B-corrected breast T mapping at ultralow field.

PURPOSE

This study aims to develop an efficient T mapping approach that is free from systematic bias caused by B inhomogeneity in ultralow-field (ULF) MRI and to determine the T values (without fat suppression) of breast tissues at 6.5 mT.

METHODS

We describe here a method for ULF T mapping using a variable flip angle approach for both mapping T and B. The B mapping is used to correct the T maps-and, unique to operation in the ULF regime, a B map acquired in a phantom can be applied to the in vivo T mapping data, reducing in vivo scan time. The T mapping method was validated in vitro with copper sulphate phantoms at seven different concentrations. A breast phantom was scanned to test the T mapping protocol. Four healthy volunteers were recruited for T mapping to obtain in vivo T values of breast tissues. No fat suppression was implemented in this preliminary study.

RESULTS

The copper sulphate phantom T map measurements have less than 13% deviation from the reference T values, and less than 6% deviation when the reference T was greater than 50 ms. Four healthy volunteers were scanned for T mapping. In these in vivo breast T maps, the 25th to 75th percentiles ranged from 79 to 243 ms at 6.5 mT.

CONCLUSION

Variable flip angle method can be used for both B and T mapping at ULFs, which enables efficient in vivo T mapping for ULF MRI.