Quantitation of total metastatic tumor volume in the rat liver: correlation of MR and histologic measurements.

Assessing tumor response to chemotherapy in the liver has always been difficult. Most investigators estimate tumor volume as either a product of the two perpendicular diameters of a tumor nodule, or, in animal studies, simply count surface tumor nodules. The authors evaluated magnetic resonance (MR) imaging as a technique for determining absolute tumor volume in the liver in an animal model. Specifically, histologic volumetric and MR imaging measurements of tumor and liver volumes were quantitatively compared over a wide range of tumor burdens in a rat model of hepatic metastasis of a colorectal carcinoma. Twenty-three rats were imaged, with two different section thicknesses used in each animal. Both section thicknesses showed highly significant correlations between MR and histologic measurements for both tumor and liver volumes (P less than .001). MR imaging may be useful for noninvasively quantifying tumor burden and temporal response of metastatic disease in the liver to novel antineoplastic regimens.