Assessing ulnar neuropathy at the elbow using magnetoneurography

OBJECTIVE

To measure neuromagnetic fields of ulnar neuropathy patients at the elbow after electrical stimulation and evaluate ulnar nerve function at the elbow with high spatial resolution.

METHODS

A superconducting quantum interference device magnetometer system recorded neuromagnetic fields of the ulnar nerve at the elbow after electrical stimulation at the wrist in 16 limbs of 16 healthy volunteers and 21 limbs of 20 patients with ulnar neuropathy at the elbow. After artifact removal, neuromagnetic field signals were processed into current distributions, which were superimposed onto X-ray images for visualization.

RESULTS

Based on the results in healthy volunteers, conduction velocity of 30 m/s or 50% attenuation in current amplitude was set as the reference value for conduction disturbance. Of the 21 patient limbs, 15 were measurable and lesion sites were detected, whereas 6 limbs were unmeasurable due to weak neuromagnetic field signals. Seven limbs were deemed normal by nerve conduction study, but 5 showed conduction disturbances on magnetoneurography.

CONCLUSIONS

Measuring the magnetic field after nerve stimulation enabled visualization of neurophysiological activity in patients with ulnar neuropathy at the elbow and evaluation of conduction disturbances.

SIGNIFICANCE

Magnetoneurography may be useful for assessing lesion sites in patients with ulnar neuropathy at the elbow.

Efficacy of D-Wave Monitoring Combined With the Transcranial Motor-Evoked Potentials in High-Risk Spinal Surgery: A Retrospective Multicenter Study of the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

STUDY DESIGN

Retrospective multicenter cohort study.

OBJECTIVES

We aimed to clarify the efficacy of multimodal intraoperative neuromonitoring (IONM), especially in transcranial electrical stimulation of motor-evoked potentials (TES-MEPs) with spinal cord-evoked potentials after transcranial stimulation of the brain (D-wave) in the detection of reversible spinal cord injury in high-risk spinal surgery.

METHODS

We reviewed 1310 patients who underwent TES-MEPs during spinal surgery at 14 spine centers. We compared the monitoring results of TES-MEPs with D-wave vs TES-MEPs without D-wave in high-risk spinal surgery.

RESULTS

There were 40 cases that used TES-MEPs with D-wave and 1270 cases that used TES-MEPs without D-wave. Before patients were matched, there were significant differences between groups in terms of sex and spinal disease category. Although there was no significant difference in the rescue rate between TES-MEPs with D-wave (2.0%) and TES-MEPs (2.5%), the false-positivity rate was significantly lower (0%) in the TES-MEPs-with-D-wave group. Using a one-to-one propensity score-matched analysis, 40 pairs of patients from the two groups were selected. Baseline characteristics did not significantly differ between the matched groups. In the score-matched analysis, one case (2.5%) in both groups was a case of rescue (P = 1), five (12.5%) cases in the TES-MEPs group were false positives, and there were no false positives in the TES-MEPs-with-D-wave group (P = .02).

CONCLUSIONS

TES-MEPs with D-wave in high-risk spine surgeries did not affect rescue case rates. However, it helped reduce the false-positivity rate.

Role of Transcranial Motor Evoked Potential Monitoring During Traumatic Spinal Injury Surgery: A Prospective Multicenter Study of the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

STUDY DESIGN

A prospective multicenter observational cohort study.

OBJECTIVE

This study aimed to investigate the role of transcranial motor evoked potential (TcMEP) monitoring during traumatic spinal injury surgery, the timing of TcMEP alerts, and intervention strategies to avoid intraoperative neurological complications.

SUMMARY OF BACKGROUND DATA

Intraoperative neuromonitoring, including TcMEP monitoring, is commonly used in high-risk spinal surgery to predict intraoperative spinal cord injury; however, little information is available on its use in traumatic spinal injury surgery.

METHODS

The TcMEP monitoring data of 350 consecutive patients who underwent traumatic spinal injury surgery (mean age, 69.3 y) between 2017 and 2021 were prospectively reviewed. In this study, a TcMEP amplitude reduction ≥70% was established as a TcMEP alert. A rescue case was defined as a case with the recovery of TcMEP amplitudes after certain procedures and without postoperative neurological complications.

RESULTS

Among the 350 patients who underwent traumatic spinal injury surgery (TcMEP derivation rate 94%), TcMEP monitoring revealed seven true-positive (TP) (2.0%), three rescues (0.9%; rescue rate 30%), 31 false-positive, one false-negative, and 287 true-negative cases, resulting in 88% sensitivity, 90% specificity, 18% positive predictive value, and 99% negative predictive value. The TP rate in patients with preoperative motor deficits was 2.9%, which was higher than that in patients without preoperative motor deficits (1.1%). The most common timing of TcMEP alerts was during decompression (40%). During decompression, suspension of surgery with intravenous steroid injection was ineffective (rescue rate, 0%), and additional decompression was effective.

CONCLUSION

Given the low prevalence of neurological complications (2.3%) and the low positive predictive value (18.4%), single usage of TcMEP monitoring during traumatic spinal injury surgery is not recommended. Further efforts should be made to reduce FP alert rates through better interpretation of multimodal Intraoperative neuromonitorings and the incorporation of anesthesiology to improve the positive predictive value.

LEVEL OF EVIDENCE

3.

Impact of Preoperative Motor Status for the Positive Predictive Value of Transcranial Motor-Evoked Potentials Alerts in Thoracic Spine Surgery: A Prospective Multicenter Study by the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

STUDY DESIGN

Prospective multicenter study.

OBJECTIVE

To investigate the validity of transcranial motor-evoked potentials (Tc-MEP) in thoracic spine surgery and evaluate the impact of specific factors associated with positive predictive value (PPV).

METHODS

One thousand hundred and fifty-six cases of thoracic spine surgeries were examined by comparing patient backgrounds, disease type, preoperative motor status, and Tc-MEP alert timing. Tc-MEP alerts were defined as an amplitude decrease of more than 70% from the baseline waveform. Factors were compared according to preoperative motor status and the result of Tc-MEP alerts. Factors that showed significant differences were identified by univariate and multivariate analysis.

RESULTS

Overall sensitivity was 91.9% and specificity was 88.4%. The PPV was significantly higher in the preoperative motor deficits group than in the preoperative no-motor deficits group for both high-risk (60.3% vs 38.3%) and non-high-risk surgery groups (35.1% vs 12.8%). In multivariate logistic analysis, the significant factors associated with true positive were surgical maneuvers related to ossification of the posterior longitudinal ligament (odds ratio = 11.88; 95% CI: 3.17-44.55), resection of intradural intramedullary spinal cord tumor (odds ratio = 8.83; 95% CI: 2.89-27), preoperative motor deficit (odds ratio = 3.46; 95% CI: 1.64-7.3) and resection of intradural extramedullary spinal cord tumor (odds ratio = 3.0; 95% CI: 1.16-7.8). The significant factor associated with false positive was non-attributable alerts (odds ratio = .28; 95% CI: .09-.85).

CONCLUSION

Surgeons are strongly encouraged to use Tc-MEP in patients with preoperative motor deficits, regardless of whether they are undergoing high-risk spine surgery or not. Knowledge of PPV characteristics will greatly assist in effective Tc-MEP enforcement and minimize neurological complications with appropriate interventions.

Comparison of intraoperative neuromonitoring accuracies and procedures associated with alarms in anterior versus posterior fusion for cervical spinal disorders: A prospective multi-institutional cohort study

A prospective multicenter cohort study. To clarify the differences in the accuracy of transcranial motor-evoked potentials (TcE-MEPs) and procedures associated with the alarms between cervical anterior spinal fusion (ASF) and posterior spinal fusion (PSF). Neurological complications after TcE-MEP alarms have been prevented by appropriate interventions for cervical degenerative disorders. The differences in the accuracy of TcE-MEPs and the timing of alarms between cervical ASF and PSF noted in the existing literature remain unclear. Patients (n = 415) who underwent cervical ASF (n = 171) or PSF (n = 244) at multiple institutions for cervical spondylotic myelopathy, ossification of the posterior longitudinal ligament, spinal injury, and others were analyzed. Neurological complications, TcE-MEP alarms defined as a decreased amplitude of ≤70% compared to the control waveform, interventions after alarms, and TcE-MEP results were compared between the 2 surgeries. The incidence of neurological complications was 1.2% in the ASF group and 2.0% in the PSF group, with no significant intergroup differences (P-value was .493). Sensitivity, specificity, negative predictive value, and rate of rescue were 50.0%, 95.2%, 99.4%, and 1.8%, respectively, in the ASF group, and 80.0%, 90.9%, 99.5%, and 2.9%, respectively, in the PSF group. The accuracy of TcE-MEPs was not significantly different between the 2 groups (P-value was .427 in sensitivity, .109 in specificity, and .674 in negative predictive value). The procedures associated with the alarms were decompression in 3 cases and distraction in 1 patient in the ASF group. The PSF group showed Tc-MEPs decreased during decompression, mounting rods, turning positions, and others. Most alarms went off during decompression in ASF, whereas various stages of the surgical procedures were associated with the alarms in PSF. There were no significant differences in the accuracy of TcE-MEPs between the 2 surgeries.

The Utility of Transcranial Stimulated Motor-Evoked Potential Alerts in Cervical Spine Surgery Varies Based on Preoperative Motor Status

STUDY DESIGN

A prospective multicenter observational study.

OBJECTIVE

The aim was to investigate the validity of transcranial motor-evoked potentials (Tc-MEP) in cervical spine surgery and identify factors associated with positive predictive value when Tc-MEP alerts are occurred.

SUMMARY OF BACKGROUND DATA

The sensitivity and specificity of Tc-MEP for detecting motor paralysis are high; however, false-positives sometimes occur.

MATERIALS AND METHODS

The authors examined Tc-MEP in 2476 cases of cervical spine surgeries and compared patient backgrounds, type of spinal disorders, preoperative motor status, surgical factors, and the types of Tc-MEP alerts. Tc-MEP alerts were defined as an amplitude reduction of more than 70% from the control waveform. Tc-MEP results were classified into two groups: false-positive and true-positive, and items that showed significant differences were extracted by univariate analysis and detected by multivariate analysis.

RESULTS

Overall sensitivity was 66% (segmental paralysis: 33% and lower limb paralysis: 95.8%) and specificity was 91.5%. Tc-MEP outcomes were 33 true-positives and 233 false-positives. Positive predictive value of general spine surgery was significantly higher in cases with a severe motor status than in a nonsevere motor status (19.5% vs . 6.7%, P =0.02), but not different in high-risk spine surgery (20.8% vs . 19.4%). However, rescue rates did not significantly differ regardless of motor status (48% vs . 50%). In a multivariate logistic analysis, a preoperative severe motor status [ P =0.041, odds ratio (OR): 2.46, 95% confidence interval (95% CI): 1.03-5.86] and Tc-MEP alerts during intradural tumor resection ( P <0.001, OR: 7.44, 95% CI: 2.64-20.96) associated with true-positives, while Tc-MEP alerts that could not be identified with surgical maneuvers ( P =0.011, OR: 0.23, 95% CI: 0.073-0.71) were associated with false-positives.

CONCLUSION

The utility of Tc-MEP in patients with a preoperative severe motor status was enhanced, even in those without high-risk spine surgery. Regardless of the motor status, appropriate interventions following Tc-MEP alerts may prevent postoperative paralysis.

Transcranial Motor-evoked Potentials for Intraoperative Nerve Root Monitoring During Adult Spinal Deformity Surgery: A Prospective Multicenter Study

STUDY DESIGN

A prospective, multicenter study.

OBJECTIVE

This study clarified the uses and limitations of transcranial motor-evoked potentials (Tc-MEPs) for nerve root monitoring during adult spinal deformity (ASD) surgeries.

SUMMARY OF BACKGROUND DATA

Whether Tc-MEPs can detect nerve root injuries (NRIs) in ASD surgeries remains controversial.

MATERIALS AND METHODS

We prospectively analyzed neuromonitoring data from 14 institutions between 2017 and 2020. The subjects were ASD patients surgically treated with posterior corrective fusion using multichannel Tc-MEPs. An alert was defined as a decrease of ≥70% in the Tc-MEP's waveform amplitude from baseline, and NRI was considered as meeting the focal Tc-MEP alerts shortly following surgical procedures with postoperative nerve root symptoms in the selected muscles.

RESULTS

A total of 311 patients with ASD (262 women and 49 men) and a mean age of 65.5 years were analyzed. Tc-MEP results revealed 47 cases (15.1%) of alerts, including 25 alerts after 10 deformity corrections, six three-column osteotomies, four interbody fusions, three pedicle screw placements or two decompressions, and 22 alerts regardless of surgical maneuvers. Postoperatively, 14 patients (4.5%) had neurological deterioration considered to be all NRI, 11 true positives, and three false negatives (FN). Two FN did not reach a 70% loss of baseline (46% and 65% loss of baseline) and one was not monitored at target muscles. Multivariate logistic regression analysis revealed that risk factors of NRI were preexisting motor weakness ( P <0.001, odds ratio=10.41) and three-column osteotomies ( P =0.008, odds ratio=7.397).

CONCLUSIONS

Nerve root injuries in our ASD cohort were partially predictable using multichannel Tc-MEPs with a 70% decrease in amplitude as an alarm threshold. We propose that future research should evaluate the efficacy of an idealized warning threshold (e.g., 50%) and a more detailed evoked muscle selection, in reducing false negatives.

Current Trends in Intraoperative Spinal Cord Monitoring: A Survey Analysis among Japanese Expert Spine Surgeons

Introduction

Although intraoperative spinal neuromonitoring (IONM) is recommended for spine surgeries, there are no guidelines regarding its use in Japan, and its usage is mainly based on the surgeon's preferences. Therefore, this study aimed to provide an overview of the current trends in IONM usage in Japan.

Methods

In this web-based survey, expert spine surgeons belonging to the Japanese Society for Spine Surgery and Related Research were asked to respond to a questionnaire regarding IONM management. The questionnaire covered various aspects of IONM usage, including the preferred modality, operation of IONM, details regarding muscle-evoked potential after electrical stimulation of the brain (Br(E)-MsEP), and need for consistent use of IONM in major spine surgeries.

Results

Responses were received from 134 of 186 expert spine surgeons (response rate, 72%). Of these, 124 respondents used IONM routinely. Medical staff rarely performed IONM without a medical doctor. Br(E)-MsEP was predominantly used for IONM. One-third of the respondents reported complications, such as bite injuries caused by Br(E)-MsEP. Interestingly, two-thirds of the respondents did not plan responses to alarm points. Intramedullary spinal cord tumor, scoliosis (idiopathic, congenital, or neuromuscular in pediatric), and thoracic ossification of the posterior longitudinal ligament were representative diseases that require IONM.

Conclusions

IONM has become an essential tool in Japan, and Br(E)-MsEP is a predominant modality for IONM at present. Although we investigated spine surgeries for which consistent use of IONM is supported, a cost-benefit analysis may be required.

Comparison of decompression, decompression plus fusion, and decompression plus stabilization: a long-term follow-up of a prospective, randomized study

BACKGROUND CONTEXT

Lumbar canal stenosis due to degenerative lumbar spondylolisthesis is one of the most common indications for lumbar spinal surgery. However, from a long-term perspective, it is still unclear which of these procedures should be performed: decompression, decompression plus fusion, or decompression plus stabilization.

PURPOSE

This study aimed to present the long-term results of a randomized controlled trial of surgery for degenerative spondylolisthesis.

STUDY DESIGN/SETTING

This is a long-term follow-up of a previously reported randomized controlled trial.

PATIENT SAMPLE

Patients aged ≤75 years with single L4/5 level lumbar canal stenosis caused by degenerative lumbar spondylolisthesis were enrolled at two hospitals from May 1, 2003, to April 30, 2012; the final follow-up was on May 20, 2021.

OUTCOME MEASURES

The following data were collected: modified Japanese Orthopedic Association (JOA) score, visual analog scale (VAS) score for lower back pain, leg pain, and numbness, and scores from eight Short-Form 36 (SF-36) subscales preoperatively, 1 year postoperatively, 5 years postoperatively, and at the final follow-up.

METHODS

Patients were randomized to undergo decompression alone, decompression plus fusion, or decompression plus stabilization. The primary outcome measure was the change in VAS for lower back pain with secondary outcomes including the modified JOA score, VAS for leg pain, VAS for leg numbness, eight SF-36 subscale scores, and occurrence of reoperation at the last follow-up.

RESULTS

Among 85 patients who were randomized, 66 responded to the current survey. The mean follow-up period was 12.3 years. The VAS score for low back pain improvement was not significantly different between the decompression and fusion groups at the mean follow-up of 12.3 years. Of the 12 secondary outcomes, 8 showed no significant difference between decompression and fusion, 12 showed no significant difference between decompression and stabilization, and 10 showed no significant difference between fusion and stabilization.

CONCLUSIONS

Although additional instrumentation surgery did not significantly improve low back pain at the mean follow-up of 12.3 years compared with decompression alone, fusion surgery provided clinically meaningful improvements in patient-reported vitality, social functioning, role limitations due to personal or emotional problems, and mental health compared with decompression alone.

TRIAL REGISTRATION

UMIN000028114.

Risk factors for recurrence and regrowth of spinal schwannoma

BACKGROUND

Spinal schwannoma recurs after initial surgery at a rate of 4%-6%, with known risk factors including subtotal resection, multilevel involvement, large tumor size, and malignant histopathology. This study examined risk factors for schwannoma recurrence and residual tumor regrowth.

METHODS

Sixty-five patients who underwent resection of spinal schwannoma in our department between July 2010 and December 2018 and were followed up for more than 1 year were retrospectively analyzed for age, sex, follow-up duration, imaging and surgical data, recurrence, reoperation, and Japanese Orthopaedic Association scores before and 1 year after surgery. Patients with postoperative recurrence or residual tumor regrowth of >10% at the final visit (R+ group) were compared with patients without recurrence or regrowth (R- group). Multivariate logistic regression analysis was performed to analyze concurrent effects of risk factors on recurrence and regrowth.

RESULTS

The 65 patients (mean age 52.4 years at surgery) had schwannomas involving cervical (n = 14), thoracic (n = 25), and lumbar (n = 26) spinal levels. Mean follow-up duration was 58 months. Location was intradural in 65%, extradural in 17%, and both intradural and extradural in 18%. There were 4 recurrences (6.2%), and the mean interval between surgery and recurrence was 18.8 months. Seven patients (10.8%) experienced regrowth. Comparing group R+ (n = 11) and group R- (n = 54), univariate analysis showed significant differences in Sridhar tumor classification, giant tumor (Sridhar classification II, IVb, and V), left-right and cranial-caudal tumor size, largest diameter, operative time, blood loss, subtotal resection, reoperation, fusion surgery, and follow-up duration. Multivariate logistic regression analysis revealed giant tumor (Sridhar classification types II, IVb, and V) as an independent risk factor for recurrence and regrowth.

CONCLUSIONS

This retrospective review of 65 consecutive patients with spinal schwannoma in a single institution demonstrated that 16.9% had recurrence or regrowth, demonstrating that this potential risk should be kept in mind.

Efficacy of Intraoperative Neuromonitoring Using Transcranial Motor-Evoked Potentials for Degenerative Cervical Myelopathy: A Prospective Multicenter Study by the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

STUDY DESIGN

A prospective multicenter observational study.

OBJECTIVE

To elucidate the efficacy of transcranial motor-evoked potentials (Tc(E)-MEPs) in degenerative cervical myelopathy (DCM) surgery by comparing cervical spondylotic myelopathy (CSM) to cervical ossification of the posterior longitudinal ligament (OPLL) and investigate the timing of Tc(E)-MEPs alerts and types of interventions affecting surgical outcomes.

SUMMARY OF BACKGROUND DATA

Although CSM and OPLL are the most commonly encountered diseases of DCM, the benefits of Tc(E)-MEPs for DCM remain unclear and comparisons of these two diseases have not yet been conducted.

METHODS

We examined the results of Tc(E)-MEPs from 1176 DCM cases (840 CSM /336 OPLL) and compared patients background by disease, preoperative motor deficits, and the type of surgical procedure. We also assessed the efficacy of interventions based on Tc(E)-MEPs alerts. Tc(E)-MEPs alerts were defined as an amplitude reduction of more than 70% below the control waveform. Rescue cases were defined as those in which waveform recovery was achieved after interventions in response to alerts and no postoperative paralysis.

RESULTS

Overall sensitivity was 57.1%, and sensitivity was higher with OPLL (71.4%) than with CSM (42.9%). The sensitivity of acute onset segmental palsy including C5 palsy was 40% (OPLL/CSM: 66.7%/0%) whereas that of lower limb palsy was 100%. The most common timing of Tc(E)-MEPs alerts was during decompression (63.16%), followed by screw insertion (15.79%). The overall rescue rate was 57.9% (OPLL/CSM: 58.3%/57.1%).

CONCLUSION

Since Tc(E)-MEPs are excellent for detecting long tract injuries, surgeons need to consider appropriate interventions in response to alerts. The detection of acute onset segmental palsy by Tc(E)-MEPs was partially possible with OPLL, but may still be difficult with CSM. The rescue rate was higher than 50% and appropriate interventions may have prevented postoperative neurological complications.Level of Evidence: 3.

Does surgical body position influence the risk for neurovascular injury in total hip arthroplasty? A magnetic resonance imaging study

BACKGROUND

Neurovascular injury is a critical complication in total hip arthroplasty (THA). However, neurovascular geographic variations around the hip joint in different body positions have not been examined. This study investigated the differences in hip neurovascular geography in the supine and lateral positions using magnetic resonance imaging (MRI).

HYPOTHESIS

The neurovascular geography of the hip is influenced by differences in surgical body position.

PATIENTS AND METHODS

This was a single-center prospective study of 15 healthy volunteers enrolled between January 2018 and March 2019. Each subject's bilateral hips were scanned with a 3-T MRI scanner in both the supine and lateral positions. In T1-weighted axial images at the level of the hip center, the anterior and posterior acetabular edges were defined as reference points at which retractors are commonly placed during surgery. We measured the distance between the anterior acetabular edge and the femoral nerve (dFN), femoral artery (dFA), and femoral vein (dFV), as well as that between the posterior acetabular edge and the sciatic nerve (dSN). The primary outcome measures were the distances in both the supine and lateral positions.

RESULTS

dFN, dFA, and dFV in the supine and lateral positions (mm, mean±standard deviation) were 25.8±5.6 and 32.4±6.4 (p<0.0001), 25.7±4.5 and 32.2±5.0 (p<0.0001), and 26.5±4.8 and 32.3±5.1 (p<0.0001), respectively. Most of these elements moved anteromedially in the lateral position compared to the supine position. There was no significant difference in dSN between the supine and lateral positions (23.7±4.9 and 24.5±6.5 (p=0.46).

DISCUSSION

THA in the supine position may be accompanied by a higher risk of femoral neurovascular injury than that in the lateral position. The application of our findings could reduce the risk of femoral neurovascular injury during THA.

LEVEL OF EVIDENCE

III; prospective diagnostic case control study.

Anterior Cervical Corpectomy with Fusion versus Anterior Hybrid Fusion Surgery for Patients with Severe Ossification of the Posterior Longitudinal Ligament Involving Three or More Levels: A Retrospective Comparative Study

Various studies have found a high incidence of early graft dislodgement after multilevel corpectomy. Although a hybrid fusion technique was developed to resolve implant failure, the hybrid and conventional techniques have not been clearly compared in terms of perioperative complications in patients with severe ossification of the posterior longitudinal ligament (OPLL) involving three or more levels. The purpose of this study was to compare clinical and radiologic outcomes between anterior cervical corpectomy with fusion (ACCF) and anterior hybrid fusion for the treatment of multilevel cervical OPLL. We therefore retrospectively reviewed the clinical and radiologic data of 53 consecutive patients who underwent anterior fusion to treat cervical OPLL: 30 underwent ACCF and 23 underwent anterior hybrid fusion. All patients completed 2 years of follow-ups. Implant migration was defined as subsidence > 3 mm. There were no significant differences in demographics or clinical characteristics between the ACCF and hybrid groups. Early implant failure occurred significantly more frequently in the ACCF group (5 cases, 16.7%) compared with the hybrid group (0 cases, 0%). The fusion rate was 80% in the ACCF group and 100% in the hybrid group. Although both procedures can achieve satisfactory neurologic outcomes for multilevel OPLL patients, hybrid fusion likely provides better biomechanical stability than the conventional ACCF technique.

Assessment of thoracic spinal cord electrophysiological activity through magnetoneurography

OBJECTIVE

Noninvasive and detailed visualization of electrophysiological activity in the thoracic spinal cord through magnetoneurography.

METHODS

In five healthy volunteers, magnetic fields around current flowing in the thoracic spinal cord after alternating unilateral and synchronized bilateral sciatic nerve stimulation were measured using a magnetoneurograph system with superconductive quantum interference device biomagnetometers. The current distribution was obtained from the magnetic data by spatial filtering and visualized by superimposing it on the X-ray image. Conduction velocity was calculated using the peak latency of the current waveforms.

RESULTS

A sufficiently high magnetic signal intensity and signal-to-noise ratio were obtained in all participants after synchronized bilateral sciatic nerve stimulation. Leading and trailing components along the spinal canal and inward components flowing into the depolarization site ascended to the upper thoracic spine. Conduction velocity of the inward current in the whole thoracic spine was 42.4 m/s.

CONCLUSIONS

Visualization of electrophysiological activity in the thoracic spinal cord was achieved through magnetoneurography and a new method for synchronized bilateral sciatic nerve stimulation. Magnetoneurography is expected to be a useful modality in functional assessment of thoracic myelopathy.

SIGNIFICANCE

This is the first report to use magnetoneurography to noninvasively visualize electrophysiological activity in the thoracic spinal cord in detail.

Understanding the effect of non-surgical factors in a transcranial motor-evoked potential alert: A retrospective cohort study

BACKGROUND

Intraoperative neuromonitoring (IONM) is important for detecting neurological dysfunction, allowing for intervention and reversal of neurological deficits before they become permanent. Of the several IONM modalities, transcranial electrical stimulation of motor-evoked potential (TES-MEP) can help monitor the activity in the pyramidal tract. Surgery- and non-surgery-related factors could result in a TES-MEP alert during surgery. Once the alert occurs, the surgeon should immediately intervene to prevent a neurological complication. However, TES-MEP monitoring does not provide sufficient data to identify the non-surgery-related factors. Therefore, this study aimed to identify and describe these factors among TES-MEP alert cases.

METHODS

In this multicenter study, data from 1934 patients who underwent various spinal surgeries for spinal deformities, spinal cord tumors, and ossification of the posterior longitudinal ligament of the spine from 2017 to 2019 were collected. A 70% amplitude reduction was set as the TES-MEP alarm threshold. All surgeries with alerts were categorized into true-positive (TP) and false-positive (FP) cases according to the assessment of immediate postoperative neurological deficits.

RESULTS

In total, TES-MEP alerts were observed in 251 cases during surgery: 62 TP and 189 FP IONM cases. Overall, 158 cases were related to non-surgery-related factors. We observed 22 (35.5%) TP cases and 136 (72%) FP cases, which indicated cases associated with non-surgery-related factors. A significant difference was observed between the two groups regarding factors associated with TES-MEP alerts (p < 0.01). The ratio of TP and FP cases (related to non-surgery-related factors) associated with TES-MEP alerts was 13.9% (22/158 cases) and 86.1% (136/158 cases), respectively.

CONCLUSIONS

Non-surgery-related factors are proportionally higher in FP than in TP cases. Although the surgeon should examine surgical procedures immediately after a TES-MEP alert, surgical intervention may not always be the best approach according to the results of this study.

Efficacy of Transcranial Motor Evoked Potential Monitoring During Intra- and Extramedullary Spinal Cord Tumor Surgery: A Prospective Multicenter Study of the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

STUDY DESIGN

Multicenter prospective study.

OBJECTIVES

Although intramedullary spinal cord tumor (IMSCT) and extramedullary SCT (EMSCT) surgeries carry high risk of intraoperative motor deficits (MDs), the benefits of transcranial motor evoked potential (TcMEP) monitoring are well-accepted; however, comparisons have not yet been conducted. This study aimed to clarify the efficacy of TcMEP monitoring during IMSCT and EMSCT resection surgeries.

METHODS

We prospectively reviewed TcMEP monitoring data of 81 consecutive IMSCT and 347 EMSCT patients. We compared the efficacy of interventions based on TcMEP alerts in the IMSCT and EMSCT groups. We defined our alert point as a TcMEP amplitude reduction of ≥70% from baseline.

RESULTS

In the IMSCT group, TcMEP monitoring revealed 20 true-positive (25%), 8 rescue (10%; rescue rate 29%), 10 false-positive, a false-negative, and 41 true-negative patients, resulting in a sensitivity of 95% and a specificity of 80%. In the EMSCT group, TcMEP monitoring revealed 20 true-positive (6%), 24 rescue (7%; rescue rate 55%), 29 false-positive, 2 false-negative, and 263 true-negative patients, resulting in a sensitivity of 91% and specificity of 90%. The most common TcMEP alert timing was during tumor resection (96% vs. 91%), and suspension surgeries with or without intravenous steroid administration were performed as intervention techniques.

CONCLUSIONS

Postoperative MD rates in IMSCT and EMSCT surgeries using TcMEP monitoring were 25% and 6%, and rescue rates were 29% and 55%. We believe that the usage of TcMEP monitoring and appropriate intervention techniques during SCT surgeries might have predicted and prevented the occurrence of intraoperative MDs.

Blue and UV-B light synergistically induce anthocyanin accumulation by co-activating nitrate reductase gene expression in Anthocyanin fruit (Aft) tomato

The tomato accession LA1996, which carries a dominant allele of anthocyanin fruit (Aft) locus, accumulates anthocyanins in the epidermis of fruits when exposed to sunlight. The involvement of blue, UV-A, UV-B and a combination of these wavelengths on anthocyanin accumulation and the molecular mechanism of their regulation was investigated in LA1996. The most effective treatment for inducing anthocyanin biosynthesis in Aft fruits was co-irradiation with blue and UV-B (blue + UV-B) light. Finding the correlated genes is an important approach towards understanding their molecular mechanisms. In the present study, the nitrate reductase (NR) gene SlNIA was isolated using RNA-seq profiling of Aft fruits given different light treatments. The functions of NR-mediated anthocyanin induction by blue + UV-B were confirmed using a series of chemical treatments, followed by assessment of NR activity and nitric oxide (NO) detection. The expression of NR was highly induced by blue + UV-B, and this specificity was also confirmed with the enzyme activity of NR and the NO concentration. The NR inhibitors, which reduce NO generation, the expression levels of anthocyanin related genes and decreased anthocyanin accumulation in LA1996. Our results suggest that NR plays a key role in blue + UV-B-mediated anthocyanin accumulation in LA1996 fruits.

Noninvasive measurement of sensory action currents in the cervical cord by magnetospinography

OBJECTIVE

To obtain magnetic recordings of electrical activities in the cervical cord and visualize sensory action currents of the dorsal column, intervertebral foramen, and dorsal horn.

METHODS

Neuromagnetic fields were measured at the neck surface upon median nerve stimulation at the wrist using a magnetospinography system with high-sensitivity superconducting quantum interference device sensors. Somatosensory evoked potentials (SEPs) were also recorded. Evoked electrical currents were reconstructed by recursive null-steering beamformer and superimposed on cervical X-ray images.

RESULTS

Estimated electrical currents perpendicular to the cervical cord ascended sequentially. Their peak latency at C5 and N11 peak latency of SEP were well-correlated in all 16 participants (r = 0.94, p < 0.0001). Trailing axonal currents in the intervertebral foramens were estimated in 10 participants. Estimated dorsal-ventral electrical currents were obtained within the spinal canal at C5. Current density peak latency significantly correlated with cervical N13-P13 peak latency of SEPs in 13 participants (r = 0.97, p < 0.0001).

CONCLUSIONS

Magnetospinography shows excellent spatial and temporal resolution after median nerve stimulation and can identify the spinal root entry level, calculate the dorsal column conduction velocity, and analyze segmental dorsal horn activity.

SIGNIFICANCE

This approach is useful for functional electrophysiological diagnosis of somatosensory pathways.

Increased Height of Fused Segments Contributes to Early-Phase Strut Subsidence after Anterior Cervical Corpectomy with Fusion for Multilevel Ossification of the Posterior Longitudinal Ligament

Introduction

Anterior decompression and fusion have shown favorable neurologic outcomes in patients with cervical myelopathy. However, implant migration sometimes occurs immediately after multilevel anterior cervical corpectomy with fusion (ACCF). Risk factors associated with early bone graft migration have not been precisely documented. The study aimed to investigate how frequently bone graft subsidence occurs after ACCF and to determine the factors affecting implant migration.

Methods

Forty-seven consecutive patients who underwent ACCF for ossification of the posterior longitudinal ligament at our hospital between 2007 and 2015 and were able to complete 1 year of follow-up were enrolled. Patients treated with hybrid fixation were excluded. Data on demographics and radiographic findings, namely, fused segment angle and fused segment height (FSH), were collected. Implant migration was defined as subsidence of >3 mm. The patients were divided into 2-segment (2F), 3-segment (3F), and ≥4-segment (4F) groups. Results were compared between the groups using one-way analysis of variance, the Mann-Whitney U test, and the chi-square test.

Results

Mean age was 61.6 years in the 2F group (n = 17), 62.1 years in the 3F group (n = 21), and 69 years in the 4F group (n = 9). There were no significant between-group differences in demographics or clinical characteristics. Implant subsidence occurred in 3 cases (17.6%) in the 2F group, 4 (19%) in the 3F group, and 3 (33.3%) in the 4F group. Revision surgery was required in 2 cases (1 patient each in the 3F and 4F groups). Logistic regression analysis showed a significant association of increased FSH and increased risk of postoperative implant subsidence.

Conclusions

A postoperative increase in FSH may affect graft stability and lead to early implant migration.

Preoperative risk factors for delirium in patients aged ≥75 years undergoing spinal surgery: a retrospective study

OBJECTIVE

The increasing number of spinal surgeries being performed in the elderly has increased the incidence of postoperative delirium. The prediction of delirium is complex, and few studies have been performed to examine the preoperative risk factors for delirium after spinal surgery in the elderly. This study was performed to clarify such risk factors in patients aged ≥75 years undergoing spinal surgery.

METHOD

This retrospective observational study included 299 patients aged ≥75 years. Comorbidities, medication history, preoperative examination findings, surgery-related characteristics, and health scale assessments, including the 36-Item Short-Form Survey (SF-36) score and prognostic nutritional index (PNI), were examined as potential risk factors for delirium.

RESULTS

Delirium occurred in 53 patients (17.7%). The preoperative risk factors for delirium were a history of stroke and mental disorders, hypnotic drug use, malnutrition, hyponatremia, anemia, respiratory dysfunction, and cervical surgery. Logistic regression analysis demonstrated that the independent predictors of delirium were a history of stroke, non-benzodiazepine hypnotic drug use, preoperative hyponatremia, the PNI, and the SF-36 physical component summary (PCS) score.

CONCLUSIONS

Independent preoperative predictors of delirium in elderly patients undergoing spinal surgery included a history of stroke, non-benzodiazepine hypnotic drug use, preoperative hyponatremia, the PNI, and the SF-36 PCS score.

Surgical Outcomes in Selective Laminectomy and Conventional Double-Door Laminoplasty for Cervical Spondylotic Myelopathy

Several postoperative problems have been reported in conventional cervical laminoplasty (C-LAMP), such as loss of cervical curvature, sagittal imbalance, and loss of range of motion (ROM). Selective laminectomy (S-LAM) is a less invasive procedure that may prevent the problems associated with conventional C-LAMP. In this study, the authors prospectively compared neurological outcomes and radiological parameters in C-LAMP and S-LAM for the treatment of cervical spondylotic myelopathy. Fifty-three patients were enrolled, with 25 patients receiving conventional double-door C-LAMP and 28 patients receiving S-LAM. Measured outcomes included operative time, intraoperative blood loss, Japanese Orthopaedic Association score for neurological recovery, cervical sagittal alignment at C2-7, cervical sagittal vertical axis from occiput to C7, C7 slope, and cervical ROM at C2-7. No difference was found in operative time, whereas intraoperative blood loss was significantly less in the S-LAM group (P<.05). No significant difference in neurological recovery was found between the 2 groups. The postoperative C2-7 angle was significantly smaller (P<.05) and cervical sagittal vertical axis greater (P<.01) in the C-LAMP group. Postoperative ROM at C2-7 was greater (P<.01) in the S-LAM group. In the CLAMP group, postoperative kyphotic change was greater in patients with high C7 slope. However, in the S-LAM group, postoperative sagittal alignment was preserved even in patients with high C7 slope. Postoperative cervical alignment, sagittal balance, and cervical ROM were better preserved in the S-LAM group compared with the C-LAMP group. Selective laminectomy is an effective, minimally invasive method for cervical spondylotic myelopathy with spinal cord compression at limited levels. [Orthopedics. 2020;43(4);e311-e315.].

Visualization of electrophysiological activity at the carpal tunnel area using magnetoneurography

OBJECTIVE

To establish a noninvasive method to measure the neuromagnetic fields of the median nerve at the carpal tunnel after electrical digital nerve stimulation and evaluate peripheral nerve function.

METHODS

Using a vector-type biomagnetometer system with a superconducting quantum interference device, neuromagnetic fields at the carpal tunnel were recorded after electrical stimulation of the index or middle digital nerve in five healthy volunteers. A novel technique for removing stimulus-induced artifacts was applied, and current distributions were calculated using a spatial filter algorithm and superimposed on X-ray.

RESULTS

A neuromagnetic field propagating from the palm to the carpal tunnel was observed in all participants. Current distributions estimated from the magnetic fields had five components: leading and trailing components parallel to the conduction pathway, outward current preceding the leading component, inward currents between the leading and trailing components, and outward current following the trailing component. The conduction velocity and peak latency of the inward current agreed well with those of sensory nerve action potentials.

CONCLUSION

Removing stimulus-induced artifacts enabled magnetoneurography to noninvasively visualize with high spatial resolution the electrophysiological neural activity from the palm to the carpal tunnel.

SIGNIFICANCE

This is the first report of using magnetoneurography to visualize electrophysiological nerve activity at the palm and carpal tunnel.

Preoperative Risk Factors for Adjacent Segment Degeneration after Two-Level Floating Posterior Fusion at L3-L5

Introduction

The aims of this study were to investigate how adjacent segment degeneration (ASD) occurs at the proximal and distal segments after L3-L5 fusion surgery, namely, floating fusion, and to identify the risk factors for ASD in patients who undergo this surgery.

Methods

Fifty patients who underwent floating fusion surgery at vertebrae L3-L5 and developed ASD were enrolled. The following parameters were evaluated: body mass index (BMI), diabetes status, dialysis status, lumbar lordosis, segmental lordosis between the L2 upper endplate and the L3 lower endplate, disc height, Cobb's angle, apical vertebral rotation using the Nash and Moe classification method, preoperative disc degeneration, surgical procedures, and the upper instrumented vertebra (UIV) tilt angle. The UIV tilt angle was defined as positive when the anterior side was directed caudally.

Results

Twenty-two (44%) of the 50 patients showed cephalad radiographic ASD (RASD) and 5 patients (10%) showed caudad RASD. Clinically symptomatic ASD was found at L2-L3 in 4 patients (8%) and at L5-S1 in 2 patients (4%). All the patients with clinically symptomatic cephalad ASD underwent revision procedures for radiculopathy or claudication because of degenerative pathology at L3-L4. Multivariate regression analysis showed a significant association of the absolute value of UIV tilt angle (mean |UIV tilt|) with cephalad RASD (odds ratio 1.09, p = 0.038). Receiver-operating characteristic curve analysis showed a significant association of |UIV tilt| >10.3° with RASD (sensitivity 67.9%, specificity 77.3%, area under the curve [AUC] 0.675).

Conclusions

RASD was more likely to occur at the adjacent segment on the cephalad side than at the adjacent segment on the caudad side after two-segment floating fusion of L3-L5. A preoperative UIV tilt angle >10° or UIV tilt < -10° was a risk factor for RASD.

Visualization of the electrical activity of the cauda equina using a magnetospinography system in healthy subjects

OBJECTIVE

To establish a method to measure cauda equina action fields (CEAFs) and visualize the electrical activities of the cauda equina in a broadly aged group of healthy adults.

METHODS

Using a 124-channel magnetospinography (MSG) system with superconducting interference devices, the CEAFs of 43 healthy volunteers (22-64 years of age) were measured after stimulation of the peroneal nerve at the knee. Reconstructed currents were obtained from the CEAFs and superimposed on the X-ray image. Conduction velocities were also calculated from the waveform of the reconstructed currents.

RESULTS

The reconstructed currents were successfully visualized. They flowed into the L5/S1 foramen about 8.25-8.95 ms after the stimulation and propagated cranially along the spinal canal. In 32 subjects (74%), the conduction velocities of the reconstructed currents in the cauda equina could be calculated from the peak latency at the L2-L5 level.

CONCLUSIONS

MSG visualized the electrical activity of the cauda equina after peroneal nerve stimulation in healthy adults. In addition, the conduction velocities of the reconstructed currents in the cauda equina could be calculated, despite previously being difficult to measure.

SIGNIFICANCE

MSG has the potential to be a novel and noninvasive functional examination for lumbar spinal disease.

Clinical and radiologic outcomes of bone grafted and non-bone grafted double-door laminoplasty, the modified Kirita-Miyazaki method, for treatment of cervical spondylotic myelopathy: Five-year follow-up

PURPOSE

To clarify whether there is any difference in mid-term clinical and radiologic outcomes between bone-grafted laminoplasty (BG LAMP) and non-bone-grafted laminoplasty (non-BG LAMP) when used to treat cervical spondylotic myelopathy.

BACKGROUND

Conventional BG LAMP includes bone grafting at the lamina hinge site to prevent closure of the lamina postoperatively, but it often results in segmental fusion and sometimes causes loss of cervical mobility and lordotic alignment. Non-BG LAMP can now be performed to address this problem and preserve mobility postoperatively. However, there have been no studies comparing BG LAMP and non-BG LAMP to date.

METHODS

Forty-one patients who underwent BG LAMP (n = 24) or non-BG LAMP (n = 17) and had 5 years of follow-up were enrolled in the study. Neurological status was assessed preoperatively and postoperatively using the Japanese Orthopedic Association (JOA) scoring system. The Numeric Rating Scale (NRS) was used to assess neck pain after surgery at the final visit. Radiographic parameters were evaluated at 1, 3, and 5 years after surgery. Postoperative segmental fusion was defined as the level at which the segmental flexion-extension range of motion was <1°.

RESULTS

There was no significant difference in JOA score or recovery rate between the groups. NRS score was significantly lower in the BG group, indicating less neck pain (P < .01). The lordotic angle and range of motion at C2-C7 were significantly decreased in the BG group (P < .05). The segmental fusion was evident from 1 year postoperatively in both groups, but the fusion rate was significantly higher in the BG group (P < .05).

CONCLUSIONS

Neurologic outcomes were similar between the two groups, whereas axial symptom was lower in the BG group than in the non-BG group.

LEVEL OF EVIDENCE

Ⅳ.

Intraoperative 5-aminolevulinic acid-induced photodynamic diagnosis of metastatic brain tumors with histopathological analysis

BACKGROUND

Fluorescence-guided surgery using 5-aminolevulinic acid (5-ALA) is a promising real-time navigation method in the surgical resection of malignant gliomas. In order to determine whether this method is applicable to metastatic brain tumors, we evaluated the usefulness of intraoperative fluorescence patterns and histopathological features in patients with metastatic brain tumors.

METHODS

We retrospectively reviewed the cases of 16 patients with metastatic brain tumors who underwent intraoperative 5-ALA fluorescence-guided resection. Patients were given 20 mg/kg of 5-ALA orally 2 h prior to the surgery. High-powered excitation illumination and a low-pass filter (420, 450, or 500 nm) were used to visualize the fluorescence of protoporphyrin IX (PpIX), the 5-ALA metabolite. We evaluated the relationships between the fluorescence and histopathological findings in both tumoral and peritumoral brain tissue.

RESULTS

Tumoral PpIX fluorescence was seen in only 5 patients (31%); in the remaining 11 patients (69%), there was no fluorescence in the tumor bulk itself. In 14 patients (86%), vague fluorescence was seen in peritumoral brain tissue, at a thickness of 2-6 mm. The histopathological examination found cancer cell invasion of adjacent brain tissue in 75% of patients (12/16), at a mean ± SD depth of 1.4 ± 1.0 mm (range 0.2-3.4 mm) from the microscopic border of the tumor. There was a moderate correlation between vague fluorescence in adjacent brain tissue and the depth of cancer cell invasion (P = 0.004).

CONCLUSION

Peritumoral fluorescence may be a good intraoperative indicator of tumor extent, preceding more complete microscopic gross total resection.

TRIAL REGISTRATION

Institutional Review Board of Osaka Medical College No. 42, registered February 17, 1998, and No. 300, registered April 1, 2008. They were retrospectively registered.

A multi-train electrical stimulation protocol facilitates transcranial electrical motor evoked potentials and increases induction rate and reproducibility even in patients with preoperative neurological deficits

This study sought to evaluate the facilitation effect of repetitive multi-train transcranial electrical stimulation (mt-TES) at 2 repetition rates on transcranial electrical motor evoked potential (Tc-MEP) monitoring during spinal surgery, and to assess the induction rate in patients with impaired motor function from a compromised spinal cord or spinal nerve. We studied 32 consecutive patients with impaired motor function undergoing cervical or thoracic spinal surgery (470 muscles). A series of 10 TESs with 5 pulse trains were preoperatively delivered at 2 repetition rates (1 and 5 Hz). All peak-topeak amplitudes of the MEPs of the upper and lower extremity muscles elicited by the 10 TESs were measured. The induction rates of the lower extremity muscles were also assessed with muscle and preoperative lower extremity motor function scores. In each of the muscles, MEP amplitudes were augmented by about 2-3 times at 1 Hz and 5-6 times at 5 Hz. Under the 5-Hz condition, all limb muscles showed significant amplification. Also, in all preoperative motor function score groups, the amplitudes and induction rates of the lower extremity muscles were significantly increased. Moreover, the facilitation effects tended to peak in the last half of the series of 10 TESs. In all score groups of patients with preoperative neurological deficits, repetitive mt-TES delivered at a frequency of 5 Hz markedly facilitated the MEPs of all limb muscles and increased the induction rate. We recommend this method to improve the reliability of intraoperative monitoring during spinal surgery.

Magnetospinography visualizes electrophysiological activity in the cervical spinal cord

Diagnosis of nervous system disease is greatly aided by functional assessments and imaging techniques that localize neural activity abnormalities. Electrophysiological methods are helpful but often insufficient to locate neural lesions precisely. One proposed noninvasive alternative is magnetoneurography (MNG); we have developed MNG of the spinal cord (magnetospinography, MSG). Using a 120-channel superconducting quantum interference device biomagnetometer system in a magnetically shielded room, cervical spinal cord evoked magnetic fields (SCEFs) were recorded after stimulation of the lower thoracic cord in healthy subjects and a patient with cervical spondylotic myelopathy and after median nerve stimulation in healthy subjects. Electrophysiological activities in the spinal cord were reconstructed from SCEFs and visualized by a spatial filter, a recursive null-steering beamformer. Here, we show for the first time that MSG with high spatial and temporal resolution can be used to map electrophysiological activities in the cervical spinal cord and spinal nerve.

Three-Dimensional Proton Beam Writing of Optically Active Coherent Vacancy Spins in Silicon Carbide

Constructing quantum devices comprises various challenging tasks, especially when concerning their nanoscale geometry. For quantum color centers, the traditional approach is to fabricate the device structure after the nondeterministic placement of the centers. Reversing this approach, we present the controlled generation of quantum centers in silicon carbide (SiC) by focused proton beam in a noncomplex manner without need for pre- or postirradiation treatment. The generation depth and resolution can be predicted by matching the proton energy to the material's stopping power, and the amount of quantum centers at one specific sample volume is tunable from ensembles of millions to discernible single photon emitters. We identify the generated centers as silicon vacancies through their characteristic magnetic resonance signatures and demonstrate that they possess a long spin-echo coherence time of 42 ± 20 μs at room temperature. Our approach hence enables the fabrication of quantum hybrid nanodevices based on SiC platform, where spin centers are integrated into p-i-n diodes, photonic cavities, and mechanical resonators.

Note: Development of real-time epithermal neutron detector for boron neutron capture therapy

The real-time detection of epithermal neutrons forms an important aspect of boron neutron capture therapy. In this context, we developed an epithermal neutron detector based on the combination of a small Eu:LiCaAlF₆ scintillator and a quartz fiber in order to fulfill the irradiation-field requirements for boron neutron capture therapy. The irradiation test is performed with the use of a reactor-based neutron source. The thermal and epithermal neutron sensitivities of our epithermal neutron detector are estimated to be 9.52 × 10^-8 ± 1.59 × 10^-8 cm² and 1.20 × 10^-6 cm² ± 8.96 × 10^-9 cm², respectively. We also subject the developed epithermal neutron detector to actual irradiation fields, and we confirm that the epithermal neutron flux can be measured in realtime.