Abdominal Applications of US Contrast Agents

Question 1

What has the clinical use on contrast-enhanced sonography (CES) been shown to do?

Answer 1

-been shown to reduce or eliminate some current limitations of US imaging and Doppler blood flow detection

Question 2

What has most work been centered on since the 1980s?

Answer 2

-developing agents that can be administered intravenously to evaluate blood vessels, blood flow, tumors and solid organs

Question 3

What are limitations of CES?

Answer 3

• spatial and contrast resolution on grayscale

- detection of low-velocity blood flow and flow in very small vessels using Doppler flow detection modes

Question 4

What are the types of US contrast agents?

Answer 4

• vascular US contrast agents

- tissue-specific US contrast agents

Question 5

What are vascular US contrast agents (UCAs)?

Answer 5

• enhance Doppler (color and spectral ) flow signals by adding more and better acoustic scatterers to the blood stream
• improve detection of blood flow from vessels often difficult to assess such as renal arteries, intracranial vessels, small capillaries within organs (i.e. tissue perfusion)
• improve gray-scale US visualization of flowing blood and demonstrate changes to grayscale echogenicity of tissues with use of contrast-specific imaging software such as harmonic imaging (HI)

Question 6

What qualifications do clinically useful UCA must meet?

Answer 6

• be non-toxic
• have microbubbles or microparticles small enough to traverse pulmonary capillary beds (i.e., less than 8 microns)
• be stable enough to provide multiple recirculations

Question 7

Which are FDA-approved for use in echocardiographic applications?

Answer 7

• Definity
• Optison
• Imagent

Question 8

What are tissue-specific UCA’s?

Answer 8

• microbubbles of agents removed from the blood pool and taken up by (or have affinity toward) specific tissues such as reticuloendothelial system (RES) in the liver and spleen or thrombus
• over time, the presence of contrast microbubble within or attached to tissue changes its sonographic appearance
• by changing the signal impedance of normal and abnormal tissues, agents improve detectability of abnormalities

Question 9

*How are tissue-specific UCAs typically administered?

Answer 9

*intravenous (IV) injection

Question 10

What is Sonazoid?

Answer 10

• tissue-specific UCA currently approved for use in Japan
• after being IV injected, it behaves as a vascular agent (i.e. enhances the detection of flowing blood)
• over time, microbubbles are phagocytosed by RES (macrophage Kupffer cells) of the liver and spleen
• intact microbubbles may remain stationary in tissue for several hours
• when insonated after uptake, stationary contrast microbubbles increase reflectivity of contrast-containing tissue

Question 11

What are oral UCAs?

Answer 11

• SonoRx contains simethicone-coated cellulose as the active ingredient
• ingestion of SonoRx results in homogeneous transmission of sound through contrast-filled stomach

Question 12

How does UCAs improve accuracy of hepatic sonography?

Answer 12

• enhanced detection and characterization of hepatic masses
• improved detection of intra and extrahepatic blood flow
• possible to distinguish various phases of blood flow to and within liver

Question 13

What usually happens in normal situations after IV administration of UCA into liver?

Answer 13

• contrast enhanced flow in hepatic artery identified first (arterial or early vascular phase), followed by enhanced portal venous flow (portal venous phase)
• detection of flow in hepatic capillaries identified later (late vascular phase) as parenchymal blush

Question 14

What is sonography limited in when it comes to the liver?

Answer 14

limited in ability to detect small (<10mm), isoechoic, and/or peripherally located lesions, particularly in obese patients or patients with diffuse liver

Question 15

What is sonography usually sensitive for when it comes to the liver?

Answer 15

detection of medium-to-large hepatic lesions