363.3 🏥 內科專科考前版

363.3.1 Mechanistic Deep Dive

363.3.1.1 DWI Physics

  • Restricted water diffusion
  • Cytotoxic edema (cell swelling)
  • Acute ischemia: ATP failure → Na/K pump failure → cell swelling → restricted diffusion
  • ADC map dark in restriction

363.3.1.2 Gadolinium + BBB

  • Normally BBB intact, no enhancement
  • Disrupted BBB: enhancement
  • Tumor angiogenesis
  • Inflammation
  • Active demyelination

363.3.1.3 Perfusion MRI Concepts

  • CBF (cerebral blood flow)
  • CBV (cerebral blood volume)
  • MTT (mean transit time)
  • DWI = infarct core
  • Perfusion = at-risk tissue
  • Mismatch = penumbra (target for treatment)

363.3.1.4 EEG Generation

  • Cortical pyramidal neurons
  • Summated postsynaptic potentials
  • 10-20 system electrode placement

363.3.2 Recent Trials & Updates

363.3.2.1 Mobile Stroke Units

  • CT scanner in ambulance
  • Earlier thrombolysis
  • Improved outcomes (B_PROUD trial 2021)

363.3.2.2 Stroke Imaging Workflow 2024-2026

  • Direct to angio suite (CTA in ED)
  • AI software (RapidAI, Viz.ai) automated detection
  • Reduces door-to-needle/groin times

363.3.2.3 Amyloid + Tau PET (Alzheimer)

  • Eligibility for anti-amyloid therapy (lecanemab, donanemab)
  • Pre-treatment confirmation
  • Pittsburgh compound B, florbetapir, flutemetamol, florbetaben (amyloid)
  • Flortaucipir (tau)

363.3.2.4 DaT-SCAN

  • 123I-FP-CIT SPECT
  • Dopamine transporter imaging
  • Differentiates PD/parkinsonism from essential tremor
  • Negative in essential tremor, vascular parkinsonism, drug-induced

363.3.2.5 Continuous EEG (cEEG)

  • ICU
  • Detect non-convulsive status epilepticus (NCSE) — 8-20% of ICU comatose
  • Prognosis after cardiac arrest

363.3.2.6 Plasma Biomarkers (Alzheimer)

  • p-tau 181, p-tau 217
  • Aβ42/40
  • GFAP
  • NfL
  • Less invasive than LP/PET

363.3.3 High-Yield Specialist Points

363.3.3.1 Stroke MRI Sequence Approach

  1. DWI: infarct core (bright, restricted)
  2. ADC: confirm restriction (dark)
  3. FLAIR: hyperintensity onset (~6 hours)
  4. T2*/SWI: hemorrhage exclusion
  5. Perfusion: penumbra
  6. MRA: vessel patency

363.3.3.2 MS Imaging

  • FLAIR/T2 hyperintensities periventricular, juxtacortical, infratentorial, spinal
  • “Dawson fingers” perpendicular to ventricles
  • Active lesions enhance
  • Atrophy with progression
  • DIS (dissemination in space) + DIT (dissemination in time)
  • 2017 McDonald criteria

363.3.3.3 Brain Tumor Imaging

  • Glioma: heterogeneous, T2 bright, enhancement variable
  • GBM: ring enhancement, central necrosis, perilesional edema
  • Meningioma: dural tail, homogeneous enhancement
  • Lymphoma: periventricular, restricted diffusion, intense enhancement
  • Metastasis: gray-white junction, multiple, edema disproportionate

363.3.3.4 Spinal Cord Imaging

  • T2 for cord lesions
  • Sagittal + axial
  • Pre + post gadolinium
  • Look for compression, intramedullary lesions, cord edema

363.3.3.5 CT Perfusion Maturation

  • Time-to-maximum (Tmax)

  • 6 sec = at-risk

  • 10 sec = severely hypoperfused

  • ATCT, CBV, CBF, Tmax maps

363.3.3.6 MRI Safety

  • Implants: check compatibility
  • Pacemakers: MR-conditional now common
  • Aneurysm clips: ferromagnetic vs non
  • Programmable shunts: may need reprogramming
  • Cochlear implants
  • Metal foreign bodies (eye especially)
  • Tattoos generally safe
  • GFR > 30 for gadolinium (NSF risk)

363.3.3.7 CSF Specific Tests

  • Oligoclonal bands: MS (also infections, vasculitis)
  • IgG index: MS
  • 14-3-3, RT-QuIC: CJD
  • Cryptococcal antigen, India ink
  • VDRL: neurosyphilis
  • ACE: sarcoidosis
  • HSV PCR: encephalitis
  • TB PCR + culture
  • Cytology + flow: LM disease, lymphoma
  • Autoantibody panels: encephalitis

363.3.4 Pearls

  • CT for acute bleed, trauma, bone
  • MRI definitive for most
  • DWI acute stroke (within minutes)
  • **T2*/SWI** for microbleeds
  • Gadolinium for BBB disruption
  • MRA/CTA/DSA for vessels
  • EEG for seizures, encephalopathy, brain death
  • EMG/NCS for peripheral nerve, NMJ, muscle
  • LP/CSF for CNS inflammation/infection
  • Amyloid PET for Alzheimer therapy eligibility
  • DaT-SCAN for parkinsonism
  • AI software in stroke workflow