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/lp/american-journal-of-neuroradiology/acr-white-paper-on-magnetoencephalography-and-magnetic-source-imaging-rpHaWY1eSs
- Publisher
- American Journal of Neuroradiology
- Copyright
- © 2022 by American Journal of Neuroradiology. Indicates open access to non-subscribers at www.ajnr.org
- ISSN
- 0195-6108
- eISSN
- 1936-959X
- DOI
- 10.3174/ajnr.a7714
- Publisher site
- See Article on Publisher Site
Abstract
WHITE PAPER ACR White Paper on Magnetoencephalography and Magnetic Source Imaging: A Report from the ACR Commission on Neuroradiology J.A. Maldjian, R. Lee, J. Jordan, E.M. Davenport, A.L. Proskovec, M. Wintermark, S. Stufflebeam, J. Anderson, P. Mukherjee, S.S. Nagarajan, P. Ferrari, W. Gaetz, E. Schwartz, and T.P.L. Roberts ABSTRACT SUMMARY: Magnetoencephalography, the extracranial detection of tiny magnetic fields emanating from intracranial electrical activity of neurons, and its source modeling relation, magnetic source imaging, represent a powerful functional neuroimaging technique, able to detect and localize both spontaneous and evoked activity of the brain in health and disease. Recent years have seen an increased utilization of this technique for both clinical practice and research, in the United States and worldwide. This report summarizes cur- rent thinking, presents recommendations for clinical implementation, and offers an outlook for emerging new clinical indications. ABBREVIATIONS: ACR ¼ American College of Radiology; AD ¼ Alzheimer disease; ASD ¼ autism spectrum disorder; CMS ¼ Centers for Medicare and Medicaid Services; CPT ¼ Current Procedural Terminology; ECD ¼ equivalent current dipole; iEEG ¼ intracranial electroencephalography; MEG ¼ magnetoence- phalography; MSI ¼ magnetic source imaging agnetoencephalography (MEG) is a noninvasive method is necessary for the successful development of a comprehensive Mof detecting neural activity in the brain with millisecond clinical MEG program. The team includes clinicians, MEG sci- time resolution. The current clinically approved indications entists, and technologists, often with complementary and/or for MEG are localization of epileptic foci and localization of el- overlapping skill sets. MEG centers across the United States op- oquent cortices for presurgical planning. The goal of the MEG erate in various clinical departments. Close collaboration with community at large is to advance current clinical practices and Radiology, Neurology, and Neurosurgery has been instrumental to develop new clinical indications for MEG. Multiple groups in advancing MEG for clinical use. While there are several pub- have researched the use of MEG in a variety of clinical disor- lications outlining good clinical practice for acquiring and ana- ders including concussion, Alzheimer’s disease, autism, and lyzing clinical MEG data, at the current time, implementation others. Additionally, MEG can be used as an adjunct to other varies across sites. In this report, we describe the current clinical therapies, such as neuromodulation. Multispecialty collaboration landscape for MEG and emerging applications, as well as pro- vide recommendations for the composition and training of Received September 30, 2022; accepted after revision October 4. multidisciplinary teams involved in the performance and inter- From the Advanced Neuroscience Imaging Research Laboratory (J.A.M., E.M.D., A.L.P.), pretation of clinical MEG studies, including the roles of the phy- MEG Center of Excellence (J.A.M., E.M.D., A.L.P.), and Department of Radiology (J.A.M., E.M.D., A.L.P.), University of Texas Southwestern Medical Center, Dallas, Texas; sician, MEG scientist, and MEG technologist in performance of Department of Neuroradiology (R.L.), University of California San Diego, San Diego, current and future clinically approved MEG studies. We advo- California; ACR Commission on Neuroradiology (J.J.), American College of Radiology, Reston, Virginia; Stanford University School of Medicine (J.J.), Stanford, California; cate that clinical reporting should be performed after consultation Department of Neuroradiology (M.W.), University of Texas MD Anderson Center, with the entire team, including technologists, MEG scientists, and Houston, Texas; Athinoula A. Martinos Center for Biomedical Imaging (S.S.), physicians. Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts; Department of Radiology and Imaging Sciences (J.A.), University of Utah School of Medicine, Salt Lake City, Utah; Department of Radiology and Biomedical Imaging (P.M., S.S.N.), University of California, San Francisco, San Francisco, Prior American College of Radiology Involvement in MEG California; Pediatric Neurosciences (P.F.), Helen DeVos Children’sHospital, Grand Rapids, Michigan; Department of Pediatrics and Human Development (P.F.), College In 2001, with the joint support of the American College of of Human Medicine, Michigan State University, Grand Rapids, Michigan; and Radiology (ACR), American Society of Neuroradiology, and Department of Radiology (W.G., E.S., T.P.L.R.), Children’s Hospital of Philadelphia, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, American Academy of Neurology, 2 neuroradiologists (Roland Lee, Pennsylvania. Steven Stufflebeam) and 1 neurologist (Michael Funke) testified at Please address correspondence to Joseph Maldjian, MD, University of Texas the Centers for Medicare and Medicaid Services (CMS) in support Southwestern Department of Clinical Sciences, Radiology, 5323 Harry Hines Blvd, Dallas, TX 75390-9178; e-mail: joseph.maldjian@utsouthwestern.edu; @EMDavenport_PhD of 3 new Current Procedural Terminology (CPT) codes for MEG: Indicates open access to non-subscribers at www.ajnr.org 95965 (MEG recording and analysis of spontaneous brain http://dx.doi.org/10.3174/ajnr.A7714 activity) E46 Maldjian Dec 2022 www.ajnr.org 95966 (MEG recording and analysis of evoked magnetic fields, epileptogenic zone localization. Recent studies have revealed good single technique) concordance between MEG and iEEG in localizing epileptogenic 95967 (MEG recording and analysis of evoked magnetic fields, activity, bolstering MEG’s potential as an alternative, noninvasive each additional technique, after invoking 95966 once). tool for preoperative planning. Inclusion of MEG in the presurgical neuroimaging battery TheRelativeValue ScaleUpdateCommittee reviewed these bestows better clinical outcomes and correlates with postoperative codes at the April 2001 meeting, and CMS implemented the codes 8,9 seizure freedom. Specifically, resection patients in whom the and payment rates in 2002, with subsequent scheduled reviews and MEG dipole cluster was completely sampled by iEEG had a strik- revisions of the payment rates. ingly higher chance of seizure freedom relative to patients with incomplete/no iEEG sampling. A similar finding was observed for fMRI versus MEG fMRI has been in clinical use for over 2 decades, slightly predat- patients in whom the MEG dipole cluster was completely resected ing the clinical adoption of MEG. Clinical indications for fMRI relative to those with partial/no resection of the MEG cluster. Finally, patients with a single tight dipole cluster, those with a involve presurgical mapping of eloquent cortex. While fMRI pro- cluster that had stable orientation perpendicular to the closest vides complementary information to MEG, the underlying neuro- major sulcus, and those with agreement between MEG and iEEG physiologic basis of the signal is quite different. Functional MR imaging relies on changes in blood flow associated with neuronal localization were more likely to be seizure-free postresection. activity, making it an indirect measure of brain function, whereas Presurgical Mapping of Eloquent Cortices. MEG is used to non- MEG provides a more direct measure. Both modalities can provide invasively map the eloquent cortex in patients before they accurate delineation of eloquent cortex. However, MEG is uniquely undergo epilepsy or brain tumor surgery. The goals are to min- suited to identification of epileptogenic activity. Mapping of elo- imize deleterious postoperative functional outcomes and/or quent cortices can be performed at the same time as the epilepsy identify whether functional reorganization has occurred. study with MEG. Clinical MR imaging scans are obtained sepa- Specifically, localization of somatosensory, motor, auditory, rately from fMRI and MEG studies, with distinct CPT codes, and and/or visual cortices, as well as localization and lateralization provide anatomic reference for functional maps. For both fMRI of language cortices may be performed to predict postsurgical and MEG, robust paradigms exist for motor, sensory, and language outcomes and optimize the preservation of these functions mapping. For both modalities, areas of activation are mapped onto postoperatively. a structural MR imaging study as part of the presurgical evaluation. Eloquent cortex mapping requires the application of specific tasks during MEG recording that are designed to elicit the func- Current Indications for MEG and Magnetic Source tions of interest. These tasks generate magnetic evoked fields, and Imaging Presurgical Mapping of Epileptogenic Zones. MEG is clinically MSI is employed to localize stereotyped deflections in, or compo- approved for preoperative planning in patients with intractable, nents of, the evoked magnetic field. The ability to capture differ- or drug-resistant, epilepsy. The millisecond time resolution of ent neurophysiological responses within 1 recording is a distinct MEG is ideally suited to capture bursts of abnormal neuroelectri- advantage of MEG relative to fMRI, and MEG may be superior cal activity, as seen in epilepsy, and the spatial precision of mag- for functional mapping in patients who have cerebrovascular netic source imaging (MSI) allows the accurate localization of the malformations or tumors near the functional cortex. However, epileptogenic zone(s) (ie, seizure-generating tissue). The onset of MEG and fMRI often serve complementary roles in eloquent cor- each interictal epileptiform discharge is projected to source space tex mapping, and their amalgamation can enhance the reliability 11,12 (ie, brain space) as an equivalent current dipole (ECD) to visual- of functional localization. ize the location of potential seizure onset zone(s). In this way, With respect to each function, somatosensory responses reli- ably map to the posterior bank of the central sulcus contralateral MEG and MSI can provide unique information for presurgical planning in intractable epilepsy. MEG is optimally beneficial dur- to the side of stimulation in a manner that follows expected ing presurgical planning for cases in which common noninvasive somatotopic organization. In a similar fashion, motor responses modalities result in an inconclusive hypothesis regarding epilep- localize to the primary motor cortex contralateral to the side of togenic zone location, MR imaging–negative (ie, nonlesional) movement. Both contralateral and ipsilateral auditory responses cases, cases in which MR imaging identifies multiple lesions (eg, may be localized and map to Heschl’s gyri. Visual responses local- tuberous sclerosis), and patients with large lesions, anatomical ize to the primary visual cortex contralateral to the stimulated vis- 13,14 1-3 ual hemifield near the calcarine fissure. Importantly, prior malformations, and/or prior resection. Empirical investigations have found that MEG and MSI con- research has found that such MEG-based localizations have high tribute added clinical value during presurgical planning in patients concordance with intraoperative cortical mapping. Finally, a dis- with intractable epilepsy, as surgical resection of the epileptogenic tributed network of bilateral cortical regions often underlies lan- 4-6 zone(s) can eliminate or reduce seizures. Presurgical planning guage processing. Receptive language responses often localize to often involves the acquisition of multiple neuroimaging modalities the posterior superior temporal gyrus (ie, Wernicke’sarea), (eg, MR imaging, FDG-PET, ictal-SPECT, single-photon emission supramarginal gyrus, and angular gyrus, while expressive lan- CT). These data are used to plan intracranial electroencephalogra- guage responses often map to the pars triangularis and pars oper- phy (iEEG), in which a grid of subdural electrodes and/or cularis in the inferior frontal cortex (ie, Broca’sarea).Alaterality depth electrodes is implanted directly into the brain to confirm index is computed to determine hemispheric dominance of AJNR Am J Neuroradiol 43:E46–E53 Dec 2022 www.ajnr.org E47 language function. Multiple studies have demonstrated high con- position indicator coils are affixed to manufacturer-specified cordance between MEG-based language mapping and invasive locations on the patient’s head. These coils generate a specific fre- procedures (eg, intracarotid amobarbital procedure or Wada), quency during MEG recording to allow for head localization. The favoring MEG as a noninvasive option for language mapping and patient’s head shape and location of head position indicator coils 10,15-18 lateralization. is digitized for subsequent co-registration of MEG and structural A key transformative step is the integration of source-modeled MR imaging data. Simultaneous MEG and scalp EEG data are MEG data with MR imaging to yield MSI, either by the overlay of recorded. Typically, 40–120 minutes of spontaneous (ie, resting- single equivalent dipole sources or by statistical mapping of either state) data are collected. Due to the limited duration of recordings 19,20 and the movement-related artifact introduced by seizures, ictal spontaneous or event-related changes. This renders MEG data discharges are rarely captured. Rather, MEG recordings primarily directly interpretable by the neuroradiologist in a fashion very analogous to fMRI, but combining both mapping of functional, capture interictal epileptiform discharges. To increase the yield eloquent cortex, as well as the sources of interictal spontaneous of interictal epileptiform discharges during the scan, patients are discharges (dysfunctional MR imaging). asked to come sleep-deprived and sleep in the scanner. These data arepreprocessed to removenoise and co-register theMEG data with a structural MR imaging (typically a 3D T1). Preprocessing CLINICAL MEG RECOMMENDATIONS algorithms and steps vary depending on the manufacturer. A profes- Roles, Training, and Certification/Accreditation sional with specialized training (eg, epileptologist, neurophysiologist, Qualifications of Physicians Interpreting Clinical MEG Studies. etc) reads the time-series EEG and MEG data and identifies epileptic Physicians interpreting and reporting clinical MEG studies should discharges. The identified discharges are localized to source space have appropriate medical licensure and proper training for the clini- viathe ECDmodel, referred to as modeling in this article. cal application. For radiologists, this may include specialized clinical Modeling can be completed by anyone with specialized training in knowledge of neurophysiology, neuroanatomy, brain mapping, the neuroscience, physics, and mathematical concepts behind the neuropsychology, and image acquisition and interpretation such as dipole model (eg, scientist, physician, technologist). Dipoles that required through the American Board of Radiology Subspecialty meet statistical cutoff criteria (eg, goodness of fit, volume of confi- Certification in Neuroradiology. In addition, MEG-specific training dence) are displayed on a structural MR imaging scan, which can be is recommended to include supervised learning or clinical practice exported to PACS. of at least 50 MEG studies for the specific indication being reported. Dipoles may form clusters within a specific region. The clus- Alternatively, a minimum of 2 years of experience interpreting clini- tering of 5 or more dipoles within a region is considered a reliable cal fMRI or MEG brain mapping studies is recommended. indicator of an epileptogenic zone. Both the tightness and ori- 1,9 entation of the dipoles within a cluster have clinical relevance. Qualifications of MEG Scientists Involved in Clinical MEG Studies. The location of these dipoles and characteristics of any clusters MEG scientists involved in clinical MEG studies should be well- formed are reported by a physician. A suggested template for versed in signal processing, source analysis, neurophysiology, cog- reporting is located in the Appendix. nitive neuroscience, image processing, physics, and other scientific In contrast to presurgical mapping of epileptogenic zones, aspects of MEG and its application to patient care. In addition, which relies on resting-state recordings, eloquent cortex mapping MEG-specific training is recommended to include supervised relies on task-based recordings. The patient should be awake and learning or clinical practice of at least 50 MEG studies for the spe- alert. During a task, identical or similar stimuli are repetitively cific indication being reported, which can also be fulfilled through delivered to the patient, and a corresponding trigger (eg, number) a minimum of 2 years of experience in the source modeling of is time-stamped into the data. Offline, the data are epoched into MEG studies by a postdoctoral fellowship with a clinical MEG meaningful windows of time surrounding each stimulus, baseline- component, or through rotations at clinical MEG facilities. normalized, and averaged together to enhance the signal-to-noise ratio. This distinguishes the magnetic evoked field generated by Qualifications of MEG Technologists. The MEG technologist the stimuli, and components of the field are modeled to localize should have a background in either EEG or imaging (eg, MR the functional cortex. The time and location of each component imaging) or related disciplines. Supervised learning or clinical modeled are reported by a physician. practice of at least 50 MEG studies, including a review of the Somatosensory cortex mapping most often employs brief elec- principles of MEG technology, technical aspects of the MEG trical stimulations to the median nerve. However, stimulation of systems, patient preparation, data acquisition, operational rou- the posterior tibial nerve and/or mechanical stimulation of the tines, tuning procedures, testing procedures, troubleshooting, hand, foot, or other body regions may also be performed. To map artifact identification, prevention, and elimination, data storage, the motor cortex, the patient is asked to perform a simple move- and basic source localization procedures. Alternatively, a mini- ment such as pressing a button, tapping a finger, or moving a mum of 6 months of supervised clinical experience in an active foot at either a self-paced or visually- or auditorily-cued time MEG center is recommended. interval. For auditory cortex mapping, often 1000-Hz tones are briefly presented through inserted ear tubes at 60 dB above the Procedure/Workflow of Clinical MEG Examination, 10,13 patient’s hearing threshold, either monaurally or binaurally. Analysis, and Reporting MEG-guided localization of epileptogenic zones involves several To map the visual cortex, stimuli, often checkerboards, are pre- key steps. Before recording, surface EEG electrodes and head sented on a projector screen to the full visual field, each hemifield, E48 Maldjian Dec 2022 www.ajnr.org or each quadrant. Language cortex mapping may utilize auditory EMERGING INDICATIONS and/or visual stimuli and can be grouped into 2 categories: recep- Concussion tive or expressive. Receptive language tasks include passively lis- Many articles in the peer-reviewed literature show that MEG can tening to words or silently reading words presented on the objectively diagnose concussions (mild traumatic brain injury) projector screen. Expressive language tasks include covert verb with significantly more sensitivity (about 85% sensitivity) than 10,14,24 generation and picture naming. the relatively insensitive standard neuroimaging techniques such 26-33 Many of the patients undergoing MEG have epilepsy that is as CT or MR imaging. EEG has long demonstrated that low- poorly controlled by medications. It is important that safeguards be frequency activity in the delta-band (1–4 Hz) is abnormal in put in place for responding to medical emergencies. This includes awake, alert adults. Studies in animal models confirm that deaf- the availability of emergency personnel and supplies depending on ferentation of neurons due to traumatic injury to axons or block- the setting. age of cholinergic transmission will generate these slow/delta- 31,34 waves. Resting-state MEG more sensitively detects delta waves than EEG, with about 85% sensitivity in diagnosing con- Billing and Reimbursement cussions compared with normal controls, even in single subjects As noted in the Background, since 2002, the CMS has authorized when using an automated voxelwise algorithm, which also local- and implemented 3 CPT codes and their payment rates for MEG: izes the areas of abnormal slow-waves. 95965, 95966, 95967. Using these 3 codes, clinical MEG is a well- Another MEG finding in patients with concussion is excessive establishedreimbursable procedure andis acceptedas the standard synchronous resting-state high-frequency gamma-band activity of care in evaluation of patients with epilepsy and in the presurgical (30–80 Hz) in certain frontal and other brain regions, which may mapping of eloquent cortices. be due to selective vulnerability of inhibitory GABAergic inter- neurons due to head trauma. Quality Improvement and Quality Control Resting-state functional connectivity studies with MEG reveal A critical component of establishing and maintaining a high- various patterns of aberrant functional connectivity in patients quality clinical MEG program is to invest in the training and with mild traumatic brain injury, likely reflecting differing mech- education of all team members. Most manufacturers offer train- anisms of injury, including disruption of networks, and injury to 32,33 ing programs for new sites. The American Board of Registration inhibitory GABAergic interneurons. of Electroencephalographic and Evoked Potential Technologists offers a MEG technologist certification program. Both the Post-Traumatic Stress Disorder American Clinical MEG Society and the American Society for Post-traumatic stress disorder affects about 7% of American adults Functional Neuroradiology offer clinical guidelines, continuing during their lifetime and is especially prevalent in combat veter- education at annual meetings, and clinical MEG fellowship train- ans. Compared with normal controls, MEG in patients with post- ing programs for neurologists and neuroradiologists, respectively. traumatic stress disorder shows differences in resting-state neuro- Other relevant conferences include the biannual meeting of the circuitry, including hyperactivity in the amygdala, hippocampus, International Society for the Advancement of Clinical MEG posterolateral orbitofrontal cortex, dorsomedial prefrontal cortex, and the biannual International Conference on Biomagnetism. A and insular cortex in high-frequency (beta and gamma) bands; number of excellent publications are available, including the hypoactivity from the ventromedial prefrontal cortex, frontal pole, MEG-EEG Primer textbook, Clinical Magnetoencephalography dorsolateral prefrontal cortex in high-frequency bands; and hypo- and Magnetic Source Imaging textbook, the November 2020 issue activity in the precuneus, dorsolateral prefrontal cortex, temporal of the Journal of Clinical Neurophysiology,and clinical MEG and frontal poles, and sensorimotor cortex in alpha and low-fre- guideline articles published by the International Federation quency bands. of Clinical Neurophysiology and American Clinical MEG 13,24,25 Society. Autism Spectrum Disorder A clear protocol for assessing the technical quality of the data The physical properties of MEG offer sensitivity not only to spa- is vital. Noise measurements and empty room recordings are tial localization of detected signals but also characterization in often collected daily or before recording each patient to monitor terms of the time course and spectral content of such brain activ- changes in the environment and identify issues with equipment. ity. As such, it may allow description of not just functional cen- During data acquisition, the position of the patient’s head ters but also “when” the brain activity is occurring and, indeed, within the MEG helmet is monitored for proper placement, “what” is the nature of such activity. This opens up considerable observations of artifact and noise are documented, and averages promise for application to psychiatric disorders, commonly with of events during evoked testing may be computed online to vis- no MR imaging–visible structural anomaly. One promising target ually inspect for the presence of the expected magnetic evoked disorder is autism spectrum disorder (ASD), a highly prevalent fields. Routine (eg, monthly) quality-assurance testing of the (2%) neurodevelopmental disorder. Although there is indeed digitization equipment, MEG system, and software is often con- an ultimate possibility (and current exploration) of identifying ducted by utilizing a phantom for recordings. Collaborative early electrophysiologic predictors of ASD in infants and young interdepartmental conferences should also be held regularly to children, an alternative promising role for MEG lies in the strati- compare MEG results with clinical outcomes (eg, stereoelec- fication, or subtyping, of the remarkably heterogeneous ASD troencephalography data). population. Such stratification may have value in terms of AJNR Am J Neuroradiol 43:E46–E53 Dec 2022 www.ajnr.org E49 potential enrichment of clinical trials for behavioral/pharmaceu- 3. 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Roberts TPL, Khan SY, Rey M, et al. MEG detection of delayed audi- ease is linked to selective disruptions in neurophysiological net- tory evoked responses in autism spectrum disorders: towards an work dynamics. Neurobiol Aging 2020;92:141–52 CrossRef Medline AJNR Am J Neuroradiol 43:E46–E53 Dec 2022 www.ajnr.org E51 All recorded data were analyzed utilizing software. MEG APPENDIX activity was superimposed on the patient’s 3D-volumetric brain Sample MEG Report images obtained on the MR imaging performed on []. Patient: Artifacts: Date of Birth: delete if none MRN: Acc#: Comparisons: include MR imaging, fMRI, PET, SPECT EXAM: MAGNETOENCEPHALOGRAPHY (MEG) FINDINGS: DATE OF EXAM: Interictal Findings: History and reason for Study: The patient was awake, drowsy, and sleeping during the record- Copy from Tech report ing. Epileptiform discharges [were/were not] observed during MEG is performed as part of presurgical planning. spontaneous MEG recordings. [] selected epileptiform discharges in the MEG were mapped by using a single equivalent current Technique: dipole (ECD) model. A single dipole was selected to represent The Magnetoencephalography (MEG) scan was performed at . each epileptiform discharge. The dipole selection criteria There were [] minutes of spontaneous magnetoencephalography included a goodness of fit of 80% or better, and a confidence vol- (MEG) with electroencephalograph (EEG) data acquired with a ume less than 1 cm . Dipole locations were calculated and pro- MEG system and individual/cap EEG electrodes. The patient jected onto the patient’s MR imaging where they appear as was asked to be sleep-deprived before the appointment. yellow triangles for interictal spikes. Somatosensory: Somatosensory functioning was assessed by using electrical stimulation of the right and left median nerves, Interictal Epileptiform Discharge Source Modeling Showed each median nerve was tested twice for waveform reproduction. Dipoles From: 200 stimuli were delivered at 800- to 1100-ms intervals. 200 trials Tight/Loose/Scattered cluster in the left/right with stable/ of 300 ms were averaged with a prestimulus baseline of 100 ms variable perpendicular/oblique/parallel orientation. and a 200-ms poststimulus time. Language: Receptive language fields were obtained by binau- Ictal Findings: ral presentation of 180 audio words. The subject was tested twice, No seizures were captured. once in a passive listening mode, and again with the task to overtly repeat 5 target words, when presented. At least 120 trials Somatosensory Findings: were averaged for each test with a 500 seconds prestimulus base- All runs produced robust responses with consistent mapping of line and 1000 ms poststimulus time. corresponding peaks for each run. Motor: The patient was instructed to press a button pad with For stimulation of the left thumb, the latency of N20m index finger of their right and left hand. There were 2 trials run response was msec. for waveform reproduction. The rate of tapping was deliberately For stimulation of the left thumb, the latency of N30m varied but averaged about one tap every 2–3 seconds. Each epoch response was msec. was 2 seconds capturing 100 button press stimuli. For stimulation of the right thumb, the latency of N20m Auditory: 1000 Hz tones were generated and delivered mon- response was msec. aurally without masking at 60-dB hearing loss to ear inserts. For stimulation of the right thumb, the latency of N30m The tone burst consisted of a 250-ms duration tone with a response was msec. 15-ms rise/fall time. The tone burst was repeated 100 times, delivered once every 2 seconds. One hundred trials were aver- Somatosensory Response Source Modeling: aged with a 200-ms prestimulus baseline and 1800 ms poststi- Localized to expected locations. mulus time. Visual: Pattern reversal stimuli were projected into the Language Findings: shielded room, reflected via one mirror onto an opaque white ECD models were calculated every millisecond from 250- to 750- screen, and then reflected directly into the patient’s eyes. The ms poststimulus onset independently for each sensor’s hemi- patient [did/did not] require vision correction glasses [rx L/rx sphere corresponding to left and right evoked fields. All ECD R]. The checkerboard had a 50° radius and size of the projected estimates meeting the statistical thresholds and localizing to tem- checkerboard squares were approximately 5°, which were alter- poral cortical areas were entered into laterality quantification. nated with a refresh rate of 0.4 Hz. Six hundred epochs of hemi- field stimulation were recorded for each hemifield with a 100-ms Language Response Source Modeling: prestimulus baseline and 3000-ms poststimulus time following Receptive language with active word recall task localized to the each pattern shift. The patient was asked to fixate on a single left/right temporal lobe with a laterality index of1/ X.XX, con- spot located just to the left or right of the pattern checkerboard centrated in the Wernicke area. image for hemifield studies. Receptive language with passive listening localized. E52 Maldjian Dec 2022 www.ajnr.org Motor Findings: Auditory Response Source Modeling: Movement of the left second digit generated a good response. Localized to expected locations in the primary auditory cortex. The motor response was seen with a latency of ms following Visual Findings: the activation of the button. All runs produced robust responses with consistent mapping of Movement of the right second digit generated a good response. corresponding peaks for each run. The motor response was seen with a latency of ms following For right visual hemifield mapping, the N75m, P100m, and the activation of the button. N145m responses were easily identified and had typical latencies, waveform morphology, topographic field maps, and dipole Motor Response Source Modeling: moments. Localized to expected locations. For left visual hemifield mapping, the N75m, P100m, and N145m had typical latencies, waveform morphology, topographic Auditory Findings: fieldmaps, anddipole moments. Trials for each ear were performed. The N100m response was a sustained response. The best fields picked to represent the contra- Visual Response Source Modeling: lateral responses had a latency of ms for the left ear stimulation Localized appropriately to the primary visual cortex (V1). and ms for the right ear stimulation. The best fields picked to represent the ipsilateral responses had latency of ms for the left IMPRESSION: ear stimulation and ms for the right ear stimulation. -attending, MD. AJNR Am J Neuroradiol 43:E46–E53 Dec 2022 www.ajnr.org E53
Journal
American Journal of Neuroradiology – American Journal of Neuroradiology
Published: Dec 1, 2022