MRI Scan vs. CT Scan – What Are the Key Differences?

MRI Scan vs. CT Scan - What Are the Key Differences?

Modern imaging technologies have advanced beyond conventional X-ray services. Many patients ask about the significant differences between a CT scan and an MRI scan. Even though both machines look similar and scan and capture detailed images inside the body, the technology used and the details captured, are different. Radiologists use both these medical diagnostic scans to diagnose, detect, monitor and treat a variety of injuries and diseases. However, they accomplish this important task in very different ways. The type and severity of injury and the urgency of the condition determine which type of scan works best for the patient. When considering MRI scanning or CT scanning services in Queens, NY area, make sure you choose an American College of Radiology-certified clinic that uses state-of-the-art technology to produce high-quality images.

Magnetic Resonance Imaging (MRI) uses a powerful magnetic field and radiofrequency pulses to capture detailed images of soft tissue in the body and is used to evaluate tumors and cysts, diseases of the liver, bile ducts, gallbladder, and pancreas, certain types of heart problems and pelvic pain in women such as endometriosis. On the other hand, Computerized Axial Tomography (CT or CAT) scan uses X-ray technology to produce diagnostic images. The scanning is conducted to evaluate –

  • Trauma
  • Fractures or broken bones
  • Fever or pain of unknown origin
  • Function of heart, kidneys or liver
  • Evaluation of the chest
  • Changes in soft tissue that can signal the spread of a disease

Let’s discuss some of the key differences between CT scan and MRI scan –

Point of Difference

CT Scan

MRI Scan

Radiation Exposure

The radiation dosage from CAT scanning ranges from 2 to 10 mSv. Generally, CT is not recommended for pregnant women or children unless absolutely necessary.

MRI machines do not emit ionizing radiation.


The entire scanning gets completed within 5 – 10 minutes. The images are captured more quickly than MRI.

The scanning time may be around 30 – 45 minutes. However, in some cases it may take longer.

Parts of the body scanned

Brain, lungs, heart, skull, abdomen, pelvis and digestive organs

Brain, spinal cord, breast, organs, blood vessels, heart, joints and extremities.


Captures image slices and creates detailed images of bones, tissues and blood vessels.

MRI produces detailed 3D images of soft tissues.

Principle used for imaging

Uses X-rays for imaging.

Uses large external field, RF pulse and 3 different gradient fields.

Comfort level of patient

Seldom creates claustrophobia

Anxiety caused by claustrophobia is quite common in MRI scanning due to the discomfort caused by having to lie still for a longer period of time.


CT machines make soft, whirring noises and have flashing lights.

MRI machines make loud noises. Patients are usually given earplugs or headphones.

Limitation for scanning

Patients with metal implants can get scanned. However, a person (above 450 lbs of weight) may not fit into the opening of the SCT scanner.

Patients with cardiac pacemakers, tattoos and implants are contraindicated due to possible injury to patient or image distortion (artifact). Patients over 350 lb may be over the table’s weight limit. Ferromagnetic objects could cause burn or trauma.

These two medical ultrasound imaging techniques provide cross-sectional pictures of the body, but they accomplish this with different techniques. CT (computerized tomography) uses multiple x-rays taken at different angles to produce the cross-sectional imaging. However, MRI (magnetic resonance imaging) uses magnetic fields and radiofrequencies. The detailed images provided by CT and MRI scans help radiologists to accurately diagnose medical conditions. Both scans typically use an intravenous or oral contrast dye and patients are advised to inform their doctor if they are allergic to such contrast dyes.