Whether CT and MRI can be performed at the same time requires specific analysis. Plain scans can be examined on the same day and MRI is not harmful. However, if a patient needs to have a CT enhancement test, it is recommended that the patient have the test on the next day. The contrast agent will increase the burden on the kidneys if the two tests are performed at the same time. Plain scans can be performed on the same day because they do not require injection of contrast into the body and because MRI is radiation-free. Enhanced CT scan requires the injection of iodine-containing contrast agent, which can cause dizziness and nausea in some patients who are allergic to it. MRI requires the injection of a gadolinium-containing contrast agent. Gadolinium-containing contrast agents now have fewer side effects, but in order to get the contrast agent out of the body as soon as possible, patients are advised to drink plenty of water after the examination is completed to promote elimination. If a plain scan is performed, CT and MRI can be performed on the same day. If an enhancement sweep is performed, it is recommended that they be performed separately and not on the same day. CT can be performed in some patients, for example, patients with brain hemorrhage are more aggressive and CT is quick and inexpensive enough to diagnose the patient’s condition. Some patients have normal CT exams, and doctors recommend a repeat MRI because MRIs are extremely sensitive to cerebral infarction and can be completely negative for cerebral infarction within six hours, which cannot be detected by CT. MRI can show a significant high signal shadow through a unique sequence, called a DWI sequence. MRI has the unique advantage of detecting infarcts in the acute phase within six hours.