Sound in the body

Sound in the body

* When the sound wave has encountered a different material density (acoustic impedance), part of the sound wave is reflected back to the adapter is detected echo. The time it takes for the echo to travel to the converter is measured and used to calculate the depth of the tissue, causing the interface echo. The biggest difference between the acoustic impedances, the largest is the echo.


* Reflects a high degree of interfaces give rise to a strong echo, which is represented on the screen and a bright spot, while the opposite is true of the interfaces, reflecting weak. The sub-interfaces, such as acoustic cavity of the cavities and other vessels containing liquid (blood, bile, ascites, or urine) do not give a reflection of any spot on the screen anywhere on the screen is black. If the waves hit the gas or solid material density difference is so great that most of the acoustic energy is reflected and it becomes impossible to see deeper.


* The speed of sound different in different materials, and depends on the resistance of the insulating materials of sound. However, the ultrasound scanner assumes that the speed of sound is fixed in 1540 m / second. And the impact of this assumption is that in the body tissues with a real non-uniform, becoming the de beam focus, accuracy and clarity of the image is reduced.


* The formula for the speed of sound is (speed = wavelength x frequency). Frequencies used in medical imaging is generally in the range of 2 to 15 MHz. Higher frequencies have smaller wavelengths (as is clear from the formula for the speed of sound), and can be used to make images with small details. However, the mitigation of the sound wave is an increase in higher frequencies, in order to get the best deep tissue penetration, a lower frequency 3-5 MHz are used. See the deep structures in the body using ultrasound it is very difficult on some acoustic energy lost each time the echo is the problem, but more importantly, they lost to absorb sound.