Ultrasound Wave: Definition and Medical Use
An ultrasound wave is a mechanical sound wave with a frequency above the range of human hearing (above 20,000 Hz). In medicine, ultrasound waves are used for diagnostic imaging and therapeutic procedures.
Things worth knowing about "Ultrasound Wave"
An ultrasound wave is a mechanical sound wave with a frequency above the range of human hearing (above 20,000 Hz). In medicine, ultrasound waves are used for diagnostic imaging and therapeutic procedures.
What is an Ultrasound Wave?
An ultrasound wave is a mechanical pressure wave that travels through a medium at a frequency greater than 20,000 Hertz (Hz) -- beyond the upper limit of human hearing, which typically ranges from 20 Hz to 20,000 Hz. In medical applications, frequencies between 1 and 40 Megahertz (MHz) are commonly used. Ultrasound waves are longitudinal waves, meaning the particles of the medium oscillate in the same direction as the wave propagates.
Physical Principles
Ultrasound waves are generated through rapid mechanical vibrations, most commonly using the piezoelectric effect. In this process, special crystals (piezocrystals) convert electrical signals into mechanical vibrations and vice versa. The key physical properties of ultrasound waves include:
- Frequency: The number of oscillations per second, measured in Hertz (Hz) or Megahertz (MHz).
- Wavelength: Higher frequencies produce shorter wavelengths, resulting in better spatial resolution.
- Speed of sound: Depends on the medium; in human soft tissue, the speed is approximately 1,540 m/s.
- Reflection and refraction: At boundaries between tissues of different densities, ultrasound waves are reflected or refracted, forming the physical basis of imaging.
- Attenuation: Wave intensity decreases as depth of penetration increases.
Medical Applications
Diagnostic Ultrasound (Sonography)
The most well-known medical use of ultrasound waves is sonography (ultrasound imaging). A transducer emits ultrasound waves into the body. When these waves encounter boundaries between different tissues, they are reflected as echoes. The transducer detects these returning echoes, and a computer processes them into a real-time image. Common clinical applications include:
- Examination of abdominal organs (liver, kidneys, gallbladder, spleen)
- Cardiac imaging (echocardiography)
- Prenatal care and fetal assessment during pregnancy
- Vascular assessment (Doppler sonography)
- Evaluation of muscles, tendons, and joints
- Thyroid gland and lymph node assessment
Therapeutic Ultrasound
Ultrasound waves are also used for therapeutic purposes. At high intensities, they generate heat within tissue and can be applied to treat musculoskeletal conditions. A specialized technique known as High Intensity Focused Ultrasound (HIFU) directs concentrated ultrasound energy at tumor tissue to destroy it non-invasively.
Lithotripsy
In Extracorporeal Shock Wave Lithotripsy (ESWL), high-energy ultrasound waves are used to break up kidney or gallstones without the need for surgery.
Safety and Risks
Diagnostic ultrasound is considered very safe when used appropriately. Unlike X-rays or CT scans, it does not use ionizing radiation, making it suitable for use during pregnancy and in children. However, at very high intensities, ultrasound waves can cause tissue heating and cavitation (formation and collapse of microscopic gas bubbles), which is why therapeutic applications must be carefully controlled and dosed.
References
- Kremkau, F. W. - Diagnostic Ultrasound: Principles and Instruments. Elsevier Health Sciences, 9th edition, 2015.
- World Health Organization (WHO) - Manual of Diagnostic Ultrasound, Volumes 1 and 2. WHO Press, Geneva, 2011.
- Claudon, M. et al. - Guidelines and Good Clinical Practice Recommendations for Contrast Enhanced Ultrasound (CEUS) in the Liver. Ultraschall in der Medizin, 2013.
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