Flashcards in Ultrasound Deck (21)
What are the physical properties of sound?
Sound is a mechanical, longitudinal wave that requires a medium to propagate through.
What is ultrasound?
Sound that exceeds the upper limit of human hearing (20 kHz)
What is the frequency range of medical ultrasound and how is it created?
2-16 MHz. By passing electricity (Alternating Current, AC) through piezoelectrical crystals.
How does ultrasound imaging work?
Longitudinal sound waves cause particles to vibrate back and forth, creating compressions (high pressure, peaks) and refractions (low pressure, troughs) that we analyze to create a visual.
What is the significance of the frequency range of ultrasound in terms of visual analysis?
Higher frequencies are used to image areas of the body close to the surface (shorter wavelengths, easily absorbed, not as penetrating).
Lower frequencies are used to image structures that are deeper down in the body.
*Lower frequencies = lower resolution but better penetration
What is the piezoelectrical effect?
How does the piezoelectrical crystal work?
Piezoelectrical effect: conversion of electrical energy to mechanical energy.
How piezoelectrical cyrstal works: Running AC through the crystal causes it vibrate, producing ultrasounds (piezoelectrical effect). The sounds bounce off objects being scanned, reflecting back to the crystal. The sound hitting the piezoelectrical crystal causes it to vibrate, converting mechanical energy (vibration) into electrical energy (signals visualized on the scan)
What are the four interactions of ultrasound with tissue?
What is impedance? Why is it relevant to our discussion of ultrasounds?
Impedance: tendency of a medium to conduct ultrasound.
It effects how well ultrasound is reflected off of various tissue surfaces. **The larger the difference in acoustic impedence between two objects, the greater the resulting reflection of their boundaries/demarcation.
What is the effect of degree of reflectivity on ultrasound imaging?
Highly reflective objects (hyper echoic) are displayed as white.
Poorly reflective objects (hypo echoic) are displayed as dark.
Examples of hyper echoic objects. Hypo echoic objects.
Hyper echoic objects: fascial planes, bones, some nerves.
Hypo echoic objects: muscle, fat, some nerves.
How to blood vessels appear on an ultrasound?
They are completely black since they are anechoic (no reflection).
What is the fundamental clinical challenge in using UGRA (ultrasound guided regional anesthesia)?
Many neural structures lie in close proximity to other structures that have similar acoustic impedance, making it difficult to distinguish it on the scan.
What is refraction?
The amount of 'bend' that occurs to the exiting wave as the entering wave hits an interface and crosses the object.
What is attenuation?
Loss of ultrasound wave energy as it travels through objects.
Lower frequency waves attenuate less than higher frequency wave (but are also inherently weaker so = less resolution)
What is gain in ultrasound?
It is basically contrast. We want a clear picture at the top and bottom view so adjust gain to attain this.
What color are solid organs on the ultrasound?
What color is viscous fluid on the ultrasound?
Same color as blood vessels – black (an/iso echoic)
How thick is the beam emanating from the ultrasound?
What is the ultimate goal of ultrasound?
To make like tissues look similar and unlike tissues look different.
What is the short axis approach? Why is it generally more preferable to use than the long axis approach?
It is viewing the vessels/nerves by orienting the beam to view their cross sections. Preferable because you can view the anterior-posterior and medial-lateral perspective.
Long axis visualizes the vessel longitudinally so you lose the medial-lateral perspective,