PM276: Neuroanatomy and Neurology Quiz

Neuroimaging

• Neuroimaging is used to identify structures and processes in the brain and nervous system through various imaging techniques.
• Frames of reference are important in neuroimaging, as they help to determine the orientation of the tumour or area of interest.

Radiographic Planes

• Radiographic planes include:
  • Sagittal (left-right, lateral)
  • Coronal (front-back, anterior-posterior)
  • Transverse or Axial (up-down, superior-inferior)

Structural Imaging

• Structural imaging allows observation and analysis of physical structures on various length scales (microns to mm).
• It can be used to measure anatomical changes over time.

Functional Imaging

• Functional imaging allows observation and analysis of biological processes on various length scales.
• It can be used to answer questions such as "does the patient have multiple sclerosis?"

Ionising Radiation

• Ionising radiation includes:
  • X-rays
  • Gamma rays
  • Neutrons
• Ionising radiation causes ionisation or excitation of atoms, leading to:
  • Direct action: damage to DNA, RNA, proteins
  • Indirect action: formation of free radicals, leading to cellular damage and death

Positron Emission Tomography (PET)

• PET uses radioactive labelling of a substance (e.g. fluorodeoxyglucose) to image functional processes.
• The isotope emits positrons, which annihilate with electrons, producing two gamma ray photons that are detected by a detector ring.
• Spatial resolution: ~4 mm
• Temporal resolution: ~30 mm
• PET is used in:
  • Functional imaging: blood flow, perfusion, glucose metabolism
  • Oncology: staging disease, monitoring response to therapy

Single Photon Emission Computed Tomography (SPECT)

• SPECT uses a radioactive substance (e.g. technetium-99m) to image functional processes.
• Two cameras detect the gamma rays emitted by the substance.

X-ray Imaging

• X-rays were discovered by Wilhelm Roentgen in 1895.
• X-rays produce a "shadow" on a flat photographic film, depending on the amount of absorbing material in the path and the attenuation coefficient of the medium.
• Advantages of X-ray imaging:
  • Quick
  • Cheap
  • Can be combined with other modalities
• Disadvantages of X-ray imaging:
  • Lack of contrast between soft tissues
  • Depth information lost
  • Ionising radiation

Computed Tomography (CT) Imaging

• CT imaging uses X-rays to produce a 2D representation of a 2D object.
• Image reconstruction is based on mathematical principles developed by Radon in 1917.
• Advantages of CT imaging:
  • Quick
  • High spatial resolution
  • Can image bones and soft tissues
• Disadvantages of CT imaging:
  • Ionising radiation
  • Limited contrast between soft tissues

Magnetic Resonance Imaging (MRI)

• MRI provides superior soft tissue contrast compared to CT.
• No ionising radiation is used.
• Many types of contrasts are possible (e.g. diffusion, perfusion, blood-oxygenation properties).
• Chemical information can be obtained via MR spectroscopy.
• Disadvantages of MRI:
  • Scans take longer than CT
  • Strong magnetic field, magnetic field gradients, and radiofrequency may prevent certain patients with implants from having a scan
  • MRI examinations are more expensive

Magnetism

• Magnetic field strength is measured in tesla (T).
• Typical MRI scanners have field strengths: 0.5T, 1.5T, 3T, 7T.
• Magnetic susceptibility tells us the extent to which materials become magnetised in a magnetic field.