Neuro MRI Basics

Dr Cameron Scott

Queensland XRay

What is an MRI?

• Imaging modality whereby images are produced by pulsing radio waves in a magnetic field.

MRI

• Patient is placed in a high strength magnetic field (1.5T or 3T).

MRI

• The protons (Hydrogen atoms) in the body align with the magnetic field.

MRI

• Radiowaves are then used to de-phase the protons.

• The timing and strength of the waves can be manipulated to produce different tissue weighting characteristics.

MRI Advantages

• Superior soft tissue characterisation

• Free of ionising radiation

MRI Disadvantages

• Time consuming

• Acquire in one plane at a time (CT acquires volume)

• Inferior spatial resolution compared with CT

• Cramped space - claustrophobia

Standard Brain Pulse Sequences

• T1 weighted

• T2 weighted

• FLAIR

• DWI

• SWI

• T1 post contrast

• TOF MRA

T1

• Fat

• Methaemaglobin (sub-acute haemorrhage)

• Mineralisation

• Slow flow

• Contrast

• Proteinaceous fluid

• Melanin

T2

• Fluid

• Fat

• T2 weighted sequences are typically sensitive for pathology

FLAIR

• FLuid Attentuated Inversion Recovery

• T2 weighted sequence with CSF signal supressed

SWI

• Susceptibility Weighted Imaging

• Gradient echo sequence

• Sensitive to

– Venous blood

– Haemorrhage

– Iron

DWI

• Diffusion Weighted Imaging

• Sensitive to restrictoin of Brownian motion of extracellular water

• Sensitive for

– Ischaemia

– Pus

– Epidermoid

Contrast Enhanced T1

• Contrast does not cross the normal BBB

• Contrast is useful for detecting and characterising diseases that disrupt the BBB

MR Angiography

• Contrast enhanced

• Time of Flight

• Lower resolution than CTA but can provide a 4D image (TRICKS/TWIST)

Basic Anatomy

Cervical Vertebra

Spinal cord

Cerebellum

Medulla Pons

Midbrain

Frontal Lobe

Pituitary Gland

Occipital Lobe

Hypothalamus

Corpus Callosum

Parietal Lobe

Prepontine Cistern

Quadrigeminal Plate Cistern

Fourth Ventricle

Foramen Magnum

Suprasellar Cistern

Third Ventricle

Cerebral Aqueduct

Anterior Cerebral Arteries

Middle Cerebral Artery

Internal Carotid Artery

Vertebral Arteries

Basilar Artery Posterior Cerebral Artery

Hard Palate

Ramus of Mandible

Parotid Gland

Lateral mass C1

Spinal Cord

Odontoid Peg

Cochlea

Medulla

Nasal airway Maxillary sinus

Cerebellum

Globe

Pons

Cavernous Sinus

Fourth Ventricle

Pituitary Gland

Midbrain

Temporal Lobe

Occipital Lobe

Cerebral Aqueduct

Head of Caudate Nucleus

Lentiform Nucleus

Third Venticle

Splenium of Corpus Callosum

Genu of Corpus Callosum

Internal Capsule

Thalamus

Trigone of lateral Ventricle

Corona Radiata

Superior Sagittal Sinus Parietal Lobe

Frontal Lobe

Central Sulcus

Pre-central Gyrus

Post-central Gyrus

The Value of the Different Pulse Sequences

Cases

Case 1

DWI ADC

Case 2

Case 3

Case 4

Case 5

Case 6

Case 7

Case 8

Case 9

Case 10

Case 11

Case 12

Questions?