MR-Guided Liver Interventions

Deep learning-based reconstruction and superresolution for MR-guided thermal ablation of malignant liver lesions

OBJECTIVE

This study evaluates the impact of deep learning-enhanced T1-weighted VIBE sequences (DL-VIBE) on image quality and procedural parameters during MR-guided thermoablation of liver malignancies, compared to standard VIBE (SD-VIBE).

METHODS

Between September 2021 and February 2023, 34 patients (mean age: 65.4 years; 13 women) underwent MR-guided microwave ablation on a 1.5 T scanner. Intraprocedural SD-VIBE sequences were retrospectively processed with a deep learning algorithm (DL-VIBE) to reduce noise and enhance sharpness. Two interventional radiologists independently assessed image quality, noise, artifacts, sharpness, diagnostic confidence, and procedural parameters using a 5-point Likert scale. Interrater agreement was analyzed, and noise maps were created to assess signal-to-noise ratio improvements.

RESULTS

DL-VIBE significantly improved image quality, reduced artifacts and noise, and enhanced sharpness of liver contours and portal vein branches compared to SD-VIBE (p < 0.01). Procedural metrics, including needle tip detectability, confidence in needle positioning, and ablation zone assessment, were significantly better with DL-VIBE (p < 0.01). Interrater agreement was high (Cohen κ = 0.86). Reconstruction times for DL-VIBE were 3 s for k-space reconstruction and 1 s for superresolution processing. Simulated acquisition modifications reduced breath-hold duration by approximately 2 s.

CONCLUSION

DL-VIBE enhances image quality during MR-guided thermal ablation while improving efficiency through reduced processing and acquisition times.

Impact of MRI Texture Analysis on Complication Rate in MRI-Guided Liver Biopsies

Magnetic resonance imaging (MRI)-derived texture features are quantitative imaging parameters that may have valuable associations with clinical aspects. Their prognostic ability in patients undergoing percutaneous MRI-guided liver biopsy to identify associations with post-interventional bleeding complications and biopsy success rate has not been sufficiently investigated. The patient sample consisted 79 patients (32 females, 40.5%) with a mean age of 58.7 ± 12.4 years. Clinical parameters evaluated included comorbidities, pre-existing liver disease, known cancer diagnosis, and hemostaseological parameters. Several puncture-related parameters such as biopsy angle, distance of needle entry to capsule, and lesion were analyzed. MRI texture features of the target lesion were extracted from the planning sequence of the MRI-guided liver biopsy. Mann-Whitney U test and Fisher's exact test were used for group comparison; multivariate regression model was used for outcome prediction. Overall, the diagnostic outcome of biopsy was malignant in 38 cases (48.1%) and benign in 32 cases (40.5%). A total of 11 patients (13.9%) had post-interventional bleeding, while nine patients (11.4%) had a negative biopsy result. Several texture features were statistically significantly different between patients with and without hemorrhage. The texture feature GrVariance (1.37 ± 0.78 vs. 0.80 ± 0.35, p = 0.007) reached the highest statistical significance. Regarding unsuccessful biopsy results, S(1,1)DifEntrp (0.80 ± 0.10 vs. 0.89 ± 0.12, p = 0.022) and S(0,4)DifEntrp (1.14 ± 0.10 vs. 1.22 ± 0.11, p = 0.021) reached statistical significance between groups. Several MRI texture features of the target lesion were associated with bleeding complications or negative biopsy after MRI-guided percutaneous liver biopsy. This could be used to identify at-risk patients at the beginning of the procedure and should be further analyzed.

Accuracy of 3D real-time MRI temperature mapping in gel phantoms during microwave heating

BACKGROUND

Interventional magnetic resonance imaging (MRI) can provide a comprehensive setting for microwave ablation of tumors with real-time monitoring of the energy delivery using MRI-based temperature mapping. The purpose of this study was to quantify the accuracy of three-dimensional (3D) real-time MRI temperature mapping during microwave heating in vitro by comparing MRI thermometry data to reference data measured by fiber-optical thermometry.

METHODS

Nine phantom experiments were evaluated in agar-based gel phantoms using an in-room MR-conditional microwave system and MRI thermometry. MRI measurements were performed for 700 s (25 slices; temporal resolution 2 s). The temperature was monitored with two fiber-optical temperature sensors approximately 5 mm and 10 mm distant from the microwave antenna. Temperature curves of the sensors were compared to MRI temperature data of single-voxel regions of interest (ROIs) at the sensor tips; the accuracy of MRI thermometry was assessed as the root-mean-squared (RMS)-averaged temperature difference. Eighteen neighboring voxels around the original ROI were also evaluated and the voxel with the smallest temperature difference was additionally selected for further evaluation.

RESULTS

The maximum temperature changes measured by the fiber-optical sensors ranged from 7.3 K to 50.7 K. The median RMS-averaged temperature differences in the originally selected voxels ranged from 1.4 K to 3.4 K. When evaluating the minimum-difference voxel from the neighborhood, the temperature differences ranged from 0.5 K to 0.9 K. The microwave antenna and the MRI-conditional in-room microwave generator did not induce relevant radiofrequency artifacts.

CONCLUSION

Accurate 3D real-time MRI temperature mapping during microwave heating with very low RMS-averaged temperature errors below 1 K is feasible in gel phantoms.

RELEVANCE STATEMENT

Accurate MRI-based volumetric real-time monitoring of temperature distribution and thermal dose is highly relevant in clinical MRI-based interventions and can be expected to improve local tumor control, as well as procedural safety by extending the limits of thermal (e.g., microwave) ablation of tumors in the liver and in other organs.

KEY POINTS

Interventional MRI can provide a comprehensive setting for the microwave ablation of tumors. MRI can monitor the microwave ablation using real-time MRI-based temperature mapping. 3D real-time MRI temperature mapping during microwave heating is feasible. Measured temperature errors were below 1 °C in gel phantoms. The active in-room microwave generator did not induce any relevant radiofrequency artifacts.

Magnetic Resonance-guided Procedures: Consensus on Rationale, Techniques, and Outcomes

Magnetic resonance (MR) image guidance has demonstrated significant potential in the field of interventional radiology in several applications. This article covers the main points of MR-guided hepatic tumor ablation as a representative of MR-guided procedures. Patient selection and appropriate equipment utilization are essential for successful MR-guided tumor ablation. Intra-procedural planning imaging enables the visualization of the tumor and surrounding anatomical structures in most cases without the application of a contrast agent, ensuring optimal planning of the applicator tract. MRI enables real-time, multiplanar imaging, thus simultaneous observation of the applicator and target tumor is possible during targeting with adaptable slice angulations in case of challenging tumor positions. Typical ablation zone appearance during therapy monitoring with MRI enables safe assessment of the therapy result, resulting in a high primary efficacy rate. Recent advancements in ablation probes have shortened treatment times, while technical strategies address applicator visibility issues. MR-imaging immediately after the procedure is used to rule out complications and to assess technical success. Especially in smaller neoplasms, MRI-guided liver ablation demonstrates positive outcomes in terms of technical success rates, as well as promising survival and recurrence rates. Additionally, percutaneous biopsy under MR guidance offers an alternative to classic guidance modalities, providing high soft tissue contrast and thereby increasing the reliability of lesion detection, particularly in cases involving smaller lesions. Despite these advantages, the use of MR guidance in clinical routine is still limited to few indications and centers, due to by high costs, extended duration, and the need for specialized expertise. In conclusion, MRI-guided interventions could benefit from ongoing advancements in hardware, software, and devices. Such progress has the potential to expand diagnostic and treatment options in the field of interventional radiology.

Efficacy and Safety of MRI and CT Guided VX2 Hepatic Para-vascular Tumor Model in Rabbits

OBJECTIVE

To compare the efficacy and safety of 1.5 T MRI and CT-guided VX2 hepatic para-vascular tumor model in rabbits.

MATERIALS AND METHODS

Sixty New Zealand white rabbits were randomly and equally divided into MRI-guided group (n=30) and CT-guided group (n=30). Rabbit VX2 tumor fragments were implanted beside the rabbit hepatic great vessels under MRI and CT guidance in the MRI and CT group to evaluate the success rate of tumor model establishment, puncture needle display and tip peripheral vascular situation, operation time and safety.

RESULTS

In the MRI-guided group, 29 rabbits (29/30, 96.7%) had a successful establishment of liver tumor model, and 1 rabbit had needle metastasis. In the CT-guided group, 24 rabbits (24/30, 80%) had a successful establishment of liver tumor model, while 2 rabbits had needle metastasis, 3 rabbits had metastases in other parts of the liver, and 1 had an unknown cause of death. The differences in tumor model establishment success rate between the two groups were statistically significant (χ2 = 4.043, P < 0.05). The fold number of artifacts at T1WI was 7.26±0.38 for the 20 G coaxial puncture needle in the MRI-guided group and 2.51±0.57 for the 20 G coaxial puncture needle in the CT-guided group, and the difference was statistically significant (t=36.76, P < 0.001), but star-shaped hypodense artifacts would appear around the needle tip. The operation time was longer in the MRI-guided group than in the CT-guided group (13.32±2.45 minutes in the MRI-guided group vs. 8.42±1.46 minutes in the CTguided group; t=9.252, P < 0.001). A small number of ascites occurred in 2 patients (2/30, 6.67%) in the CT-guided group; no serious complications such as liver abscess, jaundice or diaphragmatic perforation were observed in both groups.

CONCLUSION

Compared with CT, MRI-guided hepatic para-vascular tumor implantation in rabbits might be a more effective modeling method. Although the needle tip pseudopacity of the puncture needle is large and the operation time is long, the incidence of complications is low.

Development of a novel MR-conditional microwave needle for MR-guided interventional microwave ablation at 1.5T

PURPOSE

To develop an MR-conditional microwave needle that generates a spherical ablation zone and clear MRI visibility for MR-guided microwave ablation.

METHODS

An MR-conditional microwave needle consisting of zirconia tip and TA18 titanium alloy tube was investigated. The numerical model was created to optimize the needle's geometry and analyze its performance. A geometrically optimized needle was produced using non-magnetic materials based on the electromagnetics simulation results. The needle's mechanical properties were tested per the Chinese pharmaceutical industry standard YY0899-2013. The MRI visibility performance and ablation characteristics of the needle was tested both in vitro (phantom) and in vivo (rabbit) at 1.5T. The RF-induced heating was evaluated in ex vivo porcine liver.

RESULTS

The needle's mechanical properties met the specified requirements. The needle susceptibility artifact was clearly visible both in vitro and in vivo. The needle artifact diameter (A) was small in in vivo (A_shaft: 4.96 ± 0.18 mm for T1W-FLASH, 3.13 ± 0.05 mm for T2-weighted fast spin-echo (T2W-FSE); A_tip: 2.31 ± 0.09 mm for T1W-FLASH, 2.29 ± 0.08 mm for T2W-FSE; tip location error [TLE]_: -0.94 ± 0.07 mm for T1W-FLASH, -1.10 ± 0.09 mm for T2W-FSE). Ablation zones generated by the needle were nearly spherical with an elliptical aspect ratio ranging from 0.79 to 0.90 at 30 W, 50 W for 3, 5, 10 min duration ex vivo ablations and 0.86 at 30 W for 10 min duration in vivo ablations.

CONCLUSION

The designed MR-conditional microwave needle offers excellent mechanical properties, reliable MRI visibility, insignificant RF-induced heating, and a sufficiently spherical ablation zone. Further clinical development of MR-guided microwave ablation appears warranted.

[Local and locoregional treatment of intrahepatic cholangiocarcinoma]

CLINICAL/METHODICAL ISSUE

In the new edition of the German S3-guideline published in June 2021, the diagnosis and treatment of cholangiocarcinoma (CCA) and gallbladder carcinoma are addressed for the first time. This article discusses the local and locoregional treatment options for intrahepatic CCA (iCCA).

STANDARD RADIOLOGICAL METHODS

Mortality is high in iCCA and the incidence is rising. In unresectable patients, treatment options include local and locoregional approaches.

METHODICAL INNOVATIONS

Besides recommendations regarding surgery, biliary drainage, intraductal locoregional therapy and radiation therapy, two recommendations regarding interventional radiologic therapies are included in the updated S3-guideline. Percutaneous thermal ablation via radiofrequency or microwave ablation (RFA/MWA) is suggested for unresectable tumors with up to 3 cm in diameter as primary therapy and for recurrent tumors. In advanced, liver dominant iCCA, intra-arterial therapies such as transarterial radioembolization (TARE), transarterial chemoembolization (TACE) or hepatic arterial infusion (HAI) are recommended as single therapy or in combination with other therapies.

ACHIEVEMENTS

Due to a lack of randomized controlled studies, the efficacy of locoregional therapies in iCCA is challenging to assess; however, various cohort studies, meta-analyses and review articles confirm their efficiency.

PRACTICAL RECOMMENDATIONS

Interventional radiological therapies alone or in combination with systemic therapies have the potential to improve the prognosis of patients with iCCA. Due to the various therapeutic options, patients with iCCA should be treated in centers which cover the entire therapeutic spectrum.

A closer look to the new frontier of artificial intelligence in the percutaneous treatment of primary lesions of the liver

The purpose of thermal ablation is induction of tumor death by means of localized hyperthermia resulting in irreversible cellular damage. Ablative therapies are well-recognized treatment modalities for HCC lesions and are considered standard of care for HCC nodules < 3 cm in diameter in patients not suitable for surgery. Effective lesion treatment rely on complete target volume ablation. Technical limitations are represented by large (> 3 cm) or multicentric nodules as well as complex nodule location and poor lesion conspicuity. Artificial Intelligence (AI) is a general term referred to computational algorithms that can analyze data and perform complex tasks otherwise prerogative of Human Intelligence. AI has a variety of application in percutaneous ablation procedures such as Navigational software, Fusion Imaging, and robot-assisted ablation tools. Those instruments represent relative innovations in the field of Interventional Oncology and promising strategies to overcome actual limitations of ablative therapy in order to increase feasibility and technical results. This work aims to review the principal application of Artificial Intelligence in the percutaneous ablation of primary lesions of the liver with special focus on how AI can impact in the treatment of HCC especially on potential advantages on the drawbacks of the conventional technique.

Enabling In-Bore MRI-Guided Biopsies With Force Feedback

Limited physical access to target organs of patients inside an MRI scanner is a major obstruction to real-time MRI-guided interventions. Traditional teleoperation technologies are incompatible with the MRI environment and although several solutions have been explored, a versatile system that provides high-fidelity haptic feedback and access deep inside the bore remains a challenge. We present a passive and nearly frictionless MRI-compatible hydraulic teleoperator designed for in-bore liver biopsies. We describe the design components, characterize the system transparency, and evaluate the performance with a user study in a laboratory and a clinical setting. The results demonstrate % difference between input and output forces during realistic manipulation. A user study with participants conducting mock needle biopsy tasks indicates that a remote operator performs equally well when using the device as when holding a biopsy needle directly in hand. Additionally, MRI compatibility tests show no reduction in signal-to-noise ratio in the presence of the device.