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.
Princeton's WordNet(4.00 / 1 vote)Rate this definition: 1  estivation, aestivation(noun) (zoology) cessation or slowing of activity during the summer; especially slowing of metabolism in some animals during a hot or dry period. 2  estivation, aestivation(noun) (botany) the arrangement of sepals and petals in a flower bud before it opens.