MRI vs. CT Scan: Which Imaging Test Does Your Doctor Actually Need?

When your doctor orders an imaging test, you might wonder why they chose one method over another. Advanced diagnostics help providers see inside your body to make accurate decisions about your health. While we specialize in targeted exams like a diagnostic ultrasound, understanding broader tools like MRIs and CT scans can help you feel more confident in your care. 

At Mass Medical Imaging in Lake Forest, Illinois, our experienced team, including Dr. Joseph Calandra, MD, and Dr. Karen Mass, MD, is dedicated to providing clear answers about your diagnostic options. We believe that well-informed patients make the best partners in healthcare.

What is a CT scan and how does it work?

A computed tomography (CT) scan combines a series of X-ray images taken from different angles around your body. According to the Cleveland Clinic (2025), a computer uses these X-rays to create highly detailed, three-dimensional views of your bones, organs, and soft tissues. 

Doctors often rely on CT scans because they are incredibly fast and highly detailed. In emergency situations like suspected strokes or head trauma, medical teams prioritize CT scans because they can quickly detect life-threatening issues like internal bleeding. This speed makes them invaluable in critical care settings.

How does an MRI differ from a CT scan?

Unlike CT scans, magnetic resonance imaging (MRI) does not use any radiation. Instead, it uses powerful magnets and radio waves to capture exceptionally clear, high-resolution images of your body's soft tissues, such as ligaments, muscles, and organs. 

Because MRIs do not expose you to radiation, they are often preferred for detailed soft-tissue evaluations when speed is not the primary concern. They are highly effective for examining delicate structures like joints and brain tissue. However, because CT scans do carry a small radiation risk, researchers at the National Institutes of Health (NIH, 2025) emphasize the importance of choosing the right test to avoid unnecessary cumulative exposure over your lifetime.

Can you get a CT scan if you have a shellfish allergy?

There is a common misconception that people with shellfish allergies cannot safely receive the contrast dye used during a CT scan. Fortunately, this is simply a myth that can cause unnecessary anxiety or delays in care. 

The Radiological Society of North America (RSNA, 2026) explains that it is impossible to be allergic to elemental iodine. Any rare adverse reactions to contrast dye are actually triggered by completely unrelated molecules, meaning a shellfish allergy does not prevent you from having a safe scan.

Choosing the right imaging test depends entirely on your specific symptoms, medical history, and what your doctor needs to see. Whether you need routine screenings or specialized diagnostic testing, our team is here to guide you through every step of the process. 

If you have questions about an upcoming imaging test or need to schedule an appointment, please contact Mass Medical Imaging in Lake Forest today.