Scanning – the inside picture

The term ‘scan’ is often used to describe the method of obtaining an image of the inside of the body. This may be done with ultrasound (details of which can be found in a separate factsheet), which is often available in veterinary practices and may be performed at your vet’s surgery. Recently, more specialised scans (MRI and CAT scans) have become widely available for pets – however it is likely that your pet would need to travel to a specialist centre for one of these scans.

MRI stands for Magnetic Resonance Imaging and is a type of scan that uses a magnetic field to make a picture of the inside of the body. The area to be scanned is put inside a large magnet and radiowaves are passed through the body. This causes the atoms inside the body to vibrate and give out a signal in reply. These signals are detected by a radio antennae.

Body tissues contain different amounts of water and other components and so different tissue produce different signals. A computer puts this information together to make a picture of the separate organs in the body. MRI is particularly good for detecting changes in the brain and the soft tissues of the body (muscle, fat and internal organs) which cannot be seen well with any other form of imaging.

CT (Computed Tomography) or ‘CAT’ scanning is an advanced form of x-rays. In a normal x-ray the patient is placed under the x-ray machine and a beam of x-rays passes through the body onto a photographic plate from which a picture of the inside of the body is produced. In a CT scan the patient lies on a table and the x-ray machine moves around the body as the x-rays are produced.

The information from the x-ray beam is taken into a computer that creates an image of the inside of the body. The detail of the picture produced by a CT scan is much higher than that of ordinary radiographs and a cross sectional (like looking at thin slice of the body), or three-dimensional, image can be generated. CT images are particularly good for looking at changes in the bone and lungs.

It is quite expensive to have a pet scanned and your vet will not recommend the procedure unless they think it is likely to give important new information that may help in the treatment of your pet. Sometimes the information provided by clinical examination, x-rays, and blood tests will lead your vet to suspect a problem with a particular organ (such as the brain). There may be no way to get more information about this without performing a scan.

In other cases detailed information, for example about the extent of a cancer, may be needed in order to provide the best treatment. If you are worried about your pet having a scan then discuss your concerns with your vet and they will tell you if there is any other option.

It is essential that your pet does not move during the scan and so they will be given a short anaesthetic. As your pet will be having an anaesthetic your vet will ask you not to feed your pet the evening before the day of the scan.

The magnet in an MRI scanner is very powerful and will attract some metals from several feet away. This means that no metal objects are allowed in the scanning room – your pet’s collar will be removed before the scan and people (or pets) with heart pacemakers or some other metal implants are not allowed in the scanning room.

Every scan takes several minutes to complete, and it may be necessary to make many different scans for each examination. It is essential that your pet remains still throughout the whole scan (or the image will be blurred) so your pet will need some kind of anaesthetic. Modern anaesthetics are very safe and your pet will probably recover more rapidly from an anaesthetic than any form of sedation.

As these scans are usually performed at specialist centres it is likely that your pet’s anaesthetic will be monitored by a vet with a special interest in anaesthesia and the anaesthetic will be very safe. You will usually be able to take your pet home as soon as they have recovered from the anaesthetic unless they are receiving further treatment. In specialist centres the vets will often want to perform the scan and then go straight to the operating theatre (if surgery is needed) because this means your pet only has to have one anaesthetic.

The scan will provide your vet with detailed information about the area they are concerned about. Remember that scans only look at a small area (they do not include the whole body), so it is important your vet already knows where to look for the problem.

As your vet is unlikely to be doing these more specialist tests every day the pictures will probably be checked by another vet who specialises in reading films from scans. They will produce a report stating what the pictures show and your vet can use this information to plan further tests or treatment. Sometimes the scans will show no abnormalities in the area examined – this may be very useful information as it can help your vet rule out some serious conditions. In a pet that is having fits (seizures) your vet might want to perform a scan to rule out diseases such as cancer in the brain.

There are no known risks associated with MRI scans (aside from the risks associated with the anaesthetic). CT scans use x-rays and repeated exposure to x-rays can be dangerous – however the risks from routine medical scans are minimal.

You will probably be asked to take your pet to the scanning centre in advance of the time of your examination. The vets at the centre will want to examine your pet and prepare them for the anaesthetic. Your pet will be asleep during the scan and will not know whether you are with them or not. As soon as the scan is complete your pet will start to come round from the anaesthetic – they will be watched closely by trained staff until fully recovered. Once your pet is fully recovered from the anaesthetic you will be able to see them again, and they should be able to return home shortly after.