Today, our Quick Concepts discussion turns to understanding Density. As with so many aspects of physical science, the superficial definition does not do justice to its full value in everyday clinical application.
Most everyone ‘gets’ the raw concept. If you have ever been roped into helping a friend move, you quickly learn to avoid the boxes full of books and magazines, while searching out those packed with pillows and cushions.
However, in ultrasound imaging, you don’t have the luxury to pick and choose between ‘easy’ and ‘difficult’ scanning situations. As such, you should realize how the variations in density affect ultrasound transmission and reflection.
Because density affects propagation velocity, which I will discuss in the next installment of Quick Concepts (November 5th), many artifactual errors arise from the variable speeds produced as sound passes through distinct mediums. Acoustic impedance, and the mechanics of tissue harmonics are also based on understanding that sound ‘behaves’ differently as it moves across layers and barriers. Those subjects and more will be discussed as we continue this series.
Additionally, the fact that diseased tissue often presents as an inconsistent density relative to surrounding tissue is a huge advantage in early detection of suspicious masses. The application of elastography imaging and the practice of breast self-examination are based on this fact. It seems fitting to point this out since October is Breast Cancer Awareness Month.
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This subject matter is discussed more thoroughly in Frank Miele’s Ultrasound Physics and Instrumentation .
