MRI Anatomy

• Anatomy


  Refers to the internal and external structures of the body and their physical relationships
• Physiology


  Refers to the study of the function of those structures
• Main regions of the human body

  • Axial
  • Appendicular
• Parts of the axial region

  • Head
  • Neck
  • Thorax
  • Abdomen pelvis
• Parts of the appendicular region

  • Upper extremities
  • Lower extremities
• T1 contrast generation

  Image contrast is derived from differences in the T1 recovery of the tissues rather than any mechanism
• T2 contrast generation

  Image contrast is derived from differences in the T2 decay times of the tissues rather than any other mechanism
• Proton density contrast

  Differences in signal intensity between tissues that are a consequence of their relative number of mobile hydrogen protons per unit volume
• T1W image


  Contrast depends predominantly on the differences in the T1 recovery times between fat and water (and all the tissues with intermediate T1 recovery times)

  
• T2W image


  Contrast predominantly depends on the differences in the T2 decay times between fat and water (and all the tissues with intermediate T2 decay times)

  
• PDW image


  Differences in the number of mobile hydrogen nuclei per unit volume of tissue are the main determining factor in forming image contrast
• Fluids normally appear dark on a T1W image
• Fluids normally appear bright on a T2W image
• T1W images are used for anatomy and pathology postcontrast enhancement

  
• T2W images are used for pathology
• PDW images are used to image anatomy and physiology

  
• Intracranial tuberculosis

  • A serious, life-threatening infection of the brain caused by Mycobacterium tuberculosis
  • A form of extrapulmonary tuberculosis
• Symptoms of intracranial tuberculosis

  • Gradual onset of symptoms
  • Headache
  • Fever
  • Neck stiffness
  • Vomiting
  • Altered consciousness
  • Seizures
  • Cranial nerve palsies
• Diagnosis of intracranial tuberculosis

  A combination of clinical history, examination, and investigations like lumbar puncture, cerebrospinal fluid (CSF) analysis, imaging studies (like MRI and CT scan), and microbiological tests
• Central nervous system (CNS)

  Consists of the brain and spinal cord
• Parts of the brain

  • Cerebrum
  • Brainstem
  • Cerebellum
  • Pons
  • Medulla
  • Spinal cord
  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe

  
• Functions of the cerebrum

  Initiation of movement, coordination, body temperature, touch, vision, hearing, judgement, reasoning, problem solving, emotions and learning
• Functions of the brainstem

  Movement of the eyes and mouth, relaying sensory messages, hunger, respirations, consciousness, cardiac function, body temperature, involuntary muscle movements, sneezing, coughing, vomiting, and swallowing
• Functions of the cerebellum

  Coordinate voluntary muscle movements and to maintain posture, balance, and equilibrium
• Cranial nerves

  • Olfactory nerve
  • Optic nerve
  • Oculomotor nerve
  • Trochlear nerve
  • Trigeminal nerve
  • Abducens nerve
  • Facial nerve
  • Auditory/Vestibular nerve
  • Glossopharyngeal nerve
  • Vagus nerve
  • Accessory nerve
  • Hypoglossal nerve
• Origin of cranial nerves

  Two pairs originate in the cerebrum, the other 10 pairs start in the brainstem
• Longest cranial nerve

  The vagus nerve, which has both sensory and motor functions
• Parts of the spinal column

  • Cervical (7 vertebrae)
  • Thoracic (12 vertebrae)
  • Lumbar (5 vertebrae)
  • Sacrum (5 fused vertebrae)
  • Coccyx (4 fused vertebrae)

  
• Spinal cord

  A major part of the central nervous system, located in the vertebral canal and reaching from the base of the skull to the upper part of the lower back
• Reasons for an MRI of the brain or spine

  • Tumors
  • Abscesses
  • Congenital abnormalities
  • Aneurysms
  • Venous malformations
  • Hemorrhage, or bleeding into the brain or spinal cord
  • Subdural hematoma
  • Degenerative diseases, multiple sclerosis, hypoxic encephalopathy, or encephalomyelitis
  • Hydrocephalus
  • Herniation or degeneration of discs of the spinal cord
  • Help plan surgeries on the spine
• MRI provides detailed images of the brain and spinal cord

  
• Cerebrospinal fluid


  Fluid that surrounds the brain and spinal cord
• Spinal cord

  • Carries sensory and movement signals to and from the brain
  • Controls many reflexes
• Reasons for an MRI of the brain or spine

  • Tumors
  • Abscesses
  • Congenital abnormalities
  • Aneurysms
  • Venous malformations
  • Hemorrhage, or bleeding into the brain or spinal cord
  • Subdural hematoma
  • Degenerative diseases, multiple sclerosis, hypoxic encephalopathy, or encephalomyelitis
  • Hydrocephalus, or fluid in the brain
  • Herniation or degeneration of discs of the spinal cord
  • Help plan surgeries on the spine, such as decompression of a pinched nerve or spinal fusion
• MRI vs CT

  • MRI provides better resolution of neural structures than CT, especially for visualizing cranial nerves, brain stem lesions, abnormalities of the posterior fossa, and the spinal cord
• MRI contraindications

  • Patients with pacemakers or cardiac/carotid stents for < 6 weeks
  • Patients with ferromagnetic aneurysm clips or other metallic objects that may overheat or be displaced within the body by the intense magnetic field
• MRI contrast studies

  • Visualization of inflammatory, demyelinated, and neoplastic lesions may require enhancement with IV paramagnetic contrast agents (e.g. gadolinium)
  • Nephrogenic systemic fibrosis (nephrogenic fibrosing dermopathy) has been reported in patients with impaired renal function and acidosis
• MRI techniques

  • Diffusion-weighted imaging (DWI)
  • Flow-attenuated inversion recovery (FLAIR)
  • Magnetic resonance angiography (MRA)
• Common indications for brain MRI

  • Multiple sclerosis (MS)
  • Primary tumour assessment and/or metastatic disease
  • AIDS (toxoplasmosis)
  • Infarction (cerebral vascular accident (CVA) vs. transient ischaemic attack (TIA))
  • Haemorrhage
  • Hearing loss
  • Visual disturbances
  • Infection
  • Trauma
  • Unexplained neurological symptoms or deficit
  • Pre-operative planning
  • Radiation treatment planning
  • Follow-up (surgical or treatment)
• MRI contraindications

  • Any electrically, magnetically or mechanically activated implant
  • Intracranial aneurysm clips (unless made of titanium)
  • Pregnancy (risk vs benefit ratio to be assessed)
  • Ferromagnetic surgical clips or staples
  • Metallic foreign body in the eye
  • Metal shrapnel or bullet