Single-photon emission CT (SPECT) of the brain with 123I-FP-CIT (N - 3-fluoropropyl-2 - beta - carbomethoxy-3beta - [4-iodophenyl] - tropane), a radioactive tracer of dopamine transporter, can help detect basal ganglia dopaminergic neuronal dysfunction and function as a biomarker for diagnosing dementia with Lewy bodies.