Tendons can change in size due to growth, exercise, disease, and injury. But following those size changes accurately can be a real veterinary challenge. MRI-based tendon measurements analyzed using a color scale are far more accurate than those achieved by grayscale MRI scans, Danish researchers say.

While the tendon dimensions measured on grayscale MRI and using the color scale tendon dimensions were smaller than actual tendon dimensions, the MRIs analyzed with color were significantly more accurate than the grayscale, said Christian Couppé, PhD, researcher in the Institute of Sports Medicine at the University of Copenhagen. Specifically, the 3-tesla color MRI readings were off from the actual tendon dimensions by 2.8%, the 3-tesla grayscale reading was off by 13.2%, and the 1.5-tesla grayscale yielded a difference of 16.5%.

The color scale the researchers used doesn't represent the actual colors of the tissues, but rather are assigned to different intensities of signals coming from various kinds of tissues. Grayscale MRI scans tend to poorly distinguish the “high-intensity signals” of the surrounding tissues and the “low-intensity signals” of the tendon, he said. For similar reasons, ultrasound technology gives very poor accuracy on tendon measurements.

In this first study comparing MRI accuracy to actual tendon cross-sectional area, Couppé and his colleagues imaged and analyzed an equine cadaver knee tendon using both a grayscale MRI and one with the color scale. Then they compared the MRI results to measurements of the tendon cross-sectional area itself