MRI: A Guided Tour
Table of Contents
Slicing and Dicing
What’s that? You need me to repeat that last part? I know – it can be hard to hear anything over the periodic hammering sound the scanner generates. Which reminds me – I’ve forgotten to mention anything about what’s making all that noise (and why you’re thankful for those earplugs).
PHYSICS FACTOID: MRI patients are sometimes injected with gadolinium, a contrast agent that can make abnormalities such as tumors clearer due to the element's special magnetic properties.
Responsible for that racket are the gradient magnets. There are three of them in the machine (called x, y and z), each oriented along a different plane of your body, all of them far less powerful than the main magnet. But what they lack in strength they make up for in precision. They modify the magnetic field at very particular points and work in conjunction with the RF pulses to produce the scanner’s picture by encoding the spatial distribution of the water protons in your body. When rapidly turned on and off (which causes that banging noise), the gradient magnets allow the machine to image the body in slices – sort of like a loaf of bread. Using medical terminology, the transverse (or axial, or x-y) planes slice you from top to bottom; the coronal (x-z) plane slice you lengthwise from front to back; and the sagittal (y-z) planes slice you lengthwise from side to side. However, the x, y and z gradients can be used in combination to generate image slices that are in any direction, which is one of the great strengths of MRI as a diagnostic tool.
Starting to feel like chopped liver?
Let’s put a rush order on your MRI, so that you can see what we mean.
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