Limitations of single slice dynamic contrast enhanced MR in pharmacokinetic modeling of bone sarcomas

BACKGROUND: Single slice dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) appears to provide perfusion data about sarcomas in vivo that correlate with tumor necrosis on equivalent pathological sections. However, sarcomas are heterogeneous and therefore single slice DCE-MRI may not correlate with total tumor necrosis. PURPOSE: To determine whether changes in pharmacokinetic modeling of DCE-MRI, during chemotherapy for primary bone sarcomas correlated with histological measures of total tumor necrosis. MATERIAL AND METHODS: Twelve patients with appendicular primary bone sarcomas were included in the study. Each patient had DCE-MRI before, and after completion, of pre-operative chemotherapy. The mean arterial slope (A), endothelial permeability coefficient (K(trans)), and extravascular extracellular volume (V(e)) were derived from each data set using a modified two compartment pharmacokinetic model. Total tumor necrosis rates were compared with changes in A, K(trans), and V(e). RESULTS: Six patients had total tumor necrosis of >or=90% and six had a measure of <90%. The median percentage changes in A, K(trans), and V(e) for the >or=90% necrosis group were -52.5% (-83 to 6), -66% (-82 to 26), and 23.5% (-26 to 40), respectively. For the <90% necrosis group, A = - 35% (-75 to 132), K(trans)= - 53 (-66 to 149) and V(e)= - 14.5% (-42 to 40). One patient with >90% necrosis had increases in all three measures. Comparison of the two groups generated P-values of 0.699 for A, 0.18 for K(trans), and 0.31 for V(e). CONCLUSION: There was no statistically significant correlation between changes in pharmacokinetic perfusion parameters and total tumor necrosis. When using single slice DCE-MRI heterogeneous histology of primary bone sarcomas and repair mediated angiogenesis might both be confounding factors.