Stratification of AL and ATTR Amyloid in Systemic Amyloidosis using 18F-Florbetapir

Objectives The goal of this study was to assess the possibility of using Florbetapir to differentiate between AL and ATTR positive patients. We examine the use of dynamic imaging as a method for determination of the type of amyloid in confirmed systemic amyloidosis patients.

Methods A whole body CT low dose for attenuation and anatomic localization (50mAS) was acquired followed by dynamic PET imaging over the chest and upper abdomen for 80 minutes, which was then followed by a whole body PET scan from mid-thigh to the top of the head with 5 minute bed positions. A region of interest (ROI) was drawn in the upper right lobe of the liver avoiding common bile duct and gallbladder on all patients evaluated. Time activity curves (TAC) were generated and normalized to the peak value. Maximum and minimum normalized standard uptake values (nSUV) within a given time interval were recorded and ratios calculated. For standardization a 30 minute time interval following the peak value was chosen to evaluate across the patients. SPSS was then used to evaluate the data with discriminant function analysis used to assess statistical significance of the methodology.

Results ATTR patients had an increased values for ratios of maximum to minimum nSUV values over the selected 30 min time interval compared to AL amyloid patients. Discriminant function analysis indicated 100% classification of the small population in this study with p < 0.05 and a canonical correlation of the model to the data of > 90%.

Conclusions Based on nSUV ratio analysis there appears to be a difference in liver clearance between AL amyloid patients compared to ATTR amyloid patients. Liver clearance in the ATTR patients is faster within the given time frame than for AL patients and indicates some ability to stratify AL from ATTR patient populations.