Impact of intraoperative MRI on the surgical results for high-grade gliomas.

OBJECTIVE: The impact of intraoperative MRI (iMRI) on the surgical procedure, patient outcome and median survival for a series of patients harbouring high-grade gliomas forms the basis of this study. Their outcome has been compared to a matched cohort of patients operated in a conventional manner to determine if the use of intraoperative MRI can be shown to improve the results of surgery and prognosis for this type of patient. MATERIALS AND METHODS: 32 microsurgical open craniotomies, performed in the intraoperative iMRI scanner for grade IV supratentorial gliomas, with follow-up periods of more than 2 months, were analyzed for this study. A group of 32 primary high-grade glioma patients (no recurrent tumors) were matched for age, preoperative clinical grade, gender and histology and operated during a corresponding time interval in a conventional manner acted as controls. RESULTS: All 64 patients were examined and analyzed for the occurrence of postoperative increased neurological morbidity or death. No complications directly related to the intraoperative scanning procedures were observed and no intraoperative death occurred in either group. The average operating time in the intraoperative scanner was 5.1 hours and was significantly longer than in the conventional OR (3.4 hours). The mean overall survival time for the 32 patients in the study group was 14.5 months (95 % confidence interval 12.0 - 16.6) compared to 12.1 months (95 % confidence interval 10.2 - 14.1) for the matched control group. CONCLUSION: Although iMRI is an effective way of imaging residual tumor, this study could not demonstrate an increased efficacy of surgery utilizing this technique for patients harbouring grade IV gliomas compared to more conventional methods. No statistical significance was noted between the two groups (p = 0.14). The complication rate was within the range reported for other series, in both control as well as the study group.     

A virtual reality environment for patient data visualization and endoscopic surgical planning

Visualizing patient data in a three-dimensional (3D) representation can be an effective surgical planning tool.As medical imaging technologies improve with faster and higher resolution scans, the use of virtual reality for interacting with medical images adds another level of realism to a 3D representation. The software framework presented in this paper is designed to load and display any DICOM/PACS-compatible 3D image data for visualization and interaction in an immersive virtual environment. In "examiner" mode, the surgeon can interact with a 3D virtual model of the patient by using an intuitive set of controls designed to allow slicing, coloring,and windowing of the image to show different tissue densities and enhance important structures. In the simulated"endoscopic camera" mode, the surgeon can see through the point of view of a virtual endoscopic camera to navigate inside the patient. These tools allow the surgeon to perform virtual endoscopy on any suitable structure.The software is highly scalable, as it can be used on a single desktop computer to a cluster of computers in an immersive multiprojection virtual environment. By wearing a pair of stereo glasses, a surgeon becomes immersed within the model itself, thus providing a sense of realism, as if the surgeon is "inside" the patient.     

Neuronavigation in intraoperative MRI.

OBJECTIVE: We describe the development and implementation of an image-guided surgical system combining the best features of conventional frameless stereotactic systems and the recently developed superconductive vertically configured intraoperative magnetic resonance scanner. The incorporation of intraoperatively updated magnetic resonance imaging (MRI) data sets into the neuronavigation computer overcomes one of the main disadvantages of these systems, i.e., intraoperative brain shift. METHODS: The integrated system consists of a 0.5-T MRI scanner (Signa SP General Electric Medical Systems, Milwaukee, WI), a neuronavigation computer with associated software (OTS Radionics, Burlington, MA), and an emulation program linking the two. The scanner has a 60-cm-wide vertical gap where both imaging and surgery are conducted, in-bore infrared linear cameras and monitors for interactive surgical neuronavigation, and flexible surface coils specially designed for surgery. RESULTS: Phantom studies showed navigational accuracy to be better than that obtained using conventional preoperative images and surface markers for patient registration. Our initial 17 cases using this integrated system comprised 16 craniotomies and one biopsy, and demonstrated decreased operative duration, greater frequency of interactive image guidance utilization, and better assessment of the progress of surgery compared to the cases previously done in the intraoperative MRI. CONCLUSION: This initial study of the addition of frameless stereotactic systems to the basic intraoperative MRI concept has demonstrated its clinical usefulness. The use of the intraoperative MRI greatly reduces the basic weakness of neuronavigation inaccuracy due to target shift. The surgical procedure performed in the imaging volume of the MRI scanner eliminates the problems of patient or scanner transport during the procedure. Immobilization of the patient throughout the procedure eliminated the need for reregistration of the patient, by taking advantage of the fixed camera system in the bore of the MRI system.     

A surgical planning and guidance system for high tibial osteotomy.

OBJECTIVE: To develop a three-dimensional pre-surgical planner and an intraoperative guidance system for high tibial osteotomy. The parameters that describe the placement and orientation of the osteotomy resection planes were to be transmitted to an accompanying guidance system that allowed the surgeon to reproducibly perform the planned procedure. MATERIALS AND METHODS: The planning system and guidance system were coded using OpenGL on UNIX workstations. In vitro tests were performed to compare the reproducibility of the computer-enhanced technique to that of the traditional technique, and an in vivo pilot study was initiated. RESULTS: In vitro, the computer-enhanced technique produced a significant reduction, by one half, in both the maximum error of correction and the standard deviation of the correction error. Preliminary in vivo results on six patients suggest that similar error diminution will occur during regular clinical application of the technique. CONCLUSIONS: Both studies showed that the computer system is simple to use. The work suggests that three-dimensional planning and performance of high tibial osteotomy is essential for accurate correction of the alignment of the lower limb.     

Future perspectives for intraoperative MRI

MRI-guided neurosurgery not only represents a technical challenge but a transformation from conventional hand-eye coordination to interactive navigational operations. In the future, multimodality-based images will be merged into a single model, in which anatomy and pathologic changes are at once distinguished and integrated into the same intuitive framework. The long-term goals of improving surgical procedures and attendant outcomes, reducing costs, and achieving broad use can be achieved with a three-pronged approach: 1. Improving the presentation of preoperative and real-time intraoperative image information 2. Integrating imaging and treatment-related technology into therapy delivery systems 3. Testing the clinical utility of image guidance in surgery The recent focus in technology development is on improving our ability to understand and apply medical images and imaging systems. Areas of active research include image processing, model-based image analysis, model deformation, real-time registration, real-time 3D (so-called "four-dimensional") imaging, and the integration and presentation of image and sensing information in the operating room. Key elements of the technical matrix also include visualization and display platforms and related software for information and display, model-based image understanding, the use of computing clusters to speed computation (ie, algorithms with partitioned computation to optimize performance), and advanced devices and systems for 3D device tracking (navigation). Current clinical applications are successfully incorporating real-time and/or continuously up-dated image-based information for direct intra-operative visualization. In addition to using traditional imaging systems during surgery, we foresee optimized use of molecular marker technology, direct measures of tissue characterization (ie, optical measurements and/or imaging), and integration of the next generation of surgical and therapy devices (including image-guided robotic systems). Although we expect the primary clinical thrusts of MRI-guided therapy to remain in neurosurgery, with the possible addition of other areas like orthopedic, head, neck, and spine surgery, we also anticipate increased use of image-guided focal thermal ablative methods (eg, laser, RF, cryoablation, high-intensity focused ultrasound). By validating the effectiveness of MRI-guided therapy in specific clinical procedures while refining the technology that serves as its underpinning at the same time, we expect many neurosurgeons will eventually embrace MRI as their intraoperative imaging choice. Clearly, intraoperative MRI offers several palpable advantages. Most important among these are improved medical outcomes, shorter hospitalization, and better and faster procedures with fewer complications. Certain economic and practical barriers also impede the large-scale use of intraoperative MRI. Although there has been a concerted technical effort to increase the benefit/cost ratio by gathering more accurate information, designing more localized and less invasive treatment devices, and developing better methods to orient and position therapy end-effectors, further research is needed. Indeed, the drive to improve and upgrade technology is ongoing. Specifically, in the context of the real-time representation of the patient's anatomy, we have improved the quality and utility of the information presented to the surgeon, which, in turn, contributes to more successful surgical outcomes. We can also expect improvements in intraoperative imaging systems as well as increased use of nonimaging sensors and robotics to facilitate more widespread use of intraoperative MRI.     

Preoperative endovascular brain mapping for intraoperative volumetric image guidance: preliminary concept and feasibility in animal models

OBJECT: The authors describe a novel concept for brain mapping in which an endovascular approach is used, and they demonstrate its feasibility in animal models. The purpose of endovascular brain mapping is to delineate clearly the nonfunctional brain parenchyma when a craniotomy is performed for resection. The nonfunctional brain will be stained with sharp visual margins, differentiating it from the functional, nonstained brain. The authors list four essential criteria for developing an ideal endovascular mapping agent, and they describe seven potential approaches for accomplishing a successful endovascular brain map. METHODS: Four Sprague-Dawley rats and one New Zealand white rabbit were used to determine initial feasibility of the procedure. The animals were anesthetized, and the internal carotid artery was catheterized. Four potential brain mapping agents were infused into the right hemisphere of the five animals. Afterward, the brains were removed and each was analyzed both grossly and histologically. Fluorescein and FD&C Green No. 3 provided good visual clarity and margins, but required blood-brain barrier (BBB) manipulation. Tantalum particles enabled avoidance of BBB manipulation, but provided inadequate visual clarity, probably because of their size. A Sudan black "cocktail" provided excellent clarity and margins despite remaining in the brain capillaries. CONCLUSIONS: This is a novel application of the endovascular approach, and has broad potential for clinical neurosurgical brain mapping. The animal models in this study establish the feasibility of the procedure. However, further study is required to demonstrate safety, minimize toxicity, investigate stain durability, and improve the characteristics of potential mapping agents. The authors are planning to conduct future studies for identification of mapping agents that do not require BBB manipulation or vascular occlusion.     

Deep brain stimulation in intraoperative MRI environment - comparison of imaging techniques and electrode fixation methods.

We performed 118 consecutive DBS cases from November 1999 to June 2002. Intraoperatively there were 10 cases studied with fluoroscopy, 73 with 0.2 Tesla (T) MRI and 35 with 1.5 T MRI. Ten electrodes were secured by Medtronic caps, 25 by methyl methacrylate with titanium miniplates, and 82 by Navigus caps. The 3-dimensional displacement between the planned target and actual electrode position (3DD) was determined by fusing the postoperative MRI with the preoperative imaging. The 3DD for using Medtronic caps, methyl methacrylate with miniplates, and Navigus caps were 4.80 +/- 3.16, 2.64 +/- 1.26 and 2.23 +/- 1.15 mm (mean +/- SD), respectively. Navigus caps had statistically significant accuracy (P = 0.03) in holding the electrode when compared with Medtronic caps, and it facilitated electrode revision. The fixation devices significantly affect the final vertical position of the electrode. The 3DD for fluoroscopy, 0.2 T and 1.5 T MRI cases were 4.80 +/- 3.16, 2.31 +/- 1.21 and 2.34 +/- 1.14 mm (mean +/- SD), respectively. No statistically significant difference (P = 0.91) in 3DD was demonstrated between 0.2 T and 1.5 T MRI cases. The presence of intraoperative 1.5 T MRI allowed near real-time electrode position confirmation and early detection of hemorrhagic complications. Satisfactory microelectrode recording was feasible in low-field 0.2 T and high-field 1.5 T MRI environments. Further studies on performing DBS in real-time intraoperative MRI are warranted.     

Image fusion of fluid-attenuated inversion recovery magnetic resonance imaging sequences for surgical image guidance

BACKGROUND: Nonenhancing brain lesions can be relatively poorly defined on volumetric data sets routinely used for surgical guidance. Fluid-attenuated inversion recovery MRI sequences can provide better margin visualization of nonenhancing or poorly enhancing lesions. METHODS: Using image fusion programs, we combined data sets of SPGR imaging pulse sequence or volumetric CT with volumetrically acquired FLAIR sequences and subsequently used the fused data set for image-guided surgery. This technique was used in 50 surgical cases. Of these, 9 were nonenhancing intrinsic brain tumors, 13 were partially enhancing tumors, and 11 were enhancing tumors. In addition, FLAIR fusion was selectively used for 6 nontumoral lesions and in 11 nonlesional epilepsy surgery cases. RESULTS: Image guidance using the fused data set was accurate in all 50 cases. Despite the lack of enhancement, 3 of the 9 nonenhancing tumors were found to be high grade. One of the low-grade tumors was associated with considerable areas of gliotic change not considered to represent tumor on permanent histology. In all other cases, the FLAIR-bright resected margins were consistent with tumor, not gliosis. Radical resection (>95% volume) was achieved in 21 of 23 tumor cases in which this had been the preoperative intent. CONCLUSIONS: Nonenhancing lesions are often poorly demarcated not only on imaging studies, but also during surgery. Fluid-attenuated inversion recovery fusion allows resection of such lesions using intraoperative computer image guidance. Complementary FLAIR information can also occasionally be useful during surgical approaches to enhancing lesions or in nontumor cases. It must be kept in mind that FLAIR has high sensitivity but low specificity. Fluid-attenuated inversion recovery abnormalities do not obviate the need for mapping in potentially functional areas.     

Integration of neurosurgical image guidance and an intraoperative magnetic resonance scanner. The University Hospitals of Cleveland experience

BACKGROUND: Intraoperative magnetic resonance (MR) imaging has been employed as an alternative to image guidance using preoperative images. We integrated both systems to evaluate their clinical use. METHODS: The BrainLAB VectorVision system was integrated in an intraoperative Siemens Open Viva 0.2-tesla MR system. Clinical experience was assessed. RESULTS: Patterns of intraoperative imaging emerged, and benefit was seen in registering preoperative and intraoperative images. CONCLUSIONS: This integrated system has clinically observed effects on imaging, navigation, and surgery.     

Incorrect vector after calibration of surgical instruments for image guidance. The problem and the solution: technical note.

Recently, the use of intra-operative image guidance has gained an increasing role in neurosurgery for both spinal and cerebral interventions. Some modern neuronavigation systems are able to register any surgical instrument and create a virtual pointer. A virtual elongation of the digitized instrument is frequently used for neuroendoscopic procedures and spinal instrumentation. The instrument is equipped with a universal instrument adapter clamp and digitized by touching the tip of the instrument into a calibration cone. An algorithm calculates the vector of the instrument using two points: the tip of the instrument, and the geometrical center of the instrument adapter geometry. If a virtual elongation of the calibrated instrument is performed, the neuronavigation software may calculate an incorrect virtual target point. We developed an instrument calibration matrix (ICM) that automatically calibrates the correct vector, tip, and diameter of the instrument used for image-guided surgery. The ICM is easy to handle and does not cause a time delay during surgery. Virtual elongation of the surgical instruments shows correct anatomic data, which are fundamental for planning ventricular tapping and spinal screw placement in particular. The instrument calibration matrix is essential if surgical instruments are digitized and used for neuronavigation. It helps to avoid mis-planning of surgical vectors and mis-placement of the used instruments.     

Real-time intraoperative computed tomography can accurize virtual surgical planning on the double-barrel fibular flap for mandibular reconstruction

Real-time intraoperative computed tomography created the accuracy of less than 1 mm deviation in virtual surgical planning double barrel fibular flap for mandibular reconstruction-the symbiosis of intelligent technology in a digital OR.BackgroundWith the intelligent technology of virtual surgical planning, CAD/CAM, and intraoperative CT(iCT) in a digital OR, the secondary mandibular defect or primary amelobalstoma mandibulectomy can be restored using double barrel fibula and be achieved precision medicine purpose.Material and MethodA series of 7 patients underwent free flap for oral cancers who sustained 5 osteoradionecrosis, 2 segmental mandibular defect, and 2 ameloblastoma. They received 9 double barrel fibula flap and 2 free skin flaptransfers. The fibula flap were reconstructed using a virtual surgical planning including CAD/CAM for simulation 3D model, cutting guides for recipient sites and fibulas osteotomy, and iCT for image fusion in a digital OR.ResultThe mandibular defect was 5–16 cm (average: 9.56 cm), and 2–5 fibular struts for double barrel fibula (average: 3.67 struts) image fusion. One vein graft for artery was required and all 11 flaps were transferred successfully without reexploration. Six patients had intraoperative revision of the fibula and plate to improve the onlay image fusion volume from 74.71 to 82.57%. The postoperative inter-incisor midline deviation was less than 2 mm in 5 patients, and well reduction image in 4 edentulous patients. Five landmarks including bilateral condyles, bilateral gonions, and gnathion demonstrated deviation less than 1 mm in average.ConclusionCAD/CAM can allow a practical virtual surgery to restore mandibular defect reconstruction using a double barrel fibula. The symbiosis of intelligent technology in a digital OR, the iCT can promote the accuracy of mandibular spatialframework and occlusion plain.     

Integrated neuronavigation system with intraoperative image updating.

OBJECTIVE: Recently, MRI has entered the field of image-guided surgery as a new intraoperative imaging modality. In spite of its obvious benefits, this type of iMRI scanner has some drawbacks that have limited its utilization. The goal of the work presented here was to overcome some of these disadvantages. METHODS: A system that allows intraoperative images to be acquired during surgery and have the ability to conduct surgery outside the constraints of the narrow gap of the open magnet was implemented. Ability to conduct tasks inside the scanner with real-time image guidance was also maintained. The system allowed navigation with neuronavigation tools both inside the gap of an open magnet and outside the magnet, utilizing two different optical camera-sets and a dynamic reference frame. Automatic patient registration was implemented. RESULTS: The average difference between tracking position measured outside and inside the magnet was 0.8 +/- 0.1 mm. CONCLUSION: In the work presented in this note we have introduced a dynamic reference frame to compensate for transport of the patient to a location outside the scanner employing a second camera set. The integrated system showed adequate accuracy.     

Functional neurosurgery in the MRI environment.

OBJECTIVE: The purpose of this study was to evaluate the feasibility of microelectrode recording, electrical stimulation, and electrode position checking during functional neurosurgical procedures (DBS, lesion) in the interventional magnetic resonance imaging (iMRI) environment. METHODS: Seventy-six surgical procedures for DBS implant or radiofrequency lesion were performed in an open 0.2 T MRI operating room. DBS implants were performed in 54 patients (72 surgical procedures) and unilateral radiofrequency lesions in three for a total of 76 surgeries in 57 patients. Electrophysiological studies including macrostimulation and microelectrode recordings for localization were obtained in the 0.5 to 10 mT fringes of the magnetic field in 51 surgeries. MRI confirmation of the electrode position during the procedure was performed after electrophysiological localization. RESULTS: The magnetic field associated with the MRI scanner did not contribute significant noise to microelectrode recordings. Anatomical confirmation of electrode position was possible within the MRI artifact from the DBS hardware. Symptomatic hemorrhage was detected in two (2.6 %) patients during the operation. Image quality of the 0.2 T MRI scan was sub-optimal for anatomical localization. However, image fusion with pre-operative scans permitted excellent visualization of the DBS electrode tip in relation to the higher quality 1.5 T MRI anatomical scans. CONCLUSION: This study shows that conventional stereotactic localization, microelectrode recordings, electrical stimulation, implant of DBS hardware, and radiofrequency lesion placement are possible in the open 0.2 T iMRI environment. The convenience of having an imaging modality that can visualize the brain during the operation is ideal for stereotactic procedures.     

Value of intraoperative image intensifier prints in trauma surgery.

We have studied the use of image intensification in a trauma theatre over a period of 6 months with particular reference to the acquisition of intraoperative image intensifier thermal prints instead of formal radiographs. The quality of the prints and the savings generated have been assessed. During the study period, 476 patients underwent orthopaedic trauma procedures. The image intensifier was used for intraoperative screening in 280 patients. In 278 of these a thermal print was obtained. This was used, instead of formal check radiographs, to plan further management in 210 patients (75%). In 68 patients, the printout was insufficient in its coverage of the operated area, and a check radiograph was also obtained. In no case did the clarity of the thermal image hinder accurate interpretation. We believe that thermal images are a useful substitute for formal postoperative radiographs in many trauma cases, and that, with notable exceptions, their use could decrease costs, reduce patient discomfort and radiation dose and spare overloaded radiology services.     

Benefits and limitations of image guidance in the surgical treatment of intracranial dural arteriovenous fistulas

Summary Background. Despite major advances in endovascular embolization techniques, microsurgical resection remains a reliable and effective treatment modality for dural arteriovenous fistulas (DAVF). However, intraoperative detection of these lesions and identification of feeding arteries and draining veins can be challenging. In a series of 6 patients who were not candidates for definitive treatment by endovascular embolization we evaluated the benefits and limitations of computer-assisted image guidance for surgical ablation of DAVF. Methods. Of the 6 patients, 5 presented with haemorrhage and one with seizures. Diagnosis of DAVF was made by conventional angiography and dynamic contrast enhanced MR angiography (CE-MRA). All patients were surgically treated with the assistance of a 3D high resolution T1-weighted MR data set and time-of-flight MR angiography (MRA) obtained for neuronavigation. Registration was based on cranial fiducials and image-guided surgery was performed with the navigation system. Findings. Four of the 6 patients suffered from DAVF draining into the superior sagittal sinus, one fistula drained into paracavernous veins adjacent to the superior petrosal sinus and one patient had a pial fistula draining in the straight sinus. DAVF diagnosed with conventional angiography could be located on CE-MRA and MRA prior to surgery. MRI and MRA images were combined on the neuronavigation workstation and DAVF were located intraoperatively by using a tracking device. In 4 out of 6 cases neuronavigation was used for direct intraoperative identification of DAVF. Brain shift prevented direct tracking of pathological vessels in the other 2 cases, where navigation could only be used to assist craniotomy. Microsurgical dissection and coagulation of the fistulas led to complete cure in all patients as confirmed by angiography. Conclusions. Neuronavigation may be used as an additional tool for microsurgical treatment of DAVF. However, in this small series of 6 cases, surgical procedures have not been substantially altered by the use of the neuronavigation system. Image guidance has been beneficial for the location of small, superficially located DAVF, whereas a navigated approach to deep-seated lesions was less accurate due to the familiar problem of brain shift and brain retraction during surgery. Both authors equally contributed to this work.     

On-line flow cytometry for real-time surgical guidance

OBJECTIVE: This study tests the feasibility of using on-line analysis of tissue during surgical resection of brain tumors to provide biologically relevant information in a clinically relevant time frame to augment surgical decision making. For the purposes of establishing feasibility, we used measurement of deoxyribonucleic acid (DNA) content as the end point for analysis. METHODS: We investigated the feasibility of interfacing an ultrasonic aspiration (USA) system with a flow cytometer (FC) capable of analyzing DNA content (DNA-FC). The sampling system design, tissue preparation requirements, and time requirements for each step of the on-line analysis system were determined using fresh beef brain tissue samples. We also compared DNA-FC measurements in 28 nonneoplastic human brain samples with DNA-FC measurements in specimens of 11 glioma patients obtained from central tumor regions and surgical margins after macroscopically gross total tumor removal to estimate the potential for analysis of a biological marker to influence surgical decision making. RESULTS: With minimal modification, modern FC systems are fully capable of real-time, intraoperative analysis of USA specimens. The total time required for on-line analysis of USA specimens varies between 36 and 63 seconds; this time includes delivery from the tip of the USA to complete analysis of the specimen. Approximately 60% of this time is required for equilibration of the DNA stain. When compared with values for nonneoplastic human brain samples, 50% of samples (10 of 20) from macroscopically normal glioma surgical margins contained DNA-FC abnormalities potentially indicating residual tumor. CONCLUSION: With an interface of existing technologies, DNA content of brain tissue samples can be analyzed in a meaningful time frame that has the potential to provide real-time information for surgical guidance. The identification of DNA content abnormalities in macroscopically normal tumor resection margins by DNA-FC supports the practical potential for on-line analysis of a tumor marker to guide surgical resections. The development of such a device would provide neurosurgeons with an objective method for intraoperative analysis of a clinically relevant biological parameter that can be measured in real time.