123I-Meta-iodobenzylguanidine Sympathetic Imaging: Standardization and Application to Neurological Diseases

(123)I-meta-iodobenzylguanidine (MIBG) has become widely applied in Japan since its introduction to clinical cardiology and neurology practice in the 1990s. Neurological studies found decreased cardiac uptake of (123)I-MIBG in Lewy-body diseases including Parkinson's disease and dementia with Lewy bodies. Thus, cardiac MIBG uptake is now considered a biomarker of Lewy body diseases. Although scintigraphic images of (123)I-MIBG can be visually interpreted, an average count ratio of heart-to-mediastinum (H/M) has commonly served as a semi-quantitative marker of sympathetic activity. Since H/M ratios significantly vary according to acquisition and processing conditions, quality control should be appropriate, and quantitation should be standardized. The threshold H/M ratio for differentiating Lewy-body disease is 2.0-2.1, and was based on standardized H/M ratios to comparable values of medium-energy collimators. Parkinson's disease can be separated from various types of parkinsonian syndromes using cardiac (123)I-MIBG, whereas activity is decreased on images of Lewy-body diseases using both (123)I-ioflupane for the striatum and (123)I-MIBG. Despite being a simple index, the H/M ratio of (123)I-MIBG uptake is reproducible and can serve as an effective tool to support a diagnosis of Lewy-body diseases in neurological practice.