John G. WebsterDepartment of Biomedical Engineering

University of WisconsinMadison WI 53706 USAwebster@engr.wisc.edu

Electrosurgery and ablationElectrosurgery and ablation

Electrosurgery works by cutting, fulguration or desiccation.Electrosurgery works by cutting, fulguration or desiccation.

60 H z 100 kH z 550-1550 kH z 54-880 M H z

H ouseholdappliances AM radio T V

500 kH z-33 M H z

E lectrosurgery

Frequency (H z)

C utting D esicca tion

N erve and m usclestim ulation

Fu lgura tion / sp raycoagu la tion

(a) Block diagram for an (a) Block diagram for an electrosurgical unit. High-electrosurgical unit. High-power, high-frequency power, high-frequency oscillating currents are oscillating currents are generated and coupled to generated and coupled to electrodes to incise and electrodes to incise and coagulate tissue. (b) Three coagulate tissue. (b) Three different electric voltage different electric voltage waveforms available at the waveforms available at the output of electrosurgical units output of electrosurgical units for carrying out different for carrying out different functions.functions.

In electrosurgery, crest factor is the peak voltage divided by the In electrosurgery, crest factor is the peak voltage divided by the rms voltage. (a) represents a cutting waveform with low crest rms voltage. (a) represents a cutting waveform with low crest factor. The desiccating output in (b) has a relatively greater crest factor. The desiccating output in (b) has a relatively greater crest factor than seen in the cutting waveform. Fulguration (c) has a factor than seen in the cutting waveform. Fulguration (c) has a crest factor even higher than that for desiccation. Adapted from crest factor even higher than that for desiccation. Adapted from Duffy and Gobb (1995).Duffy and Gobb (1995).

T im eAm

plitu

de rm svoltage

Peakvoltage

T im eAm

plitu

de

Peakvoltage

rm svoltage

T im eAm

plitu

de(a )

(b)

(c)

rm svoltage

Peakvoltage

Block diagram of a typical electrosurgical unitBlock diagram of a typical electrosurgical unit

Components of a modern electrosurgical system. The waveform selection Components of a modern electrosurgical system. The waveform selection and signal generating stage provide the desired waveforms for cutting or and signal generating stage provide the desired waveforms for cutting or coagulation. The power output stage employs power transistors such as coagulation. The power output stage employs power transistors such as MOSFETs to amplify the waveforms and output them through an output MOSFETs to amplify the waveforms and output them through an output isolation transformer. This is then applied through a system of electrodes isolation transformer. This is then applied through a system of electrodes (monopolar mode shown), where the current usually takes the path from (monopolar mode shown), where the current usually takes the path from the active electrode and back through the return electrode, or alternatively the active electrode and back through the return electrode, or alternatively flows through other undesired low impedance pathways such as lead wires flows through other undesired low impedance pathways such as lead wires attached to ECG electrodes.attached to ECG electrodes.

Power contro l Power supply O scilla tor M odulator

Poweram plifie r

P la tem onitor

Actua l current pathway

A lternative currentpathway

PatientPower outputs tage

C ut/ coagcontro ls

C ut

C oagulate

S ignalgenerating

stage

M O SFET

W aveformselection

Active e lectrode

R eturne lectrode

A lternativecurrent

pathways(EC Gelectrode, e tc)

(a) An electrosurgical generator with the necessary controls for cut (a) An electrosurgical generator with the necessary controls for cut and coagulation. (a) Electrosurgical footswitches for choosing the and coagulation. (a) Electrosurgical footswitches for choosing the mode of operation. From Valleylab (2001).mode of operation. From Valleylab (2001).

(a) (b)

(a) Bipolar electrosurgery (b) Monopolar electrosurgery.(a) Bipolar electrosurgery (b) Monopolar electrosurgery.

Electrosurg ica lun it

Active

Patient

R eturn

(b)

Active

E lectrosurg ica lun it

R eturnPatient

(a)

Advantages of Monopolar and Bipolar electrosurgical methods.

Can perform several techniques, especially coagulation much faster than bipolar methods.

Eliminates the possibility of return electrode burns due to its safe and precise effect.

Allows easy repositioning of electrodes to cover the required regions.

Increased operational safety due to the use of low power levels.

Monopolar Bipolar

Can be used for a wide variety of electrosurgical procedures involving cutting and coagulation

 

Elastomeric silicone-coated cutting electrodes. From Valleylab Elastomeric silicone-coated cutting electrodes. From Valleylab (2001).(2001).

Some of the basic shapes and standard sizes of electrodes used in Some of the basic shapes and standard sizes of electrodes used in electrosurgery (a) Blade (b) Ball (c) Loop (d) Square (e) Conization electrosurgery (a) Blade (b) Ball (c) Loop (d) Square (e) Conization (f) Fine wire electrodes. Courtesy of Anthony Products (2001).(f) Fine wire electrodes. Courtesy of Anthony Products (2001).

dia

10-20cm

3-5 m m

4-8 m m

(a)

(b)

(c)

(d)

(e)

(f)

Bipolar forceps used widely for coagulation. Both the active and Bipolar forceps used widely for coagulation. Both the active and return electrodes are together unlike monopolar electrodes, which return electrodes are together unlike monopolar electrodes, which comprise only the active electrode with the inactive electrode being comprise only the active electrode with the inactive electrode being located at some remote site. Courtesy of Elmed.located at some remote site. Courtesy of Elmed.

The technique for removal of plantar warts involves inserting a The technique for removal of plantar warts involves inserting a cutting loop and rotating it to sever the wart from the plantar fascia. cutting loop and rotating it to sever the wart from the plantar fascia. Adapted from Pearce (1986).Adapted from Pearce (1986).

C utting loopelectrode

T issue

(a) Structure of the commonly used electrodes in laparoscopy (b), (a) Structure of the commonly used electrodes in laparoscopy (b), (c) &(d) some of the most commonly used electrosurgical tips in (c) &(d) some of the most commonly used electrosurgical tips in laparoscopic procedures. Courtesy: AEM Laparoscopic laparoscopic procedures. Courtesy: AEM Laparoscopic Instruments.Instruments.

(a)

(b)

(c)

(d)

insu la tion layer

O uter insu lation

Protectiveshie ld

Prim ary

Active e lectrodeelem ent

Simplified diagram of the typical resectoscope used in TURP Simplified diagram of the typical resectoscope used in TURP procedures. Adapted from Duffy and Cobb (1995).procedures. Adapted from Duffy and Cobb (1995).

C uttingloop(~sm alld iam eter)

Sheath(p lastic coated)

T elescope

(a), (b) and (c) show different views of a cutting electrode of (a), (b) and (c) show different views of a cutting electrode of rectangular shape used in dental surgery. Adapted from: US patent rectangular shape used in dental surgery. Adapted from: US patent No. 04449926No. 04449926

1 m m0.25 m m

thick

25 m mlong

Insulator coating

(a) (b)

(c)

An aluminum foil Neutralect pregelled disposable metal foil return An aluminum foil Neutralect pregelled disposable metal foil return electrode. electrode.

(a) A conductive adhesive type dispersive electrode and the (a) A conductive adhesive type dispersive electrode and the current distribution under it, leading to what is known as the ‘edge current distribution under it, leading to what is known as the ‘edge effect’, which causes heating a burning at the edges. (b) effect’, which causes heating a burning at the edges. (b) Impedance vs. frequency for a conductive adhesive electrode.Impedance vs. frequency for a conductive adhesive electrode.

Frequency (H z)

50

10

100 10K 1M

M etal fo il

C onductiveadhesive

T issue

Edge effect

Im pedance )(W

A capacitive contact electrode with its basic parts and current A capacitive contact electrode with its basic parts and current distribution under the electrode. Edge effect is smaller. Adapted distribution under the electrode. Edge effect is smaller. Adapted from Pearce (1986)from Pearce (1986)..

Adhesive foam

T issue

D ie lectric

M eta llicconductor8 02 0 - mm

(a) A capacitive contact dispersive electrode and (b) Impedance (a) A capacitive contact dispersive electrode and (b) Impedance Vs. frequency for a capacitive contact electrode. It acts like a Vs. frequency for a capacitive contact electrode. It acts like a parallel plate capacitor with the metal plate and the skin forming parallel plate capacitor with the metal plate and the skin forming the two plates and Mylar as the dielectric between them. Adapted the two plates and Mylar as the dielectric between them. Adapted from US patent 04304235.from US patent 04304235.

Insu la tingcover sheet(soft foam

polyurethane) T hin flex ib lem eta l p late(s ta in less s tee l ora lum inum )

Adhesive

Frequency (kH z)

(a) (b)

D ie lectricadhesivem ateria l

(M YLAR 75th ickness)

m m

)(WIm pedance

500

75

(a) The temperature profile as a function of electrode surface area (a) The temperature profile as a function of electrode surface area for pediatric dispersive electrodes for a power of 40 W for 1 min (b) for pediatric dispersive electrodes for a power of 40 W for 1 min (b) Temperature profile as a function of the Power applied to the Temperature profile as a function of the Power applied to the pediatric electrode with surface area of 36. Adapted from Kim pediatric electrode with surface area of 36. Adapted from Kim &Webster (1986).&Webster (1986).

Power (W )

39

36

3120 40 600 20 60 1000

34

36

41

31

C )( 0M axim al tem perature C )( 0M axim al tem perature

E lectrode area )(m2

(a) (b)

(a) An example of a resistive reusable return electrode (b) (a) An example of a resistive reusable return electrode (b) Equivalent circuit for the electrode shown in (a). Adapted from US Equivalent circuit for the electrode shown in (a). Adapted from US patent No. 06083221.patent No. 06083221.

Sem i-

res is tivelayer

(conductor)

back ing

A

tR

r=

t

AC ree 0=

(a) (b)

insu la ting

Patient contact

C onductive m eta l

(a) A return electrode monitoring system using the concept of split (a) A return electrode monitoring system using the concept of split dispersive electrodes. The arrows indicate direction of current flow. dispersive electrodes. The arrows indicate direction of current flow. (b) A Neutralect split dispersive electrode showing the two (b) A Neutralect split dispersive electrode showing the two segments, developed to provide safety against electrosurgical segments, developed to provide safety against electrosurgical burns.burns.

(a) (b)

R eturn e lectrode

Active e lectrode

Patient

segm ents

E lectrosurg ica l

generator

T est and contro lc ircuit

Burns due to gel dry-out in some dispersive electrodes. (a) When Burns due to gel dry-out in some dispersive electrodes. (a) When there is gel dry-out, intense electric fields are generated, which there is gel dry-out, intense electric fields are generated, which causes arcing to skin leading to burns. (b) Burns caused by causes arcing to skin leading to burns. (b) Burns caused by confined currents, and burns due to arcs to the skin during gel dry-confined currents, and burns due to arcs to the skin during gel dry-out. Adapted from Pearce (1986)out. Adapted from Pearce (1986)..

W et ge lc lum ps

Arc s trikes

+++ - - -- - -

+++

- - -

+++

T issue

(a)

C onfined currentburns

Burns caused byarc ing in e lectrode

(b)

D ried portions ofge l

(a) Argon beam coagulator with argon gas flowing to the active (a) Argon beam coagulator with argon gas flowing to the active electrode. Adapted from Duffy and Cobb (1995). (b) Ionized argon electrode. Adapted from Duffy and Cobb (1995). (b) Ionized argon beam produces a more conductive medium between the electrode beam produces a more conductive medium between the electrode and tissue. Adapted from Absten (2001).and tissue. Adapted from Absten (2001).

D isposablehandpiece

Ionized argonbeam

T ungstenelectrode

(a) (b)

Active e lectrode

Argon gasin le t

F inger sw itchactivation socket

4 m m activesocket

T issue

Ablation: Method of delivering physical, chemical, Ablation: Method of delivering physical, chemical, or energy treatment to tissue for the purpose of or energy treatment to tissue for the purpose of removing, altering, creating scar tissue or causing removing, altering, creating scar tissue or causing aposis (cell death). aposis (cell death).

Radiofrequency ablationRadiofrequency ablationCryo-ablationCryo-ablationMicrowave ablationMicrowave ablationUltrasonic ablationUltrasonic ablationLaser ablationLaser ablationChemical ablationChemical ablation

Calculate tissue temperature using the bioheat equation

Where T = final temperature (K) = electrical conductivity (S/m)r = tissue density (kg/m3)c = tissue specific heat(J/kgK)J = magnitude of current density (A/m2) t = duration of activation (s)T0 = initial temperature (K)

 also,

J = E,  Where E = electric field vector (V/m)

021

TtJc

T =r

Example Assume that a uniform tissue has an electrical conductivity of 0.25 S/m, a density of 1000 kg/m3 and specific heat of 4186 J/kgK. If the electric field applied is of the order of 8000 V/m, estimate the time of activation required to reach a tissue temperature of 55 C assuming the initial temperature to be the body temperature (37 C).Solution:Given = 0.25 S/m; r = 1000 kg/m3; c = 4186 J/kgK; E = 8000 V/m; T0 = 310 K; T = 328 K;Using the bioheat equation and substituting the given values yields J = 2000 A/m2

Substituting the calculated value of J yields,

 which gives the value of t = 4.7 s

K310)A/m2000(KJ/kg4186m/kg1000S/m25.0

1K328 22

03

= t

Examples of ablation procedures that are currently performed in Examples of ablation procedures that are currently performed in clinics. C = cryoablation, US = ultrasound ablation, RF = radio-clinics. C = cryoablation, US = ultrasound ablation, RF = radio-frequency, MW = microwave.frequency, MW = microwave.

Application Technique

Cardiology (cardiac arrhythmias)

RF

Urology (benign prostatic hyperplasia, gallbladder)

C, US, laser, RF, MW, chemical

Neurology (brain cancer) US, RF

Oncology (tumors) MW, RF, C, laser

Dentistry Laser, chemical

Ophthalmology (cataracted lens, corneal sculpting, astigmatism)

Laser, US

A qualitative plot of survival curves of human bone marrow cells. A qualitative plot of survival curves of human bone marrow cells. The survival fraction is on a logarithmic scale, while the time axis is The survival fraction is on a logarithmic scale, while the time axis is on a linear scale. Adapted from Bromer on a linear scale. Adapted from Bromer et alet al (1982). (1982).

Duration (min)

Su

rviv

al f

ract

ion

45.5° C

42° C

10 - 2

41° C

43° C44° C

10 - 1

10 0

0 50 100 150 200 250 300

The Joule heat generated from the catheter tip elevates the The Joule heat generated from the catheter tip elevates the temperature of the surrounding tissue. Then the thermal energy is temperature of the surrounding tissue. Then the thermal energy is transferred deep into the myocardium by thermal conduction and transferred deep into the myocardium by thermal conduction and some heat is lost due to the blood perfusion and conduction to the some heat is lost due to the blood perfusion and conduction to the metal electrode. Flowing blood in the cardiac chamber cools down metal electrode. Flowing blood in the cardiac chamber cools down the surface of the electrode and the myocardium.the surface of the electrode and the myocardium.

Catheter body

Myocardium

Blood

Convective cooling fromblood

Electrode

Joule heat

Conduction to myocardium

Conduction to electrode

50 °C after 1 s

50 °C after 60 s

Blood perfusion

A typical ablation electrode system with thermistor embedded at A typical ablation electrode system with thermistor embedded at the tip. A thermal insulating sleeve surrounding the sensing the tip. A thermal insulating sleeve surrounding the sensing element blocks the transfer of heat from the electrode to the element blocks the transfer of heat from the electrode to the temperature-sensing element. Thus, the thermistor measures temperature-sensing element. Thus, the thermistor measures temperature without being affected by the surrounding thermal temperature without being affected by the surrounding thermal mass of the electrode. Adapted from Edwards and Stern (1997).mass of the electrode. Adapted from Edwards and Stern (1997).

Pt-Ir

Polyurethane

Bead thermistor

Wire

Potting compound

Air

Thermal insulation

((aa) 7F 4 mm cardiac ablation catheter (EP Technologies). () 7F 4 mm cardiac ablation catheter (EP Technologies). (bb) Four-) Four-tine hepatic RF ablation probe (RITA).tine hepatic RF ablation probe (RITA).

a b

An ablation catheter is advanced into a cardiac chamber. The RF An ablation catheter is advanced into a cardiac chamber. The RF generator delivers current to the ablation electrode at the tip of the generator delivers current to the ablation electrode at the tip of the catheter. Adapted from Panescu catheter. Adapted from Panescu et alet al (1995). (1995).

RF generator

Handle

Reference patch electrodeon the dorsal side

Catheter body

Ablation electrode

Catheters in cardiac chambersCatheters in cardiac chambers

Fluoroscopy shows cathetersFluoroscopy shows catheters

The lesion appears whiteThe lesion appears white

Cross section of the lesionCross section of the lesion

Common cardiac ablation sitesCommon cardiac ablation sites AV Node Above the tricuspid valves Above and underneath the

mitral valves Ventricular walls Right ventricular outflow tract Etc.

Tip ElectrodeTip Electrode RF generatorRF generator

Bioheat EquationBioheat Equation

)( blb TThT

k -=n

Heat transfer coefficient Blood temperature

Density

Specific heat

Thermal conductivity

Time

Temperature

Current density

Electric field intensity

heat loss to blood

perfusionVARIABLES

Heat Change

MATERIAL PROPERTIES

Electrical conductivity

Density

Specific heat

Thermal conductivity

Time

Temperature

Current density

Electric field intensity

heat loss to blood

perfusion

heat loss to blood

perfusion

Heat Conduction

Joule Heat

Finite Element AnalysisFinite Element Analysis Divide the regions of interest into small “elements” Partial differential equations to algebraic equations 2-D (triangular elements, quadrilateral elements, etc.) 3-D (tetrahedral elements, hexahedral elements, etc.) Nonuniform mesh is allowed Software & Hardware

PATRAN 7.0 (MacNeal-Schwendler, Los Angeles ) ABAQUS 5.8 (Hibbitt, Karlsson & Sorensen, Inc.,

Farmington Hills, MI) HP C-180, 1152 MB of RAM, 34 GB Storage

Process for FEM GenerationProcess for FEM Generation

Geometry Material Properties Initial Conditions

Boundary Cond. Mesh Generation

Preprocessing (PATRAN 7.0)

Solution (ABAQUS/STANDARD 5.8)Duration Production Adjust Loads

Check for desired parameters

Postprocessing (ABAQUS/POST 5.8)Temperature Distribution Current Density

Determine Lesion Dimensions (from 50 C contour)

Convergence test (for optimal number of elements )

Modes of RF Energy ApplicationsModes of RF Energy Applications

Maintain the tip temperature at a preset valueAdjust voltage applied to the electrode

Temperature controlled ablationTemperature controlled ablation

Power controlled ablationPower controlled ablation

Maintain power delivered at a preset valueAdjust voltage applied to the electrode

Temperature distribution after 60 sTemperature distribution after 60 s

Maximum temperature ~ 95 C

Highest temperature

Sinus Rhythm with Surgery- Sinus Rhythm with Surgery- Maze ProcedureMaze Procedure

Picture of Newer Catheters Picture of Newer Catheters (NASPE)(NASPE)

FEM for Hepatic Ablation*FEM for Hepatic Ablation*

Hepatic Ablation: Use RF probe to destroy tumor cancer, or cirrhosis

Minimally invasive Present: -High recurrence rate

-Small lesions

Radio-frequency probe for liver cancer. The four wire electrodes Radio-frequency probe for liver cancer. The four wire electrodes have thermocouples for temperature sensing at the tips.have thermocouples for temperature sensing at the tips.

C onducting sta in lessstee l trocar

Insu la ted sta in lessstee l trocar

N icke l- titan iumretractab le e lectrodes

15 m m

Therm ocoup le

50 °C contour

Bifurcated blood vesselBifurcated blood vessel

+37.0

+41.1

+45.2

+49.2

+53.3+57.4+61.5

+65.5+69.6

+73.7

+77.8

+81.9

+85.9

+90.0

TEMP VALUE

Blood vessel

Liver

Probe

ABHot spot

Bipolar Hepatic AblationBipolar Hepatic Ablation

Bipolar Unipolar

Important Parameters Important Parameters Affecting Lesion DimensionAffecting Lesion Dimension

Tissue and blood properties Applied power during ablation.Duration of ablation.Target temperature in temperature mode.Blood flow around catheter.Contact condition such as penetration

depth, contact angle.

The laser beam intensity decreases with tissue depth. The mean The laser beam intensity decreases with tissue depth. The mean free paths of CO2, argon and Nd:YAG are 10 free paths of CO2, argon and Nd:YAG are 10 mmm, 30 m, 30 mmm and 2.5 m and 2.5 mm, respectively. mm, respectively. 1, 1, 2 and 2 and 3 are the absorption coefficients of 3 are the absorption coefficients of CO2, argon and Nd:YAG in blood. Note that this figure is not drawn CO2, argon and Nd:YAG in blood. Note that this figure is not drawn to scale. to scale.

I 0

10 mm x

1/e

2.5 m m

1 2 3

100%

1 = C O 2; 2 = A rgon; 3 = N d:YAG

30 mm

1 = 10 3 cm - 1

2= 330 cm - 1

3= 4 cm - 1

A simplified optical diagram of components of the laser system for A simplified optical diagram of components of the laser system for removing cataracted lens tissue. From L’Esperance (1985).removing cataracted lens tissue. From L’Esperance (1985).

A radio-frequency signal is produced by a signal generator and A radio-frequency signal is produced by a signal generator and amplified by a RF power amplifier. A power meter is used to amplified by a RF power amplifier. A power meter is used to monitor the forward and reflected power in the coaxial cable monitor the forward and reflected power in the coaxial cable connected to the transducer’s matching network.connected to the transducer’s matching network.

Sk in surface

1- 2 m m

Focal p lane

U ltrasound les ion

10- 20 m m

Beam

Lens

Tra

nsdu

cer

M atch ingnetwork

Powerm eter

R F poweram plifier

S ignalgenerator

C oaxia l cable

((aa) Endocare’s cryoprobes. () Endocare’s cryoprobes. (bb) The argon-based eight-probe ) The argon-based eight-probe CryocareCryocare system. Physicians can set the flowing rate, ablation system. Physicians can set the flowing rate, ablation duration, and the thawing rate, and apply up to eight cryoprobes duration, and the thawing rate, and apply up to eight cryoprobes simultaneously.simultaneously.

Internal structure of a typical cryoprobe. LNInternal structure of a typical cryoprobe. LN2 2 cryoprobes must have cryoprobes must have vacuum insulation to prevent freezing up the shaft of the cryoprobe vacuum insulation to prevent freezing up the shaft of the cryoprobe and subsequent destruction of normal tissue. The LNand subsequent destruction of normal tissue. The LN2 2 changes changes phase when it hits the warm metal surface of the probe tip. Thus, a phase when it hits the warm metal surface of the probe tip. Thus, a thin film of gas bubbles is formed on the metal surface. thin film of gas bubbles is formed on the metal surface.

Lesion diameter

Vacuum insulation

Vacuum insulation

GasLiquid nitrogen

Gasbubbles

r1r2

Thermocouple

Lesion diameter

System for prostate cryoablation. (System for prostate cryoablation. (aa) The needle trocar and the ) The needle trocar and the guide wire are first inserted into the body. (guide wire are first inserted into the body. (bb) The cryoprobe. ) The cryoprobe. Adapted from Zippe (1996).Adapted from Zippe (1996).

Urogenitaldiaphragm

Wire throughneedle trocar

Ultrasound transducer

Warmer Prostate

Seminalvesicle

Bladder

Rectalwall

Urogenitaldiaphragm

Cryoprobe

Ultrasound transducer

Rectalwall

Warmer Prostate

Seminalvesicle

Bladder

A schematic block diagram of a microwave power supply system A schematic block diagram of a microwave power supply system for an ablation catheter. Adapted from Warner and Grundy (1994).for an ablation catheter. Adapted from Warner and Grundy (1994).

Diagram of helical antenna microwave electrode for cardiac Diagram of helical antenna microwave electrode for cardiac ablation. The stiffener wire allows better flexure control of the ablation. The stiffener wire allows better flexure control of the catheter. The electromagnetic shield prevents the intense field in catheter. The electromagnetic shield prevents the intense field in the middle of the coil from the wire and electrodes. The insulating the middle of the coil from the wire and electrodes. The insulating material (e.g. Teflon) helps avoid charring and coagulation. material (e.g. Teflon) helps avoid charring and coagulation. Adapted from Warner and Grundy (1994).Adapted from Warner and Grundy (1994).

ElectrodeHelicalantenna

Electromagneticshield

Thermometryelement

Dielectricsupport

Insulatingmaterial

Stiffenerwire

((aa) Mechanism of tissue heating of RF ablation. () Mechanism of tissue heating of RF ablation. (bb) microwave ) microwave ablation produces an electromagnetic field and has a potential to ablation produces an electromagnetic field and has a potential to create larger lesions. Adapted from Langberg and Leon (1995).create larger lesions. Adapted from Langberg and Leon (1995).

Questions for electrosurgery and ablation: You should be able to:Questions for electrosurgery and ablation: You should be able to:

1 Describe 3 types of electrosurgery.1 Describe 3 types of electrosurgery.2 Given a waveform, calculate the crest factor.2 Given a waveform, calculate the crest factor.3 Distinguish bipolar and monopolar electrosurgery.3 Distinguish bipolar and monopolar electrosurgery.4 Describe problems resulting from the edge effect.4 Describe problems resulting from the edge effect.5 Describe a safety system for electrosurgical dispersive electrodes.5 Describe a safety system for electrosurgical dispersive electrodes.6 Given the equation, calculate temperature rise in tissue.6 Given the equation, calculate temperature rise in tissue.7 Describe the reasons for cardiac ablation.7 Describe the reasons for cardiac ablation.8 Describe terms in the bioheat equation.8 Describe terms in the bioheat equation.9 Describe the process of finite element method modeling.9 Describe the process of finite element method modeling.10 Describe the advantages of bipolar hepatic ablation.10 Describe the advantages of bipolar hepatic ablation.11 Describe equipment and limitations of optical ablation.11 Describe equipment and limitations of optical ablation.12 Describe equipment and advantages of ultrasonic ablation.12 Describe equipment and advantages of ultrasonic ablation.13 Describe equipment and advantages of microwave ablation.13 Describe equipment and advantages of microwave ablation.

http://rf-ablation.engr.wisc.edu/http://rf-ablation.engr.wisc.edu/