Correlation of MR imaging and histologic findings in mouse melanoma

M2R melanoma tumors in male C57 black mice were used to correlate magnetic resonance (MR) images with the corresponding histologic slices and to determine if analysis of the achievable correlation can provide a basis for predicting gross histologic features with MR imaging alone. The MR imaging sections obtained at 4.7 T were each 680 microns thick, with an in-plane resolution of 195 microns. The distribution of melanin within the histologic slices correlated well with the high-signal-intensity regions on the T1-weighted images (T1WIs), while these regions had low signal intensity on the T2-weighted images (T2WIs), providing evidence that melanin or melanin-associated paramagnetic species are responsible for the observed proton relaxation rate enhancement. Viable melanoma cells typically showed intermediate signal intensity on T2WIs, T1WIs, and proton-density images. Necrosis typically had high signal intensity on T2WIs, T1WIs, and proton-density images. Quantitation of the MR imaging results, followed by statistical analysis, demonstrated statistically significant differences between melanin-rich, viable-melanoma, and necrotic regions on MR images.