Molecular imaging of the prostate: Comparing total sodium concentration quantification in prostate cancer and normal tissue using dedicated 13 C and 23 Na endorectal coils.

Abstract

Background There has been recent interest in non-proton MRI including hyperpolarized carbon-13 (13C) imaging. Prostate cancer has been shown to have a higher tissue sodium concentration (TSC) than normal tissue. Sodium (23Na) and 13C nuclei have a frequency difference of only 1.66 MHz at 3T, potentially enabling 23Na imaging with a 13C-tuned coil and maximizing the metabolic information obtained from a single study.

Purpose To compare TSC measurements from a 13C-tuned endorectal coil to those quantified with a dedicated 23Na-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 1H/23Na and 1H/13C endorectal receive coils to quantify tissue sodium concentration.

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 13C-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 23Na-coil (41.8 mM) and with the 13C-coil (46.6 mM; p=0.38). Bland–Altman plots showed good repeatability for tumor TSC measurements between coils, with a reproducibility co-efficient of 9 mM; the coefficient of variation between the coils was only 12%. Pearson correlation coefficient for TSC between coils for all measurements was r = 0.71 (r2 = 0.51) indicating a strong positive linear relationship. The mean TSC within PZ tumors was significantly higher compared to normal PZ for both the 23Na-coil, 45.4 mM (p=0.02) and the 13C-coil at 49.4 mM (p=0.002).

Data Conclusion: We demonstrated the feasibility of using a carbon-tuned coil to quantify tissue sodium concentration, enabling dual metabolic information from a single coil. This approach could make the acquisition of both 23Na-MRI and 13C-MRI feasible in a single clinical imaging session.