Difference in CT Scan vs MRI

Difference in CT Scan vs MRI

CT Scan vs MRI

CT Scan vs MRI: CT scans and MRIs are both used to capture images within your body. The biggest difference is that MRIs (magnetic resonance imaging) use radio waves and CT (computed tomography) scans use X-rays.

While both are relatively low risk, there are differences that may make each one a better option depending on the circumstances.

CT Scan vs MRI
CT Scan vs MRI

What are CT scans?

A CT scan is a form of X-raying that involves a large X-ray machine. CT scans are sometimes called CAT scans. A CT scan is typically used for:

  • bone fractures
  • tumors
  • cancer monitoring
  • finding internal bleeding

During a CT scan, you’ll be asked to lie down on a table. The table then moves through the CT scan to take cross-sectional pictures inside your body.

What are MRIs?

Using radio waves and magnets, MRIs are used to view objects inside your body. They’re frequently used to diagnose issues with your:

  • joints
  • brain
  • wrists
  • ankles
  • breasts
  • heart
  • blood vessels

A constant magnetic field and radio frequencies bounce off of the fat and water molecules in your body. Radio waves are transmitted to a receiver in the machine which is translated into an image of the body that can be used to diagnose issues.

CT Scan vs MRI Radiation Level | Time Taken

CT, which is short for computerized tomography, uses x-ray technology to produce diagnostic images. These x-rays require a small dose of ionizing radiation. Basically, the CT scanner rotates on an axis, taking multiple 2D images of a person’s body from different angles. When a computer places all of these cross-sectional images together on a monitor, the result is a 3D image of the inside of the body that can reveal the presence of disease or injury to a physician.

CT Scan vs MRI Radiation Level | Time Taken 
CT Scan vs MRI Radiation Level | Time Taken

MRI scans do not work this way. Instead of using ionizing radiation, magnetic resonance imaging (MRI) uses radio waves and powerful magnets to produce diagnostic images. An MRI scanner can apply a magnetic field that lines up all of your body’s protons. Radio waves are applied to these protons in short bursts, which in turn relate a signal that is picked up by the MRI scanner. A computer processes this signal and generates a 3D image of the segment of the body being examined.

CT scans typically take diagnostic images more quickly than MRI scans. For example, a CT scan can often be completed in less than 5 minutes while MRIs take an average of 30 minutes.

Safty Measurement CT Scan vs MRI

In general, both CT and MRI scans are relatively safe. However, there can be problems. MRI scans should not be done on patients that have aneurysm clips (clips of the vessels within the brain) unless these clips are known to be MRI safe, as these clips can be pulled off and the patient could die from bleeding into the brain.

Another problem with the MRI is the presence of some cardiac pacemakers or defibrillators because the magnets can cause malfunctions in these battery-operated devices. Any metal devices that can interact with a magnetic field, for example, the presence of metal shavings in an organ, the eye, or extremity may be pulled out by the magnetic field. Moreover, other canisters that are metal (like some oxygen tanks) need to be kept away from MRI machines because they can be attracted to the magnet and injure or kill the patient.

CT scans do not have these problems; however, they do expose the patient to radiation, though it’s a relatively low dose. Certain types of CT scan may not be appropriate during pregnancy.

Uses for CT Scan vs MRI

  • Abdominal pain – CT is the preferred test. It is more readily available on an emergency basis and is very accurate. Ultrasound is used for children and pregnant women.
  • Trauma – CT is present in most emergency departments and is the best at showing bone fractures, blood and organ injury.
  • Spine – MRI is best at imaging the spinal cord and nerves.
  • Brain – CT is used when speed is important, as in trauma and stroke. MRI is best when the images need to be very detailed, looking for cancer, causes of dementia or neurological diseases, or looking at places where bone might interfere.
  • Chest – CT is much better at examining lung tissue and often used for follow up on abnormal chest x-rays. Low dose CT Scans are available and used with high-risk smokers who need to be screened annually.
  • Joints – MRI is best at showing tendons and ligaments.

Your doctor will explain the choice of test, and he or she will consult with the RAF radiologist and MIF technologists to ensure that the imaging meets your needs. Both types of scan can help determine the source of your problem and get you closer to a solution.

Considerations for the cost of different imaging studies are an important element in planning for imaging studies. There are differences in the costs for these studies based on where they are completed as well as differences in the quality of radiology and staff support. It pays to compare these factors before completing either MRI or CT imaging. An imaging study completed in a location outside the major metropolitan area could create big cost savings with the study shared digitally with whatever medical professionals are providing care.

CT Scan vs MRI Risks

CT Scan

  • The patient will be exposed to radiation when undergoing a CT scan. However, it is a safe level.
  • The biggest potential risk is with a contrast (also called dye) injection that is sometimes used in CT scanning. This contrast can help distinguish normal tissues from abnormal tissues. It also helps to help distinguish blood vessels from other structures such as lymph nodes. Like any medication, some people can have a serious allergic reaction to the contrast. The chance of a fatal reaction to the contrast is about 1 in 100,000. Those at increased risk may require special pretreatment and should have the test in a hospital setting. Anyone who has had a prior contrast reaction or severe allergic reaction to other medications, has asthmaor emphysema, or has severe heart disease is at increased risk for a contrast reaction and is referred to a hospital X-ray department for the exam. Besides an allergic reaction, the intravenous dye can damage the kidneys, particularly if an individual already has marginal kidney disease. Usually, the patient is advised to drink plenty of fluids to help flush the dye out of their system.
  • Any time an injection is done into a vein, there is a risk of the contrast leaking outside of the vein under the skin. If a large amount of contrast leaks under the skin, in rare cases, this can cause the skin to break down.


  • People with any metal on or in their bodies should tell the technologist. Most people who have metal in their body after surgery can have an MRI. For example, people with hip or knee replacements can have an MRI as soon as 6 weeks after surgery. Other implanted devices require less time after surgery.
  • Certain devices (heart pacemakers, some implanted pumps, and nerve stimulators) can never go into the MRI machine, as they may malfunction or become damaged. Some brain aneurysm clips also cannot go into the scanner.
  • People who have had prior surgery must inform the technologist prior to the scan. Also, if metal might be in any part of the body from a prior injury or accident, people must inform the technologist prior to the scan. Certain people should not be scanned. For example, in a rare case, one person went blind from being scanned because he had metal in his eye from a welding injury.
  • Some MRI exams require an injection of an MRI contrast or dye. This MRI contrast or dye is very safe and is completely different from the contrast agent or dye used for imaging tests using X-rays, such as an intravenous pyelogram (IVP) or a CT scan. Allergic reactions to the contrast used are possible but extremely uncommon. The doctor and the MRI technologist should be informed beforehand of any allergies.
  • An MRI has no known side effects on pregnancy. Most centers will scan pregnantwomen in their second and third trimesters.


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