Conference Agenda

Microwave ablation therapy is frequently used to treat liver malignancies. To ensure proper tumor treatment, intraoperative feedback regarding ablation performance and lesion size is required. By employing an electrode array around the ablation needle, changes in electrical impedance of ex vivo liver are measured in real time. Time-series trends of magnitude and phase are measured for 90 °C and 110 °C ablation temperatures. A finite element model is additionally configured to simulate the underlying biological processes. Gradients in the magnitude and phase trends can indicate the growth of the ablation zone. In combination with a preoperative simulation, impedance-based ablation monitoring can be a possible tool to improve future treatments.

Electrical impedance spectroscopy is promising for intraoperative cancer diagnosis by differentiating tissue based on its electrical properties, yet faces challenges from material nonlinearities and sensor geometry. In this study, 3D finite element simulations were performed to analyze geometric dependencies. Two different tetrapolar ring electrode layouts are placed on normal and tumor tissue with each radius varied using Monte Carlo simulations and the resulting impedances and cell constants were evaluated statistically. Additionally, a novel sensitivity quality metric is introduced, enabling the identification of the geometry more suitable for impedance measurements. The results highlight the superior sensitivity quality of the improved geometry. Future research should integrate the geometric Monte Carlo approach with variations of dielectric properties of tissue and optimizing the quality metric taking electrode polarization effects into considerations.

Introduction

Cryoablations are employed to eradicate tumor tissue by subjecting the target tissue to extreme cold. While the ablation

center reaches very low temperatures, cells in the peripheral area of the frozen tissue may survive the treatment and lead

to tumor recurrence. Active thawing using microwaves aims to enhance cell destruction through osmotic injuries,

particularly in the peripheral area of the frozen tissue, thereby making the treatment more efficient. The objective of this

study was to evaluate the effect of active thawing after cryoablation on cell destruction.

Methods

In this study, cryoablations were conducted on 20 ex-vivo porcine kidneys, followed by active thawing of the frozen

tissue using a microwave ablation system operating at 40 W. An offset arrangement of the ablation probes of 15 mm with

partial overlap of the active zones enabled a comparison between actively and passively thawed areas. The precise

positioning of the applicators was guided and monitored using CT imaging. To prevent coagulation by the microwave

applicator, heating was halted upon reaching 0 °C between the probes. For evaluation, the kidneys were immersed in a

contrast medium solution and examined using MRI imaging. Finally, intensity values were determined using regions of

interest (ROI) in actively and passively thawed areas as well as untreated tissue from T1 sequences (SE, FLASH, T1-

Map). In addition, the extracellular volume (ECV) was calculated. Based on the signal-to-noise ratio (SNR), the three

areas were compared.

Results

In the T1 sequences and ECV values, the examined kidneys showed a significantly increased SNR in the actively thawed

areas compared to the passively thawed areas and the untreated tissue.

Conclusion

In comparison, MRI imaging shows an increased SNR in the actively thawed area, which indicates increased tissue

destruction. The presented method could be a novel approach to improve the efficiency of cryoablation, especially for the

critical peripheral area of frozen tissue.

The interconnection of medical devices in an operating room (OR) represents a major step in optimizing clinical processes and increasing the quality of treatment. The IEEE 11073 SDC standard family constitutes the foundation for manufacturer-independent information exchange and remote control of medical devices. However, integrating new SDC-capable devices into an existing OR network poses a major challenge for medical device manufacturers. Thus, suitable integration models are required. This work focuses on the definition of three possible integration models and their comparison according to architectural design patterns. Thereby, the use case of integrating a high-frequency (HF) surgical device to interconnect with existing SDC-capable devices is pursued. One of the models, which focuses on high expandability and low coupling, was successfully applied to interconnect an HF surgical device with an OR light in the research OR of Reutlingen University. The results indicate transferability to other integration scenarios and are intended to further promote manufacturer-independent integrated ORs.

Introduction

Although there are already commercial tracking system solutions to guide and improve the precision of surgical procedures, such as optical and electromagnetic systems, all of them have some drawbacks to solve. The main ones are the high costs in both cases and the size of the markers of the first group, which makes them not sufficiently ergonomic in some interventions, such as biopsies. For these reasons, a novel tracking system was designed with only a monocular camera that allows tracking smaller markers, have less cost and closer distance to target.

Methods

The tracking system is based on an Allied Vision 1800 U-511m camera with a varifocal lens Computar 1/1.8" EL6Z0915UCS-MPWIR and a dodecahedron-shaped marker with a 5mm edge and ArUco markers on each of the fac-es of 4.4mm. Through the OpenCV ArUco library the markers are detected and depending on their distance in the depth axis of the camera, the zoom and focus of the lens are modified to keep a constant Field of View (FOV) and calculate the position of the marker.

Results

The accuracy of the system was measured using an NDI Polaris optical tracker, achieving a translational accuracy of 3mm and 2° rotational for a horizontal FOV of 25cm which represents 43 pixels approx. per marker side (2464 × 2064 camera resolution) in a 90cm depth workspace and a minimum distance of 10cm.

Conclusion

A tracking system has been designed with a monocular camera that has an accuracy in the order of millimeters with a small marker and potential uses in image-guided interventions. In subsequent studies, it will be implemented in a specific clinical case and some aspects to improve will be analyzed, such as the influence of the calibration of the marker and the camera, its resolution and the relationship between the number of pixels per marker side and accuracy.