Reliability in the assessment of tendon volume and intratendinous signal of the Achilles tendon on MRI: a methodological description.

The purpose is to introduce a method for accurately and objectively evaluating volume and mean intratendinous signal within the Achilles tendon using MRI. We prospectively studied MRI from 33 patients with chronic Achilles tendinosis (20 males and 13 females) with a median age of 52 years (range 29-70). In all patients, both Achilles tendons were investigated with T1-WI as well as PD-WI MRI. Thus, 66 Achilles tendons were evaluated in the study. Tendon volume and mean intratendinous signal were evaluated using a computerized 3-D seed-growing technique. In general, the computerized 3-D seed-growing technique resulted in an excellent overall observer reliability of the MRI-measurements. The reliability (R) for tendon volume measurements was highest for the T1-WI sequence (R=97.9%). For the mean intratendinous signal, the PD-WI sequence showed the highest reliability (R=88.1%). The same pattern was present when we studied the coefficient of variation (CV). For the CV, lower figures indicate more reliable estimates. CV was 4.9% for tendon volume and 8.9% for mean intratendinous signal. In conclusion, it could be said that a computerized 3-D seed-growing technique to monitor and evaluate the volume of the Achilles tendon and mean intratendinous signal, using MRI, shows an overall excellent reliability regarding inter- as well as intra-observer reliability.