PET's usefulness is shown in this study of a patient with Parkinson's disease, made in the PET installation of the Crump Institute for Biological Imaging (1). This disease is characterized by many neurological alterations, such as muscle rigidity, tremor of the hands, speech slurring, difficult gait, etc. It is caused by a widespread lesion of some areas of the brain, called basal ganglia, which then produce less endogenous chemical substances, such as DOPA, which are necessary for the motor functions.
In the sequence of image, a PET machine was used to make an image of the brain showing where there is a higher concentration of DOPA (the bean shaped regions in red and green are a part of the basal ganglia). The uppermost image shows a normal brain, the middle one the brain of a patient with Parkinson (you can see how the brain concentration of DOPA has decreased(, and the third shows the brain of the same patient after receiving an implant of DOPA-secreting tissue (tha concentration is nearly normal again). This is fabulous stuff, making possible a new window into the brain.