title: Renal ablation using magnetic resonance-guided high intensity focused ultrasound: Magnetic resonance imaging and histopathology assessment.
abstract: OBJECTIVE
  To use magnetic resonance-guided high intensity focused ultrasound (MRg-HIFU), magnetic resonance imaging (MRI) and histopathology for noninvasively ablating, quantifying and characterizing ablated renal tissue.
  
  
  METHODS
  Six anesthetized/mechanically-ventilated pigs underwent single/double renal sonication (n = 24) using a 3T-MRg-HIFU (1.1 MHz frequency and 3000J-4400J energies). T2-weighted fast spin echo (T2-W), perfusion saturation recovery gradient echo and contrast enhanced (CE) T1-weighted (T1-W) sequences were used for treatment planning, temperature monitoring, lesion visualization, characterization and quantification, respectively. Histopathology was conducted in excised kidneys to quantify and characterize cellular and vascular changes. Paired Student's t-test was used and a P-value < 0.05 was considered statistically significant.
  
  
  RESULTS
  Ablated renal parenchyma could not be differentiated from normal parenchyma on T2-W or non-CE T1-W sequences. Ablated renal lesions were visible as hypoenhanced regions on perfusion and CE T1-W MRI sequences, suggesting perfusion deficits and necrosis. Volumes of ablated parenchyma on CE T1-W images in vivo (0.12-0.36 cm(3) for single sonication 3000J, 0.50-0.84 cm(3), for double 3000J, 0.75-0.78 cm(3) for single 4400J and 0.12-2.65 cm(3) for double 4400J) and at postmortem (0.23-0.52 cm(3), 0.25-0.82 cm(3), 0.45-0.68 cm(3) and 0.29-1.80 cm(3), respectively) were comparable. The ablated volumes on 3000J and 4400J double sonication were significantly larger than single (P < 0.01), thus, the volume and depth of ablated tissue depends on the applied energy and number of sonication. Macroscopic and microscopic examinations confirmed the locations and presence of coagulation necrosis, vascular damage and interstitial hemorrhage, respectively.
  
  
  CONCLUSIONS
  Contrast enhanced MRI provides assessment of MRg-HIFU renal ablation. Histopathology demonstrated coagulation necrosis, vascular damage and confirmed the volume of damage seen on MRI.
authors.affiliation: Maythem Saeed, Roland Krug, Loi Do, Steven W Hetts, Mark W Wilson, Department of Radiology and Biomedical Imaging, School of Medicine, University of California San Francisco, San Francisco, CA 94107-5705, United States.
authors.forename: Maythem
authors.initials: M
authors.lastname: Saeed
authors.affiliation: Maythem Saeed, Roland Krug, Loi Do, Steven W Hetts, Mark W Wilson, Department of Radiology and Biomedical Imaging, School of Medicine, University of California San Francisco, San Francisco, CA 94107-5705, United States.
authors.forename: Roland
authors.initials: R
authors.lastname: Krug
authors.affiliation: Maythem Saeed, Roland Krug, Loi Do, Steven W Hetts, Mark W Wilson, Department of Radiology and Biomedical Imaging, School of Medicine, University of California San Francisco, San Francisco, CA 94107-5705, United States.
authors.forename: Loi
authors.initials: L
authors.lastname: Do
authors.affiliation: Maythem Saeed, Roland Krug, Loi Do, Steven W Hetts, Mark W Wilson, Department of Radiology and Biomedical Imaging, School of Medicine, University of California San Francisco, San Francisco, CA 94107-5705, United States.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Hetts
authors.affiliation: Maythem Saeed, Roland Krug, Loi Do, Steven W Hetts, Mark W Wilson, Department of Radiology and Biomedical Imaging, School of Medicine, University of California San Francisco, San Francisco, CA 94107-5705, United States.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Wilson
keywords: High intensity focused ultrasound; Magnetic resonance imaging; Magnetic resonance-guided high intensity focused ultrasound; Microscopy; Renal ablation