MRI contrast agents Flashcards
what is a contrast agent and why do we need them
alters image contrast
- aids in visualisation and diagnosis
what is întra-articular administration
a type of shot that’s placed directly into a joint to relieve pain.
- can be cortecosteroids or pain relief
what is the main contrast agent used in MRI
gadolinium
what is the general theory behind MRI
- abundance of water in our body is used to produce MRI images
what are the 3 types of MRI contrast agents
- extracellular fluid
- blood pool
- tumour specific
what is extracellular fluid contrast
- distributed in intravascular compartment initially
- rapidly diffuses through extravascular space
what is blood pooling contrast / intravascular contrast
- intravascular contrast agent that lasts in the blood for up to an hour rather than leaving the system in a few mins like others
- differentiated from other contrast agents due to their high molecular weight and higher relativities
what is a tumour specific contrast agent
pharmaceuticals targeted to tumoura
what type of magnetisation do majority contrast agents have?
paramagnetic ion complexes (with applied magnetic field, they are partially / weakly aligned)
most contrast agents in MRI contain a lanthanide element such as Gd3+, how does this affect the T1/2 relaxation time and what happens to the image
- these elements shorten the T1/2 relaxation time
- causing increased signal intensity on T1 weighted images OR reduced signal intensity on T2 weighted images
why are most contrast elements positive agents
- postive agents shorten T1, so enhanced parts appear bright on T1 weighted images
ferromagnetic agents and super paramagnetic agents are negative contrast agents/ how does this show on T2 weighted images
- as they are negative contrast agents, the enhanced parts appear darker on T2 weighted images
reminder :
paramagnetic = weak attraction
ferromagnetic = strongly attracted
diamagnetic = weakly repelled
what is gadolinium (what type of agent is it
- paramagnetic agent
- has large magnetic moment
MRI contrast agents
- increase T1 singnals by rapidly returning protons to their baseline
- allowing quicker regrowth of longitudinal magnetisation
- which produces a brighter t1 signal
(commonly gadolinium used)
why is gadolinium good for being used as contrast
- it is paramagnetic at body temperature
what is an isotonic solution
- isotonic solution is at the same concentration as the solution to which is it being compared to
how does osmolarity affect torleration
the more isotonic a contrast agent is, the better it is tolerated
osmolarity is directly responsible for sensations of heat