/Zusammenfassung 105 6.1 Summary 105 6.2 Zusammenfassung 108 Bibliography I Supplementary Information XXIX A Beam Deflection: Experimental Measurements XXIX A.1 Setup XXIX A.2 Film Handling and Evaluation XXX A.3 Uncertainty Estimation XXX B Beam Deflection: Monte Carlo Simulations XXXIII B.1 Magnetic Field Model XXXIII B.2 Uncertainty Estimation XXXIV C Integrated MRiPT Setup XXXVI C.1 Magnetic Field Map XXXVI C.2 Sequence Parameters XXXVI C.3 Image Quality Parameters XLII C.4 Range Verification Sequences XLI