Neurological Nuclear Medicine

Neuro Radiopharm Rx - Brainy Tracers

• 📌 Mnemonic - Key tracer types: Flow (perfusion), Food (metabolism), Dopamine, Amyloid, Tau (FFDAT).

Brain Scan Basics - Perfusion & Tumors

• Cerebral Perfusion (SPECT):
  • Tracers: $99mTc-HMPAO$, $99mTc-ECD$. Lipophilic, cross BBB, trapped, reflect rCBF.
  • Applications:
    • Stroke: Acute ↓perfusion ("cold spot"); later luxury perfusion (↑flow, ↓metabolism).
    • Epilepsy: Ictal ↑perfusion, interictal ↓perfusion at focus.
    • Dementia: Pattern-specific ↓perfusion (e.g., temporoparietal in Alzheimer's).
• Brain Tumor Imaging (PET/SPECT):
  • $^{18}F-FDG$ PET: Measures glucose metabolism. High-grade tumors: FDG-avid. Differentiates recurrence (hot) vs. radiation necrosis (cold).
  • Amino Acid Tracers (e.g., $^{11}C-MET$, $^{18}F-FET$): Higher tumor specificity vs. inflammation/necrosis than FDG.
  • $^{201}Tl$ SPECT: Uptake in viable tumor, not necrosis.

⭐ Brain death on radionuclide angiography: No intracranial arterial flow - 'hollow skull' or 'empty light bulb' sign.

Mind Matters - Dementia & Epilepsy

• Dementia Imaging (FDG-PET): Assesses regional cerebral glucose metabolism. Characteristic patterns aid diagnosis.

  Dementia Type	FDG-PET Hypometabolism Pattern
  Alzheimer's Disease (AD)	Bilateral temporoparietal, posterior cingulate, precuneus (📌 PTP: Parieto-Temporal, Posterior cingulate)
  Frontotemporal Dem. (FTD)	Predominantly frontal and/or anterior temporal lobes
  Lewy Body Dementia (LBD)	Occipital hypometabolism (sparing of mid/posterior cingulate: "cingulate island sign")
  Vascular Dementia (VaD)	Multiple, asymmetric cortical and/or subcortical areas, often patchy

  

• Epilepsy Imaging: Localizes epileptogenic foci.

  • Ictal SPECT ($^{99m}$Tc-HMPAO or $^{99m}$Tc-ECD): Shows ↑ perfusion at seizure onset site.

    ⭐ Ictal SPECT is more sensitive than interictal SPECT for localizing epileptogenic foci and requires rapid tracer injection (ideally within 30-60 seconds) during or immediately after seizure onset.

  • Interictal PET (FDG): Reveals ↓ metabolism in the epileptogenic zone.
  • Interictal SPECT: Often normal or may show ↓ perfusion in the epileptogenic zone during the interictal phase.

Shakes & Leaks - Movement & CSF

• Movement Disorders (DaT Imaging):
  • Agents: $123I$-ioflupane (DaTscan), $99mTc$-TRODAT.
  • Mech: Assesses presynaptic dopamine transporter (DaT) integrity in nigrostriatal neurons.
  • Indic: Differentiates PD (DaT deficit) from non-DaT deficit disorders (Essential Tremor, drug-induced parkinsonism).
  • Findings:
    • Normal: Symmetrical, intense "comma"/"crescent" striatal uptake (caudate, putamen).
    • PD: ↓ asymmetric putamen uptake, progressing to "period"/"dot" appearance.
  • 
• CSF Dynamics (Radionuclide Cisternography):
  • Agent: $111In$-DTPA / $99mTc$-DTPA (intrathecal).
  • CSF Leak Detection:
    • Method: Nasal/ear pledgets vs. serum activity.
    • Positive: Pledget/serum ratio > 1.5-2.0; or direct tracer visualization.
  • Normal Pressure Hydrocephalus (NPH):
    • 📌 Clinical triad: "Wet, Wobbly, Wacky".

    • ⭐ NPH Pattern: Early ventricular reflux (2-6h), persistent intraventricular activity at 24-48h, delayed/absent flow over cerebral convexities.

High‑Yield Points - ⚡ Biggest Takeaways

• SPECT with HMPAO/ECD shows hypoperfusion in ictal epilepsy and interictal stroke/dementia.
• FDG-PET reveals hypometabolism: temporoparietal (Alzheimer's), frontal (FTD), interictal epileptogenic foci.
• DaTscan (Ioflupane I-123 SPECT) differentiates Parkinson's disease (↓ striatal uptake) from essential tremor.
• Brain death scintigraphy (Tc-99m HMPAO/ECD) shows absent intracranial flow ("empty light bulb" sign).
• Amyloid PET imaging (e.g., Florbetapir F-18) detects amyloid plaques in Alzheimer's disease.
• CSF leak studies use In-111 DTPA or Tc-99m DTPA to detect rhinorrhea/otorrhea.