Brain Perfusion Imaging Flashcards
What is the role of nuclear medicine in CNS imaging?
-Dementia characterization
-Parkinsonian syndromes
-Epilepsy seizure foci localization (pre-surgery)
-Brain tumour recurrence
-Brain death
-Vascular assessment
-CSF evaluation
What are the ideal properties of a RP used in CNS imaging?
-Readily passes the blood brain barrier (high first-pass extraction)
-Localization proportional to rCBF (allows for delayed imaging which reflects perfusion at the time)
-Desirable 140 keV photons
- 99m Tc-ECD & 99m Tc-HMPAO
What are the properties of 99m Tc-ECD?
-Stable for 6 hours post reconstitution
-Neutral & lipophilic, crosses the cell membrane of neurons and undergoes enzymatic de-esterification (polar metabolites get trapped)
-Enzymatic
When to image after injecting
ECD?
-Image up to three hours later
- 30-60 min wait between injection and images creates ideal image
- 20 min wait images are still interpretible
What are the properties of 99m Tc- HMPAO?
-Stable 30 min to 4 hrs post reconstitution
-Neutral, lipophilic: once tracer crosses cell membrane, is transformed to hydrophilic and trapped in membrane
-Gluthione- mediated
- Appx 5% of the activity injected goes to brain with no significant late distribution
-40% GU and 15% GI excretion
When to image HMPAO?
- Image 20 mins to 2 hours post-injection
-90 min delay is best
-40 min delay is interpretable
Advantages of ECD?
- More stable
+ less restrictive production requirements
+ Longer shelf life - Less background activity
+ Rapid blood clearance
+ Better images
+ Earlier imaging
Advantages of HMPAO?
- Better uptake in medial temporal lobes, ideal for diagnosis of Alzheimer’s disease
- Greater uptake at high perfusion rates
+ demonstrates luxury perfusion - Higher first pass extraction
What are 3 precautions and considerations of brain perfusion imaging?
- Dementia patients must be monitored closely
- Patients with neurologic deficits may require more care and procedure modification and monitoring
- Sedation should be administered after RP injection if possible
Patient Prep?
- No prep
+ Ideal to avoid agents increasing brain bloodflow - Before injection
+ Quiet dimly lit room
+ Eyes and ears open, no sleeping
+ No stimulus
+ Laying down or sitting
+ Iv should be placed 10 minutes pre injection - During/after injection
+Do not interact with patients before, during, or up to 5 minutes after injection, to be clarified during interview
What is relevant history to note for brain perfusion imaging?
- Past drug use or trauma
- Neurologic examination
- Psychiatric examination
- Mental status examination
- Recent imaging
- Current medications and last taken
What is the time reconstitution to injection for 99mTc- HMPAO?
- Stabilized: 10 minutes post reconstitution; within 4 hours
- Unstabilized: 10 minutes post reconstitution; within 30 minutes
+Exception: patients with seizure disorders to be injected as soon as possible after reconstitution
What is the time reconstitution to injection for 99mTc- ECD?
- 10 minutes post reconstitution; within 6 hours
How long till you can image an injected HMPAO?
- 40 minutes; optimal 90 min
How long till you can image an injected ECD?
- 20 minutes; optimal 45 min
