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

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

Purpose: To compare TSC measurements from a C-tuned endorectal coil to those quantified with a dedicated Na-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/ Na and H/ C 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 Na coil and 40.1 and 36.3 mM, respectively, with the C 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 coil (41.8 mM) and with the C 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 = 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 coil (45.4 mM; P = 0.02) and the C 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-MRI and C-MRI feasible in a single clinical imaging session.

Level Of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:90-97.