Quick answer: a CT scan is fast and painless. You lie on a narrow table that moves through a short, open ring, and the actual scanning often takes only seconds to a few minutes. The whole exam is usually done within 30 minutes. If you need contrast, it may be a drink, an IV injection or both. The injection can make you feel warm or flushed, give you a metallic taste or make you feel like you need to urinate, and these sensations pass quickly. CT uses x-rays, so tell the team if you might be pregnant.
Compared with an MRI, a CT scan surprises most of my patients by how quick it is. What worries them is the contrast injection. Here is the whole process, step by step.
What is a CT scan?
Computed tomography (CT, or a «CAT scan») is an x-ray test. Instead of one picture, x-ray beams and detectors rotate around you and a computer builds detailed cross-sectional images, like slices of a loaf of bread, that can be combined into 3D views. CT shows bones, soft tissues, organs and blood vessels in much more detail than a regular x-ray.
It is one of the fastest and most accurate tools for the chest, abdomen and pelvis, and it is often the first test in emergencies, because it can reveal internal injuries and bleeding quickly. It is also used to look for cancers, blood clots in the lungs, aneurysms, appendicitis and many other conditions.
Before your appointment
- Food and drink: if your scan uses contrast, you may be told not to eat or drink for a few hours beforehand. Follow your center’s instructions.
- Medications and medical history: tell your doctor about all your medications and allergies, and about any history of heart disease, asthma, diabetes, kidney disease or thyroid problems. These can increase the risk of a reaction to contrast.
- Contrast allergy: if you have had a reaction to contrast before, your doctor may prescribe medication (usually a steroid) to take beforehand. Contact your doctor well before the exam so there are no delays. See [link: Contrast Dye Allergy].
- Pregnancy: always tell your doctor and the technologist if there is any chance you are pregnant. See [link: CT Scans During Pregnancy].
- Implants: unlike MRI, implanted devices of any kind do not prevent you from having a CT scan. Metal can still affect the images, so mention it.
More detail on contrast preparation in [link: How to Prepare for a CT Scan With Contrast].
Step 1: Changing and removing metal
Wear loose, comfortable clothing. You may be asked to change into a gown. Metal objects can affect the images, so remove jewelry, glasses, hairpins and bras with metal underwire, and for some exams hearing aids and removable dental work. Remove piercings if possible.
Step 2: Oral contrast (for some exams)
For some scans of the abdomen and pelvis, you drink a contrast liquid before the scan so the stomach and bowel show up clearly. Most people find the taste mildly unpleasant but easy to tolerate. Rarely, contrast is given by enema instead, which can cause a feeling of fullness for a short time.
From the scanner room: [TU EXPERIENCIA: cuánto tiempo antes se bebe el contraste oral en tu práctica, a qué sabe según los pacientes, trucos para tomarlo mejor.]
Step 3: The IV line (if you need IV contrast)
If your exam uses iodine-based contrast injected into a vein, your doctor will screen you for kidney disease first. A nurse or technologist places a small IV in your arm or hand; you will feel a quick pin prick. See [link: Contrast and Kidney Function].
Step 4: Positioning on the table
You lie on a narrow table, usually on your back. The technologist may use straps and pillows to keep you in the right position. When the table moves into the scanner, you may see light lines projected onto your body: they help line you up correctly.
The CT scanner is a large, donut-shaped machine with a short tunnel. It is much more open than an MRI, and most people do not feel enclosed.
Step 5: The scan
The technologist goes to a separate room with a large window. They can see, hear and talk to you through an intercom at all times.
- A quick first pass. The table moves quickly through the scanner to find the right starting position.
- The actual scan. The table moves slowly through the ring, sometimes several times. Inside the ring, the x-ray tube and detectors rotate around you. You may hear buzzing, clicking and whirring, which is much quieter than an MRI.
- Breath-holds. You may be asked to hold your breath for a few seconds. Breathing and movement blur the images, so follow the instructions carefully.
Step 6: The contrast injection (if needed)
The injection itself usually lasts less than a minute, often given by a machine while you lie on the table. As it goes in, it is common to:
- feel warm or flushed, often spreading through the body
- notice a metallic taste in your mouth
- feel like you need to urinate, or even feel as if you have (you have not)
These are normal effects of the contrast and fade within a short time. Serious allergic reactions to iodine contrast are extremely rare, and radiology departments are equipped to handle them. Tell the technologist right away if you feel itching, hives or difficulty breathing. More in [link: CT Contrast Side Effects: What Is Normal and What Is Not].
From the scanner room: [TU EXPERIENCIA: cómo avisas al paciente justo antes de la inyección y cómo describen ellos la sensación de calor. Es el momento que más miedo da y tu forma de explicarlo vale mucho.]
Step 7: Finishing up
The technologist may ask you to wait a moment while they check that the images are good enough for the radiologist. Then the IV is removed and a small bandage applied. You can return to your normal activities immediately. If you had contrast, drinking fluids afterward helps your body clear it.
How long does a CT scan take?
The exam is usually completed within 30 minutes, and the scanning itself often takes only seconds to a few minutes. If you need to drink oral contrast first, plan for extra waiting time before the scan. See [link: How Long Does a CT Scan Take?].
Radiation: what you should know
CT uses x-rays, so it involves a dose of radiation that varies by exam. There is no conclusive evidence that the small amounts used in a CT scan cause cancer, but because larger doses slightly increase cancer risk, CT is used only when the expected benefit outweighs the potential risk. No radiation stays in your body after the scan. Children are more sensitive to radiation, so their scans use low-dose techniques and are done only when necessary. For numbers and comparisons, see [link: How Much Radiation Is in a CT Scan?].
Breastfeeding after IV contrast
Contrast manufacturers advise pausing breastfeeding for 24 to 48 hours, but the American College of Radiology reports that the amount of contrast reaching the baby is extremely low. See [link: Breastfeeding After Contrast].
Getting your results
A radiologist analyzes the images and sends an official report to the doctor who ordered the scan, who will explain the results. Sometimes a follow-up exam is needed to look more closely at a finding or to check for changes over time.
Tips from the technologist
[TU EXPERIENCIA: 3-4 consejos propios para el TAC. Ideas: avisar de alergias aunque sean leves, practicar la apnea antes, no asustarse con la sensación de orinarse, beber agua después.]
Frequently asked questions
Does a CT scan hurt?
No. The scan is painless. The IV for contrast feels like a pin prick, and some people find it uncomfortable to stay still for several minutes.
Is a CT scan claustrophobic?
Usually not. The CT ring is short and open, very different from the long tube of an MRI. See [link: CT Scan vs MRI].
Why do I feel like I peed during a CT scan?
It is a common, harmless sensation caused by the IV contrast. It passes within moments.
Can I drive after a CT scan?
Yes, unless you were given a sedative.
Can I have a CT scan with a pacemaker or metal implant?
Yes. Implanted devices do not prevent a CT scan, although metal can affect the images near it.
How much does a CT scan cost?
It depends on the body part, contrast and your insurance. See [link: How Much Does a CT Scan Cost Without Insurance?].
This article is for general information and does not replace advice from your doctor or imaging team.