P3-07-48: Axillary Imaging with Dynamic MRI Following Subcutaneous Injection of Superparamagnetic Iron Oxide Nanoparticles.

Abstract

Abstract Background: Surgical axillary staging with sentinel node biopsy in clinically node negative patients is standard of care in the management of breast cancer. However sentinel node biopsy is associated with morbidity including a 5% risk of lymphoedema. Superparamagnetic iron oxide (SPIO) enhanced axillary MRI is a promising novel imaging modality that could be used to characterize sentinel nodes non-invasively. We evaluated subcutaneous SPIO enhanced axillary MRI for pre-operative axillary imaging. Material and methods: Patients scheduled for sentinel node biopsy as part of surgical management of early breast cancer were invited to undergo pre-operative axillary MRI. All images were acquired on a 1.5T scanner using a surface coil. The initial 7 scans were acquired on a Siemens Avanto and the later scans on a Achieva MRI scanner (Philips Best, Netherlands). Following a T2-weighted morphological scan, patients were injected with 2ml of SPIO (4ml in the final 3 patients) subcutaneously into the circumareolar margin in the upper outer quadrant of the affected breast. Post injection, a slightly T2*-weighted dynamic scan was performed (gradient echo, TE = 1.53ms, TR=2.9ms, flip angle 7 degrees, 3mm slice thickness). In addition to the dynamic scan, in 16 patients, a T2 mapping sequence was performed at 10minutes and 120 minutes post injection (turbo spin echo, 8 equi-spaced TEs from 10 to 80ms, TR=2136ms, 3mm slices with an in plane resolution of 1.4×1.4mm). Image analysis was undertaken using Osirix (v3.8, 64-bit). Two consultant radiologists experienced at reading breast and axillary MRI reported all scans. Results: A total of 23 patients underwent axillary MRI with subcutaneous SPIO. Of these in 18 patients (78%), uptake of SPIO was seen in sentinel nodes and lymphatic tracts. At least 1 sentinel node was identified in 17 patients (74%). A total of 106 nodes were identified (4.6 ± 1.7 nodes per patient) and of these 40 demonstrated a significant drop in signal intensity following SPIO injection (1.7 ± 1.3 nodes per patient). All 3 involved nodes were seen to contain a metastatic deposit on MRI. Discussion: Axillary MRI with subcutaneous SPIO injection is a robust method for imaging sentinel nodes. The normal node count of the axillary basin is lower than expected on histology, suggesting that only the larger nodes and those that take up SPIO are visualized on MRI. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-07-48.