CT of the Brain
When there is sudden vision loss, the brain may be imaged. There are a number of different pathologies (causes) that they will be using imaging to rule out, but common ones include brain tumors, strokes, and multiple sclerosis. While a CT and MRI have similarities, each have advantages to be able to view different disease states. Depending on your underlying diseases and presentation, they may order one or both of these.
A CT of the brain (also called a CAT scan) uses special X-rays to get multiple views of the brain in order to get more information about the tissues and brain structure. During the CT, an X-ray beam moves in a circle around the body (or body part) to get many views. A CT can be done with or without an iodine-based contrast. CT contrast dye can be given orally and/or injected into a vein. Contrast dye can help certain structures be more evident; however, the decision if you receive contrast dye will be dependent on a number of factors including your renal function. The contrast dye is iodine-based so allergic reactions are rare but can occur.
To prepare for a CT of the brain, they will have you change into a hospital gown and remove all metal objects including piercings and jewelry. You will complete a screening tool to ensure that the CT is safe for you and there are no contraindications. If you are receiving IV contrast, they will place a peripheral (arm) IV in order to give you the contrast. You will lie on a table which will be moved into a circular machine, which is the CT machine. After you are positioned correctly in the machine, the technicians in the room will move behind a window to where the scanner controls are, but they will be able to speak to you via speakers. Once the exam begins, you will lie still for the duration of the exam and the machine will circle around you. Throughout the exam, there will be a number of whirling and clicking sounds which are normal. If they use IV contrast dye, they will either inject it at the beginning of the CT scan or midway through the exam after they have images without contrast. When it is injected, you may feel a sensation of flushing, nausea, a salty taste in your mouth, or even like you peed your pants. This will only be brief and will reside quickly. Typically, a CT of the brain takes about 15 - 30 minutes with most of this being the prep time and the actual exam only lasting around 5 minutes. Once the CT scan is complete, you will be removed from the machine and if you have an IV line, this will be removed.
