Free Guide to CT Scan Procedures and Timing

What CT Scans Are and How They Work

A CT scan, also called a CAT scan (Computed Axial Tomography), is a medical imaging tool that takes detailed pictures of the inside of your body. Unlike a regular X-ray that creates a flat, two-dimensional image, a CT scanner rotates around you and takes many pictures from different angles. A computer then combines these pictures into thin cross-section images, almost like slicing through your body and looking at each layer.

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The CT scanner itself looks like a large donut or tunnel. You lie on a table that slides through the center of the machine while it rotates and takes images. The entire scan usually takes only a few seconds to a few minutes, depending on what part of your body is being scanned and whether contrast material is used.

CT scans are valuable because they show bones, soft tissues, and blood vessels all at once. Doctors use them to look for tumors, infections, internal bleeding, broken bones, kidney stones, and many other conditions. According to the American College of Radiology, CT imaging accounts for approximately 11% of all medical imaging procedures performed in the United States, with millions of scans performed annually.

The radiation dose from a CT scan varies depending on the type of scan and which body part is being examined. A chest CT scan typically involves a radiation dose of about 7 millisieverts (mSv), while an abdominal CT scan may be around 8 mSv. For comparison, the average person receives about 3 mSv of natural radiation exposure per year from sources like radon and cosmic radiation. Modern CT scanners use lower doses than older machines, and doctors weigh the benefits against risks when recommending this imaging.

Practical Takeaway: Understanding that CT scans create detailed cross-section images using X-rays and computers helps you know what to expect during the procedure and why your doctor might recommend one for specific medical concerns.

Types of CT Scans and Their Uses

Different types of CT scans focus on different areas of the body and serve different purposes. The most common types include chest CT scans, abdominal and pelvic CT scans, head and neck CT scans, and extremity CT scans (arms and legs). Each type provides specific information that helps doctors diagnose or monitor conditions.

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A chest CT scan examines the lungs, heart, and surrounding structures. Doctors order these to evaluate chest pain, shortness of breath, suspected pneumonia, lung nodules, or to monitor conditions like emphysema. A high-resolution CT of the chest can detect lung nodules as small as 2-3 millimeters, which is why it's valuable for detecting early signs of lung disease or cancer.

Abdominal and pelvic CT scans show the organs in your belly and lower abdomen, including the liver, kidneys, pancreas, stomach, intestines, and reproductive organs. These scans help doctors find causes of abdominal pain, evaluate for appendicitis or diverticulitis, detect tumors or cysts, and assess trauma injuries. They can also monitor how existing conditions are progressing.

Head and neck CT scans can show the brain, sinuses, inner ear, and neck structures. These are commonly used to evaluate severe headaches, possible strokes, head injuries, or sinus problems. CT angiography is a specialized type that focuses on blood vessels and is often used to check for blood clots or aneurysms. According to the Society of Interventional Radiology, CT angiography has a sensitivity of 94-98% for detecting pulmonary embolism, making it a standard diagnostic tool.

Some CT scans use contrast material—a special dye you either swallow or receive through an IV—to highlight certain structures and make them show up more clearly. This helps doctors see blood vessels, organs, and abnormalities better. Doctors decide whether contrast is needed based on what they're looking for.

Practical Takeaway: Knowing which type of CT scan is being performed and why your doctor ordered it helps you understand what medical questions are being answered and what you should prepare for.

Before Your CT Scan: Preparation Steps

Proper preparation ensures your CT scan produces clear images and helps the procedure go smoothly. The specific preparation needed depends on which part of your body is being scanned and whether contrast material will be used. Your doctor or the imaging facility will give you specific instructions, and it's important to follow them closely.

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For most CT scans, you'll be asked to wear comfortable, loose-fitting clothing without metal objects. Metal interferes with imaging quality, so you may need to change into a hospital gown. You should remove jewelry, eyeglasses, hearing aids, and any metal-containing items like piercings or hair clips before the scan begins.

If your scan involves contrast material, your preparation may be more involved. For abdominal CT scans, you might need to fast (not eat) for 4-6 hours before the scan. For pelvic CT scans, you may need to drink clear liquids the night before. Some facilities ask patients to take a mild laxative the evening before to clear the bowel of stool, which can interfere with image quality. Always ask your doctor whether you should continue taking your regular medications before a CT scan with contrast.

If you're receiving IV contrast, the facility will likely ask about your kidney function, as contrast material is processed through the kidneys. People with kidney disease or diabetes may need extra precautions. Tell your doctor or technologist if you're pregnant, as CT scans use radiation and alternative imaging like ultrasound or MRI may be preferred during pregnancy. Also mention any allergies, especially allergies to contrast material or iodine.

Arrive at the imaging facility 10-15 minutes early to complete paperwork and registration. Bring your insurance card and photo ID. If you have recent imaging from another facility that's relevant to your condition, bring those results or ask your doctor to send them ahead of time, as they provide comparison information.

Practical Takeaway: Following pre-scan instructions carefully—including fasting, removing metal objects, and reporting medical history—helps ensure your scan produces quality images and completes efficiently.

What Happens During a CT Scan

Understanding the steps during a CT scan helps reduce anxiety and lets you know what to expect. When you arrive at the imaging department, you'll check in and may wait briefly. A technologist will then take you to the scanning room and have you lie on the scanning table.

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The technologist will position you on the table based on what area is being scanned. For a chest scan, you'll lie on your back. For an abdominal scan, you'll typically lie on your back as well, though sometimes on your stomach. The technologist uses laser lights on the scanner to make sure you're positioned correctly. They may place pillows or straps to help you stay still and comfortable.

If you're receiving IV contrast, the technologist will insert an IV line into your arm before the scan. You may feel a cool sensation or taste contrast material in your mouth—this is normal. Some people experience a warm feeling spreading through their body, flushed skin, or a metallic taste. These reactions are usually brief and not harmful, but tell the technologist if you feel short of breath or have chest pain.

Once you're positioned, the technologist will leave the room and go to the control area. You'll hear the technologist's voice through an intercom explaining what's happening. The table will slide into the center of the scanner. The scanner ring will rotate around you, and you may hear clicking or humming sounds. The entire scanning process usually takes less than a minute for a single-body-part scan, though the whole appointment typically lasts 30-45 minutes when you include preparation and paperwork.

During the scan, you must remain very still because movement can blur the images. The technologist may ask you to hold your breath for a few seconds during certain parts of the scan. If you feel anxious or uncomfortable, you can use a call button to alert the technologist, though they can hear and speak with you at any time. Some facilities offer headphones so you can listen to music during the scan.

Practical Takeaway: Knowing that the procedure is quick, painless, and that you can communicate with the technologist at any time helps you stay calm and follow positioning instructions that ensure clear images.

Timing: How Long Does a CT Scan