PTA 110 - Physical Therapy Procedures I Lecture
Course Notes
Session 15
Page 1
I. Ultrasound
A. Acoustic energy for deep heating effect and pain relieving effect. Energy not felt by patient.
1. Is this a part of the electromagnetic spectrum?
B. Sound waves are mechanical pressure waves that are defined in terms of frequency. Audible sound with frequency of 30-20,000 CPS or Hertz.
1. US waves have frequency over 20,000
2. The most common is 1 MHZ = 1 million Hertz
a. the lower the frequency the deeper the penetration: 1 MHz will go deeper than 3 MHz
Typical depth is 3 to 5 cm
b. 1-2-3 MHz
1 MHz for deep tissue like low back
3 MHz for superficial tissue like lateral
epicondyle
C. Not a Dx Tool
II. Physical Principles
A. Units
1. Transformer boost voltage from 110 to 200-300 volts
2. Oscillating circuit increase frequency of wave
3. Coaxial cable from unit to transducer (sound head)
4. Transducer (sound head) connects high frequency electric to crystal that vibrates to create ultrasonic energy. Crystal is quartz or a synthetic. Sound heads come in different sizes and cannot be interchanged.
B. Sound Propagation
1. Positive pressure phase of wave (compression or condensation) contraction of the crystal causing decompression of tissue.
2. Negative pressure phase of wave (rarefaction) expansion of the crystal causing compression of
tissue
PTA 110 - Physical Therapy Procedures I Lecture
Course Notes
Session 15
Page 2
3. This causes molecules of the tissue to vibrate creating heat.
4. The wave does not move matter but only the wave energy
5. These waves then require a medium for transmission.
Medium can be a gas, liquid or solid
6. Waves travel longitudinal or transverse. In humans more longitudinal until hit bone then transverse
C. Absorption and Penetration
1. Absorption - the closer the molecules the quicker they collide and the sooner they respond. The energy is then impeded and absorbed.
2. Penetration - the more loose the molecules the slower they collide and respond, thus the energy is not absorbed and penetrates farther.
D. Reflection and Refraction
1. When ultrasound waves crosses from one tissue type to another i.e. fat to muscle then the reflection that occurs is dependent on the impedance of each tissue. Reflection at a metal-air interface is 99% that is why a medium is needed for ultrasound treatment. If this happens a sound head can be damaged due to heating of the crystal. A medium is used to prevent.
2. If the wave is reflected back and coincide with the source of the wave then a sum of the wave occurs and is called a standing wave. This can create increased heating and is the reason that the transducer or sound head is kept moving.
3. When the wave arrives at boundaries on a nonperpendicular path, the transmission changes the wave direction. This is called refraction.
E. Intensity
1. This is the magnitude of the force in the sound wave
2. This is the most important factor in determining
tissue response.
PTA 110 - Physical Therapy Procedures I Lecture
Course Notes
Session 15
Page 3
3. It is measured in watts and the area of the sound head is in squared cm. so intensity is measured in w/cm.
III. Equipment
A. Options for Units
1. Frequency from 1 to 3 MHz
2. Various transducer sizes - treatment area 2 x head
3. Continuous or pulsed mode (various percentages)
4. Intensity (dose) from .1 to 3.0 w/cm2
5. Treatment timer
6. Contact monitor for transducer overheating
7. Some type of display analog or digital
8. Computer controlled treatment duration
9. Appodization - hole in middle of crystal to reduce
BNR
B. Spatial Distribution
1. Transducer creates a wave beam in tissue that is cylindrical. As the beam moves deeper from a near to a far field then beam divergence occurs and a lose of energy.
2. The beam is not evenly distributed over the cross sectional area of the field. A high percentage lies in the center one third of beam.
3. Spatial peak Intensity - max intensity at any point in beam
Spatial average intensity - intensity .5mm from head
over entire area
Beam nonuniformity ratio - highest intensity would be within the beam for a given transducer.
BNR is 6:1 then at 1 w/cm2 a portion of intensity
will be at 6 w/cm2
PTA 110 - Physical Therapy Procedures I Lecture
Course Notes
Session 15
Page 4
4. Pulsed ultrasound
Ratio - 1:1 then on 5 sec off 5 sec
1:4 then on 5 sec off 20 sec
Duty Factor - 1:1 = ½ = 50%
1:4 = 1/5 = 20%
5. Intensity
Safe Limit - 3.0 w/cm2 although lower intensities
effective, so use lower levels
Acute = .1 to .5 w/cm2
Subacute = .5 to 1.0 w/cm2
Chronic = 1.0 to 2.0 w/cm2
IV. Biophysical Effects
A. Thermal Ultrasound - heat generated in the tissue from continuous mode
3mHz does not heat deep seated lesions, such as plantar
fasciitis or adhesive capsulitis of the shoulder because
heating is to superficial
Dense tissue, such as bone, scar, capsule, ligament, and tendon accumulate and retain heat better than more vascular tissue because the capillary net will dissipate heat.
Heating dose of US will diminish pain perception by slowing nerve conduction velocity, raise metabolic rate, increase blood flow which will decrease swelling, stimulate immune system, increase extensibility of soft tissue and decrease viscosity of fluid in tissue.
At 1 MHz, 1.0 w/cm2 using a stroking technique will increase temperature 4 - 6 degrees C close to bone with 8 - 15 minutes of treatment.
B. Nonthermal Ultrasound - pulsed at very low intensity cause mechanical vibration of cell (micro massage) but no heat.
PTA 110 - Physical Therapy Procedures I Lecture
Course Notes
Session 15
Page 5
Micro massage or streaming will lead to increased permeability which allows various ions and molecules to diffuse into cells which may created increased calcium or histamine to stimulate protein synthesis for tissue repair with collagen production.
V. Safety considerations
A. Precautions
1. Discomfort should not be experienced during treatment.
If pain, then add coupling gel, decrease intensity
and move transducer faster. You can burn with
US. Continued complaints then discontinue Rx
Coupling medium - lubricates skin, absorbs little
US has sufficient viscosity not to run off, no
odor, does not stain clothes, and not susceptible
to bubble formation
2. Stationary transducer is not safe, risk of overheating and hot spots.
3. Metal reflects 90% of US with increased standing waves
4. Plastic absorbs large % of US
B. Contraindications
1. Us promotes cell activity and proliferation, no use with cancer (tumors), TB or psoriasis
2. Tissue being treated with radiation therapy
3. Never over the abdomen or low back of pregnant woman
4. Over epiphyseal plates (growth plate) of children
5. Orbits of eye, gonads, area of thrombus
6. Infection that is enclosed under tension, abscesses
7. Implanted medical devices - pacemaker for heart
8. Uncontrolled bleeding
PTA 110 - Physical Therapy Procedures I Lecture
Course Notes
Session 15
Page 6
VI. Therapeutic Application
A. Goals - tissue repair, extendibility of tissue (stretch),
sedative effect on pain
B. Treat - Edema, hematomas, pain, contractures, wounds
C. Sequence of Treatment
1. Pain - prior to any activity that may increase pain
2. Contracture - stretch immediately after US with 10-
15 minutes, maintaining constant stretch.
3. Strengthening - after tissue has cooled down, after
15 minutes
4. Ice and US contradict effects, okay at end of treatment to control pain and inflammation
D. Treatment Procedures
1. In Water - best in plastic but can do in metal, do not want air bubbles in water or patient skin.
Transducer is ½ to 1 inch from surface of skin
2. With gel - best to wipe arm with damp cloth to remove air trapped on hair before applying gel
3. Explain sensation - mild warmth if anything felt, no pain
4. Turn on unit; check to see if intensity set on w/cm2
5. Positioning for comfort, but also for location of treatment. - supraspinatus insertion, shoulder extension subscapularis - shoulder abduction and external rotation, treat in axilla
6. Apply gel to skin or transducer at 1-2 mm layer, sound head moved in overlapping ½ in circle or linear path when intensity is increased. Transducer moves 3-4 cm/s which is slow. Transducer parallel to tissue surface following contour of body
7. No limit to number of treatments, but should show measurable and sustained benefits by 10-12
treatments
PTA 110 - Physical Therapy Procedures I Lecture
Course Notes
Session 15
Page 7
VII. Phonophoresis
A. Direct medication into local body tissue
B. Medication over treatment area before coupling agent is applied (Hot Pack 20 mins)
Medication mixed into coupling agent
C. Hydrocortisone, dexamethasone, lidocaine, 10% prescription from physician patient allergic to any medication pharmacist-contact