Ivan Vogt

Anthropomorphic CT phantoms are essential training tools for interventional radiology. Given the high technical demands and stringent safety requirements in this field, realistic CT phantoms are vital simulation tools that support effective hands-on training, procedural planning, and risk mitigation. However, commercially available phantom geometries are limited in their scope. This study investigates the use of polyvinyl alcohol (PVA) to fabricate customizable training phantoms. PVA, a non-toxic material, can be processed into PVA cryogels (PVA-C) with tissue-like mechanical properties. We modified PVA-C (10 wt.% PVA) by incorporating various additives to adjust X-ray attenuation and achieve Hounsfield units (HUs) similar to different soft tissues. HU values were measured at X-ray tube voltages of 70, 120, and 150 kV. The inclusion of barium sulfate (e.g., U = 120 kV; 0.1–2 wt.%: 33.29 ± 5.45–323.72 ± 12.64 HU) and iohexol (e.g., U = 120 kV; 0.1–2 wt.%: 26.05 ± 4.74–161.99 ± 5.69 HU) significantly increased HU values. Iohexol produced more homogeneous HU distributions than barium sulfate and cellulose derivatives, with the latter having air gaps and inconsistencies. The tested formulations encompassed a wide range of soft tissue densities, with HU values varying significantly across the energy range (p < 0.001). While cellulose derivatives showed variable HU modulation, their primary role appears to be in modifying phantom texture and morphology rather than precise attenuation control. In conclusion, PVA-C demonstrates strong potential for use in interventional radiology training phantoms. Further studies may enhance phantom realism by replicating tissue textures, for example, through the incorporation of cellulose-based substances.

Metasurfaces have proved valuable in magnetic resonance imaging (MRI) applications through modifying the field profiles of radiofrequency coils to enhance imaging. Using metasurfaces to enhance a conventional coil, such as the table-integrated spine coil, allows imaging with practically no cables inside the bore. This work investigated the fundamental relationship between an MRI system's field strength and the enhancement effect of a metasurface. We simulated and manufactured grid metasurfaces for field strengths of 0.55 Tesla (0.55 T), 1.5 T and 3 T and evaluated them experimentally. We found increased enhancements of the signal-to-noise ratio (SNR) with lower field strengths. At 0.55 T, the enhancement in the vicinity of the metasurface (10.9-fold) was measured 3.8 times higher than at 3 T. Moreover, the SNR decreased less with field strength next to the metasurface compared to the spine coil. Our results indicate the capability of metasurfaces in low field MRI systems and can stimulate further research. This could benefit future applications in MRI-guided interventions through simplified handling, as well as countries currently underserved with MRIs due to low manufacturing costs.

Microwave ablation (MWA) of hepatic tumors benefits from MR thermometry, enabling real-time temperature monitoring to guide treatment and protect healthy tissue. However, MR thermometry in the abdomen is challenging due to respiratory and intestinal motion. This study evaluates two advanced 3D imaging sequences, Stack-of-Stars (Stars) and Stack-of-Spirals (Spirals), for precise MWA thermometry in phantom and volunteer experiments. Spirals demonstrated superior temperature precision, with a standard deviation of 0.78 ± 0.05°C in unheated regions, compared to 2.92 ± 0.26°C for Stars. In heated regions, Spirals achieved a lower RMSE (0.5 ± 0.1°C vs. 1.2 ± 0.2°C for Stars) and a higher Dice score for ablation zone delineation (0.89 ± 0.01 vs. 0.76 ± 0.10). Spirals also produced sharper images with fewer artifacts under simulated respiratory motion, while Stars showed streaking artifacts due to higher undersampling. These findings highlight Spirals’ potential for accurate real-time thermometry in liver ablation. Future work should focus on improving reconstruction speed and mitigating susceptibility artifacts to enable clinical applications.

Objectives: Anthropomorphic phantoms offer a promising solution to minimize animal testing, enable medical training, and support the efficient development of medical devices. The adjustable mechanical, biochemical, and imaging properties of the polyvinyl alcohol cryogel (PVA-C) make it an appropriate phantom material for mimicking soft tissues. Conventional manufacturing (CM) of aqueous solutions requires constant stirring, using a heated water bath, and monitoring. Methods: To explore potential improvements in the dissolution of PVA crystals in water, a microwave-based manufacturing method (MWM) was employed. Samples created using CM and MWM (n = 14 each) were compared. Because PVA-C is a multifunctional phantom material (e.g., in magnetic resonance imaging (MRI)), its MRI properties (T1/T2 relaxation times) and elasticity were determined. Results: T1 relaxation times did not significantly differ between the two methods (p = 0.3577), whereas T2 and elasticity for the MWM were significantly higher than those for the CM (p < 0.001). The MWM reduced the production time by 11% and decreased active user involvement by 93%. Conclusions: The MWM offers a promising, easily implementable, and time-efficient method for manufacturing PVA-C-based phantoms. Nevertheless, manufacturing-related microstructural properties and sample molding require further study.

Metasurfaces enable magnetic resonance imaging (MRI) without cables inside the bore by locally improving the sensitivity of scanner-integrated receive coils. This study systematically evaluates a novel grid design to provide signal enhancement for patient imaging. The potential of the proposed metasurface grid design was analyzed regarding its unit cell density and compared with stripe type metasurfaces. The effects were examined in-depth by numerical simulation, workbench measurements, and MRI experiments at 3 Tesla. Differences in the signal-to-noise ratio (SNR) using either the integrated body or spine coils were evaluated, as well as the influence of the metasurface orientation. The grid design provided a favorable eigenmode usable for MR imaging, where it has shown significantly less dependence on orientation, compared to stripe metasurfaces. With the densest grid, more than 26% higher SNR than its most spaced design was achieved. Combining the metasurface for imaging with the spine coil proved to be superior to the body coil. Applying the metasurface for knee imaging, the SNR was locally enhanced by more than 10-fold compared to the scan with only the spine coil. The high-density grid metasurfaces provided benefits compared to the multitude of designs evaluated. This work provides a comprehensive foundation for future developments of metasurfaces for MRI, whose advantages may be exploited e.g. in the domain of interventional radiology.

Purpose: Surgical robotics have demonstrated their significance in assisting physicians during minimally invasive surgery. Especially, the integration of haptic and tactile feedback technologies can enhance the surgeon’s performance and overall patient outcomes. However, the current state-of-the-art lacks such interaction feedback opportunities, especially in robotic-assisted interventional magnetic resonance imaging (iMRI), which is gaining importance in clinical practice, specifically for percutaneous needle punctures. Methods: The cable-driven ‘Micropositioning Robotics for Image-Guided Surgery’ (µRIGS) system utilized the back-electromotive force effect of the stepper motor load to measure cable tensile forces without external sensors, employing the TMC5160 motor driver. The aim was to generate a sensorless haptic feedback (SHF) for remote needle advancement, incorporating collision detection and homing capabilities for internal automation processes. Three different phantoms capable of mimicking soft tissue were used to evaluate the difference in force feedback between manual needle puncture and the SHF, both technically and in terms of user experience. Results: The SHF achieved a sampling rate of 800 Hz and a mean force resolution of 0.26 ± 0.22 N, primarily dependent on motor current and rotation speed, with a mean maximum force of 15 N. In most cases, the SHF data aligned with the intended phantom-related force progression. The evaluation of the user study demonstrated no significant differences between the SHF technology and manual puncturing. Conclusion: The presented SHF of the µRIGS system introduced a novel MR-compatible technique to bridge the gap between medical robotics and interaction during real-time needle-based interventions.

The increased clinical relevance of image-guided procedures, particularly of interventional magnetic resonance imaging (iMRI), highlights the need for advanced devices and robotics to optimize those procedures. To enable a realistic integration of robotics into the clinical workflow, robotic-patient interfaces (RPI) are required to ensure both functionality and usability. However, current concepts have issues with patient accessibility and safety, user handling, or performing interventions on versatile body regions. This work presents a novel silicone-based RPI to flexibly mount the ’Micropositioning Robotics for Image-Guided Surgery’ (μRIGS) system on differently shaped body regions through vacuum, regulated with an electronic miniature pump. Maximum holding forces of 60N at −0.1 bar and 66N at −0.2 bar relative vacuum pressure were reached depending on the applied human body area and tensile force angles. MRI with the integrated metasurface indicated up to 200% signal enhancement, enabling improved tissue contrast within the first 20mm in depth. The multifunctional design supported the incorporation of the sterile iMRI workflow concept. This RPI enables a realistic integration of future technologies such as miniature robots, tracking markers, and instrument holders into complex interventional workflows. Further long-term studies are needed to evaluate the effects of vacuum application lasting for 1-2 hours on different skin types.

Purpose: In vivo studies are often required to prove the functionality and safety of medical devices. Clinical trials are costly and complex, adding to ethical scrutiny of animal testing. Anthropomorphic phantoms with versatile functionalities can overcome these issues with regard to medical education or an effective development of assistance systems during image-guided interventions (e.g., robotics, navigation/registration algorithms). In this work, an MRI-compatible and customizable motion phantom is presented to mimic respiratory-triggered organ movement as well as human anatomy. Methods: For this purpose, polyvinyl alcohol cryogel (PVA-C) was the foundation for muscles, liver, kidneys, tumors, and remaining abdominal tissue in different sizes of the abdominal phantom body (APB) with the ability to mimic human tissue in various properties. In addition, a semi-flexible rib cage was 3D-printed. The motion unit (MU) with an electromagnetically shielded stepper motor and mechanical extensions simulated a respiration pattern to move the APB. Results: Each compartment of the APB complied the relaxation times, dielectricity, and elasticity of human tissue. It showed resistance against mold and provided a resealable behavior after needle punctures. During long-term storage, the APB had a weight loss of 2.3%, followed by changes to relaxation times of 9.3% and elasticity up to 79%. The MU was able to physiologically appropriately mimic the organ displacement without reducing the MRI quality. Conclusion: This work presents a novel modularizable and low-cost PVA-C based APB to mimic fundamental organ motion. Beside a further organ motion analysis, an optimization of APB’s chemical composition is needed to ensure a realistic motion simulation and reproducible long-term use. This phantom enhances diverse and varied training environments for prospective physicians as well as effective R&D of medical devices with the possibility to reduce in vivo experiments.