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Do you think that it will be possible in principle to make a robot camera using nanotechnology which could be injected into a person's arteries in order to see if they are becoming blocked? You will need to consider what size a robot would need to be to move along an artery in the blood stream.
Here is some information to get you started:
Here is an image of blood components taken from http://en.wikipedia.org/wiki/File:Red_White_Blood_cells.jpg