What Is The Difference Between MRI and CT Scans?

4 min read

is cat scan and mri the same

As patients, most tend to agree on tests and procedures without sufficient knowledge — and the common question is, is there a difference between MRI and CT scans?

Some may think that knowledge as a patient is unnecessary, but that is quite debatable. For utmost safety and disclosure, a patient should know the details of procedures that will be conducted on them.

Going back, the answer is yes. The two techniques are different in many, many ways, such as their mechanics, common uses, risks, and safety measures. Read more to find out which one you should to opt for as a patient, and why.

Define: Medical Imaging

Among the many differences, a similarity between an MRI and a CT scan is their purpose in medical imaging.

Without physically opening up a body, medical imaging allows practitioners to view the internal structures in the body. The essential process typically aids diagnosis of a condition, surgical planning, and therapeutic purposes.

Apart from CT and MRI, doctors have ultrasound, X-ray, PET scan, and more, as medical imaging techniques.

With that settled, let us have a look at their differences.

How Do They Work?

Magnetic resonance imaging, or MRI, functions with a magnetic field created by strong magnets. In your body, the magnetic field causes the hydrogen atoms to align in the same direction. And as the scan occurs on a certain body part, the radio waves move these atoms out of their original alignment.

Once radio waves turn off and the hydrogen atoms realign, the generated radio signals transmit to the receiver. Lastly, the computer or device gathers information to create MRI images or scans of the internal structures within you body.

Next, CT stands for computed tomography, also known as the CAT scan. Hence its name, the scan utilises a combination of digital computer technology and X-rays in order to generate two or three-dimensional images of your internal structures.

Difference Between MRI & CT Uses

Apart from their difference in mechanics and technology, their common uses distinguish the two medical imaging methods between one another.


When your doctor opts for an MRI, they aim to diagnose within these body parts:

  • Brain and spinal cord
  • Breasts
  • Internal organs: liver, prostate gland, womb
  • Joint injury or condition
  • Internal organ damage
  • Bones and joints: ankles, wrist
  • Heart and blood vessels:
  • Tumours
  • Soft tissue injury

CT Scan

Between CT and MRI, there are a number of overlaps in terms of uses. For CT scans, the common parts are tumors, internal bleeding, bone fractures, cancer development, and response to cancer treatment.

In addition to these, it is also used for:

  • Assessment: body part structure or shape
  • Diagnosis: disease (especially vascular, cancer), trauma, injury
  • Plan: surgeries, radiotherapy
  • Visual aid: radiotherapy administration, interventional procedures (biopsy or needle aspiration)
  • Measurement of bone strength
  • Alternative to exploratory or diagnostic surgery

Read: What Do MRI Results Show?

What is the Procedure for Both?

For additional preparation, here is the step-by-step procedure for CT scans.

  1. Before the scan, your doctor may ask you to drink an oral contrast agent. If not, the first step is to wear a hospital gown and remove all metal objects from your body. Then you lie down on the scanner table, with or without straps and pillows for optimal positioning.
  2. Your radiographer may inject an intravenous injection of iodinated contrast medium or dye.
  3. As the table slides into the circular hole, it can continue moving depending on the area of concern.
  4. As they capture images, the ring moves in a circle around you, which lasts less than a second per revolution.
  5. Staying very still is very important as movement causes blur. Similar to the MRI, they may ask you to hold your breath. Note: The scanner usually makes clicks and buzzes.
  6. The whole procedure can take a few minutes to 30 minutes or more.

If you wish to mentally prepare before your MRI, this is the step-by-step procedure for patients.

  1. Change into the provided hospital gown and lie down on the table. This table will be slid into the tunnel-looking MRI scanner. The scope of the scanner depends on the area of concern.
  2. Table does not move during the scan and no physical contact will be made. However, some patients claim to feel warm during the scan.
  3. Through the intercom, you may talk to the present staff. For those feeling claustrophobic or unwell, you can press the panic button if present.
  4. As the machine can be loud, provided earplugs or headphones with music protect your hearing and provide comfort.
  5. Prior to the scan, your doctor can disclose that a contrast medium or dye needs to be injected, such as gadolinium. Additionally, they may ask you to hold your breath for some images.
  6. Once they have sufficient images, the table slides out and you are all done.

Different Risks & Safety Between MRI and CT

To start off, both medical imaging techniques are very safe for patients. However, there are additional safety measures and reminders to remember.


As an MRI can last for up to 2 hours, the confined space and loud noise can disturb patients. If this is a problem for you, your doctor may suggest medication or you can bring devices to listen to music during the scan.

Some patients cannot have MRIs, specifically those with implants due to the magnets of the scanner. Please inform your doctor if you have a/an: aneurysm clip, neurostimulator, metal fragment in the eye, magnetic dental implant, pacemaker, heart valve replacement, cochlear implant, meal foreign bodies and/or drug infusion pump. If you have any implants, let your doctor know as soon as possible in order to suggest alternatives.

As tiny metal particles can harm you, patients cannot wear makeup or hairspray. Additionally, some patients ingest a contrast agent which some patients are allergic to.

Lastly, please disclose pregnancy to your doctor for your safety.

CT Scan

For some patients, they can feel nauseous after the injection of contrast agent. And in rare cases, a patient can experience an allergic reaction in the form of a rash or itchiness. If you’ve experienced an allergic reaction to a contrast agent, please let your doctor know.

In terms of radiation, X-rays show links to cancer. CT scans should only be conducted on specific areas of concern to minimise risks as it produces more radiation than other medical imaging techniques. Ultimately, the scan should only be conducted when medically necessary.

Lastly, the radiation can harm an unborn baby, therefore, you must inform your doctor immediately about known and possible pregnancy.

what does mri stand for

Which Process Should I Do?

Depending on your concern and present symptoms, the doctors recommend which medical imaging method suits your case best. Apart from these two factors, a patient’s health status affects your doctor’s recommendation. These include implants, pregnancy, previous scans, allergies, and more.

In essence, for a safe, accurate outcome, disclose any relevant information to your doctor.

For any additional questions, please visit AskDoc or virtually consult with a general practitioner today though Clinica Finder.

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