Quantitative SPECT imaging with indium-111

The potential of SPECT (single photon emission computed tomography) to quantify the distribution of indium-111 was investigated in an experimental phantom study. Nonuniform attenuation compensation using acquired transmission data was compared to uniform compensation based on reconstructed quantitative accuracy and noise. The reconstructed transmission data provided the attenuation map for the nonuniform compensation. Results showed that nonuniform attenuation compensation improved image quality, quantitative accuracy, and noise compared to uniform compensation. Noise increased with a decrease in counts in the nonuniform attenuation map but remained substantially below the uniform compensation level. The noise effect was observed with both Chang and ML-EM (maximum-likelihood expectation-maximization) reconstruction methods. Independent reconstruction of the 172- and 247-keV emission data was compared to the reconstruction of the combined 172- and 247-keV projection data. Improved quantitative accuracy and image noise resulted when both In-111 emission energies were used. However, independent reconstruction of the two energies did not substantially improve accuracy or noise compared with the reconstruction of the combined data.>