Surgical Navigation — Precision Counts
With the invention of navigation systems using GPS (global positioning system), drivers today do not need to carry the heavy stack of road maps in their glove compartments anymore. These navigation systems have become so sophisticated that car companies, such as Volvo and Google, are able to develop cars that can drive by themselves. Navigation systems have made a splash in the medical field, guiding the needle of an interventional radiologist during a minimally invasive procedure.
Conventionally, interventional radiologists utilize CT imaging (X-ray computed tomography) or ultrasound to locate their tool (usually a needle) within the patient's body. With the usage of these imaging systems, radiologists are able to "tunnel" their needle through different blood vessels to reach their target location. Now, inventor Stephane Lavallee has developed a method which utilizes two magnetic trackers, CT imaging, and a computer system to not only track the surgical tool more accurately, but also calculate the best point of entry and path for the radiologist.
GPS for Surgical Tools
Lavallee's invention, US 8,611,985, is titled "Method and device for navigation of a surgical tool"; granted December 17, 2013.
In this patent, Mr. Lavallee establishes the background history of surgical and radiological interventions. Lavallee identifies the usage of Computed Tomography Scan (CT-Scan) and Magnetic Resonance Imaging System (MRI) as tools to both view patient's internal structures and strategize a plan of treatment. There are, however, two limitations in the current procedures that Lavallee seeks to reconcile with his new invention. Lavallee describes:
Some navigation systems using magnetic localizer technology have been developed and used to track the tip of needles in CT images, during an intervention performed inside the CT room directly. One of those systems is for instance the device produced by Traxtall (Ontario, Canada). However, those systems have two major drawbacks. First, they are not always accurate, particularly when the distance between the tip of the needle and the magnetic emitter is not small compared to the distance between the tip of the needle and the metallic table that generates artefacts. Inaccuracy can reach more than 5 millimetres which is not acceptable. Further, the existing systems are complex to use and need user interaction.
Lavallee's navagation system is comprised of the following parts: two reference markers, an image system (CT-scan), a surgical tool (with a magnetic tracker attached), and a computer system that can process all these inputs for the radiologist. With all its elements working together, the system will produce a "navigation guide" for the radiologist to follow to reach the target location. We will break down this invention into its individual parts to examine its utility and technological advancement.
Reference Markers: The reference markers innovated by Lavallee is quite interesting and unique. Lavallee describes the two reference markers having the following components:
"a magnetic element having at least two coils arranged in a manner to define at least two vectors in a coordinate system of the magnetic tracking system, and a geometric element comprising components visible on image data of the imaging system and having a unique geometry detectable by the imaging system, said components comprising hollow plastic tubes having an external part and an internal part filled with air, wherein detecting the image position of the first reference marker comprises searching for said external part having a density in Hounsfield values equal to a plastic material Hounsfield value and said internal part having a null Hounsfield value, in an image provided by the imaging system."
The two components together work to provide the localizing system with information to connect the "surgical world" with the CT images. The magnetic coils will provide spatial information to the localizing system to determine where the surgical tool is relative to the marker. The plastic tubes will provide the localizing system with geometric information to allow the system to produce a hybrid image of the "surgical reality" and the CT-images. Lavallee introduces not one, but two reference markers for two very specific purposes. Lavallee states that the secondary reference marker can be placed sterilely near the surgical entry site in the case that the primary reference point is too far away from the surgical tool. This provides the system with more accurate tracking information without the need of moving the original reference marker and re-imaging the patient again.
Image system: Lavallee states that the image system can be any of the following: "imaging systems based on X-ray, magnetic resonance imaging or ultrasound imaging." Prior to the surgery, these systems will capture images of the patient's internal structure with the geometric alignment of primary reference marker.
Computer System: The computer system is the brains of this system. The computer system will extract information from the the primary reference marker and the image system to produce a "hybrid referential system". With this information, the system can automatically determine whether the radiologists desired surgical entry site can reach the target location of treatment. If not, the computer will automatically select the best location for surgical entry. By adding the second reference marker at this surgical site, the computer system can track the surgical tool with much greater accuracy and precision, even accounting for "organ movements due to breathing since it is likely to be closest to the organs that are targeted". Furthermore, the computer system will produce a "navigation image" for the radiologist to follow to accurately reach the target location. According to Lavallee, "the real instrument trajectory should perfectly fit with the virtual position of the instrument displayed by the navigation system.
Other Imaging Advancements
It seems as though utilizing CT/MRI imaging with a live tracking system is being implemented in other fields of medicine. At the National Cancer Institute, clinical scientists have partnered with Philips (Yes, the same Philips that develops light bulbs and toothbrushes) to develop a diagnostic tool called UroNav for prostate cancer diagnosis. Traditionally, prostate cancer was diagnosed using the digital rectal exam (think gloved fingers) to feel for tumors on the prostate. This process limited the physicians to feeling only one side of the prostate. Physicians then began utilizing a random biopsy protocol where the areas of the prostate were randomly sampled for abnormal cells. However, this procedure was also limited to the back of the prostate, missing many tumor in other areas. The new diagnostic procedure combines MRI images with images produced from an ultrasound wand to create a three dimensional image of the prostate. This system further guides the physicians to obtain precise, area-specific biopsies.
From self-driving cars to autonomous surgery?
The biggest question that remains is: Will there be a future where surgery will be completely autonomous? Surgery has evolved with leaps and bounds over the past two decades. Currently, the minimally invasive Da Vinci Surgical Robot allows physicians to sit comfortably at a console that translates the surgeon's finger movements to minute movements in the robot's arms/hands. One interesting fact to note is that the surgeon and the control console can be placed at a significant distance away from the actual robot, enabling the surgeon to safely perform "telesurgery" without having to be in the same room as the patient. Is it possible to pre-load CT/MRI images of a patient into a computer system, flick on the surgery software for artery by-pass surgery, and let the robot take over? Although there are huge (and we mean HUGE) legal implications to this methodology, we certainly think it's possible.