by Barnaby Meins

Created on: January 04, 2009   Last Updated: November 11, 2010

Many parents have the first sight of their baby in the womb through the use of ultrasound. It can be very exiting for the parents to get the first picture of the baby in this manner. Well, technology has advanced such that the idea of seeing through human tissue has become a reality. Ultrasound imaging was first discovered in 1952 and used clinically in 1962. How the baby's first picture is produced by ultrasound is described briefly as follow.

Ultrasound is basically high-frequency, non-ionizing sound waves. It is in the typical frequency of 1 to 10 MHz above the range of sound audible to humans and can be used to produce images of structures within the human body, such as through the womb to get the baby's first picture.

Essentially, ultrasound is first projected into the womb and echoes from disparities in tissue density or the speed of sound are detected by the ultrasound sensor. The key assumption is that sound waves have an almost constant velocity of 1540 m/s in water and soft tissue. Size of reflected pulse detected gives acoustic impedance & brightness. The transducer is made of piezoelectric crystal which creates sound waves aimed at a specific area of the body. Differences in tissue density reflect the sound waves and the echoes are recorded. Delay of reflected signal and amplitude determines the position of the tissue. The imaging volume is usually about 20 cm and its resolution is high in the millimeter range.

Widely used in the medical fields of obstetrics and gynecology, such as in fetal health, ultrasound has proven to be a viable imaging technique. However, ultrasound does not travel well through air or bone and it is not effective at imaging the areas of the body that have gas in them, or that are hidden by bones.

Concerns from getting the first picture of the baby by ultrasound are usually the safety and effects of ultrasound. However, studies have shown that there is no direct correlation has been found between ultrasound imaging and low birth weight, dyslexia or delayed speech development or cancer.

Nonetheless, first picture of the baby is usually not extremely accurate due to the presence of artifacts. The presence of artifacts reflects the fact that the appearance of the image is not a direct result of the intrinsic properties of the tissue. Artifacts are classified as speckles, reverberations, enhancement and shadowing.

Speckles are due to the ultrasound transducer detecting the ultrasound waves scattered from many different structures.

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