Ultrasound

• Mechanism of how US works

  1. High frequency alternating electrical current is applied to a crystal within the transducer

  2. The crystal expands/contracts in response to the electrical current and produces waves

  3. Waves cause a vibration/cavitation of the local tissue

  4. Waves attenuate (lessen) as they travel through tissue
• Effective radiating area (ERA)

  Area where US energy radiates
• Frequency

  Number of compression-rarefaction cycles per unit of time
• Intensity (volume dial)

  Power in watts/cm2
• Duty cycle

  Proportion of total treatment time that the ultrasound is on
• Frequency

  Depth of penetration
• 3 MHz → more frequent compression/rarefaction cycle → heats superficial tissue (1-2 cm)
• 1 MHz → less frequent compression/rarefaction cycle → heats deeper tissues (up to 5 cm)
• Continuous duty cycle

  Used with thermal US
• Pulsed duty cycle

  Used with non-thermal US
• Uses for thermal ultrasound

  • Increase soft tissue extensibility
  • Pain control
  • Decrease inflammation in tendon and ligament injuries
  • Bone healing after fx
  • Wound healing
  • Enhance transcutaneous drug delivery
• Uses for non-thermal ultrasound

  • Decrease inflammation in tendon and ligament injuries
  • Bone healing after fx
  • Wound healing
  • Enhance transcutaneous drug delivery
• Contraindications for therapeutic ultrasound

  • Malignancy
  • Pregnancy → over abdomen, low back, pelvis
  • CNS tissue → e.g. laminectomy (avoid going directly over midline)
  • Joint cement and plastic components of joint replacements → metal is ok
  • Pacemaker or ICD → keep 6 in away
  • Eyes or reproductive organs
• Precautions for therapeutic ultrasound

  • Acute inflammation (thermal)
  • Epiphyseal (growth) plates
  • Fractures (in acute phase of healing)
  • Breast implants
• Adverse effects of therapeutic ultrasound

  • Deep tissue burns
  • Blood cell stasis
  • Damage to endothelium lining of blood vessels
  • Cross-contamination/infection
• Prevention of adverse effects

  • Keep transducer moving
  • Proper cleaning/hygiene
• Parameters for therapeutic use of thermal ultrasound

  1. Soft tissue shortening

  2. Pain control
• Techniques for moving sound head

  Move sound head 4 cm/second via circles or in a back and forth pattern
• Required components for documentation of therapeutic ultrasound

  • Area of body treated
  • Ultrasound frequency, intensity, duty cycle
  • Treatment duration and size of transducer
  • Whether delivered under water
  • Patient's response
• 62 y/o owner of pizza luce. Left inversion sprain of ankle 3 days ago. Left TKA 2 years ago. Asterisk sign

  • Acute phase = nonthermal
  • duty cycle = 20%
  • frequency = 3 MHz
• 45 y/o biology professor. Right elbow tendinopathy (ECRB). Breast cancer at age 40 with chemotherapy and mastectomy. Subsequent reconstructive surgery.

  • frequency = 3 MHz (more superficial)
  • tendinopathy = chronic (delayed healing) - nonthermal