A body scan is any medical imaging procedure that creates pictures of the inside of your body to check for disease, injury, or changes in body composition. The term covers several different technologies, from CT scans that take less than a minute to MRI scans that can last 30 minutes or more, each suited to different parts of the body and different diagnostic goals. Which type you get depends on what your doctor is looking for, or in some cases, what you’re choosing to screen for on your own.
Types of Medical Body Scans
Several imaging technologies fall under the umbrella of “body scan,” and they work in fundamentally different ways.
CT (computed tomography) scan: A CT scan uses X-ray beams that rotate around your entire body to build a 3D picture. It’s fast, often completed in under a minute, which makes it especially valuable in emergency settings where doctors need to quickly identify life-threatening conditions like internal bleeding or blood clots. CT scans are good at visualizing bones, organs, and many soft tissues. The radiation dose for a diagnostic CT typically falls between 1 and 10 millisieverts (mSv), depending on which body part is scanned. A chest CT delivers around 7 mSv, while an abdominal CT runs about 8 mSv.
MRI (magnetic resonance imaging): Instead of radiation, MRI uses strong magnets and radio waves that interact with water molecules in your tissues. This makes it particularly good at imaging soft tissue like muscles, tendons, and blood vessels. MRI can also show how the body is functioning in real time, measuring blood flow through vessels to detect small blockages or heart defects. The tradeoff is time: MRI scans take significantly longer than CT scans, and the machine is loud and enclosed, which can be uncomfortable.
PET (positron emission tomography) scan: PET scans work differently from both CT and MRI. You’re injected with a radioactive sugar that travels through your bloodstream. Cancer cells burn through glucose faster than normal cells, so they absorb more of the tracer and light up brighter on the scan. This makes PET scanning especially useful for detecting cancerous tumors that might be missed by CT or MRI alone.
Ultrasound: Ultrasound sends sound waves into the body and creates images based on how different tissues reflect those waves. It involves no radiation, which is one reason it’s the standard for monitoring a developing baby. It’s also used to examine the heart and other organs.
DEXA scan: A DEXA (dual-energy X-ray absorptiometry) scan is a specialized body scan that measures bone density and body composition. It uses two levels of X-ray energy to separate your body into fat mass, lean mass, and bone mineral mass. The procedure takes about 15 to 20 minutes and uses very low radiation. DEXA is the gold standard for diagnosing osteoporosis and is also used by people who want precise body composition data beyond what a bathroom scale provides.
Diagnostic Scans vs. Elective Screening
There’s an important distinction between a body scan ordered because you have symptoms and one you choose to get as a preventive measure. When a doctor orders a CT or MRI because of specific symptoms, a known risk factor, or a suspicious finding on another test, the scan has a clear target. The radiologist knows what to look for, and the results guide a treatment plan.
Elective full-body scans are a different situation. These are scans you pay for out of pocket, typically marketed as a way to catch problems before symptoms appear. Full-body MRIs generally provide excellent resolution of organs and can detect cancers, infections, inflammatory conditions, and vascular problems like blood vessel blockages. However, they have blind spots. MRI doesn’t work well for lung screening because breathing motion and air interfere with the image quality.
The American College of Radiology does not currently recommend total body screening for people with no symptoms, risk factors, or family history suggesting disease. Their concern is twofold: there’s no documented evidence that full-body screening extends life, and these scans frequently turn up non-specific findings that don’t ultimately affect your health but do trigger expensive follow-up testing, additional imaging, and sometimes invasive procedures to investigate something that turns out to be harmless. Doctors call these “incidental findings,” and they’re surprisingly common when you scan an entire body without a specific question in mind.
What to Expect Before and During a Scan
Preparation varies by scan type. For a standard CT scan without contrast dye, there’s generally no fasting required. If your scan involves contrast (a dye injected into your veins or swallowed to make certain structures show up more clearly), you’ll typically need to stop eating about two and a half hours beforehand. Clear liquids like water, black coffee, or apple juice are usually fine up to two hours before. If you’ve ever had a reaction to contrast dye or have an iodine allergy, let your care team know ahead of time.
For a PET scan, the radioactive tracer is injected through an IV, and you’ll wait while it circulates through your body before the scan begins. You’ll likely be asked to avoid strenuous exercise and limit sugar intake in the hours before the appointment, since the tracer is a sugar molecule and you want cancer cells, not your muscles, absorbing it.
MRI requires you to remove all metal, including jewelry, belt buckles, and sometimes even clothing with metal zippers. If you have metal implants, a pacemaker, or any metallic foreign bodies in your body, tell the imaging team beforehand, as the powerful magnets can interact with metal in dangerous ways. The scan itself involves lying still inside a narrow tube while the machine produces loud knocking and buzzing sounds. Most facilities offer earplugs or headphones.
Body Composition Scans
Not all body scans look for disease. DEXA scans and bioelectrical impedance analysis (BIA) are used to measure body composition: how much of your weight is fat, how much is muscle, and how much is bone. DEXA is the more accurate of the two. BIA, which works by sending a small electrical current through your body and measuring resistance (the technology built into many smart scales), tends to underestimate fat mass by about 1.8 kg and overestimate lean mass by about 2.5 kg compared to DEXA. The two methods are highly correlated overall, with a concordance of 0.94, meaning BIA tracks the right direction but isn’t as precise for individual measurements.
DEXA is particularly useful if you’re tracking changes in body composition over time, whether for athletic training, weight loss, or monitoring bone density as you age. Because it distinguishes between bone mineral, lean tissue, and fat at a regional level (arms, legs, trunk), it gives a much richer picture than body weight or BMI alone.
Cost and Insurance
When a body scan is ordered by a doctor for a specific medical reason, insurance typically covers it, and you’ll pay your normal copay or deductible. Elective scans are a different story. Because they’re not medically indicated, insurance rarely covers them, and the out-of-pocket cost varies widely.
A full-body MRI typically runs between $2,000 and $2,500 at most facilities, though some newer services offer abbreviated versions for around $1,350. Whole-body CT scans range from $500 to $3,000 depending on the provider and location. A DEXA scan is far more affordable, generally between $40 and $300. If you’re considering an elective scan, factor in not just the scan cost but the potential cost of follow-up tests if something ambiguous shows up, since those additional workups can be substantial.