1. Field of the Invention
The present invention is directed to a head antenna for nuclear magnetic resonance examinations of the head in the context of surgical operations in the head area, the head antenna being of the type having an examination chamber formed so as to accept the head and an antenna conductor formed as a frame antenna that surrounds the examination chamber in an examination position.
2. Description of the Prior Art
A head antenna of the general type described above is known from German OS 43 18 134. The antenna has an antenna conductor formed as a frame antenna. After the positioning the head on a patient-supporting surface of a patient positioning means, the vertically oriented frame antenna is displaced parallel to the patient positioning means until the head is located in the examination chamber of the antenna.
If nuclear magnetic resonance examinations are to be carried out during neurosurgical operations, it is necessary that the head be held stable, in order to ensure, first, that the position of the head does not change during the operation, and to cushion the forces that arise, in particular, during the production of a burr hole in the skull. During neurosurgical operations, head mounts are thus employed that include fastening means for fixing the head. A head mount that can also be used in connection with nuclear magnetic resonance examinations is described in the article "Stereotaxis Biopsy of the Brain under MR Imaging Control," by D. G. T. Thomas, C. H. Davis. S. Ingram, J. S. Olney, G. M. Bydder and I. R. Young, in AJNR 7: 161-163, January/February 1986. The mount is made of non-ferromagnetic materials. Moreover, in the mounting frame no closed metallic loops, which could cause eddy currents, are used. In addition, markings which are visible in the nuclear magnetic resonance image are attached to the head mount, by means of which a precise correlation of the nuclear magnetic resonance image to the patient's anatomy is made possible. Before the actual operation, a receiving antenna for nuclear magnetic resonance imaging is arranged around the holder. The examination chamber of this receiving antenna is larger than that of a normal head antenna, because both the head and the head mount must be housed therein. For this reason, the fullness factor, and thus also the signal-noise ratio, is worse in comparison with a normal head antenna. Moreover, the use of this known arrangement during the actual surgical procedure is complicated, due to the accessibility required and the demands of a sterile operating environment.