This month’s featured focused ultrasound researcher, Urvi Vyas, PhD, has made important contributions in the area of ultrasound beam propagation. Realizing that many newsletter readers may not be familiar with this process, we asked, Matthew Eames, PhD, a biomedical engineer and Senior Project Engineer for the FUS Foundation Brain Program, to provide an explanation. Here’s what he wrote:
Ultrasound beam propagation through thedifferent tissues of the body is roughly analogous to the bending of light as it passes through different materials. As an example, consider the accompanying photo of straws placed in glasses of water. You’ll quickly notice that, in the photo, the submerged portions of the straws do not line up with the portions above the waterline. This is because the speed of light in water is different from that in air, and as we look through the water’s surface, we perceive distortions in the image of submerged s. The lenses of cameras, telescopes, and reading glasses all capitalize on the difference in speed of light between air and the lens material in order to focus or magnify images.
Matthew Eames, PhD
With clinical ultrasound, the different tissues of the body – primarily muscle, fat, and bone – have different speeds of sound that bend, defocus, and distort the ultrasound beam as it propagates through the body. This can have a great impact on the formation of diagnostic images or on the delivery of therapy. The distorted ultrasound propagation caused by a layer of fat or the irregular surface of the skull is something that must be corrected for or taken into consideration in order to ensure accurate diagnosis or treatment.
Imagine standing at either end of a conference table from someone you know. It would be easy to recognize them. Now imagine something placed between you – a wall of glass block, for example – that altered the path of light. Now it is significantly harder to identify the other person. This glass block is analogous to a layer of fat or the irregular surface of the skull in the context of ultrasound and is something that must be corrected for or taken into consideration when delivering therapy or interpreting diagnostic images.