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Publications
Publications (511)
Background
Metasurface coils (MCs) are a promising magnetic resonance imaging (MRI) technology. Aiming to evaluate the image quality of MCs for knee and elbow imaging, we compared signal-to-noise ratio (SNRs) obtained in standard clinical setups.
Methods
Knee and elbow MRI routine sequences were applied at 1.5 T, implementing four coil scenarios:...
Background
The success of embolization, a minimally invasive treatment of liver cancer, could be evaluated in the operational room with cone‐beam CT by acquiring a dynamic perfusion scan to inspect the contrast agent flow.
Purpose
The reconstruction algorithm must address the issues of low temporal sampling and higher noise levels inherent in cone...
Background
Alzheimer’s Disease (AD), a progressively worsening neurodegenerative disorder, impacts millions globally. Understanding its progression is crucial for developing effective interventions and management strategies. However, high variability in disease progression amongst individuals and the complexity of neuroimaging data pose significant...
Objectives
The shape is commonly used to describe the objects. State-of-the-art algorithms in medical imaging are predominantly diverging from computer vision, where voxel grids, meshes, point clouds, and implicit surface models are used. This is seen from the growing popularity of ShapeNet (51,300 models) and Princeton ModelNet (127,915 models). H...
The success of embolisation, a minimally invasive treatment of liver cancer, could be evaluated in the operational room with cone-beam CT by acquiring a dynamic perfusion scan. The reconstruction algorithm must address the issues of low temporal sampling and higher noise levels inherent in cone-beam CT systems, compared to conventional CT. Therefor...
The human brain receives nutrients and oxygen through an intricate network of blood vessels. Pathology affecting small vessels, at the mesoscopic scale, represents a critical vulnerability within the cerebral blood supply and can lead to severe conditions, such as Cerebral Small Vessel Diseases. The advent of 7 Tesla MRI systems has enabled the acq...
Magnetic resonance angiography (MRA) performed at ultra-high magnetic field provides a unique opportunity to study the arteries of the living human brain at the mesoscopic level. From this, we can gain new insights into the brain's blood supply and vascular disease affecting small vessels. However, for quantitative characterization and precise repr...
High-spatial resolution MRI produces abundant structural information, enabling highly accurate clinical diagnosis and image-guided therapeutics. However, the acquisition of high-spatial resolution MRI data typically can come at the expense of less spatial coverage, lower signal-to-noise ratio (SNR), and longer scan time due to physical, physiologic...
Zusammenfassung
Kardiovaskuläre Risikofaktoren (Bluthochdruck, Rauchen, Übergewicht, Diabetes mellitus Typ 2, Dyslipidämie, körperliche Inaktivität) steigen mit zunehmendem Alter, insbesondere ab dem mittleren Erwachsenenalter, deutlich an, wobei Frauen wesentlich stärker betroffen sind. In der Bevölkerung Sachsen-Anhalts ist die Prävalenz kardiova...
Identification of vessel structures of different sizes in biomedical images is crucial in the diagnosis of many neurodegenerative diseases. However, the sparsity of good-quality annotations of such images makes the task of vessel segmentation challenging. Deep learning offers an efficient way to segment vessels of different sizes by learning their...
Wireless MR imaging is feasible by the use of meta-surfaces. This work investigates the influence of the MRI's static magnetic field on the enhancement performance of a metasurface. At 0.55 Tesla (0.55 T) superior receive enhancement was obtained, being 5-times greater compared to 3 T. This indicates the added value of metasurface developments for...
The present study investigated the neuromodulatory substrates of salience processing and its impact on memory encoding and behaviour, with a specific focus on two distinct types of salience: reward and contextual unexpectedness. 46 participants performed a novel task paradigm modulating these two aspects independently and allowing for investigating...
Magnetic resonance angiography (MRA) performed at ultra-high magnetic field provides a unique opportunity to study the arteries of the living human brain at the mesoscopic level. From this, we can gain new insights into the brain's blood supply and vascular disease affecting small vessels. However, for quantitative characterization and precise repr...
Metasurface resonators can greatly increase the sensitivity of scanner-integrated coils to practically perform wireless imaging. This work experimentally evaluates the capabilities of a metasurface at field strengths of 0.55 T, 1.5 T and 3 T, receiving only with the table-integrated spine-coils. The achieved SNR enhancements beneath the metasurface...
Objective: We present a model-based image reconstruction approach based on unrolled neural networks which corrects for image distortion and noise in low-field (
$B_{0} \sim$
50mT) MRI. Methods: Utilising knowledge about the underlying physics, a novel network architecture (SH-Net) is introduced which involves the estimation of spherical harmonic c...
The outbreak of COVID-19 has shocked the entire world with its fairly rapid spread, and has challenged different sectors. One of the most effective ways to limit its spread is the early and accurate diagnosing of infected patients. Medical imaging, such as X-ray and computed tomography (CT), combined with the potential of artificial intelligence (A...
Magnetic resonance imaging (MRI) provides high spatial resolution and excellent soft-tissue contrast without using harmful ionising radiation. Dynamic MRI is an essential tool for interventions to visualise movements or changes of the target organ. However, such MRI acquisitions with high temporal resolution suffer from limited spatial resolution -...
Metasurfaces enable magnetic resonance imaging (MRI) without cables inside the bore by locally improving the sensitivity of scanner-integrated receive coils. This study systematically evaluates a novel grid design to provide signal enhancement for patient imaging. The potential of the proposed metasurface grid design was analyzed regarding its unit...
Background
The dopaminergic system plays a crucial role in modulating learning and memory and undergoes age‐related changes that contribute to neurological disorders (Volkow et al., 1998; Pan et al., 2019) and reduced cognitive maintenance in ageing (Nyberg et al., 2016). Advanced imaging techniques can assess dopaminergic function in vivo in human...
Background
Altered fluctuations in blood oxygen level dependent (BOLD) signal during resting‐state functional magnetic resonance imaging (rs‐fMRI) have been considered indicative of decreased cerebrovascular health. Previous studies reported changes in BOLD fluctuations associated with Alzheimer’s dementia (AD) and white matter hyperintensities (WM...
In the domain of medical imaging, many supervised learning based methods for segmentation face several challenges such as high variability in annotations from multiple experts, paucity of labelled data and class imbalanced datasets. These issues may result in segmentations that lack the requisite precision for clinical analysis and can be misleadin...
Background
Altered fluctuations in blood oxygen level dependent (BOLD) signal during resting‐state functional magnetic resonance imaging (rs‐fMRI) have been considered indicative of decreased cerebrovascular health. Previous studies reported changes in BOLD fluctuations associated with Alzheimer’s dementia (AD) and white matter hyperintensities (WM...
Purpose
To investigate safety and performance aspects of parallel‐transmit (pTx) RF control‐modes for a body coil at B0≤3T$$ {B}_0\le 3\mathrm{T} $$.
Methods
Electromagnetic simulations of 11 human voxel models in cardiac imaging position were conducted for B0=0.5T$$ {B}_0=0.5\mathrm{T} $$, 1.5T$$ 1.5\mathrm{T} $$ and 3T$$ 3\mathrm{T} $$ and a bod...
Metamaterial-inspired resonators have the potential to enable wireless signal enhancement in magnetic resonance imaging (MRI) [1]. This can be favourable for MR-guided interventions due to low-cost, light-weighted flexible design, and the reduction of cabling around the patient. Especially for percutaneous interventions, sterile surface resonators...
Computed tomography (CT) and magnetic resonance imaging (MRI) are two widely used clinical imaging modalities for non-invasive diagnosis. However, both of these modalities come with certain problems. CT uses harmful ionising radiation, and MRI suffers from slow acquisition speed. Both problems can be tackled by undersampling, such as sparse samplin...
High childhood emotional maltreatment (CM-EMO) is reported in mood and anxiety disorders. The associations with an increased risk for psychopathology are not fully understood. One potential factor may be through alterations in gamma-Aminobutyric acid (GABA). The pregenual anterior cingulate cortex (pgACC) is an important brain region for emotion pr...
Iterative undersampled MRI reconstructions, such as compressed sensing, can reconstruct undersampled MRIs - but due to their slow execution speed, they are not suitable for real-time applications. Several deep learning approaches have been proposed, mostly working in image space. Some of the approaches, which work on the k-space or in a mix of spac...
Disagreements among the experts while segmenting a certain region can be observed for complex segmentation tasks. Deep learning based solution Probabilistic UNet is one of the possible solutions that can learn from a given set of labels for each individual input image and then can produce multiple segmentations for each. But, this does not incorpor...
Vessel Segmentation with deep learning is a challenging task that involves not only learning high-level feature representations but also the spatial continuity of the features across dimensions. Semi-supervised patch-based approaches have been effective in identifying small vessels of 1-2 voxels in diameter but failed to maintain vessel continuity....
Image registration is the process of bringing different images into a common coordinate system - a technique widely used in various applications of computer vision, such as remote sensing, image retrieval, and, most commonly, medical imaging. Deep learning based techniques have been applied successfully to tackle various complex medical image proce...
Multiple sites within Germany operate human MRI systems with magnetic fields either at 7 Tesla or 9.4 Tesla. In 2013, these sites formed a network to facilitate and harmonize the research being conducted at the different sites and make this technology available to a larger community of researchers and clinicians not only within Germany, but also wo...
The association between cerebral blood supply and cognition has been widely discussed in the recent literature. One focus of this discussion has been the anatomical variability of the circle of Willis, with morphological differences being present in more than half of the general population. While previous studies have attempted to classify these di...
The noradrenergic locus coeruleus (LC) is one of the protein pathology epicenters in neurodegenerative diseases. In contrast to PET (positron emission tomography), MRI (magnetic resonance imaging) offers the spatial resolution necessary to investigate the 3-4 mm wide and 1.5 cm long LC. However, standard data postprocessing is often too spatially i...
Model-based reconstruction employing the time separation technique (TST) was found to improve dynamic perfusion imaging of the liver using C-arm cone-beam computed tomography (CBCT). To apply TST using prior knowledge extracted from CT perfusion data, the liver should be accurately segmented from the CT scans. Reconstructions of primary and model-b...
Ketamine shows rapid antidepressant effects peaking 24 h after administration. The antidepressant effects may occur through changes in glutamatergic metabolite levels and resting-state functional connectivity (rsFC) within the default mode network (DMN). A multistage drug effect of ketamine has been suggested, inducing acute effects on dysfunctiona...
Perfusion imaging is a valuable tool for diagnosing and treatment planning for liver tumours. The time separation technique (TST) has been successfully used for modelling C-arm cone-beam computed tomography (CBCT) perfusion data. The reconstruction can be accompanied by the segmentation of the liver - for better visualisation and for generating com...
To protect implant carriers in MRI from excessive radiofrequency heating it has previously been suggested to assess that hazard via sensors on the implant. Other work recommended parallel transmission (pTx) to actively mitigate implant‐related heating. Here, both ideas are integrated into one comprehensive safety concept where native pTx safety (wi...
The association between cerebral blood supply and cognition has gained increasing interest, considering the remarkable anatomical variability of the circle of Willis. Thus, qualitative classifications of the arteries contributing to the hippocampal supply has been performed in previous studies to determine whether the additional presence of vessels...
At high spatial resolution, unintentional motion due to breathing or slow head drifts is of the same order as the voxel size. Further, higher resolution is prolonging scan sessions, rendering subject motion more likely. Thus, even in compliant subjects, unintentional and physiological motion can induce motion artifacts. Motion compensation or corre...
Wireless coils can be of great advantage in the workflow of an intervention in order to reduce e.g. placement and sterilization challenges. This contribution demonstrates an inductively coupled metamaterial inspired surface resonators to enhance the receive capability of the scanner internal coils and compares the coil to a commercially available w...
Multi-channel surface coils conventionally feature many discrete electric components
implemented directly at the coil elements. In order to allow high flexibility, large access area for MRI-guided interventions and minimal costs of the coil elements, this work demonstrates the prototype of a remote decoupled multi-channel receive coil free of discr...
Blood vessels of the brain provide the human brain with the required nutrients and oxygen. As a vulnerable part of the cerebral blood supply, pathology of small vessels can cause serious problems such as Cerebral Small Vessel Diseases (CSVD). It has also been shown that CSVD is related to neurodegeneration, such as Alzheimer’s disease. With the adv...
Expert interpretation of anatomical images of the human brain is the central part of neuro-radiology. Several machine learning-based techniques have been proposed to assist in the analysis process. However, the ML models typically need to be trained to perform a specific task, e.g., brain tumour segmentation or classification. Not only do the corre...
Purpose
To present electromagnetic simulation setups for detailed analyses of respiration's impact on B1+$$ {B}_1^{+} $$ and E‐fields, local specific absorption rate (SAR) and associated safety‐limits for 7T cardiac imaging.
Methods
Finite‐difference time‐domain electromagnetic field simulations were performed at five respiratory states using a br...
Purpose
To simultaneously acquire spectroscopic signals from two MRS voxels using a multi‐banded 2 spin‐echo, full‐intensity acquired localized (2SPECIAL) sequence, and to decompose the signal to their respective regions by a novel voxel‐GRAPPA (vGRAPPA) decomposition approach for in vivo brain applications at 7 T.
Methods
A wideband, uniform rate...
Model-based reconstruction employing the time separation technique (TST) was found to improve dynamic perfusion imaging of the liver using C-arm cone-beam computed tomography (CBCT). To apply TST using prior knowledge extracted from CT perfusion data, the liver should be accurately segmented from the CT scans. Reconstructions of primary and model-b...
The MRI hybrid ablation system is an approach to use the MR (magnetic resonance) scanner's radiofrequency amplifier itself as power source for ablation. Hereby, an electrode is connected to the MR internal radiofrequency amplifier. An average RF power is provided through a train of short RF pulses, which is sufficient to thermally destroy tissue. H...
Dynamic MRI is an essential tool for interventions to visualise movements or changes in the target organ. However, such MRI acquisition with high temporal resolution suffers from limited spatial resolution-also known as the spatio-temporal trade-off. Several approaches, including deep learning based super-resolution approaches, have been proposed t...
Motion artefacts in magnetic resonance images can critically affect diagnosis and the quan-tification of image degradation due to their presence is required. Usually, image quality assessment is carried out by experts such as radiographers, radiologists and researchers. However, subjective evaluation requires time and is strongly dependent on the e...
Purpose
Severe geometric distortions induced by tissue susceptibility, water–fat chemical shift, and eddy currents pose a substantial obstacle in single‐shot EPI, especially for high‐resolution imaging at ultrahigh field. View angle tilting (VAT)‐EPI can mitigate in‐plane distortion. However, the accompanied strong image blurring prevented its wide...
Motion artefacts in magnetic resonance brain images are a crucial issue. The assessment of MR image quality is fundamental before proceeding with the clinical diagnosis. If the motion artefacts alter a correct delineation of structure and substructures of the brain, lesions, tumours and so on, the patients need to be re-scanned. Otherwise, neuro-ra...
Deep learning models have shown their potential for several applications. However, most of the models are opaque and difficult to trust due to their complex reasoning - commonly known as the black-box problem. Some fields, such as medicine, require a high degree of transparency to accept and adopt such technologies. Consequently, creating explainab...
Many deep learning-based techniques have been proposed in recent years to reconstruct undersampled MRI – showing their potential for
shortening the acquisition time. Before using them in actual practice, they are usually evaluated by comparing their results against the available
ground-truth – which is not available during real applications. This r...
Deep learning methods are typically trained in a supervised with annotated data for analysing medical images with the motivation of detecting
pathologies. In the absence of manually annotated training data, unsupervised anomaly detection can be one of the possible solutions. This work
proposes StRegA, an unsupervised anomaly detection pipeline base...
Deep learning pipelines typically require manually annotated training data and the complex reasoning done by such methods make them appear as
“black-boxes” to the end-users, leading to reduced trust. Unsupervised or weakly-supervised techniques could be a possible candidate for solving
the first issue, while explainable classifiers or applying post...
Cartesian sampling techniques are available to speed up the measurement of dynamic MRI, such as k-t GRAPPA. However, radial samplings, such as
iGRASP, are more robust to motion and can be applied for abdominal dynamic MRI. In this work, k-t GRAPPA inspired iGRASP has been created (so called k-t GRASP)–which acquires the subsequent time points by st...
Deep Learning based deformable registration techniques such as Voxelmorph, ICNet, FIRE, do not explicitly encode global dependencies and track
large deformations. This research attempts to encode semantics, i.e. structure and overall view of the anatomy in the supplied image, by
incorporating self-constructing graph network in the latent space of a...
This work demonstrates the added value of using litz wire to achieve highly efficient MR coils in their optimized frequency range. The evaluated litz wire outperforms solid copper wire up to a frequency of about 15 MHz and reaches its optimum at 3 MHz. The model of Lotfi et al., leads to a theoretical optimum at 4 MHz compared to a solid wire with...
The pial arterial vasculature of the human brain is the only blood supply to the neocortex, but quantitative data on the morphology and topology of these mesoscopic arteries (diameter 50-300µm) remains scarce. Because it is commonly assumed that blood flow velocities in these vessels are prohibitively slow, non-invasive time-of-flight MRI angiograp...
We investigated whether the impact of tau-pathology on memory performance and on hippocampal/medial temporal memory function in non-demented individuals depends on the presence of amyloid pathology, irrespective of diagnostic clinical stage. We conducted a cross-sectional analysis of the observational, multicentric DZNE-Longitudinal Cognitive Impai...
Image registration is the process of bringing different images into a common coordinate system - a technique widely used in various applications of computer vision, such as remote sensing, image retrieval, and most commonly in medical imaging. Deep Learning based techniques have been applied successfully to tackle various complex medical image proc...
Reproducible resting‐state functional connectivity (rsFC) patterns and their alterations play an increasing role in neuropsychiatric research. Studies that limit the analysis of metabolites and rsFC strengths to a predefined canonical network suggest that the rsFC strength positively correlates with the local glutamate (Glu) levels and negatively c...
MRI is an inherently slow process, which leads to long scan time for high-resolution imaging. The speed of acquisition can be increased by ignoring parts of the data (undersampling). Consequently, this leads to the degradation of image quality, such as loss of resolution or introduction of image artefacts. This work aims to reconstruct highly under...
Clinicians are often very sceptical about applying automatic image processing approaches, especially deep learning-based methods, in practice. One main reason for this is the black-box nature of these approaches and the inherent problem of missing insights of the automatically derived decisions. In order to increase trust in these methods, this pap...
Magnetic resonance imaging (MRI) provides high spatial resolution and excellent soft-tissue contrast without using harmful ionising radiation. Dynamic MRI is an essential tool for interventions to visualise movements or changes of the target organ. However, such MRI acquisition with high temporal resolution suffers from limited spatial resolution -...