Therapeutic Ultrasound

1. THERAPEUTIC ULTRASOUND
Arlene Y. Aranzaso, PTRP

2. Objectives:
1. To present the physical principles and
biophysical effects of Ultrasound
2. Discuss the clinical conditions for which
ultrasound is effective
3. Discuss the clinical procedures for the
application of ultrasound
4. Present guidelines for the safe use of
ultrasound, including a discussion of the
contraindications and precautions for
treatment with this agent

3.  Ultrasound
◦ Is used in medicine for diagnosis (
imaging of internal structures)
◦ Physical therapy (functional restoration
and healing of soft tissue ailments)
◦ Tissue destruction

4. Physical Principles
 Nature of Sound
◦ Sound is a non-ionizing radiation, it is
propagation of the vibratory motion.

5.  Frequency
◦ Number of oscillations a molecule
undergoes in 1 second
◦ Hz
◦ Human ear – 16 Hz and 20, 000 Hz
◦ Greater than 20,000 Hz is Ultrasound
◦ Ultrasound beams is collimated
◦ 85 KHz and 3 MHz

6.  Attenuation – reduction of acoustical
energy as it passes through soft
tissue.
◦ Scattering
◦ Absorption - attenuation
frequency

7.  Sound Velocity
◦ Is the speed at
which the vibratory
motion is
propagated through
a material
◦ 1540 m/s –soft
tissue
◦ 4000 m/s –
compact bone

8.  Wavelength
◦ Distance between 2
successive peaks in the
pressure wave
◦ Phase shift – time delay
◦ Condensations – the
concentration of
molecules increase in
the regions
◦ Rarefactions –
decrease in alternating
regions

9. Types of Waves
 Longitudinal waves
 Transverse waves

11.  Continuous wave
 Pulsed wave

12. Duty cycle = duration of pulse (time on)
pulse period (time on + time off)
< 50% is Pulsed US

13. Intensity
 It determined the strength of an US
beam
 It is the rate at which energy is delivered
per unit
 Watts/square centimeter
 W/cm²
 The greater intensity result greater
Temperature elevation
 PT – 0.25 to 2.0 W/cm² (therapeutic
application)
- 1 to 3 W/cm² (Sullivan&Siegelman)

14.  Spatial Average Intensity
Total Power Output (watts)
area (cm²)
 Spatial Peak Intensity – the greatest
intensity anywhere within the beam.

16.  BNR (beam non-uniformity ratio)-
defines the maximum point intensity
on the transducer to the average
intensity value across the transducer
surface.
 2:1 and 6:1
 Low BNR – more even energy
distribution and less risk of tissue

18.  Example:
 CW
◦ 3.0 MHz/0.5 W/cm²/CW/5min
 PW
◦ 3.0 MHz/0.5 W/cm²/p 20%/5min

19. Generation of
Ultrasound

20. The Piezoelectric Effect
 2 forms
A. Direct Piezoelectric effect
B. Reverse Piezoelectric effect (indirect)

21. Direct Piezoelectric Effect
 Is the generation of an electric voltage
across a crystal when the crystal is
compressed.

22. Reverse Piezoelectric Effect
 Is the contraction or expansion of a
crystal in response to a voltage
applied across it face.

24. The Transducer
Is any device that converts one form of energy into
another
Piezoelectric crystal is a transducer that converts
electrical energy into sound energy, and vice versa.
1 cm² to 10 cm²
5 cm² most commonly used
ERA (effective radiating area) –the area of the faceplate
(crystal size), which is smaller than the sound head.

26. Biophysical Effects
1. Thermal
 Those effects produced by the ability of
ultrasound to elevate tissue temperature.
2. Non- Thermal
 Those effects that must be attributed to
mechanism other than an increase in tissue
temperature.

27. Thermal Effects
 Increase collagen tissue extensibility
 Alterations in blood flow
 Changes in nerve conduction velocity
 Increased pain threshold
 Increase enzymatic activity
 Changes in contractile activity of
skeletal muscle

28.  3 MHz – most of the energy is
absorbed within a depth of 1 to 2 cm
 1 MHz – absorption in deeper tissue
- deeper than 2 cm from the
skin surface

29. Tissue Attenuation (%/cm)
Blood
Fat
Muscle
Blood vessel
Skin
Tendon
Cartilage
Bone
3
13
24
32
39
59
68
96
Attenuation of a 1 MHz Ultrasound Beam

30. Non-Thermal effects
 Cavitation
 Mechanical alterations
 Chemical alterations

31.  Cavitation
◦ is the vibrational effect on gas bubbles by
an US beam.
◦ Stable cavitation – result diffusional
changes along cell membrane and alter
cell function.
◦ Unstable or transient cavitation – the
violent collapse of bubbles within the
sound field result tissue destruction.

34.  Mechanical
◦ Acoustical streaming – refer to the
movement of fluids along the boundaries of
cell membranes
 Increase fibroblastic activity
 Increase calcium fluxes
 Alteration of cell membrane activity
 Increased cell wall permeability
 Increased protein synthesis

35. Clinical Application of
Ultrasound at Therapeutic
Intensities

36. 1. Joint contracture and scar tissue
2. Reduction of pain and muscle spasm
3. Bursitis and tendinitis
4. Calcium deposits
5. Phonophoresis
6. Wound healing
7. Chronic wounds

37. Therapeutic Ultrasound Units

38. Basic components
 Power supply
 Oscillator circuit
 Transformer
 Coaxial cable
 Ultrasound applicator

39. Guidelines for Clinical
Administration
 Coupling Techniques

40.  Moving vs. Stationary Applicator
◦ Stationary
◦ Moving – slowly ~ 4 cm/s
- longitudinal stroking or circular
movements can be used
- total area covered – 2-3x the size of
the irradiating crystal for every
5 minutes exposure.

41.  Exposure Factors
◦ 5 minutes – increase tissue extensibility
◦ General use – it should be:
 an appropriate frequency for the depth of the
tissue to be treated
 A continuous wave or pulsed wave – according
to treatment aims
 The lowest intensity and duration that achieved
desired result

42.  Indirect contact
◦ Water immersion
◦ Using thin walled bag

43. Technique of Phonophoresis
 Medication is rubbed directly onto the
surface of the skin
 Coupling gel spread over the
medication
 Then sonation is initiated

45. Patient Positioning and Field
Selection

46. 3 different examples of shoulder
dysfunction
1. Capsular shortening or contracture
2. Supraspinatus tendinitis
3. Muscle-guarding spasm and pain
2°to degenerative joint dse.

47. Treatment Precautions
1. Should not be applied over the eye
2. Irradiation over the heart should be avoided
3. Over pregnant uterus
4. Over testes
5. Over malignant tissue
6. Impaired sensation
7. Impaired circulation
8. Impaired cognitive function
9. Over thrombophlebitis
10. Over epiphyseal area in children
11. Over exposed or unprotected spinal cord

48. Clinical Decision Making
1. Stage of inflammation and repair
2. Site of pathology
3. Total amount of tissue to be heated
4. Presence or absence of orthopedic
implants

49. CASE STUDY

50. Joint Contracture and Scar
Tissue
 A 28 year old man sustained partial
lacerations to the extensor tendons to
the ring and small fingers over the
metacarpophalangeal joints when he
cut his fingers on a knife in dish water.
The tendons were surgically repaired
and immobilized for 2 weeks 2° to
wound infection. You are now seeing
the patient 4 wks.postop.

51.  US
◦ 3 MHz/0.5 W/cm²/CW/5 min.
◦ Small head

52. Reduction of Pain and Muscle
Spasm
 The patient, a 45 year old woman, has
had pain in the right cervical and
interscapular area for ~ 2 wks. The
onset of pain was caused by repetitive
activity during spring cleaning.

53.  US
◦ 1.0 MHz/0.5 W/cm²/p 20%/5 min.
◦
◦ Lying in prone or
◦ Seated with UE well supported

54. Bursitis and Tendinitis
 A 26 year old male patient has a
patellar tendinitis. The insidious onset
of pain occurred ~ 3 wks. ago. The
patient was told to place ice on the
area, rest, and do range of motion
exercises.

55.  US
◦ 3.0 MHz/0.8 W/cm²/p 50%/5 min.

56. Phonophoresis
 The patient, a 38 year old man, has a
lateral epicondylitis. His symptoms,
which first began after prolonged
hammering, have continued for ~ 6
weeks. He was instructed to use ice
on the affected area and to rest. In
addition, anti-inflammatory medication
was prescribed.

57.  Phonophoresis
◦ 3.0 MHz/1.0 W/cm²/CW/3 min.

58. Chronic Wounds
 A 40 year old male factory worker
sustained a sprain of the lateral ankle.
This occurred when he overturned his
foot 1 day ago. Rest, ice,
compression, and elevation were
recommended to the patient by the
company nurse.

59.  US
◦ Days 1-5 = 3.0 MHz/0.5 W/cm²/p 20%/5
min
◦ Days 6-14 = 3.0 MHz/1.0 W/cm²/p 20%/5
min

60. References :
 Thermal Agents in Rehabilitation by
Susan L. Michlovitz 3rd edition
 Physical Agents in Rehabilitation
From Research to Practice
by Michelle H. Cameron 2nd edition
 NPTE Review & Study Guide
by O’ Sullivan & Siegelman