Reflection and refraction of animal B-ultrasound

The acoustic impedance of air is 0.000428, and the acoustic impedance of soft tissue is 1.5. The difference between the two acoustic impedance values is about 4000 times, so the interface reflection ability is particularly strong. In clinical ultrasound detection, there must be no gap between the probe and the animal's body surface to prevent the sound energy from being reflected on the animal's body surface in large quantities without sufficient sound energy reaching the detected part. This is why coupling medium must be used during ultrasound detection. The basic basis of ultrasound diagnosis is the echo condition of the detected part

Diffraction of animal B-ultrasound

When animal B-ultrasound encounters an object smaller than half of its wavelength, it will bypass the edge of the obstacle and continue to propagate forward, which is called diffraction. In fact, when the obstacle is equal to the wavelength of ultrasound, ultrasound can be diffracted, but it is not very obvious. According to the law of ultrasonic diffraction, during clinical examination, a probe with an appropriate frequency should be selected according to the size of the target to be examined, so that the wavelength of the ultrasonic wave is much smaller than the target to be examined, so that the ultrasonic wave does not diffract on the target to be examined, and relatively small lesions can also be examined to improve the resolution.

Scattering and attenuation of animal B-ultrasound

When ultrasound propagates in a medium, it will weaken as the propagation distance increases. This phenomenon is called ultrasonic attenuation.

The causes of ultrasonic attenuation are:

(1) The diffusion of the ultrasonic beam and the reflection, refraction, and scattering on different acoustic impedance surfaces weaken the sound energy in the direction of the main sound beam;

(2) In the propagation medium of animal B-ultrasound, due to the influence of the viscosity (internal friction), thermal conductivity, and temperature of the medium, part of the sound energy is absorbed (sound energy absorption), thereby reducing the sound energy. The attenuation of sound energy is related to the ultrasonic frequency and the propagation distance. The higher the ultrasonic frequency and the longer the propagation distance, the greater the attenuation of sound energy, especially the absorption attenuation of sound energy; conversely, the smaller the sound energy attenuation. Blood in animals absorbs the least amount of sound energy, followed by muscle tissue, fibrous tissue, cartilage and bone.