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

Aim: To compare magnetic resonance imaging (MRI), micro-computed tomography (CT), 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 CT 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, CT after 3 days. The in vivo MRI data correlated best with the ex vivo tumor volumes (r2=0.96), followed by CT (r 2=0.93). Thus, MRI was chosen as the reference. CT-(r 2=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:r 2=030) poorly correlated. Conclusion: MRI sensitively detects tumors and precisely determines their size; CT 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.