Brain Imaging
(This page is currently under development.)
Introduction
Non-invasive examination of the brain is crucial in performing medical diagnoses of brain disorders and damage, and for researchers studying its cognitive functions. A number of imaging techniques have been developed, and the field is growing steadily.
Some of the techniques available, each with its own set of advantages and disadvantages, are covered in this tutorial:
- CT
- MRI
- SPECT/PET
- FMRI
- EEG/ERP
- EROS
- TMS
- MEG
Computer Tomography (CT)
- Used to be called CAT scanning, short for Computer Aided Tomography
- An X-ray tube projects X-rays through the head
- As the X-rays get projected, the intervening tissue absorbs some of them. Receptors on the other side of the head detect the attenuated X-rays that have passed through.
- The more dense the tissue, the more attenuation takes place
- By rotating the X-rays 180° around the head, a computer can use algorithms to reconstruct the image:
- Though it provides good anatomical information, no information is provided on cognitive function
- Spatial resolution is not great: between 5 to 10 mm, which takes the average of a point and 1 mm of the tissue around it
- Because it uses X-rays, it may be harmful (especially for pregnant women and children)
- It is a relatively less expensive method than others such as MRI (see below)
- Below is a sample CT image. Notice the bone is white, there is very little difference between the brain's gray and white matter, and fluids such as water or bone is dark
- In summary, the color relationship between the amount of attenuation and the density of the tissue is as follows:
