June 1, 2013 | by Mark Fayez Sedrak, MD, Neurosurgeon, Kaiser Permanente, Redwood City | Deep brain stimulation (DBS) is a high tech surgical procedure, geared towards improving symptoms of neurological origin by manipulating circuits within the brain. This technology progressed after historical destructive procedures were fraught with complications and high frequency stimulation was found to produce similar clinical features to those destructive procedures.
There are many ways these surgeries can be performed and you will see many advertisements with various techniques. The “gold” standard operation contains three key elements: image guidance, microelectrode recordings, and intraoperative testing. I’m proud to say that we, at Redwood City Kaiser, utilize all three of these elements to provide the best possible patient outcome every time.
We all may know, nowadays, what a CT scan or an MRI actually displays. These are images performed of the body, brain in our circumstance, in 2D slices. There is much discussion in the world of functional neurosurgery attempting to understand where each and every target is physically located in 3D space. How do we exactly know where the targets are? Do MRI’s actually show the subthalamic nucleus and surrounding structures in enough detail? Although special MRI sequences can demonstrate where various structures are located, these targets used for movement disorder surgeries are tiny and ambiguously located.
We do two special things in our program with regards to image guidance: specialized MRI diffusion tensor imaging/colored fractional anisotropy (DTI/FA) and a calibrated XR technique for real-time imaging in the operating room. The DTI/FA method, the technique of which we have published, gives us patient specific information about these tiny regional targets. If you’ve ever looked at a regular CT or MRI, you will see that the study has low contrast, different shades of gray. The DTI/FA image, when processed, can display a colorful rainbow showing more exactly where structures are physically located. These images can even show where the neuronal tracts are located, and how bodies of neurons are organized.
Secondly, we use an amazing technique developed at Stanford, that utilizes XR machines setup in the operating room, calibrated to a very specific fixated point, which gives our bioengineer the ability to calculate positions in the brain in real-time. We uniquely, have the ability to calculate even the position of the microelectrode recordings in addition to the DBS electrode. These can be calculated relative to each other or relative to referential structures in the brain, the actual landmarks used for MRI/CT guidance. In addition, this method is the most accurate method of calculating positions that is known in the world (accurate to 0.6mm or less)! It is more accurate than intraoperative MRI, intraoperative CT, fluoroscopy, or frameless systems.
It is amazing to think that we now have the ability to measure electrical activity created by single neurons and a small cluster of neurons in the brain. This ability has led to the discovery of many structures within the brain, hinting at their role in this extremely complex organ. This method has become a very useful tool for neurosurgeons to identify many of the key targets during deep brain stimulation. During the time we measure these actual “action potentials” (actual neurons firing!), we can induce activity by manipulating the arm, the leg, or sometimes by flashing light in the eyes and many other maneuvers. This is a second layer of assurance that have identified the proper position in the brain. We perform an XR when we identify the target and ensure that the DBS electrode eventually will make it to the same exact spot we want, with the help of our calibrated XR technique.
In addition to these MER’s, we’ve recently started utilizing what are called “local field potential” recordings. This method is similar to what many know as EEG/ECOG, where pools of neurons are sampled for their electrical activity. However, we are measuring these fields of neurons deep within the brain rather than on the surface. It turns out that many of the LFP signals may in fact help us understand the overall activity in a certain portion of the brain. This information is typically not utilized during the procedure, but can be analyzed when recorded afterwards.
The last and final test is one of the most important. “What happens when we introduce electricity in the brain at a specific target?” This is a very critical step during the surgery, and is one critical reason to have our patients awake for the surgery. For example, occasionally we can map the area we think is the best target utilizing MER, have our image guidance to get us to where we want to be, and we find that with stimulation at that precise target, we induce effects that suggest we are too close to surrounding structures. When this occurs, our knowledge of the mapped area and our image guidance help steer us away from these surrounding areas, giving our patients the best possible outcome and allowing our programmers the greatest degree of flexibility.
It is important to realize that the physicians of Kaiser are truly outstanding individuals, many of which are excellent at what they do, graduating top of their respective classes, and from top universities around the country. A major benefit of being a part of Kaiser, is that these physicians are truly driven to have the best clinical results. The clinicians are outcome driven, not income driven. Our approach in Northern California Kaiser, has been to take advantage of the system and integrate a full team approach for treating our movement disorders patients. With this in mind, a board was created, incorporating: functional neurosurgeons, movement disorder neurologists, neuropsychologists, bioengineer, physician assistant, nurse practitioners, nurses, and administrators who all take part in creating a consensus decision for each patient. This is an organized meeting where patients are formally presented, they are videotaped in “On” and “Off” medication states, formal UPDRS-III (Parkinson’s Scale) scores are tabulated, MRI’s are reviewed, neuro-psychological evaluations are discussed. With all this information in mind, the board decides who will most likely have a significant benefit and who may not, who may be high risk and who should be able to tolerate the surgery without a problem. This type of board meeting is very unique, most institutions simply work using “hallway conversations” or simple consultations/referrals. The team approach, however, adds another layer of clinical excellence.