Non-uniform versus uniform attenuation correction in brain perfusion SPET of healthy volunteers

Although non-uniform attenuation correction (NUAC) can supply more accurate absolute quantification, it is not entirely clear whether NUAC provides cl earcut benefits in the routine clinical practice of brain SPET imaging. The aim of this study was to compare the effect of NUAC versus uniform attenua tion correction (UAC) on volume of interest (VOI)-based semi-quantification of a large age- and gender-stratified brain perfusion normal database. Eig hty-nine healthy volunteers (46 females and 43 males, aged 20-81 years) und erwent standardised high-resolution single-photon emission tomography (SPET ) with 925 MBq Tc-99m-ethyl cysteinate dimer (ECD) on a Toshiba GCA-9300A c amera with Gd-153 or (TC)-T-99m transmission CT scanning. Emission images w ere reconstructed by filtered back-projection and scatter corrected using t he triple-energy window correction method. Both non-uniform Chang attenuati on correction (one iteration) and uniform Sorenson correction (attenuation coefficient 0.09 cm(-1)) were applied, Images were automatically reoriented to a stereotactic template on which 35 predefined VOIs were defined for se mi-quantification (normalisation on total VOI counts). Small but significan t differences between relative VOI uptake values for NUAC versus UAC in the infratentorial region were found. VOI standard deviations were significant ly smaller for UAC, 4.5% (range 2.6-7.5), than for NUAC, 5.0% (2.3-9.0) (P< 0.01). Higher filter roll-off values of the transmission reconstruction fil ter increased noise in the emission images and altered estimated cortical a ttenuation coefficients as well as uptake values. In conclusion, semi-quant ification based upon reconstruction with UAC results in very similar Tc-99m -ECD uptake values in healthy volunteers to those obtained with NUAC, altho ugh values for the infratentorial region are slightly lower. NUAC produces a slight increase in inter-subject variability. Further study is necessary in various patient populations to establish the full clinical impact of NUA C in brain perfusion SPET.