What’s the Buzz

Doctors have a number of medical imaging tools available to them to see inside our bodies, figure out what’s going on, and make an accurate diagnosis. These tools, called diagnostic imaging tests, can be of several different types. Each of them uses a different technology to create images and detect different types of medical problems. 

This article will discuss three commonly used medical imaging tests—X-ray, computed tomography scan (CT scan), and magnetic resonance imaging (MRI). 

These imaging tests are generally non-invasive, painless, and relatively quick. Understanding how they work and what to expect will hopefully help relieve some of the anxiety you can experience at an imaging center.

Key Differences Between X-rays, CT Scans, and MRI Scans

X-Ray

• Widely available
• Creates 2D images
• Uses radiation to produce images
• Used to detect bone fractures, cancer, pneumonia

CT Scan

• Available at larger hospitals and imaging centers
• Creates 3D images and 360-degree views
• Uses radiation to create images
• Provides more detail than X-rays
• Used to see organs and soft tissues

MRI Scan

• Available at larger hospitals and imaging centers
• Creates 3D images and cross-section views
• Uses a powerful magnet and radio waves to create images without radiation exposure
• Used to see internal body structures such as the brain, spinal cord, neck, breasts, abdomen, and muscles

X-Ray Imaging

X-rays are the most widely available and commonly used diagnostic imaging tests. Even when doctors want to order multiple tests, they will likely order an X-ray before more sophisticated tests such as CT scans and MRIs. 

How It Works

During an X-ray imaging test, the machine generates a beam of radiation that passes through your body. Hard, dense internal structures like your bones block the beam and appear white on the photographic film or computer screen. Softer tissues like muscle and fat show up in shades of gray. Air in your lungs appears black on an X-ray image.

What to Expect

An X-ray is a quick, painless procedure that typically takes a few minutes to complete. The technologist performing the X-ray may position your body in various postures to get different views. You will need to remain still during image acquisition to ensure good image quality.

Uses

X-rays are used to detect:

• Fractures and dislocations in skeletal structures
• Bone degeneration
• Narrowing of joint spaces
• Misalignments
• Tumors
• Infections

Notes

Limited radiation exposure from X-rays is not harmful. However, exposure to very high doses of radiation can potentially cause damage at a cellular level. Pregnant women need to take special precautions to protect the baby from radiation. 

Computed Tomography Scan

A computed tomography scan or CT scan is a more powerful and sophisticated imaging technology than an X-ray. It provides high-quality, three-dimensional, 360-degree, cross-section images of the body’s internal organs. However, CT scanning is more expensive and usually unavailable in smaller hospitals or rural healthcare settings.

How It Works

CT imaging uses X-rays and computers to produce detailed pictures of cross-sections of the body. In other words, a CT machine takes pictures of thin slices of bones, muscles, and other organs from different angles.

What to Expect

During a CT scan, you will be asked to lie on a flat, sliding bed. The bed will pass into a ring-shaped CT scanner that will rotate and take a series of X-rays from different angles. The entire process is painless and relatively quick. You may hear a whirring sound from the CT machine. You’ll need to lie still to prevent blurring of the images.

Uses

CT images are used to detect problems with bones, soft tissue, blood vessels, and other internal organs. A CT scan may be ordered to diagnose things like:

• Blood clots
• Subtle bone fractures not visible on X-ray
• Cancer
• Traumatic organ injuries and soft tissue injuries
• Appendicitis
• Infectious diseases
• Musculoskeletal disorders
• Heart disease
• Chest and lung problems

Notes

Sometimes, doctors inject a contrast dye into your blood to see the internal structures more clearly on CAT scans. If this is the case, you may be asked to wait at the imaging center for 30 minutes or so after the test to ensure there are no reactions to the contrast material.

Positron emission tomography (PET) CT scanning is a special type of diagnostic imaging which shows activity levels in the organs and the structure. It involves swallowing, inhaling, or injecting a radioactive material called a tracer before the test that shows up as bright spots in areas of high chemical activity. Doctors use PET scans to detect cancer, heart problems, and brain diseases.

Magnetic Resonance Imaging

MRI stands for magnetic resonance imaging. It is a sophisticated diagnostic imaging method that uses a powerful magnet and radio waves to create detailed images of body structures. 

How It Works

The strong magnetic field in an MRI machine temporarily realigns water molecules in your body. Radio waves are used to generate faint signals from these realigned water molecules. The signals are then used to create cross-sectional MRI images of the scanned body part. Unlike X-rays and CT scans, there is no radiation exposure involved in MR imaging.

What to Expect

An MRI scanning procedure is painless, but it typically takes longer than X-rays and CT scans. You will be asked to lie on a flat, sliding bed that will pass into a tube-shaped MRI scanner. The magnet in the MRI machine produces repetitive thumping and tapping noises. The technologist might give you ear protection and play music to block out these noises.

Uses

MRI scans can help to detect:

• A soft tissue injury involving a ligament, tendon, muscle, or cartilage, such as an ACL tear, meniscal tear, Achilles tendon rupture, rotator cuff tear, torn ligaments, herniated discs, sprain or strain
• Joint inflammation
• Cartilage loss
• Nerve compression
• Spinal cord injuries

Similarities between X-rays, MRIs, and CT scans

• All three are imaging tools used in modern medicine. 
• All three are used to diagnose certain medical complications, injuries, and conditions.
• All three can be completed within 30-60 minutes. 
• All three are non-invasive and painless.
• All three require you to remain still to obtain clear images.

X-rays vs. CT scans and MRIs

X-ray images are 2D. MRI and CT are more advanced types of imaging that create 3D images of the part of the body that is scanned.

CT scans vs. MRIs

• CT scans use ionizing radiation to create images of internal structures and therefore expose you to a small dose of radiation. MRI scans use a magnetic field and radio waves to form images and do not involve exposure to ionizing radiation. 
• A CT scan is typically quicker than an MRI. 
• Unlike MRI machines, CT scanners do not surround the whole body, so there is a lower likelihood of causing claustrophobia. People who are claustrophobic may be able to undergo an open MRI.
• CT scan images are instrumental in detecting fractures, diseased tissue, and injuries to the head, spine, chest, or abdomen. They can also pinpoint the exact location of tumors. MRIs are better at diagnosing soft tissue problems in the brain, spinal cord, neck, breasts, and abdomen. 

References:

1. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/ct-vs-mri-vs-xray