Brain Imaging Techniques

Brain Imaging Techniques

1. CAT scans- Principle of Work- X -ray passes through head, its picked up by a detector on the opposite side, gets analyzed. Analysis of residual rays can reveal info about brain structure . Procedure- Subject Lies on a table into a large syndical apparatus. Moving source of x-Rays passes through subjects head

   • • Strengths- Quick and non-invasive method of studying brain structure. CATS can also be used for people with medical implants
       • Limitations: There is some level of radiation exposure

2. MRIs- Principle of Work: In an external magnetic field, some nuclei can emit energy. These pulses of energy can be detected. Since the hydrogen concentration differs in different types of tissues, we can use this info to make a 3d structure of the brain

   • Procedure: Similar to CAT and subject is placed on a table that slides inside a cylindrical apparatus . Strengths: No radiation exposure, better spatial resolution to CAT. Limitations: Due to high resolution, the scanner might pick up slight abnormalities that are no related to original scan. They might lead to unnecessary treatment for the individual

3. Key Definitions: Blood Oxygen Level Dependent Signal- pulses of energy emitted by oxygenated blood when placed in external magnetic field

   • KD continued: Spatial Resolution: the ability of a scanner to discriminate between nearby locations, a unit of space that is discernible in a brain scan. Temporal Resolution: smallest time period in which the brain can register changes

4. fMRI- Uses BOLD signal method. When oxygenated blood is put into an external magnetic field , it emits pulses of energy, but this depends of blood flow and level of oxygenation. The most active areas of brain are supplied with most blood, they let us see which areas of the brain are most active during particular task

   • Procedure: Subjects are required to carry out task as the brain is being scanned
   • Strengths: fMRI shows ongoing brain process
     • Limitation: Discriminate systematic patters vs random noise. Eliminating noise is an experimental procedure with many trials

5. PET- Principle of Work: A radioactive tracer is injected into a subject's bloodstream. The more active a brain area, the more blood supply it needs, hence the higher the energy level emitted by the tracer

   • Procedure: After injection, the subject is placed in an scanner that picks up the energy emissions
   • Strengths of a PET- Provides good spatial resolution, and the scanner can be small and sometimes portable
     • Limitation: Exposure to radioactivity, provides poor temporal resolution; only slow processes can be registered

6. EEG: Principle of Work: When large neurons are activated simultaneously, electric potentials are generated by these impulses are detectable on skull's surface. Electrodes can be attached to scalp to detect this activity. These are attached at the scalp through pre-determined points. Subject will have to lie for still few minutes and the EEG is produced

   • Strengths: Provides perfect temporal resolution- changes in electric potentials are measured in ms is is useful in diagnosing conditions for epilepsy or sleep disorders. Limitations: Provides poor spatial resolution-origin of signal cannot be established. Weak signals form sub-comical areas of brain to be registered on scalp