B1 transmission‐field inhomogeneity and enhancement ratio errors in dynamic contrast‐enhanced MRI (DCE‐MRI) of the breast at 3T

Purpose:

To quantify B₁ transmission‐field inhomogeneity in breast imaging of normal volunteers at 3T using 3D T₁‐weighted spoiled gradient echo and to assess the resulting errors in enhancement ratio (ER) measured in dynamic contrast‐enhanced MRI (DCE‐MRI) studies of the breast.

Materials and Methods:

A total of 25 volunteers underwent breast imaging at 3T and the B₁ transmission‐fields were mapped. Gel phantoms that simulate pre‐ and postcontrast breast tissue T₁ were developed. The effects of B₁‐field inhomogeneity on ER, as measured using a 3D spoiled gradient echo sequence, were investigated by computer simulation and experiments on gel phantoms.

Results:

It was observed that by using the patient orientation and MR scanner employed in this study, the B₁ transmission‐field field is always reduced toward the volunteer's right side. The median B₁‐field in the right breast is reduced around 40% of the expected B₁‐field. For some volunteers the amplitude was reduced by more than 50%. Computer simulation and experiment showed that a reduction in B₁‐field decreases ER. This reduction increases with both B₁‐field error and contrast agent uptake.

Conclusion:

B₁ transmission‐field inhomogeneity is a critical issue in breast imaging at 3T and causes errors in quantifying ER. These errors would be sufficient to reduce the conspicuity of a malignant lesion and could result in reduced sensitivity for cancer detection. J. Magn. Reson. Imaging 2010;31:234–239. © 2009 Wiley‐Liss, Inc.