neurosurgery navigation

Question 1

what are the ideas and motivations behind image-guided (neuro)surgery?

Answer 1

• precise, intraoperative localisation of tumors, aneurysms, …
• visualization of lesions in respect to functional relevant brain areas
• improved spatial orientation and navigation
• less complications
• improved outcome

Question 2

what are the 2 relations that need to be solved?

Answer 2

1) patient to intruments /microscope
2) patient to image data

Question 3

how is the transformation patient to instruments done?

Answer 3

optical tracking technology:
- 3D cameras
- near infrared light used to calculate 3D positions of tools (triangulation)
- data sent to application for navigation and visualization

Question 4

how is the transformation patient to image data done?

Answer 4

patient registration = mathemical transformation that allows the matching of a reconstructed surface from image data (model space) and the digitized surface of the patient (physical space) -> point in image data can be assigned to corresponding point in the patient

Question 5

what are three ways to perform point registration?

Answer 5

1) surface based
2) anatomical landmark based
3) fiducial-based

Question 6

intruments: 2 types

Answer 6

1) pre-defined geometry:
- stylet used for navigated placements of catheters
- navigated biopsy needle

2) calibrated instruments

Question 7

what are 2 necessary components in a navigation system?

Answer 7

• 3D camera system
• computer / monitor camera interface

Question 8

3 types of data we can use for planning and visualization of operative approach

Answer 8

• structural image data (MR, CT, angio)
• functional image data (fMRI, DTI)
• anatomical atlases

Question 9

what is the difference between accuracy and precision?

Answer 9

• accuracy = how close we are to the actual value
• precision = how close are the repeated measurements to each other

Question 10

how does the targeting change between a microscope and an instrument?

Answer 10

microscope = targeting by adjusting
intrument = targeting by touching

Question 11

direct and indirect methods of focal point adjustment

Answer 11

1) direct = visual adjustment: judging the visual resolution, focal point is adjusted if image appears clear and sharp

2) indirect = laser-supported adjustment: judging the overlaid position of 2 crossing laser points in field of view, focal point is adjusted if laser points are superimposed

Question 12

error analysis of the microscope: directly and indirectly introduced errors

Answer 12

1) directly introduced: caused by optical properties of the microscope
- focal point adjustment
- focal length of lens
- magnification of lens

2) indirectly introduced: caused by tracking properties of the microscope
- nb of reference markers
- size of reference plane

Question 13

how does the spatial error depend on lens magnification, focal point adjustment, nb of reference planes

Answer 13

lower error if:
- higher magnification
- laser adjustment better than visual
- more planes

Question 14

what can compromise the accuracy, and what type of imaging can help?

Answer 14

1) brain shift and liquid loss can compromise the intraoperative accuracy

2) ultrasound imaging can be used to recognize and correct this shift

Question 15

what is the principle of intraoperative ultrasound imaging?

Answer 15

1) contour of tumor is overlaid on US image, and matched
2) current position of tumor is indicated by a shifted tumor contour in respect to pre-operative MR images