This topic deals with the frameless navigation during brain surgery. We will explain the state-of-the-art techniques as well as discussing accuracy of frameless navigation. Frame-based surgery includes many problems, as it is unpleasant for the patient and due to the frame the surgeon only has a limited view and working area. Therefore the first frameless stereotaxy was developed in the 1990s and is a topic of improvement up to now. [1]
State-of-the-art
In general, a frameless navigation system consists of a workstation, a position digitizer and a pointing device. A combination of these parts allows to track the head and surgical tools in real-time during surgery. Overall, there are many different systems available for frameless treatment, which rely on different tracking methods and different software planning types.
Procedure
Before the surgery, preoperative CT and/or MRI images are taken, loaded into the workstation and merged to a 3D model of the brain. On these images markers are already visible that were attached to the patients brain and that can be aligned with the position of the markers during surgery. With available software planning tools the surgeon then plans the surgery based on these medical scans. The planning includes definition of the entry point in the skull and laying trajectories to the area of the tumor. Right before the surgery, fiducial markers are attached on different places on the head and surgical tools are equipped with markers as well. By using the pointer on the fiducial markers, the position of each marker is registered in the workstation. This allows for the alignment of the preoperative scans and the position of the markers in the operation room space. During the surgery the tools can be tracked in different ways, which will be descriped later on. All methods enable a real-time tracking. Additional (mobile) monitors are integrated into the OR or in small ways integrated into the surgeons mircoscope (AR), so that the surgeon can see the planned trajectories in relation to the actual position of the tools. Intraoperative images can be taken to further improve the accuracy of the surgery. [2] [3]
Accuracy
There are different definitions regarding the accuracy of frameless navigation. In general, the overall accuracy for frame-based systems was said to be higher than for frameless systems. However, new studies show that frameless systems can be as good as or even better than frame-based systems [8] [9]. Different reasons can be named for a difference in accuracy. First of all, in frameless navaigation only few markers are used to register the brain, instead of using a frame for the registration. Secondly, the position tracking has to pass several stages which can lead to computational inaccuracies. Other factors contributing to the overall accuracy during surgery ("application accuracy") are "mechanical" and "registration" accuracy. The former one is device-specific and describes the precision of the positions for devices in space. In arm-based systems this precision is based on technical parameters and in armfree ones the resoultion of the detector contributes to the precision, among others. The "registration" accuracy accounts for errors that occur due to matrix transformations in the registration process. Clinical factors, such as the occurence of brain shift, also contributes to a decreasing accuracy. A last contributer to inaccuracies lies in the type of coordinate systems. In some frame-based systems, the target point is the center of the frame, the movement axis is in the center and trajectories are radii of the coordiante sphere. In some frameless systems however, the movement axis is close to the skull, which accounts for a larger movement in the target area due to an increased spread of trajectories. [5] [6]
Figure 4: Schema of coordinate planning in frame-based and frameless systems [5]
Figure 6: histrogram showing magnitude and frecquency of discrepancy between image-guided and frame-based procedures [13]
Figure 7: histogram for 3D intrafractional displacement during procedures with the BrainLab mask and the BRW head frame [13]
2 Kommentare
Unbekannter Benutzer (ga85raq) sagt:
19.Juni 2017I like that you gave every part a separate page, it makes it easier to read since the pages aren't too long. Your pages are very well researched and are very detailed. Good job![(Lächeln)](/s/-tf0nrc/9104/12ei04b/_/images/icons/emoticons/smile.svg)
Unbekannter Benutzer (ga67yur) sagt:
19.Juni 2017Thanks for the feedback![(Lächeln)](/s/-tf0nrc/9104/12ei04b/_/images/icons/emoticons/smile.svg)