Intraoperative Imaging

Further development in the capacity to do image-guided surgery is the recent creation of intraoperative imaging for immediate confirmation of surgical manipulation. Over the last decade a number of solutions to the problem of immediate verification of surgical effect have been offered (47).

One of the earliest was the GE Signa System, which has an open MR design allowing navigation in real time within the magnet and immediate update of resection (48). This technology allows surgery to be done in the magnet. The patient is managed in precisely the same way he or she would be in a traditional operating room. All the instruments and anesthesia equipment are nonmagnetic. The result is an operating system in which the surgeon has MRI vision with the capacity to confirm his or her surgical effect immediately.

Using this device, which is situated at the Brigham and Women's Hospital in Boston, our group has done over 700 craniotomies for brain tumor. These have primarily been resections for low-grade or recurrent tumors, although anaplastic gliomas and glioblastomas have also been removed in this device. Our complication rate has been the same as in the traditional operating room. In terms of infection and other surgical problems, the instance of immediate neurologic deficit is lower than in the traditional operating room because of the ability to see residual tumor. With transsphenoidal procedures, the leakage of spinal fluid is slightly more prevalent because more aggressive surgery is suggested.

A similar solution to the problem of intraoperative verification of removal is the concept of moving the patient into and out of the MR scanner. This has been particularly useful in the Siemens Magnetom System, in which the operating table is moved in and out of the scanning device. Fahlbusch et al. have used this concept, first for the 0.2-T scanner and then for the 1.5-T scanner, with very good intraoperative pictures (49,50). (See Chapter 6.)

A third solution has been to bring the scanner to the patient. An elaborate example of this is the IMRIS System, in which the 1.5-T intraoperative MR scanner is brought from a shielded cage into the region of the patient to obtain high-quality images and verify removal of tissue (51). One advantage of this system is that the room can be used for traditional surgery when it is not being used for intraoperative imaging. Such devices have been described in detail, and the applications they bring to tumor surgery are significant, with markedly improved resections. They have also demonstrated their usefulness for low-grade gliomas, pituitary adenomas, and malignant gliomas.

A variant that is increasing in popularity is the Odin PoleStar System, which gives a limited view of the brain, and has modest navigational capacities but can be used within the traditional operating room (52,53). This is a very low-field (0.1-T) magnet, but it may be useful for some applications.

These developments in image-guided surgery have made it possible to consider very different approaches to be certain that the desired result is achieved in planning surgery. They are extremely important as new advances in minimally invasive neurosurgery.

These techniques may also be combined with other minimally invasive techniques so that endoscopy, for example, can be combined with image-guided frameless systems or the intraoperative MR to think about new ways of guiding endoscopes (54-56).

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