13 Apr, 2022

MRI Scans: The Complete Guide (Updated 2023)

MRI scans are valuable tools for diagnostic imaging, and can even detect some potential illnesses before they fully develop. If you've never had an MRI before, you might be wondering how they work, what the scanning experience is like, and why MRI scans are so important in clinical settings.

We've answered some commonly asked questions in this definitive guide. Read on to find out more about MRI technology and scan procedures.

What does MRI stand for?

MRI stands for Magnetic Resonance Imaging.

How does an MRI scanner work?

  1. The strong magnets in an MRI scanner force the protons within the hydrogen atoms of your body to align with the magnetic field. As your body is around 65% water, there are plenty of hydrogen atoms which are necessary for MRIs to work.
  2. A radio-frequency current is then pulsed through your body, which stimulates the protons, and they will spin out of equilibrium and produce a signal.
  3. When the radio-frequency is turned off, receiver sensors in the MRI scanner detect the energy released by the protons as they realign with the magnetic field. The time it takes for them to realign, as well as the amount of energy they release, differs depending on the type of tissue being scanned. This allows your physician to view different structures in your body.

When is an MRI scan needed?

An MRI scan is often used to gain more detail, when a CT or X-ray has been unclear, or it can be used to image the body without the harmful effects of ionising radiation.

If you or your doctor suspect a problem within your soft tissues, an MRI enables the clearest images and is often the safest and most accurate way to provide diagnosis or peace of mind.

Equally, if you are suffering from pain in any part of your body, an MRI can give an understanding of the reasons why.

MRI scans can also be necessary to check the progress of treatment, for example understanding how successful chemotherapy has been, or to check the health of cancer survivors on a regular basis.

What can an MRI be used for?

MRI scans are best suited to non-bony body parts and soft tissues. For example, the brain, nerves, spinal cord, muscles, tendons, and ligaments are able to be seen much more clearly with an MRI scan than with an X-ray or CT scan, without the damaging use of ionising radiation. If you need frequent scans to assess treatment success or manage a condition, MRIs are a preferred choice due to no radiation exposure being involved.

However, MRI scans can still be used for bones and joints, such as the hips, spine, ankle and elbow, as they can show fluid in these areas and allow diagnosis for conditions like tennis elbow, arthritis, inflammation, and more.

MRIs can also be used to differentiate between white and grey matter in the brain, and help in the diagnosis of aneurysms and tumours.

Other uses for MRI scans include scanning breast tissue, heart and blood vessels, and internal organs like the liver, womb, prostate gland, pancreas, kidneys, spleen, gallbladder and more.

What can MRI scans diagnose?

MRI scans can be used for many different body parts, which means they are a key diagnostic tool for a range of conditions.

  • Brain, head and neck: cysts and tumours, infections, blood clots, inner ear and eye disorders, swelling, inflammation
  • Back (cervical spine, thoracic spine, lumbar spine): artery or vein disorders, herniated (slipped) discs, pinched nerves, fractures, spinal cord problems, tumours, and some degenerative diseases (e.g. multiple sclerosis).

📢 Find out more about MRI scans for diagnosis of spinal issues here

  • Pelvis (including female gynaecological): bone fractures and bruises, tumours, cysts, reproductive issues, endometriosis
  • Internal organs (e.g. liver, bladder, kidneys, heart, stomach, intestines, pancreas, gallbladder, breasts): tumours, inflammation, infection, stones, liver disease, tissue damage, types of heart disease, abnormalities
  • Joints (e.g. wrist, ankle, elbow, knee and shoulder): arthritis, fractures, ligament tears, nerve damage, inflammation, dislocation
  • Nerves: pinched/pressed nerves, nerve damage, inflammation, spinal cord injuries
  • Extremities (Arm, leg, hand and foot): nerve damage, bone infections, tumours, fractures, degenerative diseases such as arthritis, ligament and tendon damage

Are MRI scans accurate?

MRI scans can provide greater detail than CT scans and X-rays when imaging certain body parts. They are an accurate method for diagnosing conditions and managing treatment.

A study into knee scans showed MRI scans to be 90.1% accurate and 90.5% sensitive. This means MRIs are highly accurate when providing positive results for certain diagnoses, and provide the necessary detail to gain an accurate insight into patients' conditions.

Are MRI scans safe?

Yes, MRI scans are a safe and non-invasive medical imaging technique. MRIs don't use harmful ionising radiation like X-rays and CT scans do, they just use very strong magnets.

This does mean that MRI scans are not suitable for everybody. For example, if you have metal in your body, such as shrapnel or a medical device (pacemaker, cochlear implants, etc), they could be negatively affected by the strong magnets in the scanner. Our expert clinicians will assess your medical history prior to your scan, and many devices are completely safe for MRI scanning.

Some people also find MRI scans uncomfortable, especially if they suffer from claustrophobia, as you must lay very still in the tube-like scanner for the duration of the process. Scanners with open sides are now available, which can help alleviate anxiety and claustrophobia.

📢 Find out more about how to manage claustrophobia during your MRI scan here.

If you require a contrast agent for your scan (injected via IV to help generate clearer images) there are some mild side effects such as a warming sensation, and more serious side effects like an allergic reaction are extremely rare.

MRI scans are also not recommended for pregnant women in their first trimester. In some cases, the benefits of an MRI during pregnancy outweigh the risks, and the risks are extremely low.

What is a contrast agent used for in MRI scans?

Contrast agents are chemical substances injected into the body, which improve the quality of MRI images in some scans. The contrast chemical is usually gadolinium-based. The kidneys will get rid of the substance from your body after your scan. If you have impaired kidney function or are pregnant, you may not be a suitable candidate for a contrast agent injection.

Contrast agents are most commonly used to highlight blood vessels, tumours and blood supply. Contrast agents can have some mild side effects, like a temporary warming sensation, dizziness, nausea or headache, but these effects subside quickly. In rare cases, an allergic reaction can take place, but this usually manifests as a skin rash that is treatable at the time of the scan.

📢 Read our guide to contrast agents for MRI scans here

How do I prepare for an MRI scan?

MRI scans usually don't require you to fast beforehand, but you might be asked to avoid eating or drinking in some cases. You might even be asked to consume a large amount of water before the scan, depending on the body part being imaged.

Our consultant clinicians will have established your medical history, but you may be asked to fill in a form about your health on the day of your scan. You will also be asked to sign a consent form before the process begins.

It is recommended that you wear soft, comfortable clothing with no metal fastenings. This is due to the strong magnetic field in the scanner. You will also be asked to remove any jewellery, watches, glasses, belts or similar before the procedure. In some cases, you may be asked to wear a hospital gown.

What do the images from an MRI look like?

MRI scan images are black and white, with several different shades of grey. The shading helps radiologists to differentiate between tissues and bodily structures.

The image clarity and shading can depend on the strength of the magnets and the radio-frequency signals used within the scan.

Based on the purpose of your scan, and the body part being imaged, the resulting images can show shaded abnormalities, any problems with the size and structure of the body part, and any lesions (damage to organs and tissues).

What is the difference between a 3T and 1.5T MRI scanner?

The key difference between the two types of scanners is simply the strength of the magnet. The 'T' stands for Tesla, which is the unit of measurement for magnetic fields, so a 3T scanner's magnetic field is twice as strong as a 1.5T scanner's.

3T scanners are better at providing finer details for intricate body parts like the brain and vascular system, and they are faster, but they usually make more noise. They can also be more prone to 'artifacts' - blemishes in the image quality caused by the movement of blood and other bodily fluids.

1.5T scanners are more commonly used, and the level of detail they provide is perfectly adequate for most purposes. They are also safer for people with medical devices that might be adversely affected by the stronger magnets in a 3T scanner. They are also less prone to artifacts and are cheaper for hospitals to purchase.

How much does a private MRI scan cost?

Our prices vary per body part for diagnosis, but start from just £289. The price you pay includes:

  • A 1-1 pre-scan consultation with a member of our expert clinical team, to assess your medical history and suitability for your chosen scan
  • A referral for your scan
  • The scan at your selected partner scanning centre
  • Digital access to your imaging report
  • Post-scan 1-1 clinician consultation as required to discuss your results and next steps

Full body preventative scans start at £1,499, and provide a general screening of vital organs and key structures, with the same high level of care from our consultant clinicians.

If you're looking to book an MRI scan privately near you, our platform offers access to over 150 scanning sites across the UK.

How long do MRI results take?

Currently, 15% of people due for NHS MRI scans are waiting more than 6 weeks to have their scan, and a further two weeks for their results. It is our mission to reduce this pressure and provide fast access to medically necessary scans for our patients. When you book with us, you'll usually receive your results within 7 working days of your scan, and we have no waiting lists.

📢 Next Steps:

    • Book a private MRI scan near you, without GP referral - our medical team will provide a quick referral and fast results with no waiting lists.
    • Visit our news page to learn more about MRI scans and how to prepare.


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