Ultrasound Flashcards
What is the purpose of ultrasound?
it is a deep heating modality that can elevate tissue temperatures to depths up to five cm
can also provide some nonthermal effects
What are the indications for ultrasound use?
- calcium deposits
- chronic inflammation
- delayed soft tissue healing
- dermal ulcers
- joint contracture
- muscle spasm
- trigger points
- pain
- warts or scar tissue
What are the contraindications for ultrasound use?
- areas of active bleeding
- areas of decreased temp sensation
- areas w/ decreased circulation
- DVT
- infection, malignancy, or thrombophlebitis
- over breast implants
- over carotid sinus or cervical ganglia
- over epiphyseal areas in young children
- over a pacemaker
- over pregnant women’s bellies or pelvic areas
What are the thermal effects of ultrasound?
- acceleration of metabolic rate
- modulation of pain
- reduction of muscle spasm
- decreased joint stiffness
- alteration of nerve conduction velocity
- increased circulation
- increased soft tissue extensibility
All effects are dependent on the intensity, duration, and frequency selected
What are the nonthermal effects of ultrasound?
- increased cell and skin membrane permeability
- increased intracellular calcium levels,
- facilitation of tissue repair
- promotion of normal cell function
What is needed to eliminate as much air as possible between the ultrasound head and the target area of affect?
a coupling agent
What are the two types of coupling agents?
Direct (gel, lotion, etc.)
Indirect (water immersion, bladder, etc.)
How far should the head of the ultrasound unit be from the skin if using water immersion indrect coupling?
.5-3 cm away
How fast should you move the transducer when performing ultrasound over an area?
approx. 4cm per second
What is the spatial-average intensity?
What is the spatial-peak intensity?
What is the beam non-uniformity ratio?
spatial-average intensity is the intensity of the ultrasound beam averaged over the area of the transducer
spatial-peak intensity is the intensity of the ultrasound beam at it’s highest point
the BNR is the ratio between the spatial-peak and the spatial-average intensities
Which is preferred, a high or a low beam non-uniformity ratio?
What should the BNR value be for ultrasound?
If an Ultrasound unit does have a high BNR how should the modality technique change?
Low because patients will be less likely to experience hot spots and discomfort during treatment
should range between 2:1 and 8:1
make sure you are moving the transducer at a good fast pace to avoid undesirable effects such as pain caused by periosteal irritation
What does ultrasound frequency a determinant of?
the depth of US penetration
What is attenuation?
Which structures have a high attenuation? Low attenuation?
attenuation is the term that describes the inevitable decrease in energy intensity as the US travels through various tissues
tissues with high attenuation are those that are more dense and high in protein such as bone
Tissues with low attenuation are those that have a high water content such as blood plasma
What frequency should be used for deep structures (up to 5 cm)?
What should be used for more shallow structures (1-2 cm)?
1Mhz
3Mhz
this is because higher frequency means it is absorbed faster so in order to reach deep structures the beam needs to take longer to be absorbed
What is a duty cycle for ultrasound?
the ratio of when the ultrasound is on and when it is off (if it is on for 1 msec and off for 4 msec the duty cycle would be 20%)
this is used for pulsed ultrasound
