Development of an optimized MRI protocol for a rapid preoperative identification of sentinel lymph nodes using superparamagnetic iron oxide - The Gothenburg fast acquisition sentinel lymph node tracking magnetic resonance imaging protocol (GO-FAST-MRI).

Abstract

Introduction: Determining sentinel lymph node (SLN) status is important for treatment decisions in patients with melanoma. Superparamagnetic iron oxide nanoparticles (SPIO) combined with MRI have emerged as an alternative to Technetium^99m lymphoscintigraphy for preoperative mapping of SLN, however, the MRI protocols so far are extensive with long in-camera time. This study aimed to evaluate an optimized MRI protocol for rapid identification of SLNs using SPIO as a tracer, without compromising diagnostic quality, the GOthenburg Fast Acquisition Sentinel lymph node Tracking MRI (GO-FAST-MRI).

Materials and methods: In this prospective single-center pilot study, patients with confirmed melanoma on the trunk or limbs, without clinically suspected lymph node metastasis, were eligible. All patients received an injection of 0.1 mL SPIO divided into four quadrants around the scar. The GO-FAST-MRI protocol, using only T1-weighted and Dixon sequences over the axillary or inguinal basins, was conducted no earlier than 30 min post-injection. Technetium and lymphoscintigraphy were used according to routine. SLN-biopsy was performed using a handheld magnetometer and gamma probe for SLN-detection.

Results: Twenty-one patients were enrolled, and SLNs were successfully identified in all with both methods. The GO-FAST-MRI protocol was performed in 4 min and detected more SLNs than lymphoscintigraphy (54 vs 42), but the number of SLNs identified during surgery with the magnetometer and gamma probe was the same (50 for both methods). Of the SLNs removed, five were found to have metastases, all of which showed uptake of SPIO and Tc99m.

Conclusion: The novel GO-FAST-MRI protocol, with a 4-min scan-time, was feasible in detecting SLNs in all patients. Both the preoperative SLN-mapping and intraoperative SLN-detection using the magnetic technique was comparable to the radioactive technique.