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Advantages
- Fast (seconds)
- Widely available
- No contraindication for pacemakers, claustrophobia
- Acute hemorrhage easy to see (hyperdense)
- Trauma evaluation excellent
- Bone, calcification
Limitations
- Beam hardening artifact (posterior fossa)
- Less sensitive for early ischemia
- Radiation exposure
- Less sensitive for white matter, demyelination, brainstem
CT Densities
- Hyperdense (white): bone, acute blood, calcification, contrast
- Hypodense (dark): air, fat, edema, infarct (subacute), CSF
- Isodense: subacute hemorrhage (1-2 weeks)
Specific Uses
- Acute stroke (rule out hemorrhage, ASPECTS score)
- ICH, SAH (also CT angio)
- Trauma (skull fracture, contusion)
- Hydrocephalus
- Mass effect, herniation
- Brain tumor (initial)
MRI (Magnetic Resonance Imaging)
Advantages
- Higher resolution
- Better soft tissue contrast
- No ionizing radiation
- Multiple sequences for different pathology
- Definitive for most neuro
Limitations
- Slower (30-60 min)
- Cost, availability
- Contraindications: pacemakers (some), aneurysm clips (ferromagnetic), metallic foreign bodies
- Claustrophobia
- Cannot use with unstable patient
Sequences
T1
- Anatomy
- Fat bright, fluid dark
- Pre + post gadolinium
T2
- Pathology bright (edema, demyelination, infarct, tumor)
- Fluid bright
FLAIR (Fluid-Attenuated Inversion Recovery)
- T2 with CSF suppressed
- Lesions adjacent to CSF more visible
- MS plaques, periventricular changes
- Cortical edema
DWI (Diffusion-Weighted Imaging)
- Acute stroke (bright within minutes-hours)
- Persists 1-2 weeks
- Cytotoxic edema
- Also: abscess (bright center), epidermoid, hypercellular tumor (lymphoma)
T2*/SWI (Susceptibility-Weighted Imaging)
- Hemosiderin, microbleeds
- Calcifications
- Iron
- CAA, hypertensive microbleeds, cavernomas
Gadolinium Enhancement
- BBB disruption
- Tumor, abscess, demyelination, infection, inflammation
- Active MS lesions
- Meningeal enhancement
Perfusion MRI
- CBF, CBV, MTT
- Penumbra (DWI-perfusion mismatch)
- Tumor angiogenesis
MRS (Spectroscopy)
- NAA (neuronal), choline (membrane), creatine, lactate, lipid
- Tumor characterization
- Metabolic disorders
DTI (Diffusion Tensor)
- White matter tracts
- Tractography
- Pre-surgical mapping
fMRI (Functional MRI)
- BOLD signal
- Pre-surgical localization
- Research
CTA (CT Angiography)
- Contrast-enhanced
- Fast
- Good for aneurysms, stenosis
- Stroke workup (LVO)
MRA (MR Angiography)
- Time-of-flight (no contrast) or contrast-enhanced
- Vessels
- Aneurysms, stenosis, dissection
DSA (Digital Subtraction Angiography)
- Gold standard
- Highest resolution
- Diagnostic + therapeutic (coiling, stenting, thrombectomy)
- Invasive, risk
Carotid Doppler
- Carotid stenosis screening
- Non-invasive
- Limited for intracranial
Transcranial Doppler (TCD)
- Intracranial vessels
- Emboli detection
- Vasospasm monitoring
EEG (Electroencephalography)
Indications
- Seizures (epilepsy diagnosis, classification, surgical evaluation)
- Encephalopathy (metabolic, infectious)
- Status epilepticus (non-convulsive)
- Brain death determination (electrocerebral silence)
- Sleep studies (polysomnography)
- Prognosis after cardiac arrest
Patterns
- Generalized (3 Hz spike-wave: absence)
- Focal (temporal sharp waves, etc.)
- Periodic discharges
- Burst suppression
- Triphasic waves (hepatic encephalopathy)
Continuous EEG (cEEG)
- ICU monitoring
- Detect non-convulsive seizures
- Status epilepticus
EMG (Electromyography)
- Needle into muscle
- Resting + activation
- Distinguishes:
- Normal
- Neuropathic (denervation, reinnervation)
- Myopathic (small motor units)
NCS (Nerve Conduction Studies)
- Distal latency, amplitude, conduction velocity
- Sensory + motor
- Distinguishes axonal vs demyelinating
- F-wave, H-reflex for proximal
Repetitive Nerve Stimulation
- Myasthenia gravis: decremental response
- Lambert-Eaton (LEMS): incremental response after exercise
Single-Fiber EMG
- Most sensitive for NMJ
- Jitter measurement
Evoked Potentials
- VEP (visual)
- BAEP (brainstem auditory)
- SSEP (somatosensory)
- MEP (motor)
- MS, prognosis
Lumbar Puncture + CSF Analysis
Indications
- Meningitis, encephalitis
- SAH (CT-negative xanthochromia)
- MS (oligoclonal bands)
- GBS (albuminocytologic dissociation)
- Autoimmune (NMDA-R, etc.)
- Cancer (LM disease cytology)
- Idiopathic intracranial HTN (high pressure)
- NPH (response to LP)
Contraindications
- â ICP with mass effect
- Coagulopathy (correct first)
- Infection at puncture site
Procedure
- L3-L4 or L4-L5 interspace
- Image first if focal signs, papilledema, immunocompromised, â age, altered LOC, seizure
CSF Studies
- Cell count + differential
- Protein
- Glucose (compare to serum)
- Gram stain + culture
- PCR (viral, TB)
- Cytology, flow cytometry
- Oligoclonal bands, IgG index
- Autoantibodies (NMDA-R, LGI1, GAD, etc.)
- 14-3-3, RT-QuIC (prion)
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- CT: acute bleed, trauma, bone
- MRI: most pathology
- DWI: acute stroke
- **T2*/SWI**: microbleeds
- Gadolinium: BBB disruption
- CTA/MRA/DSA: vessels
- EEG: seizures, encephalopathy, brain death
- EMG/NCS: peripheral nerve, NMJ, muscle
- LP: CNS inflammation, infection, malignancy, pressure