You cannot have a head MRI within three months of having a cardiac stent, but you can have a head MRI after three months.
MRI is performed by the nuclei of atoms that show specific changes in response to an electromagnetic field and form an image on a computer. Because the stent made within three months may shift when the MRI is performed, the MRI cannot be performed. After three months, because the stent is made of a drug-coated stent, which is an alloy material, the MRI can be performed (the MRI field strength should not exceed 3.0 T).
MRI works by a very large a magnetic field. Metal going in can cause problems such as displacement and heat production, and the presence of metal in the body can affect the imaging with metal artifacts. So in general, the metal should be removed before the test.
Specifically go to the hospital and have the test done under the direction of your doctor.