Non-invasive biomarkers for detecting progression toward hypovolemic cardiovascular instability in a lower body negative pressure model

Occult hemorrhages after trauma can be present insidiously, and if not detected early enough can result in patient death. This study evaluated a hemorrhage model on 18 human subjects, comparing the performance of traditional vital signs to multiple off-the-shelf non-invasive biomarkers. A validated lower body negative pressure (LBNP) model was used to induce progression towards hypovolemic cardiovascular instability. Traditional vital signs included mean arterial pressure (MAP), electrocardiography (ECG), plethysmography (Pleth), and the test systems utilized electrical impedance via commercial electrical impedance tomography (EIT) and multifrequency electrical impedance spectroscopy (EIS) devices. Absolute and relative metrics were used to evaluate the performance in addition to machine learning-based modeling. Relative EIT-based metrics measured on the thorax outperformed vital sign metrics (MAP, ECG, and Pleth) achieving an area-under-the-curve (AUC) of 0.99 (CI 0.95-1.00, 100% sensitivity, 87.5% specificity) at the smallest LBNP change (0-15 mmHg). The best vital sign metric (MAP) at this LBNP change yielded an AUC of 0.6 (CI 0.38-0.79, 100% sensitivity, 25% specificity). Out-of-sample predictive performance from machine learning models were strong, especially when combining signals from multiple technologies simultaneously. EIT, alone or in machine learning-based combination, appears promising as a technology for early detection of progression toward hemodynamic instability.

Rapid patient-specific FEM meshes from 3D smart-phone based scans

Objective.The objective of this study was to describe and evaluate a smart-phone based method to rapidly generate subject-specific finite element method (FEM) meshes. More accurate FEM meshes should lead to more accurate thoracic electrical impedance tomography (EIT) images.Approach.The method was evaluated on an iPhone®that utilized an app called Heges, to obtain 3D scans (colored, surface triangulations), a custom belt, and custom open-source software developed to produce the subject-specific meshes. The approach was quantitatively validated via mannequin and volunteer tests using an infrared tracker as the gold standard, and qualitatively assessed in a series of tidal-breathing EIT images recorded from 9 subjects.Main results.The subject-specific meshes can be generated in as little as 6.3 min, which requires on average 3.4 min of user interaction. The mannequin tests yielded high levels of precision and accuracy at 3.2 ± 0.4 mm and 4.0 ± 0.3 mm root mean square error (RMSE), respectively. Errors on volunteers were only slightly larger (5.2 ± 2.1 mm RMSE precision and 7.7 ± 2.9 mm RMSE accuracy), illustrating the practical RMSE of the method.Significance.Easy-to-generate, subject-specific meshes could be utilized in the thoracic EIT community, potentially reducing geometric-based artifacts and improving the clinical utility of EIT.

Estimating tongue deformation during laryngoscopy using a hybrid FEM-multibody model and intraoperative tracking - a cadaver study

Throat tumour margin control remains difficult due to the tight, enclosed space of the oral and throat regions and the tissue deformation resulting from placement of retractors and scopes during surgery. Intraoperative imaging can help with better localization but is hindered by non-image-compatible surgical instruments, cost, and unavailability. We propose a novel method of using instrument tracking and FEM-multibody modelling to simulate soft tissue deformation in the intraoperative setting, without requiring intraoperative imaging, to improve surgical guidance accuracy. We report our first empirical study, based on four trials of a cadaveric head specimen with full neck anatomy, yields a mean TLE of 10.8 ± 5.5 mm, demonstrating methodological feasibility.

Development of an Electrical Impedance Tomography Coupled Surgical Stapler for Tissue Characterization

OBJECTIVE

This study explores the feasibility of coupling Electrical Impedance Tomography (EIT) to a standard-of-care laparoscopic surgical stapler, stapler+EIT, with the long-term goal of enabling intraoperative tissue differentiation for tumor margin detection.

METHODS

Two custom printed-circuit-board-based electrode arrays with 60 and 8 electrodes, respectively, matching the stapler geometry, served as the jaws of an electrode-integrated surrogate stapler+EIT device. The device was evaluated through a series of simulations and bench-top imaging experiments of agar-gel phantoms and bovine tissue samples to evaluate the technique and determine optimal imaging parameters.

RESULTS

Electrodes localized to only one jaw (the 60-electrode side) of the stapler outperformed a dual-jaw distribution of electrodes. Using this one-sided electrode array, reconstructions achieved an Area-Under-the-Curve (AUC) ≥ 0.94 for inclusions with conductivity contrasts of ≥30% for any size considered on measured agar-gel tests, and an AUC of 0.80 for bovine tissue samples.

CONCLUSION

A stapler+EIT algorithm has been tuned and evaluated on challenging phantom tests and demonstrated to produce accurate reconstructions.

SIGNIFICANCE

This work is an important step in the development of a surgical stapler+EIT technique for margin assessment.

Towards intraoperative surgical margin assessment: Validation of an electrical impedance-based probe with ex vivo bovine tissue

Radical prostatectomy (RP) is a common surgical therapy to treat prostate cancer. The procedure has a high positive surgical margin (PSM) rate ranging from 4-48%. Patients with PSMs have a higher rate of cancer recurrence and often undergo noxious adjuvant therapy. Intraoperative surgical margin assessment (SMA) with an electrical impedance-based probe can potentially identify PSMs in real-time. This would enable surgeons to make data-based decisions in the operating room to improve patient outcomes. This paper focuses on characterizing an impedance sensing SMA probe with specialized electrodes to improve speed and bandwidth while maintaining accuracy. 3D electrical impedance tomography (EIT) reconstructions were generated from ex vivo bovine tissue to characterize probe imaging and to determine an optimal applied pressure range (15 Pa to 38 Pa). Classification accuracy of adipose and muscle tissue was evaluated by comparing the experimental data set to simulated data based on a ground truth binary map of the tissue. Experimental AUCs ≥0.83 were maintained up to 50 kHz. The developed impedance sensing probe successfully classified between muscle and adipose tissue in an ex vivo bovine model. Future work includes improving performance of the SMA probe with custom hardware and collecting data from ex vivo and in vivo prostatic tissues.Clinical Relevance-This technology is expected to reduce the rate of PSMs in RP and decrease the use of post-surgical adjuvant therapies. It is also anticipated that intraoperative impedance measurements will increase efficacy of nerve sparing procedures and reduce complications such as incontinence and erectile dysfunction.

Brain responses to food viewing in women during pregnancy and post partum and their relationship with metabolic health: study protocol for the FOODY Brain Study, a prospective observational study

INTRODUCTION

Food cravings are common in pregnancy and along with emotional eating and eating in the absence of hunger, they are associated with excessive weight gain and adverse effects on metabolic health including gestational diabetes mellitus (GDM). Women with GDM also show poorer mental health, which further can contribute to dysregulated eating behaviour. Food cravings can lead to greater activity in brain centres known to be involved in food 'wanting' and reward valuation as well as emotional eating. They are also related to gestational weight gain. Thus, there is a great need to link implicit brain responses to food with explicit measures of food intake behaviour, especially in the perinatal period. The aim of this study is to investigate the spatiotemporal brain dynamics to visual presentations of food in women during pregnancy and in the post partum, and link these brain responses to the eating behaviour and metabolic health outcomes in women with and without GDM.

METHODS AND ANALYSIS

This prospective observational study will include 20 women with and 20 without GDM, that have valid data for the primary outcomes. Data will be assessed at 24-36 weeks gestational age and at 6 months post partum. The primary outcomes are brain responses to food pictures of varying carbohydrate and fat content during pregnancy and in the post partum using electroencephalography. Secondary outcomes including depressive symptoms, current mood and eating behaviours will be assessed with questionnaires, objective eating behaviours will be measured using Auracle and stress will be measured with heart rate and heart rate variability (Actiheart). Other secondary outcome measures include body composition and glycaemic control parameters.

ETHICS AND DISSEMINATION

The Human Research Ethics Committee of the Canton de Vaud approved the study protocol (2021-01976). Study results will be presented at public and scientific conferences and in peer-reviewed journals.

Design of electrical impedance spectroscopy sensing surgical drill using computational modelling and experimental validation

Electrical Impedance Spectroscopy (EIS) sensing surgical instruments could provide valuable and real-time feedback to surgeons about hidden tissue boundaries, therefore reducing the risk of iatrogenic injuries. In this paper, we present an EIS sensing surgical drill as an example instrument and introduce a strategy to optimize the mono-polar electrode geometry using a finite element method (FEM)-based computational model and experimental validation. An empirical contact impedance model and an adaptive mesh refinement protocol were developed to accurately preserve the behaviour of sensing electrodes as they approach high impedance boundaries. Specifically, experiments with drill-bit, cylinder, and conical geometries suggested a 15%-35% increase in resistance as the sensing electrode approached a high impedance boundary. Simulations achieved a maximum mean experiment-to-simulation mismatch of +1.7% for the drill-bit and +/-11% range for other electrode geometries. The simulations preserved the increase in resistance behaviour near the high impedance boundary. This highly accurate simulation framework allows us a mechanism for optimizing sensor geometry without costly experimental evaluation.

Bioimpedance Sensing Surgical Drill - In Vivo Porcine Model

Surgical drilling to place dental implants in the mandible and maxilla is associated high risk of iatrogenic injuries to inferior alveolar nerve and maxillary sinus. Real-time tissue margin sensing at the drill-tip using electrical impedance spectroscopy (EIS) could reduce this risk by providing feedback to surgeons. Studies with saline analogues, ex-vivo tissues, in-situ tissues and computer models have been previously conducted to evaluate these impedance sensors. Understanding in-vivo electrical properties of tissues in the mandible and maxilla is critical to further develop the sensor and tissue margin sensing algorithms. In this paper, we propose an in-vivo animal model using pigs and discuss methods to test the sensor. Intra-operative imaging and optical tracking systems to assist in surgical navigation are described. The process of registering imaging and tracking information to localize impedance measurement sites within the anatomy are detailed. Results from one in-vivo case of drilling through the mandible are presented and discussed. Clinical Relevance- This model is crucial for characterizing in-vivo electrical properties of mandibular and maxillary tissues encountered during dental implant surgical drilling and for translating bioimpedance sensing drill technology to clinical space.

A particle filter approach to dynamic kidney pose estimation in robotic surgical exposure

PURPOSE

Traditional soft tissue registration methods require direct intraoperative visualization of a significant portion of the target anatomy in order to produce acceptable surface alignment. Image guidance is therefore generally not available during the robotic exposure of structures like the kidneys which are not immediately visualized upon entry into the abdomen. This paper proposes guiding surgical exposure with an iterative state estimator that assimilates small visual cues into an a priori anatomical model as exposure progresses, thereby evolving pose estimates for the occluded structures of interest.

METHODS

Intraoperative surface observations of a right kidney are simulated using endoscope tracking and preoperative tomography from a representative robotic partial nephrectomy case. Clinically relevant random perturbations of the true kidney pose are corrected using this sequence of observations in a particle filter framework to estimate an optimal similarity transform for fitting a patient-specific kidney model at each step. The temporal response of registration error is compared against that of serial rigid coherent point drift (CPD) in both static and simulated dynamic surgical fields, and for varying levels of observation persistence.

RESULTS

In the static case, both particle filtering and persistent CPD achieved sub-5 mm accuracy, with CPD processing observations 75% faster. Particle filtering outperformed CPD in the dynamic case under equivalent computation times due to the former requiring only minimal persistence.

CONCLUSION

This proof-of-concept simulation study suggests that Bayesian state estimation may provide a viable pathway to image guidance for surgical exposure in the abdomen, especially in the presence of dynamic intraoperative tissue displacement and deformation.

Detection of subclinical hemorrhage using electrical impedance: a porcine study

OBJECTIVE

Analyze the performance of electrical impedance tomography (EIT) in an innovative porcine model of subclinical hemorrhage and investigate associations between EIT and hemodynamic trends.

APPROACH

Twenty-five swine were bled at slow rates to create an extended period of subclinical hemorrhage during which the animal's heart rate (HR) and blood pressure (BP) remained stable from before hemodynamic deterioration, where stable was defined as < 15% decrease in BP and < 20% increase in HR - i.e. hemorrhages were hidden from standard vital signs of HR and BP. Continuous vital signs, photo-plethysmography, and continuous non-invasive EIT data were recorded and analyzed with the objective of developing an improved means of detecting subclinical hemorrhage - ideally as early as possible.

MAIN RESULTS

Best area-under-the-curve (AUC) values from comparing bleed to no-bleed epochs were 0.96 at a 80 ml bleed (~15.4 minutes) using an EIT-data-based metric and 0.79 at a 120 ml bleed (~23.1 minutes) from invasively measured BP - i.e. the EIT-data-based metric achieved higher AUCs at earlier points compared to standard clinical metrics without requiring image reconstructions.

SIGNIFICANCE

In this clinically relevant porcine model of subclinical hemorrhage, EIT appears to be superior to standard clinical metrics in early detection of hemorrhage.

Quantifying Tumor and Vasculature Deformations during Laryngoscopy

Retractors and scopes used in head and neck surgery to provide adequate surgical exposure also deform critical structures in the region. Surgeons typically use preoperative imaging to plan and guide their tumor resections, however the large tissue deformation resulting from placement of retractors and scopes reduces the utility of preoperative imaging as a reliable roadmap. We quantify the extent of tumor and vasculature deformation in patients with tumors of the larynx and pharynx undergoing diagnostic laryngoscopy. A mean tumor displacement of 1.02 cm was observed between the patients' pre- and intra-operative states. Mean vasculature displacement at key bifurcation points was 0.99 cm. Registration to the hyoid bone can reduce tumor displacement to 0.67 cm and improve carotid stem angle deviations but increase overall vasculature displacement. The large deformation results suggest limitations in reliance on preoperative imaging and that using specific landmarks intraoperatively or having more intraoperative information could help to compensate for these deviations and ultimately improve surgical success.

Novel Electrode Placement in Electrical Bioimpedance-Based Stroke Detection: Effects on Current Penetration and Injury Characterization in a Finite Element Model

OBJECTIVE

Reducing time-to-treatment and providing acute management in stroke are essential for patient recovery. Electrical bioimpedance (EBI) is an inexpensive and non-invasive tissue measurement approach that has the potential to provide novel continuous intracranial monitoring-something not possible in current standard-of-care. While extensive previous work has evaluated the feasibility of EBI in diagnosing stroke, high-impedance anatomical features in the head have limited clinical translation.

METHODS

The present study introduces novel electrode placements near highly-conductive cerebral spinal fluid (CSF) pathways to enhance electrical current penetration through the skull and increase detection accuracy of neurologic damage. Simulations were conducted on a realistic finite element model (FEM). Novel electrode placements at the tear ducts, soft palate and base of neck were evaluated. Classification accuracy was assessed in the presence of signal noise, patient variability, and electrode positioning.

RESULTS

Algorithms were developed to successfully determine stroke etiology, location, and size relative to impedance measurements from a baseline scan. Novel electrode placements significantly increased stroke classification accuracy at various levels of signal noise (e.g. p < 0.001 at 40 dB). Novel electrodes also amplified current penetration, with up to 30% increase in current density and 57% increased sensitivity in central intracranial regions (p<0.001).

CONCLUSION

These findings support the use of novel electrode placements in EBI to overcome prior limitations, indicating a potential approach to increasing the technology's clinical utility in stroke identification.

SIGNIFICANCE

A non-invasive EBI monitor for stroke could provide essential timely intervention and care of stroke patients.

CT for estimating adequacy of lymph node dissection in patients with squamous cell carcinoma of the head and neck

Background

Indices obtained from lymph node dissection specimens, specifically lymph node yield (LNY) and lymph node ratio (LNR), have prognostic significance in the setting of head and neck squamous cell carcinoma (HNSCCa). However, there are currently no validated tools to estimate adequacy of planned lymph node dissection using preoperative data. The present study sought to evaluate CT-derived estimates of lymphatic tissue volumes as a preoperative tool to guide cervical node dissection.

Methods

Fifteen cervical lymph node dissections were performed in 14 subjects with HNSCCa. Preoperative CT-derived estimates of lymphatic tissue volumes were compared with gross pathology tissue volume estimates and pathologically-determined LNY.

Results

Resected tissue volume (calculated using the triaxial ellipsoid method) correlates with CT-derived preoperative lymphatic volume estimates (r = 0.74, p = 0.003) while LNY does not(r = − 0.12, p = 0.67). When excluding pathologically enlarged lymph nodes (“refined” data), a negative correlation was observed between refined CT-derived volume estimates and refined LNY (r = − 0.65, p = 0.009).

Conclusion

In the setting of cervical lymph node dissection, CT-derived lymphatic volume estimates correlate with resected tissue volume, but refined CT-derived volume estimates correlate negatively with refined LNY.

Trial registration

Retrospectively registered.

Level of evidence

4

BandPass: A Bluetooth-Enabled Remote Monitoring Device for Sarcopenia

As the United States population ages, managing pathologies that largely affect older adults, including sarcopenia (i.e., loss of muscle mass and strength) represents a significant and growing clinical challenge. In addition to increased rates of sarcopenia with age, its incidence and impact increase after acute illness, increasing the risk of functional decline, institutionalization, or death. Resistance-based exercises promote muscle regeneration and strength and are an advised therapy for such patients. Yet, such therapeutic exercises are normally conducted either under direct clinical oversight or unsupervised by patients at home, where compliance rates are low. The presented device, BandPass, aims to create an integrated force data detection and acquisition system for monitoring and transmitting at-home exercise force data to patients and clinicians. A potentiometer-based sensor was integrated to a resistance exercise band through the use of custom designed electronics, which incorporated Bluetooth Low Energy (BLE) for wireless transmission to a mobile 'app'. A protocol for calibrating the device was developed using a range of loads and validated in static benchtop and dynamic testing. Data from a pilot study with 7 older adults was also collected and analyzed to test the device. BandPass is 94% accurate with a coefficient of variation (CoV) of 4.9% and sensitivity of 150g. The pilot study recorded 147 exercises, allowing for analysis on patients' exercise performances. BandPass was successfully able to measure force continuously over time during exercises, measure longitudinal compliance with exercises, and quantify force continuously over time. A mobile health (mHealth) force-sensing system allows for the remote monitoring of prescribed in-home resistance exercise band programs for at-risk older adults, bridging the gap between clinicians and patients.

Proposed mechanism for reduced jugular vein flow in microgravity

Internal jugular flow is reduced in space compared with supine values, which can be associated with internal jugular vein (IJV) thrombosis. The mechanism is unknown but important to understand to prevent potentially serious vein thromboses on long duration flights. We used a novel, microgravity‐focused numerical model of the cranial vascular circulation to develop hypotheses for the reduced flow. This model includes the effects of removing hydrostatic gradients and tissue compressive forces – unique effects of weightlessness. The IJV in the model incorporates sensitivity to transmural pressure across the vein, which can dramatically affect resistance and flow in the vein. The model predicts reduced IJV flow in space. Although tissue weight in the neck is reduced in weightlessness, increasing transmural pressure, this is more than offset by the reduction in venous pressure produced by the loss of hydrostatic gradients and tissue pressures throughout the body. This results in a negative transmural pressure and increased IJV resistance. Unlike the IJV, the walls of the vertebral plexus are rigid; transmural pressure does not affect its resistance and so its flow increases in microgravity. This overall result is supported by spaceflight measurements, showing reduced IJV area inflight compared with supine values preflight. Significantly, this hypothesis suggests that interventions that further decrease internal IJV pressure (such as lower body negative pressure), which are not assisted by other drainage mechanisms (e.g. gravity), might lead to stagnant flow or IJV collapse with reduced flow, which could increase rather than decrease the risk of venous thrombosis.

Usability Assessment of a Bluetooth-Enabled Resistance Exercise Band Among Young Adults

Background

Resistance-based exercises effectively enhance muscle strength, which is especially important in older populations as it reduces the risk of disability. Our group developed a Bluetooth-enabled handle for resistance exercise bands that wirelessly transmits relative force data through low-energy Bluetooth to a local smartphone or similar device. We present a usability assessment that evaluates an exercise system featuring a novel Bluetooth-enabled resistance exercise band, ultimately intended to expand the accessibility of resistance training through technology-enhanced home-based exercise programs for older adults. Although our target population is older adults, we assess the user experience among younger adults as a convenient and meaningful starting point in the testing and development of our device.

Methods

There were 32 young adults participating in three exercise sessions with the exercise band, after which each completed an adapted version of the Usefulness, Satisfaction, and Ease (USE) questionnaire to characterize the exercise system's strengths and weaknesses in usability.

Results

Questionnaire data reflected a positive and consistent user experience, with all 20 items receiving mean scores greater than 5.0 on a seven-point Likert scale. There were no specific areas of significant weakness in the device's user experience.

Conclusions

The positive reception among young adults is a promising indication that the device can be successfully incorporated into exercise interventions and that the system can be further developed and tested for the target population of older adults.

Remote Rehabilitation: A Field-Based Feasibility Study of an mHealth Resistance Exercise Band

Sarcopenia is the age-related loss of muscle mass and strength that is associated with adverse health outcomes. Resistance-based exercises are effective for mitigation and enhancement of strength; however, adherence is low and challenging to measure when patients are at home. In a single-arm, pilot study of seven older adults, we conducted a field-based usability study evaluating the feasibility and acceptability of using a system consisting of a Bluetooth-connected resistance exercise band and tablet-based app which together we call BandPass in completing four different home-based exercises. The system measured a total of 147 exercises by participants with a mean duration of 94±66 seconds, completing an average of 30±20 repetitions. Though not all patients completed each exercise type, patients were positive about use: patient activation measure: 80.7±14; system usability scale: 6.9±2.9; and confidence in use: 7.7±2.7. The BandPass system demonstrated its ability to collect data on exercise type, force during an exercise, and duration of exercise when older adults use it for monitoring exercise at home.

Phantom Studies of Fused-Data TREIT Using Only Biopsy-Probe Electrodes

Transrectal electrical impedance tomography (TREIT) is a novel imaging modality being developed for prostate biopsy guidance and cancer characterization. We describe a novel fused-data TREIT (fd-TREIT) system and approach developed to improve imaging robustness and evaluate it on challenging clinically-representative phantoms. The new approach incorporates 8 electrodes (in 2 rows) on a biopsy probe (BP) and 12 electrodes on the face of a transrectal ultrasound (TRUS) probe and includes a biopsy gun, instrument tracking, 3D-printed needle guide, and EIT hardware and software. The approach was evaluated via simulation, a series of prostate-shaped gel phantoms, and an ex vivo bovine tissue sample using only absolute reconstructions. The simulations surprisingly found that using only biopsy-probe electrode measurements, i.e. omitting TRUS-probe electrode measurements, significantly improves robustness to noise thus leading to simpler modeling and significant decreases in computational times (~13x speed-up/reconstructions in ~27 minutes). The gel phantom experiments resulted in reconstructions with area under the curve (AUC) values extracted from receiver operator characteristic curves of >0.85 for 4 out of the 5 tests, and when incorporating inclusion boundaries resulted in absolute reconstructions yielding 1.9% and 12.2% average percent errors for 3 consistent tests and all 5 tests, respectively. Ex vivo bovine tests revealed qualitatively that the fd-TREIT approach can largely discriminate a complex adipose and muscle interface in a realistic setting using data from 9 biopsy probe states (biopsy core locations). The algorithms developed here on challenging phantoms suggest strong promise for this technology to aid in imaging during routine 12-core biopsies.

Bioimpedance Sensing Surgical Drill - Computational Modelling and Experimental Validation

Surgical drilling to fixate dental implants is associated with high risk of injury to the inferior alveolar nerve (IAN) and the maxillary sinus. Current common practice is to use pre-operative radiographs to plan and drill with no real-time feedback of drill tip position with respect to these critical structures. Real-time proximity sensing of the IAN and maxillary sinus by measuring the electrical impedance properties of tissues, directly from the drill tip, while drilling may reduce and eventually eliminate this risk. Sensing impedance to detect tissue boundaries needs sensor geometry optimization for maximum detection distance. We have created a finite element method (FEM) based simulation platform that yields accurately impedances for different conductivities, frequencies and sensor geometries.

Cardiac eigen imaging: a novel method to isolate cardiac activity in thoracic electrical impedance tomography

OBJECTIVE

As the global burden of cardiovascular disease increases, proactive cardiovascular healthcare by means of accurate, precise, continuous, and non-invasive monitoring is becoming crucial. However, no current device is able to provide cardiac hemodynamic monitoring with the aforementioned criterion. Electrical impedance tomography (EIT) is an inexpensive, non-invasive imaging modality that can provide real-time images of internal conductivity distributions that describe physiological activity. This work explores and compares a standard approach of regular cardiac gated averaging (RCGA) and a newly developed method, cardiac eigen-imaging (CEI), based on the singular value decomposition (SVD) to isolate cardiac activity in thoracic EIT.

APPROACH

EIT and heart-rate (HR) data were collected from 20 heart-failure patients preceding echocardiography. Features from RCGA and CEI images were correlated with stroke volume (SV) from echocardiography and image reconstruction parameters were optimized using leave-one-out (LOO) cross-validation.

MAIN RESULTS

CEI per-pixel-based features achieved a Pearson correlation coefficient of 0.80 with SV relative to 0.72 with RCGA. CEI had 33 high-correlating pixels while RCGA had 8. High-correlating pixels tend to concentrate in the right-ventricle (RV) when referenced to a general chest model.

SIGNIFICANCE

While both RCGA and CEI images had high-correlating pixels, CEI had higher correlations, a larger number of high-correlating pixels, and unlike RCGA is not dependent on the quality of the HR data collected. The observed performance of the CEI approach represents a promising step forward for EIT-based cardiac monitoring in either clinical or ambulatory settings.

A 1 MHz Miniaturized Electrical Impedance Tomography System for Prostate Imaging

An ASIC for a high frequency electrical impedance tomography (EIT) imaging system for prostate cancer screening is presented. The ASIC enables a small form-factor architecture, which ensures high signal-to-noise ratio (SNR) at MHz frequencies. The 4-channel ASIC was designed and fabricated in a standard CMOS 0.18- μm technology and integrates a novel current driver for current stimulus, instrumentation amplifier to interface with the tissue, VGA to provide variable gain and ADC with SPI interface for digitization. A prototype miniaturized EIT system was built and it was evaluated using a model transrectal imaging probe immersed into a tank filled with saline and a metal inclusion that demonstrated the open-domain problem of imaging prostate cancer lesion. The system maintained an SNR between 66 and 76 dB over the frequency range of 500 Hz to 1 MHz. Also, it produced reconstructed EIT images that depicted the presence of the small metal inclusion that modeled a prostate cancer imaging application.

A robust and novel electrical impedance metric of pulmonary function in ALS patients

OBJECTIVE

Pulmonary function tests (PFTs) are important for assessing respiratory function in amyotrophic lateral sclerosis (ALS) patients. However, weakness of oral and glottal closure, due to concomitant bulbar dysfunction, may result in unreliable PFT values stemming from leakage of air around the breathing tube and through the glottis. In this study, we assessed whether standard thoracic electrical impedance tomography (EIT) could serve as a surrogate measure for PFTs.

APPROACH

Thoracic EIT was performed simultaneously with standard PFTs on seven ALS patients without clinical bulbar weakness (six men and one woman, mean age of 63 years) and ten healthy volunteers (seven men and three women, mean age of 57 years). A raw impedance metric along with more standard EIT measures were computed and correlated with the normalized forced vital capacity (FVC). Additionally, test/re-test metrics and EIT images were analyzed.

MAIN RESULTS

The impedance metric was found to be robust and sensitive to lung activity. We also identified qualitative EIT differences between healthy volunteers and ALS patients, with the ALS images showing greater heterogeneity. Significant correlations with FVC were found for both impedance and EIT metrics in ALS patients (r² = 0.89) and for the impedance metric only in healthy volunteers (r² = 0.49).

SIGNIFICANCE

This suggests that EIT, using our novel impedance metric, has the potential to serve as an alternative technology to standard PFTs for assessing pulmonary function in patients with ALS, offering new metrics of disease status for those with bulbar weakness.

A System for Characterizing Intraoperative Force Distribution During Operative Laryngoscopy

OBJECTIVE

This study aimed to create and validate an integrated data acquisition system for gauging the force distribution between a laryngoscope and soft-tissue during trans-oral surgery.

METHODS

Sixteen piezoresistive force sensors were interfaced to a laryngoscope and custom maxillary tooth guard. A protocol for calibrating the laryngoscope and maxilla sensors was developed using a motor-controlled linear stage and force measurements were validated against a digital scale. The system was initially tested during suspension laryngoscopy on three cadaver heads mounted on a cadaver head-holder. Intraoperative data was also collected from three patients undergoing head and neck tumor resection.

RESULTS

Mean calibration error of the scope sensors was less than 150 g (n = 3) and mean maxilla sensor error was less than 200 g (n = 3). Peak scope mag-forces of 8.09 ± 6.61 kg and peak maxilla forces of 7.62 ± 4.57 kg were experienced during the cadaver trials. The peak scope sensor mag-force recorded during the intraoperative cases was 24.7 ± 4.53 kg, and the peak maxilla force was 22.0 ± 4.60 kg.

CONCLUSION

The data acquisition system was successfully able to record intraoperative force distribution data. The usefulness of this technology in informing surgeons during trans-oral surgery should be further evaluated in patients with varying anatomic and procedural characteristics.

SIGNIFICANCE

Creation of a low-cost, integrated force-sensing system allows for the characterization of retraction forces at anatomic sites including the pharynx and larynx, brain, and abdomen. Real-time force detection provides surgeons with valuable intraoperative feedback and can be used to improve deformation models at various anatomic sites.

Multi-modal Framework for Image-guided Trans-oral Surgery with Intraoperative Imaging and Deformation Modeling

Treatment of throat cancers have improved due to minimally-invasive trans-oral approaches. Surgeons rely on preoperative imaging to guide their resection; however, large tissue deformations occur during trans-oral procedures due to placement of necessary retractors and laryngoscopes which hinders the surgeon's ability to accurately assess tumor extent and location of critical structures. We propose an image-guided framework utilizing intraoperative imaging and deformation modeling to improve surgeon accuracy and confidence. A CT-compatible laryngoscopy system previously developed was evaluated in this framework. Intraoperative images were acquired during laryngoscopy; force-sensing capabilities were enabled in the laryngoscope; and tracking of the scope and anatomic features was trialed. Tissue deformation and displacement were quantified and determined to be extensive, with values <; 4.6 cm in the tongue, <; 1.8 cm in bony structures, and <; 108.9 cm³ in airway volume change. Surgical navigation using intraoperative imaging and tracking was evaluated. Preliminary assessment of deformation modeling showed potential to supplement intraoperative imaging. Future work will involve streamlined integration of the components of this framework.

Radiation exposure alters airway deformability and bony structure displacement during laryngoscopy

Background

Prior therapeutic radiation exposure in the setting of head and neck malignancies is associated with difficult airway instrumentation. We sought to characterize the anatomic changes that produce this phenotype.

Study Design

Retrospective review.

Methods

Five individuals with prior radiation therapy to the upper aerodigestive tract (previously irradiated) and 10 with no prior history of therapeutic radiation exposure (nonirradiated) were enrolled. Computed tomography images obtained before and during laryngoscope insertion ("uninstrumented" and "instrumented", respectively) were used to reconstruct three-dimensional representations of the pharyngeal airway, hyoid, and mandible.

Results

In the instrumented state, pharyngeal airway volumes were significantly greater in nonirradiated subjects relative to previously irradiated subjects (P = .01), and overall translation of both the hyoid and mandible was also greater in nonirradiated subjects (P = .01 and .04, respectively).

Conclusion

Individuals with prior therapeutic radiation exposure to the upper aerodigestive tract differ from nonirradiated subjects with respect to airway deformation and bony structure translation during laryngoscopy.

Level of Evidence

4.

Noise-robust bioimpedance approach for cardiac output measurement

OBJECTIVE

Congestive heart failure is a problem affecting millions of Americans. A continuous, non-invasive, telemonitoring device that can accurately monitor cardiac metrics could greatly help this population, reducing unnecessary hospitalizations and cost.

APPROACH

Machine learning (ML) algorithms trained on electrical-impedance tomography (EIT) data are presented for portable cardiac monitoring. The approach was validated on a simulated thorax and a measured tank experiment. A highly detailed 4D chest model (finite element method mesh and conductivity profiles) was developed utilizing the 4D XCAT phantom to provide realistic data. The ML algorithms were trained using databases that assumed the presence of poorly contacting electrodes without any assumptions of knowing which electrodes would be bad in the experiment. The trained ML algorithms were compared to EIT evaluated with and without removing bad electrodes.

MAIN RESULTS

A regression support vector machine and a deep neural network (DNN) were found to be the most accurate and robust to poorly contacting electrodes while not needing to know which electrodes were in poor contact in the simulated and measured experiments, respectively.

SIGNIFICANCE

Although the ML algorithms are not always better than EIT (with bad electrodes removed), the comparable results without needing a priori knowledge of which electrodes are bad is seen as a very promising feature. An evaluation of computational costs showed that the DNN required comparable computational power to the other methods while requiring less memory, which could make the DNNs an attractive algorithm for a low-power, portable system. This work represents an important validation of the method using measured data, and model development, which is needed to apply this method on real clinical data. Additionally, the developed 4D simulated thorax model could be an important tool within the EIT community.

Use of Amulet in behavioral change for geriatric obesity management

Background

Obesity in older adults is a significant public health concern. Weight-loss interventions are known to improve physical function but risk the development of sarcopenia. Mobile health devices have the potential to augment existing interventions and, if designed accordingly, could improve one’s physical activity and strength in routine physical activity interventions.

Methods and results

We present Amulet, a mobile health device that has the capability of engaging patients in physical activity. The purpose of this article is to discuss the development of applications that are tailored to older adults with obesity, with the intention to engage and improve their health.

Conclusions

Using a team-science approach, Amulet has the potential, as an open-source mobile health device, to tailor activity interventions to older adults.

Toward Electrical Impedance Tomography Coupled Ultrasound Imaging for Assessing Muscle Health

This paper establishes for the first time that a coupled ultrasound (US) and electrical impedance tomography (EIT) system can serve as a non-invasive, spatially localized approach to extract clinically relevant muscle properties. The US/EIT system represents a potential enhancement to electrical impedance myography (EIM), which has shown promise as a non-invasive technology that may have important clinical use in indicating neuromuscular disease status and as a diagnostic tool. A 2.5D EIT algorithm evaluated on simulation, measured phantoms, and measured patient data was studied to evaluate US/EIT's ability to distinguish different aspects of muscle tissue. Simulated and phantom experiments revealed the depths of distinguishability of 3.2 and 4.2 mm in simulation for 10% and 20% changes in muscle properties, respectively, and 3.6 mm in measured phantom experiments assuming a 12% muscle conductivity change. Reconstructions from the patient data established that there were consistent differences 1) between longitudinal (along) and transverse (across) muscle conductivity reconstructions at frequencies of 40 and 80 kHz and 2) side-by-side comparison between healthy and diseased tissue in terms of conductivity, permittivity, and phase at 40 and 80 kHz. Comparisons were made between the EIT reconstructed values and electrical impedance spectroscopy (EIS) measurements (an available surrogate in place of standard EIM measurements) made with the US/EIT system, wherein 1) EIS and EIT show similar sensitivity to longitudinal and transverse differences and 2) EIT showed a more consistent ability to differentiate healthy and diseased tissue. These results suggest that US/EIT appears very promising for non-invasive and spatially localized diagnosis of muscle health.

Design and Implementation of an Ultra-Low Resource Electrodermal Activity Sensor for Wearable Applications ‡

While modern low-power microcontrollers are a cornerstone of wearable physiological sensors, their limited on-chip storage typically makes peripheral storage devices a requirement for long-term physiological sensing—significantly increasing both size and power consumption. Here, a wearable biosensor system capable of long-term recording of physiological signals using a single, 64 kB microcontroller to minimize sensor size and improve energy performance is described. Electrodermal (EDA) signals were sampled and compressed using a multiresolution wavelet transformation to achieve long-term storage within the limited memory of a 16-bit microcontroller. The distortion of the compressed signal and errors in extracting common EDA features is evaluated across 253 independent EDA signals acquired from human volunteers. At a compression ratio (CR) of 23.3×, the root mean square error (RMSErr) is below 0.016 μS and the percent root-mean-square difference (PRD) is below 1%. Tonic EDA features are preserved at a CR = 23.3× while phasic EDA features are more prone to reconstruction errors at CRs > 8.8×. This compression method is shown to be competitive with other compressive sensing-based approaches for EDA measurement while enabling on-board access to raw EDA data and efficient signal reconstructions. The system and compression method provided improves the functionality of low-resource microcontrollers by limiting the need for external memory devices and wireless connectivity to advance the miniaturization of wearable biosensors for mobile applications.

Gauging electrical properties of bone with a bioimpedance-sensing drill

OBJECTIVE

Multiple surgical procedures require drilling through bone to access underlying anatomy or for device placement. In dental applications, iatrogenic injury caused by accidental perforation of cortical bone into critical anatomy occurs in a significant number of dental implant procedures. Limited real-time sensing methods are available to guide clinicians while drilling through cancellous bone towards cortical interfaces. Early interface detection could prevent accidental damage to underlying anatomic structures. This study aims to demonstrate that electrical impedance spectroscopy can be integrated within a standard surgical drill to distinguish between bone types.

APPROACH

A custom bearing and insulated drill bit were designed to collect 10 cortical and cancellous impedance measurements from ex vivo femurs (2 pigs) and 80 bone measurements from in situ femurs (4 pigs). In the in situ study, two return electrodes (simulating a lip-clip and shoulder pad) were used to assess impedance differences associated with return electrode geometry.

MAIN RESULTS

Significant ex vivo differences (p  <  0.05) between cortical and cancellous bone occurred in the real resistivity from 0.1 to 100 kHz and in the imaginary resistivity from 0.3 to 10 kHz, with a maximum cortical-to-cancellous impedance ratio of 1.48. Significant in situ differences (p  <  0.01) were observed in both real and imaginary resistivities from 0.1 to 100 kHz, with a maximum impedance ratio of 2.94. AUCs for classifying bone type based on the real resistivity ranged from 0.84 to 0.96 for ex vivo bone and 0.98 to 1.0 for in situ bone. Mean differences between return electrode geometries were less than 5%.

SIGNIFICANCE

The significant cortical-to-cancellous contrast observed indicates this system's potential to provide real-time tissue differentiation during bone drilling procedures.

Development and Usability Assessment of a Connected Resistance Exercise Band Application for Strength-Monitoring

Resistance exercise bands are a core component of any physical activity strengthening program. Strength training can mitigate the development of sarcopenia, the loss of muscle mass or strength and function with aging. Yet, the adherence of such behavioral exercise strategies in a home-based setting are fraught with issues of monitoring and compliance. Our group developed a Bluetooth-enabled resistance exercise band capable of transmitting data to an open-source platform. In this work, we developed an application to capture this information in real-time, and conducted three usability studies in two mixed-aged groups of participants (n=6 each) and a group of older adults with obesity participating in a weight-loss intervention (n=20). The system was favorable, acceptable and provided iterative information that could assist in future deployment on ubiquitous platforms. Our formative work provides the foundation to deliver home-based monitoring interventions in a high-risk, older adult population.

Development and Usability Assessment of a Connected Resistance Exercise Band Application for Strength-Monitoring

Resistance exercise bands are a core component of any physical activity strengthening program. Strength training can mitigate the development of sarcopenia, the loss of muscle mass or strength and function with aging. Yet, the adherence of such behavioral exercise strategies in a home-based setting are fraught with issues of monitoring and compliance. Our group developed a Bluetooth-enabled resistance exercise band capable of transmitting data to an open-source platform. In this work, we developed an application to capture this information in real-time, and conducted three usability studies in two mixed-aged groups of participants (n=6 each) and a group of older adults with obesity participating in a weight-loss intervention (n=20). The system was favorable, acceptable and provided iterative information that could assist in future deployment on ubiquitous platforms. Our formative work provides the foundation to deliver home-based monitoring interventions in a high-risk, older adult population.

Initial experience with image-guided surgical navigation in transoral surgery

BACKGROUND

Surgical navigation using image guidance may improve the safety and efficacy of transoral surgery (TOS); however, preoperative imaging cannot be accurately registered to the intraoperative state due to deformations resulting from placement of the laryngoscope or retractor. This proof of concept study explores feasibility and registration accuracy of surgical navigation for TOS by utilizing intraoperative imaging.

METHODS

Four patients undergoing TOS were recruited. Suspension laryngoscopy was performed with a CT-compatible laryngoscope. An intraoperative contrast enhanced CT scan was obtained and registered to fiducials placed on the neck, face, and laryngoscope.

RESULTS

All patients were successfully scanned and registered. Registration accuracy within the pharynx and larynx was 1 mm or less. Target registration was confirmed by localizing endoscopic and surface structures to the CT images. Successful tracking was performed in all 4 patients.

CONCLUSION

For surgical navigation during TOS, although a high level of registration accuracy can be achieved by utilizing intraoperative imaging, significant limitations of the existing technology have been identified. These limitations, as well as areas for future investigation, are discussed.

Detection and Monitoring of Repetitions Using an mHealth-Enabled Resistance Band

Sarcopenia is defined as an age-related loss of muscle mass and strength which impairs physical function leading to disability and frailty. Resistance exercises are effective treatments for sarcopenia and are critical in mitigating weight-loss induced sarcopenia in older adults attempting to lose weight. Yet, adherence to home-based regimens, which is a cornerstone to lifestyle therapies, is poor and cannot be ascertained by clinicians as no objective methods exist to determine patient compliance outside of a supervised setting. Our group developed a Bluetooth connected resistance band that tests the ability to detect exercise repetitions. We recruited 6 patients aged 65 years and older and recorded 4 specific, physical therapist-led exercises. Three blinded reviewers examined the findings and we also applied a peak Ending algorithm to the data. There were 16.6 repetitions per exercise across reviewers, with an intraclass correlation of 0.912 (95%CI: 0.853-0.953, p<0.001) between reviewers and the algorithm. Using this novel resistance band, we feasibly detected repetition of exercises in older adults.

Usability Evaluation for the Amulet Wearable Device in Rural Older Adults with Obesity

Mobile health (mHealth) interventions hold the promise of augmenting existing health promotion interventions. Older adults present unique challenges in advancing new models of health promotion using technology including sensory limitations and less experience with mHealth, underscoring the need for specialized usability testing. We use an open-source mHealth device as a case example for its integration in a newly designed health services intervention. We performed a convergent, parallel mixed-methods study including semi-structured interviews, focus groups, and questionnaires, using purposive sampling of 29 older adults, 4 community leaders and 7 clinicians in a rural setting We transcribed the data, developed codes informed by thematic analysis using inductive and deductive methods, and assessed the quantitative data using descriptive statistics. Our results suggest the importance of end-users in user-centered design of mHealth devices and that aesthetics are critically important. The prototype could potentially be feasibly integrated within health behavior interventions. Centralized dashboards were desired by all participants and ecological momentary assessment could be an important part of monitoring. Concerns of mHealth, including the prototype device, include the device's accuracy, its intrusiveness in daily life and privacy. Formative evaluations are critically important prior to deploying large-scale interventions.

An Analog Front End ASIC for Cardiac Electrical Impedance Tomography

In this paper, an end-to-end CMOS application specific integrated circuit (ASIC) for readout channel in a cardiac electrical impedance tomography system is presented. The ASIC consists of an integrated current driver for current injection, an instrumentation amplifier, variable gain amplifier at the analog front end for voltage readout from electrodes, and an on-chip 10-bit successive approximation register analog to digital converter with serial peripheral interface. The ASIC is fabricated in the CMOS 0.18 $\mu$ m process with a supply voltage of 3.3 V. Amplitude and phase extraction of the voltages is performed in the digital domain with a matched filter. A fully integrated solution for use in multiple electrode system is demonstrated. The readout chain in the ASIC achieves a minimum signal-to-noise ratio of 71 dB over the frequency range of 500 Hz-700 kHz, while maintaining an average accuracy of 99.7 $\%$. Frame rates of 21 frames per second for a 32 electrode system is feasible, and the ASIC has an overall power consumption of 11.8 mW.

Fused-data transrectal EIT for prostate cancer imaging

OBJECTIVE

Prostate cancer is a significant problem affecting 1 in 7 men. Unfortunately, the diagnostic gold-standard of ultrasound-guided biopsy misses 10%-30% of all cancers. The objective of this study was to develop an electrical impedance tomography (EIT) approach that has the potential to image the entire prostate using multiple impedance measurements recorded between electrodes integrated onto an end-fired transrectal ultrasound (TRUS) device and a biopsy probe (BP).

APPROACH

Simulations and sensitivity analyses were used to investigate the best combination of electrodes, and measured tank experiments were used to evaluate a fused-data transrectal EIT (fd-TREIT) and BP approach.

MAIN RESULTS

Simulations and sensitivity analysis revealed that (1) TREIT measurements are not sufficiently sensitive to image the whole prostate, (2) the combination of TREIT  +  BP measurements increases the sensitive region of TREIT-only measurements by 12×, and (3) the fusion of multiple TREIT  +  BP measurements collected during a routine or customized 12-core biopsy procedure can cover up to 76.1% or 94.1% of a nominal 50 cm³ prostate, respectively. Three measured tank experiments of the fd-TREIT  +  BP approach successfully and accurately recovered the positions of 2-3 metal or plastic inclusions.

SIGNIFICANCE

The measured tank experiments represent important steps in the development of an algorithm that can combine EIT from multiple locations and from multiple probes-data that could be collected during a routine TRUS-guided 12-core biopsy. Overall, this result is a step towards a clinically deployable impedance imaging approach to scanning the entire prostate, which could significantly help to improve prostate cancer diagnosis.

Signal-to-Noise Ratio Analysis of a Phase-Sensitive Voltmeter for Electrical Impedance Tomography

In this paper, thorough analysis along with mathematical derivations of the matched filter for a voltmeter used in electrical impedance tomography systems are presented. The effect of the random noise in the system prior to the matched filter, generated by other components, are considered. Employing the presented equations allow system/circuit designers to find the maximum tolerable noise prior to the matched filter that leads to the target signal-to-noise ratio (SNR) of the voltmeter, without having to over-design internal components. A practical model was developed that should fall within 2 dB and 5 dB of the median SNR measurements of signal amplitude and phase, respectively. In order to validate our claims, simulation and experimental measurements have been performed with an analog-to-digital converter (ADC) followed by a digital matched filter, while the noise of the whole system was modeled as the input referred at the ADC input. The input signal was contaminated by a known value of additive white Gaussian noise (AWGN) noise, and the noise level was swept from 3% to 75% of the least significant bit (LSB) of the ADC. Differences between experimental and both simulated and analytical SNR values were less than 0.59 and 0.35 dB for RMS values ≥ 20% of an LSB and less than 1.45 and 2.58 dB for RMS values < 20% of an LSB for the amplitude and phase, respectively. Overall, this study provides a practical model for circuit designers in EIT, and a more accurate error analysis that was previously missing in EIT literature.

Absolute Reconstructions Using Rotational Electrical Impedance Tomography for Breast Cancer Imaging

A rotational Electrical Impedance Tomography (rEIT) methodology is described and shown to produce spatially accurate absolute reconstructions with improved image contrast and an improved ability to distinguish closely spaced inclusions compared to traditional EIT on data recorded from cylindrical and breast-shaped tanks. Rotations of the tank without altering the interior conductivity distribution are used to produce the rEIT data. Quantitatively, rEIT was able to distinguish two inclusions that were 1.5 cm closer together than traditional EIT could achieve for inclusions placed 2 to 3 cm from the center for the cylindrical tank, and rEIT was able to distinguish two tumor-like inclusions where traditional EIT could not reliably do so. Mathematical analysis showed that rEIT improves the number of stable singular vectors by up to 4.2 and 4.7 times than that of traditional EIT for the cylindrical and breast-shaped tanks, respectively, which is an indication of improved resolution. Direct investigations into measurements revealed minimum rotation angles that should yield data uncorrupted by noise. Two inverse approaches (one that inverts then fuses the data (I/DF) and one that fuses the data then inverts (DF/I)) and two mesh modeling approaches were considered. It was found that DF/I produces far better results compared to I/DF and a rotated-mesh approach produces further improvements. The ability to obtain improved absolute reconstructions using rEIT on a practical clinical scenario (breast-shaped tank experiment) is an important step towards using rEIT to improve previous EIT results in medical applications.

Comparative study of separation between ex vivo prostatic malignant and benign tissue using electrical impedance spectroscopy and electrical impedance tomography

OBJECTIVE

Currently no efficient and reliable technique exists to routinely assess surgical margins during a radical prostatectomy. Electrical impedance spectroscopy (EIS) has been reported as a potential technique to provide surgeons with real-time intraoperative margin assessment. In addition to providing a quantified measure of margin status, a co-registered electrical impedance tomography (EIT) image presented on a surgeon's workstation could add value to the margin assessment process.

APPROACH

To investigate this, we conducted a comparative study between EIS and EIT to evaluate the potential these technologies might have for margin assessment. EIS and EIT data was acquired from ex vivo human prostates using a multi-electrode endoscopic impedance acquisition probe.

MAIN RESULTS

EIS and EIT show good predictive performance with a 0.76 and 0.80 area-under-curve (AUC), respectively, when considering discrete frequencies only. A machine learning (ML) algorithm is implemented to combine features, which improves the AUCs of EIS and EIT to 0.84 and 0.85, respectively. Single-step EIT takes significantly less time to reconstruct than multi-step EIT, yet provides similarly accurate classification results, making the single-step approach a potential candidate for real-time margin assessment. While the ML-based approach clearly exhibits benefits as compared to the single feature assessment, the decision to use EIS versus EIT is unclear since each approach performs better for different subsets of tissue classifications.

SIGNIFICANCE

The results presented in this paper corroborate our previous studies and present the strongest evidence yet that an intraoperative-capable impedance probe can be used to distinguish benign from malignant prostate tissues. An in vivo study with a large cohort will be necessary to definitively determine the preferred approach and to show the clinical effectiveness of using this technology for margin assessment.

Prostate Cancer Detection Using Composite Impedance Metric

Prostate cancer (PCa) recurrences are often predicted by assessing the status of surgical margins (SM)- positive surgical margins (PSM) increase the chances of biochemical recurrence by 2-4 times which may lead to PCa recurrence. To this end, an electrical impedance acquisition system with a microendoscopic probe was employed in an ex-vivo study of human prostates. This system measures the tissue bioimpedance over a range of frequencies (1 kHz to 1MHz), and computes a number of Composite Impedance Metrics (CIM). A classifier trained using CIM data can be used to classify tissue as benign or cancerous. The system was used to collect the impedance spectra from 14 excised prostates, which were obtained from men undergoing radical prostatectomy, for a total of 23 cancerous and 53 benign measurements. The data revealed statistically significant (p < 0.05) differences in the impedance properties of the benign and tumorous tissues, and among the measurements taken on the apical, base, and lateral surface of the prostate. Further, in the leave-one-patient-out cross validation, a maximum predictive accuracy of 90.79% was achieved by combining high frequency CIM phase data to train a support vector machine classifier with a radial basis function kernel. The observations are consistent with the physiology and morphology of benign and malignant prostate tissue. CIMs were found to be an effective tool in distinguishing benign from cancerous tissues.

A Novel Regularization Technique for Microendoscopic Electrical Impedance Tomography

A novel regularization technique is developed for end-fired microendoscopic electrical impedance tomography using the dual-mesh method. The new regularization technique coupled with appropriate forward modeling and inverse mesh design is shown to produce dramatically improved reconstructions over previous methods. 3D absolute and difference reconstructions from measured saline tank and ex vivo adipose and muscle tissue experiments are used to validate the approach. The ex vivo experiments are used as a surrogate for prostate tissue, which is the primary clinical application for the probe. Inclusion center of mass errors were less than 0.47 mm for tank experiments with inclusion depths and radial offsets ranging less than 3 mm and 1.5 mm, respectively. Absolute 3D reconstructions on the tissue show quantitatively good accuracy and the ability to spatially distinguish small tissue features (adipose strands of approximately 2.5 mm in width). The reconstruction algorithm developed provides strong evidence for the promise of surgical margin detection using microendoscopic EIT.

An Inverse Problems Approach to MR-EPT Image Reconstruction

Magnetic Resonance-Electrical Properties Tomography (MR-EPT) is an imaging modality that maps the spatial distribution of the electrical conductivity and permittivity using standard MRI systems. The presence of a body within the scanner alters the RF field, and by mapping these alterations it is possible to recover the electrical properties. The field is time-harmonic, and can be described by the Helmholtz equation. Approximations to this equation have been previously used to estimate conductivity and permittivity in terms of first or second derivatives of RF field data. Using these same approximations, an inverse approach to solving the MR-EPT problem is presented here that leverages a forward model for describing the magnitude and phase of the field within the imaging domain, and a fitting approach for estimating the electrical properties distribution. The advantages of this approach are that 1) differentiation of the measured data is not required, thus reducing noise sensitivity, and 2) different regularization schemes can be adopted, depending on prior knowledge of the distribution of conductivity or permittivity, leading to improved image quality. To demonstrate the developed approach, both Quadratic (QR) and Total Variation (TV) regularization methods were implemented and evaluated through numerical simulation and experimentally acquired data. The proposed inverse approach to MR-EPT reconstruction correctly identifies contrasts and accurately reconstructs the geometry in both simulations and experiments. The TV regularized scheme reconstructs sharp spatial transitions, which are difficult to reconstruct with other, more traditional approaches.