3. NAVIGATION
⚫Developed due to advances in computer
science,digital scanning and image
processing.
Important part of
neurosurgery
otorhinolaryngology
maxillofacial
orthopaedics
4. COMPUTER AIDED SURGERY
⚫Magnetic resonance or computed
tomography images are used to
reconstruct 3D images of the oprative
volume. Used for
Surgical planning
Surgical simulation
Navigation
5. ⚫These 3D models were used to
Make measurements
drive numerically controlled
milling machines to create physical
models
To view pt’s anatomy and disease process
Segmentation from the data was done by
sofisticated image processing software.
6. ⚫In OT
, images were presented as 2D slices
within 3 orthogonal plane of spaces.
⚫Surgical tool was developed to enable the
localization of anatomical features to
confirm the precise position of a pointer
within the operative field.
7. ⚫Useful when the disease process or
previous surgery has distorted the normal
anatomy.
⚫The images are vector representations of
previously segmented and processed
data.
⚫3D data set can be superimposed on pt’s
anatomy.
8.
9. Preoperative imaging
⚫2 purposes
⚫Diagnostic tool
⚫Assess the extent of disease.
⚫Makes surgery safer
⚫Training better
⚫Surgeons plan their approach
maxillofacial surgeons were able to make
better fitting prosthesis.
10. Navigation in FESS
⚫Improves surgical accuracy-90% accurate
in identifying critical landmarks.
⚫Reduces risk of major
intracranial
o
• intraorbital complications.
• Enhances surgical efficiency
• Accelerates learning curve
• Reduces operative time.
•
11. IMAGE RECONSTRUCTION
⚫3D data from 2D sections are created
using highly complex algorithms that are
specific to the particular scanner and
scanning protocol.
⚫Slices concept
⚫Pixels and voxels
⚫Volume averaging
12. Concept of slices
⚫CT scan converts 1D xrays into 2D slices.
⚫Referred to as a single image section
which may be acquired in
axial
coronal
⚫
⚫
⚫ sagital plane
⚫By changing the gantry angle.
⚫Each section has width known as slice
thickness- width of xray beam detector
window used.
⚫Smaller width beams produce higher
resolution 2D images.
13. ⚫Slices are placed along the area to be
scanned with an interslice distancethat
varies depending on
⚫ the scanning protocol to be used
⚫ size of the anatomical str to be imaged.
⚫Spiral CT are better as
faster
less radiation
collect data in helical fashion
reconstructed into 3D data.
14.
15. Pixels and voxels
⚫Pixel: smallest picture elements
⚫The more pixels in a certain distance,the
better the image.
⚫Highest resolution in CT 512x512 pixels
per image.
⚫Image resolution is stated by no of pixels
in the x and y axis
⚫Hounsfield unit: the value of each pixel
ranging from -1000 to 3096.
16. ⚫CT scans are calibrated as 0=density of
water.
⚫High pixel values are displayed as white.
⚫The lower the value,the lower the density
of the tissue,the darker the pixel would
appear.
⚫VOXELS:3D Blocks or volumnetric picture
elements.
⚫Depending on inter slice distance can be:
⚫
⚫
cube
cuboid
17. VOLUME AVERAGING
⚫Partial volume averaging:
⚫ if a str falls partially within a pixel,the
true value of the str will be assigned a
value less than the normal value of the
str.
⚫Major problem in delineating where the
edge of a str should lie within a given
image.
⚫Overcome by complex algorithms
18.
19. VISUALIZATION OF IMAGE
RENDERING:process of generating images which
represent 3D anatomy with some degree of tissue
transperancy.
VOLUME RENDERING
SURFACE RENDERING
Triplets of data points
are grouped as the
vertices of adjacent
triangles that
interconnect to make
up entire surface
known as facets.
⚫ Projecting each voxel
on to a viewing plane
with a value related to
the physical property
⚫ Operator may choose
to display only the max
contribution for any
voxel along a ray.
⚫ This produces image
max intensity
projection.(MIP)
20. ⚫ Requires preprocessing
⚫ Voxels containing
anatomical surfaces
must be decided
⚫ The derived surfaces
are isosurfaces that
correspond to surfaces
of equal functional
activity.
⚫ Geometric primitives
obtained:
contour tracing
Surface extraction
• Segmentation:extractio
n of tissue topology
• These geometric
primitives are displayed
by computer graphics.
⚫ VOLUME RENDERED
images appear diff from
a surface rendered
image in that
anatomical structures
are presented as having
some degree of
transparency.
⚫ Enhances depth
perception
⚫ Increases accuracy
⚫ Placement of surgical
instruments with more
accuracy.
21. SURGICAL PLANNING
• Enables the surgeon to:
assess pt’s anatomy objectively
communicate with other surgeons
review these films at a later date.
• The data can be segmented and
manipulated to familiarize the surgeons
with specific features pertinent to the pt
and the procedure to be performed.
22. SURGICAL SIMULATION
⚫Operate using a 2D image on a television
monitor
⚫Develop new hand eye coordination skills
⚫Simulators create virtual surgical
environment.
⚫Esp in skull base surgery.
⚫Able to virtually manipulate and perform
endoscopic surgeries.
23. Image guidance
⚫ Alerts surgeon about variation in anatomy.
⚫ Use pt’s image data intraoperatively to
determine position
distance from vital organs
hidden anatomical features
• 2 fundamental process
• Registration
• tracking
24. REGISTRATION
⚫ Once the pt is secured in OT table, registration of
cartesian coordinates of the CT scan to that pt is
done by:
locating anotomical landmarks visible on the
pt and the image data using a probe that is
visible o the tracking device.
The position of the tip of the probe is
identified by the tracking device and the
coordinates are fed back into navigation
software.
other methods use masks and laser scanning
tools.
25.
26.
⚫ Calculations made in real time indicate the point
accuracy.
⚫ Some make use of fiducial markers that are applied
to the pt before scanning on the day of surgery.
⚫ Reference points should be adjacent to surgical field.
⚫ Registration error is only a measure of the accuracy
of correlation beetween selected points in the virtual
data sets and the anatomical markers identified on
the pt.
⚫ Target error:error that could be expected if a probe
was placed on a random point of interest in surgical
field.
influenced by the registration error
lessened if the target is within volume described
by fiducial markers.
⚫
27. TRACKING
⚫Tracking devices:sensors that provide
dynamic positional information.
⚫Should be:
very precise
consistently accurate
Fast enough to give 25 readings in 1 sec
Be insensitive to changes in temperature
unaffected by metal objects
Able to track 2 objects simultaneously.
28.
29. 1. Earlier we used mechanical arms fitted with
potentiometers
were fast
cumbersome
had restricted range of movements
hindered the movement of the tracked
object
2.Based on magnetic field distribution
effective and cheap.
affected by metal
3 .Infra red light sensors:
most commonly used
30. ⚫ Active devices
⚫ Sense infrared light
from LED attached to
the pt or location
probe.
⚫ Passive devices
⚫ Detect infrared light
reflected from
metallic balls
attached to pt or
probe.
31.
32. ⚫ To detect changes in pt’s position ,arches with LED an be
fitted to Mayfield clamp.
⚫ Accuracy of 2-5 mm .
4. Inertial trackers:
⚫ provide one rate of change of rotational measurement
only.
⚫ Not accurate for slow position changes.
5. Based on ultrasound signals:
• achieve greater accuracy.
• susceptible to changes in temperature and air currents.
• long lag times
• Interference from echoes and noises.
33. CLINICAL APPLICATION
⚫In the areas of skull base and endoscopic
surgeries.
Skull base surgery:
pre op planning
Design of bone flaps
Identification of imp str
Finding small tumours in obscure parts
34. Rhinology:
⚫ Difficult revision fess.
⚫ Localize frontal recess in DRAF procedures.
⚫ Trans nasal, trans sphenoidal
hypophysectomy.
Otology :
• Locating facial nerve
• Identifying lesions of petrous apex
• Tumours of IAC.
• meningiomas
• vestibular schwannomas
• Mastoid surgery
• locate dura ,brain,jugular bulb.
•:
