Activity quantitation in SPECT: a comparison of three attenuation correction methods in combination with pre-reconstruction restoration filtering

A study of activity quantitation with pre-reconstruction Metz filtering and the use of arithmetic mean pre-reconstruction, Chang´s post-reconstruction, or Bellini´s intrinsic attenuation correction was conducted. Tc-99m-Filled spheres of various diameters were used to study activity estimation with an elliptical cross-section phantom. The percent of air sensitivity, which is calculated as the count rate for an ROI (region of interest) per unit activity for a source in the phantom divided by the count rate per unit activity for a point source in air times 100%, was used to assess the accuracy of attenuation correction. It was determined that a transmission model which explicitly included the buildup of scattered radiation yielded more accurate quantitation of activity in a uniform tub than correcting for scatter by scaling the counts with an average scatter fraction. The use of 2-D pre-reconstruction Metz filteringcombined with Bellini´s intrinsic or Chang´s post-reconstruction attenuation correction resulted in percent sensitivities which were the least position dependent and closest to 100%