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

Rationale: 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.

Patients and methods: 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.

Results: 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%).

Conclusion: 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.