MR-guided high-focused ultrasound for renal sympathetic denervation—a feasibility study in pigs

Abstract

BackgroundRenal sympathetic denervation has recently gained clinical relevance for the treatment of therapy-resistant hypertension. Denervation is currently mainly performed using catheter-based transarterial radiofrequency ablation of periarterial sympathetic nerve fibers. Since this approach has numerous limitations, we conducted a study to evaluate the feasibility, safety, and efficacy of magnetic resonance-guided high-focused ultrasound (MRgHiFUS) for renal sympathetic denervation in pigs as an alternative to catheter-based ablation.MethodsRenal periarterial MRgHiFUS was performed under general anesthesia in ten pigs. Blood pressure measurements and magnetic resonance imaging (MRI) of the kidneys, renal arteries, and surrounding structures were obtained immediately before and after the interventions and after 4 weeks. Histological examinations of periarterial tissues and determination of renal norepinephrine (NE) concentration were performed to assess treatment efficacy.Results and discussionIn each pig, 9.8 ± 2.6 sonications with a mean energy deposition of 2,670 ± 486 J were performed. The procedure was well tolerated by all pigs. No major complications occurred. MRgHiFUS induced periarterial edema in three pigs, but only one pig showed corresponding histological changes. The NE level of the treated kidney was lower in five pigs (-8% to -38%) compared to the untreated side. Overall, there was no significant difference between the NE values of both kidneys in any of the treated pigs. Postinterventional MRI indicated absorption of ultrasound energy at the transverse process and fascia.ConclusionMRgHiFUS had some thermal periarterial effects but failed to induce renal denervation. Insufficient energy deposition is most likely attributable to a small acoustic window with beam path impediment in the porcine model. Since HiFUS treatment in humans is expected to be easier to perform due to better access to renal sympathetic nerves, further studies of this method are desirable to investigate the potential of MRgHiFUS as an alternative for patients not suitable for catheter-based renal sympathicolysis.

Renal sympathetic denervation using MR-guided high-intensity focused ultrasound in a porcine model

“…Therefore, while MR thermometry was not able to predict an acute treatment assessment, the use of the temperature probe did demonstrate the MRgHIFU beam was focused in close proximity to the renal artery. This result extends the assessment that has been performed in other HIFU RSD studies [ 13 , 12 ].…”

“…In our study, the total delivered energy per animal varied from 10–100 kJ. Other RSD HIFU studies reported total energy delivery of 18 kJ [ 12 ] and a mean of 26.2 kJ per animal [ 13 ] with varied efficacy results. This variability indicates that successful treatment outcome is a function of applied dose as well as animal position and size.…”

“…In Wang et al [ 12 ], a 51 % reduction in plasma norepinephrine was observed 6 days post-procedure. Conversely, in Freyhardt et al [ 13 ], no significant change was observed in the renal parenchyma norepinephrine concentration.…”

“…High-intensity focused ultrasound (HIFU) is an established treatment option in various disorders [ 11 ] and has been proposed as an alternative energy delivery source for RSD therapy. Recently both an ultrasound and MRI-guided approach demonstrated feasibility using HIFU to perform RSD in normotensive canine [ 12 ] and porcine models [ 13 ] with mixed efficacy results. This study furthers those feasibility assessments by performing renal denervation using magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) in a normotensive porcine model.…”

Feasibility Study on MR-Guided High-Intensity Focused Ultrasound Ablation of Sciatic Nerve in a Swine Model: Preliminary Results

“…Current clinical applications of MRgHIFU include the ablation of tumors [16–19], functional neurosurgery [20] and palliation of pain in patients with bone metastasis [21]. The lowered risk of complications due to the noninvasive nature of MRgHIFU makes it an attractive modality for neurolysis [22–24]. …”