| Background:High intensity focused ultrasound (HIFU) has been applied to the combined treatment of liver carcinoma gradually and proved to be effective. The therapeutic effect of HIFU mainly relies on its thermal mechanism which could produce instant high temperature in the targeted zone and make tumor tissue ablated. However, currently the clinical application of HIFU treatment for the liver tumors is hindered by some region specific factors. Those might reduce the energy of the focused ultrasound or increase the energy depositing in overlying tissues and further cause adverse effects, such as skin burns, gastric-intestinal perforation or residual viable tissue in focused areas.How to solve those problems depends on utilize the mechanism of HIFU thoroughly. The non-thermal mechanism is another important effect of HIFU which receives less attention currently. To our knowledge, little research dealt with the analysis of HIFU non-thermal mechanism on tumor tissue and its feeding vessels.Contrast-enhanced CT (CECT) has been the mainstay for evaluating the therapeutic efficacy of thermal ablation clinically. On the other hand, real-time contrast-enhanced ultrasound (CEUS) is the most convenient imaging modality which has been shown to be highly sensitive for detecting microbubble contrast media in tumor vasculature, it can be a valuable imaging choice for assessing residual tumor after HIFU ablation. Few studies dealt with comparison of CEUS and CECT on treatment efficacy assessment of HIFU on relatively small rabbit hepatic VX2 tumors.Objective:To assess quantitatively the enhanced effect of HIFU ablation of non-thermal mechanism on rabbit hepatic VX2 tumors and compare the diagnostic accuracy of CEUS and CECT in the early detection of residual viable tumor. To study comparatively the sequential changes of ultrastructure, apoptosis-related proteins expression and tumor cell apoptosis after ablated with thermal and non-thermal mechanism of HIFU and to analyze the therapeutic effects.Methods:1. Thirty-three rabbits with hepatic VX2 tumors on 14d after implantation were examined by CECT and CEUS and the criterion of phase timing applicable to the model was explored according to the time-density/intensity curves. Six animals were killed randomly and the specimens were stained with CD34 and VEGF antibody to observe the microangiogenesis.2. Twenty-five rabbits with hepatic VX2 tumors were randomly separated into three groups before ablation. Group I (n=3) acted as a contrast. Group II (n=11)and group III (n=11) were ablated using HIFU under the manipulation of computer to produce thermal and non-thermal effects, respectively. All the ablating procedures were under the real-time temperature monitor with thermocouple meter. Histopathologic assessment was performed immediately after ablation.3. Tumors in step 2 were examined with CEUS and CECT right before and after HIFU ablation. Histopathologic assessment was performed immediately after the completion of post treatment imaging.4. Forty rabbits with hepatic VX2 tumors were randomly divided into two groups (20 animals in each group) and subjected to HIFU ablation with thermal and non-thermal injury, respectively. On day 0,3,7, and 14 after ablation,5 animals in each group were sacrificed. The tissue in ablated zone, transient zone and surrounding zone were sampled and analyzed with light microscope, electronic microscope and immuno-histochemistry.Results:1. The initial time of hepatic arterial phase, portal phase and parenchymal phase in CEUS and CECT was (6.82±1.36)s and (9.43±2.23)s, (11.64±2.03)s and (13.77±2.01)s, (20.24±4.17)s and (22.71±4.58)s, respectively. The initial time of each phase in CEUS was earlier than that in CECT (P<0.01). The contrast enhancing characteristics in CEUS and CECT were consistent as fast wash-in and fast wash-out.2. The time-temperature curves of group II and III appeared to be "quick ascending and slow descending" and "slow ascending and slow descending" patterns, respectively. The damaged volume, complication rate, residual tumor rate and maximum diameter of destroyed vessel of the two groups was 1.10+0.22 cm3 and 1.21+0.24 cm3 (P>0.05) 72.7%and 63.6%(P>0.05),72.7%and 18.2%(P<0.05) and 135.27 +22.09μm and 877.64+253.68μm (P< 0.001), respectively. The ablating dots and time of group III were significantly lower than that of group II (P<0.001), while there was no significance on HIFU energy and necrotic rate between two groups (P>0.05)3. Completely ablated tumors showed no entrance of contrast media and appeared "dark hole" sign in CECT and CEUS. In cases of residual viable tumors, it showed fast enhancement in arterial phase and fast washout in portal phase with the ablated area. The diagnosis accuracy rate of CECT and CEUS was 90.9%and 81.8%, respectively (P>0.05). The sensitivity, negative predictive value and diagnosis accuracy rate of CECT+CEUS were higher significantly than those of CEUS alone (P< 0.05)4. The expression of various apoptosis-related proteins in transient zone of both groups was found to be of sequential changes. The expression of VEGF appeared low in day 0 and 3 and elevated gradually in day 7 and 14. The expression of Caspase-3 reached peak in day 3 and decreased in day 7 and 14. The Caspase-3 expression level of non-thermal group was significantly higher than thermal group in day 3 and 7 (P<0.05). The expression of NFκB elevated from day 3 and reached peak in day 7 and decreased in day 14. The NFκB expression level of non-thermal group showed no difference with thermal group (P > 0.05). The HSP70 expression level of non-thermal group was significantly lower than thermal group in day 0 and 3 (P<0.05). The apoptosis index of non-thermal group and thermal group in day 3 and 7 were 28.60±1.14 v.s 21.80±1.92 (P< 0.001) and 21.00±1.58 v.s 14.80±1.48 (P<0.001), respectively. Conclusions:1. The status of hemodynamic perfusion in rabbit hepatic VX2 tumor could be well displayed by CEUS and the phase timing criterion concluded in this experimental study could offer fundamental theory basis for relevant imaging evaluation.2. The non-thermal mechanism can destroy rabbit hepatic VX2 tumors and obstruct the feeding vessels. But the controllability is still to be studied.3. Our study demonstrates CEUS proves to be sensitive in early assessment of residual viable rabbit VX2 tumor after HIFU.4. Both the thermal mechanism and the non-thermal mechanism can induce apoptosis in transient zone, while the latter proved to have a more intense effect.
|
PDF Full Text Request