Sensitivity of physeal-metaphyseal tractography correlations with height velocity for fractional anisotropy threshold...

Diffusion tensor imaging (DTI) tractography of the physeal-metaphyseal complex (PMC) provides insights into skeletal maturation. Fractional anisotropy (FA) minimal and maximal thresholds of 0.15 and 1.0, respectively, are commonly used to reconstruct tracts; these values were developed for highly organized tissues and may exclude the less organized hypertrophic and transitional zones that drive growth. Whether lowering the FA thresholds better captures growth-sensitive features and correlates with annualized height velocity is unknown.

Forty-five healthy adolescents (20 boys; 12-17 years) underwent 3 T DTI of the distal femoral PMC. Deterministic tractography was performed using nine previously untested FA threshold combinations (FA_min: 0.05, 0.10, 0.15 paired with FA_max: 0.40, 0.50, 0.60) and a conventional threshold (0.15-1.0). Partial Pearson correlations between extracted metrics (tract FA, apparent diffusion coefficient [ADC], volume) and annualized height velocity were computed, controlling for Tanner stage.

Tract ADC showed strong positive correlations with height velocity across all thresholds (r = 0.55-0.63). Tract FA showed consistent negative correlations (r = -0.38 to -0.45). Tract volume correlations were threshold-dependent: positive at lower FA_min thresholds (r = 0.33-0.37, at FA_min = 0.05) but attenuated or reversed at higher FA_min thresholds (r = -0.26, at 0.15-1.0).

Tract ADC and FA are robust metrics of growth plate activity, insensitive to FA threshold selection. Tract volume associations with height velocity are threshold-dependent, with lower FA_min thresholds capturing growth-sensitive PMC tissue and lower FA_max excluding inactive PMC tissues. These findings underscore the importance of standardized tractography parameters in growth plate DTI studies.

Question How can we prevent conventional DTI FA thresholds from underestimating growth-sensitive tract volumes in the pediatric PMC? Findings Lower FA thresholds accurately capture tract volume correlations with height velocity, while tract ADC and FA correlate reliably across all thresholds. Relevance statement Optimizing FA thresholds in physeal-metaphyseal-complex DTI improves microstructural imaging correlations with height velocity, ensures reproducible data in pediatric skeletal growth studies, enhances noninvasive skeletal growth monitoring in adolescents, and potentially supplements traditional bone-age radiographs.