| BackgroundIt had been showed solicitude for thermotherapy and hyperthermia of tumor for the past few years. The former is that tumors are heated to 42.5℃～45℃for several minutes or several ten minutes in order to inhibit the growth of tumor. The latter is tumors are heated to 60℃or above 60℃to make tissue necrosis completely. High intensity focused ultrasound(HIFU) is just a kind of hyperthermia and have been used in sorts of tumor and non-tumor disease. The tissue of target region would absorb the energy of the supersonic wave which can destroy it and the tissue out of the target region would not be destroyed. It is very important for efficient monitoring means with the purpose of targeting, monitoring and estimating curative effect in HIFU pretherapy, during HIFU treatment and post-treatment, respectively. Magnetic resonance imaging has developed for more than 30 years. It is being utilized in HIFU because of many advantages such as distinct imaging, high resolution, nonionising radiation and monitoring temperature in tissue. In my study I would choose tissue ex vivo and rabbit to be treated with MR Imaging guided HIFU(MRIgHIFU). MRI T-MAP and signals would be observed to prove the feasibility of MRI guided HIFU treatment.ObjectiveTo investigate the effectiveness of MRI in HIFU treatment and study the relation among the regions of changed MRI signals, adscendent temperature in T-MAP and practical necrosis. Materials and methods1 Experiment ex vivo1.1 MRIgHIFU system was used. The parameters of therapeutic transducer were: frequency-1.0MHz, focal length-150mm.1.2 Materials: Fresh ox liver ex vivo and man-made phantom1.3 Exposure modes: dot, line and block. During the dot irradiating, the parameters were 200W, 250W, 300W and 20s or 250W and 10s, 15s, 20s. And there were ten dots in every group. In the line irradiating, the parameters were power-250W, line length-20mm, scanner speed-1mm/s, 2mm/s or 3mm/s and speed number-1 cycle. There were four lines in every group. Under the block irradiating, the modes were continuous dot irradiation or line scanning. There were five blocks which size was 3cm×3cm×3cm in every group. MRI T-MAP was observed during treatment and the region size of adscendent temperature was measured(blue:30℃-37℃,green:37℃-45℃,yellow:45℃-55℃,red:55℃-10 0℃). After treatment, firstly, scan PD_tse and T2_tse, secondly, observe the changed signals of these images and measure the regions, finally, measure the tissue necrosis. Gross inspection of local focus were performed after treatment. SPSS11.5 and excel statistical software were performed for the statistical analysis.2. Experiment in vivoMRIgHIFU thermocoagulation was carried out in muscular tissues of rabbits. The parameters were power-250W and time-15s under the dot irradiating. MRI T-MAP was observed during treatment and the region size of adscendent temperature was measured(blue:45℃-50℃,green:50℃-55℃,yellow:55℃-60℃,red:60℃-100℃).Af-ter treatment, firstly, scan PD_tse and T2_tse, secondly, observe the changed signals of these images and measure the regions, finally, observe skin damage and measure the tissue necrosis. SPSS11.5 and excel statistical software were performed for the statistical analysis.Result1. 98 percent macroscopic damages were made in ox liver by dot irradiation, and 100 percent macroscopic damages were made in phantom by line scanning, ox liver by block irradiating and normal rabbit leg muscular tissues by dot irradiation after the treatment of MRIgHIFU.2. During HIFU, T-MAP shows a dynamic regularity of blue→green→yellow→red(to appear at times), i.e. the temperature of focus went up expeditiously. At the time of the end of treatment, the temperature reached its peak value. Immediately, it descended to the foundational temperature fleetly. And just at the time of the end of treatment, a correlation existed between yellow region and tissue necrosis. The frequency of the red and the yellow region are 48 percent and 94 percent ex vivo and they were 80 and 100 percent in vivo.3. The images of PD and T2 show a low signal region ex vivo and show high signal around a low signal region in the muscular tissues of rabbits. A correlation existed between image and tissue necrosis.Conclusion1. Macroscopic damages can be made in ox liver, phantom and normal rabbit leg muscular tissues by MRIgHIFU system.2. MRI can be used to monitor the changes of temperature during HIFU non-invasively. The yellow region can response the tissue necrosis precisely.3. The two dimensional MRI images can evaluate the tissue necrosis after HIFU exposure.4. The treatment system of MRIgHIFU can be used in the foundational empirical study. It is feasible and effective.
|
PDF Full Text Request