Stereotaxy uses 3D imaging to guide surgical procedures. It began with frames attached to patients' heads but now uses frameless techniques. Frameless stereotaxy uses preoperative imaging, a tracked probe, and registration of images to guide surgery. Sources of error include imaging distortions and brain shift during surgery. Neuronavigation aids in precisely locating tumors and critical structures during brain surgery. Developments aim to improve accuracy, ease of use, and expanded applications.

1. STEREOTAXY
DR. FARRUKH JAVEED
NEUROSURGERY
JPMC

2. BACKGROUND
 “Stereotactic”: From Greek “stereos”=3-dimensional and
Latin “taxis”=arrangement or order
 Image-guided surgery (stereotaxy) is an operative
technique by which correlation between imaging
studies and the operative field is provided.

3. Types

4. BACKGROUND
1906 -- Horsley & Clarke (animal) stereotactic frame

5. PROGRESSION
1906 – Horsley & Clarke (animal) stereotactic frame
1947 – Spiegel & Wycis (human) stereotactic frame

6. FRAME BASED STEREOTAXY
1947-1980 – Proliferation of stereotactic frames.
In the late 1980s, the use of COMPUTER for the manipulation of
MRI/CT data, improved accuracy of MRI or CT scan and use of 3D
digitizers as pointing devices helped moving from frame-based
stereotaxy to frameless stereotaxy.

7. FRAMELESS STEREOTAXY
The first frameless stereotactic system; David Roberts and associates in
1986.
The advantage of a frameless system was the ability to track a surgical
instrument or probe in real time and project its position onto the
preoperative CT scan or magnetic resonance (MR) image.

8. AIMS OF NEURONAVIGATION
 Precise tumor/lesion localization.
 Decrease the surgery related morbidity and improve the quality of
surgical outcome.

9. Components of a Neuronavigation
System
 Frameless stereotactic neuronavigation requires three
essential components to function properly:
 preoperative imaging data (which will serve as a reference map
during the surgical approach and tumor resection),
 a localizing tool that will be tracked by the neuronavigation system
and will serve as a pointer,
 and a mathematical framework for calculation of the relationship
between the patient’s anatomy and preoperative imaging.

11. What equipment is involved?
 Localization device (digitizer)
 e.g., optical, electromagnetic, articulated arm
 Computer with registration algorithm
 Effector
 e.g., pointer and monitor, microscope heads-up display

12. Fiducials
 “fiducia” is a latin word meaning trust.
 Navigation is based upon targeting relative to known
reference points.
 The MRI data must be spatially accurate, and at least one of
the volumes must contain some surface reference marks or
features that can be accessed at surgery. These surface
markers (called fiducials) can take several shapes and forms.

13. Fiducials
 Bone fiducials like bone screws, most
accurate ones but with limitations.
 Skull-implanted fiducials
 Adhesive markers
 Cranial markers like tragus, canthus
but difficult to locate.

14. REGISTRATION
 Registration represents the step of relating the patient’s
anatomy to the radiographic data.
 The most common means of correlating (or “registering”)
image data with the physical space of the patient’s head is
called paired points.
 At surgery, the reference points are identified on the images
as well as touched, respectively, with a pointing device. When
surfaces are used, the physical surface is matched or
“registered” to the radiographic surface, either by touching
multiple random points on the surface (“cloud of points”) or
scanning the surface with a laser beam.

15. What types of co-registration strategies
can be used?
 Paired-point rigid transformation
 Surface (contour) matching

16. Registration

17. DEVICE TRACKING
 Device tracking refers to the use of the navigation system’s
localizing technology to track an instrument or probe in
space, relative to the patient.
 A number of different 3D digitizer technologies have been
used to allow the navigation computer to determine the
location of the tracked device in space.
 The most commonly used tracking technologies currently
include optical and electromagnetic systems.

18.  Localization device (digitizer)
 e.g., optical, electromagnetic, articulated arm
 most systems today include a reference frame to enable
OR table movement

19. Optical Tracking System
 Optical systems use infrared markers on the
tracked pointing device, with the position
determined trigonometrically by digitizing
stereoscopic solid state cameras.
 The location of the tip and axis of the pointing
device relative to the patient can be determined
by the geometry between the tracker and the
markers on the tracked device.
 This technique offers submillimetric accuracy and
allows for a large tracking volume.

20. Electromagnetic Tracking System
 Electromagnetic tracking technology is
based on generation of a magnetic field
and the presence of coils in tracking
devices.
 The advantages of this technique include
its abilities to provide tracking without the
need to maintain a free line of sight.

21. Display
 Once the registration process is completed, the
registration system can display the location and
orientation of the tracking device in relation to the
preoperative images and can be used to guide the
surgeon to a preselected target along a prescribed
trajectory.
 Common display arrangements include one that
portrays the images in anatomic coronal, axial, and
sagittal plane views that converge at the point of
interest and another that shows planes that are
steered by the pointing device, including along the
axis of the pointer (inline views) and perpendicular to
this axis (probe view).

22. Patient Head Movements
 Dynamic reference frames” (DRFs) are important for the
current optical infrared neuronavigation systems.
 They are fixed to the skull usually attached to the head
holders.
 They help to compensate the little movements of the head
during surgery.

23. Obstacles
 High initial purchase
 Learning curve
 Cost of disposables (fiducials)

24. What are different error?
 Fiducial registration error (FRE)
 Fiducial localization error (FLE)
 Target registration error (TRE)

25. Error increases as the distance of the target
from the fiducial centroid
West et al, 2001

26. Tips regarding fiducials
1. Avoid linear fiducial configurations
2. Arrange fiducials so that the center of their configuration is
close to the region of interest during surgery
3. Spread out the fiducials
4. Use as many fiducials as reasonably possible
5. Mark scalp at fiducial site
6. Avoid occipital region or distorted scalp
partially adapted from West et al, 2001

27. Sources of Error: MRI Image
Distortion
 Magnetic field inhomogeneities and non-linear magnetic field
gradients cause distortion
 Distortion often worst in coronal sections
 Frame may introduce additional distortion
 CT not subject to these distortions; CT/MRI fusion may
minimize effects of distortion

28. Image Fusion

29. Brain Movement
 One of the main limitations of frameless surgical navigation
systems is the reliance on preoperative imaging, which does not
account for movement of the brain during surgery.
 Gross movement of the brain occurs after the dura is violated,
owing to loss of CSF, is typically straight down, and is most
prominent over the convexity and poles.
 Significant “brain shift” is a problem that may occur during biopsy
but is of greater magnitude in craniotomy for tumor resection.

30.  Surgical field displacement or deformation
Dorward et al, 1998 Hill et al, 1998
Roberts et al, 1998 Ji et al, 2012

31.  Intraoperative ultrasonography, CT, or MRI may be employed
to provide updated imaging data after brain distortion has
occurred, and registration can be repeated during surgery to
provide a new image data set for continued navigation.

32. In what applications has image-guidance
been important?
 Tumor (biopsy, resection of glial and met tumor)
 Epilepsy (structural & physiologic data, resection)
 Functional (DBS)
 Spine (instrumentation)
 Radiosurgery (frameless technologies)
 Cerebrovascular (?)
 Other: ENT, Plastics, Ortho, General

33. Neuronavigation in Brain Tumor
Resection
 Surgical navigation has several uses as an aid to craniotomy
for tumor:
 planning the location and size of the craniotomy flap
 determining the relationships between the lesion and the surgical
approach to critical brain
 guidance to a subcortical lesion
 improving the extent of resection, which in turn can be associated with
improved patient outcomes.

35. What’s under development for image-
guidance?
 Automated registration
 Ease of use
 Updated imaging/registration
 Increasing accuracy
 Robotics
 Extension of application to other
 surgeries, other disciplines
Nathoo, 2005
Louw, 2004