Electrical impedance tomography (EIT) is relatively new. It is a very promising technique to be developed especially in the medical field. The advantages of EIT are that it is non-ionizing, simple, and portable and that it produces a high contrast image. Unfortunately, this modality does not have the capability to generate a highresolution image. Almost all imaging modalities has both advantages and disadvantages. Combining one modality with another is hence expected to cover the weaknesses of each other. The problem is how to develop the concepts, measurement systems and algorithm of dual modalities, particularly electrical and acoustical. The electrical modality can produce high contrast and the acoustical modality can produce high resolution. Combination of these will enhance the image resolution of EIT. High image resolution from the ultrasound reflection tomography is used as the prior information to improve the image resolution of the EIT. Finite Element Model (FEM) can be arranged by non-uniform elements, which are adapted to the boundary. Element models with higher density are arranged at the boundaries to obtain improvements of resolution and the model elements with lower density arranged at other locations to reduce the computational cost. The dual modality EIT with Ultrasound Reflection (EIT-UR) can produce high resolution and contrast image. The resolution improvement can also accelerate the convergence of the NewtonRaphson reconstruction methods.

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Abstract. MR guided interstitial laser therapy can be used to monitor the extent of tumor tissue coagulation during thermal treatment based on a temperature map. In a non-stationary object that was influenced by respiratory motion, the temperature map may show errors due to incorrect spatial baseline images. Moreover, an unwanted phase shift due to object displacement contributes to errors in the temperature map, that must be suppressed. This paper describes a strategy which addresses the difficulties of MR guided interstitial laser therapy in the presence of respiratory motion. The multi-baseline images, supported by the displacement correction scheme, were used to improve the temporal resolution of a temperature map in the respiratory cycle. In the displacement correction scheme, the object coordinates that are provided by an active tracking coil were employed to support a matching strategy between the thermal and baseline images. To avoid errors in the temperature map due to the motion artifact, a detector of low quality images was proposed as part of the displacement correction scheme.

Noninvasive temperature measurement is feasible with MRI to monitor changes in thermal therapy. Phase shift based MR thermometry gives an estimate of the relative temperature variation between thermal and baseline images. This technique is limited, however, when applied on targets under inter-frame motion. Simple image registration and subtraction are not adequate to recover the temperature properly since the phase shift due to temperature changes is corrupted by an unwanted phase shift. In this work, the unwanted phase shift is predicted from the raw registered phase shift map itself. To estimate the unwanted phase shift, a thin plate smoothing spline is fitted to the values outside the heated region. The spline value in the heated area serves as an estimate for the offset. The estimation result is applied to correct errors in the temperature maps of an ex-vivo experiment.

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