Brain MRI Overview by Dr. Hayder Jasim Taher

MRI of the Brain

• The presentation is by Dr. Hayder Jasim Taher, PhD of Medical Imaging, at the University of Hilla.
• The presentation outlines the anatomical overview, indications for brain MRI, MRI procedure, and MRI sequences.

Anatomical Overview

• The nervous system is a complex network of nerves and cells carrying messages between the brain and spinal cord and various parts of the body.
• It consists of two main parts:
  • Central Nervous System (CNS):
    • Includes the brain and spinal cord.
  • Peripheral Nervous System (PNS):
    • Consists of nerves branching out from the brain and spinal cord.
    • Forms the communication network between the CNS and the body parts.
• The brain is composed of three main parts:
  • Cerebrum:
    • Largest part, with two hemispheres.
    • Cortex contains mostly nerve cell bodies (gray matter).
    • Beneath the cortex, nerve fibers (white matter) connect areas.
  • Cerebellum:
    • Second largest part.
    • Located in the posterior cranial fossa.
    • Outer layer (gray matter) has cell bodies, inner layers (white matter) contain processes and support cells.
  • Brainstem:
    • Composed of the midbrain, pons, and medulla oblongata.
    • Midbrain: Connects the cerebrum and cerebellum to the spinal cord.
    • Pons: Located anterior to cerebellum, fibers connect the cerebrum, cerebellum, and spinal cord.
    • Medulla oblongata: Forms the lower brain stem under the pons, contains tracts that communicate between the spinal cord and brain.

Indications of Brain MRI

• MRI is advantageous over CT for detecting lesions in the posterior fossa, skull edge, and pituitary fossa.
• Useful for identifying tumors and conditions like hemorrhage and ischemic stroke.
• MRI angiography enhances detection of thrombosis and stenosis.
• Highly effective in diagnosing degenerative diseases, including multiple sclerosis, subcortical arteriosclerotic encephalopathy, gliosis, and syrinx.
• MRI is also advantageous for traumatic brain injuries by demonstrating the extent and diffuse axonal injury.

MRI Procedure

• Patient Position:

  • Supine (lying on back, head first)
  • Placed in a head coil, padded to avoid movement.
  • Mirror in coil allows patient to see out and relieve claustrophobia.

• Scout Slice Placement (for Axial Slices):

  • Sagittal localizer, aligned to a line joining the splenium and genu of the corpus callosum.
  • Sagittal localizer used to obtain coronal slices; parallel to the brainstem
  • Axial localizer used to obtain sagittal slices; parallel to the falx (midline shift is considered)
  • Coverage of axial slices includes superior to inferior (craniocervical junction to vertex), lateral to medial (temporal lobes on both sides), posterior to anterior (occipital to frontal lobes)

MRI Sequences (Routine Brain)

• The table provides details on various MRI sequences (e.g., sagittal T1, coronal T2, axial DWI, axial FLAIR) and their parameters like TR (repetition time), TE (echo time), FA (flip angle), ETL (effective echo train length), and slice thickness.

• Notes:

  • T1-weighted images provide good anatomical information.
  • FLAIR images pinpoint edema or inflammatory regions effectively and are useful for identifying multiple sclerosis plaques.
  • Diffusion-weighted imaging (DWI) is helpful in stroke, abscess, and tumor cases, due to restricted diffusion in these conditions.