Proton Density MRI — the right tool for the job

"Use the right tool for the job." --Ancient proverb

"If the only tool you have is a hammer, you tend to see every problem as a nail." --Abraham Maslow (American professor of philosophy, 1908-1970)

How many of us have tried to use the wrong tool for the job? Say, you need to remove a #2 Phillips screw, but all you've got is a #1 Phillips screwdriver (or a screwdriver someone's tried to use as a chisel). Oftentimes, you wind up stripping the screw.

X-rays are great for imaging bone, but MRI is the front-line tool of choice for imaging soft tissues in the body. There are many different types of MRI from which to choose — this is because different tissues have different signal characteristics, and those characteristics are also dependent on whether the tissue is normal or diseased. What we think of as a "standard MRI" looks for large structures made of soft tissue, like discs between the bones in your spine or large ligaments in the knees. When you're looking for a bulging disc, standard MRI sequences are perfectly acceptable.

However, for smaller structures, different MRI sequences are needed. The ligaments in the spine are a perfect example. The vertebrae in the spine have all sorts of points, nooks, and crannies, and there are many different ligaments attaching bone to bone. Since there are so many ligaments, each one can be smaller. So, most of these spinal ligaments are very thin — much thinner than ligaments in the knee, for example. So, in order to assess these ligaments on an MRI, a different sequence is needed.

Over the past decade-plus, researchers have identified a new MRI sequence to use when looking at spinal ligaments — a high-resolution, proton-density weighted sequence. According to the scientific literature, this sequence gives about one-half (½) the slice thickness or better when compared to a standard MRI. The research supporting this new tool helps up-to-date doctors diagnose and treat patients who have problems with these small spinal ligaments. As with any imaging study, however, it is imperative the treating physician clinically correlate a patient’s symptoms to the imaging findings.