How Ultrasound Technology Works – Sonography 101

by admin on March 02, 2010

Before getting into the interpretation of ultrasound technology into medical history, it is very necessary to interpret and know about the meaning of what exactly Ultrasound technology means. Ultrasound is considered as a sound wave that is not audible to human ears and range as predicted between around 20 kilohertz (20, 000) in a youthful adult.

However, among the many popular and common uses and features of ultrasound, the most vibrant one is in the field of sonography, which produces images of fetuses in the human womb. There are many other variable uses of ultrasound apart from healthcare industry, however here we would discuss about Diagnostic sonography that is an ultrasound based diagnostic imaging technique employed as to have subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. Obstetric sonography is mostly used in pregnancy and is quite popular in public.

For the propose of diagnostic value and importance sonographic scanners are operated in the frequency range of 2 to 18 megahertz, hundred time more stronger to human audibility. Frequency is kept between spatial resolution of the image and imaging depth: lower frequencies produce less resolution but image deeper into the body.

Sonography is performed by professionals who are known as Sonographers. Sonogrpahers uses a hand-held probe called a transducer is placed directly on and moved over the patient. Sonography is very useful for imaging soft tissues of the body. On the surface structures such as muscles, tendons, testes, breast and the neonatal brain are imaged at a higher frequency (7-18 MHz), which give better axial and lateral resolution. Deeper structures such as liver and kidney are imaged at a lower frequency 1-6 MHz with lower axial and lateral resolution but higher penetration.

In sonography transducers send pulses of sound into a material and whenever that sound wave encounters with a different density than that certain part of the sound wave reflects back to the probe and is captured as an echo. There time taken by echo to travel back to the probe is measured and employed in calculating the depth of the tissue interface causing the echo. The greater the difference between acoustic impedances, the larger the echo is. If the pulse hits gases or solids, the density difference is so great that most of the acoustic energy is reflected and it becomes impossible to see deeper.

In medical imaging frequencies are used in the range of 1 to 18 MHz. Higher frequencies generally have a smaller wavelength, and can be used to make sonograms with smaller details. However, the shrinking of the sound wave is increased at higher frequencies, so there have a better diffusion of deeper tissues, and there lower frequency (3-5 MHz) is used.

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