Intraoperative MRI opens new window for Parkinsons patients
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| An intraoperative magnetic resonance imaging scanner, or iMRI, allows surgeons to visualize the brain in real-time during surgery. Source: Henry Ford Hospital |
Since August 2011, Schwalb and colleagues have used iMRI to guide electrode placement in four patients who were not good candidates for awake DBS, which uses mild electrical pulses to ease or control the most debilitating effects of Parkinson's disease, essential tremor or dystonia.
Electrode placement requires accuracy at the millimeter level. In the traditional technique, neurosurgeons merge pre-operative CT and MRI data to obtain x, y and z coordinates. “When we take the patient to the operating room, the brain can shift and even 2-3 mm accuracy is not good enough,” Schwalb said.
Surgeons control for miniscule shift by keeping the patient awake during the surgery to assess the accuracy of the electrode placement. One of the primary problems, said Schwalb, is that awake surgery is not an attractive option for patients.
Most studies indicate that it takes patients about one year to adjust to the idea of awake surgery. Thus, they may delay scheduling the procedure. Other studies suggest that patient outcomes are better if surgery is performed earlier in the course of the disease. “We want to offer the procedure at the sweet spot when the disease has progressed to the point where it is severe enough to merit the risks of surgery, but not wait until it has progressed so far that it may be too late to help the patient,” Schwalb said.
Another challenge with awake DBS is that Parkinson’s medications interfere with electrophysiologic mapping during the procedure, so patients must be off their medications prior to surgery. However, symptoms may be too painful for some patients to forego medications.
Finally, in other cases, patients may hold their heads in positions that make it difficult or unsafe to perform awake DBS.
iMRI allows neurosurgeons to adjust for brain shift and precisely place the electrodes, and offer the procedure to a wider patient population.
“We still recommend DBS for patients who can tolerate it,” said Schwalb. The four patients treated via iMRI have done very well, but the data aren’t available to support using it as a replacement procedure at this time.
However, neurosurgeons may ultimately find that the iMRI-enabled procedure is superior to the awake procedure. DBS can require multiple electrode passes or a revision of the original position; neither may be good for patient cognition. “With iMRI, it’s a single pass to place the electrode,” said Schwalb.
In addition to performing DBS inside the scanner, neurosurgeons at Henry Ford also use the system to guide brain tumor removal.
The iMRI system is comprised of multiple components: a disposable, MRI-compatible head-mounted adjustable trajectory frame; hardware, including a multi-channel imaging head coil and integrated head fixation frame, dedicated computer workstation and MRI-compatible in-room computer monitor and cart; software to guide surgical planning, device alignment and navigation; and accessory components necessary for the MRI-guided neurological procedure (marking grids, marking tools, surgical draping, screwdrivers, etc.).