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.
Reactivation is associated with aging, immunosuppression, in utero exposure to varicella, and postnatal varicella occurring before 18 months of age. Approximately 300,000 cases are estimated to occur annually, and 5% are recurrences. No seasonal variation is known. Herpes zoster is not a notifiable condition.