This paper presents a simple and effective method for reconstructing 3D bio-CAD models from a sequence of computer tomography (CT) medical image data. In this work, a heterogeneous implicit solid representation method is proposed to describe a heterogeneous model of the human body. The use of implicit solid as a basis for 3D bio-CAD models facilitates the robustness and simplification of the process for converting CT images to a 3D bio-CAD model. An almost perfect 3D bio-CAD model is achieved from implicit solid interpolation combined with domain decomposition. The implicit solid is defined by a radial basis function which is a continuous scalar-value function over the domain $R^3$. The generated solid consists of the set of all points at which this scalar function value is the Houndsfield unit (HU) value obtained from the CT image. CT images of human bone were used as the case studies for the reconstruction of the 3D solid model from CT scan data. Experimental results show that the proposed method has the potential to represent internal human body details accurately and efficiently suitable for rapid prototyping, finite element analysis, and tissue engineering.