Slide 1: Ultrasound basics. Transducers. Transducers are the probe placed on the patient that generate and receive the sound waves. Frequency is the property of sound wave generated. Depth is how far the image extends. Resolution is the degree of detail visible. Image shape is what’s displayed on the screen. In a linear probe, the frequency is high, the depth is shallow, the resolution in high, the image shape is rectangular. Linear probe is best for blood vessels, pleura, and musculoskeletal. In a phased array probe, frequency is medium, depth is moderate, resolution is moderate, image shape is fan-shaped. Phased array probe is best for cardiac and abdominal structures. In a convex probe, the frequency is low, the depth is large, the resolution is moderate, the image shape is fan-shaped. Convex probe is best for abdominal structures.
Probe positioning. Moving the probe for a good image. Probe positioning options include rock, fan, rotate, slide, sweep and compress.
Modes. Modes are how the ultrasound machine creates an image using sound waves. B mode is brightness mode. The standard 2D imaging technique, used for most POCUS exams. M mode is mono-dimensional or motion mode. Represents a single plane (vertically) with respect to time (horizontally). Doppler modes are used to identify and measure movement (e.g. blood flow). Color doppler mode. Color is overlaid on a selected area of the ultrasound image representing the direction of movement as red/blue. CW doppler or Continuous wave doppler mode. Measures movement on one line within the image continuously over time. PW doppler or Pulse wave doppler mode. Measures movement within a defined area of the image in short bursts over time. Spectral or tri-mode doppler combines B mode, color doppler, and either CW or PW doppler, often used for complex measurements.
Settings. Exam type optimizes settings for a particular exam (e.g. heart, veins, abdomen, etc). Depth is how far into the tissue the ultrasound is imaging. Gain is signal amplification applied to the sound signal. Adjusting gain makes the entire image lighter or darker. Time gain compensation adjusts the brightness at different depths (e.g. near or far parts of the image). Focus defines the area of the image where the image is optimized. Distance calipers allow measurement of different areas within the ultrasound image. Calculations turns measurements into physiologic parameters.
Six tips to getting a better image.
One. Use plenty of gel. Sound waves bounce off of air/fluid interfaces. If there is air between the probe and the patient you cannot form an image. Pro-tip: warm up the gel before the exam.
Two. Rest your hand on the patient. The more stable you hold the probe the more stable the image will be. Grasp the probe with the thumb and first two fingers and place your hypothenar eminence against the patient.
Three. Optimize patient positioning. Many exams, such as cardiac or gallbladder, benefit from lateral decubitus positioning. Ask the patient to roll, use pillows to prop them up comfortably for the exam.
Four. Optimize settings. Start with the maximum depth, gain turned up. Once you acquire the imaging you can decrease to fine tune.
Five. Be patient. It can take a while to find the perfect positioning.
Six. Be respectful. Preserve patient modesty during the exam if possible. Wipe away excess gel when finished.
Tags: POCUS, ultrasound, ultrasound basics