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Abstract

Purpose:

Neoadjuvant treatment response in lymph nodes predicts patient outcome, but existing methods do not track response during therapy accurately. In this study, specialized hardware was used to adapt high-field (7T) 31P magnetic resonance spectroscopy (MRS), which has been shown to track treatment response in small breast tumors, to monitor axillary lymph nodes.
Method:

A dual-tuned quadrature coil that is a 31P (120 MHz) transceiver and a 1H (300 MHz) receiver was designed using a novel detune circuit. The transceiver/receiver coil in the axilla is used with a fractionated dipole antenna on the back of the subject and the conventional breast coil for transmit.
Results:

The novel circuit detuned the 1H resonance without disturbing the 31P resonance. In vivo demonstrations included: >80% homogeneous B1+ for 1H over the axilla, identification of a small (3-mm diameter) lymph node, and 31P MR spectra from a single healthy lymph node. The setup can detect <2 millimolar concentrations of metabolites from a 2-mL voxel.
Conclusions:

The first 31P MR spectrum from an in vivo lymph node indicates that the presented design may be sufficiently sensitive to detect metabolic response to neoadjuvant therapy. Multinuclei MRS of the lymph nodes at 7T is possible through combining lightweight antenna elements with dual-tuned transceiver/receive-only coils.