Methodological advances in electrical properties tomography

Electrical properties tomography (EPT) aims to non-invasively measure the electrical properties (EPs) of biological tissues using conventional magnetic resonance imaging (MRI). EPT has gained increased interest over the last decade thanks to its potential in various applications, ranging from the optimization of radio frequency (RF) irradiation for increased safety, to the diagnosis and staging of pathologies, such as cancer, as demonstrated in several studies.
In MRI, the electrical properties of the tissue, in addition to the coil and body geometries, affect the RF magnetic field used for spin excitation. EPT reconstructs the EPs from
local changes in the spatial distribution of this field, commonly known as B1+. Typically, a measurement of B1+ is used to correct for effects resulting from inhomogeneous excitation. Measurements used for this purpose are often performed with fast sequences and thus, at low resolution. EPT, however, needs high-resolution measurements to be sensitive to the local variations, often translating into long acquisition times when relying on existing B1+ mapping methods. In addition, both the amplitude and phase of B1+ are required for
accurate EP estimation. These components are generally measured separately, adding to the overall needed scan time. Such long scan times are a large factor in hindering the translation of EPT into the clinics.
This thesis investigated strategies to reduce the scan time for B1+ mapping methods that are suitable for EPT. In particular, a high signal-to-noise ratio and high precision requirements must be met. For this reason, three methods are proposed to improve the time efficiency of the B1+ acquisitions. Two of the implemented methods reduce the scan time by combining B1+ amplitude and phase measurement, virtually halving the acquisition time. The third method increases efficiency by measuring one B1+ component in conjunction with other relevant quantitative parameters. The proposed methods showed promising results in healthy volunteers indicating a potential translation into clinics.
In conclusion, this thesis successfully addressed the challenge of reducing the measurement time for EPT by proposing three methods with increased time efficiency. Combined with more accurate reconstruction algorithms, these methods could serve as a promising starting point for integrating EPT into clinical practice.