Molecular Imaging of the Prostate: Comparing Total Sodium Concentration Quantification in Prostate Cancer and Normal Tissue Using Dedicated 13C and 23Na Endorectal Coils

Background: There has been recent interest in nonproton MRI including hyperpolarized carbon-13 (C-13) imaging. Prostate cancer has been shown to have a higher tissue sodium concentration (TSC) than normal tissue. Sodium (Na-23) and C-13 nuclei have a frequency difference of only 1.66 MHz at 3T, potentially enabling Na-23 imaging with a C-13-tuned coil and maximizing the metabolic information obtained from a single study. Purpose: To compare TSC measurements from a C-13-tuned endorectal coil to those quantified with a dedicated Na-23-tuned coil. Study Type: Prospective. Population: Eight patients with biopsy-proven, intermediate/high risk prostate cancer imaged prior to prostatectomy. Sequence: 3T MRI with separate dual-tuned H-1/Na-23 and H-1/C-13 endorectal receive coils to quantify TSC. Assessment: Regions-of-interest for TSC quantification were defined for normal peripheral zone (PZ), normal transition zone (TZ), and tumor, with reference to histopathology maps. Statistical Tests: Two-sided Wilcoxon rank sum with additional measures of correlation, coefficient of variation, and Bland-Altman plots to assess for between-test differences. Results: Mean TSC for normal PZ and TZ were 39.2 and 33.9 mM, respectively, with the 23Na coil and 40.1 and 36.3 mM, respectively, with the C-13 coil (P = 0.22 and P = 0.11 for the intercoil comparison, respectively). For tumor tissue, there was no statistical difference between the overall mean tumor TSC measured with the Na-23 coil (41.8 mM) and with the C-13 coil (46.6 mM; P = 0.38). Bland-Altman plots showed good repeatability for tumor TSC measurements between coils, with a reproducibility coefficient of 9 mM; the coefficient of variation between the coils was 12%. The Pearson correlation coefficient for TSC between coils for all measurements was r = 0.71 (r(2) = 0.51), indicating a strong positive linear relationship. The mean TSC within PZ tumors was significantly higher compared with normal PZ for both the Na-23 coil (45.4 mM; P = 0.02) and the C-13 coil (49.4 mM; P = 0.002). Data Conclusion: We demonstrated the feasibility of using a carbon-tuned coil to quantify TSC, enabling dual metabolic information from a single coil. This approach could make the acquisition of both Na-23-MRI and C-13-MRI feasible in a single clinical imaging session.