Breast Cancer and Melanoma Metastases in Regional Lymph Nodes Identified Using In Vivo Proton Magnetic Resonance Spectroscopy at 3 Tesla

Purpose: This study investigates the use of high field (3 Tesla) in vivo proton magnetic resonance spectroscopy to non-invasively identify loco-regional lymph nodes containing metastatic disease in patients with breast cancer and melanoma.

Methods: Breast cancer and melanoma patients with lymph node masses thought to contain metastatic cancer were examined using a whole-body 3T system (Magnetom Trio, Siemens AG, Erlangen, Germany) combined with either a 4-element phased array breast coil (Invivo Corporation, Gainesville, USA) or a home-made 10-cm circular coil. For breast patients lymph nodes of interest were identified on T1-weighted (TE/TR 16/560ms, FOV 18-cm, 0.35×0.70×3.0-mm resolution) and STIR (TE/TI/TR 96/160/4500ms, FOV 18-cm, 0.35×0.70×3.0-mm resolution) sagittal images. For melanoma patients lymph nodes of interest were identified on T1-weighted (TE/TR 16/560ms, FOV 18-cm, 0.35×0.70×3.0-mm resolution) and T2-weighted (TE/TR 96/4000ms, FOV 18-cm, 0.35×0.70×3.0-mm resolution) axial images. Localized single voxel proton spectroscopy was undertaken on lymph nodes of interest using a standard double spin-echo slice-selective technique (Point REsolved Spatial Selection (PRESS)) (TE 135ms, TR 3000ms). 128 signal averages were acquired with 16-step EXOR-cycle phase cycling scheme (1024 complex data points, bandwidth of 1500Hz). Coronal 2D-CSI data was collected with outer volume suppression (OVS) pulses, offset to the frequency of lipid, used to limit lipid bleed into the region of interest (1,2)

Results: 3T MRI clearly identifies lymph node masses suspected to contain metastatic disease. For both breast cancer abnd melanoma patients localised single voxel spectroscopy accurately identified lymph nodes containing metastatic cancer based on the presence of a prominent resonance centered at 3.2 pmm consistent with choline and choline containing metabolites. 2D CSI was able to map the extent of increased choline content in the axillary nodes of a breast cancer patient with extensive lymph node involvement. Independent histopathological diagnosis confirmed the spectral diagnoses.

Conclusion: At 3T, localised single voxel MR spectroscopy and 2D CSI allow preoperative pathological diagnosis of loco-regional lymph nodes in breast cancer and melanoma patients using the presence of diagnostic metabolites. Access to such MR technology should allow more accurate staging of patients with suspected metastatic disease and ultimately remove the need for invasive lymph node resection for the purposes of diagnosis.

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