| Uterine fibroid is a common disease in childbearing women between 30 and 45.Currently myomectomy is the main treatment,however it will bring surgical trauma to patients.As a non-invasive approach,high-intensity focused ultrasound(HIFU)is becoming an option for treatment of uterine fibroids.Under image guidance,HIFU energy can be accurately delivered to planned region and coagulate the tissue in the body.Compared with traditional self-focused HIFU,phased-array HIFU technology has many advantages such as electronically steering focus and simultaneously generating multiple focal points.HIFU phased array has been extensively studied and equipped in commercial magnetic resonance-guided HIFU systems in the past two decades.And the use of phased array is also becoming a trend in HIFU systems.Though widely used around the world,the existing ultrasound-guided HIFU systems for uterine fibroid ablation usually employ self-focused transducers.Therefore study on ultrasound-guided HIFU phase-array system has strong clinical value and practical significance.Meanwhile the research on such systems still have several issues to be addressed:(1)How to realize the integration of ultrasound guidance and phased-array HIFU;(2)How to evaluate the targeting accuracy of the system to ensure treatment safety;(3)How to overcome the limited electronic steering range of HIFU phased array to enlarge the ablated volume in uterine fibroids.In order to resolve the above problems,the relevant key technologies have been systematically studied,such as the fusion design of ultrasound guidance and phase-array HIFU,the method to evaluate the targeting accuracy of the system,and the approach to expand the focal steering range.Preliminary clinical results of uterine fibroids treatment have verified the effectiveness of these key technologies.The main research contents and results are as follows:(1)To realize the fusion of ultrasound guidance and phased-array HIFU,we proposed a method by placing a rotatable ultrasound probe in the central hole of the spherical HIFU phased array.Based on this design,the guidance of HIFU phased array that can electronically deflect the focus in three-dimensional(3D)volume was achieved by using 2D ultrasound images.And the targeting,treatment planning and monitoring methods were put forward.To achieve 3D targeting,the coordinate mapping between targets in ultrasound images at different rotation angles of the ultrasound imaging probe and corresponding foci of the HIFU phased array was established.The treatment plane was reconstructed by the image sequence obtained during the rotation of the ultrasound probe.And the ultrasound probe was also rotated during the sonication interval to monitor the current target.Ex vivo experiments,in vivo experiments and clinical results confirmed that this method could effectively target tissue and monitor focus under HIFU sonication in real-time.(2)To ensure the safety of the ultrasound-guided phased-array HIFU system,a method for estimating the targeting accuracy of single focus as well as planned region was proposed.And the targeting error of the phased-array HIFU system was assessed comprehensively.According to the method,the targeting accuracy for single focus was firstly evaluated by using an acrylic plate,and the measured targeting error of the system was less than 1.0mm with error correction.On that basis,evaluation of targeting accuracy for treatment cells(3.6mm,7.2mm and 10.8mm in diameter)was considered with both degassed water and tissue acoustic path.The targeting error evaluated by defined parameters on both the focal plane and HIFU beam axis were less than 2.0mm,and therefore satisfy clinical requirements.The method can comprehensively evaluate targeting accuracy of such systems and provides a reference for the industry standard in assessing the targeting accuracy of similar HIFU systems.(3)In order to overcome the limitation of electronic steering range of HIFU phased array and improve the effectiveness of uterine fibroids ablation,we proposed a method of combining mechanically swinging treatment head with electronic focus deflection to expand the scanning range of HIFU focus.By tilting the HIFU phased array through a two-degree-of-freedom rotating platform,the position of geometric center of HIFU phased array can be shifted.And the effective focusing region can be enlarged when combined with electronic steering capability of the HIFU phased array.Theoretical calculation and experimental measurement confirmed that the treatment head can be tilted at least 5°(geometric center offset is about 24mm)after passing through multi-layered tissue,while the grating lobe and peak intensity of the acoustic field with 5-mm electronic deflection still met the requirements of safe and efficient focusing.Compared to the initial deflection range of ±6 mm on the treatment plane,the focal steering range(±29 mm)increased by 3.8times.Ablation of a square area with a side length of 25 mm at the depth of 6cm under the skin was achieved in in vivo experiment.Moreover,preliminary clinical results of 8 patients with uterine fibroids(average diameter of fibroids:58 mm)showed that the average reduction rate of fibroids was 20%(range,-15%?53%)three weeks after HIFU treatment and the average ablation rate was 69%(range,0%?100%).The skin was kept intact and no serious adverse events occurred after treatment,which further verified the effectiveness and clinical feasibility of this method. |
PDF Full Text Request