Flashcards in Clinical Cardiac MI Deck (25)
MRI and CT scanning are relatively
How does a MR scanner work?
-Very strong, superconducting magnet of 0.5-3T.
-Radio-frequency coils transmit signals into patient, and energy the body absorbs is received by surface coils.
-In a metal 'faraday' box to exclude internal RF (same as fm stations)
-A computer is then used to reconstruct the images
-ECG signal for cardiac imaging
Super conducting Magnets
Enormous tube of iron
-bathed in liquid helium
-Magnetic-field always on! only turned off when heated (dangerous)
-Large refrigeration plants required
-Emergency vent for He to boiled off
-Magnetic field strong enough to launch projectiles
-Risk to electronic implants: pacemakers/defibrillators, cochlear implants
-Metallic foreign bodies: eyes, pre-80s cerebral aneurysm clips.
Particular problems with cardiac imaging
-Small fast-moving structures
-Constant cardiac motion (gated images)
-irregular cardiac rhythms (blurry heart)
-Patients inability to co-operate
Simplest type of image to take?
If patients don't hold their breath, you get a
Take many images from different planes, and calculate volumes
green: endocardial surface
blue: epicardial surface
What happens when intima pulls away from aorta
Most people 50% die. New channel, can pull away right the way down.
Right ventricular cardiomyopathy
accumulate lipids in myocardial cells. liable sudden ventricular arrhythmias.
-Irregular crenulated ventricular lining.
Benign fibrous tumour
Delayed myocardial enhancement.
Give people contrast agents: Gd-contrast agents
-Image 10-30mins later
-how much GD depends on how much extracellular space is there, shows as white (normal should have very little!)
Used: in adult cardiology for MI and assessment of myocardial viability
Lesser Use: to assess cardiomyopathy and possible causes, degree of myocardial fibrosis, myocarditis
-can see small arteries, outline =the lumen!
How do we treat coronary artery disease?
Take arteries/veins, attach one end to aorta and the other to coronary arteries
Hold arteries open
Vein vs arterial grafts
Vein grafts clot within 5-10 years, arterial grafts much better
Balloon coronary angioplasty
-Balloon dilation of an atheromatous stenosis
-Requires extensive anticoagulant therapy (aspirin and heparin)
-High risk of acute thrombosis at the angioplasty site
-High risk of re-stenosis long-term, more scar tissue (~4-6months post procedure)
Factors that promote restenosis
-Multiple lesions treated
-diabetes increase risk by 3x
-previous history of re-stenosis
Now what is done more the ballon coronary angioplasty?
ballon with drug covered stent
-Placed to ensure continued patency at site
-Reduces re-stenosis effect and need for re-intervention
-Still risk of acute thrombosis or restenosis.
Done with large antiplatelet drug to reduce thrombus + one month oral therapy
Advantages of CT angiography
-Non-invasive, therefore cheap, and lower risk
-Images both vessel wall and lumen
-More pleasant for patient
-Visualised other thoracic pathology.
-Lower radiation and contrast load
-Non-specific so can be used for whatever
Disadvantages of CT angiography
-Need regular slow cardiac rhythm, (doesn't work with atrial fibrillation)
-Required patient co-op
-problems with heavily calcified vessels
-More difficult to interpret