In vivo lymph node CEST-Dixon MRI in breast cancer patients with metastatic lymph node involvement

Purpose: Axillary lymph nodes (LNs) often present a reservoir for metastatic breast cancer, yet metastatic LN involvement cannot be discerned definitively using diagnostic imaging. This study investigated whether in vivo CESTmay discriminate LNs with versus without metastatic involvement. Methods: 3T MRI was performed in patients with breast cancer before clinically-indicated mastectomy or lumpectomy with LN removal, after which LN metastasic involvement was determined using histological evaluation. Non- contrast anatomical imaging, as well as B-0 and B-1 field maps, were acquired in sequence with three-point CEST-Dixon (3D turbo-gradient-echo; factor= 25; TR/TE1/.TE= 851/1.35/1.1 ms; spatial-resolution= 2.5 x 2.5 x 6 mm; slices= 10; four sinc-gauss pulses with duty- cycle= 0.5, total saturation duration= 701.7 ms; B-1 = 1.5 mu T; saturation offsets=-5.5 to +5.5 ppm; stepsize= 0.2 ppm; scan duration= 6 min 30 s). The mean z-spectrum from LNs with (n= 20) versus without (n= 22) metastatic involvement were analyzed and a Wilcoxon rank-sum test (significance: p < 0.05) was applied to evaluate differences in B-0, B-1, and magnetization transfer ratio (MTR) in differing spectral regions of known proton exchange (nuclear Overhauser effect [NOE], amide, amine, and hydroxyl) between cohorts. Results: No difference in axillary B-1 (p= 0.634) or B-0 (p= 0.689) was observed between cohorts. Elevated MTR was observed for the NOE (-1.7 ppm; MTR= 0.285 +/- 0.075 vs. 0.248 +/- 0.039; p= 0.048), amine (+2.5 ppm; MTR= 0.284 +/- 0.067 vs. 0.234 +/- 0.31; p= 0.005), and hydroxyl (+1 ppm; MTR= 0.394 +/- 0.075 vs. 0.329 +/- 0.055; p= 0.002) protons in LNs from participants with versus without metastatic involvement. Conclusions: Findings are consistent with a unique metastatic LN microenvironment detectable by CEST-Dixon and suggest that CEST MRI may have potential for mapping LN metastasis non-invasively in vivo.

Automated summary

This study investigates whether in vivo imaging with CEST-Dixon can distinguish lymph nodes with metastatic involvement from those without. The results suggest that CEST-Dixon can detect a unique microenvironment in metastatic lymph nodes and has the potential for non-invasive mapping of lymph node metastasis in vivo.