Dr. brantz wants to use neuroimaging to detect which part of the brain is active when a person is lying. he asks half his participants to tell the truth about an event from their childhood and half to tell a lie about such an event. he will then use to detect brain areas that are active when the participants are lying.

Dr. Brantz wants to test the part of the brain which is active while lying. For this purpose, he will need to make use of the fMRI (functional magnetic resonance imaging) technique. This technique is used for measuring the brain activity by the means of the detecting changes in the blood flow. The neural activation affects the cerebral blood flow, and this change can be noticed using fMRI.

Hence, the answer is 'fMRI'.

sodium i think the chemical element of atomic number 11, a soft silver-white reactive metal of the alkali metal group.