Vivo = living or alive. Usually in medicine we see the words "in vivo" which means an investigation is done "on living things" or we see "ex-vivo" which means an investigation is performed on something that has come from a living organism (like a tissue sample or biopsy for example)

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Allow me to add a little to Jim's wonderful answer. MRI is used by human corpses, for example, to answer questions of forensic medicine. This situation has nothing to do with the term in vivo. If MRI is used to study images from a living person, then the term in vivo is used.

Since this is a Latin term, the term is written in italics.

In vivo in MRI brain image analysis: means to analyse MRI (Magnetic Resonance Imaging) images of the brain , and In vivo means In the living organism and here means brain of living human or anemal.

Vivo implies MRI scan is of an alive human being.