Keywords: MR-Guided Interventions, Thermometry

Motivation: 3D MR-thermometry enhances microwave ablation success by providing real-time temperature and ablation insights. However, clinical availability is limited due to challenges such as breathing motion and electromagnetic interferences. 

Goal(s): Our study conducts 3D MR-thermometry comparing stack-of-stars and a stack-of-spirals sequences using a clinically approved generator and phantoms simulating breathing motion. 

Approach: Temperature precision and precision of ablation zones of both sequences were compared.  

Results: Stack-of-spirals sequence seems to be the superior MR-thermometry sequence. Dice scores of around 90 % and temperature precisions around 1°C were reached with very little image degradation due to motion or electromagnetic interferences. 

Impact: Our study shows the possibility of motion robust 3D MR-thermometry using a clinically approved microwave generator. Future developments might provide real-time 3D MR thermometry during clinical abdominal thermal therapies, enhancing their success and increasing the total number of MR interventions. 

Keywords: Thermometry/Thermotherapy, Interventional Devices, MR-guided LITT

Motivation: MR-guided laser interstitial thermal therapy (LITT) uses laser fibres to ablate lesions under MR-thermometry monitoring. Distance between OR and MRI complicates this procedure, but previous generations of intraoperative MRIs were limited to fields up to 1.5T.

Goal(s): We investigated a dual-room setup for intraoperative 3T MRI as navigation/monitoring for LITT.

Approach: In eleven paediatric patients, we demonstrated this setup as navigation/monitoring for LITT.

Results: We quantified achievable time and precision parameters, e.g., a mean total surgery time of 4.9 hours.

Impact: Minimised surgery time and complications as well as improved treatment monitoring for laser interstitial thermal therapy make dual-room intraoperative 3T MRIs beneficial for paediatric patients.

Keywords: Thermometry/Thermotherapy, Thermometry

Motivation: In current clinical magnetic resonance-guided focused ultrasound (MRgFUS) ablation applications, only aqueous tissues are monitored with MR thermometry. Accurate thermometry of heterogeneous aqueous and fat tissue volumes would increase treatment safety and efficacy.

Goal(s): Evaluate a single reference variable flip angle (SR-VFA) sequence for hybrid proton resonance frequency shift and ΔT₁ MR thermometry in heterogeneous tissue volumes.

Approach: MRgFUS ablation in an in vivo rabbit model was monitored with SR-VFA thermometry. Cumulative thermal dose (CTD) maps calculated from SR-VFA images were compared with non-perfused volumes and histological samples.

Results: SR-VFA derived CTD maps accurately predicted volumes of thermal damage in muscle and fat.

Impact: Hybrid proton resonance frequency shift and T₁ thermometry allows for accurate temperature monitoring of heterogeneous tissue volumes. This increases the safety and efficacy of MR-guided focused ultrasound treatments in mixed-tissue treatment areas by ensuring target temperatures reach appropriate thresholds.

Keywords: Thermometry/Thermotherapy, Thermometry

Motivation: Temperature errors in PRFS occur primarily in tissues containing adipose substances because fat changes its magnetic susceptibility with temperature.

Goal(s): This study aimed to simultaneously monitor the temperatures of fat and non-fat tissues using Look-Locker (LL) technique with dual echoes.

Approach: Two-point Dixon technique can be utilized to estimate the adipose components, which may aid in the separation of adipose tissue in PRFS. In addition, the method allows for a more refined Bo correction.

Results: Compared to the temperature measured by the fiber-optic sensor, the PRFS and T1-based temperatures showed a small difference of about 0.11 ~ 0.22 ℃ and 0.06 ~ 0.15 ℃, respectively.

Impact: his study yields an evidence that Look-Locker technique with dual echoes is suitable for simultaneous acquisition of temperature mapping for adipose and non-adipose tissues, providing an accurate temperature monitoring comparable to a fiber-optic sensor as well as rapid acquisition.

Keywords: MR-Guided Focused Ultrasound, Phantoms, histotripsy, cavitation, lesioning, HIFU

Motivation: Develop tissue-mimicking phantoms for MR-guided focused ultrasound (MRgFUS) procedures, enabling precise cavitation lesion visualization.

Goal(s): Phantoms with tunable acoustic and mechanical properties, capable of producing MR image contrast when exposed to cavitation lesioning. Previous designs lacked tunable parameters or MR contrast, hindering comprehensive study of cavitation behavior.  This project seeks to fill this gap by developing versatile phantoms with MR contrast.

Approach: Combine evaporated milk, saline, agarose, and live red blood cells to create versatile phantoms. Conduct systematic experiments to validate tunable acoustic attenuation, mechanical stiffness, and lesion contrast for MRgFUS.

Results: Successfully produced customizable phantoms with excellent lesion contrast in MRgFUS.

Impact: Researchers can use the results presented here to construct MR visible phantoms that interrogate acoustic cavitation.

Keywords: MR-Guided Focused Ultrasound, Focused Ultrasound, Ultrasound, Electromagnet, Gradient, Brain

Motivation: Lack of a feedback mechanism renders focused ultrasound neuromodulation results inconsistent and difficult to reproduce.

Goal(s): This study hypothesis that electromagnets coupled with MRI can quantify low pressure acoustic fields in a gel sample.

Approach: We constructed a custom resonant electromagnet coil to encode propagating acoustic waves into the complex phase of MR images. 

Results: Acoustic propagation appeared in the phase patterns of MR images, they differed from hydrophone measurements. The speed of sound was correct, but the measured pressure amplitude was different. 

Impact: This is the first acquisition of acoustic waves using MRI with a human compatible coil.

Keywords: Other Interventional, Software Tools, fMRI Preprocessing

Motivation: Immediate changes in functionality during brain surgery in tumor and epilepsy patients are worth investigating in order to improve prediction of surgical outcomes.

Goal(s): We want to implement a preprocessing-pipeline for pre- and post-resection data that allows comparison between both scans and the application of further analysis methods.

Approach: We propose a two-step approach, where we first pre-register the anatomical data to MNI-space with consideration of the resection area and then use this data in a second step for preprocessing of fMRI data.

Results: The preprocessing gives satisfactory results that enable further analysis of intraoperative fMRI data, such as PICA.

Impact: We showed that the difficult case of pre- and post-resection data preprocessing is feasible and allows analysis of intraoperative fMRI data. This enables further investigation of changes in brain functionality during surgery which might lead to improvements in neurosurgery.

Keywords: MR-Guided Interventions, Machine Learning/Artificial Intelligence, drug outcome estimation, seizure freedom

Motivation: Implementation of AI-driven precision medicine and finding the most effective Antiseizure Medications.

Goal(s): To predict outcomes of drug interventions in epilepsy patients and categorize them into distinct seizure outcome groups.

Approach: The research employs both patient characteristic, clinical, and MRI features going throguh a feature selection step followed by binary classification using Support Vector Machine, Naïve Bayes, Decision Tree, and Ridge Regression.

Results: Ridge regression combined with genetic algorithm outperformed the others, achieving an accuracy of 0.77 and AUC (Area Under the Curve) of 0.80 in predicting seizure outcome. This success was attained using a total of 18 MRI features and 10 ASMs.

Impact: Our model may help selection of the most effective ASM for individual patients. This may reduce the need for consecutive drug trials involving ineffective medications, thereby alleviating associated burdens.

Keywords: MR-Guided Interventions, MR-Guided Interventions, needle artifact, device artifact, needle intervention, percutaneous intervention, modelling

Motivation: MR-guided needle interventions benefit from prior knowledge of needle artifact size and shape, as the artifact is important for instrument visualization and localization.

Goal(s): To investigate an analytical model for the dephasing artifact of a 20-gauge aspiration needle in GRE imaging based on material and imaging parameters.

Approach: Model accuracy was evaluated in-vitro for B₀ = 0.55T/1.5T/3T, res = (1mm)³/(2mm)³ and TE = 5ms/15ms/25ms using Dice score (DSC) and Hausdorff distance (d_H) as metrics.

Results: For isotropic voxel grids, the dephasing needle artifact could be well approximated by the model (DSC ≥ 86%, d_H ≤ 2 voxels).

Impact: The approximation of needle artifacts using an analytical model provides an instructive way for artifact size prediction and can potentially facilitate MR-guided intervention planning (e.g., the choice of imaging parameters, needle selection and system selection).