Quantitative imaging of holmium-166 with an Anger camera

The objective of this study was to develop a quantitative Anger camera imaging approach for 166Ho in the skeletal system of patients. A dual energy window method was designed to subtract the interference from septal penetration and bremsstrahlung events in Anger camera images acquired with the 80 keV x-rays emitted by 166Ho. The validity of this scatter subtraction method for 166Ho images was demonstrated as improvements of the line spread function and modulation transfer function. Camera sensitivity was found to be nearly independent of source-to-collimator distance only for images acquired with a high-energy collimator. Studies in an Alderson abdominal water phantom demonstrated scatter subtraction can provide quantitative Anger camera images of 166Ho with a scatter multiplier of k = 1.0 and a correction for attenuation. Attenuation correction factors derived from a transmission image were measured for the phantom and verified with water-equivalent blocks of known thickness. Whole-body scan images of 166Ho localized in the skeletal system of patients were significantly improved with this simple scatter subtraction method, and when used to estimate the activity distribution within separate bone regions of the skeleton.