Before we jump into ultrasound protocol, it is important to have a good understanding of the ultrasound fundamentals. This includes ultrasound physics, scanning planes, tissue interaction and common movements, as well as terminology.
Ultrasound transducers function by transmitting small pulses of sound energy into the body, receiving reflected sound waves, and translating their intensities into a grayscale image of anatomical structures. A reflected echo is generated when sound waves encounter a border of acoustic impedance, which is an intrinsic physical property for each body tissue.
Acoustic impedance is defined by the density of the tissue and the velocity of the ultrasound wave through the tissue. The intensity of the echo is proportional to the difference in acoustic impedance between the tissues on either side of the border and is represented in a sonogram as a grayscale value. It is worth noting that the intensity of the echo is dependent on the angle of incidence as well, which can result in unexpected visual representations.
Hypoechoic, anechoic, and hyperechoic, are comparative terms used to describe the echogenicity of structures seen in ultrasound. Hypoechoic structures are less echogenic – they produce less echoes - and will show up as darker areas in a sonogram. Hyperechoic structures are more echogenic – they produce more echoes - and will show up as brighter spots in a sonogram. Anechoic structures do not show up in a sonogram because no echo is returned. This can occur for several reasons.
Terms describing standard anatomical planes are also used when discussing ultrasound scanning planes. These include:
The indicator or orientation marker can be used to orient yourself as you move the transducer around. The orientation marker will typically be present on the left side of the ultrasound image; the image will always appear so that the orientation marker corresponds to the direction that the probe indicator is facing.
An ultrasound probe can be manipulated in many ways and different movements will be important depending on the structures you are targeting and the goal of the examination. For example:
