Method of and device for determining the position of a medical instrument

A device for determining the position of a medical instrument, introduced into the body of a patient, relative to a periodically moving body organ, which device includes:

• a position measuring unit for determining the spatial position (c, r) of a medical instrument introduced into the body and of a reference probe including transmitting means arranged outside the body,
• a signal measuring unit for determining a periodic motion signal (E2) r related to the periodic motion of the body organ, simultaneously with the determination of the spatial position (c, r) of the medical instrument and of the reference probe,
• a storage unit for storing an image data base containing 3D image data sets (p) of the body organ which have been acquired pre-operatively and simultaneously with the same motion signal (E1) and are associated with individual motion phases (e1, e2, . . . ), and
• a control and arithmetic unit for selecting a 3D image data set (p) from the image data base in such a manner that that 3D image data set (p) is selected which is associated with the motion phase (e1, e2) during the determination of the spatial position (c, r) of the medical instrument and of the reference probe, and for determining the position of the medical instrument relative to the body organ by converting the spatial position (c) of the medical instrument by means of the positions of the reference probe which are known in space and in the selected 3D image data set.