CNS Flashcards
Two main tracers sued for brain SPECT
Tc HMPAO (hexamethylpropyleneamine oxime); Tc ECD (ethyl cysteinate dimer)
Difference in kinetics of HMPAO an ECD
HMPAO washout is fast, ECD washout is slow
What are the similarities between HMPAO and ECD?
neutral and lipophilic (cross BBB) and both accumulate in the cortex proportional to blood flow
distribution of HMPAO
uptake favors the frontal lobe, thalamus, and cerebellum
CNS radiotracer with uptake in the frontal lobe, thalamus, and cerebellum
HMPAO
distribution of ECD
parietal and occipital lobes
CNS radiotracer with uptake in the parietal and occipital lobes
ECD
Radiotracer used to evaluate cerebral vascular flow, but not taken up by brain parenchyma
Tc DTPA. does NOT cross the BBB
for imaging of a seizure focus, when does the HMPAO or ECD need to be injected?
30 seconds of the seizure to get a good study
Alzheimer disease
corticobasal degeneration
frontotemporal dementia
frontotemporal dementia
lewy body dementia
If the frontal lobe or internal capsule is involved, hypometabolism in the contralateral cerebellum may be seen due to crossed cerebrocerebellar diaschisis
misregistration due to patient motion
atrophy –> sulcal widening –> artifact of hypometabolism (pitfall for misdiagnosis of neurodegenerative disorder)
Which radiopharmaceutical used in the evaluation of brain death does not cross the blood–brain barrier and as such requires an adequate radiotracer bolus?
DTPA
ECD SPECT of frontal dementia
SPECT ECD of Alzheimer disease (decreased uptake in the posterior temporal lobes)
Tc-99m DTPA brain death study, demonstrates hot nose sign
are interictal SPECT or PET superior for detecting complex partial seizures?
PET
interictal FDG-PET is very sensitive (80%) in localizing refractory complex partial seizures, which typically originate from the temporal lobe. Interictal SPECT or PET is frequently used to increase the specificity of the findings seen on ictal study.
Which of the following procedures is the most sensitive in diagnosing seizures of extratemporal origin?
Ictal perfusion SPECT with ECD or HMPAO is the most sensitive when extratemporal seizure focus is expected.
Interictal hypometabolism and hypoperfusion are uncommon with extratemporal epilepsy, and interictal SPECT or PET is not ideal for its evaluation.
For ictal studies, the patients are taken off their seizure medications, admitted, and continuously monitored for the onset of seizure. The radiopharmaceutical is kept at the bedside until the seizure occurs. Once seizure is identified, radiotracer is injected during or within 30 seconds after the completion of the seizure.
What is responsible for poor diagnostic utility of F-18 FDG during the ictal phase?
poor temporal resolution
FDG uptake with the brain is gradual with 95% of the peak uptake occurring around 35 minutes. This is significantly longer than an average seizure focus duration of 1 to 2 minutes.
This causes overlap of increased uptake from ictal phase and relatively decreased uptake during interictal/postictal phases. Because of this lower temporal resolution, F-18 FDG-PET cannot be performed during the ictal phase.
Interictal FDG-PET is most helpful in patients with complex partial seizures, which are frequently secondary to mesial temporal lobe epilepsy. Compared to SPECT, FDG-PET has higher spatial resolution and lower background activity.
A = interictal
B = ictal
C = interictal PET
patient with a clinical history of intractable complex partial seizures. What is your conclusion?
Mesial temporal sclerosis
The coronal ictal SPECT–CT image (B) demonstrates increased perfusion to the right temporal lobe compared to the left (arrow). Coronal interictal SPECT–CT (A) and axial F-18 FDG-PET (C) images demonstrate relatively decreased perfusion and metabolism to the right temporal lobe compared to the left, respectively (arrowheads). These findings are most compatible with seizure focus within the right temporal lobe likely from mesial temporal sclerosis. Glioblastoma multiforme is a high-grade primary brain malignancy that would demonstrate increased perfusion and metabolism.
imaging agent?
I-123 ioflupane (DaTscan)
Three-hour delayed axial images acquired after IV administration of I-123 ioflupane (DaTscan) demonstrate symmetric intense striatal activity with well-delineated borders consistent with normal examination. A normal DaTscan in a patient with movement disorder would suggest essential tremor.
what radiopharmaceutical would be most helpful in differentiating between Alzheimer disease and frontotemporal dementia?
F18- flobetapir (amyvid)
Beta amyloid imaging would be most helpful in differentiating AD from FTD as it would be markedly abnormal in AD but normal in FTD.
The first FDA-approved and most widely used radiotracer for in vivo identification of beta amyloid (Aβ) plaques was F-18 florbetapir (Amyvid). Other FDG-approved agents for imaging beta amyloid include F-18 florbetaben (Neuraceq) and F-18 flutemetamol (Vizamyl). A negative beta amyloid imaging PET scan would show predominant white matter retention, while positive scan would display increasing gray matter retention. Amyloid imaging demonstrates the earliest abnormality in AD, even before F-18 FDG-PET is abnormal.
ioflupane critical organ
bladder
ioflupane mechanism of action
pre-synapic dopamine transporter
should you discontinue L-dopa prior to a DAT scan?
Continue L-dopa!
can patients be on cocaine prior to a DaT scan?
No - ioflupane and cocaine both bind to pre-synaptic dopamine transporter protein
normal scan
Occipital lobe uptake ONLY = closed eyes
what is the significance of testicular uptake?
higher chance of CNS metastasis
important additional projections in a brain death study
picture of the injection site (make sure that it was actually injected)
image of the abdomen to check for normal biodistribution (aka uptake in the liver)
In-111 DTPA CSF leak study
positive with CSF leaking out the nose
depression (TBI) can mimic what patten of dementia on SPECT or FDG-PET?
Fronto-temporal Dementia
what part of the brain is classically spared with neurodegenerative disordes?
The motor strip
