Comparison of μCT, MRI and optical reflectance imaging for assessing the growth of GFP/RFP-expressing tumors.

AIM To compare magnetic resonance imaging (MRI), micro-computed tomography (μCT), optical reflectance imaging (ORI) and caliper measurements for subcutaneous tumor detection and size assessment. MATERIALS AND METHODS HCT 116-green- (GFP)-red-fluorescent protein (RFP) tumor volumes were measured in vivo by calipers and by ORI, MRI and μCT over 15 days and validated ex vivo. The method correlating best with the ex vivo tumor volumes was used as reference for longitudinal in vivo correlations. RESULTS MRI and ORI detected tumors at day 1 post-injection, μCT after 3 days. The in vivo MRI data correlated best with the ex vivo tumor volumes (r²=0.96), followed by μCT (r²=0.93). Thus, MRI was chosen as the reference. μCT-(r²=0.90), in vivo caliper data (r²=0.80) and fluorescence intensities (GFP:r²=0.71; RFP:r²=0.75) highly correlated with MRI-data, whereas fluorescent areas (GFP:r²=0.26; RFP:r²=0.30) poorly correlated. CONCLUSION MRI sensitively detects tumors and precisely determines their size; μCT is an accurate alternative for larger tumors; ORI is as sensitive as MRI, but overestimates small tumor sizes; and fluorescence intensity correlates better with tumor volume than fluorescence area.