An experimental study on the early diagnosis of traumatic brain injury in rabbits based on a noncontact and portable system

[Magnetic induced phase shift detection system based on a novel sensor for cerebral hemorrhage]

The main magnetic field, generated by the excitation coil of the magnetic induction phase shift technology detection system, is mostly dispersed field with small field strength, and the offset effect needs to be further improved, which makes the detection signal weak and the detection system difficult to achieve quantitative detection, thus the technology is rarely used in vivo experiments and clinical trials. In order to improve problems mentioned above, a new Helmholtz birdcage sensor was designed. Stimulation experiment was carried out to analyze the main magnetic field in aspects of intensity and magnetic distribution, then different bleeding volume and bleeding rates experiments were conducted to compared with traditional sensors. The results showed that magnetic field intensity in detection region was 2.5 times than that of traditional sensors, cancellation effect of the main magnetic field was achieved, the mean value of phase difference of 10 mL rabbit blood was (-3.34 ± 0.21)°, and exponential fitting adjusted R 2 between phase difference and bleeding volumes and bleeding rates were both 0.99. The proposed Helmholtz birdcage sensor has a uniform magnetic field with a higher field strength, enable more accurate quantification of hemorrhage and monitored change of bleeding rates, providing significance in magnetic induced technology research for cerebral hemorrhage detection.

Conductivity reactivity index for monitoring of cerebrovascular autoregulation in early cerebral ischemic rabbits

BACKGROUND

Cerebrovascular autoregulation (CVAR) is the mechanism that maintains constant cerebral blood flow by adjusting the caliber of the cerebral vessels. It is important to have an effective, contactless way to monitor and assess CVAR in patients with ischemia.

METHODS

The adjustment of cerebral blood flow leads to changes in the conductivity of the whole brain. Here, whole-brain conductivity measured by the magnetic induction phase shift method is a valuable alternative to cerebral blood volume for non-contact assessment of CVAR. Therefore, we proposed the correlation coefficient between spontaneous slow oscillations in arterial blood pressure and the corresponding magnetic induction phase shift as a novel index called the conductivity reactivity index (CRx). In comparison with the intracranial pressure reactivity index (PRx), the feasibility of the conductivity reactivity index to assess CVAR in the early phase of cerebral ischemia has been preliminarily confirmed in animal experiments.

RESULTS

There was a significant difference in the CRx between the cerebral ischemia group and the control group (p = 0.002). At the same time, there was a significant negative correlation between the CRx and the PRx (r = - 0.642, p = 0.002) after 40 min after ischemia. The Bland-Altman consistency analysis showed that the two indices were linearly related, with a minimal difference and high consistency in the early ischemic period. The sensitivity and specificity of CRx for cerebral ischemia identification were 75% and 20%, respectively, and the area under the ROC curve of CRx was 0.835 (SE = 0.084).

CONCLUSION

The animal experimental results preliminarily demonstrated that the CRx can be used to monitor CVAR and identify CVAR injury in early ischemic conditions. The CRx has the potential to be used for contactless, global, bedside, and real-time assessment of CVAR of patients with ischemic stroke.

Early assessment of acute ischemic stroke in rabbits based on multi-parameter near-field coupling sensing

BACKGROUND

Early diagnosis and continuous monitoring are the key to emergency treatment and intensive care of patients with acute ischemic stroke (AIS). Nevertheless, there has not been a fully accepted method targeting continuous assessment of AIS in clinical.

METHODS

Near-field coupling (NFC) sensing can obtain the conductivity related to the volume of intracranial components with advantages of non-invasiveness, strong penetrability and real-time monitoring. In this work, we built a multi-parameter monitoring system that is able to measure changes of phase and amplitude in the process of electromagnetic wave (EW) reflection and transmission. For investigating its feasibility in AIS detection, 16 rabbits were chosen to establish AIS models by bilateral common carotid artery ligation and then were enrolled for monitoring experiments.

RESULTS

During the 6 h after AIS, the reflection amplitude (RA) shows a decline trend with a range of 0.69 dB and reflection phase (RP) has an increased variation of 6.48° . Meanwhile, transmission amplitude (TA) and transmission phase (TP) decrease 2.14 dB and 24.29° , respectively. The statistical analysis illustrates that before ligation, 3 h after ligation and 6 h after ligation can be effectively distinguished by the four parameters individually. When all those parameters are regarded as recognition features in back propagation (BP) network, the classification accuracy of the three different periods reaches almost 100%.

CONCLUSION

These results prove the feasibility of multi-parameter NFC sensing to assess AIS, which is promised to become an outstanding point-of-care testing method in the future.

An amplitude-based characteristic parameter extraction algorithm for cerebral edema detection based on electromagnetic induction

Background

Cerebral edema is a common condition secondary to any type of neurological injury. The early diagnosis and monitoring of cerebral edema is of great importance to improve the prognosis. In this article, a flexible conformal electromagnetic two-coil sensor was employed as the electromagnetic induction sensor, associated with a vector network analyzer (VNA) for signal generation and receiving. Measurement of amplitude data over the frequency range of 1–100 MHz is conducted to evaluate the changes in cerebral edema. We proposed an Amplitude-based Characteristic Parameter Extraction (Ab-CPE) algorithm for multi-frequency characteristic analysis over the frequency range of 1–100 MHz and investigated its performance in electromagnetic induction-based cerebral edema detection and distinction of its acute/chronic phase. Fourteen rabbits were enrolled to establish cerebral edema model and the 24 h real-time monitoring experiments were carried out for algorithm verification.

Results

The proposed Ab-CPE algorithm was able to detect cerebral edema with a sensitivity of 94.1% and specificity of 95.4%. Also, in the early stage, it can detect cerebral edema with a sensitivity of 85.0% and specificity of 87.5%. Moreover, the Ab-CPE algorithm was able to distinguish between acute and chronic phase of cerebral edema with a sensitivity of 85.0% and specificity of 91.0%.

Conclusion

The proposed Ab-CPE algorithm is suitable for multi-frequency characteristic analysis. Combined with this algorithm, the electromagnetic induction method has an excellent performance on the detection and monitoring of cerebral edema.

Noninvasive real-time assessment of intracranial pressure after traumatic brain injury based on electromagnetic coupling phase sensing technology

Background

To investigate the feasibility of intracranial pressure (ICP) monitoring after traumatic brain injury (TBI) by electromagnetic coupling phase sensing, we established a portable electromagnetic coupling phase shift (ECPS) test system and conducted a comparison with invasive ICP.

Methods

TBI rabbits’ model were all synchronously monitored for 24 h by ECPS testing and invasive ICP. We investigated the abilities of the ECPS to detect targeted ICP by feature extraction and traditional classification decision algorithms.

Results

The ECPS showed an overall downward trend with a variation range of − 13.370 ± 2.245° as ICP rose from 11.450 ± 0.510 mmHg to 38.750 ± 4.064 mmHg, but its change rate gradually declined. It was greater than 1.5°/h during the first 6 h, then decreased to 0.5°/h and finally reached the minimum of 0.14°/h. Nonlinear regression analysis results illustrated that both the ECPS and its change rate decrease with increasing ICP post-TBI. When used as a recognition feature, the ability (area under the receiver operating characteristic curve, AUCs) of the ECPS to detect ICP ≥ 20 mmHg was 0.88 ± 0.01 based on the optimized adaptive boosting model, reaching the advanced level of current noninvasive ICP assessment methods.

Conclusions

The ECPS has the potential to be used for noninvasive continuous monitoring of elevated ICP post-TBI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02049-3.

A non-invasive real-time monitoring system for cytotoxic brain edema in post ischemic stroke based on near-field coupling

BACKGROUND

As a common secondary pathophysiological process in postischemic stroke (IS), cytotoxic brain edema (CBE) is an independent factor leading to poor prognosis of patients. Near-field coupling (NFC) technology has some advantages such as non-invasive, non-contact, and unimpeded penetration of the skull. In theory, it can reflect the difference between normal and edema tissues through the near-field coupling phase shift (NFCPS) in the electromagnetic wave transmission trait.

METHODS

Combining NFC detection principle and computer programming, we established a high-performance real-time monitoring system with functions such as automatic setting of measurement parameters, data acquisition, real-time filtering and dynamic waveform display. To investigate the feasibility of this system to detect CBE, a saline simulation experiment and a 24-hour real-time monitoring experiment after middle cerebral artery occlusion (MCAO) in rats were carried out.

RESULTS

The results of the saline simulation experiment showed that the change of NFCPS was proportional to the increase of the simulated edema solution, and the variation range of NFCPS was more than 9∘ after 5 ml injection. In the 24-hour monitoring after MCAO, the NFCPS of the experimental group showed an overall downward trend over time an average change of -17.7868 ± 1.6325∘ and the change rate gradually decreased. The 24-hour NFCPS in the control group fluctuates slightly around the initial value, which has no obvious upward or downward trend.

CONCLUSION

The intragroup and intergroup difference statistical analysis shows that NFCPS can effectively distinguish different intracranial pathophysiological states after IS. This work provides sufficient evidence and a technical basis for using NFCPS to monitor CBE in the future.

A noninvasive flexible conformal sensor for accurate real-time monitoring of local cerebral edema based on electromagnetic induction

Cerebral edema (CE) is a non-specific pathological swelling of the brain secondary to any type of neurological injury. The real-time monitoring of focal CE mostly found in early stage is of great significance to reduce mortality and disability. Magnetic Induction Phase Shift (MIPS) is expected to achieve non-invasive continuous monitoring of CE. However, most existing MIPS sensors are made of hard materials which makes it difficult to accurately retrieve CE information. In this article, we designed a conformal two-coil structure and a single-coil structure, and studied their sensitivity map using finite element method (FEM). After that, the conformal MIPS sensor that is preferable for local CE monitoring was fabricated by flexible printed circuit (FPC). Next, physical experiments were conducted to investigate its performance on different levels of simulated CE solution volume, measurement distance, and bending. Subsequently, 14 rabbits were chosen to establish CE model and another three rabbits were selected as controls. The 24-hour MIPS real-time monitoring experiments was carried out to verify that the feasibility. Results showed a gentler attenuation trend of the conformal two-coil structure, compared with the single-coil structure. In addition, the novel flexible conformal MIPS sensor has a characteristic of being robust to bending according to the physical experiments. The results of animal experiments showed that the sensor can be used for CE monitoring. It can be concluded that this flexible conformal MIPS sensor is desirable for local focusing measurement of CE and subsequent multidimensional information extraction for predicting model. Also, it enables a much more comfortable environment for long-time bedside monitoring.