The effects of axial transmission resolution in PET

The effect of the axial resolution of transmission data for use in positron emission tomography (PET) attenuation correction is an important considera tion for the design of transmission scanning systems. PET transmission data from five patient scans were used in conjunction with simulated uniform em ission data to quantify the effect of degraded axial transmission resolutio n. PET patient emission data were also corrected for attenuation using tran smission projection data that had various levels of axial resolution. Resul ts from the uniform emission studies show that the effects of imperfect axi al transmission resolution are always less than are those of comparable tra nsaxial resolution. Conservative limits for the axial resolution requiremen ts [Gaussian full width at half-maximum)FWHM)] for a transmission system we re deduced. For quantitative work, a 1-cm resolution limit yields a root me an square (rms) voxel deviation of less than 5% in the lung region (the wor st case) of a uniform tracer distribution. For qualitative studies, a 2-cm resolution limit yields an rms voxel-value deviation of less than 11%. Only small effects were observed on the patient emission image using transmissi on data with this resolution to produce an attenuation correction.