《Medical Physics》The working principle of B-ultrasound

When most people think of "B-ultrasound," they probably think of images of a fetus in the mother's womb, or during a routine physical examination.

1. What is B-ultrasound?

B-ultrasound is a type of ultrasonic examination.

Ultrasonic waves are a type of mechanical vibration wave. Unlike electromagnetic waves, they must have a medium to propagate. The human ear can only sense sound waves between 20 and 20 kHz. When the frequency is greater than 20 kHz, humans cannot hear it. This type of sound wave that humans cannot sense is ultrasonic waves.

The ultrasonic transducer in B-ultrasound converts electrical energy into mechanical energy of high-frequency oscillations, producing high-frequency sound waves that are inaudible to humans, but most transducers currently used operate at higher frequencies (in the megahertz range); they can also convert ultrasound waves into electrical signals. During an ultrasound examination, technicians apply gel to the skin to prevent air pockets from forming between the transducer and the skin, thereby blocking ultrasound waves from entering the body. This technology is similar to the echolocation used by bats, whales or dolphins, and the sonar used by submarines.

Different Types of Ultrasound Images

(1) 3D Ultrasound Imaging

Several 2D images are acquired by moving the probe over the body surface or rotating the inserted probe, and then the 2D scans are combined into a 3D image using specialized computer software.

(2) Doppler ultrasound

Doppler ultrasound is based on the Doppler effect. When an object reflecting ultrasound waves moves, it changes the frequency of the echoes, producing a higher frequency if it moves toward the probe and a lower frequency if it moves away from the probe. The degree to which the frequency changes depends on how fast the object is moving. Doppler ultrasound measures the change in echo frequency to calculate how fast an object is moving, for example to measure heart and blood flow.

3. What is the color ultrasound we often talk about?

Simply put, color ultrasound is a high-definition black and white B-ultrasound plus color Doppler, which provides richer medical information.

4. Are there any risks?

Ultrasound testing is non-invasive, safe, and painless to patients, and does not produce ionizing radiation like X-rays, CT scans, and magnetic resonance imaging (MRI) magnetic fields. However, ultrasound can still produce some biological effects in the body under certain circumstances and conditions:

(1) Thermal effect: Tissue or water absorbs ultrasonic energy, thereby increasing the local temperature.

(2) Bubble formation: Bubbles may be generated when dissolved gases escape from the solution due to the localized heat caused by ultrasound.

However, no adverse effects of ultrasound have been demonstrated in human or animal studies. That being said, ultrasound should still be used only when necessary.