Understanding The Difference Between MRI and CT

It definitely is not uncommon to walk into a doctor’s office for some sort of an appointment and not really understand what is going on. This is especially true in regards to undergoing specific procedures, especially if their functions tend to somewhat overlap. For instance, unless you clearly broke your leg and need an X-Ray, diagnosing a leg injury can be difficult. Maybe you cracked your femur, maybe you tore your ACL, or maybe you strained something. In order to figure out exactly what happened and what you need to do to better the injury, you must undergo certain procedures to see what happened to your body.

In such cases, as well as many others, the patient will undergo either an MRI or a CT scan. These procedures seem very similar on the surface, especially since they look almost identical. There is no need to ask why someone might not know the difference between the two, as they are very commonly confused. However, the difference is critical in determining the injury and the best means to recovery. So, it is important to understand what sets apart MRIs and CT scans. Let's take a look by first examining what exactly MRIs and CT scans are, and then how they are different.

What is an MRI?

MRI scans utilize very powerful magnetic fields and high-frequency radio waves in order to provide detailed images of various things inside a patient’s body. MRIs provide such detailed pictures by reading energy that is produced by water molecules after they re-align themselves following each pulse of radio waves.

What is a CT scan?

Unlike MRI scans, which use magnetic fields, CT scans utilize X-rays to provide details inside a patient’s body. CT scanners send X-ray beams through the patient’s body to the X-ray detector on the other side as the body moves through an arc-looking structure. While doing so, the CT scanner takes many pictures of what’s going on inside the body by comparing the strength of the beams, which are measured at about 1000 times per second.

Key Differences:

Primary Focus- One of the most significant differences between MRIs and CT scans is what they are typically used for, which, of course, is usually the determining factor for whether a patient would undergo an MRI or a CT scan, which is why understanding how a CT scan works versus an MRI is so crucial. MRIs provide very detailed images for soft tissue injuries due to how they function, so patient’s generally get MRIs for possible soft tissue injuries such as ones involving ligaments, tendons, spinal cord, brain tumors, etc. MRIs, however, cannot detect details regarding bone injuries because the lack of water in bones results in a black image where the bone is. On the other hand, CT scans are usually better for bone injuries, lung imaging, chest imaging, and cancer detection. So, depending on what the primary focus of your possible diagnosis, MRIs and CT scans might be of different help to you.

Accessibility- CT scans are more widely available than MRIs, but MRIs are also readily available to patient's just about anywhere. The difference in their accessibility might come down to price for some patients. A CT scan costs anywhere between $1500 and $3000, whereas an MRI can cost just over $4000 in some institutions. However, there is a reason for the price difference. CT scans are generally considered to be slightly more limited than MRIs in instances where the primary focus of the procedure does not distinguish between which machine would be better. Using X-ray to capture images, CT scans struggle to capture multiple, layered angles for more comprehensive imaging. So, often times when various angles are needed, patients receiving a CT scan must be repositioned. Contrarily, MRIs produce images using nearly every plane involved. While CT scanners might cause certain limitations regarding angles, MRIs cause certain limitations concerning implants. Patients with cardiac pacemakers, tattoos, and metal implants are sometimes unable to have the procedure due to the magnetism, whereas CT scanners can accommodate those patients.

Comfortability- While MRIs tend to be more versatile for the patient's needs, CT scans are definitely slightly advantaged in one category: patient comfortability. CT scans take a considerably shorter time than MRIs as they take about 5-10 minutes, including preparation time. MRIs, on the other hand, take between 30 and 90 minutes to capture the images alone. During that time, MRI patients are expected to remain still while the noisy machine performs its imaging. Many MRI patients could attest to the general discomfort, but it is not overwhelming. And, although CT scans are inarguably shorter and more comfortable, they are limited by size so heavier patients might prefer an MRI, especially when the patient's weight surpasses the 375-400-pound range.

Radiation Exposure- One of the significant differences between MRIs and CT scans that people typically find substantial is the difference in radiation exposure. While MRIs emit no radiation whatsoever, CT scans certainly do. CT scans emit an effective radiation dose of anywhere between 2 and 10 mSv. Such an amount is similar to the background radiation an average person is exposed to after 5 years of normal activity. Because of this, certain individuals, such as pregnant women, are very strongly advised not to undergo CT scans.

At the end of the day, your doctor is there to help you understand these differences as they are absolutely integral to following the best path for your injuries and issues. MRIs aren't better than CT scans and vice versa, they're simply just different procedures. However, doctors do not initiate conversations and discussions about whatever injury with patient's. Such a responsibility is on the patient, which is why we choose to go to the doctor's office. So, whether you want to know for the sake of knowing it or you actually want to know because you have a sore need and want to know the best approach moving forward, there is a critical difference between MRIs and CT scans. But, if you are not sure which procedure is best do not panic – your doctor should always be there to help you make sure you are taking the best course for whatever struggle you may be facing. So talk with your doctor about whether an MRI or a CT scan would be better for you and the conditions of your issue. 

Written by: Russell McBurnie