Ultrasound is a form of non-ionizing radiation that uses high-frequency sound waves to image the body. It is a real-time investigation that allows clinicians to visualize internal organs and tissues without the use of invasive procedures. Understanding the physics of ultrasound is critical to applying clinical ultrasound, particularly as it applies to the optimization, interpretation, and clinical integration of images captured at the bedside. Here are some key physics principles related to ultrasound:

• Sound Waves: Ultrasound refers to any sound waves with frequencies greater than 20kHz. Sound is a series of pressure waves propagating through a medium. One cycle of the acoustic wave is composed of a complete positive and negative pressure change. The wavelength is the distance traveled during one cycle. The frequency of the wave is measured in cycles per second or Hertz (cycles/s, Hz) .

• Pulse-Echo Principle: The production and interpretation of ultrasound waves are based on the so-called ‘pulse-echo-principle’ . The source of the ultrasound wave is the piezoelectric crystal, which is housed in the transducer. These crystals have the ability to transform an electrical current into mechanical pressure waves (ultrasound waves) and vice versa. Once the ultrasound wave is generated and travels through the medium, the crystal switches from ‘sending’ into ‘listening’ mode and awaits returning ultrasound echoes. Transducers spend over 99% of the time “listening” for returning waves. This cycle is repeated several million times per second. Returning sound waves are converted into images on the ultrasound monitor.

• Ultrasound Interactions with Tissues: As the ultrasound wave travels through tissues, it is subject to a number of interactions. The most important features are reflection, refraction, and attenuation. Ultrasound waves travel into tissue and are reflected back to the probe at a rate determined by the target tissues consistency. Reflections of the ultrasound waves are used to create images of the internal structures of the body.

• Primary Ultrasound Physics Principles: The crucial physics principles needed to understand and optimize clinical ultrasound include frequency, propagation speed, pulsed ultrasound, waves’ interaction with tissue, angle of incid...