Abstract
Abstract Background: Superparamagnetic iron oxide (SPIO) enhanced axillary MRI is a promising novel imaging modality that could be used to characterize sentinel nodes non-invasively. In order to better characterize lymph nodes and evaluate their morphological features, we imaged nodes ex-vivo using high resolution MRI, following a pre-operative subcutaneous injection of SPIO. Material and methods: Prior to surgery patients received a circumareolar injection of SPIO (Endorem, Guerbet, Paris) into the upper outer quadrant of the affected breast. Sentinel lymph nodes excised during surgery were transported to the imaging department fresh. Nodes were placed in glass tubes and scanned using a Bruker 9.4T MRI system (T2 mapping: turbo spin echo, 16 equi-spaced TEs from 7.1 to 113.6 ms, TR = 1616 ms. T2* mapping: gradient echo, 6 equi-spaced TEs from 3.5 to 21 ms, TR = 1000 ms, flip angle = 30 degrees. Diffusion-weighted: spin echo, b-values 0 and 1000 s/mm2, TE = 18 ms, TR = 6500 ms.). Slice thickness was 1 mm with an in plane spatial resolution of 100μm. Image analysis was undertaken using Osirix (v3.8, 64-bit). Results: A total of 40 nodes were successfully imaged, excised from 14 patients. The internal architecture of nodes was clearly seen and in the 3 involved nodes, a macrometastasis was identified. Three patients received a 4ml injection of SPIO and 11 patients, a 2ml injection. More SPIO deposition was seen within nodal sinuses following 4ml of SPIO, but there was no significant decrease in mean T2 value. Four nodes were re-imaged following formalin fixation and nodal architecture was unchanged with a trend towards an increase in mean T2 values within nodes. SPIO was identified in all sentinel nodes. Discussion: Ex-vivo MRI with subcutaneous SPIO contrast, is a useful method for imaging and characterization of sentinel nodes. A better understanding of ex-vivo features is a useful aide to understanding the morphological features seen following in-vivo SPIO enhanced axillary MRI. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-08-07.
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