Contrast agents
CT
· Iodine used iv
· Z= 53
· K edge 33 keV-attenuation high
· Photo electric absorption greater than in tissue or bone due to high atomic number of I
· Can get renal failure and allergic reactions
US
· encapsulated micro bubbles
· used in perfusion and vascular imaging
· Large diff in acoustic impedance between bubbles and fluids /tissue
· Small bubbles =point source =they are smaller than wave =reflections in all directions
· Bubbles compressible -produces shifts in returning frequencies (harmonics)
· Reflections of bubbles travel only 1/2 the distance the US beam has to travel
MRI
· Gadolinium DTPA
· paramagnetic contrast agent
· reduces T1 significantly -- strong signal -- and T2 slightly -- weak signal
· Can get nephrogenic systemic fibrosis
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