MRI and knee surgery

Yesterday I met with my orthopedist to review MIR images of my right knee prior to surgery next Monday to remove those pieces of the meniscus cartilage that were broken loose. It was amazing how clear the MIR images were of the knee structure and how obvious it was that something was missing. The outside of the knee had a distinct layer of cartilage and the inside had none. The cartilage showed up as a dark area next to the bone. In the space between the bones there was some dark material which may be the cartilage which was broken from the inner circumference of the meniscus. They gave me all sorts of exercises to do to strengthen the muscles around the knee prior to surgery. I assume that I will also have to do them after the slicing and dicing.

MRI is a magical technique which uses a very strong magnetic field coupled with radio waves to create pictures of soft tissue. It is better with soft tissues than cat scans which use X-rays. The link given with this post provides a background on MRI for those with a technical bent. The technique used to be called NMR or nuclear magnetic resonance and was used extensively in chemistry to define how different atoms were connected to other atoms in complex molecules. Basically, in a strong magnetic field certain atomic nuclei with act like little radio transmitters when stimulated by a radio frequency pulse. The chemical environment of the nuclei determines the wavelength of the weak radio frequency response. Thus, by looking at the frequency of the response one can tell something about the chemical bonding in the vicinity of the molecule that is responding.

The early techniques did not produce images but numbers. With advances in computers and imaging techniques it was possible to configure NMR to produce images. However, the N or Nuclear in NMR caused people to believe that radioactive materials were used in the technique. The N only means that the technique looks at the magnetic properties of atomic nuclei and there is nothing radioactive about it. Therefore the name was changed from NMR to MRI or magnetic resonance imaging. Such instruments are difficult to construct (typically 2 million $ per device). It is even more of a problem to define how they work but the URL provided makes a good stab at an explanation.