Towards optimized MR thermometry of the human heart at 3T

Catheter ablation using radio frequency (RF) has been used increasingly for the treatment of cardiac arrhythmias and may be combined with proton resonance frequency shift (PRFS) ?based MR thermometry to determine the therapy endpoint. We evaluated the suitability of two different MR thermometry sequences (TFE and TFE‐EPI) and three blood suppression techniques. Experiments were performed without heating, using an optimized imaging protocol including navigator respiratory compensation, cardiac triggering, and image processing for the compensation of motion and susceptibility artefacts. Blood suppression performance and its effect on temperature stability were evaluated in the ventricular septum of eight healthy volunteers using multislice double inversion recovery (MDIR), motion sensitized driven equilibrium (MSDE), and inflow saturation by saturation slabs (IS). It was shown that blood suppression during MR thermometry improves the contrast‐to‐noise ratio (CNR), the robustness of the applied motion correction algorithm as well as the temperature stability. A gradient echo sequence accelerated by an EPI readout and parallel imaging (SENSE) and using inflow saturation blood suppression was shown to achieve the best results. Temperature stabilities of 2 °C or better in the ventricular septum with a spatial resolution of 3.5 × 3.5 × 8mm³ and a temporal resolution corresponding to the heart rate of the volunteer, were observed. Our results indicate that blood suppression improves the temperature stability when performing cardiac MR thermometry. The proposed MR thermometry protocol, which optimizes temperature stability in the ventricular septum, represents a step towards PRFS‐based MR thermometry of the heart at 3 T. Copyright © 2011 John Wiley & Sons, Ltd.     

Validation of fast MR thermometry at 1.5 T with gradient-echo echo planar imaging sequences: phantom and clinical feasibility studies

The purpose of this work was to validate in phantom studies and demonstrate the clinical feasibility of MR proton resonance frequency thermometry at 1.5 T with segmented gradient-echo echo planar imaging (GRE-EPI) sequences during liver tumour radiofrequency (RF) ablation. Classical GRE acquisitions and segmented GRE-EPI acquisitions were performed at 1.5 T during simultaneous RF heating with an MR-compatible RF electrode placed in an agar gel phantom. Temperature increments were calculated and compared with four optical temperature probe measurements using Bland- Altman analysis. In a preliminary clinical feasibility study, the rapid GRE-EPI sequence (echo train length = 13) was used for MR temperature monitoring of RF ablation of liver tumours in three patient procedures. For phantom experiments, the Bland-Altman mean of differences between MR and optical probe temperature measurements was <0.4 degrees C, and the 95% limits of agreement value was <1.4 degrees C. For the in vivo studies, respiratory-triggered GRE-EPI acquisitions yielded a temperature accuracy of 1.3 +/- 0.4 degrees C (acquisition time = 0.6 s/image, spatial coverage of three slices/respiratory cycle). MR proton resonance frequency thermometry at 1.5 T yields precise and accurate measurements of temperature increment with both classical GRE and rapid GRE-EPI sequences. Rapid GRE-EPI sequences minimize intra-scan motion effects and can be used for MR thermometry during RF ablation in moving organs. Copyright (c) 2008 John Wiley & Sons, Ltd.     

植入式心电记录器在心房颤动射频消融术后随访中的应用

目的探讨植入式心电记录器（ILR）在观察心房颤动射频消融术后疗效中的价值。方法收集2010年10月至2012年8月心房颤动射频消融术后复发患者7例,其中男性2例,女性5例;年龄23～67岁,平均年龄51岁。经常规检查未能明确复发原因,根据病情分别选择植入Medtronic公司RevealRDX9528型、Reveal XTTM9529型ILR监测复发时的心电事件,以帮助确诊。结果 7例植入ILR的患者平均随访（12.7±5.1）个月。随访期内7例患者共记录心电图191段,其中患者手动触发记录49段,ILR自动触发记录142段,64段心电图为心律失常事件。根据症状-心律相关性,监测到6例患者出现胸闷、晕厥等症状,其中5例患者明确为心律失常性事件引起,1例为非心律失常性事件引起。1例无症状发作。提示ILR诊断复发原因的效率为85.71%。根据ILR监测结果明确病因的6例患者得到进一步治疗,症状发作好转或减少。结论 ILR用于诊断心房颤动射频消融术后复发具有安全、高效、监测时间长、信息量大等优点,动态优化ILR系统,将进一步提高ILR在临床诊断、疗效追踪、指导治疗等方面的临床应用价值。     

射频消蚀对心肌结构影响的实验研究

经导管对犬和兔心房、心室行射频消蚀，观察消蚀后心肌结构的变化及消蚀能量与心肌损伤程度的关系。结果显示：射频消蚀引起的心肌损伤范围局限、坏死彻底，损伤区由肉芽组织和纤维瘢痕替代；在２０～５００Ｊ的射频输出范围内，消蚀损伤程度与能量输出呈正相关；射频消蚀也应有限量地进行，过多或大范围的消蚀可引起弥漫性的心内膜增厚。同时时消蚀后心肌损伤的组织学、超微结构变化与细胞电生理改变的关系进行了讨论。     

Experimental membrane-destructive model of cardiac arrhythmia

We propose a method for experimental modeling of cardiac arrhythmias. The method consists in intravenous injection of LPO inductors: 5% ascorbic acid (50 mg/kg), 1 min later 1% iron sulfate (10 mg/kg), and after the appearance of giant T waves on ECG infusion of 10% calcium chloride in a nonarrhythmogenic dose 100 mg/kg. Cardiac arrhythmias were induced in 100% animals. A significant relationship between increased permeability of erythrocyte membranes and development of fatal cardiac arrhythmias was detected. We assumed that this methodologically simple membrane-destructive model of cardiac arrhythmia is pathogenetically close to arrhythmogenesis in patients with coronary heart disease.     

肾脏射频消融中超声图像特征参数与温度关系的研究

为探索肾脏射频消融中超声图像特征参数与温度的相关性，设计并进行了新鲜离体猪肾脏射频消融实验。记录热 消融过程中的温度（侵入式热电偶测量）和B超影像数据，采用将温度探针视为圆形的方法和阈值分割法去除感兴趣区域 中的探针，提取灰度均值、灰度标准差和灰度梯度值等特征参数，使用MATLAB软件对得到的灰度均值、灰度标准差和温 度作回归分析，采用连续分段函数模型进行数据拟合。证明了阈值分割法可用于探针去除，肾脏射频消融中的超声图像 特征参数与温度具有相关性，得到拟合良好的灰度均值-温度、灰度标准差-温度模型。但所得模型中的参数会随图像增 益、消融组织差异变化，在后续研究中应排除此类干扰，得到更具有临床价值的温度测量模型。     

Pathomorphological changes after radiofrequency ablation in the liver

Radiofrequency ablation (RFA) has become a widespread treatment option for liver carcinoma. There is limited knowledge regarding the macroscopic and histomorphological changes of induced lesions. Twelve domestic pigs underwent RFA using a Starburst XL device with ablation diameter of 3 cm. One animal died within 24 h, two animals were killed after 2 weeks, and nine after 4 weeks. Their livers were used for macroscopic and histological investigation. Six human liver resection specimens after previous treatment with RFA were also investigated. In pig samples, acute RFA change showed a necrosis zone demarcated by resorption zone with granulocytes and hyperemia. In subchronic and chronic RFA change, the zone of thermofixation was followed by a fibrous capsule and a liver reaction zone. Small blood vessels in the lesions showed damage involving endothelial destruction and thrombosis. Larger vessels within the lesions were observed with intact vessel walls, surrounded by a rim of vital hepatocytes. In the human samples, tumor‐infiltrating lymphocytes were reduced (CD3+ cells: 8.4 ± 3.7/10 high‐power fields (HPF); CD4+ cells: 4.2 ± 1.9/10 HPF), whereas the number of histiocytes was found to be increased (CD68+ cells: 15.5 ± 9.02/10 HPF). The recognition of thermofixation and the process of resorption of the RFA lesion is important for the interpretation of biopsies and surgical resection specimens.     

A survey of radiation dose to patients and operators during radiofrequency ablation using computed tomography

Computed tomography (CT) fluoroscopy is able to give real time images to a physician undertaking minimally invasive procedures such as biopsies, percutaneous drainage, and radio frequency ablation (RFA). Both operators executing the procedure and patients too, are thus at risk of radiation exposure during a CT fluoroscopy.This study focuses on the radiation exposure present during a series of radio frequency ablation (RFA) procedures, and used Gafchromic film (Type XR-QA; International Specialty Products, USA) and thermoluminescent dosimeters (TLD-100H; Bicron, USA) to measure the radiation received by patients undergoing treatment, and also operators subject to scatter radiation.The voltage was held constant at 120 kVp and the current 70mA, with 5mm thickness. The duration of irradiation was between 150-638 seconds.Ultimately, from a sample of 30 liver that have undergone RFA, the study revealed that the operator received the highest dose at the hands, which was followed by the eyes and thyroid, while secondary staff dosage was moderately uniform across all parts of the body that were measured.     

鼻内镜下射频消融治疗青年人腺样体肥大

目的探讨在鼻内镜下青年人腺样体肥大的射频治疗。方法7例青年病人，年龄为16～27岁，其中男性4例，女性3例。在鼻内镜下应用射频消融进行治疗，观察疗效。结果在鼻内镜下应用射频治疗后，6例一次性治愈，仅1例术后1个月复查有肥大的腺样体残留并仍导致鼻塞，再次射频治疗后治愈，术后6～12个月复查未见有复发的患者。结论对长期鼻腔通气困难而无显著鼻腔疾病影响鼻通气的青年患者，应用鼻内镜和／或影像学检查以确定有无腺样体肥大。应用鼻内镜在直视下射频治疗青年人腺样体肥大，可以收到良好的治疗效果。     

X线图像引导射频消融系统的研制

目的研制一种用于快速治疗心律失常的X线图像引导射频消融系统。方法通过X射线图像来引导消融导管,确定导管顶端的电极位置,在病灶处放出交电流,实现病灶的消融。并结合了多道电生理记录的功能,在进行消融手术的同时,可以观察和监控病人的电生理状况,保障病人的手术安全。结果一例隐性左侧旁道患者通过系统治疗,经过图像引导的消融后,A波与V波分开,获得了心脏消融的成功。结论通过X线图像的引导并结合多到电生理记录系统的射频消融系统,能有效快速的治疗简单的快速心律失常。     

Contrast-enhanced ultrasonography follow-up after radiofrequency ablation in normal rabbit kidney

Introduction

The aim of this study was to evaluate the diagnostic performance of SonoVue-enhanced ultrasonography in the follow-up of rabbit kidney lesions induced by percutaneous radiofrequency ablation.

Material and methods

New Zealand rabbits (28) underwent percutaneous radiofrequency ablation (RFA) to generate renal lesions. Lesions were evaluated by conventional 2D ultrasound and contrast-enhanced ultrasonography (CEUS) at 1 day, 1 week, 1 month and 3 months after RFA, and the results were compared to gross pathology.

Results

One day and 1 week after RFA, renal lesions were wedge-shaped in the gross dissection cross-sectional profiles. Conventional ultrasound could not indicate the extent of the lesions; however, CEUS could exactly delineate the lesion shape and size. At 1 and 3 months, lesions were observed as hyperechogenic areas on conventional ultrasound, and as small perfusion defects on CEUS. The differences in the lesion measurements obtained by CEUS and in pathological specimens were not statistically significant (p > 0.05).

Conclusions

The conclusion could be deduced from the study that SonoVue-enhanced ultrasonography was effective for the follow-up of normal rabbit kidney percutaneous radiofrequency ablation.     

术中超声在冷循环射频治疗肿瘤中的应用

目的 探讨术中超声(10US)在冷循环射频治疗肿瘤中的临床应用价值。方法 48例肝癌患者，5例胰体尾癌患者。将术中探头直接置于脏器表面，首先观察肿瘤的部位、大小、数量和周围血管的毗邻关系，取活检后在超声引导下将射频电极针穿刺入肿瘤内部，多点分次进行治疗。结果 53例患者全部在超声引导下完成治疗。5例患者经术中超声检查发现新病灶。术中观察到治疗后肿瘤颜色变暗，瘤体变瘪凹陷，声像图上肿瘤呈高回声改变。术后随访2—12个月，46例存活。结论 开腹下应用术中超声引导冷循环射频治疗，定位准确，安全性高，可多点多次对肿瘤进行射频灭活，坏死区域大。并且术中超声能够弥补术前影像学的不足，发现术前漏诊的病灶而使患者及时得到治疗。     

MRI-guided Thermal Ablation Therapy: Model and Parameter Estimates to Predict Cell Death from MR Thermometry Images

Solid tumors and other pathologies can be treated using laser thermal ablation under interventional magnetic resonance imaging (iMRI) guidance. A model was developed to predict cell death from magnetic resonance (MR) thermometry measurements based on the temperature–time history, and validated using in vivo rabbit brain data. To align post-ablation T2-weighted spin-echo MR lesion images to gradient-echo MR images, from which temperature is derived, a registration method was used that aligned fiducials placed near the thermal lesion. The outer boundary of the hyperintense rim in the post-ablation MR lesion image was used as the boundary for cell death, as verified from histology. Model parameters were simultaneously estimated using an iterative optimization algorithm applied to every interesting voxel in 328 images from multiple experiments having various temperature histories. For a necrotic region of 766 voxels across all lesions, the model provided a voxel specificity and sensitivity of 98.1 and 78.5%, respectively. Mislabeled voxels were typically within one voxel from the segmented necrotic boundary with median distances of 0.77 and 0.22 mm for false positives (FP) and false negatives (FN), respectively. As compared to the critical temperature cell death model and the generalized Arrhenius model, our model typically predicted fewer FP and FN. This is good evidence that iMRI temperature maps can be used with our model to predict therapeutic regions in real-time during treatment.     

特殊左侧房室旁路的射频导管消融策略

目的探讨特殊左侧旁路射频导管消融中的策略。方法行射频消融手术治疗房室旁路引起的房室折返性心动过速合并永存左上腔静脉患者3例,其中男性2例,女性1例,年龄51、42和48岁。经主动脉逆行途径在二尖瓣心室侧、穿间隔途径在二尖瓣心房侧行射频消融。随访4~12个月,观察患者有无室上性心动过速复发及心电图检查有无显性旁路恢复。结果具有一定特殊性左侧旁路的3例患者均消融成功,手术成功率100%,无并发症发生。3例患者合并永存左上腔静脉,其中1例经房间隔穿刺途径在二尖瓣心房侧消融时出现迷走神经反射,心率、血压下降,广泛导联ST-T改变,经冠状动脉造影证实非冠状动脉病变,为完全性左束支传导阻滞。术后随访4~12个月,3例患者均无室上性心动过速发作。结论左侧房室旁路导管射频消融存在特殊情况时,需仔细鉴别,通过不同的方法及途径消融,仍可获得较高的成功率。     

高频电刺激指导肾动脉射频消融的实验研究

目的:用电刺激的方法指导肾脏去神经术(renal denervation,RDN)中射频消融靶点的选择,同时比较电刺激与射频消融时血压变化的异同。方法:成年健康昆明犬6只,行肾动脉造影排除肾动脉畸形后,每侧肾动脉从远段开始,由远及近选择数个位点进行电刺激并消融。连续记录术中血压的变化,术后通过软件分析血压的变化情况。采用常规HE和Masson染色观察肾动脉壁结构及其周围组织;采用酪氨酸羟化酶(tyrosine hydroxylase,TH)免疫组化染色观察消融后肾动脉去神经效果。结果:本实验中刺激/消融位点共计50个,其中对电刺激有反应的位点占34%,无反应位点占66%。对有反应位点进行120 s电刺激时,其收缩压按每20 s分段与基线血压相比分别变化(0.34±3.38)、(0.41±3.04)、(10.47±5.73)、(13.27±3.63)、(10.17±1.87)和(0.78±1.87)mm Hg;将120 s连续消融时的收缩压数据同样按每20 s与基线血压相比,变化分别为(0.88±3.44)、(-1.64±3.47)、(13.17±3.12)、(12.82±3.21)、(9.50±2.68)和(-6.09±2.21)mm Hg。无反应位点进行电刺激和射频消融时均无明显血压升高。组织病理学检查显示,有反应位点肾动脉神经面积为(0.51±0.28)mm~2,无反应位点处为(0.09±0.06)mm~2,差异有统计学显著性(P0.01);免疫组化染色表明消融部位神经TH的表达显著低于未消融部位(P0.01)。结论:高频电刺激可以标测肾交感神经,且电刺激指导下的射频消融能对肾动脉交感神经造成有效损伤。     

探索不用Halo电极射频消融治疗典型心房扑动的方法

目的探讨不用Halo电极消融典型心房扑动(AF)的方法和右心房峡部传导时间间期的意义。方法对9例AF患者进行了心脏电生理检查和射频消融。将普通标测电极分别放置高位右房(HRA、A点)、低位右房(LRA、B点)、希氏束(His、C点)、冠状窦(CS、CS34为D点),标测AF发作时右房激动顺序,起搏时测量右心房峡部传导时间间期,然后,对峡部行线形消融直至双向传导阻滞,测量右心房峡部传导时间间期(BD、DB)。结果不用Halo电极成功消融所有典型心房扑动病例,消融后冠状窦口处起搏时,起搏信号至右房下侧壁的时间间期(DB=140.7±66.1ms)和右房下侧壁起搏时起搏信号至冠状窦口CS34的时间间期(BD=123.2±42.1ms)均较消融前(DB=66.0±12.5ms,BD=62.5±13.0ms)明显延长,P<0.01。结论不用Halo电极能成功消融典型心房扑动(AF),右心房峡部传导时间间期的定量测定可作为判断峡部完全性双向传导阻滞的方法之一。     

脑组织射频消融的有限元仿真与分析

目的 运用有限元方法（finite element method,FEM）模拟颅内病灶射频消融过程中的温度场分布,以合理有效利用热疗方案,提高射频消融对颅内病灶的治疗效果.方法 建立电导率不变和电导率随温度变化的两种有限元模型,并对两种模型的中心温度、电场强度、热生成率、比吸收率（specific absorption rate,SAR）,以及热损伤区域进行对比分析.结果 对比电导率不变的有限元模型,在电导率随温度变化的情况下,电场强度减小,电流密度增大,中心温度升高,热损伤范围增大;当消融温度接近100 ℃时电导率变化明显,其对消融效果影响较大.结论 射频热疗手术中考虑随温度变化的组织参数有较高的临床参考价值.     

Thermal model for fast simulation during magnetic resonance imaging guidance of radio frequency tumor ablation

Thermal ablation of a tumor with radio frequency (rf) energy from a small probe inserted into the solid tumor can be accomplished with minimal invasiveness under guidance with magnetic resonance imaging (MRI). A theoretical study is presented of 3D temperature distribution dynamics in tissue with rf heating to show the feasibility of fast numerical solution for repeated simulations during an ablation procedure. Model simulations are intended to be used during an ablation treatment together with temperature field images obtained by MR to predict the effect of alternative strategies of source heating and placement. A feature of the model is that it incorporates a heat source term that varies with distance from the rf probe to avoid the need for solving electric field equations. The effects of perfusion and internal cooling of the rf probe on the temperature distribution are simulated to show the model flexibility. Using a personal computer (PC), numerical solution of the model equations required 10 s to 2 min depending on the perfusion–temperature relationship. The results show the feasibility of using thermal model simulations in an iterative manner with MR images to help guide thermal ablation procedures in the clinical setting. © 2002 Biomedical Engineering Society. PAC2002: 8750Jk, 8719Xx, 8761-c     

心房颤动导管射频消融对心脏起搏器安全性影响的临床研究

目的评价植入起搏器患者经导管射频消融治疗慢性心房颤动(房颤)的安全性。方法18例永久性心脏起搏并房颤患者,其中男性12例,女性6例,年龄55～78岁,平均年龄68.67岁(标准差8.72岁)。分析其接受导管射频消融术中全程记录的心电信息,判断有无感知、起搏功能不良及房室失夺获、噪声反转等现象,并用起搏器程控仪于导管射频消融术前及术后第1天观察房室感知、起搏阈值及电极阻抗等参数的变化。结果18例患者均顺利完成导管射频消融,肺静脉前庭电学隔离率为100%。导管射频消融前后起搏器感知、起搏阈值及阻抗的变化无统计学意义(P>0.05)。导管射频消融过程中,3例(17%)出现噪声反转,3例(17%)出现感知不良,1例(6%)出现起搏功能不良致心室失夺获,均于停止放电后恢复正常。3例(17%)慢性持续性房颤患者在电复律后出现一过性感知不良。结论射频电流和电复律可引起一过性感知、起搏功能的障碍,但一般不引起起搏、感知阈值及电极阻抗的改变。对于已植入心脏起搏器的慢性房颤患者,在需行导管射频消融术时是安全的。