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Which of the following are true about MRI contrast agents? a. Chelates of gadolinium are used in MRI due to their diamagnetic properties b. The mechanism of action of gadolinium involves shortening of the T1 relaxation time c. Gadolinium-based contrast agents are eliminated mainly through renal excretiond. Iron oxide particles are used as negative-contrast agents e. Super paramagnetic iron oxide (SPIO) particles are used in contrast-enhanced angiography |
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Answer» a. False. Gadolinium ions are paramagnetic, which means that they have a large electron magnetic moment that can cause rapid T1 relaxation in nearby protons. b. True. Therefore, they cause signal enhancement in regions of gadolinium accumulation on T1-weighted sequences. c. True. Most are eliminated via the kidneys. Some agents (e.g. gadoxetic acid) are also excreted with bile. d. True. Iron oxide nanoparticles are super paramagnetic. They have been used as negative-contrast agents due to their strong susceptibility effect, which shortens T2 and T2 relaxation time of nearby protons. e. False. SPIO particles are taken up by the reticulo-endothelial system of the liver (Kupfer cells) and are used in the diagnosis of hepatic tumours. Ultra-small SPIOs (USPIOs) accumulate mainly in lymph nodes, but their small size also makes them potentially useful as blood pool agents for magnetic resonance angiography (MRA). However, they are not currently commercially available for this application. |
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