Methods of Measuring Equine Tendons on MRI Studied

Methods of Measuring Equine Tendons on MRI Studied

Tendons can change in size due to growth, exercise, disease, and injury. But following those size changes accurately can be a real veterinary challenge.

Photo: Stephanie L. Church, Editor-in-Chief

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.

However, measuring actual tendon dimensions is a challenge all of its own, Couppé said. Cadaver tendons are easily damaged and dehydrate very rapidly—thus changing in size very easily—so Couppé’s team used a tendon-measurement technique developed by Alan Goodship, PhD, DVM, and Helen Birch, PhD, of University College London. The researchers cast a mold of the tendon and then measured the mold (instead of the actual tendon). Couppé and his colleagues discovered that the mold shrinks 3.6% compared to the original model (they tested their molding and measuring method on an easily measured glass tube to be sure their calculations were accurate). They therefore adjusted the final measurements to be 3.6% larger than the real measurements they got when calculating the actual dimensions of the real tendon.

Dimensions measured on the MRIs analyzed with color are more accurate probably because they differentiate better between the tendon and the surrounding tissues, said Couppé, who worked in collaboration with René Svensson, PhD, and Professor S. Peter Magnusson,

Tendon measurements allow veterinarians to monitor tendon growth during training, Couppé said, and are also necessary when monitoring tendon disease, and injury progression and healing. Still, he noted, such accuracy in measuring exact tendon dimensions might not always be called for.

“You can still use grayscale if you’re just measuring between two time points (so, if a tendon is measured once and then measured again a few days later),” he said. “But, if you need to be sure that you are close to the true size, then our study indicates that you will have more accuracy by using the 3-tesla and analyzing with National Institute of Health color code scheme.

“This is something that we have been speculating on for years,” he said. “Now we know we can have more precision when analyzing data.”

The study, "Accuracy of MRI technique in measuring tendon cross-sectional area," was published in Clinical Physiology and Functional Imaging

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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