Mind reading or brain-reading is the use of neuroimaging techniques to read human minds.
Brain-reading or thought identification uses a fMRI (functional magnetic resonance imaging) scan which is a machine that uses “echoes” created by radio waves to peer inside living tissue. This allows us to pinpoint the location of the various signals, producing 3d images of inside the brain. A fMRI scan allows scientists to locate the presence of oxygen contained within hemoglobin in the blood. Since oxygenated hemoglobin contains the energy that fuels cell activity, detecting the flow of this oxygen allows one to trace the flow of thoughts in the brain.
Scans can detect the motion of thoughts in the living brain to less than a millimeter, which corresponds to thousands of neurons, thus giving 3d pictures of the energy flow inside the thinking brain. Advancements will probe to the level of single neurons, picking out the neural patterns corresponding to specific thoughts. Eventually, a computer will scan thousands of fMRI patterns that come pouring out of a thinking brain and decipher each one. In this way, one may be able to decode a person’s stream of consciousness. Of course this would be quite a tricky thing to accomplish for it would use a lot of computing power (as said below) so it is reason to think that this could only be accomplished by a highly advanced civilization that has advanced computing algorithims and has successfully mapped a human brain.
Recording dreams are possible using fMRI scan to record where the brain stores visual thought. Mental images and dreams are fuzzy and will require advanced computing algorithms and extensive testing to produce fidelity in image or video streams from scans.
Medical tricorders and hand-held devices like the MRI-MOUSE (mobile universal surface explorer) will be used to scan a person's thoughts. There are ethical and privacy issues with this, such as currently experienced with lie-detector devices, and by Type I there will be laws passed on the usage of mind reading or enhancement devices.
Mind reading is also associated with telepathy (reading a mind using something other than the five senses), for example the Betazoids from Star Trek, or Professor Xavier from Marvel.