What is Ultrasound?

Ultrasound uses high-frequency sound waves (>20 kHz) to create images based on how those waves reflect off different tissues. The amount of reflection back to the probe determines how structures appear on the screen:

Fluid appears black (anechoic) because it reflects very little sound.
Solid organs appear gray due to moderate reflection.
Bone appears white due to strong reflection.

Sound travels best through fluid, moderately through soft tissue, and poorly through air or bone. That's why gel is used—to remove air between the probe and skin, reducing scatter and improving image quality. As sound waves move through tissue, they lose energy (a process called attenuation), which can affect how deep structures appear.

Knobs

Depth: This adjusts how deep returning echoes are received. Depth markers (dots or lines) on the right side of the screen correspond to depth in centimeters.

Gain: This controls image brightness by adjusting the wave amplitude (affecting the power).

Under-gained: Image appears too dark.
Over-gained: Image appears too bright.
Time Gain Compensation (TGC): Adjusts gain at specific depths (e.g., darkens near field, brightens far field).

Freeze: This pauses the live image to allow for detailed viewing and stores ~10 seconds of data.

Image Capture: This saves still images or video clips of your scan.

Calipers (measure): This allows for measurement of distances between structures of interest.

Common Ultrasound Transducers (Probes)

Linear Probe (5-15 MHz)

Higher frequency results in less penetration but better resolution/clarity of images
Good for superficial structures, such as skin, soft tissue, blood vessels, DVT; procedures (e.g., central lines, peripheral IV)

Curvilinear Probe (Low, 2-5 MHz)

Lower frequency allows for increased penetration
Good for deeper structures such as lung B lines, abdomen, pelvis, IVC, eFAST exam

Phased Array (Cardiac) Probe (Low, 1-5 MHz)

Good for cardiac views, lungs, thoracic aorta, IVC, abdomen