Unlocking the Power of Ultrasonic Therapy: Understanding Effects

 

Ultrasonic Therapy

By definition, sound is the periodic disruption of an elastic medium, such the air, by mechanical means. In contrast to electromagnetic waves, sound cannot travel through a vacuum and needs a medium to do so. To generate sound waves, an oscillating source is needed, such a tuning fork. The sound wave's frequency stays constant throughout the medium and is equal to the source's rate of oscillation. The medium's particles alternately compress and rarefy (move apart) as a result of sound waves, which are traveling pressure waves. Thus, the particles themselves only oscillate back and forth, each around a mean point; only the wave's structure advances. Since energy transfer from particle to particle is not 100% efficient, energy is lost with each transfer, which is how sound waves propagate (attenuation).

Understanding Wave Properties and Mediums

The distance between the two nearest points on a wave that are moving in the same direction at any given time is known as the wavelength. The frequency is the number of full cycles that a particle travels through in a second. The speed at which a wave travels through a medium is known as its velocity, and it varies according to the physical properties of the medium. Water is a very good sound transmitter, while air is very poor. In certain media, the sound velocities are:

Air    344 ms^-1

Water   1410 ms^-1

Muscle  1540 ms^-1

Ultrasound

A little bit over 20 kHz (20 000 cycles per second) is the upper limit of human hearing. Therapeutic frequencies for ultrasound are in the range of 1 MHz to 3 MHz, which is far higher than this.

THE ULTRASOUND PRODUCTION

A vibrating source with a frequency of one million cycles per second is required for a machine operating at one megahertz. Either a quartz or a barium titanite crystal is used to do this. When a piezo-electric effect a changing potential difference is applied to these crystals, they distort. High-frequency current originates from a source and travels via coaxial cable to a transducer circuit or treatment head. A linking electrode in the transducer circuit applies high-frequency current to the crystal, fusing it to the treatment head's metal front plate. Any modification to the crystal's form results in movement of the metal front plate, which generates an ultrasonic wave. The high-frequency current (1 MHz or 3 MHz) must be strictly controlled in order to provide a constant and predictable rate of distortion. the impact of applying a prospective alteration to the crystal and how that impacts nearby cells. Up until the end of the near-field, where the beam begins to diverge, ultrasound propagates linearly.

Ultrasound treatment parameters

When using ultrasound, it can be pulsed, with intervals of ultrasound followed by quiet, or continuous, with the treatment head producing ultrasonic energy continually. The following details must be mentioned while using ultrasound.

Efficacy

Although the watt is the unit of intensity when employing ultrasound, an averaged intensity is typically utilized because this is a crude measure of the power being emitted by the treatment head. Space averaged intensity, such as watts per square centimeter (Wcm-2), which indicates the average intensity over a specific area. When using ultrasound in a pulsed mode, two options are available for calculating intensity: time averaged/space averaged, which provides the average intensity (per second) for a given area (Wcm-2) for the course of the therapy. For instance, the average intensity (as if the ultrasound were continuous) would be 0.1 Wcm-2 in one second if 0.5 Wcm-2 was administered pulsed 1:4. When employing pulsed ultrasound, some ultrasonic generators' output meters automatically adjust.

Space ratio for the pulsed mark

When ultra should be expressed, it is applied in its pulsed form using printed ultrasound. This is the ratio of mark to space, or the mark to time ultrasonography is on, with space measured in milliseconds. While certain units, like 1:1, 1:4, and 1:7, have a flexible range, others have a single set M:S ratio of 2:8.

Ultrasound reflection

Sound travels according to the rules of reflection, and reflection occurs when an ultrasonic beam passing through one medium comes into contact with another that will not permit it to pass through and enter the new medium. Since air cannot transmit ultrasonic waves, extreme caution is used during ultrasonic treatment to reduce reflection by keeping air between the treatment head and the patient. At every interaction the ultrasonic beam comes into contact with, there will be some reflection, though. The ratio of the reflected to the transmitted ultrasound at an interface is called the acoustic impedance (Z). Transmission is high when the acoustic impedance is low, and vice versa.

Ultrasound transmission

The ultrasonic beam may be refracted, or bent from its initial course, similar to how light is, if it passes across an interface between two media. It is refracted away from the normal when moving from a medium with a low velocity into one with a high velocity. Refraction is significant because it would cause the ultrasonic beam to miss T if it were the target. Treatment should be administered with the majority of the waves traveling along the normal, or perpendicular to the interface between the media, wherever possible, since refraction does not happen when the incident waves travel along the normal.

Attenuation of ultrasonography

The word "attenuation" refers to the ultrasonic beam's progressive decrease in intensity after it leaves the treatment head. There are two main causes of attenuation.

Take-up

At that point, the tissues absorb the ultrasound and transform it into heat. This is the ultrasound's thermal effect.

Ultrasonic fields

The separation of the ultrasonic beam into a near and a far field is another factor to take into account when determining the strength and depth of penetration. The transducer's radius (r) and the medium's ultrasonic wavelength (1) determine how large the near field is. The following formula can be used to determine the near field's depth: The near field's depth changes in proportion to the ultrasound's frequency since wavelength and frequency have an inverse relationship.

Understanding Ultrasonic Near and Far Fields

Due to interference between neighboring fronts caused by the wave fronts from various regions of the source having to travel different distances, the near and far fields are created. The interference between the two waves can be helpful at times, combining their energy, or destructive, reducing each other's energy. There will therefore be high and low intensity areas in the ultrasonic beam when seen in both longitudinal and transverse profiles. This is especially noticeable in the near field where significant pressure variations occur. Given that the near field is more intense than the far field and may have a more significant impact on the treatment of specific illnesses, its extent is important. On the other hand, the near field exhibits a significantly wider range of intensity than the far field. Consequently, when treating tissues at a depth higher than 6.5 cm (the shortest near field), the ultrasound's frequency and transducer's radius may need to be taken into account.

Combining media

Since air cannot transmit ultrasonic waves, a couplant that can must be positioned between the patient's skin and the treatment head (transducer). Regretfully, no couplant can guarantee flawless transmission; even the most effective couplant reduces the applied dose by a quarter. Only a portion of the original intensity gets conveyed to the patient. The ultrasonic beam will actually be reflected back into the treatment head by air (zero transmission), which could create a standing wave that could harm the crystal. As a result, when the treatment head is not in contact with a transmitting medium, it is never left on.

EFFECTS OF ULTRASONIC WAVES ON TISSUES

Heat-related effects

Heat is produced as the ultrasonic vibrations enter the tissues and are absorbed. The following determines how much heat is produced:

1. Absorption properties of the tissue protein: It generates a lot of heat by effectively absorbing ultra-sound.
2. The quantity of times the portion is passed over by the treatment head.
3. The effectiveness of the tissues' insonated circulation.
4. In continuous ultrasound, the duration and intensity of insonation strongly correlate with the amount of heat created (Macdonald and Shipster 1981).
5. There is less thermal effect with pulsed ultrasound compared to continuous ultrasound, and a mark: space ratio of 1:4 generates less heat than il (Sandler and-Fiengold 1981).
6. A concentrated heating effect is produced at a particular site when ultrasonic reflection occurs at a tissue contact. This is especially prone to occur where the periosteum and bone meet. The ultrasonic intensity in the periosteal region doubles as reflection from bone occurs, potentially leading to regional warming and periosteal pain. This practically means that if at all possible, the ultrasonic treatment head should not be passed over subcutaneous bone points.

Applications for the thermal effect

Healing could be sped up by taking advantage of the local temperature increase. Temperature increases cause collagen to become more extensible, which makes it simpler to stretch scars or adhesions after ultrasonography. Additionally, the heat impact might lessen pain. Ultrasound was formerly thought to be a heat treatment, but more recent research has revealed that ultrasonography has a variety of non-thermal effects that could be useful in therapy.

Effects of cavitation, mechanics, and biology

These effects are all related to one another and result from the ultrasound's significant force generation in the tissues.

Cavitation

This is the extremely compressible bodies' oscillatory activity inside the tissues, like gas or vapour-filled spaces. Because a large local temperature increase results from the bursting of the bubbles, cavitation may be unstable and potentially harmful to the tissues. Moving the treatment head (to minimize standing waves), utilizing a high frequency (1 or 3 MHz), and employing a low intensity (below 3 Wcm-2) are the ways to avoid it. Because stable cavitation alters the ultrasonic beam in a way that causes micro-streaming, which influences the direction of molecules' migration into cells and the permeability of cell membranes, it is not harmful and may even be advantageous.

Micromassage or mechanical

Here, the ultrasonic beam's longitudinal compression waves cause cells to compress or rarefy and have an impact on the flow of tissue fluid through interstitial gaps. This may lessen oedema. The extensibility of adhesions and scars may be impacted in a way that makes stretching them easier when combined with the heat effect. It's also feasible that the mechanical impact will lessen discomfort.

Biological

The non-thermal effects of ultrasound on healing have been the subject of extensive research. In each of the three stages of repair, ultrasound can be helpful: It's likely that inflammatory ultrasound weakens lysosome membranes, which facilitates the release of the enzymes they contain. These enzymes will assist in removing any material from the area so that the following stage can start.

Proliferative

Ca+ ions may be present in proliferative fibroblasts and myofibroblasts. This makes them more mobile and motivates them to move in the direction of the repair. Myofibroblasts contract to pull the edges together, and fibroblasts are stimulated to make collagen fibers to form the scar. It has been demonstrated that remodeling ultrasound can improve the scar's tensile strength by influencing the elasticity, strength, and orientation of the fibers that comprise the scar. Standing waves and phenomena like reversible blood cell stasis, in which all the blood cells in a conduit are forced to gather in columns divided by plasma, have been the subject of extensive research. Moving the treatment head helps to prevent standing waves in therapeutic terms, therefore this finding is mainly interesting from an academic standpoint when treating big blood pools like those seen in the heart and major blood veins.