Abstract Angiography is critical for visualizing cerebral blood flow in intracranial steno-occlusive diseases. Current 4D magnetic resonance angiography (MRA) techniques primarily focus on macrovascular structures, yet few have quantified hemodynamic timing. This study introduces a novel model to estimate macrovascular arterial transit time (mATT) derived from arterial spin labeling (ASL)-based 4D-MRA. We provide examples of our method that visualize mATT differences in patients with intracranial steno-occlusive disease (moyamoya and atherosclerosis) and changes in mATT resulting from the cerebrovascular reactivity response to an acetazolamide (ACZ) injection. Furthermore, we present a method that projects sparse arterial signals into a 3D native brain-region atlas space and correlate regional mATT with other hemodynamic parameters of interest such as tissue transit time and cerebrovascular reactivity. This approach offers a non-invasive, quantitative assessment of macrovascular dynamics, with potential to enhance understanding of large-vessel and tissue-level hemodynamics and augment monitoring of treatment outcomes in steno-occlusive disease patients. Furthermore, it sets the stage for more in-depth investigations of the macrovascular contribution to brain hemodynamics.
Objectives The objective of this study was to evaluate the use of dielectric pads for improving high spatial resolution imaging of the inner ear at 7 T. Materials and Methods Two sets of dielectric pads were designed using electromagnetic simulations and implemented using a deuterated suspension of barium titanate. Their effect on transmit efficiency, contrast homogeneity, and diagnostic image quality was evaluated in vivo (N = 10). In addition, their effect on the specific absorption rate was evaluated numerically. Results Statistically significant improvements (P < 0.001) in several measures of the image quality were obtained by using dielectric pads. The dielectric pads lead to an increase in the transmit efficiency and uniformity at the location of the inner ear, which is reflected in both an increased contrast homogeneity and an increased diagnostic value. Simulations show that the dielectric pads do not increase the peak local specific absorption rate. Conclusions Using geometrically tailored dielectric pads enables high spatial resolution magnetic resonance imaging of the human inner ear at 7 T. The high spatial resolution improves the depiction of the fine inner ear structures, showing the benefit of magnetic resonance imaging at ultrahigh fields.
This literature review presents a comprehensive overview of machine learning (ML) applications in proton magnetic resonance spectroscopy (MRS). As the use of ML techniques in MRS continues to grow, this review aims to provide the MRS community with a structured overview of the state-of-the-art methods. Specifically, we examine and summarize studies published between 2017 and 2023 from major journals in the magnetic resonance field. We categorize these studies based on a typical MRS workflow, including data acquisition, processing, analysis, and artificial data generation. Our review reveals that ML in MRS is still in its early stages, with a primary focus on processing and analysis techniques, and less attention given to data acquisition. We also found that many studies use similar model architectures, with little comparison to alternative architectures. Additionally, the generation of artificial data is a crucial topic, with no consistent method for its generation. Furthermore, many studies demonstrate that artificial data suffers from generalization issues when tested on in-vivo data. We also conclude that risks related to ML models should be addressed, particularly for clinical applications. Therefore, output uncertainty measures and model biases are critical to investigate. Nonetheless, the rapid development of ML in MRS and the promising results from the reviewed studies justify further research in this field.
Initial 7T Clinical Cardiovascular MR imaging results are presented.Although there are many basic problems that have to be resolved, 7T cardiovascular MRI has high potential for advanced imaging.Clinical practice has to prove what the specific advantages are of highfield cardiovascular MR imaging.
Functional magnetic resonance imaging (fMRI) enables sites of brain activation to be localized in human subjects. For auditory system studies, however, the acoustic noise generated by the scanner tends to interfere with the assessments of this activation. Understanding and modeling fMRI acoustic noise is a useful step to its reduction. To study acoustic noise, the MR scanner is modeled as a linear electroacoustical system generating sound pressure signals proportional to the time derivative of the input gradient currents. The transfer function of one MR scanner is determined for two different input specifications: 1) by using the gradient waveform calculated by the scanner software and 2) by using a recording of the gradient current. Up to 4 kHz, the first method is shown as reliable as the second one, and its use is encouraged when direct measurements of gradient currents are not possible. Additionally, the linear order and average damping properties of the gradient coil system are determined by impulse response analysis. Since fMRI is often based on echo planar imaging (EPI) sequences, a useful validation of the transfer function prediction ability can be obtained by calculating the acoustic output for the EPI sequence. We found a predicted sound pressure level (SPL) for the EPI sequence of 104 dB SPL compared to a measured value of 102 dB SPL. As yet, the predicted EPI pressure waveform shows similarity as well as some differences with the directly measured EPI pressure waveform.
Abstract Purpose Uveal melanoma with a bad prognosis contain high numbers of infiltrating macrophages, especially of the M2 phenotype, and different subsets of lymphocytes. The aim of this study is to determine the presence of inflammatory cells in uveal melanoma‐containing eyes enucleated after different types of irradiation, i.e. ruthenium‐106 brachytherapy, sandwich therapy, or proton beam irradiation. Methods We analyzed 46 eyes enucleated due to tumor recurrence, non‐responsiveness, or complications after irradiation. Immunofluorescence staining was performed to determine the presence of CD68+ and CD68+CD163+macrophages, CD3+, CD8+ and Foxp3+ regulatory T lymphocytes. Outcomes were compared with known clinical and histological prognostic parameters. Results Numbers of CD68+ and CD68+CD163+ macrophages in secondarily‐enucleated eyes varied widely, but was not related to the reason for enucleation. The median of CD3, CD8, FoxP3+ lymphocyte counts was 55, 99 and 9 cells/mm2, respectively. When compared to primarily‐enucleated eyes, the lymphocytic infiltration was significantly (p<.02) higher in irradiated eyes. Conclusion Numbers of T‐lymphocytes and macrophages varied widely. Irradiation has no clear effect on the number and type of macrophages in uveal melanoma. However, there were higher numbers of lymphocytes in previously irradiated uveal melanoma.
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