Influence of single-photon-transmission scan duration measured with the ECAT ART PET-scanner

Aim: The aim was to study the influence of single-photon-transmission scan duration in 3D-PET on the quantitative values of attenuation coefficients a nd noise in transmission images and of activity concentrations and noise in attenuation corrected emission images of thorax phantom- and patient data. Method and material: Using dual collimated Cs-137 singles transmission sou rces (E-gamma = 662 keV, A = 2* 614 MBq) on an ECAT ART tomograph series of transmission scans of a thorax phantom were acquired pre- and post-injecti on of 18F. 17 patients underwent two transmission scans. The scan time of t he short transmission was chosen according to the results of the phantom st udies (noise of Poisson statistics less than 4%). Transmission and attenuat ion corrected emission images were evaluated with respect to estimated line ar attenuation coefficients, noise and specific activities in organs. Resul ts: The phantom studies reveal little variation of the estimated linear att enuation coefficients as a function of scan duration. The estimates of the attenuation coefficients are found to be 1% lower than the expected values for pre- and up to 6.5% lower for post-injection transmissions. The noise l evel in the transmission images increases as expected for Poisson date. The noise level in the attenuation corrected emission images shows only little increase with decreasing transmission scan time whereas it is strongly inf luenced by a variation of emission scan time. In patient studies, less than 3% difference was found in the estimated linear attenuation coefficients a s well as in the activity concentrations between short (pre or post-injecti on) and long transmission scans. The noise levels in transmission and emiss ion images ore 1% (pre-injection) and 4% (post-injection) higher for short transmission scans. Conclusion: Due to the high photon flux, single photon transmission offers good clinical performance with significantly reduced tr ansmission scan durations (<2 min/bed in pre-, < 4 min/bed in post-injectio n transmission).