A method for simultaneous RF ablation and MRI

Radiofrequency (RF) energy has many advantages in thermal tumor ablation protocols. With the recent development of open MRI systems, interventional MRI procedures, including thermal ablation, have become the focus of great research interest. However, the significant interference between RF generators and MR imagers has prevented simultaneous imaging and RF ablation and, until now, has limited the role of RF-based thermal therapy in interventional MRI. Here, a simple switching circuit designed with consideration of patient safety provides compatibility between open MRI systems and RF thermal lesion generators. The experimental results show that the switching circuit allows imaging during RF ablation and opens new opportunity for MR-guided thermal therapy.     

Detection of pulmonary vein and left atrial scar after catheter ablation with three-dimensional navigator-gated delayed enhancement MR imaging: initial experience

PURPOSE: To prospectively evaluate whether scar caused by radiofrequency (RF) ablation of the left atrium (LA) in patients with atrial fibrillation can be depicted with high-spatial-resolution delayed enhancement magnetic resonance (MR) imaging. MATERIALS AND METHODS: All 23 subjects (16 men, seven women; mean age, 54 years +/- 13 [standard deviation]) provided written informed consent; the study was approved by the local institutional review board and was HIPAA compliant. A high-spatial-resolution free-breathing delayed enhancement MR imaging method was developed to detect scar (ie, ablated tissue) in the LA and pulmonary veins (PVs). The LA in 15 patients before ablation and in 18 patients at least 30 days after ablation was examined. A reader with 4 years of experience assessed presence of delayed enhancement on images and circumferential completeness. Signal-to-noise and contrast-to-noise ratios were measured and compared with an unpaired t test. The relationship between measurements of enhancement thickness at the interatrial septum and the number of days after ablation was investigated. RESULTS: No subject demonstrated preablation delayed enhancement of the atrial or PV wall, whereas postablation delayed enhancement was identified in all (100%). In patients after ablation, a partial to completely circumferential delayed enhancement pattern could be identified for the left inferior PV that encompassed 88% +/- 11 of the circumference, but only 62% of patients demonstrated more than 90% circumferential delayed enhancement. The signal-to-noise ratio of blood was 12, and the signal-to-noise ratios of the pre- and postablation left atrial wall were 15 and 22, respectively (P<.05). A relationship between delayed enhancement wall thickness and the inverse of the time interval from ablation was identified (P<.05). CONCLUSION: High-spatial-resolution delayed enhancement MR imaging allows noninvasive identification of scar induced by RF ablation following isolation therapy of the PV.     

Aktueller Stand und Entwicklungen der Laserablation in der Tumortherapie

PURPOSE: The purpose of this paper is to present technical innovations and clinical results of percutaneous interventional laser ablation of tumors using new techniques. METHODS; Laser ablation was performed in 182 patients (liver tumors: 131, non hepatic tumors-bone, lung, others: 51) after interdisciplinary consensus was obtained. The procedure was done using a combination of imaging modalities (CT/MRI, CT/US) or only closed high field MRI (1.5 T). All patients received an MRI-scan immediately after laser ablation. RESULTS: In 90.9% of the patients with liver tumors, a complete ablation was achieved. Major events occurred in 5.4%. The technical success rate of laser ablation in non-hepatic tumors was high, clinical results differed depending on the treated organ. CONCLUSIONS: The treatment of tumors of the liver and other organs up to 5 cm by laser ablation was a safe procedure with a low rate of complications and side effects. Image guidance by MRI is advantageous for precise tumor visualization in all dimensions, therapy monitoring, and control of laser ablation results.     

ADC mapping of the aging frontal lobes in mild cognitive impairment

Normal aging, leukoaraiosis (LA) and vascular disease particularly involve the human frontal lobes. We decided to investigate a population of elderly patients referred for neuroimaging because of progressive minor cognitive deficits but no dementia. They underwent conventional Magnetic resonance imaging (MRI) using axial T1 and T2-weighted imaging as well as coronal FLAIR sequences in addition to the axial diffusion-weighted MRI. MRI allowed us to differentiate patients with leukoaraïosis (LA+) from those without it (LA-) and mapping of the apparent diffusion coefficient (ADC) to investigate local tissular water motion.We observed an increase in the ADC in all investigated patients with increasing age (r=0.326, p=0.002). This increase was observed in both patients groups (LA+ and LA-) . In addition, the LA+ group had significant higher ADC values than the LA- group after controlling for age (p<0.0001).     

Measurement of left atrial volume by 2D and 3D non-contrast computed tomography compared with cardiac magnetic resonance imaging

BackgroundCardiac magnetic resonance imaging (MRI) is considered the gold standard for assessment of left atrial (LA) volume. We assessed the feasibility of evaluating LA volume using 3D non-contrast computed tomography (NCCT). Furthermore, since manual tracing of LA volume is time consuming, we evaluated the accuracy of the LA area using 2D NCCT imaging for LA volume assessment.MethodsMRI and NCCT imaging were performed in 69 patients before and one year after aortic valve replacement. In 3D MRI and 3D NCCT, each slice was manually traced, excluding the pulmonary veins and atrial appendage, and multiplied by slice spacing, thus generating a measure of LA volume. The LA volume was indexed to body surface area. On 2D NCCT, the largest axial cross-section LA area was traced manually.ResultsThe mean LA volume was 102 ± 28 ml in MRI compared with 103 ± 28 ml in 3D NCCT. 3D NCCT showed good agreement with MRI measurements (mean difference −0.7 ml/m²; 95% confidence interval (CI) −2.2 to 0.9). By Bland-Altman, 3D NCCT also showed good agreement with MRI (limits of agreement: −18.7–17.4 ml/m²). Furthermore, good correlation was found between 2D NCCT and 3D NCCT LA volume (r = 0.93).Conclusion2D and 3D measurements of LA volume in non-contrast computed tomography are feasible and accurate.     

MR-guided microwave thermocoagulation therapy of liver tumors: initial clinical experiences using a 0.5 T open MR system

PURPOSE: To utilize a microwave coagulator for MR-guided interstitial thermal therapy of liver tumors as a clinically feasible heating device. MATERIALS AND METHODS: MR-guided microwave thermocoagulation therapy was carried out 34 times in 30 patients with liver tumors (eight hepatocellular carcinoma, 22 metastatic tumors) using a 0.5 T open configuration MR system. RESULTS: Percutaneous puncture could be accomplished both accurately and safely while monitoring real-time magnetic resonance imaging (MRI). Using a notch filter, MR images could be observed without electromagnetic interference even during microwave ablation. Temperature monitoring during ablation was possible using the proton resonance frequency method. All procedures could be successfully carried out without any complications, and the therapeutic effects were deemed satisfactory. CONCLUSION: MR-guided microwave thermocoagulation therapy could be one promising procedure of minimally invasive treatment for liver tumors.     

MR-Guided High-Intensity Focused Ultrasound Ablation of Breast Cancer with a Dedicated Breast Platform

Optimizing the treatment of breast cancer remains a major topic of interest. In current clinical practice, breast-conserving therapy is the standard of care for patients with localized breast cancer. Technological developments have fueled interest in less invasive breast cancer treatment. Magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) is a completely noninvasive ablation technique. Focused beams of ultrasound are used for ablation of the target lesion without disrupting the skin and subcutaneous tissues in the beam path. MRI is an excellent imaging method for tumor targeting, treatment monitoring, and evaluation of treatment results. The combination of HIFU and MR imaging offers an opportunity for image-guided ablation of breast cancer. Previous studies of MR-HIFU in breast cancer patients reported a limited efficacy, which hampered the clinical translation of this technique. These prior studies were performed without an MR-HIFU system specifically developed for breast cancer treatment. In this article, a novel and dedicated MR-HIFU breast platform is presented. This system has been designed for safe and effective MR-HIFU ablation of breast cancer. Furthermore, both clinical and technical challenges are discussed, which have to be solved before MR-HIFU ablation of breast cancer can be implemented in routine clinical practice.     

DWI findings of periventricular ischemic changes in patients with leukoaraiosis.

In this report the diffusion-weighted imaging (DWI) findings and ADC values of leukoaraiosis (LA) and associated periventricular ischemic lesions were assessed. Seventy-eight patients with LA were examined with magnetic resonance imaging (MRI) and DWI. Twenty one patients (28%) were found to have focal acute white matter infarction on DWI which could not be detected and discriminated on the basis of MRI findings alone. LA and acute white matter infarction both showed hyperintensity on standard T2W MRI, whereas acute infarction revealed focal hyperintensity on DWI. Thirteen patients (16%) had chronic lacunar infarctions in the white matter. ADC values of LA, acute and chronic white matter infarctions were calculated and found to be significantly different from each other (p<0.05). It is concluded that DWI is necessary in the detection of acute periventricular white matter infarction from LA.     

Interventional and intraoperative MR: review and update of techniques and clinical experience

The concept of interventional magnetic resonance imaging (MRI) is based on the integration of diagnostic and therapeutic procedures, favored by the combination of the excellent morphological and functional imaging characteristics of MRI. The spectrum of MRI-assisted interventions ranges from biopsies and intraoperative guidance to thermal ablation modalities and vascular interventions. The most relevant recently published experimental and clinical results are discussed. In the future, interventional MRI is expected to play an important role in interventional radiology, minimal invasive therapy and guidance of surgical procedures. However, the associated high costs require a careful evaluation of its potentials in order to ensure cost-effective medical care.     

Percutaneous radiofrequency ablation for unresectable large hepatic tumours during hepatic blood flow occlusion in four patients

AIM: To evaluate percutaneous radiofrequency (RF) ablation therapy for unresectable large hepatic tumours combined with regional interruption of hepatic blood flow, and to assess the safety and efficacy of this procedure. MATERIALS AND METHODS: Four patients with hepatic tumours were enrolled in this study. Patients were treated by a single session of RF ablation during occlusion of both hepatic artery and hepatic vein. Tumour size ranged from 45-57 mm (mean 50.2 mm). Initial therapeutic efficacy was evaluated with helical computed tomography (CT) performed within 9 days after the treatment. CT or magnetic resonance imaging (MRI) was performed every 2-3 months thereafter. RESULTS: The largest axis of coagulated lesions after the ablation was 50-60 mm (mean 56.5 mm) in diameter. The ablation therapy was considered complete in three patients; after a mean follow-up of 12.7 months, CT and MRI revealed complete destruction of their tumours. One patient required further treatment. No severe complications occurred. CONCLUSION: Although further studies are needed, in this limited clinical trial a local ablation area exceeding 50 mm in diameter was achieved safely.     

Imaging features of hepatocellular carcinoma after transcatheter arterial chemoembolization and radiofrequency ablation

OBJECTIVE: The purpose of this pictorial essay is to show the imaging features of hepatocellular carcinoma (HCC) after transcatheter arterial chemoembolization (TACE) and radiofrequency thermal ablation on CT, MRI, and contrast-enhanced sonography and to describe the advantages and limitations of each imaging technique in evaluating the therapeutic effect on HCC. CONCLUSION: CT is the standard imaging technique for monitoring the effectiveness of TACE and radiofrequency ablation. Contrast-enhanced sonography and MRI can complement CT in evaluating the therapeutic response.     

MRI-compatible manipulator with remote-center-of-motion control

Purpose

To develop and assess a needle‐guiding manipulator for MRI‐guided therapy that allows a physician to freely select the needle insertion path while maintaining remote center of motion (RCM) at the tumor site.

Materials and Methods

The manipulator consists of a three‐degrees‐of‐freedom (DOF) base stage and passive needle holder with unconstrained two‐DOF rotation. The synergistic control keeps the Virtual RCM at the preplanned target using encoder outputs from the needle holder as input to motorize the base stage.

Results

The manipulator assists in searching for an optimal needle insertion path which is a complex and time‐consuming task in MRI‐guided ablation therapy for liver tumors. The assessment study showed that accuracy of keeping the virtual RCM to predefined position is 3.0 mm. In a phantom test, the physicians found the needle insertion path faster with than without the manipulator (number of physicians = 3, P = 0.001). However, the alignment time with the virtual RCM was not shorter when imaging time for planning were considered.

Conclusion

The study indicated that the robot holds promise as a tool for accurately and interactively selecting the optimal needle insertion path in liver ablation therapy guided by open‐configuration MRI. J. Magn. Reson. Imaging 2008. © 2008 Wiley‐Liss, Inc.     

Recurrent osteoid osteoma: interstitial laser ablation under magnetic resonance imaging guidance

Thermal ablation has become a therapy of choice in the treatment of osteoid osteomas. To date, computed tomography has been the standard imaging modality for minimally invasive treatment regimes. We report a case of a 46-year-old man with a recurrent osteoid osteoma in the right tibial head after CT-guided drill excision and repeat treatment with laser ablation under open high-field MRI guidance. We describe the steps of the interventional MRI procedure and discuss related innovative guidance and monitoring features, and potential benefits of MRI compared with CT-guided techniques. In conclusion, MR-guided laser ablation was proved to be safe and effective.     

不同MR成像方式对肝细胞癌射频消融术后的评估

以射频消融为主的肝细胞癌消融治疗已经广泛应用于临床,但治疗后肿瘤残存和复发是影响疗效的主要问题,所以消融后的评估显得尤为重要。MRI具有多参数、多序列、任意平面成像及多种功能成像方式,使其对肿瘤消融术后的评估更具优势。因此,本文就MRI常规平扫、MRI增强、DWI、DKI、PWI及MRS在肝细胞癌射频消融术后评估中的应用作出综述。     

脑白质疏松的扩散张量成像(DTI)研究

目的 应用扩散张量成像（DTI）检查脑白质疏松（LA）病灶的平均扩散系数（DCavg）、各向异性（FA）值与LA严重程度的关系,探讨常规MBI检查正常的脑白质微结构在DTI中的变化及与认知功能的关系。资料与方法 对55例LA患者和22名健康老年人行DTI检查,测量LA病灶和正常白质区域的DCavg、FA值。结果 LA程度越严重,DCavg值越高,呈正相关;FA值越低,呈负相关。神经心理学测试（简易智能精神状态量表,MMSE）与LA患者的正常脑白质区域的DCavg、FA值明显相关,尤其是前角白质、半卵圆中心的正常脑白质。结论 DTI检查LA,其DCavg、FA值显示出特征性的改变,DTI能够发现常规MRI检查正常的脑白质微结构改变,且这种改变与认知功能相关。     

MRI-guided thermal therapy of transplanted tumors in the canine prostate using a directional transurethral ultrasound applicator

PURPOSE: To evaluate MRI-based techniques for visual guidance, thermal monitoring, and assessment during transurethral ultrasound thermal therapy of implanted tumors in an in vivo canine prostate model. MATERIALS AND METHODS: Transmissible venereal tumors (TVT) were grown in the right lobe of the prostate in four dogs. High-temperature thermal therapy was selectively applied to the tumor-bearing lobe using a transurethral ultrasound applicator with a 180 degrees directional heating pattern. Temperature-sensitive MRI (MRTI) using a fast interleaved gradient-echo echo-planar (iGE-EPI) imaging sequence was used for cumulative thermal dose calculations in multiple image planes during the treatment. The results from MRTI-based dose maps and post-treatment MRI were compared to those from histologic analysis. RESULTS: MRTI monitoring in multiple planes across the prostate guided the use and control of a directive ultrasound applicator for the selective ablation of the sections of the prostate that contained implanted tumors. Findings in gadolinium enhanced MRI obtained immediately after thermal therapy slightly underestimated the size of tissue necrosis after treatment, as verified by histopathologic analysis. CONCLUSION: The use of multiplanar MRTI with a transurethral ultrasound applicator shows significant potential for selective thermal ablation of prostate tumor and tissue.     

Magnetic resonance guidance for radiofrequency ablation of liver tumors

Image-guided thermal ablation of liver tumors is a minimally invasive treatment option. Techniques used for thermal ablation are radiofrequency (RF) ablation, laser interstitial thermotherapy (LITT), microwave (MW) ablation, high-intensity focused ultrasound (HIFU), and cryoablation. Among these techniques RF ablation attained widespread consideration. Image guidance should ensure a precise ablation therapy leading to a complete coagulation of tumor tissue without injury to critical structures. Therefore, the modality of image guidance has an important impact on the safety and efficacy of percutaneous RF ablation. The current literature regarding percutaneous RF ablation mainly describes the use of computed tomography (CT) and ultrasonography (US) guidance. In addition, interventional MR systems offer the possibility to utilize the advantages of MR imaging such as excellent soft-tissue contrast, multiplanar and interactive capabilities, and sensitivity to thermal effects during the entire RF ablation procedure. Monitoring of thermally induced coagulation by MR imaging is supportive to control the ablation procedure. MR imaging can be advantageously used to guide overlapping ablation if necessary as well as to define the endpoint of RF ablation after complete coverage of the target tissue is verified. Furthermore, monitoring of thermal effects is essential in order to prevent unintended thermal damage from critical structures surrounding the target region. Therefore, MR-guided RF ablation offers the possibility for a safe and effective therapy option in the treatment of primary and secondary hepatic malignancies. The article summarizes the role of MR guidance for RF ablation of liver tumors.     

MRI-guided interventions of the breast

MRI has proven to be a very reliable diagnostic tool in the detection and differential diagnosis of breast lesions. Some lesions are, even in retrospect, not detectable in x-ray or ultrasound images but MRI is able to detect lesions at a much smaller size than the average size of lesions depicted by x-ray and ultrasound. The aim in the future is to develop combined procedures where imaging, biopsy, and interventional therapies are combined in a single outpatient procedure. As a step toward this goal different interventional procedures are useful that include interstitial laser therapy (ILT), radiofrequency ablation (RFA), high-intensity focused ultrasound (HIFU), microwave ablation therapy, and cryotherapy. In this overview the main features and initial results of these procedures are described and discussed.     

FDG positron emission tomography in the surveillance of hepatic tumors treated with radiofrequency ablation

PURPOSE: Radiofrequency thermal ablation (RFA) is an emerging technique in the treatment of focal hepatic tumors. Magnetic resonance imaging (MRI) and computed tomography (CT) are currently used to monitor hepatic tumors after RFA for residual disease and recurrence. Fluorodeoxyglucose (FDG) positron emission tomography (PET) is an excellent imaging method for the detection of liver metastases, but it has not been thoroughly evaluated as an alternative to anatomic imaging in the surveillance of liver tumors treated with RFA. The purpose of this investigation was to determine the role of FDG-PET imaging in the surveillance of liver tumors treated with RFA. METHODS: Thirteen patients with histories of malignant tumors of the liver treated with RFA and who had received post-treatment FDG-PET scans were assessed retrospectively. One patient had two post-RFA FDG-PET scans, eight patients had concurrent MRI scans, and six patients had concurrent CT scans. Imaging findings were compared with the results of clinical follow-up. RESULTS: There were either recurrent tumors at the ablation site (8 patients) or new metastases (3 patients) in 11 patients. FDG-PET identified all 11 cases and did not misidentify any cases. Of the seven patients with positive PET findings who received an MRI scan, three were also positive on MRI (42.9%); the other four cases were either negative or equivocal. Of the four patients with positive PET findings who received a CT scan, only two had positive CT scan findings (50%). All recurrences diagnosed by PET were confirmed on clinical follow-up. CONCLUSION: In this preliminary study, FDG-PET was superior to anatomic imaging in the surveillance of patients treated with RFA for malignant hepatic tumors.     

Non‐contrast‐enhanced pulmonary vein MRI with a spatially selective slab inversion preparation sequence

We propose a non‐contrast‐enhanced, three‐dimensional, free‐breathing, electrocardiogram‐gated, gradient recalled echo sequence with a slab‐selective inversion for pulmonary vein (PV) MRI. A sagittal inversion slab was applied prior to data acquisition to suppress structures adjacent to the left atrium (LA) and PVs, thereby improving the conspicuity of the PV and LA. Compared with other MR angiography methods using an inversion pulse, the proposed method does not require signal subtraction and the inversion slab is not parallel to the imaging slab. The feasibility of the proposed method was demonstrated in healthy subjects. The inversion slab thickness and inversion time were optimized to be 60 mm and 500 ms, respectively. Compared to conventional gradient recalled echo imaging without inversion, the proposed technique significantly increased the contrast‐to‐noise ratios between the LA and the right atrium by 20‐fold (P < 0.01), increased the contrast‐to‐noise ratios between the PVs and right atrium by 10‐fold (P < 0.03), and increased the contrast‐to‐noise ratios between the PVs, LA and pulmonary artery by 4‐fold (P < 0.01 for both). The signal‐to‐noise ratios of the PVs and the LA were similar with and without the inversion slab (P > 0.3). The proposed technique greatly enhances the conspicuity of the PVs and LA without significant loss of signal‐to‐noise ratio. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.