Analysis Of The Dosage And Thermal Effect Of HIFU Treatment For Fibroids With Different Signal Intensity On T2 Weighted Image Of MRI

IntroductionUterine fibroids are the most common benign tumors in childbearing age women.The prevalence is ranged from 20%to 40%,and more than half of the patients have different clinical symptoms,which seriously affect the quality of life of patients.The treatment for uterine fibroids including surgery,uterine artery embolization,high intensity focused ultrasound（HIFU）.As a noninvasive treatment,HIFU has the advantages of short recovery time after treatment,which has been accepted by more and more patients and physicians.HIFU is a thermal ablation treatment that uses the thermal effect,cavitation effect and mechanical effect of ultrasound to make the temperature at the target region in the tumor increased to over60°C,resulting in irreversible coagulative necrosis of the tumor.The previous studies have found that the signal intensity of uterine fibroids on T2 weighted image（T2WI）of magnetic resonance imaging（MRI）is closely related to the results of HIFU ablation.However,no dosage prediction model of HIFU treatment for uterine fibroids with different signal intensity on T2WI was established and no basic study on thermal effects of HIFU ablation of uterine fibroids with different T2WI signal intensity in vitro was performed.Therefore,this study intended to investigate the mechanism of thermal effects of HIFU in clinical therapeutic dosage for fibroids with different T2 signal intensity.Firstly,we retrospectively analyzed the results of HIFU treatment for uterine fibroids with different signal intensity on T2WI.Secondly,based on the results of the retrospective study,the sonication time was set as the dependent variable,and the multiple factors affecting HIFU treatment are analyzed using optimal scale regression analysis to establish a prediction model based on the sonication time for fibroids with different T2 signal intensity.The model can be used to guide clinical applications of HIFU treatment.Lastly,thermocouple thermometry was used to monitor the temperature changes at the targetand TTC staining was used to evaluate the volume of coagulative necrosis zone in different MRI-T2WI signals of uterine fibroids in vitro.Finally,through the thermocouple temperature measurement technology and Triphenyl Tetrazolium Chloride（TCC）dyeing technology,the basic experiment to evaluate the volume of coagulative necrosis zone in uterine fibroids with different signal intensity on T2 of MRI in vitro using the same HIFU ablation dosage was performed.PurposeThe purpose of this study was firstly to retrospectively investigate the treatment results of HIFU and compare the difference in dosimetry of HIFU treatment between uterine fibroids with different signal intensities on T2WI of MRI;then,to establish the models of HIFU treatment for uterine fibroids with different signal intensity on T2WI to predict sonication time.Lastly,to investigate the difference of temperature changes and coagulative necrosis volume in the fibroids with different signal intensity on T2WI treated using the same dosage of HIFU.MethodFrom January 2016 to January 2017,284 patients with solitary uterine fibroid and treated with HIFU in the department of obstetrics and gynecology at Suining Central Hospital were enrolled.Based on the signal intensity on T2WI,these patients were classified as hypointense,isointense,and hyperintense fibroids and the treatment results were compared.We further compared the HIFU treatment results of the fibroids with different signal intensities on T2WI based on the locations.HIFU treatment power,sonication time,treatment time,EEF（energy efficiency factor）,and sonication time per cubic centimeter of the fibroids were compared.Based on the results from the first part,the sonication time of HIFU treatment for uterine fibroids with different signal intensity on T2WI was set as dependent variable.Body mass index（BMI）,age,the volume of fibroids,the location of uterine fibroids,the thickness of the rectus abdominis,the thickness of fat layer and the distance from the posterior surface of fibroids to the skin were set as independent variables to establish optimal scale regression model.The correlation between the predict sonication time and the true values was compared.Thirty-three fibroids were obtained from patients who had total hysterectomy.These samples were scanned by MRI before the experiment and then classified as hypointense（n=12）,isointense（n=13）and hyperintense（n=10）groups.Every fibroid was treated with the same dosage of HIFU.The peak temperature,time to peak temperature,heating slope,cooling slope and coagulative necrosis volume after HIFU were observed.ResultThe average non-perfused volume（NPV）ratio of 78.3±13.7%was achieved in all fibroids in the three groups of patients.The average NPV ratio in hypointense,isointense and hyperintense fibroids was 82.2±11.5%,83.3±12.6%and 76.5±26.2%respectively（P<0.05）.Using the similar treatment power,the median treatment time for patients with hypointense fibroids,isointense fibroids,and hyperintense fibroids was 39.5 min,44.0min,and 67.0 min respectively（P<0.05）;the median sonication time for hypointense fibroids,isointense fibroids,and hyperintense fibroids was262.0s,300.0s,600.0s,respectively（P<0.05）.The median EEF（energy efficiency factor）for treating hypointense fibroids,isointense fibroids,and hyperintense fibroids was 4.2J/mm³,5.7J/mm³,and7.9J/mm³,respectively（P<0.05）;the median sonication time for ablating one unit volume of hypointense fibroids,isointense fibroids,and hyperintense fibroids was13.2s,18.9s,and 22.0s,respectively（P<0.05）.Based on the location of uterine fibroids,the median EEF for hypointense fibroids,isointense fibroids,and hyperintense fibroids located on anterior wall of the uterus was 4.0 J/mm³,5.0 J/mm³,and 5.0 J/mm³,respectively;the median sonication time required for ablation one unit volume of hypointense fibroids,isointense fibroids,and hyperintense fibroids located on anterior wall of the uterus was 17.0s,25.0s and 24.0s,respectively（P<0.05）.The median EEF（P<0.05）for hypointense fibroids,isointense fibroids,and hyperintense fibroids located on lateral wall of the uterus was 3.0 J/mm³,5.0 J/mm³ and 8.0 J/mm³,respectively;the median sonication time for ablating 1 mm³ of hypointense fibroids,isointense fibroids,and hyperintense fibroids located on lateral wall of the uterus was13.5 s,29.0 s and 36.0 s,respectively（P<0.05）.The median EEF for hypointense fibroids,isointense fibroids,and hyperintense fibroids located on posterior wall of the uterus was 4.0 J/mm³,8.0 J/mm³,8.0 J/mm³,respectively.The median sonication time for ablation one unit volume of hypointense fibroids,isointense fibroids,and hyperintense fibroids located on posterior wall of the uterus was 18.0s,41.0s and 42.0s,respectively（P<0.05）.The median EEF for hypointense fibroids,isointense fibroids,and hyperintense fibroids located at the fundus of the uterus was 4.0J/mm³,4.0J/mm³,7.5J/mm³;the median sonication time for ablation 1 mm³ of hypointense fibroids,isointense fibroids,and hyperintense fibroids located at the fundus of the uterus was 22.0s,19.0s and 37.0s,respectively（P<0.05）.For hypointense fibroids:the volume and the location of fibroids were significantly correlated with sonication time（P<0.05）,the prediction model was established as:Y₁=0.413X₁+0.162X₂（X₁ represents the quantitative value of fibroid volume;X₂ represents the quantified value of fibroid position）.For isointense fibroids:the volume of fibroid was significantly correlated with sonication time（P<0.05）,the prediction model was established as:Y2=0.489X₁.For hyperintense T2WI signal fibroids:the volume and the location of fibroids were significantly correlated with the predicted sonication time（P<0.05）,and the prediction model was established as:Y₃=0.379X₁+0.185X₂.The correlation coefficients between the predicted values and the actual sonication time of the fibroids were0.344,0.576,and 0.448,respectively（P<0.05）.Using the same dosage of HIFU treatment,the mean peak temperatures in the three groups of fibroids in vitro were 86.45±10.64°C,82.3±10.88°C,and 71.29±8.81°C,respectively（P<0.05）.The average coagulative necrotic volume of the three groups of fibroids in vitro was642.23±208.9 mm³,316.36±88.83 mm³,and 131.07±55.15 mm³,respectively（P<0.05）.ConclusionThe results of this study demonstrated that uterine fibroids with hypointensity,isointensity on T2 are more suitable for HIFU treatment than hyperintense fibroids.The hypointense fibroids located on anterior or posterior wall of the uterus are all suitable for HIFU treatment;Both isointense and hyperintense fibroids located on posterior wall of the uterus are difficult to treat;it is more difficult to treat if the fibroids are located on the lateral wall,posterior wall,and the fundus.The sonication time prediction models that established based on T2 signal intensity of uterine fibroids have significant correlations between predicted values and actual values,and have certain practical value.Using the same sonication dosage,compared with hypointense or isointense fibroids,the lower peak temperature and smaller coagulative necrosis volume were observed in hyperintense fibroids.