Basic Physics

Ultrasound, or high frequency sound waves, serves as the basis for visualizing umbilical venous catheters through the liver parenchyma.

Ultrasounds are sound waves inaudible to human hearing. Human hearing 20-20,000 Hz. Anything above 20,000Hz = ‘ULTRA’ sound.

We are using 4-12 ‘mega’ hz (mHz). Mega = million, therefore using 4-12 million hz to visualize our images.

Ultrasound waves pass through tissues of varying densities and a portion of energy will reflect back to the transducer, whilst the rest carries on. The time delay and intensity provides information about the tissues composition and spacial relationship.

As densities increase, so does the speed at which ultrasound propagates through. This is helpful when calculating the distance/depth of an object from the transducer

Distance = speed x time

The crystals within the transducer (probe) detect the returning echos and there is a conversion of mechanical energy into electrical signals that facilitates the creation of ultrasound images.

A note about Air. Air is a poor medium for ultrasound waves as they do not transmit efficiently. They are partially reflected back and these can cause unwanted lines, shadows, distortions that can interfere with interpretation of the scan. The presence of air can significant degrade the quality of an image (think extremely preterm lungs with poor echo images) and hinder the accuracy of diagnostic information.