Ultrasound physics, artifacts and knobs

Point-of-care ultrasonography (POCUS) is defined as ultrasonography brought to the patient's bedside and performed by the clinician in real time. 

US penetrates well through fluid and solid organs (e.g., liver, spleen); it does not penetrate well through bone or air, limiting its usefulness in the skull and areas of the abdomen where bowel gas obscures the image. 

Fluid (e.g, blood, urine, ascites, pleural effusion) is completely anechoic and appears black. This makes US particularly useful for detecting fluid in areas where it's not supposed to be and for differentiating cystic or vascular areas from solid structures. 

A brief history of the evolution of transducers:

Early transducers (i.e. probes) used a single crystal to create a one-dimensional image known as A-mode. The standard images that machines now generate is known as B-mode (also called two-dimensional (2D) or gray-scale ultrasonography) and is created by an array of crystals across the face of the transducer.  

These “crystals” (made out of quartz or other piezoelectric material) generate sound waves when an electric current is applied and is what conventional transducers still use.  Some newer transducers are using "ultrasound-on-chip" technologies that allow for more portability and can emulate different transducer types in a single probe (i.e linear and phased array). 

The principle remains the same as the probes are able to transmit and receive sound. When the sound wave returns, the material in turn generates a current that is then converted to an image. 

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