CT perfusion is a feasible, reproducible technique for assessing tissue perfusion in locally advanced HCC[14
]. Measures of tumor perfusion have been correlated with angiogenesis and microvessel density within the tumor[14,15
]. It is logical to speculate that high perfusion values indirectly suggest a high rate of angiogenesis and microvessel density within the tumor.
However, to our knowledge, there are few studies on the role of CT perfusion in evaluating the therapeutic efficacy of TACE, although Tsushima et al[11
] presented their data on CT perfusion and demonstrated decreased values of HAP and HAF in viable tumors post-treatment compared with pre- treatment, which are consistent with our findings.
In our study, the number of cases collected allowed us to divide them into different treatment response groups for observation. In the CR group, CT perfusion imaging of post-TACE lesion displayed complete absence of signal on the CT perfusion maps. We observed significant differences in some CT perfusion parameters of viable tumors per- and post-TACE in the treatment response PR and PD groups. In the PR group of HCC, after TACE treatment, the change in perfusion parameters was consistent with previous findings[11,16
]. The decreased HBV and HBF within liver tumors indicate the reduction of vascular capacity and microvessel density, which are due to the lipiodol embolism (Figure and ). Kan et al[16
] reported that post-embolization MTT is elongated in intrahepatic lesions of a rat model, while post-embolization PS is significantly decreased. However, we did not find any significant difference in values of MTT and PS pre- and post-treatment, which may be due to the difference in observational time windows, in which the microvascular function within tumors dynamically changes. In the SD group, the perfusion parameters remained unchanged pre- and post-TACE treatment, suggesting a perfusion recovery within the tumor after treatment. In the PD group, HBF, HAF, and HAP were increased after treatment, reflecting the increased angiogenesis and microvessel density within the liver tumor. The value of PVP was further increased in HCC of the PD group after treatment, suggesting involvement of hepatic portal vein during tumor advancement. In our study, the value of HBV was not further increased during tumor advancement, suggesting that the vascular capacity within the tumor mass has reached its limit and thus, cannot further expand. Further histological research is needed to prove this speculation.
In addition, many CT perfusion analyses were performed using a single arterial input[8,9,15
], but the liver has a dual arterial-portal blood supply, and the tumor and portal vein could not be consistently included. In our study, 64-rows multi-detector CT was introduced to offer a greater coverage (up to 4 cm), thus overcoming this limitation by including both the tumor and portal vein in dual-input analysis. The introduction of multi-detector CT has stimulated further interest in perfusion CT techniques and their future implementation in clinical practice[14
We believe that comparison of the results from different CT perfusion studies has to be made cautiously, as the values measured are dependent on mathematic model and pharmacokinetics of the contrast medium used. Thus, application of different models to the same data may well yield different perfusion values. It should be emphasized that our results were specific to the method of analysis and the software employed in this study.
The limitations of our study are as follows. The grouping of patients did not involve factors such as differentiation of HCC, cirrhosis, invasion of portal vein, dosage of chemotherapeutant and lipiodol, and use of gelfoam particles, all of which could influence the therapeutic response of HCC to TACE and change the CT perfusion parameters after TACE. Because the determinants for therapeutic response of HCC to TACE are complicated and numerous, this study did not take into account these determinants of therapeutic response to TACE, but rather it only correlated the changes in CT perfusion parameters with different treatment responses to TACE.
In conclusion, CT perfusion imaging can be used in the assessment of perfusion changes resulting from TACE therapy. Post-treatment changes in perfusion parameters are correlated with different therapeutic efficacies for HCC. Thus, CT perfusion imaging is a feasible and non-invasive technique for monitoring treatment response to TACE.