Quantitative sodium MR imaging at 7 T: Initial results and comparison with diffusion-weighted imaging in patients with breast tumors

To investigate the clinical feasibility of a quantitative sodium 23 (²³Na) magnetic resonance (MR) imaging protocol developed for breast tumor assessment and to compare it with 7-T diffusion-weighted imaging (DWI). Materials and Methods: Written informed consent in this institutional review board-approved study was obtained from eight healthy volunteers and 17 patients with 20 breast tumors (five benign, 15 malignant). To achieve the best image quality and reproducibility, the ²³Na sequence was optimized and tested on phantoms and healthy volunteers. For in vivo quantification of absolute tissue sodium concentration (TSC), an external phantom was used. Static magnetic field, or B₀, and combined transmit and receive radiofrequency field, or B₁, maps were acquired, and image quality, measurement reproducibility, and accuracy testing were performed. Bilateral ²³Na and DWI sequences were performed before contrast material-enhanced MR imaging in patients with breast tumors. TSC and apparent diffusion coefficient (ADC) were calculated and correlated for healthy glandular tissue and benign and malignant lesions. Results: The ²³Na MR imaging protocol is feasible, with 1.5-mm inplane resolution and 16-minute imaging time. Good image quality was achieved, with high reproducibility (mean TSC values 6 standard deviation for the test, 36 mmol per kilogram of wet weight ± 2 [range, 34-37 mmol/kg ± for the retest, 37 mmol/kg ±1 [range, 35-39 mmol/kg]; P = .610) and accuracy (r = 0.998, P <.001). TSC values in normal glandular and adipose breast tissue were 35 mmol/kg 6 3 and 18 mmol/kg ± 3, respectively. In malignant lesions (mean size, 31 mm ± 24; range, 6-92 mm), the TSC of 69 mmol/kg 6 10 was, on average, 49% higher than that in benign lesions (mean size, 14 mm 6 12; range, 6-35 mm), with a TSC of 47 mmol/kg ± 8 (P = .002). There were similar ADC differences between benign ([1.78 6 0.23] 3 10^-3 mm²/sec) and malignant ([1.03 ± 0.23] 3 10^-3mm²/sec) tumors (P = .002). ADC and TSC were inversely correlated (r = 20.881, P < .001). Conclusion: Quantitative 23Na MR imaging is clinically feasible, may provide good differentiation between malignant and benign breast lesions, and demonstrates an inverse correlation with ADC.