B₁ Field Correction of T1 Estimation Should Be Considered for Breast Dynamic Contrast-enhanced MR Imaging Even at 1.5 T.

Abstract

Purpose To prospectively quantify the effect of T1 estimation in fat by B₁ correction in breast magnetic resonance (MR) imaging at 1.5 T and to examine the subsequent quantitative dynamic contrast material-enhanced parameters in breast cancer with and without B₁ correction. Materials and Methods This study had institutional review board approval, and informed consent was obtained from 72 patients with breast cancer before breast MR imaging studies were performed between January and July 2015. B₁⁺ field and variable flip angle (FA) mapping were included in the dynamic contrast-enhanced breast MR imaging protocol with a 1.5-T MR imaging system. Precontrast T1 relaxation in fat and breast tumors was computed with and without B₁ correction. The pharmacokinetic parameters of breast cancer were calculated by using the Tofts model with T1 values before and after B₁ correction. The Mann-Whitney U test and linear regression model were used for statistical analysis. Results The FA was 19% higher in the left breast and 3% lower in the right breast than the prescribed value. This 22% average FA difference created a 43% T1 estimation bias in fat between the breasts. The T1 variation in fat was reduced to 0.96% after B₁ correction. There was a 50% overestimation and a 7% underestimation of tumor T1 in the left breast and the right, respectively, associated with B₁ error. Assuming T1 after B₁ correction represents the true tumor T1, 41% underestimation in the left breast and 10% overestimation in the right without B₁ correction were seen in the dynamic contrast-enhanced parameters (including the volume transfer constant, or K^trans, fraction of extracellular extravascular space, or v_e, and blood normalized initial area under the gadolinium concentration curve to 90 seconds, or IAU_GCBN90). Conclusion B₁ correction for more accurate T1 values should be considered for quantitative dynamic contrast-enhanced breast MR imaging, even at 1.5 T, to offset significant systemic error. ^© RSNA, 2016.