Efficacy and acute volume of ablation will be assessed by contrast-enhanced MRI 48 - 72 hours after laser illumination to allow time for the appearance of coagulative necrosis and prior to reconfiguration of tissue by lytic action. An appearance of a 'void' on MRI would be more generally expected than lesion shrinkage. Efficacy of focal ablation of prostate tissue will be assessed by MRI /Ultrasound guided biopsy at 3 months (primary endpoint) and again at 1 year after laser treatment. Per standard of care patient follow up will continue on a 6 month basis beyond the one year follow up but will be outside the scope of the study.