Emergency Medicine Bite-Sized Basics
- Thallium acts as K+ analogue.
- Taken up by myocardial cells and reveals myocardial perfusion.
- Can do stress testing with exercise or dipyridamole.
- “Cold” spots show areas of ischaemia, if irreversible infact
- Higher radiation dose than sestamibi scan.
99mTc (Technetium) sestamibi
- 99mTc decay (isomeric transition to 99Tc) detected using a gamma camera for single photon emission computed tomography (SPECT)
- Acute imaging (while patient having chest pain) highly sensitive for sig. IHD.
- Imaging performed 60-90min post-radioisotope injection.
- Scanning can be performed up to 5hr after injection.
- Images acquired at rest and after stressing (exercise or pharmacologically).
- Scans compared to find ischaemic/infracted areas and & wall motion abnormalities
- 99mTc sestamibi has T½ of 6hrs so may need rpt dosages.
- Longer T½ than sestamibi so only 1 injection needed.
- Early (1st 7d) diagnosis of AMI
- Necrotic tissue takes up radioisotope and forms a “hot” spot.
99mTc labeled RBC
- Gated cardiac blood pool scan
- Looks at ejection fraction, wall motion, regurgitation fraction
- Used prognostically in AMI, pre-chemo, or for SOB investigation.
Other Tc Scans
- V/Q scan
- Labelled RBC scans for GIT bleeding
- Bone scans – detects 95% #s at 72hr, also detects Ca, mets, arthritis, infection & avascular necrosis
- DTPA, DMSA & MAG3 renal scans
- Shows areas of acute infection/inflammation
- Binds lactoferrin & transferrin
- Shows areas of chronic infection/inflammation, PCP in immunosuppressed.
Positron Emission Tonmography (PET)
- Positrons (e+) from 11C, 15O, 13N, 18F collide with an e- 2 x gamma rays as particles annihilated.
- Uses: Localisation of epileptic foci, myocardial function, brain area activity (glucose utilization)
- Can be used to measure: local blood flow, metabolic activity, drug movement, neurotransmitter receptors, enzymes