Bryan Johnson is the self-proclaimed “most measured person in human history.”br br Johnson, who became a millionaire selling his online payments startup to PayPal for $800 million, is the new poster boy for an old Silicon Valley obsession: “biohacking” your body to extend your lifespan. He takes routine measurements of everything from his blood to his stool as part of his anti-aging quest.br br But Johnson told Forbes he believes there is one “gold standard” measurement tool to rule them all: the full-body MRI.br br While startup Ezra and biohackers are trying to make MRIs mainstream, medical experts are concerned the full-body scans could do more harm than good — setting up people who have no specific risk of cancer or another illness for overtreatment and overdiagnosis.br br Read the full story on Forbes: br Forbes Daily Briefing shares the best of Forbes reporting on wealth, business, entrepreneurship, leadership and more. Tune in every day, seven days a week, to hear a new story. Subscribe here: br Fuel your success with Forbes. Gain unlimited access to premium journalism, including breaking news, groundbreaking in-depth reported stories, daily digests and more. Plus, members get a front-row seat at members-only events with leading thinkers and doers, access to premium video that can help you get ahead, an ad-light experience, early access to select products including NFT drops and more:br br br Stay Connectedbr Forbes newsletters: Forbes on Facebook: Forbes Video on Twitter: Forbes Video on Instagram: More From Forbes: br Forbes covers the intersection of entrepreneurship, wealth, technology, business and lifestyle with a focus on people and success.