gms | German Medical Science

Neuronavigation has become a standard tool especially for surgery of subcortical lesions, allowing precise targeting, better positioned craniotomies and anatomical orientation. During surgery the anatomy may change, making an update of the intraoperative situation desirable. Recent systems for intraoperative magnetic resonance imaging vary in complexity, ease of use, spatial demands and costs. The PoleStar NC 20 represents an addition to intraoperative magnetic resonance imaging (i-MRI). It is a novel, compact device for magnetic resonance (MR) imaging that has been developed for use in a standard neurosurgical operating room.

Developments of iMRI are reviewed and the preliminary experience with iMRI-guided resection of intracranial tumors in 29 patients using the PoleStar N-20 iMRI system is described (19 men, 10 women, aged 23-74 years, mean age 53,1 years). Operations included craniotomy for tumor or other lesion in 19 patients and transsphenoidal resection of tumor in 10 patients. The device includes a permanent magnet with a field strength of 0.15 tesla. The poles of the magnet are vertically aligned, with a gap of 25 cm. The magnet is easily moved into position and attaches to a regular operating table. The magnet is raised for imaging when needed and may be lowered to allow surgery to proceed unencumbered. Instant surgical navigation with optical probes is incorporated.

After gaining experience with the positioning of the patient, this was done in 6 minutes for supine and in 15 minutes for park bench or prone positions. The number of intraoperative scans ranged from two to seven per surgery. It took approximately 6 minutes for imaging to start after removing all metal from the operating field. Image quality, depending on the scan time invested, was excellent in 19 cases, adequate in 8 cases and poor in 2 cases. Intraoperative imaging confirmed that the goals of surgery had been attained, so that potentially harmful dissection in and around the brain was avoided.

Intraoperative imaging with low field strength MRI is the latest evolution in the increasing precision of neurosurgery. The advantages of this technology will probably make it a ubiquitous feature in the neurosurgical operating room. The introduction of new sequences has made the PoleStar N-20 a beneficial tool for intracranial surgery. Further development in contrast agent and surface coils will improve and maximize image quality in the near future.