23-05-2014, 02:49 PM
Deep Heat Ultrasound & Diathermy
Deep Heat Ultrasound.ppt (Size: 184 KB / Downloads: 39)
Ultrasound
Ultrasound is the most commonly used deep heating modality in use today. Penetration is between 3-5 cm.
Acoustical energy, not electromagnetic as most other units
frequency is between .8 and 3 MHz (audible f= 15-20,000 Hz)
Equipment
Electrical generator with step up or down transformer to overcome impedance of the crystal
Oscillating circuits: optimizing frequency and allows us to impose a duty cycle
coaxial cable carries current and minimizes any distortion
transducer converts electrical energy into crystal into mechanical vibration (sound waves)
The Crystal
piezoelectric effect: electricity across the crystal causes deformation and vibration
The quartz crystal requires high amount of voltage to cause piezoelectric effect and must therefore have well insulated coaxial cables to deliver electricity to the transducer.
Capable of delivering mechanical and thermal effects to the tissue
Terminology for Effects:
Continuous or pulsed: this determines the production of heat. If the US is pulsed the % means the percent of time the sound will be delivered in a unit of time (i.e. 20% duty cycle will give 2 msec of sound every sec.)
Condensation: areas of high energy collection
Rarefraction areas of lower energy, gaps between waves of molecules
Propagation:
Sound waves are most effectively transmitted through dense materials.
Soft tissue is analogous to liquid when US travels in longitudinal manner
Bone may be longitudinal or transverse. Bone can cause a shear force near tissue interfaces
US travels best in homogeneous material, interfaces cause more scattering of waves.
since fat is homogeneous it will transmit the waves and allow deeper penetration
Special considerations for Equipment
Spatial peak intensity: because the US beam is not uniform, some regions will be more intense. The spatial peak intensity is the greatest intensity anywhere within the beam
Spatial average: a measurement of the average intensity It is a measurement of the total power output (Watts) divided by the area (cm)
Absorption
Directly proportional to the protein content of the tissues sonated.
bone, cartilage, tendon and skin are 20-25% protein content
blood vessels are 15-20%
muscle, fat and blood are 10-15%
Tissues which are selectively heated by US are the "target tissues” for US use.
Superficial bone, joint capsules, tendon, scar tissue, peripheral nerves, myofascial interface and cell membranes
Intensity:
Everyone’s tolerance is different
The feeling of warmth is desired (if using for thermal properties)
Begin at 1.0 W/cm2 and increase intensity until the patient feels heat (not pain) and reduce until a gentle heating if felt
Some researchers site: 1.0 W/cm2 for “thin” tissues and 1.0-2.0 W/cm2 for “thick” tissues
Diathermy Precautions
Physician's Prescription (some states)
Never allow cables to touch (short circuit)
Do not allow for perspiration
Never allow direct contact with skin
Excessive fat in area may overheat area
Difficult to tx localized areas
Overheating tissues may cause damage
deep acing
fat neurosis
burning