Extracting equilibrium Blood Flow (eBF) values of CTp liver perfusion from tissue peak: a new promising perfusion parameter

Aims and objectives: To evaluate the potentiality of the new BF-based feature we computed, the equilibrium Blood Flow (eBF), which measures BF values at the arterial inflow-venous output balance, to improve reliability of liver CT perfusion values in a cohort of patients with colorectal cancer. Methods and materials: 46 patients with colorectal cancer underwent axial CTp examinations of normal liver at diagnosis. A voxel-based and patient-oriented non parametric model of the tissue time concentration curves (TCCs) are obtained by an in-house algorithm directly exploiting the native CTp Hounsfield Unit (HU) first-pass data. The tissue eBF values are achieved with normalizing the TCCs peak by the area under the TCC. For comparison purposes, the “common” BF is computed using the maximum slope. Overall mean and standard deviation are calculated, the coefficient of variation (CV) is computed to assess means repeatability. Correlations between BF and eBF colormaps are evaluated through Pearson (r). Results: eBF computed on the whole cohort of 46 patients yields CV=13%, almost half than MS, where CV=21%. Mean values for eBF[119±16]ml/min/100g are lower than BF[129±27]ml/min/100g, this being expected, because eBF include outflow measurements. Nonetheless, eBF and BF colormaps show excellent correlations (r>0.97) for 42 patients, and 0.80≤r<0.90 in 4 cases only. Conclusion: eBF allows for the vascular outflow measurements, as confirmed by mean values lower than BF ones, although their colormaps are highly correlated. eBF measures are also much more repeatable (almost twice) than BF ones, this making eBF a new promising perfusion feature that could benefit all CTp studies and, ultimately, CTp standardization.