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, we have determined scatter fractions 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 a 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 detector and the HPGe detector energy resolution compared to that for a NaI(Tl) Anger camera. For the hot sphere, the HPGe scatter fraction values are validated by the Monte Carlo results with good agreement across the sphere and with changes in depth of the sphere within the cylinder. For the cold sphere, the two methods agree in scatter fraction dependence, but the HPGe values are too large. The HPGe scatter fractions for ¹³¹I depends on hot sphere depth in a way that is similar to the dependence for ^99mTc. The values are smaller as expected. Copyright © 1990 by The Institute of Electrical and Electronics Engineers, Inc.

Duke Scholars

Author Ronald J. Jaszczak Radiology