The hypothesis that physiological and biochemical changes associated with proliferating malignant tumors may cause an increase in total tissue sodium concentration (TSC) was tested with non-invasive, quantitative sodium (²³Na) magnetic resonance imaging (MRI) in patients with benign and malignant breast tumors.

²³Na and ¹H MRI of the breast was performed on 22 women with suspicious breast lesions (≥1 cm) at 1.5 Tesla. A commercial proton (¹H) phased array breast coil and custom solenoidal ²³Na coil were used to acquire ¹H and ²³Na images during the same MRI examination. Quantitative 3-dimensional ²³Na projection imaging was implemented with negligible signal loss from MRI relaxation, or from radio-frequency field inhomogeneity, in less than 15 min. Co-registered ¹H and ²³Na images permitted quantification of TSC in normal and suspicious tissues on the basis of ¹H MRI contrast enhancement and anatomy, with histology confirmed by biopsy.

Sodium concentrations were consistently elevated in (N = 19) histologically proven malignant breast lesions by an average of 63% compared to glandular tissue. The increase in sodium concentration in malignant tissue was highly significant compared to unaffected glandular tissue (P < 0.0001, paired t-test), adipose tissue, and TSC in three patients with benign lesions.

Elevated TSC in breast lesions measured by non-invasive ²³Na MRI appears to be a cellular-level indicator associated with malignancy. This method may have potential to improve the specificity of breast MRI with only a modest increase in scan time per patient.