Alfred Mertins’s research while affiliated with University of Lübeck and other places

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Publications (441)


Equilibrium Model With Anisotropy for Model-Based Reconstruction in Magnetic Particle Imaging
  • Article
  • Full-text available

November 2024

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58 Reads

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4 Citations

IEEE Transactions on Computational Imaging

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Magnetic particle imaging is a tracer-based tomographic imaging technique that allows the concentration of magnetic nanoparticles to be determined with high spatio-temporal resolution. To reconstruct an image of the tracer concentration, the magnetization dynamics of the particles must be accurately modeled. A popular ensemble model is based on solving the Fokker-Plank equation, taking into account either Brownian or Néel dynamics. The disadvantage of this model is that it is computationally expensive due to an underlying stiff differential equation. A simplified model is the equilibrium model, which can be evaluated directly but in most relevant cases it suffers from a non-negligible modeling error. In the present work, we investigate an extended version of the equilibrium model that can account for particle anisotropy. We show that this model can be expressed as a series of Bessel functions, which can be truncated based on a predefined accuracy, leading to very short computation times, which are about three orders of magnitude lower than equivalent Fokker-Planck computation times. We investigate the accuracy of the model for 2D Lissajous magnetic particle imaging sequences and show that the difference between the Fokker-Planck and the equilibrium model with anisotropy is sufficiently small so that the latter model can be used for image reconstruction on experimental data with only marginal loss of image quality, even compared to a system matrix-based reconstruction.

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Citations (47)


... Recently, a more advanced model-based approach incorporating magnetic anisotropy in equilibrium has been proposed [23], [24]. This extended model has also been applied to the direct Chebyshev reconstruction (DCR), leading to the development of an adapted version (DCR-EQANIS) [4]. ...

Reference:

Efficient Chebyshev Reconstruction for the Anisotropic Equilibrium Model in Magnetic Particle Imaging
Equilibrium Model With Anisotropy for Model-Based Reconstruction in Magnetic Particle Imaging

IEEE Transactions on Computational Imaging

... Embodied communication improves the feelings of collaboration with perceived presence compared to text-based communication [56]. Furthermore, multimodal communication, such as combining visuals with verbal interactions, has been found to improve user experience [85]. For instance, the integration of voice, embodied communication, dialogue, and facial expressions provides users with a more accurate perception of AI, improving feelings of collaboration and social presence [71,87]. ...

CoSy - AI enhanced assistance system for face to face communication trainings in higher healthcare education: AI enhanced assistance system for face to face communication trainings in higher healthcare education
  • Citing Conference Paper
  • August 2023

... This dual focus on time and frequency domains allows for a more nuanced understanding of the physiological processes underlying sleep. Studies such as those by Chen et al. [27] and Phan et al. [36] have demonstrated the effectiveness of TFRs. However, this approach is not without its challenges. ...

L-SeqSleepNet: Whole-cycle Long Sequence Modeling for Automatic Sleep Staging
  • Citing Article
  • August 2023

IEEE Journal of Biomedical and Health Informatics

... This model can be reduced in two ways. First of all, one can assume that the Chebyshev series, which can be derived for 2D Lissajous excitation, is reduced to a single coefficient (reduced EQANIS model), see [37]. Second, one can assume isotropic particles leading to the EQ model. ...

Adaption of direct Chebyshev reconstruction to an anisotropic particle model

... As in the stationary case, the measurement time can be reduced by exploiting prior information, which is done in the form of sparsity in [36], [37], and in the form of a spherical harmonic representation in [38]. With a PSEQ as a transmitted signal, position tracking of the microphone using only the recorded sound can be done [39], leading to minimal cost associated with moving microphone measurements. ...

Positional Tracking of a Moving Microphone in Reverberant Scenes by Applying Perfect Sequences to Distributed Loudspeakers
  • Citing Conference Paper
  • September 2022

... The authors in [4] argue that multi-label fits the reality better but often multi-class, i.e., only one active sound type per clip, seems to perform better due to learning more class interactions, resulting in a cumbersome handling for practical systems. They propose to handle the problem by creating combinatorial polyphonic classes and use a divide and conquer group splitting to keep the exploding number of classes tractable. ...

Polyphonic Audio Event Detection: Multi-Label or Multi-Class Multi-Task Classification Problem?
  • Citing Conference Paper
  • May 2022

... 16 To address the demands on clinician time and the subjectivity of sleep staging in PSG, machine learning algorithms to automate sleep staging have been developed. These include algorithms developed specifically for children of varying ages, [17][18][19][20][21][22][23][24][25] due to differences in brainwave morphology at different stages of development, 26 and because adult sleep staging algorithms are known to be less performant when applied to children. 27 However, these pediatric-specific sleep staging algorithms are not freely available. ...

Pediatric Automatic Sleep Staging: A Comparative Study of State-of-the-Art Deep Learning Methods
  • Citing Article
  • May 2022

IEEE transactions on bio-medical engineering

... CNNs excel at capturing spatial hierarchies in data, making them particularly effective in tasks where fine-grained detail is necessary. This preference is prominently reflected in studies CNN Sequence Many-tomany Zan and Yildiz [11] CNN + RNN + FCN Sequence Many-tomany Phan et al. [38] Transformer TFR Many-tomany FCN refers to fully convolutional network such as those by Phan et al. [26], Chambon et al. [28], and many others listed in Table 1. However, the dynamic nature of sleep, characterized by transitions through various stages over time, necessitates modeling temporal dependencies alongside local features. ...

SleepTransformer: Automatic Sleep Staging With Interpretability and Uncertainty Quantification
  • Citing Article
  • January 2022

IEEE transactions on bio-medical engineering

... The reconstruction problem is typically formulated as a system of linear equations and solved using regularized least squares techniques [1], [18], [32]. Direct reconstruction approaches, on the other hand, can be categorized into time-domain methods, commonly known as x-space MPI [8], and frequency-domain methods, such as Chebyshev reconstruction [5], [28]. For one-dimensional MPI excitation, the mathematical equivalence between x-space and Chebyshev reconstruction has been established [10]. ...

Direct multi-dimensional Chebyshev polynomial based reconstruction for magnetic particle imaging