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N.P. van Dam
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Contrast Source Inversion Electrical Property Tomography
Is the two-dimensional CSI algorithm feasible on realistic three-dimensional data?
Electrical property tomography (EPT) reconstructs the human body’s conductivity and relative permittivity using the radio frequency field from a magnetic resonance machine. Since conductivity and relative permittivity can be biomarkers for many illnesses, it is necessary to reconstruct them accurately. To this end, this thesis focuses on the two-dimensional tranceive phase corrected contrast source inversion algorithm (2D-CSI).
This 2D-CSI algorithm is significantly faster than its three-dimensional (3D) counterpart. However, reconstruction artefacts may appear since the 2D field description is not always applicable. In this thesis, these artefacts are identified and it is investigated if the 2D-CSI algorithm can be improved to handle them. In particular, the proposed updates are, first, implementing the early stopping principle, then adding a positivity constraint to the conductivity and relative permittivity, and lastly, initialising with Helmholtz electrical property tomography (HEPT). The first two enhancements create a more robust algorithm, while the third update could be useful only in specific cases (with no fine structures and low noise levels).
After achieving a more robust algorithm, the 2D-CSI algorithm is applied to the realistic 3D dataset ”A Database for MR-based Electrical Properties Tomography” (ADEPT). The first and foremost challenge is accurately simulating the incident field, as the reconstructions depend a lot on the incident fields. If the incident fields do not match perfectly, the algorithm can only produce satisfactory reconstruction results in a part of the reconstruction domain. The reconstructions are only partly accurate because the reconstructed electric fields converge to a line creating line artefacts. It is shown that small changes in the incident fields produce small changes in the position of the artefacts. Based on this observation, a reconstruction strategy has been developed in which a reconstruction without artefacts is produced by combining reconstruction results of multiple incident fields. Integrating all modifications of the 2D-CSI
algorithm in one single framework shows that the conductivity and relative permittivity of the brain in the middle of the birdcage coil can be reconstructed accurately ...
This 2D-CSI algorithm is significantly faster than its three-dimensional (3D) counterpart. However, reconstruction artefacts may appear since the 2D field description is not always applicable. In this thesis, these artefacts are identified and it is investigated if the 2D-CSI algorithm can be improved to handle them. In particular, the proposed updates are, first, implementing the early stopping principle, then adding a positivity constraint to the conductivity and relative permittivity, and lastly, initialising with Helmholtz electrical property tomography (HEPT). The first two enhancements create a more robust algorithm, while the third update could be useful only in specific cases (with no fine structures and low noise levels).
After achieving a more robust algorithm, the 2D-CSI algorithm is applied to the realistic 3D dataset ”A Database for MR-based Electrical Properties Tomography” (ADEPT). The first and foremost challenge is accurately simulating the incident field, as the reconstructions depend a lot on the incident fields. If the incident fields do not match perfectly, the algorithm can only produce satisfactory reconstruction results in a part of the reconstruction domain. The reconstructions are only partly accurate because the reconstructed electric fields converge to a line creating line artefacts. It is shown that small changes in the incident fields produce small changes in the position of the artefacts. Based on this observation, a reconstruction strategy has been developed in which a reconstruction without artefacts is produced by combining reconstruction results of multiple incident fields. Integrating all modifications of the 2D-CSI
algorithm in one single framework shows that the conductivity and relative permittivity of the brain in the middle of the birdcage coil can be reconstructed accurately ...
Electrical property tomography (EPT) reconstructs the human body’s conductivity and relative permittivity using the radio frequency field from a magnetic resonance machine. Since conductivity and relative permittivity can be biomarkers for many illnesses, it is necessary to reconstruct them accurately. To this end, this thesis focuses on the two-dimensional tranceive phase corrected contrast source inversion algorithm (2D-CSI).
This 2D-CSI algorithm is significantly faster than its three-dimensional (3D) counterpart. However, reconstruction artefacts may appear since the 2D field description is not always applicable. In this thesis, these artefacts are identified and it is investigated if the 2D-CSI algorithm can be improved to handle them. In particular, the proposed updates are, first, implementing the early stopping principle, then adding a positivity constraint to the conductivity and relative permittivity, and lastly, initialising with Helmholtz electrical property tomography (HEPT). The first two enhancements create a more robust algorithm, while the third update could be useful only in specific cases (with no fine structures and low noise levels).
After achieving a more robust algorithm, the 2D-CSI algorithm is applied to the realistic 3D dataset ”A Database for MR-based Electrical Properties Tomography” (ADEPT). The first and foremost challenge is accurately simulating the incident field, as the reconstructions depend a lot on the incident fields. If the incident fields do not match perfectly, the algorithm can only produce satisfactory reconstruction results in a part of the reconstruction domain. The reconstructions are only partly accurate because the reconstructed electric fields converge to a line creating line artefacts. It is shown that small changes in the incident fields produce small changes in the position of the artefacts. Based on this observation, a reconstruction strategy has been developed in which a reconstruction without artefacts is produced by combining reconstruction results of multiple incident fields. Integrating all modifications of the 2D-CSI
algorithm in one single framework shows that the conductivity and relative permittivity of the brain in the middle of the birdcage coil can be reconstructed accurately
This 2D-CSI algorithm is significantly faster than its three-dimensional (3D) counterpart. However, reconstruction artefacts may appear since the 2D field description is not always applicable. In this thesis, these artefacts are identified and it is investigated if the 2D-CSI algorithm can be improved to handle them. In particular, the proposed updates are, first, implementing the early stopping principle, then adding a positivity constraint to the conductivity and relative permittivity, and lastly, initialising with Helmholtz electrical property tomography (HEPT). The first two enhancements create a more robust algorithm, while the third update could be useful only in specific cases (with no fine structures and low noise levels).
After achieving a more robust algorithm, the 2D-CSI algorithm is applied to the realistic 3D dataset ”A Database for MR-based Electrical Properties Tomography” (ADEPT). The first and foremost challenge is accurately simulating the incident field, as the reconstructions depend a lot on the incident fields. If the incident fields do not match perfectly, the algorithm can only produce satisfactory reconstruction results in a part of the reconstruction domain. The reconstructions are only partly accurate because the reconstructed electric fields converge to a line creating line artefacts. It is shown that small changes in the incident fields produce small changes in the position of the artefacts. Based on this observation, a reconstruction strategy has been developed in which a reconstruction without artefacts is produced by combining reconstruction results of multiple incident fields. Integrating all modifications of the 2D-CSI
algorithm in one single framework shows that the conductivity and relative permittivity of the brain in the middle of the birdcage coil can be reconstructed accurately
Bachelor thesis
(2022)
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N.P. van Dam, M.L. Jonker, C.J.M. Verhoeven, A.J.M. Montagne, R.T. Rajan, I.E. Lager
Unmanned underwater vehicles benefit from communication with a high data rate on relatively small distances (under 100 m). Existing communication methods are not able to provide this or present other shortcomings. Therefore, this bachelor end project focuses on a new type of underwater communication, quasi-static electric field communication. The software and modulation techniques in such a communication system are covered in this thesis. This includes a detailed analysis of modulation techniques, and especially of differential methods such as pi/M-DPSK, which can be demodulated non-coherently. Our system implements OFDM and according to simulations, it is able to achieve data rates of up to 1 Mbit/s. Additionally, this research focuses on the effect of error correction coding on the performance of the system. Moreover, an adaptive data rate control system is designed. The efficiency of the system is optimized by a power distribution algorithm. Finally, suggestions are given for a communication protocol.
...
Unmanned underwater vehicles benefit from communication with a high data rate on relatively small distances (under 100 m). Existing communication methods are not able to provide this or present other shortcomings. Therefore, this bachelor end project focuses on a new type of underwater communication, quasi-static electric field communication. The software and modulation techniques in such a communication system are covered in this thesis. This includes a detailed analysis of modulation techniques, and especially of differential methods such as pi/M-DPSK, which can be demodulated non-coherently. Our system implements OFDM and according to simulations, it is able to achieve data rates of up to 1 Mbit/s. Additionally, this research focuses on the effect of error correction coding on the performance of the system. Moreover, an adaptive data rate control system is designed. The efficiency of the system is optimized by a power distribution algorithm. Finally, suggestions are given for a communication protocol.