Perspective

MRI was introduced in the neurosurgical operating room in the mid 1990s (10-12). We now face the transition from its first experimental application to routine use. The first reports on larger patient series have been published now (16-18).

We have investigated low-field intraoperative MRI using a 0.2-T Magnetom Open scanner for 572 yr in 330 patients. Without doubt it can be stated that intraoperative MRI allows a reliable evaluation of the extent of tumor removal in most cases. Advances in scanner design, e.g., active magnetic shielding, allowed us to adapt a high-field system to the operating room environment. Even though our experience in intraoperative high-field MRI is preliminary, involving more than 30 patients, it can be stated that intraoperative high-field

Fig. 6. A 57-yr-old male patient with a large intra- and suprasellar, hormonally inactive pituitary adenoma. (A,B) Preoperative sagittal scans. (C,D) Intraoperative images, depicting complete removal. (A,C) Images are available after 5 s, measured with a HASTE sequence. (B,D) T1-weighted.

imaging is clearly superior to low-field imaging. We expect that this excellent intraoperative image quality will result in a higher validity of intraoperative diagnostic evaluation of the extent of tumor resection. There is increasing consensus that achieving gross total resection of brain tumors can make a big difference (58), so intraoperative imaging for quality control gains increasing importance. Up to now, high-field intraoperative MRI seems to be the most advanced possibility to give the neurosurgeon an intraoperative tool, for reliabe evaluation of intraoperative actions permitting immediate modification, i.e., further resection of the tumor during the same operation.

Besides enhanced image quality compared with low-field intraoperative systems, intraoperative high-field MRI offers further modalities, such as functional imaging, angiography, spectroscopy, and diffusion-weighted imaging,

Fig. 7. Same patient as in Fig. 6. Intraoperative T2-weighted image, illustrating the high image quality. The floor of the sella is covered with a wax plate to give a good contrast.

Fig. 8. In glioma surgery the head is fixed in an MR-compatible four-pin head holder (black arrow in A), which is integrated into the standard head coil. (B) Sterile adapters (white arrow) are placed on the lower part of the head coil before sterile draping. (C) After tumor removal, the sterile upper part of the head coil is placed on the adapters, and then imaging can start.

Fig. 8. In glioma surgery the head is fixed in an MR-compatible four-pin head holder (black arrow in A), which is integrated into the standard head coil. (B) Sterile adapters (white arrow) are placed on the lower part of the head coil before sterile draping. (C) After tumor removal, the sterile upper part of the head coil is placed on the adapters, and then imaging can start.

all contributing to an advanced neuronavigational setup. All these modalities have to be integrated into the navigational setup, providing not only functional neuronavigation but also multimodality neuronavigation. Progress in navigation technologies such as laser scanning (59) or automatic registration of ytC.

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