Background/Objectives: Microwave ablation (MWA) is the leading therapy method for treating patients with liver cancer. MWA simulation is used to further improve the therapy and to help develop new devices. Methods: A water-cooled ablation needle was reconstructed. MWA simulations of a polyacrylamide phantom were carried out and compared with a representative clinical example (tumor diameter: 8.75 mm). The Arrhenius damage model and a critical temperature approach of 60 °C were applied to assess the necrosis zones. Finally, the simulation results were compared to the corresponding MR measurements. Results: Most of the heating in the simulation took place at a distance of 5 mm along the transverse axis and 20 mm along the longitudinal axis above the needle tip. The calculated Dice scores for the Arrhenius model were 0.77/0.53 for the phantom/clinical case. For the critical temperature approach, Dice scores of 0.60/0.66 for the phantom/clinical case were achieved. Conclusions: The comparison between simulated and measured temperature increases showed an excellent agreement. However, differences in the predicted necrosis volume might be caused by omitting consideration of the heat sink effect, especially in the clinical case. Nevertheless, this workflow enables short MWA simulation times (approximately 3 min) and demonstrates a step towards possible integration into daily clinical use.

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.

Objective: To identify MRI features of desmoid tumors (DTs) that predict the growth of residual disease following ablation. Methods: Patients who underwent MRI-guided ablation for DTs between February 2013 and April 2021 were included in this single-center IRB-approved retrospective study. MRI scans assessed three suspicious tissue features: intermediate T2 signal [+iT2], nodular appearance [+NOD], and contrast enhancement [+ENH]. Percent-monthly change in diameter (PMCD) of suspicious foci determined growth (PMCD > 1%), unchanged (PMCD between −1% and +1%), or regression (PMCD < −1%). Statistical tests compared mean PMCD between groups and evaluated sensitivity and specificity. Results: Thirty-three patients (32 years ± 13.3; 22 females) with 34 DTs underwent 47 MRI-guided ablations, with a median follow-up of 269 days (IQR 147). Of 93 suspicious foci, 62 (67%) grew (PMCD: +5.6% IQR: 5.8), 13 (14%) remained unchanged (PMCD: −0.1% IQR: 0.6), and 18 (19%) regressed (PMCD: −3.9% IQR: 4.2). Features [+iT2], [+ENH], and [+NOD] were associated with PMCDs of +5.2% IQR: 6.0, +3.4% IQR: 6.0, and +3.4% IQR: 6.5, respectively, compared to −1.5% IQR: 4.7 (p < 0.0001), −0.5% IQR: 0.8 (p = 0.003), and +0.4% IQR: 7.5 (p = 0.0056) for their respective negative counterparts. Sensitivity, specificity, and accuracy for distinguishing growth were [+iT2]: 0.95, 0.71, 0.87, [+ENH]: 1.00, 0.32, 0.77, and [+NOD]: 0.84, 0.42, 0.70. Combining [+iT2 + NOD + ENH] yielded PMCD +5.9% IQR: 6.2 and the best performance for distinguishing growth (sensitivity 0.81, specificity 0.94, accuracy 0.85). Discussion: MRI features reliably predict the growth of residual or recurrent DTs post-ablation, with [+iT2] being the most accurate. Adding nodular enhancement to [+iT2] improved specificity without sacrificing accuracy. Key Points: Question Post-ablation imaging of desmoids is challenging due to tumor heterogeneity and treatment-related inflammation. This study evaluates MRI features for assessing future tumor growth. Findings Foci of intermediate T2 signal post-ablation predicted desmoid growth with high sensitivity (0.95), while T2 signal, nodularity, and enhancement combined offer high specificity (0.94). Clinical relevance Intermediate T2 signal predicts desmoid tumor growth post-ablation with high sensitivity and accuracy but moderate specificity. Combining nodularity and enhancement improves specificity and predictive value, helping clinicians in managing desmoid tumor patients post-ablation.

Background: Metasurface coils (MCs) are a promising magnetic resonance imaging (MRI) technology. Aiming to evaluate the image quality of MCs for knee and elbow imaging, we compared signal-to-noise ratio (SNRs) obtained in standard clinical setups. Methods: Knee and elbow MRI routine sequences were applied at 1.5 T, implementing four coil scenarios: (1) 15-channel transmit/receive knee coil; (2) four-channel multipurpose coil (flex coil); (3) MC + spine coil; and (4) MC + multipurpose coil. Three regions of interest (ROIs) at different anatomical depths were compared. Results: Seven participants (aged 28 ± 2 years; 6 males) were enrolled. In elbow MRI, the MC + spine coil demonstrated the highest SNR across all ROIs (superficial-anterior: +114%, p = 0.008; middle: +147%, p = 0.008; deep-posterior: +24%, p = 0.039) compared to the flex coil and all ROIs, except the deepest from the MC, compared to the knee coil (superficial-anterior: +28%, p = 0.016; middle: +104%, p = 0.008; deep-posterior: −1%, p = 0.531). In knee MRI, the MC + spine coil provided higher SNR compared to the flex coil, except posterior (superficial-anterior: +69%, p = 0.008; middle: +288%, p = 0.008; deep-posterior: −12%, p = 0.148) versus the knee coil, the MC + spine coil was superior in the middle but non-different in superficial pre-patellar areas and less in deep-posterior areas (superficial-anterior: −8%, p = 0.188; middle: +44%, p = 0.008; deep-posterior: −36%, p = 0.016). Conclusion: Wireless MCs exhibited great potential for knee and elbow MRI outperforming the flex coil. Future developments will improve the posterior illumination to increase its clinical value. Relevance statement: MCs offer enhanced versatility, flexibility, and patient comfort. If universal MC designs can achieve image quality comparable to those of standard coils and simultaneously be utilized across multiple body areas, the technology may revolutionize future musculoskeletal MRIs. Key Points: MCs are promising in MRI, but homogeneity is challenging depending on the design. Signal-to-noise-ratio was improved for knee and elbow imaging with slight inhomogeneous illumination. MCs could match the image quality of standard coils in both knee and elbow imaging. Graphical