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MRI vs Xray: The Difference Between MRI and Xray and Which To Choose

This guide will help you understand the processes, benefits, limitations, and differences between X ray and MRI and CT scans.

Written by Chelsea Okonkwo
Last updated 28 Mar, 2024

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If you are experiencing painful symptoms due to an injury or an undiagnosed condition, your doctor—after reviewing your medical history and conducting a physical examination—may recommend a diagnostic imaging test. Diagnostic imaging methods such as MRI, X-ray, and CT scans are tools that provide healthcare professionals with a detailed view and evaluation of what’s going on inside your body. 

This guide will help you understand the processes, benefits, limitations, and differences between X ray and MRI and CT scans. Once you gain all the necessary information, you will feel calm and confident as you prepare for your scan appointment. You may also feel empowered to have an informed discussion with your healthcare provider about which one is best for you. 

MRI vs Xray - What Are They?

What Is an MRI Scan, and How Does It Work?

Magnetic resonance imaging (MRI) is a painless, non-invasive imaging technique that uses a powerful magnetic field and radio waves to create three-dimensional (3D) detailed images of structures inside the body, including organs, bones, joints, and soft tissues (e.g., nerves, muscles, blood vessels, etc.).

The traditional MRI scanner is a large, cylindrical (tube-shaped) machine that acts like a giant magnet. There's also a flat motorised bed that moves into the scanner, and depending on the part of your body to be scanned, you might go in head or feet first.

MRI’s magnetic field attracts hydrogen atoms, particularly protons (i.e., the positively charged particles at the centre of an atom). Hydrogen (H) is abundant in water and fat. The human body is approximately 60% water (H2O); it flows freely in the blood and is bound to every cell, tissue, and organ. And well, fat is distributed throughout the body, around your heart and blood vessels, inside your brain, bones and nerves, and behind your eyes. This is a valid explanation for MRI being super sensitive to diseases that manifest as an increase in fat or mass (e.g., tumours) or water (e.g., cysts).

Learn more about MRI technology, processes and uses in our complete guide to MRI scans.

What Is an X-Ray Scan, and How Does It Work?

X-ray is an imaging test that uses electromagnetic waves (radiation) to create two-dimensional (2D) images of tissues and bony structures in the body.

The radiation used by the X-ray is similar to that of ultraviolet (UV) light emitted by the sun, except that it has a much greater energy. But, it is usually used in very low doses, which can vary depending on the area being scanned. 

So, how does an X-ray scan work? - The scanning procedure would involve lying on a motorised bed (or standing, in the case of a chest X-ray or mammogram) between an X-ray source and a detector (e.g., photographic plates or fluorescent screens).

As the X-ray source directs a beam of rays through your body to the detector, an image representing the shadows cast by different tissues will be formed, depending on how much of the X-rays are absorbed. 

Here's a quick colour (or should we say, shadow) guide to help you understand why a typical chest X-ray looks the way it does:

  • Bones: Being extremely dense, they absorb X-rays greatly and cast a shadow that appears white on a radiograph.

  • Fluids, fats and muscles: They absorb significant amounts of X-rays, although not as much as bones. They appear as different shades of grey.

  • Lungs: Being filled with air, which poses no resistance to X-rays, they allow them to pass through. They often appear black.

Now, let’s get into a quick MRI vs Xray comparison.

Difference Between MRI and Xray

  • Diagnostic capabilities: X-ray is best suited for imaging bones, so it is highly accurate in detecting diseases in the bone, such as fractures and dislocations, dental problems, and spinal bone issues. MRI has a broader diagnostic scope as its advanced technology allows it to create more detailed images of bones, organs, and soft tissues. It is an invaluable tool for investigating a wide range of abnormalities and diseases, including tumours, cysts, inflammation, neurological disorders, joint and muscle injuries, spinal cord abnormalities, vascular diseases, and more.

  • Availability: X-ray scans are a commonly used diagnostic imaging tool so they are widely available and affordable. In contrast, MRI is less widely available and is used for more detailed examinations. 

  • Risks: X-rays utilise ionising radiation, which can pose a cancer risk when administered in high doses. Repeat use isn't advised to avoid the accumulation of radiation exposure, but X-ray scans typically employ low doses of radiation. However, they can still present risks, especially during pregnancy.

MRIs are generally safe because they don’t use radiation. However, their use of strong magnetic fields presents contraindications (situations where MRI may not be suitable) such as if a patient has metallic implants (e.g., cardiac pacemaker, defibrillator, drug-infusion pump, neurostimulators, and intracranial aneurysm clips).

With MRI, there’s also the risk of experiencing mild side effects from the gadolinium-based contrast dye. Furthermore, individuals with claustrophobia and restricted mobility might find it uncomfortable being inside the MRI scanner. The open MRI scanner offers a stress-free alternative to mitigate this risk.

  • Costs: An MRI scan is usually more expensive than an X-ray.

  • Speed: Depending on the body part being examined, an X-ray can take only a few minutes, say 5 to 15 minutes, whereas an MRI scan can take around 15 to 90 minutes to complete. 

What Does an MRI Show That an X Ray Does Not?

An MRI is better at investigating musculoskeletal pain caused by soft tissues that the X-ray can't capture. These conditions may include: 

  • Ligament and tendon injuries (such as rotator cuff tears and Achilles tendon ruptures)

  • Degenerative disc diseases (DDD)

  • Muscle tears or strains

  • Nerve compression and damage

  • Cartilage injuries (such as meniscus tears in the knee)

  • Joint abnormalities (such as osteoarthritis or rheumatoid arthritis)

In cases where an X-ray is used as a first-line imaging tool to rule out suspected conditions, an MRI or CT scan may be used as a supplemental test to get a confirmative diagnosis and comprehensive evaluation of the problem.  

MRI scans can be used to detect abnormalities, infections, degeneration, inflammation, and diseases in soft, dense, and fluid-filled tissues around different body parts, including: 

There are also special types of MRI scans, namely the magnetic resonance cholangiopancreatography (MRCP), which detects stones, inflammation, and diseases in the pancreas, gallbladder, and pancreatic and bile ducts, and the magnetic resonance angiography (MRA), which evaluates the health of the blood vessels. 

What Can X Rays Detect?

X-rays can be used to detect the following conditions: 

  • Bone injuries such as fractures and dislocations.

  • Bone tumours, which may be cancerous or non-cancerous. A follow-up test may be required for a definitive diagnosis.

  • Osteopenia (bone density loss).

  • Scoliosis (abnormal curvature of the spine)

  • Dental problems such as cavities, tooth decay, and abscesses.

  • Lung conditions, including pneumonia and lung nodules (tumour).

  • Calcifications (harden deposits of calcium buildup) within soft tissues, which may indicate certain medical conditions. 

  • Foreign objects trapped in the body. Except for objects made with plastic, rubber (e.g., toys), and wood, X-rays can detect objects made of metal, steel, ceramics, or stone.

Difference Between X Ray and CT Scan, and MRI

Computed tomography (CT) scan is a diagnostic imaging tool that combines X-ray technology with computer processing to create cross-sectional images (slices) of the body's internal structures from different angles. Like the X-ray and MRI, it is painless and non-invasive. 

A CT scan is often used to obtain more detailed images of bones, organs, and soft tissues. 

While plain x-rays only produce 2D images, the CT scan provides 3D views like an MRI. Although, it is not as precise as the MRI in capturing subtle differences between tissues.

Here are some differences between X Ray and CT scans and MRI

  • Unlike X-ray and CT, MRI doesn’t use radiation. 

  • Speaking about contrast agents, X-rays only require them when examining internal organs (e.g., the stomach), in which case, their use is infrequent. CT scans, which use iodine-based dyes, use them more commonly. And MRI? It is capable of producing detailed images without requiring contrast agents. Some MRI scans, however, may require contrast agents, in which case, a gadolinium-based contrast is used. There are fewer side effects to gadolinium and rare incidents of adverse reactions, compared to iodine.

  • MRI is generally more expensive than X-rays and CT scans due to its advanced technology, limited availability, and longer scan times.

  • Both MRI and CT scans use a tunnel-shaped machine, but MRI can be noisy, so you should be given earplugs and/or to wear during the procedure. CT scans are much quieter. 

A CT scan is mostly used to visualise the lungs, assess fractures and internal bleeding, and for cancer staging or monitoring response to treatment. It also makes for a great alternative in cases where contraindications for people with metallic implants wouldn’t allow an MRI. 

For a detailed comparison of the CT scan and MRI, check our guide: CT vs MRI Scans: What are the differences, use cases, and risks?

Next Steps

Book an MRI scan and fast-track your diagnosis. No waiting lists. No lengthy paperwork. 

Book your X-ray without a GP referral. No hidden costs.

Book a private CT scan and get 1:1 expert clinical care from a dedicated team that truly cares. 

Scan.com is the UK’s largest imaging network with over 150 scanning centres at convenient locations near you.

If you aren’t sure which scan to choose, consider booking a private consultation for just £50. A dedicated clinician will call to discuss your medical history and provide tailored advice about which scan will be most beneficial for investigating your unique health concern. 

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