Ultrasound questions Flashcards
What does ultrasound mean
It is a form of mechanical energy, caused by vibrations. It is the name of energy above the human hearing range (1mhz-3mhz)
How is the ultrasound beam produced
it is produced by mechanical vibrations in the applicator head the human ear cannot hear. This is done by electrical energy being applied to the crystal in he applicator head
How does US energy travel through gel and human tissues
All materials present some impedance to the sound energy produced by an ultrasound machine. The greater the difference of impedance the greater the amount of energy reflected. There is a large difference between the metal and air interface so there is a gel used to minimize this as it means that the waves do not come into contact with air so less is reflected and more is transmitted through to the tissues.
Why isnt a US beam uniform in intensity?
It changes in its nature with distance from the transducer. In the field closest to the transducer there is a lot of interference and the behavior of the beam is not regular. The US energy in parts of this field can become much greater than the actual output of the machine. Crystal quality also affects the intensity of the beam
What is attenuation?
term given to the loss of wave amplitude due to the processes such as scattering and absorption
What is scatter
Occurs at interfaces involving structures of small dimensions. When the wave is larger than the structure it creates a uniform amplitude in all directions.
What is absorption?
When a tissue retains the energy produced by the US machine. More energy is absorbed in superficial tissues than in deeper tissues so the therapeutic effects are less in the deeper tissues
When do standing waves occur?
Is the interaction of oncoming ultrasound waves with those reflected back from a tissue interface. Effect = creates risk of tissue cavitation (gas bubbles). It is the formation and growth of gas bubbles by accumulation of dissolved gas in the medium. They take approx 1000 cycles to reach their max size. Happens when the applicator isn’t continuously moving.
What is stable cavitation
formation and growth of gas bubbles by accumulation of dissolved gas in the medium. The ‘cavity’ acts to enhance the acoustic streaming phenomena so therefore can be seen as beneficial.
What is transient cavitation?
The formation of bubbles at the low pressure part of the cycle. The bubbles then collapse very quickly releasing a large amount of energy which is detrimental to the tissue. This shouldn’t happen if a good technique is used.
Benefits of acoustic streaming
described as a small scale eddying of fluids near a vibrating structure such as cell membranes & the surface of stable cavitation gas bubble. It is the combined effects of stable cavitation and acoustic streaming is that the cell membrane becomes excited, and increasing the activity levels of the whole cell. The US energy acts as a trigger for this process, but it is the increased cellular activity which is in effect responsible for the benefits
What is micromassage
The sound wave travelling through the medium is claimed to cause molecules to vibrate, possibly enhancing tissue fluid interchange and affecting tissue mobility.
Thermal effects of US
It requires US to be at a high intensity in order to reach the deep collagenous tissues - usually continuous ultrasound.If the tissue temperature is raised to between 40-45 degrees then hyperaemia (excess blood) will occur which can be very theraputic. believed that these temperatures can help solve chronic inflammatory states. Can cause pain relief, increased ROM and increased blood flow.
Benefits of US during the inflammatory stage of tissue repair
Helps to stimulate mast cells, platelets, WBCs and macrophages. US also induces the degranulation of mast cells which causes the release of inflammatory mediators. US does not have an anti-inflammatory effect but is effective at promoting the normality of the inflammatory events so helps to promote repair of tissues.
Benefits of US during the proliferation stage
US targets fibroblasts and endothelial cells which are normally active during scar production and therefore US is pro-proliferative as it maximises the efficiency of the scar production.
