1. Algorithmic Port Placement for Robot-assisted CABG Pierre Dupont Aerospace and Mechanical Engineering Boston University Collaborators: Jeremy Cannon, CHC Shaun Selha, BU Jeff Stoll, BU Robert Howe, Harvard David Torchiana, MGH endoVia Medical Seminar – August 23, 2002

2. Boston University2 Coronary Artery Bypass Graft (CABG) n Consists of two procedures 1.Harvest of the Left Internal Mammary Artery (LIMA) 2.Anastomosis of LIMA and coronary artery. Coronary Artery Aorta Internal Mammary Artery (from chest) Saphenous Vein (from leg) Plaque Blockages Illustration by Mitchell Christensen copyright ViaHealth 1999 Anastomosis Site

3. Boston University3 Procedure History n Non-endoscopic suturing Median SternotomyMedian Sternotomy Mini SternotomyMini Sternotomy Anterior ThoracotomyAnterior Thoracotomy n Endoscopic CABG ZEUS and AESOP Robotic System at MGHZEUS and AESOP Robotic System at MGH Top Notch of Sternum Xiphoid Process

4. Boston University4 How are the port locations selected? n Literature - templates n Practice – use external landmarks and size of patient’s torso to make their best guess. Top Notch of Sternum Xiphoid Process

5. Boston University5 Problems encountered - MGH 1. Inability to reach the surgical site, 2. Inability to perform the surgical procedure due to the orientations of the tools with respect to each other and the surgical site, 3. Internal instrument / endoscope collisions, 4. Robot singularities and joint limits, 5. Robot collisions.

6. Boston University6 Approach n n Port placement and robot placement problems can be solved independently. ● Port placement ● Robot placement 1. Inability to reach the surgical site, 2. Inability to perform the surgical procedure due to the orientations of the tools with respect to each other and the surgical site, 3. Internal instrument / endoscope collisions, 4. Robot singularities and joint limits, 5. Robot collisions. Robot placement Port placement

7. Boston University7 How do we define dexterity? n Preserve surgeon’s intuition n Orient instruments by task and with respect to the surgical site n Avoid internal collisions n Permit flushing of endoscope lens n Minimize the amount of the endoscope inserted into the chest cavity Right Instrument Left Instrument Line of Sight Invasive CABG Procedure

8. Boston University8 Surgical site coordinate frame Figure Key Instrument Angles  = Yaw angle in instrument plane =  Elevation angle of instrument plane Endoscope Angles = Azimuthal angle  = Elevation angle = Constant offset angle

9. Boston University9 Dexterity Metric Definition: Sum, over all surgical sites, of the weighted squared “distance” of the instruments and the endoscope from their optimal orientation angles. = vector of optimal orientation angles

10. Boston University10 Rationale for optimal angles LIMA take-down Optimal values based on surgeon’s experience in performing invasive and minimally invasive CABG’s  Instrument angles are task based.  Endoscope angles are viewpoint based Anastomosis

11. Boston University11 Implementation 5. 5. Locating Ports on the Patient 1. 1. CT Scan 2. 2. Image Processing 3. 3. Surgical Planning System 4. 4. Operating Room Registration

12. Boston University12 System evaluation n Thorax model: ribs with neoprene skin n Task: vessel dissection 3 mm diameter “vessel” of stiff clay encased in “soft tissue” matrix of modeling dough and then shrink wrapped.3 mm diameter “vessel” of stiff clay encased in “soft tissue” matrix of modeling dough and then shrink wrapped. Three dissections: two at extremes of LIMA takedown and one at site of coronary artery.Three dissections: two at extremes of LIMA takedown and one at site of coronary artery.

13. Boston University13 System evaluation = Endoscope Port = Instrument Ports n Six staff cardiac surgeons. n Three sets of ports compared 1.LIT = template from literature. 2.SURG = cardiac surgeons with thoracoscopic and minimally invasive surgery experience. 3.ALG = algorithmic port placement

14. Boston University14 Dissection Speed 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 ProximalDistalCoronaryMean Literature Surgeon Algorithm Dissection speed (mm/min)

15. Boston University15 Length of Gouges > 1.5 mm deep 0.00 5.00 10.00 15.00 20.00 25.00 30.00 ProximalDistalCoronaryMean Gouge Length (%) Literature Surgeon Algorithm

16. Boston University16 Summary n Decoupled robot placement from port placement n Developed a dexterity metric based on optimal orientations n Preliminary in vitro trials Dissection speed increased 25%Dissection speed increased 25% Gouge length decreased 50% or moreGouge length decreased 50% or more

17. Boston University17 Long-term role of algorithmic port placement n Routine use versus special cases? Image library comparison of algorithmic port selectionsImage library comparison of algorithmic port selections n Development of new procedures Beating heart intracardiac ASD repairBeating heart intracardiac ASD repair