Feasibility of breast MRI after sentinel procedure for breast cancer with superparamagnetic tracers

The gold standard for detection of axillary sentinel lymph nodes uses injection of a radioisotope (99Tc Nanocoll). As an alternative to this method, a magnetometer detecting the superparamagnetic tracer Sienna+^® can be applied for detection of sentinel lymph nodes. The goal of this study was to determine whether interpretation of breast MRI is impaired by Sienna+^® tracer residues in the operated breast and axillary lymph nodes after a sentinel procedure using this tracer.

34 patients who received the Sienna+^® tracer for marking the sentinel node were invited to undergo a follow-up breast MRI. Native MR images were obtained from breast and axilla. The breast MRIs were evaluated by two independent breast radiologists for Sienna+^® tracer related artefacts and for the degree of impairment of the MR imaging.

24 of the 34 invited patients took part in this study. The mean time since injection of Sienna+^® was 42 months (40.6-45.4 months). Two patients had bilateral surgery with injections in both breasts, leading to a total of 26 separate cases. One case had to be excluded due to breathing artefacts. In 10 cases (40%), impaired imaging was found. In three cases (12%), the MRI scan reading was impossible due to Sienna+^® tracer residues, the other 12 cases (48%) showed no restriction. In the subgroup of patients treated with breast conserving surgery, tracer residue artefacts were found in 13 of 17 patients (76.5%).

To our knowledge, in this study for the first time MR feasibility after Sienna injection was investigated. Sienna+^® impaired breast MRI after a mean follow-up time of 42 months in half of the cases. Further research is needed to investigate time and field-strength dependency of tracer detectability as well as the diagnostic impact of these artifacts on contrast-enhanced imaging in a clinical setting.