At the Brigham, neurosurgeons could perform a craniotomy while literally standing inside the MR scanner. In Minnesota, two surgical theaters were available: at the rear of the scanner inside the 5 Gauss (5G) line and at the front end, well outside the 5G line. The Minnesota investigators’ notion was that the patient could be advanced out the back end of the scanner just enough such that the patient’s head would be accessible to the surgeon. Initially, the architecture allowed for 40 cm of extension beyond the bore of the scanner [12]. In this way, both minimally invasive procedures and open craniotomy would proceed in much the normal fashion, constrained only by limitations related to the table and the need for MR-compatible surgical cutlery. The patient’s surgical field (i.e., the head) could be placed at isocenter to obtain pre-procedure, intradissection, and post-procedure images. In this manner, an approach quite similar to that of the Brigham and Women’s hospital would be possible, albeit at high-field strength. This concept would reveal itself to be ideal for minimally invasive procedures such as neurobiopsy was and feasible for open craniotomy.

The Minnesota suite also included the ability to operate just beyond the 5G line, in which case patients would be placed on a pseudo-surgical table (modified angiography table) that could be rotated in such a manner that all draping, instrumentation, and the microscope could be safely deployed outside the 5G line and, when appropriate, removed such that the patient could be pivoted back into alignment with the MR scanner couch. With appropriate surgical draping, the patient could be shuttled into the scanner for imaging (Fig. 33.2). In addition, a modest degree of Trendelenburg positioning could be achieved which was not possible inside the bore, even if the patient were extended 40 cm beyond the bore opening.

Though the “rear” approach had its many advantages, ultimately the “inside the fringe field” approach practiced in Minnesota would prove to be too far removed from current conventional neurosurgical practice for many surgeons to embrace. Instead, they would opt for Minnesota’s other surgical approach (outside the 5G line) or, alternatively, for the Calgary approach (move the magnet), or a dual room approach with a MR-operating room (OR) trolley to shuttle patients from the OR to the MR. While more cumbersome than at the rear of the scanner, these other approaches proved to be less disruptive to – and therefore, more acceptable to – neurosurgeons wanting to undertake iMR-guided neurosurgery.

Thus, for many tumor resections, surgeons preferred having access to the scanner while operating outside the 5G line. This approach was rapidly adopted by other centers. The group at Case Western Reserve University (Cleveland, OH) worked with Siemens Medical Systems (now Siemens Healthcare Solutions, Erlangen, Germany) to develop a pivoting, tilting, and canting MR surgical table [13]. This elegant solution was implemented at Case as well as at the University of California Los Angeles and the University of Erlangen, where neurosurgeons successfully operated immediately outside the 5G line.

While investigators in Minnesota and at other sites were comfortable with the concept of shuttling their patients into and out of the scanner during surgery, investigators in Calgary approached this issue in a different manner. The Calgary group felt strongly that moving the patient was not optimal and proposed to move the scanner. Working with image-guided magnetic resonance imaging systems (IMRIS, Winnipeg, CA), the Calgary team found a solution to moving the magnet (Fig. 33.3). Suspended from two rails, the magnet was moved easily from a parked position into the suite, literally enveloping the patient and surgical table. Initially, this transport proved to be costly in time, but eventually, the system proved both versatile and appealing to neurosurgeons who envisioned the MR scanner as a step up from intraoperative US and wanted to be able to update their frameless neuronavigation data sets.

As has been described extensively in the literature, investigators were initially focused on the issues of brain shift and the completeness of resection. At the Brigham, surgeons had clearly demonstrated the value of intradissection imaging to identify residual tumor after the neurosurgeon had determined the resection to be complete, by his or her visual inspection of the tumor bed [2]. In fact, the pioneering work at the Brigham revealed to the neurosurgery community at-large that what exceptionally competent neurosurgeons were used to declaring total resection was, in fact, incorrect, with residual tumor revealed by intradissection imaging in the majority of cases. Additionally, what would be confirmed quite rapidly at the Brigham and all other sites was that brain shift was not only quite real and rate-limiting in many cases of tumor resection, but that it could be addressed easily by the addition of intradissection MR imaging. Surgeons could “update” their frameless stereotaxy data sets in order to be able to continue to use the frameless systems safely throughout the surgical procedures.

These stunning revelations spurred great interest in iMR-guided neurosurgery as a useful adjunct to optimize conventional tumor resection. Indeed, if these were to be the only gains, many surgeons would argue that this was value enough to advance their field, akin to the introduction of the neurosurgical microscope [14].