title: Renal sympathetic denervation using MR-guided high-intensity focused ultrasound in a porcine model.
abstract: BACKGROUND
  Initial catheter-based renal sympathetic denervation (RSD) studies demonstrated promising results in showing a significant reduction of blood pressure, while recent data were less successful. As an alternative approach, the objective of this study was to evaluate the feasibility of using magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) to perform RSD in a porcine model.
  
  
  METHODS
  An intravascular fiber optic temperature probe was used to confirm energy delivery during MRgHIFU. This technique was evaluated both in a vascular phantom and in a normotensive pig model. Five animals underwent unilateral RSD using MRgHIFU, and both safety and efficacy were assessed. MRI was used to evaluate the acoustic window, target sonications, monitor the near-field treatment region using MR thermometry imaging, and assess the status of tissues post-procedure. An intravascular fiber optic temperature probe verified energy delivery. Animals were sacrificed 6 to 9 days post-treatment, and pathological analysis was performed. The norepinephrine present in the kidney medulla was assessed post-mortem.
  
  
  RESULTS
  All animals tolerated the procedure well with no observed complications. The fiber optic temperature probe placed in the target renal artery confirmed energy delivery during MRgHIFU, measuring larger temperature rises when the MRgHIFU beam location was focused closer to the tip of the probe. Following ablation, a significant reduction (p = 0.04) of cross-sectional area of nerve bundles between the treated and untreated renal arteries was observed in all of the animals with treated nerves presenting increased cellular infiltrate and fibrosis. A reduction of norepinephrine (p = 0.14) in the kidney medulla tissue was also observed. There was no indication of tissue damage in arterial walls.
  
  
  CONCLUSIONS
  Performing renal denervation non-invasively with MRgHIFU was shown to be both safe and effective as determined by norepinephrine levels in a porcine model. This approach may be a promising alternative to catheter-based strategies.
authors: CARMA Center, Department of Cardiology, University of Utah, 30 North 1900 East, Salt Lake City, UT 84132 USA.
authors: Matthias
authors: M
authors: Koopmann
authors: Department of Surgery, University of Utah, 30 North 1900 East, Salt Lake City, UT 84132 USA.
authors: Jill
authors: J
authors: Shea
authors: Department of Radiology, University of Utah, 729 Arapeen Drive, Salt Lake City, UT 84108 USA.
authors: Eugene
authors: E
authors: Kholmovski
authors: Department of Radiology, University of Utah, 729 Arapeen Drive, Salt Lake City, UT 84108 USA.
authors: Joshua
authors: J
authors: de Bever
authors: Department of Radiology, University of Utah, 729 Arapeen Drive, Salt Lake City, UT 84108 USA.
authors: Emilee
authors: E
authors: Minalga
authors: Department of Bioengineering, University of Utah, 36 S. Wasatch Drive, Rm. 3100, Salt Lake City, UT 84112 USA.
authors: Matthew
authors: M
authors: Holbrook
authors: Department of Radiology, University of Utah, 729 Arapeen Drive, Salt Lake City, UT 84108 USA.
authors: Robb
authors: R
authors: Merrill
authors: Department of Radiology, University of Utah, 729 Arapeen Drive, Salt Lake City, UT 84108 USA.
authors: J Rock
authors: JR
authors: Hadley
authors: Department of Cardiology, University of Utah, 30 North 1900 East, Salt Lake City, UT 84132 USA.
authors: Theophilus
authors: T
authors: Owan
authors: Department of Pathology, University of Utah, 15 North Medical Drive East Ste #1100, Salt Lake City, UT 84112 USA.
authors: Mohamed E
authors: ME
authors: Salama
authors: CARMA Center, Department of Cardiology, University of Utah, 30 North 1900 East, Salt Lake City, UT 84132 USA.
authors: Nassir F
authors: NF
authors: Marrouche
authors: Department of Radiology, University of Utah, 729 Arapeen Drive, Salt Lake City, UT 84108 USA.
authors: Allison
authors: A
authors: Payne
keywords: High-intensity focused ultrasound; MRI; Renal sympathetic denervation