CAT Scans vs MRIs. What’s the Difference?


CAT scans and MRIs are both medical imaging techniques used to visualize the internal structures of the body. However, they use different technologies to create these images. The purpose of this article is to highlight the key similarities and differences between CAT scans and MRIs, looking at how they work, their uses, risks, and costs. This will help readers understand when one method may be preferred over the other.


Definition of a CAT Scan

CAT scan stands for computed axial tomography scan. It is also known as computed tomography or CT scan. A CAT scan is a medical imaging test that uses a combination of X-rays and computing technology to produce detailed images of structures inside the body (Mayo Clinic, 2022).

During a CAT scan, the patient lies on a table that slides into a large donut-shaped machine. X-rays are taken at different angles around the body and a computer processes the images to generate cross-sectional views or “slices” of the inside of the body. This allows doctors to see more detailed images of organs, bones, soft tissues and blood vessels compared to a regular X-ray (WebMD, 2023).

The images generated by a CAT scan allow doctors to examine the body for various medical conditions and detect issues such as tumors, blood clots, head injuries, internal bleeding or organ damage (Mayo Clinic, 2022). It provides more detailed images than regular X-rays or ultrasound.

Definition of an MRI

MRI stands for magnetic resonance imaging. An MRI scan uses magnetic fields and radio waves to create detailed images of the inside of the body (Mayo Clinic, 2022). When getting an MRI scan, the patient lies inside a large tube-shaped scanner that generates a strong magnetic field. The magnetic field causes hydrogen atoms in the body’s cells to line up in one direction. Next, radio waves are directed at the lined-up atoms, causing them to produce faint signals that are detected by the scanner. The scanner builds up a detailed picture of the area being scanned based on these signals (Hopkins Medicine, 2022).

MRIs create very clear, cross-sectional images of the body. They allow doctors to see organs, soft tissues, bone and other internal body structures without using radiation like X-rays or CT scans (Mayo Clinic, 2022).

Key Similarities

Both CAT scans and MRIs are medical imaging techniques that allow doctors to see inside the human body without performing surgery. This allows images of organs, bones, and tissues to be obtained in a non-invasive manner.

Another key similarity is that neither CAT scans nor MRIs use ionizing radiation like X-rays or CT scans. This makes them safer diagnostic tools, especially for repeated imaging. Both techniques rely on sophisticated technology and computer processing to generate cross-sectional images of the body.

Overall, the main similarities are that CAT scans and MRIs are non-invasive imaging techniques that do not use harmful ionizing radiation. This allows key insights into the body’s internal structures without surgery or radiation exposure.

Key Differences

The main differences between CAT scans and MRIs are in how they work and what they can detect. A CAT scan, also called a CT scan, uses X-rays to take pictures of the inside of the body from different angles. An MRI, on the other hand, uses strong magnetic fields and radio waves to produce detailed images of organs and tissues.

Some key differences include:

  • CAT scans use radiation while MRIs do not.
  • MRIs provide more detailed soft tissue imaging while CAT scans are better for examining bones.
  • CAT scans are faster, taking just minutes, while an MRI can take up to an hour.
  • MRIs are more expensive on average.
  • CAT scans are preferred for abdominal scans while MRIs are better for neurological scans.

In summary, the choice between having a CAT scan versus an MRI depends on the specific body part being examined as well as considerations like cost and scan time. Doctors will determine which test is most appropriate based on the medical need and goals of the imaging exam.

Use Cases for CAT Scans

CAT scans, also known as CT scans or computed tomography scans, are particularly useful for getting images of bones, fractures, and dental issues in the body (source 1). The X-rays used in CT scans are able to penetrate bone and provide clear, detailed images that can help doctors diagnose and treat bone-related conditions.

Some common use cases for CT scans related to bones and fractures include (source 2):

  • Identifying the presence and extent of fractures
  • Locating bone fragments from traumatic injuries
  • Diagnosing osteoporosis
  • Detecting bone cancer
  • Guiding treatments and procedures on bones

In addition, CT scans are frequently used in dentistry to evaluate issues like impacted teeth, tumors, cysts, infections, and temporomandibular joint disorders (source 3).

Compared to MRI scans, CT scans have a much faster imaging time, taking just seconds to minutes to complete. This makes them well-suited for situations where a quick scan is needed, such as emergency medicine.

Use Cases for MRIs

MRIs are often the imaging test of choice when looking at soft tissues in the body. According to the source When is MRI Appropriate?, MRIs provide more detailed images than X-rays, ultrasounds, or CT scans when examining soft tissues like the brain and spinal cord, joints, tumors, etc. This is because MRIs utilize strong magnetic fields and radio waves to generate images, providing excellent contrast between the different soft tissues of the body. For example, MRIs can detect subtle changes in the brain associated with multiple sclerosis, tumors, stroke, or other conditions that may not show up well on other scans.

MRIs are also frequently used to examine joints and the spinal cord because they allow physicians to see soft tissue structures like ligaments, tendons, and spinal nerve roots in great detail. This detailed visualization aids in diagnosing back pain, sports injuries, arthritis, and more. Overall, MRIs excel at providing highly detailed images of soft tissues throughout the body, making them the preferred choice for evaluating many soft tissue structures and pathologies compared to other imaging modalities.

Risks and Side Effects

One of the key differences between CAT scans and MRIs are the potential risks and side effects. CAT scans expose patients to ionizing radiation from the X-ray beams used to generate images. There is some evidence that repeated CAT scans over time may slightly increase cancer risk, especially in children ( The amount of radiation exposure from a single scan is generally low, but the risks add up with multiple scans.

In contrast, MRIs use strong magnetic fields and radio waves to generate images, so they do not involve ionizing radiation. This eliminates the cancer risks associated with CAT scans. However, the MRI machine itself can cause certain side effects. Some patients experience claustrophobia from being inside the enclosed MRI scanner. The noise from the MRI scanner can also be uncomfortable. Additionally, patients with metal implants or pacemakers may not be suitable candidates for MRIs since the magnetic fields can interfere with those devices (

Cost Difference

CAT scans are generally less expensive than MRIs. According to DocPanel, the average CT scan costs around $1,200 while an MRI is about $2,000. MedicineNet confirms this, stating that a CT scan costs about half as much as an MRI. One reason for the price difference is that CT scanners are more widely available and have been used for longer than MRI machines.

Since CT scans use X-rays while MRIs use strong magnetic fields and radio waves, the technology behind MRIs is more complex. This accounts for some of the increased costs. However, both tests are typically covered by insurance when medically necessary.


Overall, CAT scans and MRIs offer different technologies to produce detailed images of the inside of the body that can assist in detecting, diagnosing, and monitoring health conditions. While the imaging tests have some similarities, their key differences make certain scans better suited for particular medical uses.

CAT scans provide faster imaging and are generally preferred for examining bones, blood vessels, and detecting issues like injuries, infections, tumors, and bleeding in the brain. The ionizing radiation does carry some risks, so CAT scans may not be ideal for pregnant women or repeated screening.

MRIs utilize magnetic fields and radio waves, avoiding radiation exposure. The longer scan times and motion artifacts make them less ideal for trauma imaging. However, MRIs produce superior soft tissue contrast, making them preferable for examining organs, ligaments, the spinal cord and brain.

Ultimately, medical imaging should be determined by a doctor based on a patient’s specific symptoms and medical history. While weighing the pros and cons of each technology, they can make the most informed decision on which scan will provide maximum diagnostic value.

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