Absolute choline tissue concentration mapping for prostate cancer localization and characterization using 3D 1H MRSI without water-signal suppression

Purpose Until now, H-1 MRSI of the prostate has been performed with suppression of the large water signal to avoid distortions of metabolite signals. However, this signal can be used for absolute quantification and spectral corrections. We investigated the feasibility of water-unsuppressed MRSI in patients with prostate cancer for water signal-mediated spectral quality improvement and determination of absolute tissue levels of choline. Methods Eight prostate cancer patients scheduled for radical prostatectomy underwent multi-parametric MRI at 3 T, including 3D water-unsuppressed semi-LASER MRSI. A postprocessing algorithm was developed to remove the water signal and its artifacts and use the extracted water signal as intravoxel reference for phase and frequency correction of metabolite signals and for absolute metabolite quantification. Results Water-unsuppressed MRSI with dedicated postprocessing produced water signal and artifact-free MR spectra throughout the prostate. In all patients, the absolute choline tissue concentration was significantly higher in tumorous than in benign tissue areas (mean +/- SD: 7.2 +/- 1.4 vs 3.8 +/- 0.7 mM), facilitating tumor localization by choline mapping. Tumor tissue levels of choline correlated better with the commonly used (choline + spermine + creatine)/citrate ratio (r = 0.78 +/- 0.1) than that of citrate (r = 0.21 +/- 0.06). The highest maximum choline concentrations occurred in high-risk cancer foci. Conclusion This report presents the first successful water-unsuppressed MRSI of the whole prostate. The water signal enabled amelioration of spectral quality and absolute metabolite quantification. In this way, choline tissue levels were identified as tumor biomarker. Choline mapping may serve as a tool in prostate cancer localization and risk scoring in multi-parametric MRI for diagnosis and biopsy procedures.

Automated summary

This study investigates the feasibility of water-unsuppressed MRSI in patients with prostate cancer for spectral quality improvement and absolute tissue choline level determination. Results show significantly higher choline tissue concentrations in tumorous areas compared to benign tissue, with choline mapping potentially serving as a tool for tumor localization. This technique enables improved spectral quality and absolute metabolite quantification for prostate cancer diagnosis and biopsy procedures.