Virtual-reality surgery. A PHANToM thimble enables a trainee surgeon to experience what it feels like to perform a needle biopsy on the brain. In the background is a MRI scan of a brain with an orange line showing the direction of a virtual-reality needle inserted into a suspected brain tumour. PHANToM (Personal HAptic iNTerface Mechanism) consists of a freely moving thimble on a motorized arm linked to a computer. By applying forces to the fingertip through the thimble, the device enables the user to touch, feel and stroke" 3-D virtual-reality objects. In this example the surgeon feels a "pop" as each tissue layer in the brain scan is pierced by the virtual needle."