What is a CT scan?

If you’ve been injured, have symptoms of unclear origin or are being screened or treated for cancer, your doctor may order a CT scan to gather more information about what is going on inside your body.

A CT scan is a form of medical imaging that can show doctors various rigid and soft structures inside of your body such as bones, organs, blood vessels or tumors.

One of the first times a CT scan machine was ever used with a patient was in 1971, when doctors and engineers used it to really “see” a female patient’s brain tumor for the first time.

“CT” stands for computed tomography. “Tomography” creates a 3-dimensional image of an object by passing waves of energy through it. In a CT scan, these waves are X-rays.

Just as light passes differently through different materials (think of glass, water or a curtain), X-rays pass differently through bones, tissues and other biological materials.

By passing X-rays through your body and recording them on the other side with a sensor, a radiographer can create a picture of the internal structures of your body.

A CT scan combines a series of X-rays images taken from different angles around your body and computes these into a 3-dimensional image.

A CT scan machine looks like a narrow table-like bed with a donut-shaped scanner around part of it. The bed moves through the “donut” as it takes X-rays of the part of your body being imaged.

Unlike an MRI scan, the scanner doesn't surround your whole body at once, so you shouldn't feel claustrophobic.

A CT scan usually takes 15 to 30 minutes. If you are getting a whole body scan it can take a few hours. You will be laying down during this time while the “donut” scanner rotates around you.

A CT scan is not painful. The scanner only makes light whirring and clicking sounds. But you will need to lie very still during the scan, which can become uncomfortable.

Most CT scans don’t require any special preparation on your part. You will simply need to prepare to lie very still for the duration of the scan. You may be asked to hold your breath at times.

However, some scans require you to drink or get an injection of a special dye called a contrast material. You may have to avoid eating or drinking a few hours before this.

CT contrast materials or dyes can have some side effects including diarrhea. You may also experience a sense of flushing, although this is not dangerous and will pass.

CT scans are safe for people with metal implants or devices in their bodies. However, you should still let your doctor or radiographer know of any metal implants you have.

There are risks associated with CT scans. The X-rays expose you to some ionizing radiation that in many or large doses can damage your DNA and increase your risk of cancer.

You can discuss the benefits versus the risks of a CT scan for you with your doctor. The risks from a single scan are generally very small and the benefits outweigh them.