Effect of Dual Vascular Input Functions on CT Perfusion Parameter Values and Reproducibility in Liver Tumors and Normal Liver

Abstract

Objective To assess the impact on absolute values and reproducibility of adding portal venous (PV) to arterial input functions in computed tomography perfusion (CTp) evaluations of liver tumors and normal liver. Methods Institutional review board approval and written informed consent were obtained; the study complied with HIPAA regulations. CTp source datasets, obtained from seven patients (containing 9 liver tumors) on two occasions, 2-7 days apart, were analyzed by deconvolution modeling using dual (“Liver” protocol, PV and aorta) and single (“Body” protocol, aorta only) vascular inputs. Identical tumor, normal liver, aortic and, where applicable, PV ROIs were used in corresponding analyses to generate tissue blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability (PS) values. Test-retest variability was assessed by within-patient coefficients of variation (wCV). Results For liver tumor and normal liver, median BF, BV and PS were significantly higher for the Liver protocol than Body protocol: 171.3-177.8 vs. 39.4-42.0 mL/min/100g, 17.2-18.7 vs. 3.1-4.2 mL/100g, 65.1-78.9 vs. 50.4- 66.1 mL/min/100g, respectively (all p<0.01). There were no differences in MTT between protocols. wCVs were lower for all parameters with the Liver protocol than Body protocol: BF, 7.5-11.2% vs 11.7-20.8%; BV, 10.1-14.4% vs. 16.6-30.1%; MTT, 4.2-5.5% vs. 10.4-12.9%; and PS, 7.3-12.1% vs. 12.6-20.3%, respectively. Conclusion Utilization of dual vascular input CTp liver analyses has substantial impact on absolute CTp parameter values and test-retest variability. Incorporation of the portal venous inputs may yield more precise results, however, it imposes substantial practical constraints on acquiring the necessary data.

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“…However, this assumption may not hold true for all histologic types of metastases as some liver metastases may have a mixed vascular supply (42,43). Ng et al (44) recently reported that a dual vascular input model (arterial and portal venous) for analysis of CT perfusion data sets improves test-retest reproducibility. Indeed, the separation of Plot of time-intensity curve of spleen and liver from CT perfusion study using maximum slope method.…”

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