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

Abstract

) (CCGII Program).q RSNA, 2016 Purpose:To prospectively quantify the effect of T1 estimation in fat by B 1 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 B 1 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. B 1 + 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 B 1 correction. The pharmacokinetic parameters of breast cancer were calculated by using the Tofts model with T1 values before and after B 1 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 B 1 correction. There was a 50% overestimation and a 7% underestimation of tumor T1 in the left breast and the right, respectively, associated with B 1 error. Assuming T1 after B 1 correction represents the true tumor T1, 41% underestimation in the left breast and 10% overestimation in the right without B 1 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 GC BN90). Conclusion:B 1 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.q RSNA, 2016

Correcting time‐intensity curves in dynamic contrast‐enhanced breast MRI for inhomogeneous excitation fields at 7T

“…However, a completely homogeneous field is nontrivial to achieve even with state‐of‐the‐art hardware, so some amount of field inhomogeneity is always expected. This is illustrated by recent works showing that corrections for can be beneficial even at 1.5T and 3T …”

Estimating B1+ in the breast at 7 T using a generic template

“…As is commonly done in quantitative DCE‐MRI, we used B 1 + maps to correct for the effects of B 1 + inhomogeneities using a variable flip‐angle T 1 mapping method . This method uses several T 1 ‐weighted gradient echo scans at different flip angles to estimate the T 1 value at every recorded voxel by performing a fit of the signal equation, which is a function of the applied flip angle.…”

“…As is commonly done in quantitative DCE-MRI, we used B 1 + maps to correct for the effects of B 1 + inhomogeneities using a variable flip-angle T 1 mapping method. 10,11,22,28,29 This method uses several T 1 -weighted gradient echo scans at different flip angles to estimate the T 1 value at every recorded voxel by performing a fit of the signal equation, which is a function of the applied flip angle. Since this is a voxel-wise method, B 1 + correction can be easily applied by fitting the function while using the actual flip angle as the independent variable, i.e.…”

“…It has been shown that applying B 1 + correction at 3 T has a significant effect on the results of quantitative analysis and serves to reduce differences in quantitative parameter estimations between the right and left breasts . Recent work shows that, even at 1.5 T, refraining from B 1 + field corrections leads to a 50% estimation error in tumor T 1 and consequently a 41% estimation error in pharmacokinetic parameters . At 7 T, the B 1 + field variations manifest themselves on a smaller spatial scale, such that variations within a single breast become significant.…”

“…10 Recent work shows that, even at 1.5 T, refraining from B 1 + field corrections leads to a 50% estimation error in tumor T 1 and consequently a 41% estimation error in pharmacokinetic parameters. 11 At 7 T, the B 1 + field variations manifest themselves on a smaller spatial scale, such that variations within a single breast become significant. Therefore, when applying DCE-MRI at 7 T, corrections using B 1 + field maps are imperative.…”