CT vs MRI Scan - What Is the Difference?

The key difference between an MRI and a CT scan is that MRIs use strong magnetic fields in order to produce images, while CT scans use radiation. While many people are wary of radiation, CT scans are still quite safe and sometimes are a better choice than MRIs for people with certain contraindications. 

What is a CT scan?

A CT scan, sometimes called a CAT scan, is a computerized imaging procedure that uses X-ray technology. These scans generate cross-sectional images of the body and internal organs by using X-ray beams.

CT scans visualize all parts of the body to diagnose an injury or disease. The cross-sections show bones, blood vessels, and soft tissue. They can detect:

• Muscle and bone disorders
• Tumors
• Infections
• Blood clots
• Cancer
• Heart disease
• Lung nodules
• Liver mass
• Internal injuries
• Internal bleeding

CT scans can be ordered with or without contrast. In a CT scan with contrast, a dye is injected into the patient’s arm before the procedure begins. This helps the doctor better visualize internal structures. Procedures with contrast typically cost more than those without contrast.

During a CT scan, the patient lies down in a large tunnel-shaped machine. Inside, the machine rotates to take X-ray images of the body at different angles.

What is an MRI?

MRI, or magnetic resonance imaging, is a radiology scan that uses magnetic fields. It can take detailed three-dimensional, black-and-white images of tissue structures and organs within your body. Your doctor will read these images and explain what they mean to you in detail.

There are two main types of MRIs: closed MRIs and open. A closed MRI provides quick, accurate, and high-quality images of deep organ tissue. The patient lies down inside the scanner, making sure to keep still during the procedure. Due to the narrow size of the machine and loud noise, it can make some people feel claustrophobic.  

An open MRI provides lower-quality images than a closed MRI, but doctors have more control. In an open MRI, technicians are able to tilt the machine to get a better image. They also allow the patient to be in non-lying positions. Open MRIs may take longer than closed MRIs, but they emit less noise.

MRIs can also be taken with or without contrast, depending on what type of visualization is needed. These tests can take anywhere from 15 to 90 minutes, depending on the area being examined. In some cases, the test can take as long as 2 hours.

How do I know whether I need an MRI or a CT scan? 

CT vs MRI: which one is better for you? This ultimately depends on what area you are trying to take images of and for what purpose. If you are looking for general pictures of the inside of your body, CT scans would be the choice to make. If you need images that are clearer or if you have already received a CT scan with inconclusive results, an MRI scan may be more appropriate. While MRIs create images of a higher quality, that level of detail is not always needed. In these cases, a CT scan would be just as effective. This is a decision you should make during a consultation with a doctor. He or she can walk you through your possible diagnosis and weigh the pros and cons of each approach with you. Here are some reasons your provider may choose one scan over another: 

- CT scan vs MRI for the brain 

CT scans can be done very quickly. This can be advantageous in instances of traumatic brain injury, or other neurological emergencies that require immediate attention. However, an MRI can show soft tissue and other parts of your anatomy in much greater detail than a CT scan. There are several factors at play when determining whether to order a CT scan vs an MRI for the brain. 

- CT scan vs MRI for the abdomen

MRIs provide greater detail, and can detect many things that CT scans cannot. However, when deciding whether to get a CT scan vs an MRI for the abdomen, an MRI's use of strong magnets must be taken into account. People who have cardiac pacemakers, cochlear implants, shrapnel, artificial joints, or anything else that contains metal are not able to undergo an MRI procedure. 

- CT scan vs MRI for cancer 

Both types of scans are used to diagnose and monitor cancer, so how do you know when to use a CT scan vs an MRI for cancer? In general, MRIs are more adept at capturing fine detail and focusing on a specific organ. However, CT scans are often used to track the spread and diagnose the stage of cancer, since they can easily capture a whole-body image. 

- CT scan vs MRI for a brain tumor 

Doctors will order a CT scan vs an MRI for a brain tumor when they need to hone in on the bone structures near a tumor, like the skull or spinal column. Otherwise, MRIs are more frequently used to monitor brain tumors, as they can show soft tissue and blood flow more closely. 

Main differences between MRI & CT scans

While MRIs and CT scans share some similar uses, the way they produce images is quite different. CT scans use radiation, while MRIs use magnetic fields. CT scans are more commonly ordered, because they are more affordable while still providing adequate detail for most diagnoses. MRIs are used when doctors need more accurate, minute details of the body. MRIs are also usually used to diagnose issues with bones, organs, and joints.

Advantages of MRI scans vs CT scans

CT scans are typically less expensive and faster. CT scans are also safer for people with medically implanted devices, since they do not utilize magnetic fields. On the other hand, MRIs produce clearer images and can show abnormalities deep within tissues and organs.

Disadvantages of the two imaging methods

Each imaging method holds its own inherent risks and side effects. Here is how the two compare.

For MRIs, the risks include:

• Magnetic interference of medical devices or implants during the scan
• Overheating of medical implants that could cause burns
• Potential of increasing amniotic fluid
• Allergy to contrast dye
• Hearing issues due to loud noises from MRI machine
• Possible claustrophobia due to staying in an enclosed space during the scan

For CT scans, the risks are:

• Small amounts of radiation exposure
• Allergy to contrast dye
• Possible harm to unborn babies

CT scan vs MRI: which is safer?

There is no absolute answer to which one is safer. While CT scans do expose you to radiation, the dosage is low enough that the risk of developing cancer cannot be reliably measured. These tests are also quicker and easier for patients.

MRI scans use magnetic fields, which can be safer for patients who have a sensitivity towards radiation. However, it may not be the best option for people with medical implants. MRIs are also very loud and require you to be in an enclosed space for much longer than a CT scan. If you are claustrophobic and sensitive to loud sounds, MRIs might pose a problem for you.

Both CT scans and MRIs are linked to a higher life expectancy and declining cancer death rates. This is because they can discover and catch most abnormalities. They are also less invasive and safer than exploratory surgery.

What can an MRI scan & a CT scan detect

CT scans take images of a wide range of body parts:

• CT angiography takes images of blood vessels
• CT abdomen scans take images of the organs within the digestive tract
• CT bone scans detect fractures or other abnormalities within the bones
• Head CT scans capture images of the brain and surrounding tissue
• CT scans for chest/lungs take images of a patient’s lungs
• Cardiac CT scans also take pictures of the chest, but focus on the patient’s heart 
• Neck CT scans capture images of the area from the base of the skull to the top of the lungs
• Pelvic CT scans take pictures of the area inside the body between the hipbones
• Kidney CT scans take images of the kidneys
• Spine CT Scans take images of the discs between the bones and the soft tissue of the spinal column

MRI scans are ordered to diagnose problems in:

• Blood vessels
• Joints
• Wrists
• Ankles
• Brain
• Heart
• Spinal cord
• Liver
• Prostate
• Womb
• And many other regions

Finding a CT scan or MRI near you

Diagnostic imaging can be expensive, especially for the uninsured. Even if you have good coverage, you may have a high deductible, and could find yourself paying thousands of dollars out-of-pocket for an MRI or CT scan. If you're worried about how much an MRI costs without insurance, you can look for MRIs near you at Tripment Health, and find them for as little as $360. You can also use Tripment to find out how much a CT scan costs without insurance, and you may be surprised to find that you can get a CT scan through Tripment at a lower price than through your insurance company. With Tripment, you can search for MRIs and CT scans near you, with vetted, affordable doctors you can trust.