This study is designed to obtain an imaging training set that will be used to evaluate images in future trials. Currently, no radiopharmaceutical diagnostic imaging agent has been approved by the FDA in the U.S. for use in diagnosing Parkinson disease and related Parkinsonian syndromes. The diagnosis of Parkinsonian syndromes in the U.S. is based on clinical criteria only. The goal is to demonstrate that 123I-ALTROPANE® paired with SPECT imaging permits a more accurate early diagnosis of Parkinson disease than a clinical diagnosis by a general neurologist.