Indigenization Of Fiducials In Image Guided Neurosurgery


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Indigenization Of Fiducials In Image Guided Neurosurgery

  1. 1. Fiducials: Achilles heel of image guided neurosurgery An attempt at indigenization & improvement Dr Deepak Agrawal
  2. 2. Background <ul><li>Image-guided neurosurgery is becoming more popular </li></ul><ul><li>It increases accuracy and … </li></ul><ul><li>Improves the quality of neurosurgical output in a centre </li></ul><ul><li>A step towards consistency in surgical results </li></ul><ul><li>(References to be put) </li></ul>
  3. 3. <ul><li>Limitations </li></ul><ul><li>High initial purchase cost </li></ul><ul><li>Learning curve </li></ul><ul><li>Cost of disposables (fiducials) and MR/CT </li></ul>
  4. 4. <ul><li>High Initial purchase cost </li></ul><ul><li>Initial systems cost 2-4 crores </li></ul><ul><li>AIIMS was the first centre to have IG system (Stealthstation) in India ?1999 </li></ul><ul><li>Now a image guidance system can be purchased for RS 80 lakhs </li></ul>
  5. 5. <ul><li>Learning curve </li></ul><ul><li>Systems are getting more user friendly </li></ul><ul><li>Initially added 2-3hrs to the operating time </li></ul><ul><li>With experience, only 15-20 minutes are needed to set up the system </li></ul>
  6. 6. <ul><li>Cost of diposables </li></ul><ul><li>Propriety item. </li></ul><ul><li>In stealthstation 10 disposable fiducials are used </li></ul><ul><li>Literature shows less tha 8-10 fiducials may cause Incr errors </li></ul><ul><li>Set of 10 fiducials costs $100 (approx Rs 4000) </li></ul>
  7. 7. <ul><li>Disposable fiducials can be reused upto a max of 2-3 times </li></ul><ul><li>Problems may arise in registration due to movement of scalp </li></ul>
  8. 8. Process of image guided surgery <ul><li>Fiducials are applied to the patients scalp </li></ul><ul><li>Ideally should be around the site of pathology </li></ul><ul><li>May need to shave the hair </li></ul>
  9. 9. <ul><li>Thin Slice CT/MRI is done with the fiducials in place according to prtocol </li></ul><ul><li>1mm slices starting from the hard palate in </li></ul><ul><li>Read </li></ul>
  10. 10. <ul><li>The CT/MRI may be contrast or plain depending on the pathology </li></ul><ul><li>The images are saved on a CD in the standard DICOM format </li></ul><ul><li>CD loaded on the stealthstation wokstation (inside the OT, just prior to surgery) </li></ul>
  11. 11. <ul><li>Loaded images checked for orientation & windowing </li></ul><ul><li>The fiducials are marked visually </li></ul>
  12. 12. <ul><li>Following intubation, the patient is positioned & head fixed rigidly on mayfield clamp </li></ul><ul><li>The actual fiducials are then matched with those marked on the MR/CT images </li></ul><ul><li>This gives a 3D localisation of any point in space in the patients brain </li></ul>
  13. 13. <ul><li>Sources of error </li></ul><ul><li>Wrong marking on CT/MR </li></ul><ul><li>Errors during reg due to movement of scalp & affixed fiducial </li></ul><ul><li>Head fixation not rigid </li></ul>
  14. 14. <ul><li>Aim of this study: </li></ul><ul><li>To indigenize the fiducials for use in image-guided neurosurgery </li></ul><ul><li>To improve upon the accuracy obtained using conventional fiducials </li></ul>
  15. 15. <ul><li>Prerequisites for a potential fiducial </li></ul><ul><li>Cheap and easily available </li></ul><ul><li>Can be used with both CT/MRI </li></ul><ul><li>Good contrast ratio with scalp </li></ul><ul><li>Easy & good fixation to scalp </li></ul><ul><li>Easy to register with stealthstation </li></ul><ul><li>Should allow mm accuracy during registration </li></ul>
  16. 16. <ul><li>Copper sulphate paste </li></ul><ul><li>Filled into syringe and applied wet to the scalp </li></ul><ul><li>Allowed to dry </li></ul>
  17. 17. <ul><li>Rubber caps from vials filled with copper sulphate </li></ul><ul><li>Poor contrast ratio with surroundings </li></ul><ul><li>Difficult to stick to scalp </li></ul>
  18. 18. <ul><li>Vitamin E capsules </li></ul><ul><li>Good contrast ratio (?Fat content) </li></ul><ul><li>Potential problem: Being curved,no identifiable point to register </li></ul><ul><li>Tried making a hole in it-vitamin leaked out </li></ul>
  19. 19. <ul><li>Vitamin E capsule </li></ul><ul><li>Easier to fix to scalp </li></ul><ul><li>Cleaned the area with Tinc Benzoin </li></ul><ul><li>Put the capsule & taped it with leukoplast/dynapore </li></ul><ul><li>Being compact, whole head shave not required </li></ul>
  20. 20. <ul><li>Vitamin E (Registration) </li></ul><ul><li>As expected, registration difficult on scalp as no identifiable point present. </li></ul>
  21. 21. <ul><li>For want of a nail the shoe was lost, For want of a shoe the horse was lost, For want of a horse the rider was lost, For want of a rider the battle was lost, For want of a battle the Kingdom was lost, And all for the want of a horseshoe nail. </li></ul><ul><li>Attributed to Benjamin Franklin </li></ul>
  22. 22. <ul><li>Vitamin E (Registration) </li></ul><ul><li>Decided to mark the tips of the capsule instead of a point on the scalp </li></ul>
  23. 23. <ul><li>Registration using this method yielded overall accuracy < 1.5 mm </li></ul><ul><li>Improved accuracy could be attributed to decreased scalp movement </li></ul>
  24. 24. <ul><li>Only 5 capsules were required </li></ul><ul><li>(each tip on either end serves as a fiducial) </li></ul><ul><li>Total cost comes to Rs 5 </li></ul><ul><li>As a backup measure 5 additional capsules may be applied </li></ul>
  25. 25. <ul><li>Conclusions </li></ul><ul><li>Vitamin E capsules serve as excellent fiducials for image guided neurosurgery </li></ul><ul><li>Save more than 99% costs on the disposables </li></ul><ul><li>Improve accuracy of the procedure as scalp movement is diminshed </li></ul>
  26. 26. <ul><li>Representative cases (1-2) </li></ul>
  27. 27. <ul><li>Indigenization of fiducials in Image-guided neurosurgery </li></ul>