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Adv. Vas. Son.
Test 4 Vascular Applications of Contrast Agents
| Question | Answer |
|---|---|
| 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
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