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This thesis contributes to our knowledge of how MRI can be used to identify markers for Parkinson's disease. The research in this thesis demonstrates that changes in certain parts of the brain, like the white matter and default mode network, play a crucial role in causing cognitive issues in individuals with Parkinson's. Additionally, the use of advanced MRI technology known as ultra-high field MRI is explored. This technology allows us to examine small brain regions that are difficult to detect on standard MRI scans. The thesis includes a description of a new study protocol using ultra-high field MRI, which enables us to investigate Parkinson's disease in more depth over a longer period of time. It is expected that this study will help provide answers to many more research questions regarding the use of MRI in Parkinson's disease in the near future. It was already shown that there is potential for using specific brainstem regions to differentiate between Parkinson's patients and healthy individuals.

Resting-state (rs) functional magnetic resonance imaging (fMRI) is used to detect low-frequency fluctuations in the blood oxygen-level dependent (BOLD) signal across brain regions. Correlations between temporal BOLD signal fluctuations are commonly used to infer functional connectivity. However, because BOLD is based on the dilution of deoxyhemoglobin, it is sensitive to veins of all sizes, and its amplitude is biased by draining veins. These biases affect local BOLD signal location and amplitude, and may also influence BOLD-derived connectivity measures, but the magnitude of this venous bias and its relation to vein size and proximity is unknown. Here, veins were identified using high-resolution quantitative susceptibility maps and utilized in a biophysical model to investigate systematic venous biases on common local rsfMRI-derived measures. Specifically, we studied the impact of vein diameter and distance to veins on the amplitude of low-frequency fluctuations (ALFF), fractional ALFF (fALFF), Hurst exponent (HE), regional homogeneity (ReHo), and eigenvector centrality values in the grey matter. Values were higher across all distances in smaller veins, and decreased with increasing vein diameter. Additionally, rsfMRI values associated with larger veins decrease with increasing distance from the veins. ALFF and ReHo were the most biased by veins, while HE and fALFF exhibited the smallest bias. Across all metrics, the amplitude of the bias was limited in voxel-wise data, confirming that venous structure is not the dominant source of contrast in these rsfMRI metrics. Finally, the models presented can be used to correct this venous bias in rsfMRI metrics.

The main goal of this methodological thesis was to present optimised magnetic resonance imaging (MRI) sequences for ex vivo and in vivo studies in ultra-high field scanners (UHF, from 7 T and above, beyond the conventional 1.5 or even 3 T available in the clinics). The researchers mainly worked with the STEAM sequence, which overcame several of its restrictions in these scanners. It resulted in ultra-high resolution whole-brain MRI data for ex vivo studies (achieving 400 μm , or 0.4 mm, isotropic resolution), and very highly accelerated acquisition protocols for in vivo studies (up to x 54 times the current total possible acceleration). With the current feasibility of acquiring ultra-high resolution data and highly sampled multi-contrast MRI images, data-expensive signal models can be employed; but above all, the biological microstructure features in the brain can be easily more revealed from the resulted analysis.

Patients with a glioblastoma (GBM), the most aggressive type of brain tumor, are presented with a dismal prognosis. In this thesis, several innovations in the diagnosis and treatment of GBM are investigated. Part I considers methods to monitor and predict treatment response which can be included into clinical decision support systems such as a CT radiomics signature, which are developed in order to aid physicians and patients to choose an optimal treatment strategy. Part II discusses relevant technical aspects of 7 Tesla MRI for GBM and the necessary steps to integrate this into radiation treatment planning. In Part III treatment aspects, specifically the safety of autophagy inhibition through the addition of chloroquine to chemoradiation for GBM in a phase Ib trial, are discussed. A daily dose of 200 mg chloroquine was determined as the maximum tolerated dose when combined with radiotherapy and concurrent temozolomide. EGFRvIII was identified as a potential predictive biomarker.

Patients with a glioblastoma (GBM), the most aggressive type of brain tumor, are presented with a dismal prognosis. In this thesis, several innovations in the diagnosis and treatment of GBM are investigated. Part I considers methods to monitor and predict treatment response which can be included into clinical decision support systems such as a CT radiomics signature, which are developed in order to aid physicians and patients to choose an optimal treatment strategy. Part II discusses relevant technical aspects of 7 Tesla MRI for GBM and the necessary steps to integrate this into radiation treatment planning. In Part III treatment aspects, specifically the safety of autophagy inhibition through the addition of chloroquine to chemoradiation for GBM in a phase Ib trial, are discussed. A daily dose of 200 mg chloroquine was determined as the maximum tolerated dose when combined with radiotherapy and concurrent temozolomide. EGFRvIII was identified as a potential predictive biomarker.

Background: Cortical lesions are abundant in multiple sclerosis (MS), yet difficult to visualize in vivo. Ultra-high field (UHF) MRI at 7 T and above provides technological advances suited to optimize the detection of cortical lesions in MS. Purpose: To provide a narrative and quantitative systematic review of the literature on UHF MRI of cortical lesions in MS. Methods: A systematic search of all literature on UHF MRI of cortical lesions in MS published before September 2020. Quantitative outcome measures included cortical lesion numbers reported using 3 T and 7 T MRI and between 7 T MRI sequences, along with sensitivity of UHF MRI towards cortical lesions verified by histopathology. Results: 7 T MRI detected on average 52 ± 26% (mean ± 95% confidence interval) more cortical lesions than the best performing image contrast at 3 T, with the largest increase in type II-IV intracortical lesion detection. Across all studies, the mean cortical lesion number was 17 ± 6 per patient. In progressive MS cohorts, approximately four times more cortical lesions were reported than in CIS/early RRMS, and RRMS. Yet, there was no difference in lesion type ratio between these MS subtypes. Furthermore, superiority of one MRI sequence over another could not be established from available data. Post-mortem lesion detection with UHF MRI agreed only modestly with pathological examinations. Mean pro- and retrospective sensitivity was 33 ± 6% and 71 ± 10%, respectively, with the highest sensitivity towards type I and type IV lesions. Conclusion: UHF MRI improves cortical lesion detection in MS considerably compared to 3 T MRI, particularly for type II-IV lesions. Despite modest sensitivity, 7 T MRI is still capable of visualizing all aspects of cortical lesion pathology and could potentially aid clinicians in diagnosing and monitoring MS, and progressive MS in particular. However, standardization of acquisition and segmentation protocols is needed.

Background: Cortical lesions are abundant in multiple sclerosis (MS), yet difficult to visualize in vivo. Ultra-high field (UHF) MRI at 7 T and above provides technological advances suited to optimize the detection of cortical lesions in MS. Purpose: To provide a narrative and quantitative systematic review of the literature on UHF MRI of cortical lesions in MS. Methods: A systematic search of all literature on UHF MRI of cortical lesions in MS published before September 2020. Quantitative outcome measures included cortical lesion numbers reported using 3 T and 7 T MRI and between 7 T MRI sequences, along with sensitivity of UHF MRI towards cortical lesions verified by histopathology. Results: 7 T MRI detected on average 52 ± 26% (mean ± 95% confidence interval) more cortical lesions than the best performing image contrast at 3 T, with the largest increase in type II-IV intracortical lesion detection. Across all studies, the mean cortical lesion number was 17 ± 6 per patient. In progressive MS cohorts, approximately four times more cortical lesions were reported than in CIS/early RRMS, and RRMS. Yet, there was no difference in lesion type ratio between these MS subtypes. Furthermore, superiority of one MRI sequence over another could not be established from available data. Post-mortem lesion detection with UHF MRI agreed only modestly with pathological examinations. Mean pro- and retrospective sensitivity was 33 ± 6% and 71 ± 10%, respectively, with the highest sensitivity towards type I and type IV lesions. Conclusion: UHF MRI improves cortical lesion detection in MS considerably compared to 3 T MRI, particularly for type II-IV lesions. Despite modest sensitivity, 7 T MRI is still capable of visualizing all aspects of cortical lesion pathology and could potentially aid clinicians in diagnosing and monitoring MS, and progressive MS in particular. However, standardization of acquisition and segmentation protocols is needed.

Post mortem magnetic resonance imaging (MRI) studies on the human brain are of great interest for the validation of in vivo MRI. It facilitates a link between functional and anatomical information available from MRI in vivo and neuroanatomical knowledge available from histology/immunocytochemistry. However, linking in vivo and post mortem MRI to microscopy techniques poses substantial challenges. Fixation artifacts and tissue deformation of extracted brains, as well as co registration of 2D histology to 3D MRI volumes complicate direct comparison between modalities. Moreover, post mortem brain tissue does not have the same physical properties as in vivo tissue, and therefore MRI approaches need to be adjusted accordingly. Here, we present a pipeline in which whole-brain human post mortem in situ MRI is combined with subsequent tissue processing of the whole human brain, providing a 3-dimensional reconstruction via blockface imaging. To this end, we adapted tissue processing procedures to allow both post mortem MRI and subsequent histological and immunocytochemical processing. For MRI, tissue was packed in a susceptibility matched solution, tailored to fit the dimensions of the MRI coil. Additionally, MRI sequence parameters were adjusted to accommodate T1 and T2∗ shortening, and scan time was extended, thereby benefiting the signal-to-noise-ratio that can be achieved using extensive averaging without motion artifacts. After MRI, the brain was extracted from the skull and subsequently cut while performing optimized blockface imaging, thereby allowing three-dimensional reconstructions. Tissues were processed for Nissl and silver staining, and co-registered with the blockface images. The combination of these techniques allows direct comparisons across modalities.

Multiple sclerosis (MS) is an autoimmune disorder of the brain and spinal cord, and the most common cause of neurological disability in young adults. The presentation of MS is highly heterogeneous with an unknown aetiology and no known cure, presenting as inflammation, demyelination and axonal injury/loss. MS pathology is disseminated throughout the central nervous system leading to a broad range of symptoms including cognitive dysfunctions, bowel and bladder problems, fatigue, sensory disturbances and difficulties with walking and balance. Up to 90% of people with MS experience motor impairments that significantly worsen with increasing disease severity, and which can affect both the upper and lower limbs. Motor impairments are often highly debilitating, ranging from muscle weakness, coordination loss, tremors to spasticity. However, while the pathophysiological mechanisms underpinning motor impairments in MS have been widely studied, they are not currently well understood. This is particularly true for early disease, a time when personalised treatment strategies can be formulated and will have maximal effect, preventing future deterioration and accumulation of disability. Consequently, there is an urgent need to understand the pathophysiology underlying motor impairments in MS and elucidate the microstructural and functional changes that occur at their earliest manifestation. To this end, we investigated the pathophysiology of motor impairments associated with dexterity and mobility in people with MS using advanced magnetic resonance imaging (MRI). Our investigations included functional resting-state (Chapters 2.1 and 2.2) and task (Chapter 3.1) MRI, diffusion weighted imaging (Chapter 3.2) and ultra-high field MRI (Chapters 3.1 and 3.2). Our findings consistently demonstrated a clear link between the development of motor impairments and alterations in the structure/function of the sensorimotor system, a system responsible for the integration of sensory informatio

Purpose In neuro-oncology, 3 Tesla (3T) MRI is the current clinical standard for tumor localization, radiotherapy volume delineation and stereotactic (radio)surgery. With superior SNR and image resolution, anatomical 7T MRI can visualize micro-vascularization in glioblastomas potentially allowing improved target volume delineation. However, concerns regarding geometrical distortion (GD) with increasing field strength (B0) are detrimental for applications of 7T MRI in image-guided interventions. For high-precision treatment strategies, the spatial integrity of anatomical images needs to be warranted within ±1 mm. The aim of the study was to evaluate B0- and sequence-related GD in clinically relevant 7T pulse sequences and compare it to equivalent 3T sequences, and CT images. Material & Methods To quantify B0- and sequence-related GD in T1-GRE, T1-TFE, T2-TSE, T2-TSE FLAIR on 7T pulse sequences, a dedicated anthropomorphic head-phantom (CIRS Model 603A) was used. The phantom is composed of bone- /soft-tissue equivalent materials and contains a rigid 3D grid (3 mm rods spaced 15 mm apart). System-based distortion correction methods were applied to restore the gradient uniformity for 3T and 7T. For all CT and MR images, 436 points of interests (POIs) were defined by manual reconstruction of the 3D grid points in the respective images. GD was assessed in 3 ways. Firstly, global GD was estimated by the mean absolute difference (MADglobal) between the measured and the true Euclidian distances of all unique combinations of POIs, independent of location within the phantom. Secondly, local GD was estimated by MADlocal between the measured and the true Euclidian distances of all POIs relative to the magnetic field isocenter. Thirdly, a distortion map was created by evaluating 3D displacement vectors for each individual grid point. Results MADglobal in 3T and 7T images ranged from 0.19−0.75 mm and 0.27−1.91 mm, respectively, and was more pronounced than in CT images. CT was not

The recent introduction of advanced magnetic resonance (MR) imaging techniques to characterize focal and global degeneration in multiple sclerosis (MS), like the Composite Hindered and Restricted Model of Diffusion, or CHARMED, diffusional kurtosis imaging (DKI) and Neurite Orientation Dispersion and Density Imaging (NODDI) made available new tools to image axonal pathology non-invasively in vivo. These methods already showed greater sensitivity and specificity compared to conventional diffusion tensor-based metrics (e.g., fractional anisotropy), overcoming some of its limitations. While previous studies uncovered global and focal axonal degeneration in MS patients compared to healthy controls, here our aim is to investigate and compare different diffusion MRI acquisition protocols in their ability to highlight microstructural differences between MS and control tissue over several much used models. For comparison, we contrasted the ability of fractional anisotropy measurements to uncover differences between lesion, normal-appearing white matter (WM), gray matter and healthy tissue under the same imaging protocols. We show that: (1) focal and diffuse differences in several microstructural parameters are observed under clinical settings; (2) advanced models (CHARMED, DKI and NODDI) have increased specificity and sensitivity to neurodegeneration when compared to fractional anisotropy measurements; and (3) both high (3 T) and ultra-high fields (7 T) are viable options for imaging tissue change in MS lesions and normal appearing WM, while higher b-values are less beneficial under the tested short-time (10 min acquisition) conditions.

OBJECTIVES: The use of 7 Tesla (T) magnetic resonance imaging (MRI) has recently shown great potential for high-resolution soft-tissue neuroimaging and visualization of microvascularization in glioblastoma (GBM). We have designed a clinical trial to explore the value of 7 T MRI in radiation treatment of GBM. For this aim we performed a preparatory study to investigate the technical feasibility of incorporating 7 T MR images into the neurosurgical navigation and radiotherapy treatment planning (RTP) systems via qualitative and quantitative assessment of the image quality.MATERIALS AND METHODS: The MR images were acquired with a Siemens Magnetom 7 T whole-body scanner and a Nova Medical 32-channel head coil. The 7 T MRI pulse sequences included magnetization-prepared two rapid acquisition gradient echoes (MP2RAGE), T2-SPACE, SPACE-FLAIR and gradient echo sequences (GRE). A pilot study with three healthy volunteers and an anthropomorphic 3D phantom was used to assess image quality and geometrical image accuracy.RESULTS: The MRI scans were well tolerated by the volunteers. Susceptibility artefacts were observed in both the cortex and subcortical white matter at close proximity to air-tissue interfaces. Regional loss of signal and contrast could be minimized by the use of dielectric pads. Image transfer and processing did not degrade image quality. The system-related spatial uncertainty of geometrical distortion-corrected MP2RAGE pulse sequences was ≤2 mm.CONCLUSION: Integration of high-quality and geometrically-reliable 7 T MR images into neurosurgical navigation and RTP software is technically feasible and safe.

Recently, several magnetic resonance imaging contrast mechanisms have been shown to distinguish cortical substructure corresponding to selected cortical layers. Here, we investigate cortical layer and area differentiation by automatized unsupervised clustering of high-resolution diffusion MRI data. Several groups of adjacent layers could be distinguished in human primary motor and premotor cortex. We then used the signature of diffusion MRI signals along cortical depth as a criterion to detect area boundaries and find borders at which the signature changes abruptly. We validate our clustering results by histological analysis of the same tissue. These results confirm earlier studies which show that diffusion MRI can probe layer-specific intracortical fiber organization and, moreover, suggests that it contains enough information to automatically classify architecturally distinct cortical areas. We discuss the strengths and weaknesses of the automatic clustering approach and its appeal for MR-based cortical histology.

Introduction: The subthalamic nucleus, substantia nigra, and globus pallidus, three nuclei of the human basal ganglia, play an important role in motor, associative, and limbic processing. The network of the basal ganglia is generally characterized by a direct, indirect, and hyperdirect pathway. This study aims to investigate the mesoscopic nature of these connections between the subthalamic nucleus, substantia nigra, and globus pallidus and their surrounding structures. Methods: A human post mortem brain specimen including the substantia nigra, subthalamic nucleus, and globus pallidus was scanned on a 7 T MRI scanner. High resolution diffusion weighted images were used to reconstruct the fibers intersecting the substantia nigra, subthalamic nucleus, and globus pallidus. The course and density of these tracks was analyzed. Results: Most of the commonly established projections of the subthalamic nucleus, substantia nigra, and globus pallidus were successfully reconstructed. However, some of the reconstructed fiber tracks such as the connections of the substantia nigra pars compacta to the other included nuclei and the connections with the anterior commissure have not been shown previously. In addition, the quantitative tractography approach showed a typical degree of connectivity previously not documented. An example is the relatively larger projections of the subthalamic nucleus to the substantia nigra pars reticulata when compared to the projections to the globus pallidus internus. Discussion: This study shows that ultra-high field post mortem tractography allows for detailed 3D reconstruction of the projections of deep brain structures in humans. Although the results should be interpreted carefully, the newly identified connections contribute to our understanding of the basal ganglia.

Interindividual differences play a crucial role in research on mental imagery. The inherently private nature of imagery does not allow for the same experimental control that is possible in perception research. Even when there are precise instructions subjects will differ in their particular imagery strategy and, hence, show different brain activations. Here, we show results of a time-resolved searchlight analysis for 12 individual subjects who perform a visual motion imagery task. The data show the spatial and temporal extent of brain areas and time windows that allow for a successful decoding of the direction of imagined motion out of four options. Accuracy maps for six different time windows are shown for every individual subject and are made freely available on NeuroVault. These data accompany the findings in the publication "Decoding the direction of imagined visual motion using 7 T ultra-high field fMRI" (Emmerling et al., 2016) [1].

Objectives: The use of 7 Tesla (T) magnetic resonance imaging (MRI) has recently shown great potential for high-resolution soft-tissue neuroimaging and visualization of microvascularization in glioblastoma (GBM). We have designed a clinical trial to explore the value of 7 T MRI in radiation treatment of GBM. For this aim we performed a preparatory study to investigate the technical feasibility of incorporating 7 T MR images into the neurosurgical navigation and radiotherapy treatment planning (RTP) systems via qualitative and quantitative assessment of the image quality. Materials and methods: The MR images were acquired with a Siemens Magnetom 7 T whole-body scanner and a Nova Medical 32-channel head coil. The 7 T MRI pulse sequences included magnetization-prepared two rapid acquisition gradient echoes (MP2RAGE), T2-SPACE, SPACE-FLAIR and gradient echo sequences (GRE). A pilot study with three healthy volunteers and an anthropomorphic 3D phantom was used to assess image quality and geometrical image accuracy. Results: The MRI scans were well tolerated by the volunteers. Susceptibility artefacts were observed in both the cortex and subcortical white matter at close proximity to air-tissue interfaces. Regional loss of signal and contrast could be minimized by the use of dielectric pads. Image transfer and processing did not degrade image quality. The system-related spatial uncertainty of geometrical distortion-corrected MP2RAGE pulse sequences was ≤2 mm. Conclusion: Integration of high-quality and geometrically-reliable 7 T MR images into neurosurgical navigation and RTP software is technically feasible and safe.

Recently, several magnetic resonance imaging contrast mechanisms have been shown to distinguish cortical substructure corresponding to selected cortical layers. Here, we investigate cortical layer and area differentiation by automatized unsupervised clustering of high-resolution diffusion MRI data. Several groups of adjacent layers could be distinguished in human primary motor and premotor cortex. We then used the signature of diffusion MRI signals along cortical depth as a criterion to detect area boundaries and find borders at which the signature changes abruptly. We validate our clustering results by histological analysis of the same tissue. These results confirm earlier studies which show that diffusion MRI can probe layer-specific intracortical fiber organization and, moreover, suggests that it contains enough information to automatically classify architecturally distinct cortical areas. We discuss the strengths and weaknesses of the automatic clustering approach and its appeal for MR-based cortical histology.

Introduction: The subthalamic nucleus, substantia nigra, and globus pallidus, three nuclei of the human basal ganglia, play an important role in motor, associative, and limbic processing. The network of the basal ganglia is generally characterized by a direct, indirect, and hyperdirect pathway. This study aims to investigate the mesoscopic nature of these connections between the subthalamic nucleus, substantia nigra, and globus pallidus and their surrounding structures. Methods: A human post mortem brain specimen including the substantia nigra, subthalamic nucleus, and globus pallidus was scanned on a 7 T MRI scanner. High resolution diffusion weighted images were used to reconstruct the fibers intersecting the substantia nigra, subthalamic nucleus, and globus pallidus. The course and density of these tracks was analyzed. Results: Most of the commonly established projections of the subthalamic nucleus, substantia nigra, and globus pallidus were successfully reconstructed. However, some of the reconstructed fiber tracks such as the connections of the substantia nigra pars compacta to the other included nuclei and the connections with the anterior commissure have not been shown previously. In addition, the quantitative tractography approach showed a typical degree of connectivity previously not documented. An example is the relatively larger projections of the subthalamic nucleus to the substantia nigra pars reticulata when compared to the projections to the globus pallidus internus. Discussion: This study shows that ultra-high field post mortem tractography allows for detailed 3D reconstruction of the projections of deep brain structures in humans. Although the results should be interpreted carefully, the newly identified connections contribute to our understanding of the basal ganglia.

OBJECTIVES: The use of 7 Tesla (T) magnetic resonance imaging (MRI) has recently shown great potential for high-resolution soft-tissue neuroimaging and visualization of microvascularization in glioblastoma (GBM). We have designed a clinical trial to explore the value of 7 T MRI in radiation treatment of GBM. For this aim we performed a preparatory study to investigate the technical feasibility of incorporating 7 T MR images into the neurosurgical navigation and radiotherapy treatment planning (RTP) systems via qualitative and quantitative assessment of the image quality.MATERIALS AND METHODS: The MR images were acquired with a Siemens Magnetom 7 T whole-body scanner and a Nova Medical 32-channel head coil. The 7 T MRI pulse sequences included magnetization-prepared two rapid acquisition gradient echoes (MP2RAGE), T2-SPACE, SPACE-FLAIR and gradient echo sequences (GRE). A pilot study with three healthy volunteers and an anthropomorphic 3D phantom was used to assess image quality and geometrical image accuracy.RESULTS: The MRI scans were well tolerated by the volunteers. Susceptibility artefacts were observed in both the cortex and subcortical white matter at close proximity to air-tissue interfaces. Regional loss of signal and contrast could be minimized by the use of dielectric pads. Image transfer and processing did not degrade image quality. The system-related spatial uncertainty of geometrical distortion-corrected MP2RAGE pulse sequences was ≤2 mm.CONCLUSION: Integration of high-quality and geometrically-reliable 7 T MR images into neurosurgical navigation and RTP software is technically feasible and safe.

Interindividual differences play a crucial role in research on mental imagery. The inherently private nature of imagery does not allow for the same experimental control that is possible in perception research. Even when there are precise instructions subjects will differ in their particular imagery strategy and, hence, show different brain activations. Here, we show results of a time-resolved searchlight analysis for 12 individual subjects who perform a visual motion imagery task. The data show the spatial and temporal extent of brain areas and time windows that allow for a successful decoding of the direction of imagined motion out of four options. Accuracy maps for six different time windows are shown for every individual subject and are made freely available on NeuroVault. These data accompany the findings in the publication "Decoding the direction of imagined visual motion using 7 T ultra-high field fMRI" (Emmerling et al., 2016) [1].

Ultra-high ?eld prostate MR imaging (?7T) becomes increasingly difficult due to insufficient radio frequency ?eld excitation penetration. RF coils used at ultra-high ?elds are adapted from lower ?eld strengths but their performance is suboptimal. These coils are designed as near-?eld antennas; however, better signal penetration can be obtained using far-?eld concept, speci?cally in the case of prostate which is located deep in the body. In this project the optimization of an RF coil for prostate imaging at 7T Magnetic Resonance system is investigated. This RF coil was designed following far-?eld-based concept recently proposed by Raaijmakers et al., who has demonstrated that higher transmit B1+ at depth can be obtained; thus increasing the transmit performance necessary to acquire good images. The RF coil consists of a fractionated dipole antenna mounted on an acrylic substrate, and it is used as part of a surface array. The optimization is evaluated in terms of safety (local SAR), transmit performance (B1+), and coupling measurements. A parameters study was performed to improve the performance of the RF coil. Numerical simulations were used to evaluate new designs obtained from the parameters study. From the simulated results, three designs were constructed for validation purposes. Two different measurements were performed to validate the simulations: B1 measurements in the 7 Tesla MR scanner and coupling measurements with a network analyzer; these measurements were performed on a phantom with tissue electrical properties. Finally, an in vivo measurement using two identical sinusoidal-shaped snake antennas (s20) aligned on the pelvis was performed to image a healthy prostate. Both, simulations and measurements in the snake antennas demonstrated that despite the improvement gained in safety with lower levels of SAR, the radiation ?eld penetration pattern is less homogeneous affecting the imaging process. Therefore, these antennas might show more efficiency imaging r, Biomedical Engineering, Mechanical, Maritime and Materials Engineering

Ultra-high ?eld prostate MR imaging (?7T) becomes increasingly difficult due to insufficient radio frequency ?eld excitation penetration. RF coils used at ultra-high ?elds are adapted from lower ?eld strengths but their performance is suboptimal. These coils are designed as near-?eld antennas; however, better signal penetration can be obtained using far-?eld concept, speci?cally in the case of prostate which is located deep in the body. In this project the optimization of an RF coil for prostate imaging at 7T Magnetic Resonance system is investigated. This RF coil was designed following far-?eld-based concept recently proposed by Raaijmakers et al., who has demonstrated that higher transmit B1+ at depth can be obtained; thus increasing the transmit performance necessary to acquire good images. The RF coil consists of a fractionated dipole antenna mounted on an acrylic substrate, and it is used as part of a surface array. The optimization is evaluated in terms of safety (local SAR), transmit performance (B1+), and coupling measurements. A parameters study was performed to improve the performance of the RF coil. Numerical simulations were used to evaluate new designs obtained from the parameters study. From the simulated results, three designs were constructed for validation purposes. Two different measurements were performed to validate the simulations: B1 measurements in the 7 Tesla MR scanner and coupling measurements with a network analyzer; these measurements were performed on a phantom with tissue electrical properties. Finally, an in vivo measurement using two identical sinusoidal-shaped snake antennas (s20) aligned on the pelvis was performed to image a healthy prostate. Both, simulations and measurements in the snake antennas demonstrated that despite the improvement gained in safety with lower levels of SAR, the radiation ?eld penetration pattern is less homogeneous affecting the imaging process. Therefore, these antennas might show more efficiency imaging r, Biomedical Engineering, Biomedical Engineering, Mechanical, Maritime and Materials Engineering