| BACKGROUND AND OBJECTIVEThe word hyperthermia comes from the ancient Greek, means"pyrogenic"or"overheating". Hyperthermia therapy was used to treat tumors in several thousand years ago. In China, the ancient traditional Chinese medicine practitioners have used moxibustion to treat neck neoplasms; at the same time in western countries, the ancient physicians used a small piece of burning iron to treat superficial tumors. Currently, radio frequenecy ablation (RFA), microwave, laser and high-intensity focused ultrasound (HIFU) have been used to treat tumors and have offered the best results for those patients. Among the above techniques, HIFU is the only non-invasive technique. Recently, Zhang et al. have demonstrated that HIFU can achieve complete tumor necrosis even when the lesion is located adjacent to the major hepatic blood vessels. Short-term and long-term follow up results show that HIFU might be safely used to ablate the tumors adjacent to major vessels.This phenomenon could be explained by"heat sink effect"because of the blood flow in the major blood vessels could take some thermal energy away to cool down the wall of blood vessels. On the other side,"heat sink effect"may also cause problem to completely ablate the tumor. Thus, in this research, we wanted to use MRI-guided high-intensity focused ultrasound system to test the effect of the main branch of portal vein on ultrasonic energy deposition in the liver tissue at different distances from portal vein. METHODS:1. The accuracy of real-time monitoring of MRI T-mapOx liver and phantom were ablated with magnetic resonance imaging-guided high intensity focused ultrasound (MRIgHIFU): First, we inserted a Luxtron fiber into the phantom or ox liver; then, we found the target next to the Luxtron fiber and ablated with 300 W for 20 seconds. MRI T-map and Luxtron fiber were used to monitor the temperature changes at same time.2. The effects of hepatic portal vein on ultrasound energy deposition in the liverFifty healthy goats (average age 16.02±4.33 months; range 8-24 months) with average weight of 27.54±1.88 kg (25-30 kg) were treated with magnetic resonance image-guided high intensity focused ultrasound (MRIgHIFU): First, we selected a section with portal vein larger than 5 mm in diameter, then put the focus at 0, 5 mm and 10 mm away from the portal vein. Dot sonication was used, when the temperature at the target region increased to 60°C, three more sonications followed before termination. The total energy, the energy required to increase 1℃and the coagulative necrotic volume were recorded.We also tested if different power could produce different effects. The 200 W or 250 W of power was used and the effect of PV on the total energy, the energy required to raise 1℃and coagulative necrotic volume in the liver tissue at different distances from portal vein were evaluated.RESULTS1.Accuracy of the real-time MRI T-mapping(1) In the phantom, the average temperature on MRI T-mapping or Luxtron were (54.40±16.48)℃or (54.76±16.44)℃, respectively. There was no significant statistic difference.(2) In the ox liver, the average temperature on MRI T-map or Luxtron were (69.96±17.86)℃or (68.78±15.81)℃, respectively. There was no significant statistic difference.2. The effects of hepatic portal vein on ultrasound energy deposition in the liver(1) There was no significant difference was observed before and after HIFU ablation in internal diameter of portal vein.(2) Average matrix temperature was (66.8±2.7)℃, (67.3±2.6)℃and (66.5±2.5)℃when the foci were 0, 5 mm and 10 mm away from the PV (P>0.05 ). There was no significant statistic difference.(3) When the focus was 0 ,5 mm and 10 mm away from the portal vein, the average total energy needed to raise temperature to (66.8±2.7)℃,(67.3±2.6)℃and (66.5±2.5)℃at the target was (3 111.0±398.4) J,(2 780.9±351.3) J and (2 411±281.4) J, respectively; The energy required to increase 1℃was (46.6±6.5) J, (41.4±5.5) J and (36.3±4.2) J, respectively. Significantly statistic difference was observed.(4) The coagulative necrotic volume was (1 653.0±847.0) mm3,(1 689.0±962.0) mm3 and (1 565±707.8) mm3 (P>0.05) when the focus at 0mm, 5mm and 10mm away from the PV (P>0.05 ). There was no significant statistic difference.(5) There was no statistic difference in average total energy, the energy required to increase 1℃and the coagulative necrotic volume between 250 W and 250 W of sonication power.CONCLUSION1. MRI T-mapping is accurate in temperature monitoring.2. HIFU seems to be safe and effective in ablating liver tissue adjacent to large blood vessels (diameter was more than 5 mm). No blood vessel injury was observed. The closer of the foci to large blood vessel, the more average total energy was needed to increase the temperature at the point that could produce necrosis, and the energy required to raise 1℃. Different level of sonication power was not associated with this phenomanon. |
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