Microwave tomography
Doktorsavhandling, 2006
Microwave tomography for non-destructive detection of internal
dielectric properties has received increasing interest during the last
decades. Several application areas are under research, including
applications in geoscience, biomedical applications, safety and
security etc. The goal with this work is development of an microwave
imaging equipment for breast cancer detection. Potentially this is
very beneficial due to the large contrast in dielectric properties
between the tumour and the healthy breast tissue. Within the frames of
this work a microwave tomography prototype has been constructed. Since
the image reconstruction is generally requiring computationally
intensive optimisation algorithms comparison with a more
computationally efficient algorithm, based on a low contrast
approximation of the target, has been made. The results show that the
reconstructions are comparable up to 10% contrast. For biomedical
applications this is not sufficient and thus the iterative
optimisation algorithms have been selected as the preferred algorithm
for the rest of the work and as a platform for further
developments. In the work with the experimental prototype some
limitations in the performance of the algorithm have been
identified. One is the inability to image large and small objects
simultaneously, using a single electromagnetic pulse in the
measurement. This is a problem in breast cancer tomography where the
entire breast mass should be imaged together with potential
tumours. The problem has been resolved by performing a reconstruction
in several steps using successively increased frequency of the
illuminating pulses. Another question that is addressed is whether it
is feasible to utilise a priori knowledge about the
dielectric properties of the object to improve the accuracy of the
reconstructions. A reconstruction algorithm has been developed that is
capable of reconstructing objects with given dielectric values. The
results show that smaller objects can be resolved with the same
frequency content of the illuminating pulse compared to when the
a priori data is not taken into account.
inverse algorithms
microwave tomography
image reconstruction
FDTD
inverse Maxwell problem
mammography