Quantitative CBF measurement using an integrated SPECT/CT system: validation of three-dimensional ordered-subset expectation maximization and CT-based attenuation correction by comparing with O-15 water PET.

Rationale And Objectives: As spreading integrated SPECT/CT scanners, reconstruction method based on three-dimensional ordered-subset expectation maximization (3D-OSEM) with attenuation correction (AC) using an X-ray CT image (CTAC) is easily available in brain imaging. For quantitative cerebral blood flow (CBF) measurements, however, the accuracy of this method has not been fully evaluated clinically. To validate this new algorithm, we sequentially studied quantitative PET-CBF and SPECT-CBF measurements in the same healthy volunteers and compared CBF values.

Methods: Ten healthy subjects underwent quantitative PET-CBF and SPECT-CBF measurements on the same day. PET-CBF data were obtained by the intravenous injection of O-15 water and the quantitative IMP-ARG method followed. Three types of SPECT images were reconstructed: (1) filtered back projection (FBP) with Chang's AC (FBP + Chang's AC), (2) 3D-OSEM with Chang's AC (3D-OSEM + Chang's AC), and (3) 3D-OSEM with CTAC (3D-OSEM + CTAC). The mean CBF difference, the linearity, and the correlation between the PET-CBF and SPECT-CBF values were compared among the SPECT reconstruction algorithms.

Results: The mean SPECT-CBF values of all the algorithms were significantly lower in the pons (P = 0.000-0.007) and higher in the frontal lobe (P = 0.002-0.022). All the SPECT-CBF values were significantly correlated with the PET-CBF values (r = 0.749-0.829, P < 0.001). The SPECT-CBF values obtained using the 3D-OSEM + CTAC method showed the best regression with the PET-CBF values.

Conclusion: The present clinical study validated accuracy of CBF image reconstructed by the 3-D OSEM method with CTAC and the integrated SPECT/CT system.