SU‐GG‐I‐146: Characterization of Mouse Mammary Glands by Measuring T2*: A Comparison of SV40Tag and FVB/N Mice

Abstract

Purpose: An improved understanding of T2* in normal breast and intraductal cancer could lead to improvements in diagnostic accuracy. This study characterizes T2* in both a preclinical model of breast/mammary cancer (SV40Tag) and in healthy (FVB/N) mice. At ∼12 weeks, C3(1)SV40Tag mice develop mammary in situ neoplasms (MIN) that resemble ductal carcinoma in situ (DCIS) in women. Method and Materials: Eight SV40Tag and six FVB/N mice were imaged using a 9.4T Bruker magnet. Respiratory gated multi‐gradient echo pulse sequences were used to measure T2* with equivalent TR ∼1000ms, minimum TE of 1.5ms, 9 echoes at 3ms spacing. Generally, T2* was calculated by fitting the MRI signal intensity to a single exponential decay function. However, when fat was present, a modulus of complex double exponential decay function was needed. Results: For SV40Tag mice, T2* of muscle, lymph node, and tumor can be calculated from a single exponential function. T2* of normal mammary gland (NMG) and MIN need to be extracted from the modulus of complex function due to the fatty signal. Conversely, for FVB/N mice, all T2* can be calculated from single exponential function. On average muscle, tumor and NMG water components have slightlysmaller T2* values (∼15ms), but lymph node and NMG water components have slightly smaller T2* values (∼9.5ms). The fat in NMG and MIN have the smallest T2* values (∼3.8ms). In addition, NMG in SV40Tag is fattier than in FVB/N mice (57% vs. 12%, p<0.0001) for the selected ROIs. Conclusion: To accurately determine T2*, it is necessary to separate water/fat in fat‐rich mammary glands. In this pilot study, MIN lesions exhibit a larger separation between the long and short T2* values in comparison to NMG. Additionally, SV40Tag mice exhibit a higher percentage fat in NMG ROIs due to genetic differences.