Quantification of Prostate Cancer Metabolism Using 3D Multiecho bSSFP and Hyperpolarized [1-13 C] Pyruvate: Metabolism Differs Between Tumors of the Same Gleason Grade

Abstract

Background: Three-dimensional (3D) multiecho balanced steady-state free precession (ME-bSSFP) has previously been demonstrated in preclinical hyperpolarized (HP) ¹³ C-MRI in vivo experiments, and it may be suitable for clinical metabolic imaging of prostate cancer (PCa).

Purpose: To validate a signal simulation framework for the use of sequence parameter optimization. To demonstrate the feasibility of ME-bSSFP for HP ¹³ C-MRI in patients. To evaluate the metabolism in PCa measured by ME-bSSFP.

Study type: Retrospective single-center cohort study.

Phantoms/population: Phantoms containing aqueous solutions of [1-¹³ C] lactate (2.3 M) and [¹³ C] urea (8 M). Eight patients (mean age 67 ± 6 years) with biopsy-confirmed Gleason 3 + 4 (n = 7) and 4 + 3 (n = 1) PCa. FIELD STRENGTH/SEQUENCES: ¹ H MRI at 3 T with T₂ -weighted turbo spin-echo sequence used for spatial localization and spoiled dual gradient-echo sequence used for B₀ -field measurement. ME-bSSFP sequence for ¹³ C MR spectroscopic imaging with retrospective multipoint IDEAL metabolite separation.

Assessment: The primary endpoint was the analysis of pyruvate-to-lactate conversion in PCa and healthy prostate regions of interest (ROIs) using model-free area under the curve (AUC) ratios and a one-directional kinetic model (k_P ). The secondary objectives were to investigate the correlation between simulated and experimental ME-bSSFP metabolite signals for HP ¹³ C-MRI parameter optimization.

Statistical tests: Pearson correlation coefficients with 95% confidence intervals and paired t-tests. The level of statistical significance was set at P < 0.05.

Results: Strong correlations between simulated and empirical ME-bSSFP signals were found (r > 0.96). Therefore, the simulation framework was used for sequence optimization. Whole prostate metabolic HP ¹³ C-MRI, observing the conversion of pyruvate into lactate, with a temporal resolution of 6 seconds was demonstrated using ME-bSSFP. Both assessed metrics resulted in significant differences between PCa (mean ± SD) (AUC = 0.33 ± 012, k_P = 0.038 ± 0.014) and healthy (AUC = 0.15 ± 0.10, k_P = 0.011 ± 0.007) ROIs.

Data conclusion: Metabolic HP ¹³ C-MRI in the prostate using ME-bSSFP allows for differentiation between aggressive PCa and healthy tissue.

Evidence level: 2 TECHNICAL EFFICACY: Stage 1.

Keywords: bSSFP; hyperpolarized [1-13C] pyruvate; metabolic 13C-MRI.