Validation of CT attenuation correction for the quantitative SPECT-CBF image reconstruction: A comparative study with O-15 water PET

Objectives New SPECT/CT image reconstruction based on an attenuation correction using an X-ray CT image (CTAC) is expected to provide more accurate CBF image than that reconstructed by a conventional phantom-based attenuation correction (AC). To validate this assumption, we performed quantitative SPECT-CBF measurement by an integrated SPECT/CT scanner, and reconstructed images by means of various types of algorithms to compare quantitative PET-CBF images.

Methods Nine healthy subjects (4 male and 5 female; aged, 39-66 yr) underwent quantitative PET-CBF and SPECT-CBF measurements in the same day. PET-CBF was obtained by intra-venous injection of O-15 water (370 MBq), and quantitative IMP-ARG method followed with the injection of I-123 IMP (167 MBq) and one point arterial blood sampling. Four types of SPECT images were reconstructed: 1) filtered-back projection (FBP) with Chang’s AC, 2) 3-dimensional ordered subsets expectation maximization (3D-OSEM) with Chang’s AC, 3) FBP with CTAC, and 4) 3D-OSEM with CTAC. Linearity and correlation of SPECT-CBF values to PET-CBF values were evaluated.

Results All types of SPECT-CBF values showed simple linear regressions with PET-CBF value. The equation of regressions was 1) y=0.739x+9.466, 2) y=0.911x+5.309, 3) y=1.089x+2.226, and 4) y=0.954x+1.913, respectively. Correlation coefficient (r) did not show significant difference among reconstruction types (r=0.722-0.798, n=117 regions). The gradient of the coefficient of regression between PET-CBF and the type 4) SPECT-CBF was the closest to 1.0, and the y intercept was the nearest to 0. FBP with Chang’s AC showed the highest underestimation in CBF value compared to PET.

Conclusions CT attenuation correction in combination with 3D-OSEM method provides the most accurate CBF image reconstruction in the quantitative SPECT-CBF measurement