Poor agreement between ultrasound and inbuilt diffusion tensor MRI measures of biceps femoris long head fascicle length

Objectives This study aimed to determine whether diffusion tensor MR imaging (DTI) methodology inbuilt within manufacturer software can reliably measure biceps femoris long head (BFlh) fascicle length (FL) and to investigate agreement between ultrasound (US) measures and inbuilt DTI measures of BFlh FL. Methods Both legs of 20 males were examined (40 legs). FL of the BFlh was determined utilizing two‐dimensional ultrasound and diffusion tensor MRI assessment. Results Reliability of DTI measures of BFlh FL was found to be acceptable (ICC: 0.804; 95% CI: 0.482 to 0.926); however, minimal detectable change (MDC) values were found to be clinically unacceptable (3.5 cm). Poor agreement was found between US and DTI measures of BFlh FL (ICC: 0.096; MDC: 4.1 cm; Mean bias (limits of agreement): 0.31 cm (−2.74 to 3.36 cm)). Conclusions Diffusion tensor MR imaging measures inbuilt within manufacturer software of BFlh fascicle length do not display clinically acceptable reliability nor do they agree with validated US‐derived measures. In practice, either US measures should continue to be implemented or with the available expertise, algorithm‐based DTI‐derived measures should be utilized to measure BFlh FL.