3.6 Static neuroimaging techniques

Static neuroimaging techniques

Static neuroimaging techniques

• X-RAYS

• PNEUMOENCEPHALOGRAPHY

• COMPUTED TOMOGRAPHY (CT SCAN)

• MAGNETIC RESONANCE IMAGING (MRI)

• MAGNETIC RESONANCE SPECTROSCOPY (MRS)

• DIFFUSION TENSOR IMAGING (DTI)

X-RAYS

• First method for imaging the brain

• Produced static 2-D image of the brain

Involves → Conventional radiography

Conventional radiography

• Passing X-rays through the skull onto an X-ray sensitive film

• Differenttypes of tissue absorb the rays to different degrees, producing an image that shows the tissue location

• Still used for examining the skull for fractures & looking for gross brain abnormalities

PNEUMOENCEPHALOGRAPHY

• Small amount of cerebrospinal fluid (CSF) is removed from the subarachnoid space & replaced by air

→ X-rays are not absorbed by air

• X-rays are taken as the air moves up the spinal cord & into ventricular system

• Ventricles stand out in image due to air in them

• Is painful & invasive

• Not currently used much

Arteriography

• Asubstance that absorbs X-rays is injected into the bloodstream

• X-ray produces an excellent image of the blood vessels

• Can be dangerous & painful procedure

COMPUTED TOMOGRAPHY (CT SCAN)

• Passes narrow X-ray beams through the brain at different angles to create many images; then combines the images to create a 3-D image of the brain

– Bone shows white; fluid & lesions shows darker

• CT scan cannot discriminate between gray & white matter

• Ventricles & major fissures can be seen → Damaged areas have fewer neurons & more fluid, so show dark

MAGNETIC RESONANCE IMAGING (MRI)

• Uses a large magnet & a specific radiofrequency pulse to generate a brain signal that produces an image

• Image resolution derived from strength of magnetic field, measured in teslas

• Magnets: 1.5 tesla in strength (1.5T)

• High image resolution

MAGNETIC RESONANCE IMAGING (MRI) →  T1-weighted

• the CSF is dark, grey mater is darker than white mater

MAGNETIC RESONANCE IMAGING (MRI) → T2-weighted

• the CF is brighter, grey mater is lighter than white mater

MAGNETIC RESONANCE IMAGING (MRI) → T2-flair

• the CSF is dark, grey mater is lighter than white mater

MAGNETIC RESONANCE IMAGING (MRI) → observed lesion due to CSF

• due to relaxation time of hydrogen atoms (CSF) → they manipulate the MRI sequence to attenuate any signal coming from the CSF & therefore, any lesion that might be abutting in the CSF can be seen.

MAGNETIC RESONANCE SPECTROSCOPY (MRS)

• 20% of brain tissue that an MRI is unable to image; does it by varying the frequency of the radio waves

• Provides biochemical information

• Detects N-acetylaspartate (neuron & glia) & creatin (neurons, not glia), etc…

• Can detect Alzheimer’s, loss of myelin in MS, brain abnormalities…

DIFFUSION TENSOR IMAGING (DTI)

• MRI method that images fiber pathways by detecting directional movements of water molecules in ventricles

• Movement in nerve fibers tends to follow the longitudinal axis, a property called anisotropy

• Can detect degeneration of axons & distortion of and damage to fibers

• Can be combined with MRI, fMRI, & ERP