Therapeutic ultrasound devices range in frequency from 1 to 3 MHz, with research supporting both frequencies as effective treatments for treating musculoskeletal conditions such as CTS.
Ultrasound waves penetrate tissues, where they’re absorbed to some extent, producing thermal effects. To transfer this energy effectively into tissues, some kind of conductor must be present – typically gel, mineral oil, lotions or water immersion are ideal solutions.
Attenuation
Ultrasound waves may reflect off tissue or be absorbed by it and attenuate, decreasing their strength and thus their ability to penetrate tissues. This is similar to electromagnetic radiation being reduced when passing through materials like x-rays or radio signals, where its attenuation depends on how dense and chemical composition of materials.
Ultrasound therapy penetrates the body through various means, such as attenuation, effective radiating area and beam nonuniformity. A physiotherapist must understand these impacts on ultrasound therapy treatment efficacy in order to ensure its successful implementation.
Ultrasound waves are generated by the transducer, a crystal that exhibits piezoelectric effect (the expansion and contraction of crystal when exposed to an electric current). When voltage is applied to this crystal, vibrations travel into tissues which come into contact with it, returning with echos that are recorded and interpreted into images of body structures.
Gel facilitates ultrasound transmission from an ultrasound probe to a patient’s skin and deeper tissues by helping sound waves transfer between the ultrasound crystal in the transducer and their skin.
Once sound waves have made contact with a patient’s skin, they reflect back to the transducer and then are transmitted again through refraction and scattering to different parts of their tissues – this reduces how much energy penetrates deeper levels of their bodies.
Attenuation can also depend on the characteristics and thickness of tissues being treated. For instance, high collagen tissues like ligaments, tendons and fascia absorb less of the ultrasound energy than dense structures like bone or muscle; 3MHz and 1MHz treatment frequencies are typically available; studies support 3MHz’s effectiveness for treating superficial lesions while 1MHz provides better depth treatments.
Conduction Media
The material through which ultrasound waves travel (known as the medium) has an influence on their transmission speed and attenuation, due to its acoustic impedance being dependent upon density and sound speed through it. A higher impedance results in slower transmission speeds and attenuations levels.
Medium can also affect how effectively ultrasound waves penetrate tissue. High collagen tissues like ligaments, tendons and fascia tend to absorb ultrasound energy effectively while dense tissues such as bone or cartilage tend to reflect it back at us.
There are two different kinds of ultrasound waves: continuous and pulsed. Continuous waves move continuously while pulsed waves have rest periods between each pulse. The intensity of an ultrasound wave can play an integral part, as its heating of tissue varies significantly from just a couple of degrees up to enough heat up muscle tissue.
Another indicator is the acoustic beam non-uniformity ratio, which measures how evenly ultrasound waves are distributed over the surface of a soundhead. More even distribution indicates better results.
Final consideration is knowing what type of tissue you are treating with ultrasound. To minimize damage to tissues and ensure best results, low to moderate intensity continuous wave settings are the ideal approach. Research on nerve entrapment with carpal tunnel syndrome, for example, shows efficacy when treating it using a one megahertz setting – more of a continuous wave than pulsed wave. This guideline can also work well when treating most other forms of muscular distress. Ultrasound therapy is an invaluable way to address many musculoskeletal ailments within the body, when combined with exercise therapy, mobilisation techniques and rehabilitation programs. Ultrasound therapy offers more than pain relief; it increases local blood circulation and metabolism in the treated area to accelerate healing processes and enhance other physiotherapy interventions, speeding healing processes while amplifying their effectiveness. As such, ultrasound can make an invaluable addition to any treatment plan. Ultrasound imaging has become widely utilized during prenatal care scans of fetuses while it is widely employed today in medical imaging to identify heart disorders.
Effective Radiating Area
Ultrasound is a mechanical wave which interacts with tissues at both the surface and depth, creating both thermal and non-thermal interactions, making high intensity focused ultrasound (HIFU) a revolutionary new technique capable of ablation by inducing coagulative necrosis and cavitation – two processes which cause ablation through ablation by creating ablation zones in which any surrounding tissue remains undisturbed by this therapy.
HIFU is a non-invasive thermal ablation method that utilizes concentrated pulses of ultrasound energy to generate very high temperatures in targeted areas. The method causes lesion of coagulative necrosis in tumor tissue as well as cavitation and tissue damage; once healing has occurred in normal healthy bodies cells will re-grow; however in targeted tumor tissues they won’t have this opportunity and die, leaving behind scar tissue that looks unlike its healthy neighbors.
An ultrasound probe is used to direct ultrasound energy toward specific target tissues. The size of its treatment head determines its cross-sectional area and thus how much energy will be delivered to that tissue. Furthermore, frequency, power and duty cycle affect how quickly effects may take effect on that target tissue.
Ultrasound energy can produce both thermal and non-thermal effects, such as acoustic microcirculation and cavitation. Non-thermal effects typically appear with lower energy levels and pulsed mode; they’re associated with cell “upregulation.” Non-thermal effects are considered beneficial in stimulating fibroblast activity, increasing protein synthesis and improving circulation – factors which promote healing by speeding tissue repair.
As ultrasound waves use mechanical energy instead of electromagnetic waves such as X-rays, they won’t penetrate as deeply into human bodies compared with electromagnetic waves such as X-rays. This can be beneficial when treating important blood vessels in the brain, liver or kidneys where thermal ablation could pose risks.
Duty Cycle
Your ultrasound machine’s duty cycle will depend on what kind of tissue it’s treating, as each responds differently to this form of energy. While some dense tissues reflect it back, others absorb and heat up from it; ligaments and tendons in particular absorb ultrasound energy very effectively while bone and cartilage reflect it back, meaning you should steer clear from using the machine there.
As part of any treatment, it’s also important to consider both its depth and type. The deeper you go in your treatments, the greater your risk is of creating hot spots at tissue interfaces – this can cause discomfort as well as damage in extreme cases if left too hot; to avoid this using low intensity soundhead treatment in shallower areas with speed is key in order to avoid this situation.
Always keep in mind whether the tissue you are treating is thermal or non-thermal when considering ultrasonic treatment options, as this will affect power, frequency, mode and pulse ratio (if applicable). Many textbooks suggest a continuous 50% pulse ratio as being non-thermal but recent research indicates this can actually create temperature changes within tissue.
Reason being, heating connective tissues allows them to become more elastic, making stretching possible. Therefore, most treatments like friction massage, joint mobilizations and muscle stretching should take place while tissues are still warm – particularly important when treating nerve entrapments like carpal tunnel syndrome (CTS) with pulsed machines set at about 1.0 MHz with 20% duty cycle for five to 10 minutes of continuous treatment. Studies have proven their efficacy against such issues.
