MRI of a knee. MRIs employ powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field. When a radiofrequency current is then pulsed through the patient, the protons are stimulated, and spin out of equilibrium, straining against the pull of the magnetic field.
Noun. 1. aestivation - (zoology) cessation or slowing of activity during the summer; especially slowing of metabolism in some animals during a hot or dry period. estivation. zoological science, zoology-the branch of biology that studies animals.
For the purposes of this article, we'll use the term hibernation to describe any long-term reduction in body temperature (hypothermia) and metabolism during winter months. When an animal enters a hibernationlike state during the summer, it's known as estivation. It's much less common than hibernation. Hibernation in reptiles is sometimes called brumation. It differs from mammalian hibernation because reptiles are cold-blooded -- they can't control their own body temperature, so they need to spend the winter in a place that will stay warm enough.