Ch 7a Contrast Agents Flashcards
What is a contrast agent?
A substance introduced to the body that allows the area of interest to stand out from other regions
What type of contrast agent is used in fluoro/xray?
Barium
What type of contrast agent is used in CT?
Iodinated contrast
What type of contrast agent is used in MRI?
Gadolinium
What type of contrast agent is used in u/s?
Microbubbles
Do we use contrast agents often in u/s?
No, m/c used in cardiac
How are u/s contrast agents administered to the pt?
They are injectable
What do u/s contrast agents consist of?
A solution containing gas filled microbubbles 1-4 microns in size
What do microbubbles consist of?
A shell + a gas core
Microbubble shells can be composed of what 4 things?
Albumin, galactose, lipid or polymers
Gas cores can be composed of what 3 things?
Air, nitrogen or heavy gases (such as perfluorocarbon)
Contrast agents are injected into what part of the body? It passes through which circulatory system?
-A peripheral vein
-Passes through systemic circulation
The u/s microbubbles are taken up by the immune system + what other organs over time (6-8 min)?
The liver + spleen
As the microbubbles pass through the u/s window, they act as strong or weak reflectors?
Strong (relative to the blood + tissue)
What type of echoes are produced when the microbubbles pass through the u/s window?
Harmonic echoes are produced as they expand + contract
The harmonic frequencies that get produced as the microbubbles pass through the u/s window produce what?
Produce contrast harmonic imaging
What is the mechanical index (MI) of u/s contrast agents?
0.1 - 0.2 MI
What can lengthen the duration of the u/s contrast effect?
Encapsulation of the gas will slow its diffusion back into the solution, therefore lengthening the duration
What is flash mode of an u/s contrast agent?
It is a short u/s pulse with a very high MI, resulting in almost complete destruction of the contrast agent microbubbles in the imaging plane
Flash mode is a technique specific to what u/s devices?
CEUS capable u/s devices
When flash mode is triggered by the user, what happens?
The probe emits a short u/s pulse with a very high MI
(typically at least a magnitude greater than that of the CEUS preset itself)
By using flash mode, microbubbles that previously were accumulated within the area of interest can now be what?
Annihilated (destroyed)
Is the sudden loss of microbubbles when using flash mode an advantage or disadvantage?
Advantage
(ex. to evaluate the portal venous phase refilling dynamics of a liver lesion, which was previously already filled in completely during the early arterial phase)
Describe what the u/s image looks like during pre-flash, flash + post-flash?
Pre-flash: some orange seen
Flash: really bright orange
Post-flash: dark image with no orange seen