We investigated MRI changes in quantitative T2 parameters in lesions and healthy tissue in men on active surveillance (AS) for prostate cancer (PCa) taking dutasteride or placebo for six months. The protocol included a multi-echo sequence for quantification of the T2 relaxation times. A synthetic signal contrast (T2Q) between lesion and healthy tissue was assessed using quantitative T2 values. Signal contrast was calculated using T2-weighted sequence (T2W contrast). No differences for T2W contrast were observed. A significant correlation between T2Q and T2W contrast was shown. Dutasteride does not influence T2 contrast and relaxation in men on AS for PCa.