MRI of the Brain and Nervous System Anatomy

MRI of the Brain

• MRI of the brain is a specialized neurological investigation
• It's used to assess various neurological conditions, including multiple sclerosis and headaches
• It helps characterize strokes and space-occupying lesions.

Anatomical Overview

• The nervous system comprises a complex network of nerves and cells carrying messages between the brain and spinal cord to body parts.
• It's divided into:
  • Central Nervous System (CNS): Includes the brain and spinal cord.
  • Peripheral Nervous System (PNS): Consists of nerves branching from the brain and spinal cord, forming a communication network between the CNS and body parts.
• The brain has three main parts:
  • Cerebrum: The largest part, comprised of two hemispheres. The cortex, appearing as gray matter, contains nerve cell bodies. White matter consists of nerve fibers traveling toward and from the cortex.
  • Cerebellum: The second largest part located in the posterior cranial fossa. It has an outer layer (grey matter) with cell bodies and a deeper layer (white matter) with cell processes and support cells.
  • Brain Stem: Consists of:
    • Midbrain: Connects the cerebrum to the cerebellum and spinal cord.
    • Pons: Located anterior to the cerebellum, joining fibers from the cerebellum, cerebrum and spinal cord.
    • Medulla Oblongata: The lower brain stem, containing ascending and descending tracts communicating between the spinal cord and brain.

Indications of Brain MRI

• Tumors: MRI is superior to CT in detecting lesions in the posterior fossa, at the skull's edge, and near the base of the skull and pituitary fossa.
• Hemorrhage-Ischemic Stroke: Both conditions are easily identifiable using MRI, with detection of thrombosis/stenosis in brain vessels being a promising application of MR angiography.
• Trauma: MRI is better than CT at demonstrating the full extent of extracerebral collections and evaluating diffuse axonal injury. However, CT is better at showing the bony cranium.
• Degenerative Diseases: MRI is effective in diagnosing multiple sclerosis, subcortical arteriosclerotic encephalopathy, gliosis, and syrinx.

MRI Procedures

• Patient Position:
  • Supine position, head first.
  • Placed in a head coil.
  • Well-padded to prevent image degradation and malalignment.
  • If the coil has a mirror, the patient should see out of the bore to ease claustrophobia.
• Scout Slice Placement:
  • Axial Slices: Sagittal localizer aligned parallel to the line joining the splenium and genu of the corpus callosum, covering the craniocervical junction to the vertex, temporo-lateral lobes, and occipital to frontal lobes. Coronal localizers can also be used.
  • Sagittal Slices: Sagittal localizers aligned parallel to the brainstem, covering the craniocervical junction to the vertex, temporo-lateral lobes, and occipital to frontal lobes. Axial localizers can also be used.
  • Coronal Slices: Sagittal localizers aligned parallel to the brainstem, covering the craniocervical junction to the vertex, temporo-lateral lobes, and occipital to frontal lobes. Axial localizers can also be used.

MRI Sequences (Routine Brain)

• A table listing specific MRI sequences (T1, T2, FLAIR, DWI, SWI) with parameters like TR, TE, FA, ETL, and slice thickness is included. Specific values are provided in the table.

MRI Sequences Notes

• T1-weighted images (T1WI) are best for anatomical details.
• Flair images are helpful for edema and inflammation, especially identifying plaques in multiple sclerosis.
• Diffusion-weighted imaging (DWI) is preferred for stroke, abscesses, and cellular tumors due to restricted diffusion in these conditions.