RF physics by zhangyun

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									Radiofrequency Technologies
   and Their Applications
      Michael Kreindel, PhD.
• Founder and CTO in Invasix Ltd., inventor of RF
  assisted liposuction.

• Founder and Chief Technology Officer (CTO) of
  Syneron Medical Ltd., inventor of ELOS
• Chief scientist and project manager for ESC
  (Lumenis), developer of the IPL technology
                       RF History
The development of the first
electrosurgical device is associated
with Dr. William T. Bovie, who
developed the device during the
period of 1914 to 1927 at Harvard

The first use of an electrosurgical
generator in an operating room
occurred on October 1, 1926. The
surgery was performed by Dr.
Harvey Williams Cushing.
                 RF Market
• 5x larger than the laser market
• Strong position in aesthetic and medical
• Main medical players: Smith & Nephew,
  Conmed, Arthrocare, Ellman, Valleylab, Bovie,
• Main aesthetic players: Solta (Thermage),
  Syneron, Invasix, Alma
         Types of Electrical Current
• DC (direct current) – constant
  current flowing without
  changing of direction.
  Frequency is 0Hz.                    Time

• AC (alternating current) - sine
  shape current changing
  polarity periodically. AC causes     Time
  electrical shock. Frequency is
  higher than 0Hz.

• RF (radio-frequency) current –
  with frequency above                 Time
  100,000Hz. Nerve system is
  not sensitive to RF current.
           Electromagnetic Spectrum

  0 Hz       60 Hz         1 kHz                   100 MHz    1 GHz
 Battery     House      Muscle and                 FM Radio    UHF
powered    appliances      nerve
 devices                stimulation
               Electromagnetic Spectrum

     Low frequencies                  Radio-frequencies                 Microwave
       (0-100KHz)                     (100kHz-300MHz)                 (300MHz-3GHz)

        Iontophoresis   Muscle and        Electrosurgery                Hyperthermia
Electrolysis            stimulation                    Cosmetic use
                 Basics of Electricity
Ohm’s law                    I
    S 
Joule heating
                        P  I V      I2  R
I – electrical current, Amperes
V – voltage, Volts
R – electrical resistance or impedance, Ohms
P – dissipated power or heat, Watts
L – is distance between electrodes
S – cross section area of the conductive media
σ – conductivity of tissue
    Tissue Electrical Parameters

Tissue                Conductivity, S m-

Blood                 0.7
Skin                  0.25
Bone                  0.02
Fat                   0.03
              Data at 1 MHz
Electrical Properties of Tissue as Function of the RF

Camelia Gabriel, PhD., Sami Gabriel, MSc., Physics Department, King's College London
          RF Treatment Variables
•   Electrode configuration
•   Power setting
•   Waveform
•   Time of treatment
•   Manipulation of electrode
 Common Electrode Configuration

• Mono-polar RF is used      • Bipolar RF limited in
  mostly for cutting           treatment area, has higher
  application when small       efficiency of energy
  contact area is critical     utilization and is preferred
                               when larger volume need
                               be thermally effected
RF Circuit Should Always be Closed
• It can be closed through galvanic (conductive)
• Through the plasma (ionized air or vapor)
• Through the parasitic capacitance between
  patient and ground at high frequencies of
  40MHz and higher (RF closes loop in form of
RF Distribution Between Typical
   Geometries of Electrode
• Continues sine wave

• Burst sine wave

• Non-sine

• Modulated
       Types of RF Thermal Effect
• Ablation of tissue
   – Cutting and tissue removing.
   – Very high power density is
• Coagulation of tissue
   – Blood and tissue coagulation.
   – Medium power density is
• Sub necrotic heating
   – Collagen remodeling
   – Low power density
               Electrode Size Effect
High density of RF      Medium density of RF       Low density of RF
Most of power is        Most of power is           Most of power is
utilized for ablation   utilized for coagulation   utilized for heating
    Monitoring of Parameters


RF Power
RF Voltage
RF Current
Tissue impedance

                           •Contact with tissue
                             Tissue Impedance as a Function of
     Impedance, arb. units

                                   Heating                          Coagulation                  Evaporation

                             0      25                  50                   75                  100           T, oC
1.   Enrique J Berjano, Theoretical modeling for radiofrequency ablation: state-of-the-art and challenges for the future,
     BioMedical Engineering OnLine 2006, 5:24
2.   Pop M, Molckovsky A, Chin L, Kolios MC, Jewett MA, Sherar MD: Changes in dielectric properties at 460 kHz of
     kidney and fat during heating: importance for radio-frequency thermal therapy.
3.   Bhattacharya A, Mahajan RL: Temperature dependence of thermal conductivity of biological tissues.Physiol Meas
     2003, 24:769-783.
          Prevention of Burns
• Limiting peak-to-peak voltage to avoid plasma
• Monitoring tissue impedance to ensure good
  coupling of external (return) electrode and
  changes in tissue impedance
• Smooth shape of electrodes
• Understanding of RF behavior and training
• Eschar is dead tissue covering living tissue
• Usually, eschar is more dry than normal tissue and
  prevents RF delivery
• Slows tissue healing
• It adheres to electrosurgical instruments and may
  damage it
• Methods of prevention: Optimization of RF parameters
  for more effective ablation. Production of instrument
  from less adhesive materials. Removing eschar for
  faster tissue healing. Regular cleaning instrument
  during the surgery.
• Carbonization is process of thermal
  transformation of organic tissue into a pure
  carbon, mostly in form of coal
• Prevents RF delivery and tissue healing
               Main RF Applications
•   Vision Correction (Keratoplasty)
•   Liver Cancer and Other Tumor coagulation
•   Snoring
•   Cosmetic Surgery
•   Enlarged Prostate ablation
•   Rapid Heartbeat Syndrome: especially Wolff-Parkinson-White syndrome.
•   Tightening Loose Joints
•   Endometrial ablation
•   Vessels sealing
•   Varicose veins
•   Others
Is RF Dangerous?
      • Radiation became
        significant at frequencies
        of tens of MHz
      • There is no clear
        evidence for cell phone
      • Electrosurgical devices
        has the same risk as any
        other electrical device
      • 100 yrs safety record
What’s New in RF World?

               with other

 Combination with Other Energies
• Combination with light and
  laser (ELOS, Syneron)

• Combination with Ultrasound
  (multiple companies producing
  cosmetic equipment)
• Electrode array for
  fractional RF ablation
  (Syneron, Alma)

• Tri-polar (Pollogen)
RF Assisted Liposuction – New Concept
 of Electrodes for a New Application
      Computer Simulation

External electrode

Internal electrode

Thermal Image Of Porcine Skin

        5mm between electrodes
Thermal Image Of Porcine Skin

        25mm between electrodes
Summary: Advantages of RF Energy
• High efficiency of RF sources (up to 80%)
• Unlimited power
• High versatility of parameters and
• Directionality of energy
• The best control of parameters
• Significant knowledge and experience
  accumulated during 100 yrs of use
• RF is the 1st candidate for the body contouring
  – Good track record on collagen contraction
  – Ability to treat high volumes
  – Real-time monitoring of parameters and
    treatment effect
• RF and future facial applications

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