A review on the role of water Diffusion modeling in Magnetic Resonance Imaging of Prostate cancer

Prostate Cancer (PCa) is among of the tumors with highest incidence in men. Diagnosis of PCa is usually based on different techniques as digital rectal examination, prostate-specific antigen (PSA), transrectal ultrasonography, Magnetic Resonance Imaging (MRI) and transrectal biopsy. Thanks to its intrinsic ability to obtain anatomical, functional and molecular information, MRI is one of the most spread and powerful tools to diagnosis and staging of PCa. In particular, Diffusion-Weighted Imaging (DWI) MRI technique allows to obtain images with contrast depending on the microscopic mobility of water molecules in tissue, probing the microscopic structure. Moreover, from DWI images is possible to quantify the Apparent Diffusion Coefficient of water (ADC) using different diffusion models, as "Mono-exponential", "Bi-exponential", "Kurtosis", "Gamma distribution" and "Stretched exponential", all of them based on different assumptions on the water mobility in the tissue microenvironment. Despite that the diagnostic and prognostic power of some of these models be known, a clear connection with the physical, biological and physiological underlying features is lacking. In this work we will review all these models, showing results for patients suffering PCa, for which we have a complete clinical picture thanks to transrectal biopsy and other examinations.