Wolfgang Wein obtained the doctoral degree in computer sciencefrom Technical University of Munich in 2007. His research wasconducted jointly at the chair for Computer-Aided MedicalProcedures (CAMP) at TU Munich, Germany, and Siemens CorporateResearch (SCR) in Princeton, New Jersey, USA. He is currentlyworking as a research scientist at SCR.

Ultrasound is a popular, cost-effective andnon-invasive medical imaging modality. If anultrasound probe is equipped with a 3D positionsensor, the acquired images can be obtained in theirspatial context, a technique commonly denoted 3Dfreehand ultrasound.Combining ultrasound and a pre-operative ComputedTomography (CT) scan of the same patient can bebeneficial for a number of clinical applications. Thecore of this thesis is the development of novelmethods for fully automatic alignment (i.e.registration) of 3D freehand ultrasound and CT data,based on the image content and the physicalproperties of both modalities.Furthermore, we introduce new techniques for 3Dfreehand ultrasound calibration and reconstruction,as well as visualization of fused CT and ultrasound data.Two clinical applications are investigated in detail.We use a designated version of an automaticregistration algorithm to integrate diagnosticultrasound into radiation treatment planning for headand neck cancer.Different methods are applied, in the context oftreating liver and kidney metastases, for fusing CTwith both diagnostic and interventional ultrasound ofthe abdomen. While diagnostic fusion helps doctors toassess indeterminate lesions in those organs,interventional fusion using our techniques allows foradvanced image-guided navigation, in particular, forneedle biopsies and radio-frequency ablations.