Indigenization Of Fiducials In Image Guided Neurosurgery

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  • 1. Fiducials: Achilles heel of image guided neurosurgery An attempt at indigenization & improvement Dr Deepak Agrawal
  • 2. Background
    • Image-guided neurosurgery is becoming more popular
    • It increases accuracy and …
    • Improves the quality of neurosurgical output in a centre
    • A step towards consistency in surgical results
    • (References to be put)
  • 3.
    • Limitations
    • High initial purchase cost
    • Learning curve
    • Cost of disposables (fiducials) and MR/CT
  • 4.
    • High Initial purchase cost
    • Initial systems cost 2-4 crores
    • AIIMS was the first centre to have IG system (Stealthstation) in India ?1999
    • Now a image guidance system can be purchased for RS 80 lakhs
  • 5.
    • Learning curve
    • Systems are getting more user friendly
    • Initially added 2-3hrs to the operating time
    • With experience, only 15-20 minutes are needed to set up the system
  • 6.
    • Cost of diposables
    • Propriety item.
    • In stealthstation 10 disposable fiducials are used
    • Literature shows less tha 8-10 fiducials may cause Incr errors
    • Set of 10 fiducials costs $100 (approx Rs 4000)
  • 7.
    • Disposable fiducials can be reused upto a max of 2-3 times
    • Problems may arise in registration due to movement of scalp
  • 8. Process of image guided surgery
    • Fiducials are applied to the patients scalp
    • Ideally should be around the site of pathology
    • May need to shave the hair
  • 9.
    • Thin Slice CT/MRI is done with the fiducials in place according to prtocol
    • 1mm slices starting from the hard palate in
    • Read
  • 10.
    • The CT/MRI may be contrast or plain depending on the pathology
    • The images are saved on a CD in the standard DICOM format
    • CD loaded on the stealthstation wokstation (inside the OT, just prior to surgery)
  • 11.
    • Loaded images checked for orientation & windowing
    • The fiducials are marked visually
  • 12.
    • Following intubation, the patient is positioned & head fixed rigidly on mayfield clamp
    • The actual fiducials are then matched with those marked on the MR/CT images
    • This gives a 3D localisation of any point in space in the patients brain
  • 13.
    • Sources of error
    • Wrong marking on CT/MR
    • Errors during reg due to movement of scalp & affixed fiducial
    • Head fixation not rigid
  • 14.
    • Aim of this study:
    • To indigenize the fiducials for use in image-guided neurosurgery
    • To improve upon the accuracy obtained using conventional fiducials
  • 15.
    • Prerequisites for a potential fiducial
    • Cheap and easily available
    • Can be used with both CT/MRI
    • Good contrast ratio with scalp
    • Easy & good fixation to scalp
    • Easy to register with stealthstation
    • Should allow mm accuracy during registration
  • 16.
    • Copper sulphate paste
    • Filled into syringe and applied wet to the scalp
    • Allowed to dry
  • 17.
    • Rubber caps from vials filled with copper sulphate
    • Poor contrast ratio with surroundings
    • Difficult to stick to scalp
  • 18.
    • Vitamin E capsules
    • Good contrast ratio (?Fat content)
    • Potential problem: Being curved,no identifiable point to register
    • Tried making a hole in it-vitamin leaked out
  • 19.
    • Vitamin E capsule
    • Easier to fix to scalp
    • Cleaned the area with Tinc Benzoin
    • Put the capsule & taped it with leukoplast/dynapore
    • Being compact, whole head shave not required
  • 20.
    • Vitamin E (Registration)
    • As expected, registration difficult on scalp as no identifiable point present.
  • 21.
    • 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.
    • Attributed to Benjamin Franklin
  • 22.
    • Vitamin E (Registration)
    • Decided to mark the tips of the capsule instead of a point on the scalp
  • 23.
    • Registration using this method yielded overall accuracy < 1.5 mm
    • Improved accuracy could be attributed to decreased scalp movement
  • 24.
    • Only 5 capsules were required
    • (each tip on either end serves as a fiducial)
    • Total cost comes to Rs 5
    • As a backup measure 5 additional capsules may be applied
  • 25.
    • Conclusions
    • Vitamin E capsules serve as excellent fiducials for image guided neurosurgery
    • Save more than 99% costs on the disposables
    • Improve accuracy of the procedure as scalp movement is diminshed
  • 26.
    • Representative cases (1-2)
  • 27.
    • Indigenization of fiducials in Image-guided neurosurgery
  • 28.  
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  • 31.