T₂^* relaxation times of intraductal murine mammary cancer, invasive mammary cancer, and normal mammary gland

Purpose: This study investigates the feasibility of T₂ ^* to be a diagnostic indicator of early breast cancer in a mouse model. T₂^* is sensitive to susceptibility effects due to local inhomogeneity of the magnetic field, e.g., caused by hemosiderin or deoxyhemoglobin. In these mouse models, unlike in patients, the characteristics of single mammary ducts containing pure intraductal cancer can be evaluated. Methods: The C3(1)SV40Tag mouse model of breast cancer (n=11) and normal FVBN mice (n=6) were used to measure T₂^* of normal mammary gland tissue, intraepithelial neoplasia, invasive cancers, mammary lymph nodes, and muscle. MRI experiments were performed on a 9.4T animal scanner. High resolution (117 microns) axial 2D multislice gradient echo images with fat suppression were acquired first to identify inguinal mammary gland. Then a multislice multigradient echo pulse sequence with and without fat suppression were performed over the inguinal mammary gland. The modulus of a complex double exponential decay detected by the multigradient echo sequence was used to fit the absolute proton free induction decay averaged over a region of interest to determine the T₂^* of water and fat signals. Results: The measured T₂^* values of tumor and muscle are similar (∼15 ms), and almost twice that of lymph nodes (∼8 ms). There was a statistically significant difference (p<0.03) between T₂^* in normal mammary tissue (13.7±2.9 ms) and intraductal cancers (11±2.0 ms) when a fat suppression pulse was applied. Conclusions: These are the first reported T ₂^* measurements from single mammary ducts. The results demonstrated that T₂^* measurements may have utility for identifying early pre-invasive cancers in mouse models. This may inspire similar research for patients using T₂^* for diagnostic imaging of early breast cancer.