Assessment of Osteosarcoma Response to Preoperative Chemotherapy Using Dynamic FLASH Gadolinium-DTPA–Enhanced Magnetic Resonance Mapping

RATIONALE AND OBJECTIVES.To improve the accuracy of magnetic resonance imaging (MRI) in evaluating the response of osteosarcomas to preoperative chemotherapy, the authors developed a technique of mapping tumor necrosis and viability by quantitating slope values of gadolinium-DTPA (Gd-DTPA) uptake on dynamic fast low-angle shot (FLASH) images. METHODS.Dynamic contrast-enhanced FLASH imaging of a single representative plane was performed on six osteosarcomas. Tumors were mapped by dividing resultant images into contiguous regions of interest and deriving slopes representing percentage increase in signal intensity (SI) per minute over the baseline for each region. The results were compared with estimations of viable tumor volume on subtracted Gd-DTPA–enhanced T1-weighted images and histologic maps of necrotic and viable tumor. RESULTS.Dynamic FLASH estimations of percent tumor necrosis using a critical slope value of 45% per minute correctly predicted histologic response to chemotherapy in all six patients. Comparison of dynamic FLASH and histologic maps showed a high degree of correlation. Static enhanced T1- weighted images overestimated the amount of residual viable tumor. CONCLUSIONS.Dynamic FLASH Gd-DTPA–enhanced mapping is a potentially useful noninvasive method of quantitating tumor response to chemotherapy.