Contrast Enhancement in MRI Using Combined Double Action Contrast Agents and Image Post-Processing in the Breast...

Gd- and Fe-based contrast agents reduce T₁ and T₂ relaxation times, respectively, are frequently used in MRI, providing improved cancer detection. Recently, contrast agents changing both T₁/T₂ times, based on core/shell nanoparticles, have been introduced. Although advantages of the T₁/T₂ agents were shown, MR image contrast of cancerous versus normal adjacent tissue induced by these agents has not yet been analyzed in detail as authors considered changes in cancer MR signal or signal-to-noise ratio after contrast injection rather than changes in signal differences between cancer and normal adjacent tissue. Furthermore, the potential advantages of T₁/T₂ contrast agents using image manipulation such as subtraction or addition have not been yet discussed in detail. Therefore, we performed theoretical calculations of MR signal in a tumor model using T₁-weighted, T₂-weighted, and combined images for T₁-, T₂-, and T₁/T₂-targeted contrast agents. The results from the tumor model are followed by in vivo experiments using core/shell NaDyF₄/NaGdF₄ nanoparticles as T₁/T₂ non-targeted contrast agent in the animal model of triple negative breast cancer. The results show that subtraction of T₂-weighted from T₁-weighted MR images provides additional increase in the tumor contrast: over two-fold in the tumor model and 12% in the in vivo experiment.