Abstract Aims The gold standard for detection of Sentinel Lymph Nodes (SLN) is a combined radioisotope and blue dye breast injection, using a gamma probe (GP). A new, non-radioactive method was developed, using a tracer (Sienna+® ) of superparamagnetic iron oxide (SPIO) nanoparticles and a manual magnetometer (SentiMag® ) (SM). The IMAGINE study was designed to show the non-inferiority of SM compared to GP, for the detection of SLN in breast cancer patients with SLN biopsy indication. Methods From November 2013 to June 2014, 181 patients were recruited, and 321 nodes were excised and assessed ex-vivo. Readings from both SM and GP devices were recorded during transcutaneous, intraoperative, and ex-vivo detection attempts. Results At the patient level, ex-vivo detection rates (primary variable) with SM and GP were 97.8% and 98.3% (concordance rate 99.4%). Transcutaneous and intraoperative detection rates were 95.5% vs 97.2%, and 97.2% vs 97.8% for SM and GP respectively (concordance rates > 97%). At the node level, intraoperative and ex-vivo detection rates were 92.5% vs 89.3% and 91.0% vs 86.3% for SM and GP respectively. In all cases the non-inferiority of SM compared to SM was shown by ruling out a predefined non-inferiority margin of 5%. Conclusions Our study showed the non-inferiority of SM as compared to GP. Moreover, the ex-vivo and intraoperative detection rates at the node level were slightly higher with SM.