Image-guided Systems in Neurotology.pptx

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1. Image-guided Systems in Neurotology /Skull base Surgery DR Suman Raut ENT JR 2 nd year Nobel Medical College Biratnagar

2. History The term stereotactic surgery, originally coined by Clarke in 1908, refers to surgery incorporating devices that maintain spatial correspondence between the operating instrument and an image of the operative site . virtual reality : the combination of human-computer interfaces, graphics , sensor technology, high-end computing, and networking to allow a user to become immersed in and interact with an artificial environment

3. HISTORY Hoarsley and Clarke used these early stereotactic systems for placing electrodes in specific areas of animal brains . In 1947, Spiegel adapted the above stereotactic concepts to human use the methodology was tedious and laborious

4. HISTORY With the advent of CT, digital image databases, combined with more sophisticated surgical instrumentation, greatly enhanced the development of stereotactic surgery Pioneered by Brown , Kelly, and other neurosurgeons, modern conventional stereotactic surgery employs a head frame to register image space to surgical space

5. Preoperatively, digital image data via CT or resonance imaging (MRI) are obtained with a localization system ( fiducials ) attached to a head frame .

6. Aims of image guided systems localization of small intracranial lesions , skull-base surgery, intra cerebral biopsies , intracranial endoscopy, functional neurosurgery and spinal navigation

7. IGS SETUP The systems consist of ( 1) a set of markers on a patient (called ‘‘ fiducial markers’’ or simply ‘‘ fiducials ’’), which are present during preoperative CT or MRI scanning, ( 2) a computer tracking system used in the operating room that aligns the markers in the CT or MRI to the current anatomy and tracks a patient’s fiducial markers within the operating room Registration is the alignment of anatomic points from the radiographic scan ( eg , CT or MRI) with their true positions in the operating room .

8. IGS SETUP

9. Different types of IGS The four leading commercial IGS systems used for sinus surgery are : BrainLAB system ( BrainLAB , Feldkirchen , Germany) InstaTrak System (GE Medical Systems, Lawrence, Massachusetts) LandmarX and StealthStation system (Medtronic, Minneapolis, Minnesota) StrykerImage Guidance System (Stryker Leibinger , Kalamazoo, Michigan)

10. ERRORS IN IGS There can be two types of error: First is ‘‘ fiducial localization error’’ (FLE), which is the error in identifying the positions of the fiducial markers in the radiographic images ( FLErad ) and in the operating room (FLEOR ). Second The resultant error in aligning fiducial markers termed as ‘‘ fiducial registration error ’’ ( FRE)

11. FRAMELESS STEREOTAXY Do not use conventional head frame for recording information Consists of two basic components: Sensor : relays positional information A computer : translates the sensor ‘s positional information to a visual aid for real time anatomic information Broadly classified as:Mechanically linked system and Non mechanically linked system

12. Mechanically Linked Systems are based on arms that are mounted to the operating table. are equipped with sensitive potentiometers, or angle detectors, located within their joints . By sampling the output of rotary optical encoders at each point, a computer can determine the localization of the top of the arm and provide "arm coordinates“ that are referenced to the base of the arm . the patient's head is registered to the image of the head a transformation can be calculated to map any common point in the two coordinate systems . have proven to be accurate, although they are somewhat bulky and restrictive , have limited application in the field of otology and neurotology

13. Non Mechanically linked systems More recently, nonmechanically linked sensor systems have been developed for the registration of image data to the surgical patient . R ely on the active or passive detection of signals generated by various emitters that are attached to surgical instruments . these frameless stereotactic systems are able to localize and track surgical instruments in three-dimensional space. There are essentially three types of nonmechanically linked digitizing systems:ultrasonic , electromagnetic, and optoelectric .

14. Ultrasonic dizitizers determine position by measuring the time flight of sound from an emitter to at least three microphones. The distinct drawback to ultrasonic digitizers is that the speed of sound varies with temperature and humidity gradients, which may result in positional error . may be compromised by echoes within the operating room (OR) or by interference from extraneous radiofrequency emissions. sonic referenced systems are no longer used.

15. Electromagnetic reference systems Electromagnetic reference systems ( eg , InstaTrak System, GE Medical Systems, Lawrence, Massachusetts) R referenced by a headset, worn by the patient during the CT scan and again later during the surgical procedure. Registration more rapid and user-friendly than other commercially available frameless systems. drawback of potential interference from other electromagnetic systems This interference, as well as minor inconsistencies in the repositioning of the headset for imaging and surgery, contributes to positional error and inaccuracy. These inaccuracies are relatively minor and inconsequential for most anterior skull base surgery ( eg , endoscopic sinus surgery) where this system finds its primary application in otolaryngologic surgery. currently not well suited for lateral skull base applications.

16. Optoelectric digitizers require an unobstructed path from emitters to the overlying camera array. Three cameras, containing a 1 x4096 element linear charged-coupling device, are required to determine the three-dimensional position of infrared light-emitting diodes (LEDs) attached to the surgical instruments The overlying camera array is positioned 1.5 to 2 m above the surgical field camera can track the instrument- attached LEDs, detects and tracks the precise position of the surgical instrument in three-dimensional space.

17. VOLUMETRIC STEREOTAXY Developed by Kelly and colleagues enhanced volumetric routines are reconstructed by the computer and stacked into a "volume" that can be displayed or manipulated in stereotactic space . I mage data can be displayed in the operating microscope in the correct scale , orientation, and position superimposed on the focal plane of the surgical field. Can be used for interactive volumetric resection of intracranial tumors. displays cross-sectional volumetric contours at progressive depths along the view line so that CT-defined margin of the tumor can be localized . The tissue volume can then be resected either passively or with laser ablation via the computer or actively by the surgeon.

18. REAL-TIME INTRAOPERATIVE IMAGING relevant for neurosurgical procedures such as the removal of intracranial tumors for which surgical manipulation may produce edema and soft tissue shift . X-ray fluoroscopy, ultrasonography , and CT have permitted sufficient interactive visualization for percutaneous biopsies and some intravascular interventions, limited by the degree of spatial resolution of volumetric images as well as radiation exposure Due to its improved soft tissue contrast, volumetric resolution , multiplanar and functional capabilities, and lack of ionizing radiation, MRI is ideally suited for real-time image guided therapy. Mid-field open configurations with vertical magnets are available that permit full surgical access to patients.

19. ROBOTICS Robots offer the advantages of reliability, repeatability, and control of tremor for the neurotologic surgeon. Autonomously acting robots in concert with image-guided systems have recently been investigated for mastoidectomy by Labadie et al. at Vanderbilt Preliminary studies show the robot can achieve low-level milling of the mastoid cavity in approximately 4 min, leaving the high-level tasks of drilling on vital structures to the neurotologic surgeon. Federspil and colleagues have used robotics to accurately drill the receiving well for cochlear implants . More recently, robots have been explored for minimally invasive surgical approaches to the facial recess and cochleostomy for cochlear implantation .

20. ROBOTICS Conceivably, in the near future, robots could be used to facilitate minimally invasive access to other neurotologic anatomic structures, such as the internal auditory canal, the endolymphatic sac, and the semicircular canals. The efficacy depend upon the fiducial accuracy of the associated image-guided system

21. THANK YOU

22. REFERENCES Glasscock- Shambaug Surgery of the ear Sixth edition Otolaryngol Clinics North America 40 (2007) 611–624