New ultrasound techniques and their application in neurosurgical intra-operative sonography

Abstract

We describe a variety of new ultrasound techniques by their physical background, potentials and applications regarding usefulness during intra-operative neurosurgical procedures. Transducers like highfrequency and small rotating probes fitting into neuroendoscopes, imaging techniques as extended field-ofview technique, harmonic imaging, echo-enhancers, 3-D imaging and the real-time integration of neurosonography with pre-operative CT- or MR-data are mentioned. The technical or physical principles are explained, followed by a discussion of these techniques from available literature dealing with their intra-operative neurosurgical applications and the experience of the authors with the techniques. With higher frequencies micromillimeter imaging is possible and small probe allows endoneurosonography. Echo-enhancers and harmonic imaging improve the signal-to-noise ratio and 3-D imaging and extended field-of-view techniques allows a better understanding of the pathoanatomy. With the real-time integration of intra-operative ultrasound images and pre-operative CT or MR images additional information, like hemodynamic pattern, are available for the neurosurgeon. Although until now only a limited number of reports about new sonographic techniques during intra-operative application in neurosurgery exist, the methods seem to be promising in creating images easier to understand, incorporating more information about pathoanatomy and supplying the neurosurgeon with information additional to that provided by CT and MRI. [Neurol Res 2001; 23: 697-705]     

Ultrasonographic superb microvascular imaging for emergency surgery of intracerebral hemorrhage

Ultrasonography (US) has been used as a reliable imaging modality, providing real-time information during neurosurgical operations. One recent innovative US technique, superb microvascular imaging (SMI), visualizes small vessels and flow, which are not detected with standard US with doppler. We apply SMI to intraoperative US monitoring in emergency surgery for intracerebral hemorrhage (ICH).Eleven consecutive patients with ICH underwent endoscopic emergency surgery under US monitoring with SMI. After performing a small craniotomy, US images were obtained using SMI, a fusion technique, and a contrast agent technique, with the probe on the brain surface during surgery. Fusion images were obtained with the probe on the head before craniotomy in some patients.Animated US images with SMI could differentiate hematoma containing no vessels from brain tissue, and flow images using SMI and contrast agent techniques clarified the borderlines. Animated fusion images of intraoperative US and preoperative CT provided information on the extent of hematoma and residual hematoma during emergency surgery. We made various fusion CT images showing intracranial hematoma with US probes and decided on the skin incision line before beginning surgery, as if we were using a neuronavigation system.US with SMI, contrast agent, and fusion techniques provide information on the extent of intracranial hematoma and residual hematoma with no vessels and no flow. Monitoring by US and fusion CT images is useful for ICH surgery as a next-generation neuronavigator.     

Intraoperative MRI in neurosurgery: technical overkill or the future of brain surgery?

The development of image-guided neurosurgery represents a substantial improvement in the microsurgical treatment of tumors, vascular malformations and other intracranial lesions. Despite the wide applicability and many fascinating aspects of image-guided navigation systems, a major drawback of this technology is they use images, mainly MRI pictures, acquired preoperatively, on which the planning of the operative procedure as well as its intraoperative performance is based. As dynamic changes of the intracranial contents regularly occur during the surgical procedure, the surgeon is faced with a continuously changing intraoperative field. Only intraoperatively acquired images will provide the neurosurgeon with the information he needs to perform real intraoperative image-guided surgery. A number of tools have been developed in recent years, like intraoperative ultrasound and dedicated moveable intraoperative CT units. Because of its excellent imaging qualities, combined with the avoidance of ionizing radiation, MRI currently is and definitely will be in the future for the superior imaging method for intraoperative image guidance. In this short overview, the development as well as some of the current and possible future applications of MRI-guided neurosurgery is outlined.     

Neurotraumatology: Ultrasonic evaluation of the central nervous system

Abstract

In this study we describe the technique of intraoperative ultrasound imaging of brain and spinal cord in trauma patients. The images are shown and their interpretation is discussed. This intraoperative imaging allows for localization of hematomas, bone fragments and indriven foreign bodies (j.e., pieces of plastic, glass, metal, etc.). DISC matenal and bone fragments deep to the spinal cord can be localized with this technique. Real-time ultrasound can be used to guide instruments within the brain and, thereby, provide dynamic guidance for removal of bone fragments and foreign bodies dynamically. In summary, Intraoperative real-time ultrasonic Imaging is of use to the neurosurgeon in the treatment of the neurotrauma patient. [Neural Res 1997; 19: 317–322]

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Resection of pediatric intracerebral tumors with the aid of intraoperative real-time 3-D ultrasound

Purpose  

Intraoperative ultrasound (IOUS) has become a useful tool employed daily in neurosurgical procedures. In pediatric patients, IOUS offers a radiation-free and safe imaging method. This study aimed to evaluate the use of a new real-time 3-D IOUS technique (RT-3-D IOUS) in our pediatric patient cohort.     

Transforming electrocortical mapping data into standardized common space.

Subdural grid electrodes are implanted routinely for the pre-surgical work up of epilepsy. While different approaches are available, many centers, including ours, visualize electrode locations by co-registering pre-operative 3-D MR images with post-implantation 3-D CT images. This method allows the determination of the electrode positions in relation to the individual patient's anatomy, but does not easily allow comparison across patients. The goal of this study was to develop and validate a method for transforming electrode positions derived from 3-D CT images into standardized space. We analyzed data from twelve patients with subdurally implanted electrodes. Volumetric CT and MRI images were co-registered and then normalized into common stereotactic space. Electrode locations were verified statistically by comparing distances between the anterior commissure and a representative sampling of 8 electrode sites per patient. Results confirm the accuracy of our co-registration method for comparing electrode locations across patients.     

Harmonic imaging. A new method of ultrasound imaging of brain perfusion

In this review, methodological aspects of cerebral perfusion imaging with ultrasound contrast agents are described. The various experimental concepts contributing to an understanding of the phenomena are summarised and the resulting investigation techniques on patients are illustrated. By means of harmonic imaging, human cerebral perfusion can be depicted as a two-dimensional scan. The two major principles of contrast measurement are analysis of the bolus kinetics and analysis of the refill kinetics. Using the bolus method, hypoperfused areas in stroke patients can be visualised and parameter images of wash-in and wash-out curves can be generated off-line. The recently developed theory on the refill kinetics of UCA enables us to calculate parameters for describing the cerebral microcirculation, as they are less affected by the depth dependence of the contrast effect. These parameters can also be visualised as images. The ultrasound methods described in this article represent new minimally invasive bedside techniques for analysing brain perfusion. Although their development is still in an early stage, the potential of these ultrasound technologies to compete with perfusion CT, perfusion MRI, and SPECT in the diagnostic arsenal of brain imaging techniques is becoming evident.     

Optimizing brain tumor resection. Midfield interventional MR imaging

The development of the intraoperative MR imager represents an important example of creative vision and interdisciplinary teamwork. The result is a remarkable tool for neurosurgical applications. MRT allows surgical manipulation under direct visualization of the intracranial contents through the eye of the surgeon and through the volumetric images of the MR imaging system. This technology can be applied to cranial and spinal cases, and forseeably can encompass application to the entire gamut of neurosurgical efforts. The author's experience has been that this device is easy and comfortable for the surgeon to use. Image acquisition, giving views in the plane of choice, lasts no more than 2 to 60 seconds (depending on the imaging method), and does not increase the duration of a given procedure substantially. The author believes that the information received through intraoperative MR imaging scanning ultimately will contribute to decreasing the duration of surgery. Future possibilities include combining the intraoperative MR imager with other technologies, such as the endoscope, focused ultrasound, robotics, and the evaluation of brain function intraoperatively. The development of the intraoperative MR imager marks a significant advance in neurosurgery, an advance that will revolutionize intraoperative visualization as fully as the operating microscope. The combination of intraoperative visualization and precise surgical navigation is unparalleled, and its enhancement of surgical applications will be widespread. Considering the remarkable potential of the intraoperative MR imager for neurosurgical applications, optimal magnet design, image quality, and navigational methods are necessary to capitalize on the advantages of this revolutionary tool. The intraoperative MR imaging system that the author's team has developed and used has combined these features, and allows the performance of open surgical procedures without the need of patient or magnet repositioning. By using advanced navigational tools and computer technology, it represents an integration of frameless stereotactic methods with real-time interactive imaging. The midfield imager provides sufficient spatial and temporal resolution and image quality to assess anatomy and pathology adequately, to monitor a surgical procedure, and make image-based decisions. The intraoperative use of this unique system is not limited to biopsies or limited-access procedures. The entire range of neurosurgical procedures can be performed, if the requisite instrumentation is available. Much work remains to be done, however. The team did not develop this system only to enable the performance of current neurosurgical procedures. Forty years ago, the operating microscope enabled not only the performance of undreamt-of procedures but opened the door to entire new subspecialties. The entire landscape of neurosurgery will change at a fundamental level as the full ramifications of this exciting idea come to fruition. The holy grail of image-guided surgery is a seamless interface between the eye and hand in the purest sense (i.e., the mind's eye and hand). Ideally, this seamless interface represents effortless flow between the procedural goal compared with the present situation and the manipulation of the tools available to accomplish the task, whether they be the scalpel, drill, laser, ultrasonic aspirator, phased array focused ultrasound, microrobot, or high-dose irradiator. As in the realm of high-performance military jet fighters, the physical limits of the human being demarcate the confining boundary of the system. Those limits are much tighter around the domain of tool manipulation, where the surgeon will yield, early on, to the enhanced performance of robotics and other technical adjuncts. The era of large open magnet imaging systems for surgical procedures then will come to a close; however, the grander era of the surgeon's integration of precision-guided, multimodality therapeutics will just be beginning. The future will be very bright, indeed.     

Evaluation of intra-operative ultrasound imaging in brain tumor resection: a prospective study

AIMS: The purpose of our study was to evaluate intra-operative ultrasound (IOUS) as a tool of resection control after brain tumor surgery. In addition, we looked for tumor species suitable for ultrasound representation. METHODS: Using a Siemens Omnia Sonoline Ultrasound, 36 tumors were examined, high-grade gliomas (62%), metastases (22%) and others (16%). We focused on tumor imaging by ultrasound with regard to its reliability of tumor expansion and margins. Evaluation of the images was carried out by correlating the ultrasound-based intra-operative measured tumor volume before and after resection with a pre- and post-operative (within 48 hours) measured volume by MRI. The IOUS measurements were performed by the neurosurgeon and the MRI measurements by the neuroradiologist. Thus, the measurement procedures were blinded. Corresponding to a deviation of the ultrasound volume by 10, 20 and > 20% from the MRI volume, the correlation was ranked good, moderate and poor. For assessing the agreement between these two methods of imaging, the statistical analysis was conducted using a method described by Bland and Altman. RESULTS: High-grade gliomas mostly showed a moderate or poor correlation in comparing IOUS- and MRI-tumor volumetry resulting in incomplete resection. Metastases resulted in a good to moderate correlation with a satisfactory extent of resection. The other tumors had poor images with larger tumor residues. The MRI measured volumes tended to be larger on average; the deviation grew with tumor size .CONCLUSION: The reliability of IOUS depends on tumor type. It is beneficial to use IOUS for the resection of metastases and a few high-grade gliomas. Concerning the volumetric accuracy, the value of IOUS is worse than its value of navigation and resection control.     

等体积胶质瘤摘除术

目的：利用立体定向技术和ＭＲＩ的三维成像技术结合,对颅内胶质瘤实行等体积切除。方法：使用Ｌｅｋｓｅｌ－Ｇ或ＡＳＡ－６０２型定向仪,１．０Ｔ的ＭＲＩ对颅内病灶进行三维成像,立体定位颅内病灶,选择适当头皮切口及环钻开颅,术中配合超声刀进行等体积切除胶质瘤。结果：所有２５例胶质瘤均做到了全切除,术后一过性面瘫８例,癫痫发作２例,语言障碍１例,均能恢复。无伤口感染,无脑脊液漏,无手术死亡率。结论：立体定向技术与ＭＲＩ三维成像技术相结合,能对颅内病灶如胶质瘤做到等体积切除,手术侵袭性小、安全、快捷,易被病人接受     

Becker muscular dystrophy: carrier detection by real-time ultrasound

Summary The applicability was tested of real-time ultrasound imaging to the thigh musculature for the carrier detection of Becker muscular dystrophy (BMD). A total of 17 obligate carriers were examined. Ultrasound images in 3 patients, aged between 46 and 59 years, showed moderate differences compared with the controls. In 3 other obligate carriers, aged between 46 and 71 years, only doubtfully abnormal findings could be made; ultrasound images showed no differences in 11 BMD carriers aged between 10 and 47 years. In women aged over 40 years, compared with adequate controls of the same body type, real-time ultrasound imaging may provide additional evidence and thus help in the detection of BMD carriers.     

Advanced neuroimaging in children with nonaccidental trauma

Physical abuse associated with nonaccidental trauma (NAT) affects approximately 144,000 children per year in the USA and, frequently, these injuries affect the developing brain. Most infants with suspected NAT are initially evaluated by skull X-rays and computed tomography to determine whether fractures are present, the severity of the acute injury and the need for urgent neurosurgical intervention. Increasingly, magnetic resonance imaging (MRI) is conducted as it provides additional diagnostic and prognostic information about the extent and nature of the injury. In this review, we examine 4 MRI techniques as they apply to children who present acutely after NAT. Susceptibility-weighted imaging is a 3-D high-resolution MRI technique that is more sensitive than conventional imaging in detecting hemorrhagic lesions that are often associated with diffuse axonal injury (DAI). Magnetic resonance spectroscopy acquires metabolite information reflecting neuronal integrity and function from multiple brain regions and provides a sensitive, noninvasive assessment of neurochemical alterations that offers early prognostic information regarding outcome. Diffusion-weighted imaging (DWI) is based on differences in the diffusion of water molecules within the brain and has been shown to be very sensitive in the early detection of ischemic injury. It is now being used to study the direct effects of traumatic injury as well as those due to secondary ischemia. Diffusion tensor imaging is a form of DWI and allows better evaluation of white matter fiber tracts by taking advantage of the intrinsic directionality (anisotropy) of water diffusion in the human brain. It has been shown to be useful in identifying white matter abnormalities after DAI when conventional imaging appears normal. Although these imaging methods have been studied primarily in adults and children with accidental traumatic brain injury, it is clear that they have the potential to provide additional value in the imaging and clinical evaluation of children with NAT.     

颅内巨大动脉瘤的显微外科手术治疗

目的研究影像诊断技术和改进显微外科手术技术，以提高颅内巨大动脉瘤的手术疗效。方法回顾性分析作者自1985年10月至2004年6月手术治疗颅内巨大动脉瘤2l例。在诊断上，术前采用CT、3D-CTA、MRI和MRA、DSA，以了解动脉瘤的部位、大小和形状。并与DSA对照。在手术上采用颅底入路、近侧载瘤动脉暂时性阻断、动脉瘤内减压、多瘤夹夹闭、瘤颈逐步缩窄、动脉瘤切除等技术。结果CT和MRI能清楚地显示动脉瘤的形状、大小。MRA和3D-CTA能显示瘤颈，以及与附近血管和骨质的关系。出院时优良者17例、轻残2例、死亡2例。结论术前有必要进行详细的影像学研究，有助于术者计划手术的方法。我们采用和改进的一些手术技术，对于提高颅内巨大动脉瘤的手术效果很有帮助。     

Neurosurgical simulation and navigation with three-dimensional computer graphics

We developed a pre-operative simulation and intra-operative navigation system with three-dimensional computer graphics (3D-CG). Because the 3D-CG created by the present system enables visualization of lesions via semitransparent imaging of the scalp surface and brain, the expected operative field could be visualized on the computer display pre-operatively. We used two different configurative navigators. One is assembled by an arciform arm and a laser pointer. The arciform arm consists of 3 joints mounted with rotary encoders forming an iso-center system. The distal end of the arm has a laser pointer, which has a CCD for measurement of the distance between the outlet of the laser beam, and the position illuminated by the laser pointer. Using this navigator, surgeons could accurately estimate the trajectory to the target lesion, and the boundaries of the lesion. Because the other navigator has six degrees of freedom and an interchangeable probe shaped like a bayonet on its tip, it can be used in deep structures through narrow openings. Our system proved efficient and yielded an unobstructed view of deep structures during microscopic neurosurgical procedures.     

螺旋CT三维重建技术在骨盆骨折中的应用

背景：螺旋CT三维重建技术可以提供直观的三维图像，而且可以根据需要向任何方向旋转，使医生可以在任意设定的角度观察骨盆骨折移位情况，从而得到清晰直接的印象。 目的：观察螺旋CT三维重建技术在骨盆骨折中的应用价值。 方法：选择2007-11/2009-03遵义医学院附属医院骨科收治的骨盆骨折患者42例，男30例，女12例，分别进行X射线摄片和螺旋CT扫描，利用表面遮盖法(SSD)三维重建，同时利用三维成像软件进行多平面重建(MPR)，选择能最佳显示骨折的图像进行存储并进行摄片，比较两种方法的效果。 结果与结论：所有骨盆骨折患者经螺旋CT三维成像摄片均显示骨折，能较准确地描述出骨折分型和碎骨部位，其效果明显优于X射线摄片(P < 0.05)。提示螺旋CT三维成像技术在骨盆骨折的诊断中具有非常重要的作用，能较准确地显示骨折的情况，能为治疗方法的选择提供依据。     

Dynamic intraoperative imaging and instrumentation of brain and spinal cord using ultrasound

Intraoperative real-time ultrasound imaging in the neurosurgical operating room is most useful in localizing, characterizing, and guiding the instrumentation of lesions of the brain and spinal cord. In the future, more and more operative procedures will be done using intraoperative ultrasound guidance. The ultrasound scanner, as developed for neurosurgery, will become another instrument in the neurosurgeon's armamentarium.     

Three-dimensional Intraoperative Ultrasound of Vascular Malformations and Supratentorial Tumors

The benefits and limits of a magnetic sensor-based 3-dimensional (3D) intraoperative ultrasound technique during surgery of vascular malformations and supratentorial tumors were evaluated. Twenty patients with 11 vascular malformations and 9 supratentorial tumors undergoing microsurgical resection or clipping were investigated with an interactive magnetic sensor data acquisition system allowing freehand scanning. An ultrasound probe with a mounted sensor was used after craniotomies to localize lesions, outline tumors or malformation margins, and identify supplying vessels. A 3D data set was obtained allowing reformation of multiple slices in all 3 planes and comparison to 2-dimensional (2D) intraoperative ultrasound images. Off-line gray-scale segmentation analysis allowed differentiation between tissue with different echogenicities. Color-coded information about blood flow was extracted from the images with a reconstruction algorithm. This allowed photorealistic surface displays of perfused tissue, tumor, and surrounding vessels. Three-dimensional intraoperative ultrasound data acquisition was obtained within 5 minutes. Off-line analysis and reconstruction time depends on the type of imaging display and can take up to 30 minutes. The spatial relation between aneurysm sac and surrounding vessels or the skull base could be enhanced in 3 out of 6 aneurysms with 3D intraoperative ultrasound. Perforating arteries were visible in 3 cases only by using 3D imaging. 3D ultrasound provides a promising imaging technique, offering the neurosurgeon an intraoperative spatial orientation of the lesion and its vascular relationships. Thereby, it may improve safety of surgery and understanding of 2D ultrasound images.     

Diagnostic imaging of cerebrovascular disease on multi-detector row computed tomography (MDCT)

In this study, we reviewed characteristic diagnostic findings of vascular diseases in the central nervous system with 3-dimensional computed tomographic angiography (3D-CTA) using multi-detector row computed tomography (MDCT) and a novel 320-row area detector CT (320-ADCT). With coverage of 160 mm in a single rotation, 320-ADCT enables acquisition of both 4-dimensional CT angiography (dynamic 4D-CTA) and whole-brain CT perfusion imaging. We describe our experience of investigating cerebrovascular diseases with MDCT and 320-ADCT, as well as several postprocessing techniques to acquire images useful for diagnosis, therapy planning, and simulation of neurosurgical and endovascular intervention. 3D-CTA demonstrates has high accuracy in detecting and evaluating cerebral aneurysms and steno-occlusive diseases. Angiographic analysis, including information of surrounding tissues on 3D-CTA, allows assessment of the feasibility of neurosurgical or endovascular approaches and the technique to accomplish the therapy. However, 3D-CTA using MDCT is limited in its detection of aneurysms less than 3 mm in size and aneurysms embedded in the skull base region. In addition, discrimination between intradural paraclinoid aneurysms and extradural intracavernous aneurysms remains an unresolved problem in imaging of cerebral aneurysms. 320-ADCT may solve this problem with its high accuracy in discriminating arteries from the venous system. 3D-CTA could be used as an alternative to DSA for detection of severe carotid artery disease. 3D-CTA enables measurement of the lesions, plaque imaging, prediction of anatomical variants, screening for asymptomatic vascular lesions, and exclusion of patients with risk factors from carotid endoarterectomy (CEA) or carotid artery stenting (CAS). The diagnosis of intracranial dural arteriovenous fistula (DAVF) with CTA is challenging. Recently, several authors proposed diagnostic findings of ADVF by CTA and reported high sensitivity and specificity. 320-ADCT may offer comprehensive information for diagnosis and therapy planning of intracranial DAVF. Although DSA is a standard modality to detect spinal vascular malformations, selective catheterization requires considerable time and a certain amount of contrast medium, and is associated with a risk of neurological complications. Spinal 3D-CTA prior to DSA is useful in selective catheterization to arteries at certain spinal levels as well as when considering treatment options and therapy planning.     

American College of Surgeons: Southern California Chapter Neurosurgical Section

Abstract

Usefulness of endoscopic imaging of cerebral aneurysms is presented. 3-D luminal images were obtained using a new processing technique which extracts CT numbers in the boundary region between the vessel wall and contrast media filled in the vascular lumen. Clinical application of this technique to complicated large cerebral aneurysms showed that, with this 3-D CT endoscopic imaging, anatomical details of cerebral aneurysms such as the orifice of the aneurysmi, intraluminal thrombus, and calcification of the wall could be clearly demonstrated. Using a 3-D imaging method by Helical CT, virtual views of various surgical approaches were compared preoperatively. With this technique, not only virtual surgical views of aneurysms and related vasculature, but also surgical views after virtual resection of skull base bone to a desirable extent are freely available. We operated on two large, complicated aneurysms and one broad-based aneurysm after obtaining 3-D CT endoscopic images of the aneurysms. Such information was found to be very useful for determining difficult and complicated cerebral aneurysms and broad-based aneurysms for coil embolization or direct open surgery. [Neurol Res 1996; 18: 98–102]     

Iterative neuronavigation using 3D ultrasound. A feasibilty study

Abstract

Intra-operative ultrasound (iUS) can generate 2D images in real-time as well as near real-time 3D datasets of the current situation during an intervention. Tracked ultrasound can locate the images in 3D space and relate them to patient, devices, and pre-operative planning data. Therefore, tracked US is an efficient means for controlling the validity of pre-operative planning, recognition of changes (brain shift) during the intervention, replanning of the operational path due to situational changes (iterative navigation), and finally, controlling the results (residual tumor). This paper describes a neuronavigation system exploiting this potential of interventional tracked US for permanent control of intervention progress and iterative adaptation of the planned procedure to the current situation.