Magnetic source imaging and brain surgery: presurgical and intraoperative planning in 26 patients

2000 ◽  
Vol 92 (1) ◽  
pp. 79-90 ◽  
Author(s):  
Cary D. Alberstone ◽  
Stephen L. Skirboll ◽  
Edward C. Benzel ◽  
John A. Sanders ◽  
Blaine L. Hart ◽  
...  
Keyword(s):  
Surgical Resection ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Content Type ◽  
Intracranial Mass ◽  
Ms Imaging ◽  
Magnetic Source ◽  
Neurosurgical Technique ◽  
Mass Lesions ◽  
Fine Print

Object. The availability of large-array biomagnetometers has led to advances in magnetoencephalography that permit scientists and clinicians to map selected brain functions onto magnetic resonance images. This merging of technologies is termed magnetic source (MS) imaging. The present study was undertaken to assess the role of MS imaging for the guidance of presurgical planning and intraoperative neurosurgical technique used in patients with intracranial mass lesions.Methods. Twenty-six patients with intracranial mass lesions underwent a medical evaluation consisting of MS imaging, a clinical history, a neurological examination, and assessment with the Karnofsky Performance Scale. Magnetic source imaging was used to locate the somatosensory cortex in 25 patients, the visual cortex in six, and the auditory cortex in four. The distance between the lesion and the functional cortex was determined for each patient.Twenty-one patients underwent a neurosurgical procedure. As a surgical adjunct, a frameless stereotactic navigational system was used in 17 cases and a standard stereotactic apparatus in four cases. Because of the results of their MS imaging examination, two patients were not offered surgery, four underwent a stereotactic biopsy procedure, 10 were treated with a subtotal surgical resection, and seven were treated with complete surgical resection. One patient deteriorated before a procedure could be scheduled and, therefore, was not offered surgery, and two patients were offered surgery but declined. Three patients experienced surgery-related complications.Conclusions. Magnetic source imaging is an important noninvasive neurodiagnostic tool that provides critical information regarding the spatial relationship of a brain lesion to functional cortex. By providing this information, MS imaging facilitates a minimum-risk management strategy and helps guide operative neurosurgical technique in patients with intracranial mass lesions.

Magnetic source imaging guidance of gamma knife radiosurgery for the treatment of epilepsy

2000 ◽  
Vol 93 (supplement_3) ◽  
pp. 136-140 ◽  
Author(s):  
Joseph R. Smith ◽  
Don W. King ◽  
Yong D. Park ◽  
Mark R. Lee ◽  
Gregory P. Lee ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Gamma Knife Radiosurgery ◽  
Imaging Data ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Content Type ◽  
Ms Imaging ◽  
Magnetic Source ◽  
Fine Print ◽  
Image Focus

Object. The purpose of this study was to determine if magnetic source (MS) imaging could provide useful information in the planning and performance of gamma knife radiosurgery (GKS) for epilepsy. Methods. Magnetic source imaging of interictal epileptiform dipoles was studied in 53 epilepsy surgery candidates. All patients underwent volumetric magnetic resonance (MR) imaging. Subsequently, magnetoencephalography (MEG) was performed using single or dual 37—channel units. The MR images and MEG recordings were then coregistered to produce the MS imaging data. Magnetic source imaging epileptiform data were reviewed in a blinded fashion and spatial distributions were classified as focal, regional, multiple, scattered, or none. Postresection operative photographs were compared with MS image results to determine whether extensive or partial/no resection of the MS image focus had been accomplished. Magnetoencephalography dipoles were identified in 47 patients (89%), in 46 of whom the lesions were resected. This included 20 (80%) of 25 anterior temporal lobe (ATL) cases, and 26 (93%) of 28 extratemporal lobe (ETL) cases. Of the six patients who underwent extensive ATL resections, three (50%) were seizure free. Of 14 patients who underwent partial/no resection of the ATL, seven (50%) were seizure free. There was no clear relation between MS image spatial distribution and surgery-related outcome. Of the seven ATL cases with hippocampal atrophy, five patients (71%) were seizure free. Of 12 ETL cases (three lesional), 10 patients (83%) were seizure free. Of 14 patients who underwent partial/no ETL resections (three lesional), two (14%) were seizure free. Of five nonlesional ETL cases with focal MS image dipoles, four patients (80%) were seizure free. Of five nonlesional ETL cases with regional dipoles, three patients (60%) were seizure free. Of eight ETL cases with multiple MS image dipoles, two patients (25%) were seizure free. Spatial agreement of MS imaging and electrographic data had no apparent effect on outcome of either ATL or ETL cases. Conclusions. Nonlesional ETL cases with focal (and in some cases multiple or regional) epileptiform MS image dipole distributions benefit significantly from inclusion of the MS image epileptiform focus in the resections. Nonlesional ETL cases suitable for GKS may similarly benefit from including the MS image focus in the irradiated area.

Preoperative magnetic source imaging for brain tumor surgery: a quantitative comparison with intraoperative sensory and motor mapping

2002 ◽  
Vol 97 (6) ◽  
pp. 1333-1342 ◽  
Author(s):  
Hagen Schiffbauer ◽  
Mitchel S. Berger ◽  
Paul Ferrari ◽  
Dirk Freudenstein ◽  
Howard A. Rowley ◽  
...  
Keyword(s):  
Brain Tumors ◽  
Cortical Mapping ◽  
Volume Data ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Somatosensory Stimulation ◽  
Content Type ◽  
Ms Imaging ◽  
Magnetic Source ◽  
Fine Print

Object. The aim of this study was to compare quantitatively the methods of preoperative magnetic source (MS) imaging and intraoperative electrophysiological cortical mapping (ECM) in the localization of sensorimotor cortex in patients with intraaxial brain tumors. Methods. Preoperative magnetoencephalography (MEG) was performed while patients received painless tactile somatosensory stimulation of the lip, hand, and foot. The early somatosensory evoked field was modeled using a single equivalent current dipole approach to estimate the spatial source of the response. Three-dimensional magnetic resonance image volume data sets with fiducials were coregistered with the MEG recordings to form the MS image. These individualized functional brain maps were integrated into a neuronavigation system. Intraoperative mapping of somatosensory and/or motor cortex was performed and sites were compared. In two subgroups of patients we compared intraoperative somatosensory and motor stimulation sites with MS imaging—based somatosensory localizations. Mediolateral projection of the MS imaging source localizations to the cortical surface reduced systematic intermodality discrepancies. The distance between two corresponding points determined using MS imaging and ECM was 12.5 ± 1.3 mm for somatosensory—somatosensory and 19 ± 1.3 mm for somatosensory—motor comparisons. The observed 6.5 mm increase in site separation was systematically demonstrated in the anteroposterior direction, as expected from actual anatomy. In fact, intraoperative sites at which stimulation evoked the same patient response exhibited a spatial variation of 10.7 ± 0.7 mm. Conclusions. Preoperative MS imaging and intraoperative ECM show a favorable degree of quantitative correlation. Thus, MS imaging can be considered a valuable and accurate planning adjunct in the treatment of patients with intraaxial brain tumors.

Localization of language-specific cortex by using magnetic source imaging and electrical stimulation mapping

1999 ◽  
Vol 91 (5) ◽  
pp. 787-796 ◽  
Author(s):  
Panagiotis G. Simos ◽  
Andrew C. Papanicolaou ◽  
Joshua I. Breier ◽  
James W. Wheless ◽  
Jules E. C. Constantinou ◽  
...  
Keyword(s):  
Temporal Cortex ◽  
Receptive Language ◽  
Cortical Stimulation ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Content Type ◽  
Language Functions ◽  
Ms Imaging ◽  
Magnetic Source ◽  
Fine Print

Object. In this paper the authors demonstrate the concordance between magnetic source (MS) imaging and direct cortical stimulation for mapping receptive language cortex.Methods. In 13 consecutive surgical patients, cortex specialized for receptive language functions was identified noninvasively by obtaining activation maps aided by MS imaging in the context of visual and auditory word-recognition tasks. Surgery was then performed for treatment of medically intractable seizure disorder (eight patients), and for resection of tumor (four), or angioma (one). Mapping of language areas with cortical stimulation was performed intraoperatively in 10 patients and extraoperatively in three. Cortical stimulation mapping verified the accuracy of the MS imaging—based localization in all cases.Conclusions. Information provided by MS imaging can be especially helpful in cases of atypical language representation, including bihemispheric representation, and location of language in areas other than those expected within the dominant hemisphere, such as the anterior portion of the superior temporal gyrus, the posteroinferior portion of the middle temporal gyrus, the basal temporal cortex, and the lateral temporooccipital cortex.

Magnetoencephalography-directed surgery in patients with neocortical epilepsy

2002 ◽  
Vol 97 (4) ◽  
pp. 865-873 ◽  
Author(s):  
Adam N. Mamelak ◽  
Nancy Lopez ◽  
Massoud Akhtari ◽  
W. William Sutherling
Keyword(s):  
Imaging Data ◽  
Interictal Spikes ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Content Type ◽  
Ms Imaging ◽  
Depth Electrodes ◽  
Magnetic Source ◽  
Neocortical Epilepsy ◽  
Fine Print

Object. Magnetoencephalography (MEG) and magnetic source (MS) imaging are techniques that have been increasingly used for preoperative localization of epileptic foci and areas of eloquent cortex. The use of MEG examinations must be carefully balanced against the high cost and technological investments required to perform these studies, particularly when less expensive alternative localization methods are available. To help elucidate the value of MEG, the authors have critically reviewed their experience with whole-head MEG in the case management of patients undergoing epilepsy surgery. Methods. The authors identified 23 patients with suspected focal epilepsy who underwent whole-head MEG and MS imaging at Huntington Memorial Hospital and, subsequently, underwent invasive intracranial electrode monitoring and electrocorticography (ECoG) to localize the zone of seizure origin for surgical resection. The results of the MS imaging were retrospectively stratified into three groups by the number of interictal spikes recorded during a 4-hour recording session: Class I (no spikes), Class II (≤ five spikes), and Class III (≥ six spikes). Class III was further subdivided according to the clustering density of the interictal spikes: Class IIIA represents a mean distance between interictal spikes of 4 mm or greater (that is, diffusely clustered) and Class IIIB represents a mean distance between interictal spikes of less than 4 mm (that is, densely clustered). The authors analyzed these groups to determine to what extent the results of MS imaging correlated with the ECoG-determined zone of seizure origin. In addition, they assessed whether the MS imaging study provided critical localization data and correlated with surgical outcome following resection. A statistical analysis of these correlations was also performed. Of the 40 patients studied, 23 underwent invasive monitoring, including 13 with neocortical epilepsy, four with mesial temporal lobe epilepsy, and six with suspected neocortical epilepsy that could not be clearly localized by ECoG. Depth electrodes were used in nine cases, subdural grids in nine cases, depth electrodes followed by subdural grids and strips in four cases, and intraoperative ECoG in one case. Electrocorticography was able to localize the zone of seizure origin in 16 (70%) of 23 cases. In 11 (69%) of the 16 cases in which ECoG was able to localize the zone of seizure origin, the interictal spikes on the MS images were classified as Class IIIB (densely clustered) and regionally correlated to the MS imaging—determined localization in all cases (that is, the same lobe). In contrast, no Class IIIB cases were identified when ECoG was unable to localize the zone of seizure origin. This difference showed a trend toward, but did not achieve, statistical significance (p < 0.23), presumably because of the relatively small number of cases available for analysis. In three cases (all Class IIIB), MS imaging was used to guide invasive electrodes to locations that otherwise would not have been targeted and provided unique localization data, not evident from other imaging modalities, that strongly influenced the surgical management of the patient. The classification of findings on MS images into subgroups and subsequent statistical analysis generated a model that predicted that Class IIIB MS imaging data are likely to provide reliable information to guide surgical placement of electrodes, but all other data groups do not provide localization information that is reliable enough to guide surgical decision making. Conclusions. Magnetic source imaging can provide unique localization information that is not available when other noninvasive methods are used. Magnetic source imaging appears most useful for cases of neocortical epilepsy. In particular, when an MS imaging study revealed six or more interictal spikes that were densely clustered in a single anatomical location, the MS image was highly correlated with the zone of seizure origin identified by ECoG. In these cases the MS imaging data may be useful to guide placement of intracranial electrodes.

Presurgical localization of functional cortex using magnetic source imaging

1995 ◽  
Vol 82 (6) ◽  
pp. 988-994 ◽  
Author(s):  
Christopher C. Gallen ◽  
Barry J. Schwartz ◽  
Richard D. Bucholz ◽  
Ghaus Malik ◽  
Gregory L. Barkley ◽  
...  
Keyword(s):  
Somatosensory Cortex ◽  
Preoperative Planning ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Minimum Risk ◽  
Content Type ◽  
Magnetic Source ◽  
Two Measures ◽  
Eloquent Cortex ◽  
Mass Lesions

✓ The boundaries of somatosensory cortex were localized noninvasively by means of a large-array biomagnetometer in six patients with mass lesions in or near eloquent cortex. The results were used by neurosurgeons and neurologists in preoperative planning and for reference in the operating room. The magnetic source imaging (MSI) localizations from somatosensory evoked potentials were used to predict the pattern of phase reversals measurable intraoperatively on the cortical surface, providing a quantitative comparison between the two measures. The magnetic localizations were found to be predictive in all six cases, with the two sets of localizations falling within an 8-mm distance on average. Somatosensory localizations using MSI offer accuracy in localizing somatosensory cortex stereotactically and in depicting its relationship to lesions. Such data are valuable preoperatively in assessing the risks associated with a proposed surgical procedure and for optimizing subsequent minimum-risk surgical strategy.

Magnetic source imaging of late evoked field responses to vowels: toward an assessment of hemispheric dominance for language

2001 ◽  
Vol 94 (3) ◽  
pp. 445-453 ◽  
Author(s):  
Michael D. Szymanski ◽  
David W. Perry ◽  
Nicole M. Gage ◽  
Howard A. Rowley ◽  
John Walker ◽  
...  
Keyword(s):  
Right Hemisphere ◽  
Magnetic Resonance Images ◽  
Hemispheric Dominance ◽  
Speech Sounds ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Content Type ◽  
Language Dominance ◽  
Magnetic Source ◽  
Fine Print

Object. The goal of this study was to determine whether the late neuromagnetic field elicited by simple speech sounds, which is detected by magnetoencephalography, may be used to estimate hemispheric dominance for language and to guide or constrain the intraoperative search for essential language sites. If sufficiently robust, a noninvasive method for assessing hemispheric dominance for language could reduce the necessity for amobarbital testing and the extent of intraoperative cortical stimulation—based mapping, both of which carry the risk of morbidity. Methods. Fifteen patients undergoing surgery for tumors during which intraoperative language mapping would be performed and two additional patients in whom intracarotid amobarbital testing confirmed right-hemisphere language dominance participated. Following a primary auditory response sources of late neuromagnetic fields elicited by vowel stimuli were modeled and coregistered using magnetic resonance images to form magnetic source (MS) images. A laterality index (LI) was calculated by summing the number of equivalent current dipolar sources in the late fields detected from each hemisphere. In 14 right-handed patients, 10 displayed left asymmetric LIs (0.37 ± 0.16, mean ± standard error of the mean in 14 patients). For both right-hemisphere dominant patients in whom an LI was obtainable, the LI was rightward. Stimulation-mapped essential language sites were found in 7 of 15 patients. For six of these seven patients, the MS image—derived LI was leftward. Conclusions. Asymmetry in single equivalent dipole modeling of the late neuromagnetic field evoked by simple speech sounds correlates with hemispheric language dominance, although not to the degree necessary for individual clinical predictions. With further development, MS imaging of simple language tasks may be used preoperatively to predict language dominance and even to identify or constrain the intraoperative search for likely sites of essential language cortex.

Mapping of receptive language cortex in bilingual volunteers by using magnetic source imaging

2001 ◽  
Vol 95 (1) ◽  
pp. 76-81 ◽  
Author(s):  
Panagiotis G. Simos ◽  
Eduardo M. Castillo ◽  
Jack M. Fletcher ◽  
David J. Francis ◽  
Fernando Maestu ◽  
...  
Keyword(s):  
Functional Imaging ◽  
Receptive Language ◽  
Language Mapping ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Content Type ◽  
Magnetic Source ◽  
Practical Implications ◽  
Language Cortex ◽  
Fine Print

Object. There are conflicting claims in the functional imaging literature concerning whether different languages are represented by distinct brain mechanisms in individuals who are proficient in more than one language. This interesting theoretical issue has practical implications when functional imaging methods are used for presurgical language mapping. To address this issue the authors compared the location and extent of receptive language cortex specific to English and Spanish in neurologically intact bilingual volunteers by using magnetic source imaging. Methods. Areas of the cortex that were specialized for receptive language functions were identified separately for each language in 11 healthy adults who were bilingual in English and Spanish. The authors performed exactly the same procedures used routinely for presurgical receptive language mapping. In each bilingual individual, the receptive language—specific map always encompassed the posterior portion of the superior temporal gyrus. In every case, however, substantial differences in the receptive language maps were also observed for the two languages, regardless of whether each participant's first language was English or Spanish. Conclusions. Although the reasons for such differences and their ultimate significance in identifying the cerebral mechanisms of language are subject to continuing investigation, their presence is noteworthy and has practical implications for the surgical management of patients with lesions in the temporal and parietal regions of the dominant hemisphere.

scholarly journals Magnetic source imaging for the surgical evaluation of electroencephalography-confirmed secondary bilateral synchrony in intractable epilepsy

2009 ◽  
Vol 111 (6) ◽  
pp. 1248-1256 ◽  
Author(s):  
Edward F. Chang ◽  
Srikantan S. Nagarajan ◽  
Mary Mantle ◽  
Nicholas M. Barbaro ◽  
Heidi E. Kirsch
Keyword(s):  
Mr Imaging ◽  
Intractable Epilepsy ◽  
Focal Lesion ◽  
Seizure Type ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Ms Imaging ◽  
Epileptiform Discharges ◽  
Magnetic Source ◽  
Imaging Results

Object Routine scalp electroencephalography (EEG) cannot always distinguish whether generalized epileptiform discharges are the result of primary bilateral synchrony or secondary bilateral synchrony (SBS) from a focal origin; this is an important distinction because the latter may be amenable to resection. Whole-head magnetoencephalography (MEG) has superior spatial resolution compared with traditional EEG, and can potentially elucidate seizure foci in challenging epilepsy cases in which patients are undergoing evaluation for surgery. Methods Sixteen patients with medically intractable epilepsy in whom SBS was suspected were referred for magnetic source (MS) imaging. All patients had bilateral, synchronous, widespread, and most often generalized spike-wave discharges on scalp EEG studies, plus some other clinical (for example, seizure semiology) or MR imaging feature (for example, focal lesion) suggesting focal onset and hence possible surgical candidacy. The MS imaging modality is the combination of whole-head MEG and parametric reconstruction of corresponding electrical brain sources. An MEG and simultaneous EEG studies were recorded with a 275-channel whole-head system. Single-equivalent current dipoles were estimated from the MEG data, and dipole locations and orientations were superimposed on patients' MR images. Results The MS imaging studies revealed focal dipole clusters in 12 (75%) of the 16 patients, of which a single dipole cluster was identified in 7 patients (44%). Patient age, seizure type, duration of disease, video-EEG telemetry, and MR imaging results were analyzed to determine factors predictive of having clusters revealed on MS imaging. Of these factors, only focal MR imaging anatomical abnormalities were associated with dipole clusters (chi-square test, p = 0.03). Selective resections (including the dipole cluster) in 7 (87%) of 8 patients resulted in seizure-free or rare seizure outcomes (Engel Classes I and II). Conclusions Magnetic source imaging may provide noninvasive anatomical and neurophysiological confirmation of localization in patients in whom there is a suspicion of SBS (based on clinical or MR imaging data), especially in those with an anatomical lesion. Identification of a focal seizure origin has significant implications for both resective and nonresective treatment of intractable epilepsy.

scholarly journals Preoperative magnetic source imaging for brain tumor surgery: a quantitative comparison with intraoperative sensory and motor mapping

2003 ◽  
Vol 15 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Hagen Schiffbauer ◽  
Mitchel S. Berger ◽  
Paul Ferrari ◽  
Dirk Freudenstein ◽  
Howard A. Rowley ◽  
...  
Keyword(s):  
Brain Tumors ◽  
Cortical Mapping ◽  
Volume Data ◽  
Current Dipole ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Somatosensory Stimulation ◽  
Motor Mapping ◽  
Ms Imaging ◽  
Magnetic Source

Object The aim of this study was to compare quantitatively the methods of preoperative magnetic source (MS) imaging and intraoperative electrophysiological cortical mapping (ECM) in the localization of sensorimotor cortex in patients with intraaxial brain tumors. Methods Preoperative magnetoencephalography (MEG) was performed while patients received painless tactile somatosensory stimulation of the lip, hand, and foot. The early somatosensory evoked field was modeled using a single equivalent current dipole approach to estimate the spatial source of the response. Three-dimensional magnetic resonance image volume data sets with fiducials were coregistered with the MEG recordings to form the MS image. These individualized functional brain maps were integrated into a neuronavigation system. Intraoperative mapping of somatosensory and/or motor cortex was performed and sites were compared. In two subgroups of patients we compared intraoperative somatosensory and motor stimulation sites with MS imaging–based somatosensory localizations. Mediolateral projection of the MS imaging source localizations to the cortical surface reduced systematic intermodality discrepancies. The distance between two corresponding points determined using MS imaging and ECM was 12.5 ± 1.3 mm for somatosensory–somatosensory and 19 ± 1.3 mm for somatosensory–motor comparisons. The observed 6.5 mm increase in site separation was systematically demonstrated in the anteroposterior direction, as expected from actual anatomy. In fact, intraoperative sites at which stimulation evoked the same patient response exhibited a spatial variation of 10.7 ± 0.7 mm. Conclusions Preoperative MS imaging and intraoperative ECM show a favorable degree of quantitative correlation. Thus, MS imaging can be considered a valuable and accurate planning adjunct in the treatment of patients with intraaxial brain tumors.

Cortical reorganization after digit-to-hand replantation

2000 ◽  
Vol 93 (5) ◽  
pp. 876-883 ◽  
Author(s):  
Katja Wiech ◽  
Hubert Preißl ◽  
Werner Lutzenberger ◽  
Ralph-Thomas Kiefer ◽  
Stephanie Töpfner ◽  
...  
Keyword(s):  
Somatosensory Cortex ◽  
Cortical Reorganization ◽  
Source Imaging ◽  
Magnetic Source Imaging ◽  
Continuous Increase ◽  
Content Type ◽  
Somatosensory Evoked Fields ◽  
Evoked Fields ◽  
Hand Replantation ◽  
Fine Print

✓ Functional recovery after digit-to-hand replantation depends on the interaction of various factors. In addition to peripheral mechanisms, cortical and subcortical reorganization of digit representation may play a substantial role in the recovery process. However, cortical processes during the first months after replantation are not well understood.In this 25-year-old man who had traumatically lost digits II to V (DII—V) on his right hand, the authors used magnetoencephalographic source imaging to document the recovery of somatosensory cortical responses after tactile stimulation at four sites on the replanted digits. Successful replantation of DIV and DV was accomplished at the original position of DIII and DIV with mixed innervation. Cortical evoked fields could be recorded starting from the 10th week after digit-to-hand replantation. Initially, signals from all sites showed decreased amplitudes and prolonged latencies. In the subsequent six recordings obtained between the 12th and 55th week postreplantation, a continuous increase in amplitude but only a slight recovery of latencies were observed. Components of the recorded somatosensory evoked fields were localized in the primary somatosensory cortex (SI). The localizations of the replanted DIV showed a gradual lateral-inferior shift in the somatosensory cortex over time, indicating cortical reorganization caused by altered peripheral input. The authors infer from this shift that the original cortical area of the missing finger (DII) was taken over by the replanted finger.From these data the authors conclude that magnetic source imaging might be a reliable noninvasive method to evaluate surgical nerve repair and that cortical reorganization of SI is involved in the regeneration process following peripheral nerve injury.

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