Makindo Medical Notes

Related Subjects: |Neurological History taking |Alzheimer disease |Dementia with Lewy bodies |Frontotemporal dementia |Corticobasal degeneration |Creutzfeldt Jakob disease |Vascular Dementia |Ischaemic Stroke |Hypertension |CADASIL |CARASIL

🧲 MRI Basics

• ⚡ Unlike CT, which uses ionising radiation, MRI uses radio waves + magnetic fields. ✅ No radiation risk.
• 📸 MRI provides high-resolution, multiplanar imaging (axial, sagittal, coronal, oblique).
• 🔬 CT pixel intensity = electron density; MRI = hydrogen (H⁺ nuclei) density modified by tissue relaxation times (T1, T2).
• 🌀 Hydrogen protons align in strong magnetic field; gradients encode spatial location.
• 🛠️ MRI components: main magnet, gradient coils, RF transmitter/receiver, computer for image reconstruction.
• 📡 Emitted “spin echo” at the Larmor frequency → Fourier transform → detailed image.

💡 Teaching pearl: MRI signal depends not only on hydrogen density but also on tissue environment (T1, T2 relaxation, flow, diffusion).

⚠️ Challenges of MRI Scanning

• ⏱️ Scan duration: 10–30 min → difficult for claustrophobic/anxious patients.
• 🔊 MRI is noisy; limited communication during scan.
• 🏥 Open MRI exists for claustrophobia, but limited availability.
• 🎯 Aim: shortest protocol to answer the clinical question.

📸 Examples

T2 FLAIR	T2
DWI	ADC
SWI	T1 Sagittal

🛡️ MRI Safety Considerations

• Most prosthetic valves, IVC filters, vascular stents, IUDs, and metallic prostheses are MRI-safe ✅.
• Key risk = movement or heating of ferromagnetic implants. Always check manufacturer guidance.
• Resources: MRI Contraindications Policy | MRI Safety.com

💉 MRI with Gadolinium

• Contrast shortens T1 → brighter images. Used for tumours, inflammation, abscess, meningitis.
• Not usually needed in acute stroke unless diagnostic uncertainty.

📊 Understanding MRI Sequences

• ⏳ T1: Fat bright, CSF dark. Best for anatomy. Acute stroke = hypointense.
• 💧 T2: Water bright, fat darker. Best for oedema/infarcts.
• ⭐ T2* / GRE: Detects blood products, iron, microbleeds.
• 🚫 FLAIR: Suppresses CSF signal → highlights periventricular oedema/lesions.
• ⚡ DWI/ADC: Bright in acute ischaemic stroke (cytotoxic oedema).
• 🧲 SWI: Very sensitive to blood/iron → detects microbleeds & calcification.

🧠 Imaging Patterns in Stroke

🩸 Imaging Patterns in Haemorrhage

📖 Exam pearls:
- DWI = most sensitive for acute stroke (<30 mins).
- GRE/T2* = microbleeds and haemorrhage detection.
- FLAIR = MS plaques, periventricular oedema.
- T1 = anatomy & post-contrast detail.