Q: I was injured while working out and my primary care physician ordered an X-ray. However, after reviewing the results, my doctor recommended that I have an MRI. I am a very anxious person. Can you explain more about what this type of testing entails and what I can expect?

A: MRI, or magnetic resonance imaging, is a medical imaging technique that uses a magnetic field and radio waves to create a detailed image of organs and tissues in the body.

People often come into an MRI with a lot of questions, such as the following.

How long will it take?: MRI exams take longer than X-ray and CT scans. The routine appointment time is 45 minutes, though some exams could take as long as four hours to complete.

There are many reasons for this extreme time difference. First, electromagnetism is used to create these images. We can only go as fast as the human body will magnetize. Second, the intention is to create the best imaging possible, which inherently means more time inside the scanner.

Why do I have to change my clothes and remove my jewelry?: MRI machines have superconducting magnets that generate heat and create an extremely strong magnetic field. The magnets can pull ferrous objects, or those containing iron, into the machine with a lot of force. This also can cause the machine to rotate and twist with the magnets’ flux lines. Nonferrous objects like aluminum or copper will generate heat once inside the scanner, which may cause burns. It’s possible that clothing can be set on fire.

To prevent these issues, patients are asked to change into hospital- approved clothing and remove all jewelry and any devices such as cellphones, hearing aids and other items from the body.

My doctor said my implanted device is safe. Why do you need my information?: To ensure safety, it is important to know if certain devices, such as pacemakers, stimulators, clips or coils, have been implanted inside the body.

These devices often have generators or batteries and, thus, require precautions to ensure that nothing interferes with the machine, its ability to obtain the most accurate imaging or our ability to keep you safe. When we know that a patient has an implanted device, we adjust how the scanner operates based on the manufacturer’s guidelines.

We also must ensure the device is placed in “MRI safe” mode before we begin scanning. If a patient were to enter the MRI environment without all safety measures in place, it could damage the device or burn or shock the patient.

What, if any, injections am I going to receive?: During some MRI exams, patients receive a contrast injection that is used to help enhance the imaging. The injection typically is given through an IV and does not hurt.

Depending on the exam being performed, some patients may also receive a drug called glucagon, which slows the motion in the abdomen for more precise images.

I am claustrophobic. What happens if I feel unwell during an exam?: There is a camera inside the MRI tube so technologists can monitor you. Patients wear headphones so they can hear instructions and communicate with the technologists. If you feel anxious during the exam, you can speak up and staff will help you.

Additionally, sedation may be available. If you are unable to have the MRI performed, the radiologist and your physician will determine if another exam is more appropriate.

Another question I often hear relates to whether it matters which type of facility is visited to obtain an MRI scan. Speak with your provider about the reason for the scan and to seek out the best facilities for your MRI.

— Fabian Gonzalez, Radiology, Mayo Clinic, Jacksonville, Florida

Mayo Clinic Q&A is an educational resource and doesn’t replace regular medical care. Email a question to MayoClinic Q&A@mayo.edu.