MRI - Magnetic Resonance Imaging

At Valley Farm we have daily access to MRI scanning facilities for our patients.

MRI is an excellent imaging method for soft tissue structures within the body, as soft tissue structures often cannot be seen in much detail on x-rays (unlike bone). This makes MRI very useful for brain scans, and evaluation of the spinal cord and surrounding structures.

MRI is a non-invasive procedure that does not use ionizing radiation (x-rays) but uses a powerful magnetic field to align the hydrogen atoms within the water in the body. The magnetic field used is 40,000 times as strong as the earth’s magnetic field. Radiofrequency fields are used to systematically alter the alignment of the magnetisation, causing the hydrogen nuclei to produce a rotating magnetic field detectable by the scanner. This signal can be manipulated by additional magnetic fields to build up enough information to construct an image of the body.

The MR image is dependent on computer processing of the signals. Diagnoses utilising MRI are based on the fact that abnormal tissue displaces normal structures and results in contrast-enhanced areas which can be visualised.
MRI examinations are carried out with the patient either heavily sedated or anaesthetised as the procedure takes between 20 and 90 minutes,,during which the patient must remain absolutely still. The animal’s ears are muffled with cotton wool as the machine makes very loud noises during the procedure.

MRI interpretation requires a firm knowledge of sectional anatomy as well as knowledge of the physics of the imaging system.

Below Top: Sagittal MRI of a dog with a large disc extrusion, indicated by the white arrow. The spinal cord is shown as the medium dark band extending the length of the image, indicated by the *

Below Bottom: MRI scans of the thoracic vertebrae A: A normal dog to show the spinal cord surrounded by fat and bone . B: A dog with a large disc extrusion