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Adv. Vas. Son.

Test 4 Vascular Applications of Contrast Agents

QuestionAnswer
Ultrasounf contrast agents in the United States are currently limited to what applications? Echocardiographic applications, In other countries contrast is used in many applications
Contrast has been shown to improve what? Eval of blood flow in both large and small vessels, Contrast specific imaging modes have also been created to enhance visualization even more
Contrast helps overcome several ultrasound limitations, such as: Contrast resolution on grey scale, Detection of low blood fow, Detection of flow in very small vessels
In order for an ultrasound contrast agent to be used, it should what? Be nontoxic, Have microbubbles that are small enough to pass through pulmonary capillary beds, Be large enough to reflect ultrasound signals, Be stable enough to provide multiple recirculation
Typical administration of contrast is? An intravenous bolus injection, Usually via upper extremity vein, Provides several mins of enhancement, Second dose may be administered if needed
IV infusion can also be used: Gives prolonged enhancement times, Useful for difficult or time-consuming evals
Vascular agents stay within the blood pool & when microbubbles rupture what happens? Their products are metabolized and the gas is exhaled, Tissue specific agents leave the blood pool & are taken up by specific tissues
To be clinically effective, Tissue specific agents must what? Have an affinity for the targeted tissues, Have the ability to alter that tissue's sonographic appearance
Tissue specific agents change the signal impedance of what? Normal or abnormal tissues, Improve the detection of abnormalities, Permit more specific diagnosis, Administered through IV, May also enhance visualization of blood flow
Of interest for vascular application-thrombus-specific agent does what? Agents attach to fibrin, platelets, or other components & enhance thrombus detection
Microbubble contrast agents can be used with: Conventional grey scale, and Spectral Doppler- Will enhance detection of blood flow, Utility of contrast agents is improved
Harmonic imaging: US system receives @ a freq twice the transmit freq(2nd harmonic)
Microbubbles oscillate in the US energy field: Reflected echoes form oscillating microbubbles contain harmonic energy, Makes system better at visualizing blood flow on B-mode
Low mechanical index imaging & intermittent imaging: Low acoustic output is needed w/ use of contrast-Minimizes destruction of microbubbles, Intermittent imaging reduces exposure to acoustic energy & allows additional microbubbles to enter field between pulses-additional MB allow greater reflectivity
"Flash echo" modes allow what? Brief increases in output power in order to rapid destroy microbubbles
Limitations in the periphery that contrast can help with: Poor visualization of deeply located or small vessels, Low velocity flow, Low volume blood flow
Peripheral arterial applications: Contrast agents can be used to assist in visualization in situations where atherosclerosis plaquing causes signal attenuation, Stenosis can be differentiated from occlusion
Agents can be used as a "rescue tool" to? Turn a non-diagnostic exam into a diagnostic exam, Also used for calf muscle perfusion & degree of arterial collateralization
Peripheral Venous applications: Although compression sonography has been proven effective for evaluating DVT, there are some limitations, Contrast agents can be used to ↑ the diagnostic accuracy in identifying thrombis-Calf & Iliac Vs seemed to have greatest benefit
Cerebrovascular Applications: Contrast agents can be used both intra- & extracranially, Permits direct assessments of functional lumen & plaque morphology, Has potential to reduce need for additional, more pricey diagnostic imaging studies
Extracranial applications: Contrast enhances Doppler signals & improves visualization of blood flow- Results in improved delineation of residual lumen, Can be used to differentiate tight sten from occlusion. Use of 3D image w/contrast may be even more useful
Intracranial applications: Vasculature assessment is limited by insufficient acoustic windows, Low Vel flow, & signal atten.
Contrast agents can overcome these problems: Improves ability to eval intracranial flow, Leads to higher # of diagnostic exams
Indications include: Assesing PTs w/ arterial occlusions/sten, Venous thrombosis, Detecting blood flow in brain tumors, Intraoperative localization of vessels in arteriovenous malformations
What is one cerebrovascular application? Eval of carotid artery vaso vasorum & plaque neovascularity, May prove to be useful to identify vulnerable plaques & determine risk of cardiovascular events
Atherosclerotic plaque may be more like a what? Tumor- requires a nutrient ricj blood supply
Plaque neovascularization comes from what? Arterial wall vaso vasorum- changes occur before obvious plaque develop & luminal narrowing (these changes can be identified using contrast)
Contrast agents can improve visualization of: Ao & branches, Vs of the systemic, Vs of the portal venous system, Blood flow in abdominal organs, Has improved use of sonography for evaluating organ perfusion & tumor characterizations
Hepatic applications: Enhanced detection & characterization of hepatic masses, Improved detection of intra-& extrahepatic blood flow (Both in normal subjects & those w/ portal HTN) Can be used to assess flow through TIPS
What does TIPS stand for? Transjugular intrahepatic portosystemic shunt
Renal artery stenosis: Eval of main renal & intrarenal vessels limited by- Depth of vessels, Overlying bowel & PT obesity, Limited sonographic windows or adequate Doppler angles, Anatomical variants (duplicate or accessory renal arteries)
Contrast agents improve signal intensity for what? Doppler flow- Useful in exams where renal arteries are not well visualized or the Spectral WFs are of poor quality- More diagnostic exams &/or reduced exam times
Aortic graft & stent surveillance: Stent grafts require surveillance for the detection of endoleaks (CT angiography typically used-in some individuals CT contrast is contraindicated & repeated CTs cause high levels of radiation exposure)
Why is contrast sonography a viable alternative? Ability to assess blood flow in real time using CES improves detection & characterization of endoleaks
Contrast sonography can be used to asses: Flow in mesenteric As for mesenteric ischemia, Ao & Iliac As for evaluation of aneurysms, stenoses, or dissections, IVC to evaluate filters or thromboses
Created by: EmilyGriffin