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Measuring in-vivo tissue conductivity and permittivity using MRI.



Titel: Electrical conductivity mapping by B1 phase mapping at high field strengths
Titel: Feasibility and potential of Electric Properties Tomography at ultra high field strengths
Titel: Comparing Electric Properties Tomography at 1.5, 3 and 7 T


Samenvatting van de aanvraag

In the numerical analysis of RF exposure to humans, whole body models segmented into various tissue types are loaded into electromagnetic solvers. Literature values of dielectric properties are allocated to the segmented tissues. These literature values were collected in several studies through impedance measurements of freshly excised animal tissue and human autopsy material. However, there are some shortcomings of this methodology. First of all quickly after death changes take place in human autopsy material which are likely to alter the dielectric properties. Second, the validity of one standard lookup table for the whole human population can be questioned. It is known that the composition of tissues and organs changes with age and body weight. These uncertainties end up as error margins in SAR modeling of RF exposure to humans hampering the definition of RF exposure guidelines. These issues underline the need for an method which can image in-vivo the dielectric properties of the human body. Electric Properties Tomography using Magnetic Resonance Imaging (EPT-MRI) has been developed very recently and enables the mapping of tissue electric conductivity and permittivity under in-vivo conditions. The method is based on the analysis of spatial variations in the socalled B1 field, the magnetic component of the RF field employed in MRI to excite hydrogen nuclei. EPT-MRI answers the need to have an in vivo technique to measure dielectric properties of human tissue for RF safety studies. In addition to this, first experiments indicate that EPT-MRI has the potential to become a new diagnostic tool to identify pathologies based on altered dielectric properties. In this study an international collaboration between the Radiotherapy group of Prof. Lagendijk at the University Medical Centre Utrecht (UMCU) and the Philips Research group in Hamburg is proposed. The Philips Hamburg group (most notable members Dr. Katscher and Dr. Voigt) has been the pioneer of EPT-MRI and has a vast expertise on B1 mapping, reconstruction algoritms and other relevant skills. More recently, the UMCU has entered the young field of EPT-MRI and has made innovative contributions to the application of EPT-MRI in the human brain at high magnetic field strenghts (7 Tesla). The aim of this collaboration is to transfer expertise from Philips Hamburg to the UMCU group to make the UMCU a leading center in the in vivo application of EPT-MRI. The scientific context of this collaboration is a comparison study of EPT-MRI at different magnetic field strengths. Theoretical considerations indicate that the sensitivity and accuracy of EPT-MRI will benefit from higher magnetic field strengths (=higher RF frequencies). Phantom and human volunteers (brain) studies will be performed to determine the sensitivity and accuracy of EPT-MRI at 1, 1.5, 3 and 7 Tesla (T). The measured dielectric properties will be compared to literature values. The research will be performed in the UMCU by PhD Student Astrid van Lier and by a visiting scientist (post-doc) with expertise on B1 mapping. The Philips Hamburg group will support this research by providing direct support and entrance to their facilities. For this purpose regular meetings between the Philips Hamburg group and the UMCU are organized as well as visits of PhD student Astrid van Lier to Hamburg. The final product of this project is the creation of an expertise center at the UMCU of in vivo mapping of dielectric properties of the human body with MRI. The exploration of the potential of EPT-MRI as a medical diagnostic tool for a range of pathologies will be a logical continuation of this project.



Looptijd: 100%
Looptijd: 100 %
Onderdeel van programma:
Gerelateerde subsidieronde:
Projectleider en penvoerder:
Prof. dr. ir. C.A.T. van den Berg
Verantwoordelijke organisatie:
Universitair Medisch Centrum Utrecht