Liver displacement during ventilation in Thiel embalmed human cadavers – a possible model for research and training in minimally invasive therapies

MRI-guided lumbar spinal injections with body-mounted robotic system: cadaver studies

INTRODUCTION

This paper reports the system integration and cadaveric assessment of a body-mounted robotic system for MRI-guided lumbar spine injections. The system is developed to enable MR-guided interventions in closed bore magnet and avoid problems due to patient movement during cannula guidance.

MATERIAL AND METHODS

The robot is comprised by a lightweight and compact structure so that it can be mounted directly onto the lower back of a patient using straps. Therefore, it can minimize the influence of patient movement by moving with the patient. The MR-Conditional robot is integrated with an image-guided surgical planning workstation. A dedicated clinical workflow is created for the robot-assisted procedure to improve the conventional freehand MRI-guided procedure.

RESULTS

Cadaver studies were performed with both freehand and robot-assisted approaches to validate the feasibility of the clinical workflow and to assess the positioning accuracy of the robotic system. The experiment results demonstrate that the root mean square (RMS) error of the target position to be 2.57 ± 1.09 mm and of the insertion angle to be 2.17 ± 0.89°.

CONCLUSION

The robot-assisted approach is able to provide more accurate and reproducible cannula placements than the freehand procedure, as well as to reduce the number of insertion attempts.

Validation of the soft-embalmed Thiel cadaver as a high-fidelity simulator of pressure during targeted nerve injection

INTRODUCTION

Although administration of regional anesthesia nerve blocks has increased during the COVID-19 pandemic, training opportunities in regional anesthesia have reduced. Simulation training may enhance skills, but simulators must be accurate enough for trainees to engage in a realistic way-for example, detection of excessive injection pressure. The soft-embalmed Thiel cadaver is a life-like, durable simulator that is used for dedicated practice and mastery learning training in regional anesthesia. We hypothesized that injection opening pressure in perineural tissue, at epineurium and in subepineurium were similar to opening pressures measured in experimental animals, fresh frozen cadavers, glycol soft-fix cadavers and patients.

METHODS

We systematically reviewed historical data, then conducted three validation studies delivering a 0.5 mL hydrolocation bolus of embalming fluid and recording injection pressure. First, we delivered the bolus at 12 mL/min at epimysium, perineural tissue, epineurium and in subepineurium at 48 peripheral nerve sites on three cadavers. Second, we delivered the bolus at using three infusion rates: 1 mL/min, 6 mL/min and 12 mL/min on epineurium at 70 peripheral nerve sites on five cadavers. Third, we repeated three injections (12 mL/min) at 24 epineural sites over the median and sciatic nerves of three cadavers.

RESULTS

Mean (95%) injection pressure was greater at epineurium compared with subepineurium (geometric ratio 1.2 (95% CI: 0.9 to 1.6)), p=0.04, and perineural tissue (geometric ratio 5.1 (95% CI: 3.7 to 7.0)), p<0.0001. Mean (95%) injection pressure was greater at 12 mL/min compared with 1 mL/min (geometric ratio 1.6 (95% CI: 1.2 to 2.1), p=0.005). Pressure measurements were similar in study 3 (p>0.05 for all comparisons).

DISCUSSION

We conclude that the soft-embalmed Thiel cadaver is a realistic simulator of injection opening pressure.

Thiel's embalming method with additional intra-cerebral ventricular formalin injection (TEIF) for cadaver training of head and brain surgery

Thiel’s embalming method provides natural coloration, flexibility, and tissue plasticity, and is used widely to prepare specimens for cadaver surgical training. However, this method causes brain softening, thereby restricting the cadaver surgical training of intra-cranial procedures. In this study, three cadavers were embalmed using formalin fixation, Thiel’s embalming method, and Thiel’s embalming method with additional intra-cerebral ventricular formalin injection, respectively. We also established rat models of the three embalming methods to develop and determine the best method for retaining adequate brain elasticity. The intra-ventricular formalin injection in the cadaver was performed through the Kocher’s point, as in the classical external ventricular drain procedure. Both, the cadaver brains and rat models yielded consistent shear wave measurements and brain surface stiffness data. Notably, the Thiel’s embalming method with additional intra-cerebral ventricular formalin injection yielded suitable elasticity for brain cadaver surgical training in terms of brain mobilization and surgical field deployment, and also discharged formaldehyde in undetectable quantities. To our knowledge, this is the first report in which a fixed quality, namely, brain elasticity for the performance of head and brain cadaver surgical training, has been evaluated in a cadaver subjected to the Thiel’s embalming method with immersion fixation in the cerebrospinal fluid space. We conclude that the Thiel’s embalming method with additional intra-cerebral ventricular formalin injection can maintain the brain elasticity, and may therefore improve the quality of head and brain cadaver surgical training safely and easily.

Thiel-embalming technique: investigation of possible modification in embalming tissue as evaluation model for radiofrequency ablation

Contrary to freezing preservation and formalin embalming, Thiel embalmed cadaver presents soft texture and color very close to that of living organism, and many applications based on Thiel embalmed cadavers have been reported. However, Thiel embalmed cadavers cannot be used as reliable evaluation model for radiofrequency ablation (RFA) due to dramatic changes of electrical conductivity in the embalmed tissue. To address this issue, we investigated various modifications of the original Thiel embalming solution. By altering the chemicals' species and concentration we figured out a formula that can greatly reduce the embalming fluid's electrical conductivity without significantly compromising the 18-day embalmed kidney samples' suppleness and color. We also investigated a two-stage embalming technique by first submerging the kidney sample into original Thiel's tank fluid for 28 days, then the sample was withdrawn from the tank fluid and placed into modified dilution fluids for additional two weeks. Stiffening and discoloration occurred in these diluted samples implying the reversibility of Thiel-embalmed tissues' suppleness and color with the removal of the strong electrolytes. This study presents a modified embalming method which could be used for RFA evaluation and also helps our understanding of the mechanism of embalmment process.

Translaryngeal Tracheostomy Needle Introducer: a simple device to improve safety and reduce complications during Fantoni's translaryngeal tracheostomy procedure: trial on human cadavers

Background

Percutaneous dilatational tracheostomy (PDT) is the most frequently performed procedure in patients requiring prolonged mechanical ventilation. A crucial step in such procedures is needle insertion into the trachea. To simplify this procedure and increase its safety, we developed a new device, the translaryngeal Tracheostomy Needle Introducer (tTNI), for use with Fantoni’s method. This cadaver study was designed to assess the performance of the tTNI on human anatomy.

Methods

We tested the tTNI in a cadaver laboratory; the operators included two experts trained in PDT and three without specific training in the procedure. We performed 58 needle insertion attempts on 13 cadavers. We compared the tTNI technique with the standard needle insertion approach using external landmarks. We recorded the number of attempts needed to optimise needle insertion, time required in seconds, final position of the needle and complications related to needle insertion.

Results

tTNI use resulted in fewer puncture attempts (1.91 ± 1.34 vs. 1.19 ± 0.5, p < 0.001), less time (36.8 ± 51.6 s vs. 13.14 ± 15.57 s, p < 0,001) and increased precision on the first puncture (18.87 ± 25.38° vs. 7.5 ± 12.95°, p < 0,005). We did not observe any complication with tTNI use, whereas complications found using the standard method were in line with the literature.

Conclusions

The tTNI is a device that simplifies needle insertion by enhancing the accuracy of insertion with fewer attempts and higher precision, even when used by less experienced operators. Clinical testing is required to evaluate the device performance in patients.

Electronic supplementary material

The online version of this article (10.1186/s40635-019-0221-x) contains supplementary material, which is available to authorized users.

Reference-less MR thermometry on pre-clinical thiel human cadaver for liver surgery with MRgFUS

PURPOSE

Reference-less MR thermometry can be a promising technique for temperature mapping during liver treatment with Magnetic Resonance-guided Focused Ultrasound (MRgFUS), as it is more robust to breathing motion than Proton Resonance Frequency MR thermometry. However, there is a lack of a pre-clinical model for repeatable testing of reference-less thermometry. The purpose of this work was to verify the explanted Thiel embalmed human liver and whole Thiel embalmed human cadaver for application of a custom made reference-less thermometry algorithm during MRgFUS sonication.

MATERIAL AND METHODS

Phase maps were generated during sonication as an input to the algorithm. A square Region-of-Interest (ROI) was designed around the heated area. The ROI was interpolated using a two-dimensional polynomial to the surrounding phase map to calculate the background phase.

RESULTS

Using the phase information from the images, the temperature rise was measured. Validation of the methodology showed accordance of temperatures with actual temperatures.

CONCLUSIONS

The explanted liver and the whole cadaver constitute a promising and feasible model to study reference-less techniques for thermometry during MRgFUS, before clinical trials.

A new physiological model for studying the effect of chest compression and ventilation during cardiopulmonary resuscitation: The Thiel cadaver

BACKGROUND

Studying ventilation and intrathoracic pressure (ITP) induced by chest compressions (CC) during Cardio Pulmonary Resuscitation is challenging and important aspects such as airway closure have been mostly ignored. We hypothesized that Thiel Embalmed Cadavers could constitute an appropriate model.

METHODS

We assessed respiratory mechanics and ITP during CC in 11 cadavers, and we compared it to measurements obtained in 9 out-of-hospital cardiac arrest patients and to predicted values from a bench model. An oesophageal catheter was inserted to assess chest wall compliance, and ITP variation (ΔITP). Airway pressure variation (ΔPaw) at airway opening and ΔITP generated by CC were measured at decremental positive end expiratory pressure (PEEP) to test its impact on flow and ΔPaw. The patient's data were derived from flow and airway pressure captured via the ventilator during resuscitation.

RESULTS

Resistance and Compliance of the respiratory system were comparable to those of the out-of-hospital cardiac arrest patients (C_RS^TEC 42 ± 12 vs C_RS^PAT 37.3 ± 10.9 mL/cmH₂O and Res^TEC 17.5 ± 7.5 vs Res^PAT 20.2 ± 5.3 cmH₂O/L/sec), and remained stable over time. During CC, ΔITP varied from 32 ± 12 cmH₂O to 69 ± 14 cmH₂O with manual and automatic CC respectively. Transmission of ΔITP at the airway opening was significantly affected by PEEP, suggesting dynamic small airway closure at low lung volumes. This phenomenon was similarly observed in patients.

CONCLUSION

Respiratory mechanics and dynamic pressures during CC of cadavers behave as predicted by a theoretical model and similarly to patients. The Thiel model is a suitable to assess ITP variations induced by ventilation during CC.

Acoustic characterization of Thiel liver for magnetic resonance-guided focused ultrasound treatment

BACKGROUND

The purpose of this work was to measure the essential acoustic parameters, i.e., acoustic impedance, reflection coefficient, attenuation coefficient, of Thiel embalmed human and animal liver. The Thiel embalmed tissue can be a promising, pre-clinical model to study liver treatment with Magnetic Resonance-guided Focused Ultrasound (MRgFUS).

MATERIAL AND METHODS

Using a single-element transducer and the contact pulse-echo method, the acoustic parameters, i.e., acoustic impedance, reflection coefficient and attenuation coefficient of Thiel embalmed human and animal liver were measured.

RESULTS

The Thiel embalmed livers had higher impedance, similar reflection and lower attenuation compared to the fresh tissue.

CONCLUSIONS

Embalming liver with Thiel fluid affects its acoustic properties. During MRgFUS sonication of a Thiel organ, more focused ultrasound (FUS) will be backscattered by the organ, and higher acoustic powers are required to reach coagulation levels (temperatures >56 °C).

Cadaveric Spinal Surgery Simulation: A Comparison of Cadaver Types

Study Design Single-blinded study. Objective To assess the suitability of three types of cadaver for simulating pedicle screw insertion and establish if there is an ideal. Methods Three types of cadaver-Thiel-embalmed, Crosado-embalmed, and formaldehyde-embalmed-were draped and the spines exposed. Experienced surgeons were asked to place pedicle screws in each cadaver and give written questionnaire feedback using a modified Likert scale. Soft tissue and bony properties were assessed, along with the role of simulation in spinal surgery training. Results The Thiel cadaver rated highest for soft tissue feel and appearance with a median score of 6 for both (range 2 to 7). The Crosado cadaver rated highest for bony feel, with a median score of 6 (range 2 to 7). The formaldehyde cadaver rated lowest for all categories with median scores of 2, 2.5, and 3.5, respectively. All surgeons felt pedicle screw insertion should be learned in a simulated setting using human cadavers. Conclusion Thiel and Crosado cadavers both offered lifelike simulation of pedicle screw insertion, with each having advantages depending on whether the focus is on soft tissue approach or technical aspects of bony screw insertion. Both cadaver types offer the advantage of long life span, unlike fresh frozen tissue, which means cadavers can be used multiple times, thus reducing the costs.

Understanding Thiel embalming in pig kidneys to develop a new circulation model

The quality of tissue preservation in Thiel embalmed bodies varies. Research on the administered embalming volume and its vascular distribution may elucidate one of the mechanisms of tissue preservation and allow for new applications of Thiel embalming. Vascular embalming with (group 1, n = 15) or without (group 2, n = 20) contrast agent was initiated in pig kidneys. The distribution of Thiel embalming solution in group 1 was visualized using computed tomography. The kidneys in both groups were then immersed in concentrated salt solutions to reduce their weight and volume. Afterwards, to mimic a lifelike circulation in the vessels, group 2 underwent pump-driven reperfusion for 120 minutes with either paraffinum perliquidum or diluted polyethylene glycol. The circulation was imaged with computed tomography. All of the kidneys were adequately preserved. The embalming solution spread diffusely in the kidney, but fluid accumulation was present. Subsequent immersion in concentrated salt solutions reduced weight (P < 0.01) and volume (P < 0.01). Reperfusion for 120 minutes was established in group 2. Paraffinum perliquidum filled both major vessels and renal tissue, whereas diluted polyethylene glycol spread widely in the kidney. There were no increases in weight (P = 0.26) and volume (P = 0.79); and pressure further decreased (P = 0.032) after more than 60 minutes of reperfusion with paraffinum perliquidum, whereas there were increases in weight (P = 0.005), volume (P = 0.032) and pressure (P < 0.0001) after reperfusion with diluted polyethylene glycol. Arterial embalming of kidneys results in successful preservation due to complete parenchymatous spreading. More research is needed to determine whether other factors affect embalming quality. Dehydration is an effective method to regain the organs’ initial status. Prolonged vascular reperfusion with paraffinum perliquidum can be established in this model without increases in weight, volume and pressure.

From "silent teachers" to models

In this essay Roos Eisma and Tracey Wilkinson describe how the Thiel technique has expanded the range of applications in which embalmed human cadavers can be used.

For decades, embalmed cadavers have played an important role in teaching anatomy to the scientists and doctors of the future. Most anatomy departments use a traditional formaldehyde-based embalming method, but formalin embalming makes the bodies very rigid, which limits their usefulness for procedures other than dissection. A more recent embalming method developed by W. Thiel has allowed these “silent teachers” to take on a further role in applied anatomy research and teaching: to act as models for surgical training and medical research.

Wireless mobile technology to improve workflow and feasibility of MR-guided percutaneous interventions

PURPOSE

A wireless interactive display and control device combined with a platform-independent web-based user interface (UI) was developed to improve the workflow for interventional magnetic resonance imaging (iMRI).

METHODS

The iMRI-UI enables image acquisition of up to three independent slices using various pulse sequences with different contrast weighting. Pulse sequence, scan geometry and related parameters can be changed on the fly via the iMRI-UI using a tablet computer for improved lesion detection and interventional device targeting. The iMRI-UI was validated for core biopsies with a liver phantom ([Formula: see text] [Formula: see text] 40) and Thiel soft-embalmed human cadavers ([Formula: see text] [Formula: see text] 24) in a clinical 1.5T MRI scanner.

RESULTS

The iMRI-UI components and setup were tested and found conditionally MRI-safe to use according to current ASTM standards. Despite minor temporary touch screen interference at a close distance to the bore ([Formula: see text]20 cm), no other issues regarding quality or imaging artefacts were observed. The 3D root-mean-square distance error was [Formula: see text] (phantom)/[Formula: see text] mm (cadaver), and overall procedure times ranged between 12 and 22 (phantom)/20 and 55 min (cadaver).

CONCLUSION

The wireless iMRI-UI control setup enabled fast and accurate interventional biopsy needle placements along complex trajectories and improved the workflow for percutaneous interventions under MRI guidance in a preclinical trial.

Wireless MR tracking of interventional devices using phase-field dithering and projection reconstruction

PURPOSE

Device tracking is crucial for interventional MRI (iMRI) because conventional device materials do not contribute to the MR signal, may cause susceptibility artifacts and are generally invisible if moved out of the scan plane. A robust method for wireless tracking and dynamic guidance of interventional devices equipped with wirelessly connected resonant circuits (wRC) is presented.

METHODS

The proposed method uses weak spatially-selective excitation pulses with very low flip angle (0.3°), a Hadamard multiplexed tracking scheme and employs phase-field dithering to obtain the 3D position of a wRC. RF induced heating experiments (ASTM protocol) and balloon angioplasties of the iliac artery were conducted in a perfused vascular phantom and three Thiel soft-embalmed human cadavers.

RESULTS

Device tip tracking was interleaved with various user-selectable fast pulse sequences receiving a geometry update from the tracking kernel in less than 30ms. Integrating phase-field dithering significantly improved our tracking robustness for catheters with small diameters (4-6 French). The volume root mean square distance error was 2.81mm (standard deviation: 1.31mm). No significant RF induced heating (<0.6°C) was detected during heating experiments.

CONCLUSION

This tip tracking approach provides flexible, fast and robust feedback loop, intuitive iMRI scanner interaction, does not constrain the physician and delivers very low specific absorption rates. Devices with wRC can be exchanged during a procedure without modifications to the iMRI setup or the pulse sequence. A drawback of our current implementation is that position information is available for a single tracking coil only. This was satisfactory for balloon angioplasties of the iliac artery, but further studies are required for complex navigation and catheter shapes before animal trials and clinical application.

MRI of Thiel-embalmed human cadavers

PURPOSE

To explain the observed considerable loss of signal and contrast when Thiel-embalmed human cadavers are imaged using clinical magnetic resonance imaging (MRI) sequences, especially those based on spin-echo MRI.

MATERIALS AND METHODS

All cadavers were imaged with a medical 1.5T scanner using standard MRI sequences. Dual angle B1+ magnitude mapping and electromagnetic (EM) simulations that characterize the radiofrequency (RF) penetration in a male human body model (HBM) were carried out for a range of tissue conductivities.

RESULTS

The EM simulations show that RF penetration issues begin to affect the image quality for values of electrical conductivity as low as 2.6 S/m. The electrical conductivity values of the embalming fluids were found to be within the range of 5-10.6 S/m, thus strongly suggesting that the observed loss in signal and contrast is due to diminished RF penetration inside the cadavers. Furthermore, it was demonstrated that gradient-echo (GRE)-based MRI sequences perform better than spin-echo (SE)-based sequences, as they are less susceptible to imperfections in the flip angle that are inevitably present when imaging Thiel cadavers.

CONCLUSION

The diminished signal and contrast observed when imaging Thiel-embalmed human cadavers may be attributed to the high conductivity of the embalming liquids.