What is High Frequency Ultrasound?
1. What is high frequency ultrasound?
High Frequency Ultrasound (HFUS) refers to sound waves with an ultrasonic frequency of linear probe exceeding 10 MHz. It has a shorter wavelength, which is more easily absorbed and less penetrating. Therefore, HFUS is applied in superficial structure scanning and is increasingly used in skin examinations.
HFUS is a simple, reliable and non-invasive technique used in combination with physical examinations to assess, diagnose skin diseases. In addition, ultrasound of linear probe is used to evaluate normal skin structure.
2. Why does ultrasound use high frequency?
The frequency of ultrasound is above the upper limit of human hearing (20 kHz). Medical ultrasound devices use sound waves in range of 1-20 MHz. To choose a right transducer frequency is important to provide an optimal image resolution in ultrasonic diagnosis.
High frequency ultrasound (short wave) produces images with high axial resolution. For a given distance, increasing the number of compression and sparse waves can distinguish two separate structures more accurately, along the axial plane of the wave propagation. However, for a given distance, the attenuation of high frequency is greater than that of low frequency. Therefore, pocket ultrasound devices are suitable for imaging major superficial structures (2-3 cm from the skin).
In contrast, low frequency ultrasound (long wave) produces images with low resolution, but it can penetrate into deeper structures due to lower attenuation. Therefore, high frequency transducers (up to 10-15 MHz) and low frequency transducers (usually 2-5 MHz) of handheld ultrasound probe are more suitable to image superficial structures (such as nerves on clavicles, in obliquus and axillary regions). The high frequency linear probe is applied to scan the subclavian clavicles, imaging the deeper lumbar nerve structure in adults.
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