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How to get the best out of your MRI scanner
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Magnetic resonance imaging

An MRI (or magnetic resonance imaging) scan is a radiology technique that uses magnetism, radio waves, and a computer to produce images of body structures. The MRI scanner is a tube surrounded by a giant circular magnet.



A dog having a brain MRI at Stone Lion Veterinary Hospital
Magnetic resonance imaging
An MRI (or magnetic resonance imaging) scan is a radiology technique that uses magnetism, radio waves, and a computer to produce images of body structures. The MRI scanner is a tube surrounded by a giant circular magnet.
MRA of the circle of Willis
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Frequently asked questions
How does MRI Work?
MRI is dependent on the inherent magnetic properties of the body. Each water molecule consists of two hydrogen ions, each with a single, spinning, positively charged proton. This spinning charge is analogous to a tiny bar magnet. When the patient is placed in a magnetic field and subjected to a short radiofrequency pulse the protons are excited and spin “in sync”. When the pulse is switched off the protons relax and emit a signal, which is used to reconstruct a picture of the tissue.
 Based on the relaxation properties of the protons, three basic MRI images can be created: T1-weighted, T2-weighted and proton density. T1 refers to the time constant for protons to relax from a higher to a lower energy level. T2 is the time constant for the protons to spin out of sync. Each tissue has different T1 and T2 properties and this forms the basis of contrast. A T2-weighted image depicts fat and fluid as high signal (white) and a T1 weighted image depicts fluid as a low signal (black). A proton density image is neither T1- nor T2-weighted and is influenced by differences in proton density i.e. the more protons the more signal. Proton density images depict the CSF as dark grey, the white matter as light grey and the grey matter as white. They are generally superior for detecting changes in brain structure. T2-weighted images are invaluable for indicating oedema and other fluid related abnormalities. T1-weighting is often used in association with an intravenous paramagnetic contrast agent, Gadolinium, which shortens the T1 (i.e. is high signal) in its surroundings. Vascularised tumours and areas with a disrupted blood brain barrier are therefore enhanced.

Why do you use MRI?
An MRI scan is accurate method of disease detection throughout the body. Veterinary Neurologists use an MRI scan to defining brain and spinal cord anatomy and can detect problems such as tumours, cysts, inflammation and bleeds. It is also useful when considering problems associated with the vertebrae or intervertebral discs of the spine.

Is an anaesthetic necessary?
The pet must be absolutely motionless during the procedure and this can only be achieved with heavy sedation or light anaesthesia. At Stone Lion Veterinary Centre we prefer a light anaesthesia as we can be more confident that the pet receives enough oxygen.

Will the whole body be done?
No – the area imaged depends on the clinical signs. The amount that can be imaged at once depends on the Field of View of the MRI machine concerned.

How do I arrange a MRI scan at Stone Lion Veterinary Centre?
With the exception of the syringomyelia screening scheme for CKCS, Bruxellois Griffon and Chihuahua breeders (
what is this) a referral for a neurology consultation must be made by the primary veterinary surgeon (how to make a referral
Why do I have to see a neurologist first – why can my pet not have a MRI scan without a consultation?
The neurology consultation is essential to ascertain 1) if an MRI scan is the most appropriate test for the pet’s problem 2) Which area of the nervous system is to be imaged  and 3) to ensure there are no obvious reasons precluding a general anaesthetic.
What are the risks of MRI? An MRI scan is a painless radiology technique that has the advantage of avoiding x-ray radiation exposure. There are no known side effects of an MRI scan. The benefits of an MRI scan relate to its precise accuracy in detecting structural abnormalities of the body. If you know your pet has any metallic materials within their body then you should notify us. Metallic chips, materials, surgical clips, or foreign material (artificial joints, metallic bone plates, or prosthetic devices, etc.) can significantly distort the images obtained by the MRI scanner and there is a risk that the magnet may move the metal in these areas. Microchips are not affected although occasionally image distortion can prevent good images of the cervical spine.
What happens on the day? In most cases your pet will be admitted after the neurology consultation and the procedure is performed the same day. After admission the pet has a sedative. This reduces anxiety and the amount of anaesthetic required The MRI scan takes ~ 60 minutes. However your pet is discharged when fully recovered from the anaesthetic and so the whole process can take several hours.
When do I hear the results? You will either be informed of the results by a phone call after the MRI scan is completed or when your pet is discharged. There is an opportunity to discuss the results and their implication with the neurologist.
When does my vet hear the results?  Your vet receives an interim report by fax after your pet is discharged and later receives a full report by post.
My pet / client has already had a MRI scan – can you do a independent opinion on the images?  Images and case history can be sent directly to Clare Rusbridge. There is a charge of £150 plus VAT for interpretation of outside MRI scans and £50 plus VAT (£35 plus VAT for multiple) for providing a report for outside syringomyelia screening MRI schemes.