Ultrasound is a procedure as common as X-ray and those who have undergone this procedure know well that application of gel is a part of it. The gel is mostly water which is a medium of contact between the ultrasound probe and the body. The primary purpose of the gel is to relay the acoustic energy from the transducer to the tissue without passing through air at any point of time. The reason it is so important is that both refraction and reflection are reduced while it crosses an air interface. Before you jump on to the concept of refraction and reflection, you must learn about acoustic impedance.
Acoustic impedance can be described as the amount of resistance that the Ultrasound beam encounters when it travels through molecules of the human body tissues. Anything with high level of acoustic impedance, like bones, have higher resistance to the beam passing through as compared to the material that has lower impedance like air or water. The acoustic impedance depends on the density of the tissue, its composition and the pace at which the ultrasound waves travel through it. Thus, it is safe to say that the impedance is a product of acoustic wave velocity and material density. When the ultrasound beam strikes an acoustic boundary, which is a point where two different interfaces with different acoustic impedance values are in touch with each other, like soft tissue and water, most of the acoustic energy passes through the tissue while some part of it gets reflected and some of it is refracted. When it gets reflected from the boundary the angle of reflection is same as the angle of incidence. The refraction angle, on the other hand, is different from the angle of incidence. Refraction is a change in direction and is best demonstrated by the example of a pencil in a glass of water.
The energy that is reflected from the interface is known as the echo and it is received by the transducer in order to build the image. The pulse-echo principle is the core principle of Ultrasound imaging. The strength of the echo mainly depends on the difference between the acoustic impedance values of the objects that it interacts with. The energy reflected from the air interface is approximately 500 times weaker than that of water. This means that the efficiency of any diagnostic imaging technique is enhanced up to five hundred times when using gel. This shows how massive the difference is and how much of a significant role the gel plays in the Ultrasound scanning.
So, next time you visit a radiology clinic in Auckland for an ultrasound scan you would know why gel is being used. For same day appointments and free ACC Ultrasound procedures visit EastMed Radiology. They offer a full range of Ultrasound examinations including General, Musculoskeletal and Pregnancy scans.
And they use a special warmer to warm gel up, so you do not feel cold during the ultrasound examination! For more information or to book an appointment online, please visit their official web site www.eastmedradiology.co.nz.