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
Name another reason flash can be useful to use, other than to destroy the microbubbles?
For reducing contrast to the near background level before a re-injection of a contrast agent
(ex. for the re-evaluation of a lesion whose fill in dynamics were missed initially)
List 5 reasons contrast agents are used for in u/s?
-LV opacification + endocardial border detection in echocardiography
-Lesion detection when its echogenicity is similar to the surrounding tissue
-Lesion characterization by showing both the arterial + portal phases of the agent in real time
-Doppler u/s detection when doppler signals are weak (deep, slow + small vessel flows)
-Small bowel imaging (Crohn’s disease)
List 4 u/s contrast agent brands?
-Definity/Optison (m/c used in Island Health)
-Sonovue
-Sonazoid (targeted by liver)
-Luminity
How many benefits are there for using u/s contrast agents?
7
Does u/s imaging allow real time evaluation of blood flow?
Yes!
(benefit of using u/s contrast agents)
The destruction of microbubbles by u/s in the image plane allows for what?
Absolute quantification of tissue perfusion
(benefit of using u/s contrast agents)
Is ultrasonic molecular imaging safer than molecular imaging modalities (such as radionuclide imaging)?
Yes! B/c does not involve radiation
(benefit of using u/s contrast agents)
Are alternative molecular imaging modalities (such as MRI, PET + SPECT) more or less costly compared to u/s?
They are very costly compared to u/s. U/s is very cost efficient + widely available.
(benefit of using u/s contrast agents)
Since microbubbles can generate such strong signals, a lower or higher intravenous dosage is needed?
Lower - micrograms of microbubbles are needed compared to milligrams for other molecular imaging modalities, such as MRI contrast agents
(benefit of using u/s contrast agents)
Targeting strategies for microbubbles are what?
Versatile + modular
(benefit of using u/s contrast agents)
How many disadvantages are there when using u/s contrast agents?
4
Do microbubbles last very long in circulation? Why or why not?
No - b/c they have low circulation residence times since they either get taken up by immune system cells or by either the liver or spleen, even when they are coated with PEG
(disadvantage of using u/s contrast agents)
Does u/s produce more or less heat as the frequency increases?
More - the ultrasonic frequency must be carefully monitored
(disadvantage of using u/s contrast agents)
Are contrast reactions possible?
Yes!
(disadvantage of using u/s contrast agents)
Do microbubbes burst at low or high u/s frequencies + mechanical indices (MI)?
-Low u/s frequencies
-High MI
(this is the measure of the negative acoustic pressure of the u/s imaging system)
Does increasing or decreasing MI cause an increase in image quality?
Increasing MI causes better image quality
(but there are tradeoffs with microbubble destruction)
Microbubble destruction could cause what 2 things to the local microvasculature?
Ruptures + hemolysis
(disadvantage of using u/s contrast agents)
List common side effects of definity (u/s contrast)?
-Headache + dizziness
-Flushing (warmth, redness, tingly feeling)
-Nausea
-Chest pain
-Pain in side or lower back
-Pain, swelling or irritation where injection was given
List serious side effects of definity (u/s contrast)?
-Light headed feeling, like you might pass out
-Severe dizziness or cold sweat
-Chest pain, wheezing, trouble breathing
-Fast or slow heartbeats
-Severe headache, blurred vision, pounding in neck or ears, anxiety, confusion
-Slow HR, weak pulse, fainting, weak or shallow breathing
How should we treat serious side effects of definity?
As an anaphylactic shock
Microbubbles are targeted with what?
Ligands
What do targeting ligands do?
They bind certain molecular markers that are expressed by the area of imaging interest, such as inflamed cells or cancer cells
What can u/s contrast targeting agents, such as ligands, be used for?
Used to image a certain area of the body specifically by allowing the microbubbbles to accumulate there
Can ligands be used to deliver drugs?
Yes, can deliver a drug to a target area
Are targeted agents, such as ligands, fully clinically developed?
No, still under pre-clinical development
