A Novel Camera System for Thoracoscopic Surgery

Final PresentationRobert Hinshaw

Group 23Team Members: John Mandile, Patrick Wu

Need

• New camera system for video assisted thoracoscopic surgery

• Current camera system irritates intercostal nerves and causes postoperative pain for patient

Scope

Design a novel camera system that redresses the challenges of current thoracoscopic surgery solutions while retaining the advantages of VATS.

Functions required of design• provide posterior and apical views of lungs and

hilum • reduce or eliminate traction on intercostal nerves • illuminate the thoracic cavity

Specific Design RequirementsAttribute Value NotesSafety Autoclavable 134°C Operating range 5-40 °C Electrically/thermally insulated

For 100-240 VAC (0.6A) @ 50-60 Hz power supply

Ease of Use Extended periods of use ~6 hours

Support camera head <150 g Must be lightweightThoracoscope Features Light Source 1000 Lumens 10 W LED Camera 720p standard A/V Output Must resist obstruction by blood spatter

Diameter Max width: 1 cm Must also fit through 4cm incision

Movement must provide multiple points of view

Furling Arm Camera System

Operation of System

Device inserted through 4 cm incision in the 6th, 7th, or 8th

intercostal space

Device is pressurized

Base clamps around

thoracic wall

Arms unfurl moving

cameras into position

Thoracic Wall

Incision

Camera Head

Camera Positioning

• Apical view of hilum

• Posterior/Anterior view of thoracic cavity

• Stereoscopic view of

primary surgical field

Analytic Efforts: Light Source• Brightness

>1000 lm total, 300 lm per• LED power requirements

700 mA * 2.85 V = 2.00 W• Heat output

junction temperature 85˚C• Required heat sink

required Rt < 17 ˚C/W

Rt = thickness/(area*conductance)

= 10 ˚C/W

Analytic Efforts: LED Circuit

• Sensitive to voltage change

• Use constant current– Current limiting resistor

• Voltage regulator puts finely controlled voltage across R1

• 700 mA

Analytic Efforts: Supporting Arms

• Changes with pressure– 1 cm x 2 cm rectangular with wall thickness 0.25 cm– Convert to circular cross section

• 1*2-1.5*.5 = π(ro2 – ri

2) ro – ri = 0.25 cm

– ro= 0.925 cm ri= 0.675 cm

• Support camera head– Bending moment calculated 20 cm long– Solved simple cantilever problem, acceptable

deflection <3 cm (pressure stiffness not included)

Analytic Efforts: Furling Motion

• Furling SpringM=EI*k, EI=stiffnesskspring = karm

• Stiffness: resting arm < furling spring < pressurized arm

EI pressurized = EIcircular + pressure stiffness

EI resting = EIrectangular

Irect = BH3/12 – bh3/12 = 0.53 cm4

Icirc = π/4*(ro4 – ri

4) = 0.41 cm4

Analytic Efforts: Operating Pressure

• Safety Factor of 5

• Bursting pressure of arms= tensile strength of PTFE* (OD2 – ID2)/(OD2 –

ID2)= 5 MPa

• Max Operating Pressure: 1 Mpa– For reference: this is roughly 10 atmospheres which is

about the water pressure at 100 m

Analytic Efforts: Base

Distributes weight of device– Total Device Weight: 300 g– Top Flange Surface Area: 58.1 cm2

– Pressure on Thoracic Wall: 506 PaFor reference: Air pressure difference in lungs during breathing is roughly 300 Pa

Camera Head Details

• Camera– 2MP pcDuino V3

• Light Source– Cree XLamp XM-L2 LED

• Shield– Custom glass ‘dome’– Flat sides for contact

• Wiper – Rotating spring loaded

shaft – Removable blade– Replaceable contact

sponge with surfactant

Camera Head Details

Part Material Weight (g)

Dome Glass 0.34

Camera - 4.5

Wiper System Titanium & Polymer 0.35

LED - 1.0

Body PTFE (Teflon) 0.53

Total - 6.7

mm

Camera Head Details

Building custom camera outside of scope• Resolution– 2M pixel

• Size– 6 mm x 6 mm

Arm Details• Unfurling motion– Small initial profile fits through incision– Unfurling along wall safely places cameras– Pressure stiffened arms support camera heads

• Furling motion– Depressurization lowers arm stiffness– Internal spring furls arm– Easy removal from cavity, no abrasion of organs

• Fine camera angle adjustment– Slight curling back of tip with small pressure decrease

• Serve as insulating conduits for power supply and video output

Arm Details: Dimensions• 5 arms• Hilum View (single

arm)– 0˚ branch from axis of

symmetry– 20 cm long

• Main Field View (pair)– 25˚ branch– 12 cm

• Posterior/Anterior View (pair)– 30˚ branch– 16 cm

Base Details• Dimensions– Top flange SA: 58 cm2

– At incision: 4 cm wide, 0.5 cm deep– Distance between flanges: 3 cm• Average thoracic wall thickness 2.9 cm

• Luer lock valve for manual pressure hookup• Wiring seal• User Interface (outside scope) not mounted

on patient

Part List~$2000 in prefabricated parts for 100 units ($20 per)

Majority of cost will come from custom parts/manufacturing

Manufacturing

• Teflon components– Arms extruded– Base and camera heads molded

• Head assembly– Camera &LED adhered to circular Teflon base– Wiper mechanism, two torsion springs attached to

titanium shaft under camera head– Glass shield adhered in groove

Manufacturing

• Arms - Base– Attached to base during molding process– Wiring & springs run through base and arms

• Wiring attached to camera heads• Camera heads adhered in molded slots at end

of arms

Safety Considerations• Material selection: PTFE (Teflon)– Thermal and electrical insulation– Non-allergenic– Flexible– Autoclavable

• Furling motion– System does not contact thoracic organs

• Wall mounting position– lowest chance of interaction with surgical tool like

electrocautery knife• Heat dissipation at camera heads

Does it solve the problem?• Provides and maintains necessary views• Sufficiently illuminates thoracic cavity• Requires no extra incisions• Does not irritate intercostal nerves• Advantages over competitive systems– Stationary– No risk of irritating friction– Does not require extra operators– Does not interfere with surgical instruments

Future Directions• Determine Furling Spring– Calculate stresses, determine furled radius of curvature that

remains in Teflon’s elastic region• Control Systems– Zoom, rotate, take still, switch between camera views

• Automate Pressurization• Image Processing– surgeon orientation– Exposure adjustment– Image stabilization

• External power supplies• Increase degrees of freedom of camera heads

Furling Arm Camera System

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