In order to avoid the gross registration error and the singular point in the current registration method of the navigation of stereotactic brain surgery,a novel registration method with electromagnetic positioning is proposed based on unit-quaternion. In this method,by using the characteristics of fast iteration and nonsingular solution of unit-quaternion,three space mappings are realized during the registration. Moreover,the optimal transformation
matrix from the surgery space to the computer space is solved according to the description of the rigid body posture transform in unit-quaternion and to the theory of odd coordinates. Experimental results show that the registration errors of the proposed algorithm are all less than 2mm,and the registration accuracy of the system is higher when 7 ~12 registration points lie symmetrically and surround the lesion uniformly and compactly.