Using a CT vs. MRI - Primary Differences and Use Cases

CT vs MRI: What’s the Difference?

The ability to see within a patient's body allows doctors to more accurately diagnose certain diseases or conditions. This ability can be gained through specific technology, such as CT (computed tomography) scanner or MRI (magnetic resonance imaging) machines. Although both CTs and MRIs are diagnostic imaging tools that share a lot in common (the machines themselves are very similar looking), there are some major differences between the two. Knowing what the differences are will make it easier for you to decide between the two if your hospital is looking to invest in new diagnostic imaging technology.

​Primary Differences Between CTs and MRIs

Although the basic purpose of a CT and an MRI are the same in that they allow doctors to record diagnostic images of their patients, the process in which they capture those images is very different. The following are the different diagnostic imaging processes used by CT scanners and MRI machines.

CT Scan

CT scanners make use of x-ray technology to capture images of a patient's internal organs and structures. The machine works by focusing a narrow beam of X-rays at the patient, which is then rotated around the patient's body to generate cross-sectioned images, which are called tomographic images.

These tomographic images offer more detail than what a conventional X-ray can provide. The tomographic images are combined by the computer to create a 3-D image, thereby making it easier for the doctor to pinpoint any abnormalities in the patient's internal organs or structures.

MRI

Unlike CT scans, MRIs do not make use of X-rays to record diagnostic images. Instead, it makes use of high-powered magnets. Like a CT scanner, the patient lies on their back and is inserted through a tube-like opening into the machine. While the patient is inside, a strong magnetic field will be produced while radio waves are directed at the patient's body. During the procedure, the magnetic field produced by the MRI will cause the water molecules in the body of the patient to be aligned. This will cause the protons inside of the water molecules to absorb the energy produced by the magnetic field. Once this happens, the spin of the protons will be flipped.

When the magnetic field is shut off, the protons will return to their normal spin. This return process will produce a radio signal the MRI scanner's receivers will measure and which will be formed into the image.

Are There Safety Concerns With CT Scans?

One of the concerns some people have in regards to CT scans is that it requires patients to be exposed to X-rays, which are radioactive. However, the radiation patients are exposed to when they undergo a CT scan is relatively minimal. Generally, a patient will be exposed to around two to 10 mSV (the measurement for radiation doses), which is about the equivalent to the background radiation a normal person will experience in three to five years.

While the radiation produced by a CT scan shouldn't affect the patient, it's not recommended for pregnant women or children since any amount of radiation exposure could affect a developing fetus or child. Unlike CT scans, MRI machines do not expose patients to any kind of radiation whatsoever.

Differences in Costs

When deciding between CT scanners and MRI machines, the cost is an important factor. Both of these types of machines vary in cost depending on many factors. For example, there are several different types of MRI machines and they can be equipped with different sized magnets--the bigger the magnet, the more expensive it is.

CT scanners cost anywhere from $100,000 for an older refurbished model to several hundred thousand for a high-end model. MRI machines can cost as much as $3 million. You'll also need to take into consideration the cost of installing and maintaining these machines. The bigger they are, the more costly they'll be to both install and maintain. You can expect to pay somewhere between $50,000 and  $100,000 a year to maintain either type of machine. Installation is typically included in the purchase price.

One big difference is that MRI machines have to be installed in a closed off area because the magnetic fields it produces could affect certain devices, including pacemakers.

Besides the initial and ongoing costs to the hospital, take into consideration what a CT scan or MRI scan costs your patients. CT scans tend to be a bit cheaper. Without insurance, they cost between $1,200 and $3,200, whereas MRI cost between $1,200 and $4,000. The cost depends heavily on what part  (or parts) of the body is being scanned.

CT vs MRI: When is Each Scan Better?

One of the major factors to consider when choosing between a CT scanner and an MRI machine is what you plan to use them for. This depends greatly on the types of patients you tend to see and treat. Although both machines are diagnostic imaging tools, they are used for different reasons.

Use Cases for When CT Scan is Better

The following are a few situations in which a CT scanner performs better than an MRI machine:

• CT scanners can capture diagnostic images of the patient within as little as five minutes, whereas MRI machines usually take around 30 minutes or longer to scan. Because of how quickly a doctor can obtain diagnostic images of a patient using a CT scan, CT machines are commonly used in emergency rooms where time is of the essence.
• CT scanners don't cause problems when it comes to patients that have pacemakers or that have any metal in their bodies. Such patients will have issues getting an MRI.
• CT scanners outline bone inside of the patient's body extremely accurately, which is why CT scans are particularly useful for detecting bone injuries, such as fractures.
• CT scans are frequently used to detect cancer. They are also commonly used for lung and chest imaging.

Use Cases for When MRI is Better

The following are a few of the uses for which an MRI machine is superior to a CT scan:

• MRI scans are extremely effective at recording images of the brain, which is why they are more often used to look for abnormalities of the brain, such as tumors, bleeding, and swelling. MRI scans will often be ordered if a patient has experienced trauma to the head.
• MRI machines offer a precise look at the heart, allowing doctors to look for certain heart conditions, such as tears, aneurysms, and other heart-related defects.
• MRI machines allow for a clearer picture of the patient's spine. Not only does this make it easier for doctors to examine a patient's spinal cord for inflammation or tumors, but surgeons will often make use of MRI scans to evaluate the potential damage following serious trauma caused by a sports injury or a car accident.
• In general, MRI scans are useful for viewing soft tissue, such as tendons and ligaments, allowing doctors to identify injuries such as strains and tears.

Which Machine Is Better?

MRI machines and CT scanners both offer many pros and cons. CT scanners are less expensive, but they do expose patients to radiation. MRI machines can examine a larger variety of medical conditions, but the process takes longer. The most important factor is your diagnostic imaging need -- what types of patients do you tend to see and under what kind of situation are you seeing them? Both machines are extremely effective solutions to specific diagnostic imaging needs despite some of their drawbacks, which is why they both have a place within the medical industry.