Intraoperative MRI Scans a Boon to Memorial Sloan-Kettering Neurosurgery

Typically, every Memorial Sloan-Kettering patient who is going to have surgery to remove a brain tumor will have an MRI scan performed the day before surgery. In the operating room (OR) on the day of surgery, the surgeon compares his or her impression of the surgical field with this preoperative image and makes judgments about brain shift, the extent of tumor removed, and the location of critical structures. For some tumors, this remains an effective approach. However for certain tumors -- for example, low-grade gliomas, that may have the look and feel of normal brain tissue, and pituitary tumors, in which surgeons access the tumor through the nose, with a restricted field of view -- the iMRI is an invaluable tool.

An iMRI allows a surgeon to begin an operation with a scan performed when the patient is first brought into the OR. As surgery proceeds, a surgeon can obtain additional MRIs as many times during a procedure as he or she feels it necessary. "Usually, we get an MRI in the beginning of the case, and then again at the end, or approaching the end, that tells us if there is residual tumor left," explained Memorial Sloan-Kettering neurosurgeon Cameron W. Brennan, Director of the Intraoperative MRI. "In certain operations it's common to reach a point where you're not sure about the edge of a tumor. You're getting close to the edge and you know that is the area where some tumors merge into the brain seamlessly -- and it is just that seamless edge which is often in a functionally important part of the brain. The ability to get an MRI means that you can update your navigation. As soon as you feel that navigation information is going to make the surgery safer or is going to pick up additional tumor, you can get the patient right into the iMRI and find out where the boundaries of the tumor are and see the relationship between the tumor and the surrounding structures."

Memorial Sloan-Kettering's BrainSUITE consists of two main pieces of equipment: a 1.5 Tesla intraoperative MRI scanner integrated with an image-guided neuronavigation system. The scanner uses the same high-field strength magnet used in standard diagnostic MRIs. These very strong magnets produce high-quality images in addition to allowing scans to be obtained quickly.

When a surgeon wants to obtain an MRI scan during an operation, the table on which the patient is lying pivots, and the patient -- along with the anesthesia lines and the lines connected to equipment monitoring the patient's vital signs -- are all put into the scanner. The acquisition of the images takes approximately ten minutes. The table then pivots out and surgery continues.

Because a powerful magnetic field is involved, performing surgery using iMRI comes with special challenges. First, the walls of the room in which the iMRI sits are magnetically shielded to keep the field contained within the room. The walls are further electrically shielded -- sheathed in copper -- to prevent interference from outside radiofrequency fields. The MRI scanner itself contains a magnet so strong that objects drawn to it can become dangerous projectiles. Therefore, patients are prescreened for any metallic objects or implants, and numerous other precautions are put in place.

	Perioperative clinical nurse specialist Mary Duffy

Perioperative clinical nurse specialist Mary Duffy, who was involved from early on in helping to get the iMRI up and running and is the safety nurse who works in the iMRI, has also been responsible for the safety training of more than 375 Memorial Sloan-Kettering personnel. These included, during the construction phase, staff from the Facilities Management shops and members of the Center's Fire Response Team, the Electric, Carpentry, Plumbing and Mechanics, and Paint Shops, as well as Plant Operations. No one may enter the iMRI OR who has not been properly trained. In order to gain access, a staff member's identification card must be specially coded; only those who have completed training are entitled to receive such coding. Ms. Duffy has now developed an online training course that anyone who requires access to the iMRI OR in the future must complete before he or she can be certified to enter.

In the OR itself, any equipment that is used within the boundary known as the 5-Gauss line (the perimeter around an MR scanner) -- including, for example, patient stretchers -- must be MRI compatible. (A Gauss is a unit of magnetic field strength and there are certain metals, such as some grades of stainless steel, titanium, and aluminum, that are MRI compatible.) However, during an operation, the patient's head is outside the 5-Gauss line, which is clearly marked on the operating room floor. "Because we are operating outside the 5-Gauss line, we're able to use our conventional instruments," Dr. Gutin explained. "We can also bring in any of the tools we'd use in a conventional OR," added Dr. Brennan, "ultrasound for example. So we still have available the full resources of the hospital." In addition, large wall-mounted screens display intraoperative images and data that are visible to the entire OR team.

While making surgery safer and more successful, iMRI also is expected to play an important role in the research pursued under the auspices of the BTC as investigators work to understand how biology, physiology, and metabolism vary across tumor regions that may be targeted using this imaging technique.