What Is an MRI vs. CT Scan vs. X-Ray?

Medical imaging has transformed modern medicine, allowing physicians to visualize the body's interior in extraordinary detail without surgery. Yet the options — X-ray, CT scan, MRI, ultrasound, PET scan — can be confusing to patients. Why does a doctor order one type of imaging rather than another? What is each modality actually measuring? What are the risks? Understanding the fundamentals of the major imaging types empowers you to understand your care and ask the right questions.

X-Rays (Radiography)

How they work: X-rays are a form of ionizing radiation — high-energy electromagnetic waves that can pass through soft tissue but are absorbed by denser materials like bone. When X-rays pass through the body onto a detector (digital sensor or film), denser structures appear white (bone, calcifications, metal), and less dense structures appear various shades of gray. Air appears black.

What X-rays are good for:

• Bones: Fractures, dislocations, bone density assessment, alignment
• Chest: Lung conditions (pneumonia, collapsed lung, fluid around the lungs, enlarged heart), rib fractures, lung masses
• Abdomen: Bowel obstruction (air-fluid levels), constipation, some foreign bodies
• Joints: Arthritis, joint space narrowing
• Dental imaging
• Checking device placement (pacemaker leads, feeding tubes, chest tubes)