RF field visualization of RF ablation at the Larmor frequency

Comparison of microwave ablation treatments in patients with renal secondary and primary hyperparathyroidism

Purpose

Microwave ablation (MWA) is feasible for severe renal secondary hyperparathyroidism (SHPT) and primary hyperparathyroidism (PHPT) patients ineligible for parathyroidectomy (PTX). Here we compared the clinical manifestations and characteristics of parathyroid glands in these two groups, and summarized the techniques, safety and efficacy of MWA.

Methods

Baseline clinical characteristics, ablation-related techniques, adverse events/complications, and efficacy were recorded.

Results

In SHPT group, malnutrition, cardiovascular/pulmonary complications, and abnormal bone metabolism were severe. SHPT patients had more hyperplastic parathyroid glands. The volume of each gland was smaller, and the time of ablation for a single parathyroid was shorter in the SHPT group, although there were no significant differences compared with patients in the PHPT group. Three patients in both groups had recurrent laryngeal nerve injuries and all recovered, except for one SHPT patient. By the end of follow-up, serum iPTH levels had decreased from 2400.26 ± 844.26 pg/mL to 429.39 ± 407.93 pg/mL (p < .01) in SHPT and from 297.73 ± 295.32 pg/mL to 72.22 ± 36.51 pg/mL in PHPT group (p < .01). Hypocalcemia was more common (p < .001) and serum iPTH levels were prone to rebound in SHPT patients after MWA.

Conclusion

MWA can be reserved for those who had high surgical risks because of less invasiveness. Injuries of recurrent laryngeal nerves should be noticed. The health status, perioperative, and intraoperative procedures were more complicated and all parathyroids found by ultrasound should be ablated completely in SHPT patients.

Setup of an Ablation Magnetic Resonance Imaging Hybrid System: Using MR Imaging Sequences to Destroy Tissue

The need of external ablation generators complicates the setup of magnetic resonance (MR) guided interventions, e. g. due to inserting devices with ferrite components into the MR room or because of image distortions due to RF interferences. By using the power provided from the MR internal power amplifier, it is possible to avoid external ablation generators. Using imaging sequences with a high duty cycle, a sufficient mean power value can be generated to destroy tissue. In this paper, it has been shown that it is possible to destroy tissue with such an ablation MRI hybrid system. Simulations were done to calculate the specific absorption rate (SAR) generated by an ablation electrode at the Larmor frequency for a 3 T MR device. The SAR values were then compared with ablation experiments performed inside an MR device with protein phantoms.

Lesion modeling, characterization, and visualization for image-guided cardiac ablation therapy monitoring

In spite of significant efforts to improve image-guided ablation therapy, a large number of patients undergoing ablation therapy to treat cardiac arrhythmic conditions require repeat procedures. The delivery of insufficient thermal dose is a significant contributor to incomplete tissue ablation, in turn leading to the arrhythmia recurrence. Ongoing research efforts aim to better characterize and visualize RF delivery to monitor the induced tissue damage during therapy. Here, we propose a method that entails modeling and visualization of the lesions in real-time. The described image-based ablation model relies on classical heat transfer principles to estimate tissue temperature in response to the ablation parameters, tissue properties, and duration. The ablation lesion quality, geometry, and overall progression are quantified on a voxel-by-voxel basis according to each voxel's cumulative temperature and time exposure. The model was evaluated both numerically under different parameter conditions, as well as experimentally, using ex vivo bovine tissue samples undergoing ex vivo clinically relevant ablation protocols. The studies demonstrated less than 5°C difference between the model-predicted and experimentally measured end-ablation temperatures. The model predicted lesion patterns were within 0.5 to 1 mm from the observed lesion patterns, suggesting sufficiently accurate modeling of the ablation lesions. Lastly, our proposed method enables therapy delivery feedback with no significant workflow latency. This study suggests that the proposed technique provides reasonably accurate and sufficiently fast visualizations of the delivered ablation lesions.

Focused Magnetic Resonance Coupling Coils for Electromagnetic Therapy Applications

This paper presents the design and construction of a pair of figure-of-eight coils, coupled by magnetic resonance coupling (MRC), which could generate (150 V/m per Ampere) electric field at the focal points for electromagnetic therapy related applications. The E field generated at the targeted site would be significantly enhanced under the same amount of current flowing through the MRC figure-of-eight coils compared to normal coils, due to the superposition of E field contributed by the coils. Furthermore, the MRC figure-of-eight coil is designed and the results are verified in theory, simulation, and experiments. In the ex vivo tissue measurement, 35% current and 82% ohmic power improvements were observed. Since it can enhance the current and ohmic power, the MRC figure-of-eight coils are promising solutions for electromagnetic therapy applications. The potential applications of the coils include noninvasive radio frequency (RF) stimulation, thermoacoustic imaging, electromagnetic field therapies, and RF ablation, etc.