Lecture 8 - Neuroimaging Flashcards
Brain Imaging: Anatomy
CAT
Photograph
PET
MRI
Structural Brain Imaging – CT scans
- Computerized Axial Tomography (CAT scan or CT).
- X-rays passed through the head at many different angles.
- Different tissues (brain, CSF, white and grey matter) have different densities – therefore a different proportion of the X-ray is absorbed and an image can be formed.
Details about the Structural Brain Imaging – CT scans
- Spatial resolution not so good. (lil fuzzy)
- Lesions often take some time (hours) to become evident on CT.
Good at picking up:
- tumour
- brain injury
- easily accessible
Structural Brain Imaging – MRI scans
- Spatial resolution very good. (much stronger)
- Immediate imaging of lesions.
small lesion would pop out right away
CT vs. MRI
MRI is clearier
Hydrogen protons and MRI
huge electromagnetic
- magnetizes your entire body
- Hydrogen protons most readily available atoms in human body.
- Protons spin around a given axis.
spin in same direction –> magnetized the image
Radio Frequency and Resonant Frequency
- Protons precess around the main magnetic axis (spinning top analogy).
- The frequency of their precession is dependent on the strength of the magnet.
- A RADIO FREQUENCY (RF) pulse is used in MRI to push protons out of alignment with the magnetic field.
Protons pushed out of alignment with the magnetic field (left)
– longitudinal relaxation refers to the time it takes for them to come back into alignment with the magnetic field (right).
- Align protons
- Add energy
- Recording how that energy comes off of them & travels through the brain & diff. tissues & creating an image out of that diff. in energy field
A T1 weighted image
Different types of tissue approach equilibrium at different rates allowing us to differentiate things like white and grey matter.
Angiogram
- measures the structure of the cerebral blood supply.
- used to image aneurysms (balloon - potential brain burst) and other vascular defects (e.g., arteriovenous malformations).
- twists/knots in capillary blood supply
- X-ray in combination with contrast agents.
- made blood look black
Anatomy vs. Function
Brain anatomy
CT & MRI
Brain function
EEG, PET, fMRI
Functional Neuroimaging
Electrical activity
Metabolism
Electrical activity (v. direct)
- Event-related potentials (ERP), visual evoked potentials (VEP) all derivative from electroencephalogram (EEG).
Metabolism (indirect measures of brain activation)
- Positron Emission Tomography (PET) and Blood Oxygenated Level Dependent (BOLD) functional MRI (fMRI).
Electroencephalogram (EEG)
- Large populations of neurons firing produce electrical potentials that can be measured at the SCALP.
- Brain, skull and scalp passively conduct signals that can be amplified and measured.
- Important tool for diagnosis in epilepsy and sleep disorders.