Magnetic Resonance Imaging (MRI) uses a radio signal sent out by water molecules to form a virtual image of a body part. It is a reconstructed image, computer enhanced, and not a direct image the way a shadow would be. So there will always be limitations of MRI, sometimes caused by the signal itself, a particular body shape or size, or other artifacts that interfere with imaging.

When the image is good, MRI can be very useful in imaging cartilage. Patients should know that MRI scanners come in many different sizes, and each with potentially different software. Furthermore, a particular radiologist may use a specific “sequence” to get a better look at cartilage, while someone else may have no such interest, or ability. For these reasons, not all MRIs are alike! As the test is expensive, your doctor should put careful thought into where an MRI exam is ordered and how it is to be interpreted.

This animation shows an experimental MRI courtesy of Virtualscopics, Inc. When you run the animation you will see firstly how the layers of cartilage can be color coded in terms of thickness. Then, the computer rotates the knee and separates the three bones for a better view. Finally, the bones themselves are eliminated and we can look at the remaining cartilage in 3D space, like the icing upon the cake—but without the cake! Tool such as this will greatly increase our ability to conceptualize cartilage loss and to track repair processes.