Advanced approach for intraoperative MRI guidance and potential benefit for neurosurgical applications

PURPOSE: To present an advanced approach for intraoperative image guidance in an open 0.5 T MRI and to evaluate its effectiveness for neurosurgical interventions by comparison with a dynamic scan-guided localization technique. MATERIALS AND METHODS: The built-in scan guidance mode relied on successive interactive MRI scans. The additional advanced mode provided real-time navigation based on reformatted high-quality, intraoperatively acquired MR reference data, allowed multimodal image fusion, and used the successive scans of the built-in mode for quick verification of the position only. Analysis involved tumor resections and biopsies in either scan guidance (N = 36) or advanced mode (N = 59) by the same three neurosurgeons. Technical, surgical, and workflow aspects were compared. RESULTS: The image quality and hand-eye coordination of the advanced approach were improved. While the average extent of resection, neurologic outcome after functional MRI (fMRI) integration, and diagnostic yield appeared to be slightly better under advanced guidance, particularly for the main surgeon, statistical analysis revealed no significant differences. Resection times were comparable, while biopsies took around 30 minutes longer. CONCLUSION: The presented approach is safe and provides more detailed images and higher navigation speed at the expense of actuality. The surgical outcome achieved with advanced guidance is (at least) as good as that obtained with dynamic scan guidance.     

CT-MR image data fusion for computer assisted navigated neurosurgery of temporal bone tumors

PURPOSE: To demonstrate the value of multi detector computed tomography (MDCT) and magnetic resonance imaging (MRI) in the preoperative work up of temporal bone tumors and to present, especially, CT and MR image fusion for surgical planning and performance in computer assisted navigated neurosurgery of temporal bone tumors. MATERIALS AND METHODS: Fifteen patients with temporal bone tumors underwent MDCT and MRI. MDCT was performed in high-resolution bone window level setting in axial plane. The reconstructed MDCT slice thickness was 0.8 mm. MRI was performed in axial and coronal plane with T2-weighted fast spin-echo (FSE) sequences, un-enhanced and contrast-enhanced T1-weighted spin-echo (SE) sequences, and coronal T1-weighted SE sequences with fat suppression and with 3D T1-weighted gradient-echo (GE) contrast-enhanced sequences in axial plane. The 3D T1-weighted GE sequence had a slice thickness of 1mm. Image data sets of CT and 3D T1-weighted GE sequences were merged utilizing a workstation to create CT-MR fusion images. MDCT and MR images were separately used to depict and characterize lesions. The fusion images were utilized for interventional planning and intraoperative image guidance. The intraoperative accuracy of the navigation unit was measured, defined as the deviation between the same landmark in the navigation image and the patient. RESULTS: Tumorous lesions of bone and soft tissue were well delineated and characterized by CT and MR images. The images played a crucial role in the differentiation of benign and malignant pathologies, which consisted of 13 benign and 2 malignant tumors. The CT-MR fusion images supported the surgeon in preoperative planning and improved surgical performance. The mean intraoperative accuracy of the navigation system was 1.25 mm. CONCLUSION: CT and MRI are essential in the preoperative work up of temporal bone tumors. CT-MR image data fusion presents an accurate tool for planning the correct surgical procedure and is a benefit for the operational results in computer assisted navigated neurosurgery of temporal bone tumors.     

An integrated visualization system for surgical planning and guidance using image fusion and an open MR

A surgical guidance and visualization system is presented, which uniquely integrates capabilities for data analysis and on-line interventional guidance into the setting of interventional MRI. Various pre-operative scans (T1- and T2-weighted MRI, MR angiography, and functional MRI (fMRI)) are fused and automatically aligned with the operating field of the interventional MR system. Both pre-surgical and intra-operative data may be segmented to generate three-dimensional surface models of key anatomical and functional structures. Models are combined in a three-dimensional scene along with reformatted slices that are driven by a tracked surgical device. Thus, pre-operative data augments interventional imaging to expedite tissue characterization and precise localization and targeting. As the surgery progresses, and anatomical changes subsequently reduce the relevance of pre-operative data, interventional data is refreshed for software navigation in true real time. The system has been applied in 45 neurosurgical cases and found to have beneficial utility for planning and guidance. J. Magn. Reson. Imaging 2001;13:967-975.     

CT-MR image data fusion for computer-assisted navigated surgery of orbital tumors

Purpose

To demonstrate the value of multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) in the preoperative assessment of orbital tumors, and to present, particularly, CT and MR image data fusion for surgical planning and performance in computer-assisted navigated surgery of orbital tumors.

Materials and methods

In this retrospective case series, 10 patients with orbital tumors and associated complaints underwent MDCT and MRI of the orbit. MDCT was performed at high resolution, with a bone window level setting in the axial plane. MRI was performed with an axial 3D T1-weighted (w) gradient-echo (GE) contrast-enhanced sequence, in addition to a standard MRI protocol. First, MDCT and MR images were used to diagnose tumorous lesions compared to histology as a standard of reference. Then, the image data sets from CT and 3D T1-w GE sequences were merged on a workstation to create CT-MR fusion images that were used for interventional planning and intraoperative image guidance. The intraoperative accuracy of the navigation unit was measured, defined as the deviation between the same landmark in the navigation image and the patient. Furthermore, the clinical preoperative status was compared to the patients’ postoperative outcome.

Results

Radiological and histological diagnosis, which revealed 7 benign and 3 malignant tumors, were concordant in 7 of 10 cases (70%). The CT-MR fusion images supported the surgeon in the preoperative planning and improved the surgical performance. The mean intraoperative accuracy of the navigation unit was 1.35 mm. Postoperatively, orbital complaints showed complete regression in 6 cases, were ameliorated notably in 3 cases, and remained unchanged in 1 case.

Conclusion

CT and MRI are essential for the preoperative assessment of orbital tumors. CT-MR image data fusion is an accurate tool for planning the correct surgical procedure, and can improve surgical results in computer-assisted navigated surgery of orbital tumors.     

超声与CT或MRI融合导航技术在介入诊疗中的临床应用

目的 评价超声(US)与CT或MRI融合导航技术在介入放射诊断和治疗中的作用.方法 回顾性分析47例接受US与cT或MRI融合导航技术行多种介入诊断和治疗患者的临床资料,包括操作方法、成功率、临床效果和并发症.对38例肝脏肿瘤行经皮穿刺活检和射频消融治疗;4例肝脓肿行经皮穿刺置管引流;5例骨骼及软组织病变行经皮穿刺活检和(或)射频消融、骨水泥填充治疗.结果 38例肝脏肿瘤行1次经皮射频消融治疗后,27例肿瘤达到了完全消融,随访3.0～6.0个月(中位随访时间4.8个月)无复发;11例在复查期内病灶范围未见明显变化.5例骨骼及软组织病变介入治疗效果显著,成功穿刺取材.4例肝脓肿经引流后痊愈.仅1例射频消融患者发生局部皮肤灼伤并发症,无其他操作相火并发症.结论 US与CT或MRI融合导航技术充分利用了多种影像手段的优势,提高了介入操作的定位准确性和安全性,扩大了介入诊断和治疗工作的应用范围.     

Cortical mapping by functional magnetic resonance imaging in patients with brain tumors

The aim of our study was to establish the effectiveness of the functional MRI (fMRI) technique in comparison with intraoperative cortical stimulation (ICS) in planning cortex-saving neurosurgical interventions. The combination of sensory and motor stimulation during fMRI experiments was used to improve the exactness of central sulcus localization. The study subjects were 30 volunteers and 33 patients with brain tumors in the rolandic area. Detailed topographical relations of activated areas in fMRI and intraoperative techniques were compared. The agreement in the location defined by the two methods for motor centers was found to be 84%; for sensory centers it was 83%. When both kinds of activation are taken into account this agreement increases to 98%. A significant relation was found between fMRI and ICS for the agreement of the distance both for motor and sensory centers (p=0.0021–0.0024). Also a strong dependence was found between the agreement of the location and the agreement of the distance for both kinds of stimulation. The spatial correlation between fMRI and ICS methods for the sensorimotor cortex is very high. fMRI combining functional and structural information is very helpful for preoperative neurosurgical planning. The sensitivity of the fMRI technique in brain mapping increases when using both motor and sensory paradigms in the same patient.     

Navigation in diagnosis and therapy

Image-guided navigation for surgery and other therapeutic interventions has grown in importance in recent years. During image-guided navigation a target is detected, localized and characterized for diagnosis and therapy. Thus, images are used to select, plan, guide and evaluate therapy, thereby reducing invasiveness and improving outcomes. A shift from traditional open surgery to less-invasive image-guided surgery will continue to impact the surgical marketplace. Increases in the speed and capacity of computers and computer networks have enabled image-guided interventions. Key elements in image navigation systems are pre-operative 3D imaging (or real-time image acquisition), a graphical display and interactive input devices, such as surgical instruments with light emitting diodes (LEDs). CT and MRI, 3D imaging devices, are commonplace today and 3D images are useful in complex interventions such as radiation oncology and surgery. For example, integrated surgical imaging workstations can be used for frameless stereotaxy during neurosurgical interventions. In addition, imaging systems are being expanded to include decision aids in diagnosis and treatment. Electronic atlases, such as Voxel Man or others derived from the Visible Human Project, combine a set of image data with non-image knowledge such as anatomic labels. Robot assistants and magnetic guidance technology are being developed for minimally invasive surgery and other therapeutic interventions. Major progress is expected at the interface between the disciplines of radiology and surgery where imaging, intervention and informatics converge.     

Intraoperative,real-time,functional MRI

Functional MRI (fMRI) methods have been demonstrated to noninvasively identify motor-sensory, visual, and other areas of eloquent cortex for guiding surgical intervention. Typically, fMRI data are acquired preoperatively during a conventional surgical planning MRI examination. Unlike direct cortical stimulation at the time of surgery, however, preoperative fMRI methods do not account for the potential movement of tissues (relative to the time of functional imaging) that may occur in the surgical suite as a direct result of the intervention. Recently, an MRI device has been demonstrated for use in the surgical suite that has the potential to reduce the extent of cortical exposure required for the intervention. However, the invasive requirements of cortical mapping may supersede the invasive requirements of the surgical intervention itself. Consequently, we demonstrate here a modification to the intraoperative MRI device that facilitates a noninvasive, real-time, functional MR examination in the surgical suite.     

Intraoperative magnetic resonance image guidance in neurosurgery

Recently, there has been a burgeoning interest in the use of image-guided navigation to improve the safety and effectiveness of neurosurgical procedures. The intraoperative use of magnetic resonance imaging (MRI) provides the most accurate guidance available. This report discusses the hardware and software improvements that have made intraoperative MRI a reality and describes the use of this technology for neurosurgical intraoperative guidance.     

Contrast-Enhanced Abdominal Angiographic CT for Intra-abdominal Tumor Embolization: A New Tool for Vessel and Soft Tissue Visualization

C-Arm cone-beam computed tomography (CACT), is a relatively new technique that uses data acquired with a flat-panel detector C-arm angiography system during an interventional procedure to reconstruct CT-like images. The purpose of this Technical Note is to present the technique, feasibility, and added value of CACT in five patients who underwent abdominal transarterial chemoembolization procedures. Target organs for the chemoembolizations were kidney, liver, and pancreas and a liposarcoma infiltrating the duodenum. The time for patient positioning, C-arm and system preparation, CACT raw data acquisition, and data reconstruction for a single CACT study ranged from 6 to 12 min. The volume data set produced by the workstation was interactively reformatted using maximum intensity projections and multiplanar reconstructions. As part of an angiography system CACT provided essential information on vascular anatomy, therapy endpoints, and immediate follow-up during and immediately after the abdominal interventions without patient transfer. The quality of CACT images was sufficient to influence the course of treatment. This technology has the potential to expedite any interventional procedure that requires three-dimensional information and navigation.     

Multimodality Image Fusion–Guided Procedures: Technique, Accuracy, and Applications

Personalized therapies play an increasingly critical role in cancer care: Image guidance with multimodality image fusion facilitates the targeting of specific tissue for tissue characterization and plays a role in drug discovery and optimization of tailored therapies. Positron-emission tomography (PET), magnetic resonance imaging (MRI), and contrast-enhanced computed tomography (CT) may offer additional information not otherwise available to the operator during minimally invasive image-guided procedures, such as biopsy and ablation. With use of multimodality image fusion for image-guided interventions, navigation with advanced modalities does not require the physical presence of the PET, MRI, or CT imaging system. Several commercially available methods of image-fusion and device navigation are reviewed along with an explanation of common tracking hardware and software. An overview of current clinical applications for multimodality navigation is provided.     

Computer-based imaging and interventional MRI: applications for neurosurgery.

Advances in computer technology and the development of open MRI systems definitely enhanced intraoperative image-guidance in neurosurgery. Based upon the integration of previously acquired and processed 3D information and the corresponding anatomy of the patient, this requires computerized image-processing methods (segmentation, registration, and display) and fast image integration techniques. Open MR systems equipped with instrument tracking systems, provide an interactive environment in which biopsies and minimally invasive interventions or open surgeries can be performed. Enhanced by the integration of multimodal imaging these techniques significantly improve the available treatment options and can change the prognosis for patients with surgically treatable diseases.     

MR-guided and MR-monitored neurosurgical procedures at 1.5 T

A combined MR suite and operating room (MR-OR) has been developed and extensively assessed for its use in a wide spectrum of therapeutic applications. Equipped with a 1.5 T short bore clinical MR scanner and standard neurosurgical OR equipment, in this MR surgical suite, surgeons can obtain intraoperative planar and volumetric MR images with superior soft tissue contrast and spatial resolution for surgical planning, guidance, and monitoring. Besides MR morphologic imaging capability, blood oxygen level-dependent functional MRI and proton MR spectroscopic imaging have been demonstrated intraoperatively in the same MR-OR to aid in surgical planning and guide tumor resections. A perspective surgical navigation device and remotely operated instrument have been developed and successfully used to assist surgeons in aligning and introducing biopsy needles under fluoroscopic MRI in brain biopsy procedures. Furthermore, surgical complications can be assessed immediately before the closure. There are numerous advantages offered by this unprecedented MR-guided surgical approach, most of which are demonstrated and presented herein. Since 1997, >270 neurosurgical cases (42% brain biopsies, 25% tumor resections, 11% functional neurosurgeries, 10% cyst drainages and shunt placements, and 12% others) have been performed in the MR-OR with a <1% overall complication rate. The tumor recurrence rate for the MR-guided surgical approach is significantly less than that of the conventional one. Exemplary neurosurgical cases that have been performed in the MR-OR suite within the last 24 months are included. Overall, this high magnetic field approach to the MR-guided minimally invasive surgical procedures has been shown to be practical and acceptable to neurosurgeons as well as to neuroradiologists for a wide range of neurosurgical and neuroradiologic applications.     

Interventional MRI using multiple 3D angiography roadmaps with real‐time imaging

Purpose:

To enhance real‐time magnetic resonance (MR)‐guided catheter navigation by overlaying colorized multiphase MR angiography (MRA) and cholangiopancreatography (MRCP) roadmaps in an anatomic context.

Materials and Methods:

Time‐resolved MRA and respiratory‐gated MRCP were acquired prior to real‐time imaging in a pig model. MRA and MRCP data were loaded into a custom real‐time MRI reconstruction and visualization workstation where they were displayed as maximum intensity projections (MIPs) in distinct colors. The MIPs were rendered in 3D together with real‐time multislice imaging data using alpha blending. Interactive rotation allowed different views of the combined data.

Results:

Fused display of the previously acquired MIP angiography data with real‐time imaging added anatomical context during endovascular interventions in swine. The use of multiple MIPs rendered in different colors facilitated differentiation of vascular structures, improving visual feedback during device navigation.

Conclusion:

Interventional real‐time MRI may be enhanced by combining with previously acquired multiphase angiograms. Rendered as 3D MIPs together with 2D slice data, this technique provided useful anatomical context that enhanced MRI‐guided interventional applications. J. Magn. Reson. Imaging 2010;31:1015–1019. ©2010 Wiley‐Liss, Inc.     

Improving the temporal resolution of functional MR imaging using keyhole techniques

Using a keyhole technique, it is shown that the data acquisition rate of gradient-echo imaging for functional MRI (fMRI) studies can be increased substantially. The resulting enhancement of the temporal resolution of fMRIs was accomplished without modifying the hardware of a conventional MRI system. High spatial resolution fMRI images were first collected with conventional full k-space acquisition and image reconstruction. Using the same data set, simulation reconstruction using the keyhole principle and zero-padding were performed for comparison with the full k-space reconstruction. No significant changes were found for fMRI images generated from the keyhole technique with a data sharing profile of 50% of the k-space. As k-space data sharing profiles increased to 75 and 87.5%, the keyhole fMRI images began to show only modest changes in activation intensity and area compared with the standard images. In contrast, zero-padding fMRI images produced a significant disparity both in activation intensity and area relative to the truly high-resolution fMRI images. The keyhole technique's ability to retain the intensity and area of fMRI information, while substantially reducing acquisition time, makes it a promising method for fMRI studies.     

US-CT影像融合容积导航技术可重复性的实验研究

目的探讨US-CT影像融合容积导航技术在肝脏体模应用中的价值。方法采用包含3条肝静脉及6枚囊肿模型的体外肝脏体模,应用融合导航定位系统将其CT薄层扫描图像导入超声检查仪虚拟导航系统进行影像融合,在囊肿模型的最大截面层,应用matlab软件计算影像重合率。实验共进行2次:1)2名不同资质的操作者应用影像融合容积导航技术,分别在1天内各自独立完成3次对6枚囊肿模型的融合对位;2)1周后重复上述步骤。结果高年资操作者和低年资操作者都能获得较高的影像重合率和较低的变异系数。2次实验中,2名操作者组间影像重合率明显相关;不同操作者,前后两次组内实验影像重合率明显相关。结论US-CT影像融合容积导航技术可以达到较高的影像重合率,在组间及组内都具有较高的可重复性。并且,不同操作经验的医师只要在标准操作的前提下,不会显著影响影像重合率的可重复性。     

3T高场强功能MRI在脑功能区胶质瘤皮质电刺激手术中的应用

目的研究应用3T高场强功能MRI（fMRI）定位脑运动功能区，及在脑胶质瘤直接皮质电刺激手术中的指导作用。方法26例邻近或累及脑运动功能区的胶质瘤患者术前采用双手握拳刺激策略，根据血氧水平依赖（BOLD）原理进行功能成像。经工作站提供的BOLD功能图像分析软件包进行分析，获得脑运动功能区的激活图像，制定手术方案。所有患者均在唤醒麻醉下进行显微外科手术，在术前fMRI指导下利用直接皮质电刺激定位运动区。在保护脑功能不受损的前提下，最大程度地切除胶质瘤。术前、术后均行Karnofsky生活状态（KPS）评分，判断患者的状态。结果26例术前BOLD运动fMRI有23例获得良好的手运动脑功能区激活图像。患者在唤醒麻醉下，在术前fMRI指导下利用直接皮质电刺激快捷、准确定位初级运动皮质区，并且两者具有良好的一致性。同时术前fMRI提供术中未检测到的脑功能区的信息，相互补充。术前KPS评分80．0～90．0分患者21例（平均85．7分）术后恢复至平均95．2分，术前KPS评分40．0～70．0分患者5例（平均68．0分）术后恢复至平均90．0分。结论术前fMRI可活体和无创地描绘出脑运动功能区与肿瘤的功能解剖位置关系，优化手术方案，在唤醒麻醉下指导直接皮质电刺激定位运动区的手术，实现最大程度保护脑功能，并最大程度地切除肿瘤。     

Microwave ablation assisted by a real-time virtual navigation system for hepatocellular carcinoma undetectable by conventional ultrasonography

Objectives

To evaluate the efficiency and feasibility of microwave (MW) ablation assisted by a real-time virtual navigation system for hepatocellular carcinoma (HCC) undetectable by conventional ultrasonography.

Methods

18 patients with 18 HCC nodules (undetectable on conventional US but detectable by intravenous contrast-enhanced CT or MRI) were enrolled in this study. Before MW ablation, US images and MRI or CT images were synchronized using the internal markers at the best timing of the inspiration. Thereafter, MW ablation was performed under real-time virtual navigation system guidance. Therapeutic efficacy was assessed by the result of contrast-enhanced imagings after the treatment.

Results

The target HCC nodules could be detected with fusion images in all patients. The time required for image fusion was 8–30 min (mean, 13.3 ± 5.7 min). 17 nodules were successfully ablated according to the contrast enhanced imagings 1 month after ablation. The technique effectiveness rate was 94.44% (17/18). The follow-up time was 3–12 months (median, 6 months) in our study. No severe complications occurred. No local recurrence was observed in any patients.

Conclusions

MW ablation assisted by a real-time virtual navigation system is a feasible and efficient treatment of patients with HCC undetectable by conventional ultrasonography.     

Integration of interventional MRI with computer-assisted surgery

Interventional MRI (IMRI) has entered into a new stage in which computer-based techniques play an increasing role in planning, monitoring, and controlling the procedures. The use of interactive imaging, navigational image guidance techniques, and image processing methods is demonstrated in various applications. The integration of intraoperative MRI guidance and computer-assisted surgery will greatly accelerate the clinical utility of image-guided therapy in general and interventional MRI in particular. J. Magn. Reson. Imaging 2001;13:69-77.     

Einsatzmöglichkeiten eines offenen magnetresonanztomographen in der therapiesimulation und dreidimensionalen bestrahlungsplanung

PURPOSE: A system for digital integration of an open MR scanner (0.23 T, Figure 1) in therapy simulation and 3D radiation treatment planning is described. METHOD: MR images were acquired using the body coil and various positioning and immobilization aids. A gradient echo sequence (TR/TE 320 ms/24 ms) was used to create axial and coronal data sets. Image distortions were measured and corrected using phantom measurements (Figure 2) and specially developed software. RESULTS: Maximal and mean distortions of the MR images could be reduced from 19 mm to 8.2 mm and from 2.7 mm to 0.7 mm, respectively (Figure 3 to 5, Table 1). Coronal MR images were recalculated in fan beam projection for use at the therapy simulator. Tumor and organ contours were transferred from the MR image to the digitally acquired and corrected simulator image using a landmark matching algorithm (Figure 6 and 7). For 3D treatment planning, image fusion of axial MR images with standard CT planning images was performed using a landmark matching algorithm, as well (Figure 8). Representative cases are shown to demonstrate potential applications of the system. CONCLUSION: The described system enables the integration of the imaging information from an open MR system in therapy simulation and 3D treatment planning. The low-field MR scanner is an attractive adjunct for the radio-oncologist because of the open design and the low costs.