Stereotactic accuracy of a 3-tesla magnetic resonance unit

Recently, magnetic resonance imagers (MRIs) with 3-tesla magnets were approved for clinical use. The spatial accuracy of these high-resolution scanners has yet to be proven. In the present study, a computed tomography (CT)- and MRI-compatible phantom was scanned on a CT, a 1.5-tesla MRI and a 3-tesla MRI scanner. The model was registered to the images using an infrared-based surgical navigation system. The distance between the predicted position of the navigation probe tip and the actual target on the image was measured on the x, y and z axes for 13 points on each image. Error was compared across imaging modalities, peripheral versus central targets and along each axis. We found that 3-tesla MRI scans are accurate as stereotactic data sets.     

Application of low-field intraoperative magnetic resonance imaging in transsphenoidal surgery for pituitary adenomas: technical points to improve the visibility of the tumor resection margin

Background

Intraoperative magnetic resonance imaging (iMRI) is proven to be advantageous in transsphenoidal surgery (TSS) for pituitary adenomas. We evaluated the efficacy of low-field iMRI. Also, we described several techniques to enhance the visibility of the tumor resection margin.

Methods

Two hundred twenty-nine patients who underwent TSS using low-field iMRI were analyzed. iMRI was acquired in cases where the tumor removal was thought to meet the surgical goal after the tumor resection cavity had been packed with contrast-soaked cotton pledgets to improve the visibility of the tumor resection margin. Suspicious remnants were localized and explored using updated iMRI-based semi-real-time navigation. A merging technique was adopted for very small tumors. The final outcome was evaluated using postoperative 3-T diagnostic magnetic resonance imaging (MRI).

Results

Among 198 patients in whom total resection was attempted, total resection seemed to have been achieved in 184 patients based on iMRI findings. However, immediate postoperative MRI revealed remnant tumors in 4 out of 184 patients (false-negative rate, 2.2 %). The other 31 patients underwent intended subtotal resection of the tumors. Overall, in 47 patients (20.5 %), the use of iMRI led to further resection. Those patients benefited from the use of iMRI to achieve the planned extent of tumor resection.

Conclusions

iMRI maximizes the extent of resection and minimizes the possibility of unexpected tumor remnants in TSS for pituitary adenomas. It is essential to reduce imaging artifacts and enhance the visibility of the tumor resection margin during the use of low-field iMRI.     

Stereotactic accuracy of a compact intraoperative MRI system

OBJECTIVE: To analyze the stereotactic accuracy of the PoleStar N-20, a compact intraoperative magnetic resonance imaging (iMRI) system, based on a 0.15-Tesla (T) magnet. METHODS: An MRI-compatible phantom was scanned after being positioned in both the center of the magnetic field (COF) and the periphery of the field (POF) of the PoleStar N-20 magnet. Scans were acquired at various slice thicknesses in 3 sequences: T(1) weighted, T(2) weighted and Esteady (reversed fast imaging with steady-state precession, also known as 'PSIF'). The distance between the actual location of the probe tip in space and the location of the target on the image was measured on the axial, coronal, and sagittal planes for 9 points on each image. Each measurement was repeated 3 times. We also compared the structural features of the PoleStar N-20 to those of its predecessor. RESULTS: T(1)-weighted scans yielded the most accurate measurements. There was no statistically significant difference between scans acquired at thicknesses of 2, 3, 4 and 8 mm; all were accurate for clinical purposes. Comparison of COF with POF measurements using T(1)-weighted scans did not demonstrate a statistically significant difference in accuracy. CONCLUSIONS: The PoleStar N-20 0.15-T iMRI system provides surgical navigation that is at least as accurate as the first generation model of this system, which employed a 0.12-T magnet. Further analysis of stereotactic accuracy on clinical cases using the PoleStar N-20 is needed to confirm that these results will bear out in surgical reality.     

Stereotactic target localization accuracy in interventional magnetic resonance imaging

OBJECTIVE: To compare stereotactic target determination, based on images obtained from interventional MRI (iMRI), conventional closed MR and CT. METHODS: Stereotactic coordinates for 55 targets in an artificial scull were derived from iMRI scans and compared using CT as the standard. Stereotactic coordinates were also derived from iMRI scans in a series of patients and compared using iMRI fused with CT as the standard. RESULTS: The mean difference between targets in the skull phantom determined from iMRI and CT images was 0.90 +/- 0.28 mm, with a maximum difference of 1.57 mm. The mean difference between targets in the patients derived from iMRI alone and interventional MR fused with CT was 1.39 +/- 0.54 mm, with a maximum difference of 2.47 mm. DISCUSSION: The results indicate that iMRI can be used for stereotactic target localization.     

3.0T术中磁共振成像引导下唤醒麻醉联合术中语言皮质定位技术在语言区脑胶质瘤手术中的应用

目的 评价3.0 T术中磁共振成像(iMRI)下采用唤醒麻醉联合术中语言皮质定位技术辅助语言区脑胶质瘤切除的临床有效性.方法 2010年12月至2011年4月以集成3.0 TiMRI数字一体化神经外科手术中心为平台,采用唤醒麻醉、改良手术铺巾技术、联合直接电刺激语言皮质定位和iMRI实时影像神经导航,对11例右利手患者实施左侧语言区脑胶质瘤切除.术中采用简易语言任务模式,包括语言流利度、图片命名和文字测读,评估患者语言功能状况.围手术期采用汉语失语检查法,评估新技术的临床有效性.结果 通过iMRI实时影像导航,6/11的患者可以定量提升胶质瘤切除范围,其中影像学全切除率提高3/11,最终肿瘤全切除7例,次全切除4例.语言皮质定位阳性率为8/11.患者术后1周内出现一过性失语率为4/11,随访至术后1个月,所有患者语言功能均恢复到术前水平或以上;围手术期患者无肢体运动功能障碍.结论 应用3.0 T超高场强iMRI实时影像导航可在术前设计脑胶质瘤个体化手术方案,术中精确定位病灶,等体积定量切除肿瘤,提高肿瘤切除率;在唤醒麻醉下实施术中皮质电刺激定位语言区,能最大程度保护患者语言皮质,避免出现不可逆的语言功能损伤,提高术后社会生活质量.

Abstract：

Objectives To evaluate preliminary clinical experience for combining awake craniotomy and intraoperative language brain mapping within the integrated 3.0 T intraoperative maguetic resonance imaging (iMRI) suite.Methods From December 2010 to April 2011,11 right hand-dominant patients with left glioma were involved in, or adjacent to, eloquent cortex was carried out awake craniotomies with cortical stimulation within an integrated 3.0 T iMRI suite.Aphasia battery of Chinese was used to test the language function before the operation.During the procedure, after the occipital, temporal, and supraorbital nerves were blocked by the anesthesiologists, the head was fixed with a custom high-field MRI-compatible head holder.The skull and dura was opened as usual and language brain mapping was then performed.Language testing followed a set protocol:counting numbers from 1 to 50, naming objects, reading single words.Resection of the tumor was guided by neuronavigation system and continued until eloquent areas were encountered or the margin of assessment was reached.An interdissection MRI was aquired to evaluate the glioma removal in a movable MRI scanner after minimal draping. Meanwhile, adverse effects caused by electrical stimulation and iMRI were recorded.The follow-up speech tests were assessed on 7th day and 1 month at least after the operation.Results The combined use of 3.0 T iMRI and awake craniotomy was performed safely in all patients.No adverse effects were reported.The duration of surgery was prolonged by 2 to 4 h.The patients' perception of iMRI during surgery was favorable.First-look MRI studies led to further resection attempts in 6/11 cases as well as a 3/11 increase in the number of gross-total resections.One week after surgery, baseline language function worsened in 4 cases. However, no patients had a persistent language deficit one month after surgery. Conclusions Awake craniotomy and direct cortical electrical stimulation can be performed safely and effectively within a 3.0 T iMRI suite.The combination of high-field iMRI and awake craniotomy may facilitate safe removal of eloquent glioma.     

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.     

功能磁共振成像定位皮质运动区与术中电刺激运动诱发电位的前瞻对照研究

目的以术中电刺激运动诱发电位（MEP）监测为对照,评价中央区脑肿瘤术前运用血液氧饱和水平检测（BOLD）技术的功能磁共振成像（fMRI）定位皮质运动区的准确性。方法此项前瞻性研究选取了16例中央区脑肿瘤。开颅手术前分别执行手运动激发程式,运用BOLD技术的fMRI定位皮质运动区。将fMRI影像与磁共振导航序列影像融合。以术中MEP监测作为皮质运动区定位的标准技术。在神经导航下定位fMRI的各个激活区,单独或联合运用短串经颅电刺激（TCES）和直接皮质电刺激（DCES）,在前臂及手部记录复合肌肉动作电位。比较两种技术的吻合度,以评价fMRI定位的皮质运动区的准确性。结果fMRI与MEP的吻合率为92．3％,其中与TCES的吻合率为100．0％,与DCES的吻合率为66．7％。结论运用BOLD技术的fMRI敏感度高,可实现中央区脑肿瘤术前皮质运动区的准确定位。     

Stereotactic targeting of the ventrointermediate nucleus of the thalamus by direct visualization with high-field MRI

OBJECTIVE: To evaluate the ability of high-field MRI to consistently produce high-resolution, anatomical images of the thalamic ventrointermediate nucleus (Vim) suitable for stereotactic targeting. METHODS: MR images of the thalamus of patients treated for essential tremor were acquired prior to treatment using a 3-tesla MR system. Similar images were acquired in 6 volunteers using, for comparison, both a 1.5-tesla and a 3.0-tesla system. RESULTS: The thalamic Vim was clearly and consistently delineated on the 3-tesla images. These images were successfully used for target localization in essential tremor patients. In the volunteers data, images acquired using the 1.5-tesla system were inferior to those acquired using the 3-tesla system, lacking the ability to consistently provide reliably defined borders of the Vim. CONCLUSION: 3-Tesla MRI can provide high-quality depiction of the Vim, potentially enabling accurate treatment planning by direct visualization and definition of the targeted Vim.     

功能和纤维成像在脑功能区胶质瘤中的应用

目的研究功能磁共振成像（fMRI）定位脑运动功能区和弥散张量纤维束示踪成像（diffusion tensor tractography,DTT）显示锥体束与肿瘤位置关系在脑胶质瘤行直接皮质电刺激手术的指导作用。方法对28例邻近或累及脑运动功能区的患者,术前在常规成像基础上,分别行双手握拳刺激策略的血氧水平依赖性功能磁共振成像（BOLD-fMRI）和弥散张量成像（DTI）,经工作站提供的BOLD．fMRI和DTI图像分析软件包获得脑运动功能区的激活图像、二维的部分各向异性伪彩图（fractional anisotropy,FA Color）和三维的白质纤维束示踪图。提供脑肿瘤与脑运动皮质区和运动传导束即锥体束的位置关系信息,制定手术方案。所有患者均行术中皮质直接电刺激定位运动区。术前、术后均行Karnofsky生活状态（KPS）评分,判断患者的状态。结果28例患者的fMRI和DTI获得良好的脑双手握拳运动功能区激活图像和锥体束纤维束走形图像,显示初级运动皮质区、运动前皮质区、辅助运动皮质区等手运动相关的脑功能区和运动传导束——锥体束与肿瘤的位置关系。在术前脑功能磁共振图像指导下,直接皮质电刺激快捷、准确定位初级运动皮质区,发现两者具有良好的一致性。术后患者KPS评分结果较术前提高。结论术前BOLD-fMRI和DTT可于活体、无创地描绘脑运动功能区和锥体束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,实现最大程度保护患者重要的功能,并最大程度地切除肿瘤。     

Intraoperative magnetic resonance imaging for ablation of hepatic tumors

BACKGROUND: The most significant rise in the use of hepatic ablation has come from image-guided techniques with both computed tomography (CT) and ultrasound (US). The recent development of open-configuration magnetic resonance scanners has opened up an entire new area of image-guided surgical and interventional procedures. Thus the aim of this study was to evaluate the use of intraoperative MRI (iMRI) ablation of hepatic tumors performed by surgeons. METHOD: Percutaneous iMRI hepatic ablation was performed from January 2003 to February 2005 for control of either primary or secondary hepatic disease. RESULTS: Eighteen hepatic ablations were performed on 11 patients with a median age of 71 (range: 51-81) years for metastatic colorectal cancer (n = 6), hepatocellular cancer (n = 2), cholangiocarcinoma (n = 2), and metastatic neuroendocrine (n = 1). Median hospital stay was 1 day, with complications occurring in 2 patients. After a median follow up of 18 months, there have been no local ablation recurrences, 5 patients are free of disease, 4 are alive with disease, 1 has died of disease, and 1 has died of other causes. CONCLUSIONS: Image-guided hepatic ablations represent a useful technique in managing hepatic tumors. Intraoperative MRI represents a new technique with initial success that has been limited to European centers. Further evaluation in U.S. centers has demonstrated iMRI to be useful for certain hepatic tumors that cannot be adequately visualized by US or CT.     

Anesthesia for brain tumor resection using intraoperative magnetic resonance imaging (iMRI) with the Polestar N-20 system: experience and challenges

The Polestar N-20 Scanner (Medtronic Navigation, Louisville, CO) is an intraoperative magnetic resonance image (iMRI) guidance system designed for neurosurgery. Sixty-five patients underwent craniotomy for tumor resection using the iMRI during the period from April 2005 to December 2006. Anesthesiologists used an iMRI-compatible patient monitoring system (Veris MR, MEDRAD, Indianola, PA), anesthesia machine (Aestiva/5 MRI, Datex-Ohmeda, Madison, WI), and infusion pumps (Continuum; MEDRAD). Average setup time for each case (from intubation to incision) was one hour, 33 minutes and showed learning improvement over the 21-month period. The challenges facing the anesthesiologists in these cases included the need to use longer intravenous (IV) catheters and gas delivery and sampling lines, which increased dead space. Electrocardiographic signals became contaminated with electrical noise during iMRI scan procedures, which made it difficult to distinguish rhythm changes. None of our iMRI patients underwent a repeat resection, whereas the repeat resection rate for conventional tumor resection is reported to be as high as 30%. The use of a small, low-field iMRI system provided adequate imaging for resection of lesions without the need of repeat resections in the weeks following the initial procedure, and did not significantly alter the anesthetic procedure. A team effort between the anesthesiologists, surgeons, nurses, and MRI technicians is paramount for the practical and efficient use of these iMRI systems.     

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.     

Lumbar modic changes-a comparison between findings at low- and high-field magnetic resonance imaging

STUDY DESIGN.: A cross-sectional observational study. OBJECTIVE.: To investigate whether there is a difference in findings of lumbar Modic changes in low-field (0.3 T) magnetic resonance imaging (MRI) compared with high-field (1.5 T). SUMMARY OF BACKGROUND DATA.: It is a challenge to give patients with low back pain a specific diagnosis. Modic changes as seen on MRI have been reported to be a possible source of pain. However, it is unclear whether the diagnosis is independent on the field strength. METHODS.: Twenty patients with Modic changes, 11 women and 9 men (mean age, 53.6 yr; range, 29-81 yr), with or without sciatica, seen in a Danish outpatient low back pain clinic were included. All patients obtained MRI scans on both a high-field and a low-field MRI scanner. Two radiologists evaluated all lumbar endplates independently, using a standardized evaluation protocol. Kappa statistics were used to analyze the interobserver reproducibility. We used paired t test to analyze the difference between low- and high-field MRI. RESULTS.: The total number of Modic changes diagnosed with high-field MRI was significantly higher than that with low-field MRI. However, 3 to 4 times as many Modic type 1 changes were found with low-field MRI compared with high-field MRI. Contrarily, with high-field MRI type 2 changes were diagnosed twice as often. CONCLUSION.: There was a significant difference between low- and high-field MRI regarding the overall prevalence of any Modic change, but this had opposite directions for types 1 and 2: type 2 dominated in low field and conversely in high field. The type of MRI unit should be taken into consideration when diagnosing patients with Modic changes.     

How to overcome the limitations to determine the resection margin of pituitary tumours with low-field intra-operative MRI during trans-sphenoidal surgery: usefulness of Gadolinium-soaked cotton pledgets

Summary   Objective. Intra-operative MRI (iMRI) is used as an immediate intra-operative quality control, allowing surgeons to extend resections in situations involving residual tumour remnants. Despite these advantages, low-field iMRI has some limitations with regards to image quality and artefacts. The aim of this study is to report our experience with bone wax and Gadolinium-soaked cotton pledgets in obtaining precise tumour resection margins using low-field iMRI. Patients and methods. The study group included 63 consecutive patients who underwent endonasal trans-sphenoidal surgery with use of intra-operative low-field iMRI (0.15 T, PoleStar N20, Medtronic Navigation, Louisville, CO, U.S.A.). The indications for intra-operative MRI use included a suprasellar or retrosellar extension (n = 23), cavernous sinus invasion (n = 21), a tumour located in the vicinity of critical anatomic structures (such as the internal carotid artery, n = 10), recurrent or revision procedures (n = 5), and pre-operative imaging revealing unusual anatomy (n = 4). Results. Overall, among the 51 patients with intended complete tumour removal, iMRI revealed definite tumour remnants or suspicious findings in 13 patients (25.5%), leading to an extended resection and allowing completion of the resection in 10 patients. There was an increased rate of complete tumour removal from 74.5% (38 out of 51) to 94.1% (48 out of 51). The iMRI scan for complete tumour removal was more efficient in the group receiving Gadolinium-soaked cotton pledgets (85.2–100%) than in the group receiving bone wax or the conventional method (62.5–87.5%). The results of iMRI and the estimation by the surgeon concerning the extent of resection revealed a discrepancy in five patients (15.6%) in the Gadolinium-soaked cotton pledgets application group, and in 14 (45.2%) of the bone wax application group. Conclusions. More valuable information for determining the resection margin can be obtained with the use of contrast-soaked cottonoid packing in the tumour resection cavity during iMRI scanning. We believe that the use of this simple method reduces the false-positive results and also overcomes the disadvantages of low-field iMRI. First two authors are contributed equally to this work. Correspondence: Sun Ho Kim, MD, Department of Neurosurgery, Yonsei University College of Medicine, 134 Shinchon-dong, Sudaemoon-gu, Seoul 120-752, Republic of Korea.     

Visualization of the eloquent motor system by integration of MEG,functional, and anisotropic diffusion-weighted MRI in functional neuronavigation

BACKGROUND: In this study, we visualized the eloquent motor system including the somatosensory-motor cortex and corticospinal tract on a neuronavigation system, integrating magnetoencephalography (MEG), functional magnetic resonance imaging (fMRI), and anisotropic diffusion-weighted MRI (ADWI). METHODS: Four patients with brain lesions adjacent to the eloquent motor system were studied. Motor-evoked responses (MER) by finger-tapping paradigm were acquired with a 1.5-Tesla MR scanner, and somatosensory-evoked magnetic fields (SEF) by median nerve stimulation were measured with a 204-channel MEG system. In the same fMRI examination, ADWI and anatomic three-dimensional T1-weighted imaging (3-D MRI) were obtained. Activated areas of MER, estimated SEF dipoles, and the corticospinal tract on ADWI were coregistered to 3-D MRI, and the combined MR data were transferred to a neuronavigation system (functional neuronavigation). Intraoperative recording of cortical somatosensory-evoked potentials was performed for confirmation of the central sulcus. RESULTS: Combination of fMRI and MEG enabled firm identification of the central sulcus. Functional neuronavigation facilitated extensive tumor resection, having the advantage of sparing the motor cortex and corticospinal tract in all cases. CONCLUSIONS: The proposed functional neuronavigation allows neurosurgeons to perform effective and maximal resection of brain lesions, identifying and sparing eloquent cortical components and their subcortical connections. Potential clinical application of this technique is discussed.     

Presurgical mapping with functional MRI: comparative study with transcranial magnetic stimulation and intraoperative mapping]

PURPOSE: The accuracy of preoperative mappings in patients with brain tumors near the central sulcus using functional magnetic resonance imaging (fMRI) or transcranical magnetic stimulation (TCS) was evaluated by comparative reference to intraoperative mapping. METHODS: The thumb movement was evoked by TCS for the mapping of the motor cortex. After the placement of the marker determined by TCS on the scalp, fMRI under motor tasks consisting of repetitive grasping was performed. For motor cortex activation, an axial oblique plane to maximize gray matter sampling in the rolandic cortex was employed in order to compare these different mapping techniques more precisely. Sixteen patients with brain tumors were included in this study. RESULTS: In nine patients, fMRI disclosed activation in one restricted gyrus or in the localized area around one restricted sulcus. Of these nine patients, preoperative TCS mapping corresponded closely with fMRI in six, while in the remaining three, the TCS marker fell between 1 and 2 cm apart from the fMRI-activated area. However, in these three patients, intraoperative electrocortical stimulation corresponded with the preoperative mapping with fMRI. In six patients, contigucus two gyri were activated by motor tasks. The TCS marker was disclosed on one of the two activated gyri. Of these six patients, the position of the TCS marker and fMRI-activated site corresponded with each other in four cases. They were found on the same gyrus but there was 1.0-2.0 cm distance between them in two cases. Intraoperative somatosensory evoked potential was monitored in two of these six cases. They corresponded well with the mapping by fMRI and TCS together. In only one patient, no significant activation area was obtained by fMRI because of excessive head motion during motor tasks. The TCS marker in this patient was identical with intraoperative electro-cortical stimulation mapping. CONCLUSION: For presurgical planning in patients with brain tumor near the central sulcus, comparative evaluation with fMRI and TCS is applicable and provides accurate functional mapping.     

Complex hepatic surgery aided by a 1.5-tesla moveable magnetic resonance imaging system

BACKGROUND: Resection represents the best treatment for potentially curable liver tumors; radiofrequency ablation (RFA) is an alternative. The curative potential of RFA may be hampered because the extent of burn is difficult to estimate by ultrasound. We postulated that intraoperative MRI (iMRI) would enable a more accurate assessment of ablation completeness. METHODS: We performed open hepatic surgery in an operating room equipped with a unique, retractable 1.5-T magnet. Patients were selected because it was anticipated that RFA (with or instead of resection) was likelihood and that iMRI might be helpful in making intraoperative decisions. After baseline MRI, lesions were further assessed by ultrasound at the time of open surgery. Lesions were resected and/or ablated, and further imaging confirmed the margins of the procedure. RESULTS: Nine patients underwent the procedure: 1 with metastatic carcinoid, 4 with hepatocellular carcinoma, and 4 with colorectal liver metastases. In 4 patients, iMRI had an effect on decision-making. In 5 individuals, there were nonlocal recurrences, and 1 patient who was never disease-free had a local recurrence. COMMENTS: Intraoperative MRI could potentially impact operative decision-making when ablating extensive disease. Its ability to prevent local recurrences must be determined. Moreover, the role of this technology in the overall treatment armamentarium must be defined.     

The safety and effectiveness of low field intraoperative MRI guidance in frameless stereotactic biopsies of brain tumours—design and interim analysis of a prospective randomized trial

The aim of the study was to assess the safety and effectiveness of stereotactic brain tumour biopsy (STx biopsy) guided by low-field intraoperative magnetic resonance imaging (iMRI) in comparison with its frameless classic analogue based on a prospective randomized trial. A pilot group of 42 brain tumour patients was prospectively randomized into a low-field iMRI group and a control group that underwent a frameless STx biopsy. The primary endpoints of the analysis were postoperative complication rate and diagnostic yield, and the secondary endpoints were length of hospital stay and duration of operation. The iMRI group (21 patients) and the control group (21 patients) did not differ significantly according to demographic and epidemiological data. No major postoperative complications were noted in either group. In addition, no significant differences in the diagnostic yield (p?=?1.00) and length of hospital stay (p?=?0.16) were observed. The mean total OR time was 111?±?24 min in iMRI and 78?±?29 min in the control group (p?=?0.0001). Usage of iMRI may prolong the time of the procedure but seems to be comparable in safety and effectiveness to the standard frameless STx biopsy.     

Adaptation of a standard low-field (0.3-T) system to the operating room: focus on pituitary adenomas

iMRI is a reliable and safe tool to monitor the extent of resection and to avoid complications in the transsphenoidal surgical approach for pituitary tumors. The best indication for its application in transsphenoidal surgery is for patients with pituitary macroadenomas with suprasellar extension. The low-field 0.3-T magnet has a diagnostic imaging quality that provides surgeons with good intraoperative detail of the anatomic relations in the sellar region. In our experience, iMRI provided a distinct benefit in planned STR for invasive macroadenomas that compress the optic chiasm and in planned GTR for noninvasive tumors. The iMRI design adopted at our center includes important features, such as the use of ferromagnetic surgical instruments, elimination of patient transportation, and capability as a shared resource, that allow multipurpose diagnostic use and increased cost-effectiveness.     

Comparison of navigated transcranial magnetic stimulation and functional magnetic resonance imaging for preoperative mapping in rolandic tumor surgery

Navigated transcranial magnetic stimulation (nTMS) is a novel tool for preoperative functional mapping. It detects eloquent cortical areas directly, comparable to intraoperative direct cortical stimulation (DCS). The aim of this study was to evaluate the advantage of nTMS in comparison with functional magnetic resonance imaging (fMRI) in the clinical setting. Special focus was placed on accuracy of motor cortex localization in patients with rolandic lesions. Thirty consecutive patients were enrolled in the study. All patients received an fMRI and nTMS examination preoperatively. Feasibility of the technique and spatial resolution of upper and lower extremity cortical mapping were compared with fMRI. Consistency of preoperative mapping with intraoperative DCS was assessed via the neuronavigation system. nTMS was feasible in all 30 patients. fMRI was impossible in 7 out of 30 patients with special clinical conditions, pediatric patients, central vascular lesions, or compliance issues. The mean accuracy to localize motor cortex of nTMS was higher than in fMRI. In the subgroup of intrinsic tumors, nTMS produced statistically significant higher accuracy scores of the lower extremity localization than fMRI. fMRI failed to localize hand or leg areas in 6 out of 23 cases. Using nTMS, a preoperative localization of the central sulcus was possible in all patients. Verification of nTMS motor cortex localization with DCS was achieved in all cases. The fMRI localization of the hand area proved to be postcentral in one case. nTMS has fewer restrictions for preoperative functional mapping than fMRI and requires only a limited level of compliance. nTMS scores higher on the accuracy scale than fMRI. nTMS represents a highly valuable supplement for the preoperative functional planning in the clinical routine.