Image-guided diagnosis and therapy are widely used in medicine nowadays. Going one step further involves methods that allow physicians to further improve their diagnosis and to plan therapy or surgery by quantitative analysis and simulation. Fundamental require-ments for this kind of quantitative medicine are methods for reliable creation of 3D patient models that faith-fully represent the individual anatomy. We demonstrate the impact of geometric patient models in medicine by presenting several case studies on work that is based on the 3D geometry recon-struction and visualization software amira®.