Use of Electrical Impedance Spectroscopy for Intraoperative Tissue Differentiation During Thyroid and Parathyroid Surgery

The Use of Virtual Tissue Constructs That Include Morphological Variability to Assess the Potential of Electrical Impedance Spectroscopy to Differentiate between Thyroid and Parathyroid Tissues during Surgery

Electrical impedance spectroscopy (EIS) has been proposed as a promising noninvasive method to differentiate healthy thyroid from parathyroid tissues during thyroidectomy. However, previously reported similarities in the in vivo measured spectra of these tissues during a pilot study suggest that this separation may not be straightforward. We utilise computational modelling as a method to elucidate the distinguishing characteristics in the EIS signal and explore the features of the tissue that contribute to the observed electrical behaviour. Firstly, multiscale finite element models (or 'virtual tissue constructs') of thyroid and parathyroid tissues were developed and verified against in vivo tissue measurements. A global sensitivity analysis was performed to investigate the impact of physiological micro-, meso- and macroscale tissue morphological features of both tissue types on the computed macroscale EIS spectra and explore the separability of the two tissue types. Our results suggest that the presence of a surface fascia layer could obstruct tissue differentiation, but an analysis of the separability of simulated spectra without the surface fascia layer suggests that differentiation of the two tissue types should be possible if this layer is completely removed by the surgeon. Comprehensive in vivo measurements are required to fully determine the potential for EIS as a method in distinguishing between thyroid and parathyroid tissues.

Bioelectrical impedance spectroscopy can assist to identify the parathyroid gland during thyroid surgery

OBJECTIVE

This study aimed to explore the effectiveness of bioelectrical impedance spectroscopy in the identification of parathyroid glands during thyroid surgeries.

METHOD

All patients who received thyroid surgeries at our department from January 2018 to February 2020 were recruited for this study. The bioelectrical impedance spectroscopy analyzer was applied to analyze on following tissues: thyroid tissues, lymph nodes, adipose tissues, and the tissues suspected to be parathyroid glands. Postoperative pathological reports were obtained as the golden standard to compare with the characteristic parameters obtained from bioelectrical impedance spectroscopy. The receiver operating characteristic curve analysis was used to assess the diagnostic value and the selection of the optimal threshold of these parameters from bioelectrical impedance spectroscopy.

RESULTS

A total of 512 patients were enrolled in the study and 1898 specimens were measured by the bioelectrical impedance spectroscopy analyzer. There were significant differences in the parameter of f _c among parathyroid glands, thyroid tissues, lymph nodes, and adipose tissues (252.2 ± 45.8 vs 144.7 ± 26.1, 491.7 ± 87.4, 602.3 ± 57.3; P<0.001, P<0.001, P<0.001). The area under the receiver operating characteristic curves was 0.993 (95%CI: 0.989-0.996) for f _c. When the diagnostic criterion of f _c was set at 188.85 kHz~342.55 kHz, the sensitivity and specificity to identify parathyroid glands from lymph nodes and adipose tissues were both 100%. At this f _c, the sensitivity and specificity to identify parathyroid glands from thyroid tissues were 91.1% and 99.0%, respectively.

CONCLUSION

In conclusion, bioelectrical impedance spectroscopy could assist to differentiate parathyroid glands from peripheral tissues during thyroid surgeries.

Tensor electrical impedance myography identifies clinically relevant features in amyotrophic lateral sclerosis

Objective.Electrical impedance myography (EIM) shows promise as an effective biomarker in amyotrophic lateral sclerosis (ALS). EIM applies multiple input frequencies to characterise muscle properties, often via multiple electrode configurations. Herein, we assess if non-negative tensor factorisation (NTF) can provide a framework for identifying clinically relevant features within a high dimensional EIM dataset.Approach.EIM data were recorded from the tongue of healthy and ALS diseased individuals. Resistivity and reactivity measurements were made for 14 frequencies, in three electrode configurations. This gives 84 (2 × 14 × 3) distinct data points per participant. NTF was applied to the dataset for dimensionality reduction, termed tensor EIM. Significance tests, symptom correlation and classification approaches were explored to compare NTF to using all raw data and feature selection.Main Results.Tensor EIM provides highly significant differentiation between healthy and ALS patients (p< 0.001, AUROC = 0.78). Similarly tensor EIM differentiates between mild and severe disease states (p< 0.001, AUROC = 0.75) and significantly correlates with symptoms (ρ= 0.7,p< 0.001). A trend of centre frequency shifting to the right was identified in diseased spectra, which is in line with the electrical changes expected following muscle atrophy.Significance.Tensor EIM provides clinically relevant metrics for identifying ALS-related muscle disease. This procedure has the advantage of using the whole spectral dataset, with reduced risk of overfitting. The process identifies spectral shapes specific to disease allowing for a deeper clinical interpretation.

Geometry Factor Determination for Tetrapolar Impedance Sensor Probes

Even after successful tumor resection, cancer recurrence remains an important issue for bladder tumors. Intra-operative tissue differentiation can help for diagnostic purposes as well as for ensuring that all cancerous cells are completely removed, therefore, decreasing the risk of recurrence. It has been shown that the electrical properties of tumors differ from healthy tissue due to an altered physiology. This work investigates three sensor configurations to measure the impedance of tissue. Each relies on a four terminal measurement and has a distinct electrode arrangement either inline or as a square. Analytical expressions to calculate the geometry factor of each sensor based on Laplace's equation are derived. The results are verified experimentally and in a finite element simulation. Furthermore, several measurements on pig bladders, both fresh and from frozen storage, are carried out with each sensor.It is shown that the calculated and simulated geometry factors yield the same results and are suitable and uncomplicated methods to determine the geometry factor without an experimental setup. These methods also allow for sensor optimization by knowing the measured potentials before the actual fabrication of the sensor. Moreover, conductivity values close to listed data are obtained for pig bladders, which validates the sensors. Ultimately, the square electrode configuration turns out to be a valid option for minimally invasive sensors, which are necessary for the envisaged application of transurethral bladder cancer diagnostics and surgery. This arrangement both assures reliable data and allows for easier miniaturization than the inline electrode placement.

Biopsy Needle System With a Steerable Concentric Tube and Online Monitoring of Electrical Resistivity and Insertion Forces

OBJECTIVE

Biopsies are the gold standard for clinical diagnosis. However, a discrepancy between the biopsy sample and target tissue because of misplacement of the biopsy spoon can lead to errors in the diagnosis and subsequent treatment. Thus, correctly determining whether the needle tip is in the tumor is crucial for accurate biopsy results.

METHODS

A biopsy needle system was designed with a steerable, flexible, and superelastic concentric tube; electrodes to monitor the electrical resistivity; and load cells to monitor the insertion force. The degrees of freedom were analyzed for two working modes: straight-line and deflection.

RESULTS

Experimental results showed that the system could perceive the tissue type in online based on the electrical resistivity. In addition, changes in the insertion force indicated transitions between the interfaces of adjacent tissue layers.

CONCLUSION

The two monitoring methods guarantee that the biopsy spoon is at the desired position inside the tumor during an operation.

SIGNIFICANCE

The proposed biopsy needle system can be integrated into an autonomous robotic biopsy system.

Physical Validation of a Residual Impedance Rejection Method during Ultra-Low Frequency Bio-Impedance Spectral Measurements

Accurate and reliable measurement of the electrical impedance spectrum is an essential requirement in order to draw relevant conclusions in many fields and a variety of applications; in particular, for biological processes. Even in the state-of-the-art methods developed for this purpose, the accuracy and efficacy of impedance measurements are reduced in biological systems, due to the regular occurrence of parameters causing measurement errors such as residual impedance, parasitic capacitance, generator anomalies, and so on. Recent observations have reported the necessity of decreasing such inaccuracies whenever measurements are performed in the ultra-low frequency range, as the above-mentioned errors are almost entirely absent in such cases. The current research work proposes a method which can reject the anomalies listed above when measuring in the ultra-low frequency range, facilitating data collection at the same time. To demonstrate our hypothesis, originating from the consideration of the determinant role of the measuring frequency, a physical model is proposed to examine the effectiveness of our method by measuring across the commonly used vs. ultra-low frequency ranges. Validation measurements reflect that the range of frequencies and the accuracy is much greater than in state-of-the-art methods. Using the proposed new impedance examination technique, biological system characterization can be carried out more accurately.

Systematic review of incidence, risk factors, prevention and treatment of post-laryngectomy hypoparathyroidism

Purpose

Post-laryngectomy hypoparathyroidism is associated with significant short- and long-term morbidities. This systematic review aimed to determine incidence, risk factors, prevention and treatment of post-laryngectomy hypoparathyroidism.

Methods

Medline, EMBASE and the Cochrane library were searched for relevant articles on hypocalcaemia and/or hypoparathyroidism after laryngectomy or pharyngectomy. Two authors independently screened titles and abstracts from the search. Data from individual studies were collated and presented (without meta-analysis). Quality assessment of included studies was undertaken. The review protocol was registered in the PROSPERO database (CRD42019133879).

Results

Twenty-three observational studies were included. The rates of transient and long-term hypoparathyroidism following laryngectomy with concomitant hemi- or total thyroidectomy ranged from 5.6 to 57.1% (n = 13 studies) and 0 to 12.8% (n = 5 studies), respectively. Higher transient (62.1–100%) and long-term (12.5–91.6%) rates were reported in patients who had concomitant oesophagectomy and total thyroidectomy (n = 4 studies). Other risk factors included bilateral selective lateral neck dissection, salvage laryngectomy and total pharyngectomy. There is a lack of data on prevention and management.

Conclusion

Hypoparathyroidism occurs in a significant number of patients after laryngectomy. Patients who underwent laryngectomy with concomitant hemithyroidectomy may still develop hypoparathyroidism. Research on prevention and treatment is lacking and needs to be encouraged.