This ppt describes about newly adapted technique of image guided surgery in ENT

1. IMAGE GUIDED SURGERY IN
NOSE AND PNS

2. INTRODUCTION
 Image-guided surgery (IGS) has become a widely adopted technology in
otolaryngology.
 Since its introduction nearly three decades ago, IGS technology has developed
rapidly and improved real-time intraoperative visualization for a diverse array of
clinical indications.

3.  MRI or CT images are used to reconstruct 3D images of the operative volume used
for
 Surgical planning
 Surgical simulation
 Navigation

4.  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 set can be superimposed on patients anatomy

5. SURGICAL PLANNING
 Enables the surgeon to assess the patients anatomy objectively
 Review these slides later
 The data can be segmented and manipulate to familiarize the surgeon with specific
features pertinent to the patient and the procedure to be performed.

6. SURGICAL SIMULATION
 Simulators create a virtual surgical environment.
 Especially in skull base surgeries.
 Able to virtually manipulate and perform endoscopic surgeries.

7. NAVIGATION
 Improves surgical accuracy to 905 in identifying critical landmarks.
 Reduces risk of major intracranial and intra orbital complications
 Enhances surgical efficiency
 Accelerates learning curve
 Reduces operative time

8. IMAGE RECONSTRUCTION
 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

9. CONCEPT OF SLICES
 Slices are placed along the area to be scanned with an interslice distance that
varies depending on
 the scanning protocol to be used
 size of the anatomical str to be imaged.
• Spiral CT are better
1. as faster
2. less radiation
3. collect data in helical fashion
4. reconstructed into 3D data.

10. PIXELS AND VOXELS
 Pixel: smallest picture elements
 • The more pixels in a certain distance, the better the image.
 • Highest resolution in CT 512×512 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.

11.  • 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 volumetric picture elements.
 • Depending on inter slice distance can be: cube or cuboid

12. 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

13. RENDERING
 process of generating images which represent 3D anatomy with some degree of
tissue transparency.
 SURFACE RENDERING • Triplets of data points are grouped as the vertices of
adjacent triangles that interconnect to make up entire surface known as facets.
 VOLUME RENDERING • 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 protection.

14. IMAGE GUIDANCE
 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

15. REGISTRATION
•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 between 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

16.  Once the patient secured on the OT table the registration of the cartesian
coordinates to the CT of the patient is done by
 Locating anatomical landmarks visible on the patient and image data using a probe
 The position of the tip of the probe is detected by the tracker and the coordinates
is fed to the navigation system
 Other methods use masks and laser tools.

17. TRACKING
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.

18. 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