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Could you kindly elaborate on the various applications of helium? I'm curious to understand its diverse usage in different fields. Could you explain how helium is utilized in the medical industry, particularly in imaging techniques? Also, could you provide examples of its use in the scientific community, specifically in experiments that require inert atmospheres? Additionally, I'm interested in knowing about the role of helium in the aerospace industry, particularly in the construction of lighter-than-air vehicles. Lastly, could you discuss any other significant applications of helium that might not be widely known?