Oncological Prognosis of Prostate Lesions by Chemical Exchange Saturation Transfer Magnetic Resonance Imaging (CEST-MRI)

Plain-language summary

Prostate cancer is the second most common type of cancer in men only after lung cancer, and accounts for \~3.8% of all deaths caused in men in 2018. Multiparametric MRI, which combines anatomical MRI sequences (T2-weighted acquisitions) and functional sequences (DWI Diffusion-Weighted Imaging or dynamic contrast-enhanced (DCE) acquisitions), constitutes a key tool in the detection and monitoring of the therapeutic response in the context of the management of this prostate cancer. In this context, a recognized radiological consensus has been established in order to standardize MRI acquisition protocols and the data processing scheme (Prostate Imaging Reporting and Data System, PI-RADS protocol). Although the improvement provided by multiparametric MRI is significant for the detection of prostate cancer in the clinic, approximately one third of cases remain equivocal. There is therefore a clear clinical advantage in having additional information to support the diagnosis by discriminating between low-grade, intermediate-grade and high-grade tumors and thus reduce the need for biopsies. CEST (chemical exchange saturation transfer) MRI is a promising molecular imaging tool for specifically detecting metabolites containing exchangeable protons present on amide, amine or even hydroxyl functions. MRI-CEST allows non-invasively to highlight molecules of interest such as lactate, glutamate, citrate and other mobile proteins and peptides involved in the carcinogenesis process and usually impossible to visualize by MRI or MRS (Magnetic Resonance Spectroscopy). Exchangeable protons also have the property of seeing their exchange rates modified depending on the surrounding pH, making this CEST contrast sensitive to pH variations. Then, it is APT-CEST (Amide Proton Transfer CEST). The first efforts to translate this method from the preclinical to the clinic were made for brain imaging of gliomas with a significant contribution of APT-CEST in the stratification of tumors. Now, work is expanding to the imaging of other types of tumors such as pelvic tumors, digestive tumors or even breast or lung cancer. Currently, only a few studies have explored CEST MRI in prostate cancer with several limitations both in terms of data acquisition strategy and signal processing. The expertise of the preclinical component of the IVIA platform (In vivo Imaging Auvergne) will make it possible to remove these obstacles and highlight the interest of CEST MRI for the diagnosis and identification of the tumor stage. Thus, the addition of CEST-MRI to the multiparametric MRI strategy will complete the morphological and functional analysis with metabolic criteria that can be decisive in guiding the diagnosis. The main objective of this study is to study the relationship between the APT-CEST parameter measured in CEST MRI and the gold standard given by the Gleason score (from the anatomopathological analysis of prostate biopsies), these two data being established for each patient. Secondary objectives are: * To study the association between all the CEST MRI parameters (APT-CEST, and magnetization transfer ratio with asymmetric analysis (MTRasym) measurements, Guanidyl/APT ratio, Nuclear Overhauser Enhancement (NOE) signal) and: * The Gleason score * The PI-RADS score, calculated from the readings taken for each of the suspicious lesions identified on multiparametric MRI (T2-weighted anatomical acquisitions and diffusion-weighted DWI or dynamic DCE acquisitions); * The measurement of the blood prostate-specific antigen (PSA) level; * The volume of the prostate, determined on the anatomical MRI images. * To situate the predictive potential of CEST measurements in relation to other variables a priori associated with the Gleason score.

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