Relationship of perfusion to edema in the 9L gliosarcoma

The relationship between tumor perfusion and edema was analyzed, with edema characterized as tumor wet/dry weight ratio. Perfusion of subcutaneous 9L gliosarcoma was measured by injection of 133Xe in saline into the tumor core, followed by gamma camera imaging of 133Xe washout kinetics. A significant inverse correlation was found between edema and tumor perfusion (p < 0.0002), suggesting that edema can limit tumor perfusion, perhaps through a mechanism of increased interstitial fluid pressure. The perfusion rate of highly edematous tumors was reduced to less than 10% of the perfusion rate of less edematous tumors (p < 0.001). It was also found that tumor edema increased significantly with increasing tumor volume (p < 0.001), which could account for the finding that perfusion declined significantly with increasing tumor volume (p < 0.02). These findings are potentially important because it is possible to quantify tumor edema in vivo, with millimeter resolution, using 1H magnetic resonance imaging (MRI). Thus MRI may provide a non-invasive technique for characterizing tumor perfusion or tumor drug delivery.