What Is Mobile Ultrasound?

Ultrasound refers to mechanical vibration waves with a frequency above 20,000 Hz, which cannot cause normal human auditory responses. The method of applying ultrasound to the human body to achieve therapeutic purposes is called ultrasound therapy. Ultrasound with a frequency of 500 to 2500 kHz has a certain therapeutic effect. Frequently used in physical therapy is generally 800 ~ 1000 kHz.

Ultrasound therapy

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Ultrasound means that the frequency is above 20000Hz and cannot cause normal people

Ultrasound therapy

(Ultrasonic therapy)

In recent years, the use of ultrasound therapy has become increasingly widespread, and has far exceeded the original general therapies in physical therapy, such as ultrasound treatment of cancer, urinary lithotripsy and stomatology. Therefore, the concept of ultrasound therapy should be broad (including Special ultrasound therapy) and narrow sense (referring to the non-invasive dose therapy commonly used in physiotherapy). At the same time, with the advancement of modern science and technology, ultrasound is not only used for treatment, but also widely used in diagnostic, basic and experimental medicine, so it has been called "ultrasonic medicine".

Ultrasound and sound waves are essentially the same. They are all mechanical vibration waves formed by the propagation of mechanical vibrations of an object in an elastic medium.

1. Because sound waves are a form of material propagation energy, their propagation must depend on the medium, but they cannot propagate in a vacuum. This is different from light waves and electromagnetic waves.

2. When the ultrasonic wave propagates to the surrounding medium, it produces a dense and dense waveform. The elastic waves formed by this continuous compression layer and sparse layer alternately coincide with the direction of the sound source oscillation, which is an elastic longitudinal wave). Because the ultrasonic wave has a very short wavelength, it can be gathered into a narrow emission line beam and spread straight in a beam shape, so the propagation has a certain directivity.

3. Propagation speed The propagation speed of sound waves is related to the characteristics of the medium, and has nothing to do with the frequency of sound waves. The propagation speed of sound waves in the air is 340 m / s, 1500 m / s in liquids, and 5000 m / s in solids. Human soft tissues are similar to liquids, with an average of about 1540 m / s. Human bone tissue About 3380 m / s. The propagation speed of sound waves increases as the temperature of the medium rises. The temperature increases by 1 ° C, and the speed of sound increases by 0.6 m / s.

4. The absorption and penetration of ultrasound When ultrasound propagates in a medium, its intensity decreases with its propagation distance, which indicates that the ultrasonic energy is absorbed. The absorption of ultrasound is related to the density, viscosity, thermal conductivity and frequency of the ultrasound . Ultrasound is absorbed most in gas, less absorbed in liquid, and smallest absorbed in solid. The absorption coefficient in air is about one thousand times larger than that in water. And the absorption coefficient of the medium is directly proportional to the square of the ultrasonic frequency, so the attenuation of high-frequency ultrasound in the air is extremely severe. Therefore, although there is a very small air bubble under the acoustic head during treatment, it should also be avoided.

A semi-absorptive layer is commonly used in practice to indicate the ability of a medium to absorb ultrasonic waves. The semi-absorbing layer refers to the thickness when the ultrasonic wave is attenuated to half the original energy in a certain medium. The thickness of the semi-absorptive layer is large, indicating that the absorption capacity is weak. Different tissues have different half-absorptive layer values for the same frequency of ultrasound. For example, at 300 kHz, the semi-absorptive layer of muscle is 3.6 cm, the fat is 6.8 cm. It is 4.9 cm. The same tissue also absorbs different frequencies of ultrasound. The higher the ultrasound frequency, the more it absorbs and the shallower it penetrates. For example, 90 thousand cycles of ultrasound can penetrate 10 cm of soft tissue, and 1 trillion cycles of ultrasound will penetrate 5 cm. Megacycle ultrasound only penetrates a depth of 1 cm. Therefore, the ultrasound commonly used in physiotherapy at present is 8000 kcycles / second, and the penetration depth is about 5 cm.

5. When refraction, reflection and focused ultrasound propagates from one medium to another, a part of the interface will reflect back to the first medium (reflection), and the rest will enter the second medium through the interface, but the propagation direction will occur Deflection (refraction). The degree to which sound waves are reflected at the interface depends on the difference in sound resistance between the two media. The larger the difference in sound resistance, the greater the degree of reflection. The reflection between the acoustic head and the air is nearly 100%, so paraffin oil is used as a contact agent during ultrasound treatment to reduce the reflection. Experiments have shown that only 35 to 40% of the ultrasonic energy entering the tissue from the acoustic head is reflected, while 60 to 65% is reflected. Due to the reflection between air and tissue, a large amount of ultrasonic energy is lost, so the ultrasound cannot pass through the lungs and the inflated stomach.

Based on the principle of reflection and refraction propagated by ultrasound, the lens and the arc reflection are used to focus the sound beam on the focal point to generate powerful energy, and to treat certain diseases, such as destroying brain tumors with beam ultrasound

Speed, density and sound resistance of several substances

name

Speed of sound m / s

Density g / cm3

Sound resistance g 105 / cm 2 s

air

water

Barium titanate

Paraffin oil

aluminum

Human soft tissue

muscle

fat

skeleton

340

1500

5000

1420

6400

1500

1400

1580

3380

0.00129

1.000

5.4

0.835

2.7

1.06

1.07

0.95

1.80

0.000439

1.500

27.000

1.186

17.28

1.59

1.498

1.501

6.184

Ultrasound beaming method

The spatial range in which ultrasonic waves propagate in a medium, that is, the area where the medium is subjected to ultrasonic vibration energy, is called an ultrasonic sound field. Because of its high frequency, ultrasound has similar beam emission characteristics. The section near the acoustic head is an almost parallel beam, which is called the near-field region. The beam then spreads and is called the far-field region. Due to this characteristic of the ultrasound field, in order to overcome the uneven energy distribution, the acoustic head should be moved slowly at the treatment site during treatment.

Ultrasonic sound field

The main physical quantities describing the ultrasonic sound field are sound pressure and sound intensity.

1. Sound pressure is the pressure of sound energy, which represents the intensity of ultrasonic waves. When the ultrasound is propagating, it generates positive pressure in the dense area and negative pressure in the sparse area.

Because of its high frequency, ultrasound also has a high sound pressure. Medium-dose ultrasound produces an additional sound pressure in the tissue of approximately ± 2.6 atmospheres. (Figure 7.6)

Sound pressure in human tissues during ultrasound treatment

2. Sound intensity is the intensity of sound energy per unit of time, that is, the sound energy per square centimeter of area that passes through vertically per second. A common measurement unit is Watt / cm2 (W / cm2). The commonly used clinical treatment dose is 0.1 2 2.5W / cm2, and the deafening cannon sound intensity is only equivalent to 0.0. 0.0001W / cm2. It can be seen that when ultrasonic waves propagate in the medium, its huge energy will cause a large acceleration of the particles of the medium. Generally, when a medium-sound sound wave passes through water, the acceleration obtained by water molecules is only a percentage of the acceleration of gravity (about 9.8m / s). For example, under the action of ultrasonic waves with a frequency of 800 to 1000 KHz and a sound intensity of 0.5 to 2 W / cm2, the acceleration obtained by moisture can exceed the acceleration of gravity by 5 to 100,000 times.

There are various methods for generating ultrasonic waves. Currently, piezoelectric ultrasonic generators are mainly used, which are made according to the principle of piezoelectric effect. When a crystal with piezoelectric effect is compressed or stretched, an equal amount of charges with opposite signs will be generated on its force surface. This physical phenomenon is called piezoelectric effect.

Sketch of positive piezoelectric effect

If a high-frequency voltage of a certain frequency is applied to both sides of the crystal, the crystal flake can periodically and accurately change its thickness (compression and expansion) with the frequency of the alternating electric field. This creates ultrasonic vibrations that propagate to the surrounding medium.

(A) mechanical action

Mechanical action is a fundamental primary action of ultrasound. During the propagation of ultrasonic waves in the medium, the particles of the medium are alternately compressed and stretched to form an alternating sound pressure. Vigorous exercise, friction with each other, and can cause changes in volume and movement of tissue cells, which can cause strong cytoplasmic movement (original plasma microfluid or circulation), thereby promoting the movement of cell contents and changing the relative space The location (observed that low-intensity ultrasound can rotate the plasma particles of eosinophils, and even when the dose is large, the particles are thrown out of the cell), showing that ultrasound has a "fine Massage ".

This effect can cause changes in cell function and cause many reactions in the organism. Can improve blood and

(I) Impact on the nervous system

Low-dose ultrasound enables

Ultrasound treatment machine

(1) Main structural principle: It consists of two parts, a high-frequency oscillator and an output head.

(2) Output form

Continuous ultrasound: During the entire treatment process, the acoustic head continuously emits sound energy to act on the body. It has a uniform effect and a large heat production effect.

Pulsed ultrasound: It radiates sound energy intermittently in the middle of the treatment process and acts on the body, and its thermal effect is small.

2. Auxiliary equipment is an accessory prepared for special treatment needs or convenient operation surfaces. Such as water pillows, water bags, sinks, water funnels, etc.

3. The contact agent should choose a person whose acoustic resistance is close to that of human tissues to reduce the reflection consumption between the interface and the skin. Commonly used are boiled water, liquid paraffin, and petrolatum oil.

1. Direct contact method The ultrasonic head is directly contacted with the skin of the treatment site for treatment. At this time, a contact agent such as paraffin oil, vaseline, etc. should be added between the skin and the acoustic head.

(1) Moving method This method is most commonly used. During treatment, the acoustic head gently presses the skin, and it moves slowly at the treatment site, and the speed of movement is preferably 1-2 cm per second. The commonly used strength is 0.5-1.5W / cm2.

(2) Fixation method The ultrasound head is fixed to the treatment site with appropriate pressure. This method is prone to overheating and "periosteal pain response". Therefore, the treatment dose should be small, the commonly used intensity is 0.2-0.5W / cm2, and the time is 3-5 minutes.

2. Indirect contact method

(1) During the underwater treatment, the ultrasonic head and the treatment limb are immersed in warm water at 36-38 ° C. The distance between the head and the skin is 1-5 cm, and the dose is slightly larger than the direct contact method.

This method is often used on irregular body surfaces, areas with local pain sensitivity or inaccessible areas such as fingers, toes, ankles, elbows, ulcers, etc.

(2) Auxiliary treatment methods are commonly used water funnel method, water pillow or water bag method. The latter is a bag made of a thin rubber film, filled with boiled warm water, and then coated with a contact agent for treatment, used on the face,

1. The treatment intensity is preferably 0.4-1.5W / cm2. The intensity can be slightly greater in the underwater method and the water pillow method. Refer to Table 7.2 for practical use. Low and medium intensity are usually used in clinical practice.

Table 7.2 Ultrasonic intensity level table

treatment method

Fixed method

Move method

strength level

low

in

high

generation

in

high

Continuous

W / cm2

0.1-0.2

0.3-0.4

0.5-0.6

0.6-0.8

1-1.2

1.2 -2

Pulsed

W / cm2

0.3-0.4

0.5-0.7

0.8-1.0

1.0-1.5

1.5-2

22.5

2. The treatment time is generally 3-5 minutes for fixed method, 5-10 minutes for moving method, and large area movement can be appropriately extended to 10-20 minutes.

3. The course of treatment is generally 6-8 times, 10-15 times or more for chronic diseases. Daily or every other day. The treatment interval is 1-2 weeks.

1. Sports support organ traumatic diseases

1. All malignant tumors (curable by high-dose aggregation), active tuberculosis, heart regions and stellate ganglia of severe heart disease, bleeding tendency, and venous thrombosis are prohibited.

2. Pregnant women (early) belly and pediatric bone are best to choose other treatments. The dosage should be strictly controlled when treating the head, eyes, heart, and genitals.