A MRI contrast used for imaging liver is:
Correct Answer: Gadoxetate
Description: Ans: (b) GadoxetateRef: J Magn Resort Imaging, 2012 Nov; 36(5):1060-71 5.Hepatobiliary MRI contrast agents are specialised agents used to aid diagnosis in MRI.They are separated into three categories: gadolinium-based agents, manganese-based agents and superparamagnetic iron oxide particles.Gadolinium-based AgentsHepatobiliary specific gadolinium agents include two of the high relaxivity agents: gadobenate disodium (Gd-BOPTA) and gadoxetate disodium (Gd-EOB-DTPA)Gadoxetate disodium (Gd-EOB-DTPA): has almost equal biliary and renal excretion ( 50% each). Compared to gadobenate, it has more intense liver parenchymal enhancement.Manganese-based AgentsMangafodipir trisodium (Mn-DPDP) is specifically taken up by hepatocytes due to its chemical similarity to Vitamin B6. This property results in the increase in signal intensity of normal hepatic parenchyma, giving high lesion-liver contrast.Unlike the gadolinium agents, mangafodipir trisodium readily dissociates to yield free manganese ions. This in vivo instability of the chelate rose concerns about potential toxicity.Free manganese, in chronic exposure, causes a parkinsonism-like syndrome due to accumulation in the brain, other neurological features and cardiac suppression.Hence, mangafodipir trisodium was effectively withdrawn from the market.Superparamagnetic Iron Oxide ParticlesSuperparamagnetic iron oxide particles do not leak into the interstitium. They, therefore, act as intravascular contrast agents or blood pool agents as long as the vessel endothelium is intact and unaltered by any pathological process. Their elimination from the blood is by uptake into the reticuloendothelial system cells in liver, spleen, bone marrow and lymph nodes and are phagocytosed by macrophages throughout the body.The superparamagnetic iron oxide particles agents are preferentially entrapped by the Kupffer cells in the liver and spleen and reduce their T2 relaxation time. Thus, normal liver appears dark on T2 weighted images. Most liver tumours which are usually deficient in Kupffer cells, do not exhibit superparamagnetic iron oxide particles agent uptake and appear relatively hyperintense.
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