Keywords
neuronavigation - benefits - equipment - tips and tricks - future perspectives
Introduction
Advances and innovation in neuroimaging, surgical techniques, and medical equipment
over the last decade have given an enormous boost to the improvement and success of
contemporary neurosurgery. One of these advances has been image-guided neurosurgery,
which is any method that uses imaging technology to promote the successful performance
of brain and spine surgery.[1]
Roentgen's discovery and transformation of X-ray technology in the 1890s led to image-guided
surgical procedures,[1]
[2] the importance of which was reinforced in the 1970s with the development of computed
tomography (CT) and frame-based stereotaxy.[3]
[4] A microscope embedded with a frameless stereotactic positioning system was introduced
by Roberts in 1986.[5]
The frameless neuronavigation system aims for a simultaneous virtual link between
preoperative radiological images and real anatomical structures on the patient.[6] Three main components make up the technical features, namely the following:
-
The patient's preoperative CT scan or magnetic resonance images (MRI) supply the raw
data for the image generation software.
-
The optical system, which determines the position of a pointer device and patient
in the operating room by using a camera to track the positions of optical markers,
affixed to them. The markers are attached directly to the pointer device or a dynamic reference frame connected to a support mechanism secured to the patient or very close to the patient.
-
The image processing system is a computer workstation that allows for data storage and 3D reconstruction. Tri-planar 2D images in axial,
sagittal, and coronal planes, as well as 3D reconstruction images, provide a real-time
dynamical display on a monitor screen.
With the help of an optically linked pointer, the landmarks on the patient are synchronized
with the same structures obtained from the radiological images allowing for synchronization
of the 3D model. The coordinates of the external fiducials are then adjusted to the
neuroradiological coordinates, establishing the correlation of the patient's head
relative to the 3D digitizer. From this point on, the optically linked pointer is
able to show an exact localization either in three perpendicular sectional 2D views
or in a 3D reconstructed image.[7]
Benefits of Neuronavigation
Benefits of Neuronavigation
Apart from the operative microscope introduced by Yasargil in the 1960s,[8]
[9] neuronavigation has been of utmost benefit to neurosurgeons worldwide. Navigation
systems such as the StealthStation Treon Plus have proven to be safe, effective, accurate, and assistive instruments to modern
neurosurgery. This image-guided surgical modality supports and facilitates intraoperative
orientation, making neurosurgical operations more precise and less traumatic, resulting
in minimal brain damage and hence completing the goal of maximal safe resection.
The following are the benefits of neuronavigated brain surgery:
-
Accurate localization on the surface of the skull is realized and procedures such
as craniotomy can be tailored per patient for an exact and appropriate dimension.
-
When performing skull base surgery, the accurate orientation of fixed bony structures
by neuronavigation allows for precise orientation.
-
Neuronavigation allows for precise intradural guidance through the demonstration of
sulci, gyri, or cisterns in cases of deep-seated intra-axial lesions. Without neuronavigation,
deep-seated intra-axial lesions will have to be “searched” for during surgery, as
they are usually encased in the normal brain, thereby subjecting it to potentially
fatal traumatic injury and damage ([Fig. 1]).
-
Neuronavigation allows for percutaneous puncture and biopsy without the need for screwed
ring fixation as in a stereotaxy frame.
-
Via neuronavigation, the surgeon is able to go through a repetitive “virtual walk”
of the region of interest, providing invaluable visualization of the patient-based
anatomy. The 3D representation provides clues to the exact location of the lesion
along with neighboring eloquent structures. Thereafter, prospective surgical interventions
can be simulated and a tailored approach suitable for the lesion can be determined.
Consequently, neuronavigational systems are an excellent tool for presurgical planning
and neurosurgical training.[7]
[10]
-
The aim of image-guided neurosurgery has been lately to incorporate anatomical image
data and functional information. Positron emission tomography (PET) and functional
magnetic resonance imaging (fMRI) data seem to be promising for this goal. PET is
able to demonstrate the pathological area, especially in gliomas with the injected
tracer but is insufficient in providing precise anatomical localization. fMRI adds
information regarding eloquent brain areas.[2]
[11]
[12]
[13]
[14] The integration of this information into presurgical planning has led to refined
strategies of resection and may facilitate more extensive resection near eloquent
brain areas.
-
Utilization of neuronavigation via 3D visualization of the vital tracts during brain
tumor surgery has been reported[15] and may aid in the salvage of this tract during surgery.
-
During epilepsy surgery, specifically for foci that are detectable by electroencephalogram
(EEG) only, intraoperative or chronic extraoperative electrocorticography is essential
for resection. The electrocorticographic mapping data can be integrated into the neuronavigation
system allowing for visualization at the operative site. It can be used to determine
the extent of resection in selective amygdalohippocampectomy, whenever the epileptogenic
cortex is not significantly altered with respect to color, texture, or consistency.[16]
-
Ear, nose, and throat (ENT) and maxillofacial surgery is able to benefit from neuronavigation
as well. Both endonasal sinus and skull base surgeries pose a risk for the damage
of vascular and neural structures in a confined space. Moreover, due to the destructive
nature of diseases and previous procedures, surgical landmarks may be lacking. This
limited intraoperative orientation during such procedures implicates a definite risk
for complications. Neuronavigation is a beneficial tool for surgery of the anterior,
middle, and posterior skull base, fossa infratemporalis, retromaxillary space, and
paranasal sinuses. It has also proven to be effective during surgeries involving the
upper neck and upper mediastinal approaches.[17]
[18]
Fig. 1 (A) A 66-year-old male patient with a butterfly tumor. (B) Neuronavigation was not used and the follow-up control computed tomography (CT)
showed that the lesion was direly missed. (C) A 60-year-old male patient with a deep-seated lesion. (D) Neuronavigation-assisted biopsy was successfully performed.
Computer-aided technology was primarily developed for neurosurgeons for accurate guidance
during neurosurgical operations, but nowadays neuronavigation has become an interdisciplinary
tool. With studies proving its benefits in cranial surgery, promising studies have
evaluated its applicability in spinal surgery as well.[11]
[12]
[19] Aside from the clinical benefits, neuronavigation is an invaluable tool for training
of young surgeons, allowing for a thorough understanding of the complex anatomy and
appropriate surgical steps.
The Equipment
All neuronavigation systems have, basically, the same principle of operation. Each
system is usually a hardware platform that enables real-time surgical navigation using
radiological patient images. The software's primary aim is to render the patient's
radiological images into a variety of perspectives (axial, sagittal, coronal, and
oblique) allowing for rotation, zoom, and slicing. Although different systems may
request specific unique details, slices thinner than 1 mm and inclusion of scalp landmarks
(nose, ear, and eyes) are prerequisites for radiological images. The patient must
remain completely still, especially during MR imaging as the distortion would decrease
the accuracy of intraoperative targeting. The surgeon can manipulate the 3D model
in order to simulate a trajectory. The number of 3D models can be increased to aid
visualization of the lesion allowing for a rehearsal of the surgery. During the operation,
the system is able to track the position of the instruments or a pointer while simultaneously
portraying the position in regard to the radiological images.[20] This is the main core of navigation as the system is able to portray the exact position of the tip of a pointing device
after the patient has been registered on a translation map. The translation map is created before the surgical incision, after the patient has been positioned. The
external anatomical structures are used to register the points on the 3D render and
thereafter the system displays within multiple patient image planes and other anatomical
renderings.[20]
For simplicity, the equipment described here shall be the StealthStation Treon Plus, otherwise referred to as the Treon Treatment Guidance System (TTGS). This system
is essentially made up of two separate but complementary carts: the Viewing Cart and the Nav Cart. The carts can be docked together or used separately, depending on the preference
of the surgeon or the operating room setup. The viewing cart should be in a clear
view of the surgeon and the Nav Cart should be in the sight of the patient to allow
for precise and simultaneous navigation. The Viewing Cart contains the power supply, computer, and all related peripheral devices ([Fig. 2]). The Viewing Cart can be used as a standalone surgical planning station and has
a touchscreen monitor.
Fig. 2 The viewing cart exterior (A) front and (B) back views. (1) Articulating arm; (2) touchscreen; (3) chicane; (4) storage drawer;
(5) keyboard/mouse drawer; (6) system side panel; (7) media bays; (8) cart docking
mechanism; (9) cart communication cable connection; (10) On/off switch; (11) power
cord outlet; (12) caster; (13) cable wraps.
The touchscreen monitor is a high-resolution and flat-panel computer screen. When
placed in the surgical field, it allows the physician to control the system without
the need for an assistant, keyboard, or mouse, using a sterilized stylus. For any
software fields that require text entry, a virtual keyboard appears onscreen with
buttons that can be touched like a typewriter. Although the touchscreen eliminates
the need for a keyboard and mouse, a keyboard and mouse may be utilized in certain circumstances.
Breakout Box
The Breakout Box acts as a junction box for various hardware devices, such as footswitch,
reference frame, and probes. The breakout box does not contain any user-serviceable
parts and can be hooked onto the operating room bed rail or the Nav Cart. During transportation
and storage, the breakout box can be attached to the lower right-hand side of the
Nav Cart.
The Nav Cart and Optical System
The Nav Cart and Optical System
The Nav Cart ([Fig. 3]) acts as the base for the camera and contains the Tool Interface Unit (TIU) and a storage drawer. The Nav Cart is connected to the Viewing cart via a communication
cable, which also supplies the necessary power for the camera and the TIU. The optical system determines the position of an instrument (such as a probe of a pointing device) and
the patient in the operating room by using a camera to track the positions of optical markers affixed to them. In the case of instruments, the markers are attached directly to
the instrument being used while the optical makers on the dynamic reference frame
([Fig. 4]) allows for tracking of the patient's position. The dynamic reference frame is securely
connected to a mechanism to avoid any deviation throughout surgery.
Fig. 3 The Nav Cart exterior (A) front and (A) back views. (1) Camera boom; (2) camera; (3) laser pointer; (4) camera docking port;
(5) chicane; (6) post; (7) post lock; (8) cart docking mechanism; (9) storage drawer;
(10) cable wraps; (11) cart communication cable; (12) breakout box; (13) caster locks.
Fig. 4 Dynamic reference frame with passive spheres.
There are two types of optical markers. Some components may have light-emitting diode
(LED) optical markers, and others may have sterile spheres. LEDs generate and emit
infrared light. Sterile spheres reflect infrared light that is emitted by the camera.
The camera (sometimes called the localizer) detects the optical markers, determines
their spatial positions using the principle of triangulation, and continuously reports
this information to the computer. The computer uses this spatial information, in conjunction
with information regarding the geometry of the instrument currently in use, to determine
exactly where the tip of the instrument is located on the patient's anatomy. The system
camera uses two lenses to geometrically triangulate the spatial coordinates of each
optical marker on the instrument and reference frame. In the case of cabled devices
(such as the active registration probe), the camera lenses receive infrared light
signals directly from the LEDs on each device. In the case of passive (wireless) devices,
the passive spheres on each device reflect light emitted by infrared illuminators
on the camera back into the camera lenses. The camera continuously communicates the
location of each LED or passive sphere to the system. In order to effectively detect
the LEDs or passive spheres, the camera must be aimed toward the devices and positioned
at the proper distance from them.
Dynamic Referencing
To maintain accuracy, the new generation of TTGS continuously tracks the position
of the anatomy during registration and navigation. This is extremely vital as the
patient's or the localizer's position may unintentionally be changed after the registration.
Thus, the position of the dynamic reference frame should continuously be monitored
to avoid inaccurate navigation.
This is unlike the first-generation TTGS, which had either system- or user-dependent
intraoperative or application inaccuracy ranging from 0.5 to 6.5 mm.[7] The inaccuracy was due to inaccurate patient registration procedure on the one hand
and brain shift (due to retraction with a spatula, working in the ventricles, or gravitational
action due to the position of the patients' head) on the other hand. Thus, the new-generation
TTGSs have an added advantage over previous-generation TTGSs due to dynamic referencing.
Setting up the Equipment
Certain precautions must be taken before setting up and starting the neuronavigation
system. The system must be positioned at least 25 cm away from any source of flammable
gas including anesthetic agents, oxygen, or nitrous oxide. For electrical safety reasons,
any local area network (LAN) cables must be disconnected from the TTGS before proceeding
with the system setup. Fluid must also be prevented from entering any part of the
system. If fluid is suspected to have entered any part of the unit, adequate dry time
is allowed before connecting the system to power.
To Set Up and Start the System
To Set Up and Start the System
-
The communication cable is connected from the Nav Cart to the Viewing Cart.
-
The system power cord is plugged into an electrical outlet.
-
The footswitch is connected to the Button port on the breakout box.
-
The green power on button on the left side of the Viewing Cart is pressed and briefly
held down. The system would power up and the login screen would appear when all bootup
diagnostics are completed.
-
The application icon is double-clicked to launch the software.
Docking the monitor is done by first adjusting (pushing down) the articulating arm such that the arm
button is in the lock position. There will be an audible click when the arm locks.
Second, the monitor arm is adjusted such that it is in the lock position. The lower
elbow of the chicane would be at its closest point to the back of the system cart.
Third, the monitor is rotated such that the face is pointing downward. Fourth, the
monitor is pushed down toward the back of the cart.
The breakout box can hook onto the operating room bed rail or the Nav Cart. During
transportation and storage, the breakout box is attached to the lower right-hand side
of the Nav Cart. This is done by aligning the posts on the breakout box with the slots
on the side of the cart and firmly pushing the posts into the slots.
Registration
Registration (to match the 3D position of the patient and the preoperative images)
can be done using the following modalities:
-
Tracer registration.
-
Reg options.
-
PointMerge.
-
Touch-n-Go.
The TTGS tracer registration is always preferred as it gathers more points, does not
require the use of fiducials, and has more flexibility ([Fig. 5]). For first-generation navigation systems, it is important to ensure that the frame
does not move with respect to the anatomy from the time of registration until navigation
is complete because the position of the anatomy is defined by the position of the
reference frame. Slippage or rotation of the reference frame concerning the anatomy
after registration would result in inaccurate navigation. Fortunately, the newer-generation
navigation systems do not have this problem due to dynamic referencing.
Fig. 5 Treon Treatment Guidance System (TTGS) screen during registration.
After the equipment is properly set up and the software launched, registration can
begin by simply following the instructions on the touchscreen such as the following:
-
Slice choice (of CT or MRI), of which 100 to 120 is often chosen.
-
Navigation with Skin or Tumor, of which Skin is often chosen.
-
Defining or circumscribing the tumor.
-
Building the 3D image.
-
Setting the point of Entry.
-
Setting the Target (by clicking on the circumscribed brain lesion).
-
Choice of pointing device, of which a small passive planner is often chosen.
Instruments designed for use with the TTGS have a precise instrument geometry and
LED/sphere configuration. The specific geometry of each instrument is stored in a
file to which the computer refers to determine where the tip of the instrument is
located in relation to the instrument LEDs or spheres. Before commencing navigation,
the user must inform the system in which instrument has been chosen, for example,
the small passive planar. When the instrument to be used is selected from the probe
list in the application software, verification must be done to ensure that the instrument chosen is not bent or otherwise damaged.
This is done by placing the tip of the instrument into a metal divot on the reference
frame and pressing the footswitch. The camera and computer then confirm that the instrument
being used matches the specifications for the instrument selected in the software.
The progress of registration would be displayed on the screen. After the pointing
device is selected and verified, tracing is done on the patient for registration to
be completed. When the navigation system is ready for use, the information would be
displayed on the screen ([Fig. 6]). The workflow of the neuronavigation system is summarized in [Fig. 7].[21]
Fig. 6 Touchscreen of a neuronavigator showing a patient's brain images with a deep-seated
lesion (arrow).
Fig. 7 Workflow of neuronavigation. The first step is acquiring the images, which are then
uploaded to the system to allow for preoperative evaluation. This is followed by the
registration of the patient via the use of the navigation probe and divots.[21]
Tips and Tricks on Preoperative Patient Images Before Neuronavigation
Tips and Tricks on Preoperative Patient Images Before Neuronavigation
Neuronavigation is multidisciplinary, involving neurosurgeons, ENT surgeons, neuroradiologists,
biomedical engineers, etc. Preoperative images (CT or MRI) used for neuronavigation
must have the following specifications (in collaboration with the neuroradiologist
and radiologic technician) for effective use:
-
The scan quality must be of high resolution.
-
The slice thickness must be maximum 2 mm for CT and 1.5 mm for MRI. Minimum of 16-sliced
CT and 1.5-T MRI are recommended.
-
Specific prominent areas of the head and face such as the tip of the nose and tragus
must be seen on the radiologic images. This is often done as a special request by
the neurosurgeon to the radiology technician or neuroradiologist as these areas are
used for careful and adequate registration.
Pitfalls
One of the most common pitfalls encountered while using neuronavigation in cranial
surgeries is brain shift. This is a popular topic of investigation and continues to
receive attention and research. Intraoperative brain deformation occurs almost in
all cranial oncological surgeries as the brain parenchyma is distortable and dynamic.
MRI is acquired in the anatomic supine position, whereas preoperative positioning
of the patient and the head varies significantly. One way of overcoming this is acquiring
the MRI in the planned surgical position of the patient where possible such as prone
or park bench. In cases of further brain distortion due to active removal of malignant
tissue, loss of cerebrospinal fluid (CSF) or shrinkage of healthy brain parenchyma,
intraoperative ultrasonography (USG) may prove to be beneficial.[22]
[23] USG is an inexpensive and simple alternative to intraoperative real-time MRI. As
USG images vary greatly and are distorted after surgical intervention, a baseline
USG imaging should be obtained following durotomy.
Furthermore, most brain shifts occur in the gravitational direction; thus, a vertical
view of the lesion by the surgeon would only cause a downward distortion that needs
to be compensated for. Positioning the patient with this manner in mind would prevent
a more complex 3D distortion. Avoiding diuretics and hyperventilation when possible
is also another way to prevent or minimize the distortion. If the lesion is close
to an eloquent area, the most critical area should be removed first before distortion.
En bloc removal if possible is recommended and in the cases where piecemeal tactic
is to be employed, placing large cotton patties in the resection cavity can help preserve
preoperative dimensions of the lesion. Avoiding cyst puncture before total control
over the boundaries of the lesion is also recommended.[22]
In order to compensate for intraoperative changes, solutions such as coherent point
drift and fusion techniques have been advised. However, these solutions were unable
to predict volumetric deformations and failed to register an accurate whole image
from just visible landmarks and tissues.[22]
Neuroendoscopy
Neuronavigation-assisted endoscopy is gaining popularity with an increasing use. However,
its necessity is debatable. Usage of endoscopy in hydrocephalus, cysts, and ventricular
malignancies is replacing shunting and microneurosurgery. The employment of neuronavigation
has been evaluated to be beneficial in over 50% of endoscopic surgeries.[24] However, it has not proved to be beneficial in endoscopic third ventriculostomy
but rather essential for tumor biopsy or resection. It is also beneficial in defining
the best trajectory even without the visualization of landmarks. Neuronavigation assistance
has also aided in the detection of visually invisible subependymal tumors along with
the basilary artery location beneath an opaque third ventricular floor.[24] A pitfall in using neuronavigation with endoscopes is the margin of error is much
less compared to microsurgery. Thus, the positioning of the reference and navigation
arrays on the navigated endoscope is of vital importance.[25] The classical random registration points used in neuronavigation may cause a great
margin of error as neuroendoscopy addresses millimetric pathologies.
Future Perspectives
The benefits of contemporary neuronavigation in complicated brain, skull base, and
spine surgery cannot be overemphasized. It is clear that small lesions in eloquent
brain areas can be operated more radically with less morbidity compared to the preneuronavigation
era. Therefore, manufacturers are urged to offer updated and specific systems for
different applications. Workflow analyses and also cost–benefit evaluations have to
be carried out to increase the efficiency of neuronavigation in the future. Apart
from some initial work on evidence-based medicine, a sound basis for an assessment
of neuronavigation from the perspective of health care system efficiency, effectiveness,
and economy is required.[7]
Innovation in the medical equipment industry has led to the update of neuronavigation
equipment such that the systems are now more user friendly, have dynamic referencing,
and offer multiple tracking capabilities. The systems can also be integrated with
external devices like microscopes, endoscopes, and ultrasound; a broad array of instrument
offerings and core software applications for neurosurgery and spine procedures. In
addition, modern neuronavigation systems are capable of interfacing with intraoperative
imaging systems including intraoperative MRI (iMRI), intraoperative CT (iCT), C-arms,
and O-arms to orient surgeons with 3D images of the patient's anatomy.
In addition to the foregoing capabilities of present-day neuronavigation systems,
the ideal and desired future navigation system should adapt intraoperatively in an
online fashion to the continuously changing anatomy (dynamic referencing) and possess
automatic registration ability. The multidisciplinary aspect of neuronavigation has
to be encouraged due to the rapidly evolving computer technology. Therefore, a continuous
cooperation and exchange of information between clinicians, scientists, and medical
equipment manufacturers have to occur to improve the systems for the benefit of the
patients. Also, a common scientific language must be developed to create a global
understanding not only for methods and techniques in the field of image-guided surgery
but also for allowing adequate interdisciplinary communication.[1]
There is an ongoing development of new systems along with elaborating and improving
present systems. In order to train new surgeons and primarily prepare surgeons for
navigation-aided surgery, phantom models have been used. A stereotactic neuronavigation
phantom with rigid or deformable parts would allow the surgeon before surgery to evaluate
all aspects of entry point, patient and surgeon position, and parameters such as angle
and depth.[26] This training method or preparation of the surgeon for surgery can also be improved
by virtual reality (VR) training.[27] As the term “metaverse” is continuing to gain popularity, digital platforms providing
a virtual world based on mostly visual cues may allow the surgeon to actually perform
a surgery virtually while facing complications and difficulties that they may experience
in the real scenario. This would also allow trainees to learn from their possible
mistakes without harming any patient. The possibilities of VR training are endless,
as this type of training has been used in the aviation field for decades.
Neuronavigation has also become a part of techniques and utilities used in complex
pathologies that deemed impossible to treat surgically. Surgeons are finding unique
ways to combine neuronavigation with other adjunct techniques to successfully operate
on patients such as the removal of 2.3-cm midbrain pilocytic astrocytoma in a pediatric
patient using tractography, neuronavigation, 3D exoscope, and a tubular retractor.[28] We believe further understanding of navigation will allow surgeons to create a “toolbox”
of techniques and modalities to further improve the care for their patients.
Conclusion
The advantages of neuronavigation are enormous and well established. However, due
to the cost, underdeveloped and developing parts of the world have limited access
and experience. This review aimed to put forth a narrative guide to the use of neuronavigation,
especially for surgeons with minimal or no access. The review also emphasized some
key points and tips and tricks. It also aimed to provide evidence and framework for
possible educational references at training institutions.
