# Nuclear medicine: what the exam is and how it differs from CT and MRI

*A tracer shows how an organ is working, not only how it looks. What the day is like at our Central center, and how the exam compares with CT and MRI.*

October 9, 2026 · Desert Imaging

Most imaging exams take a picture of what something looks like. An X-ray shows the shape of a bone. A CT shows the shape of an organ in slices. Nuclear medicine does something different. It shows how an organ is working.

That is why doctors order it when the question is not "what does this look like" but "what is this doing." Is the gallbladder emptying? How fast does the stomach empty after a meal? Is the thyroid taking up iodine the way it should? Is blood reaching every part of the heart muscle? Where in the bones is there activity that should not be there?

## How it works

You receive a tiny amount of a radioactive tracer, by injection, capsule or breath, depending on the study. The tracer is chosen because it travels to a particular organ. Then a gamma camera picks up the energy the tracer gives off and turns it into pictures of that organ at work.

Because it shows function, nuclear medicine often finds a problem early, before it has changed the shape of an organ enough to show on other scans.

Doctors order nuclear medicine studies for bone pain and infection, gallbladder and liver problems, kidney function, how fast the stomach empties, thyroid and parathyroid disease, and blood flow to the heart. Some thyroid conditions are treated with nuclear medicine as well. Radioiodine, I-131, is given as a capsule and taken up by the thyroid.

## How it differs from CT

A CT scan sends X-rays through you from many angles and builds slices. The machine is the source of the energy, and the pictures show structure: bone, organs, blood vessels, soft tissue. It is fast, a few minutes of scanning.

In nuclear medicine the tracer inside you is the source. The camera is quiet, does not touch you and gives off no radiation of its own. It sits a few inches above you while you lie on a bed, and it collects the signal over minutes rather than seconds. The pictures are less sharp than CT and were never meant to be. They answer a different question.

## How it differs from MRI

MRI uses a strong magnet and radio waves, with no radiation at all. It is excellent at soft tissue detail: the brain, the spine, joints, organs. Like CT, it shows structure.

Nuclear medicine does involve radiation, from the tracer, in a very small amount. The tracer is chosen to be safe and approved by the FDA, and reactions are rare. Tell us if you are pregnant or breastfeeding.

## What the day is like

Nuclear medicine is done at our Central center, 7812 Gateway Blvd. East, Suite 120, in El Paso. It needs a doctor's order, and your insurance may need to approve it first.

Wear loose clothing. Preparation depends on the scan. Bone, liver and spleen scans need none. Gallbladder, gastric emptying, thyroid uptake and stress tests need an empty stomach, and some need you to hold certain medications. We go over your list when you book. Do not stop any medication without talking to the doctor who prescribed it.

Many scans happen in two visits on the same day, or on two days. For a bone scan you get the injection, leave, and come back in 2 to 3 hours for pictures. For a thyroid uptake you swallow a capsule and return at 4 hours and again at 24 hours. The wait is not a delay. The tracer needs time to collect in the organ being studied, and the wait is part of the exam.

One detail people ask about: for a gastric emptying study, you bring a meat burrito. The tracer goes in the food, and the camera follows it through your stomach.

All told, a study can take from 30 minutes to a full day in two visits. We tell you which when you book, so you can plan your day.

## Afterward

The tracer wears off and leaves your body on its own.

A board-certified radiologist reads the study. The report goes to your doctor and to your patient portal, and your doctor goes over it with you. The radiologist's job is to describe what the pictures show. What it means for you, and what happens next, is a conversation with your own doctor.