Measurement of Compton scattering in phantoms by germanium detector

Quantitative Anger camera tomography requires correction for Compton scattering. The Anger camera spectral-fitting technique can measure scatter fractions at designated positions in an image, allowing for correction. To permit verification of those measurements for ¹³¹I, scatter fractions were determined with a high-purity germanium (HPGe) detector and various phantom configurations. The scatter fraction values for ^99mTc were also measured and are compared to results from Monte Carlo simulation. The phantom consisted of a 22.2-cm-diameter×18.6-cm-high cylinder filled with water and 6-cm-diameter water-filled sphere placed at various locations inside the cylinder. Radioisotope is added to either the sphere or the cylinder. The source is collimated by an Anger camera collimator, and the active area of the HPGe detector is defined by a 0.6-cm-diameter hole in a lead shielding mask. Corrections include accounting for the HPGe detector efficiency as a function of gamma ray energy, the finite energy resolution of the detector, and the HPGe detector energy resolution compared to that for a NaI(Tl) Anger camera