Basic Study
Copyright ©The Author(s) 2016. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Radiol. Mar 28, 2016; 8(3): 298-307
Published online Mar 28, 2016. doi: 10.4329/wjr.v8.i3.298
Renal ablation using magnetic resonance-guided high intensity focused ultrasound: Magnetic resonance imaging and histopathology assessment
Maythem Saeed, Roland Krug, Loi Do, Steven W Hetts, Mark W Wilson
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
Author contributions: Saeed M designed the study, performed the experiments, analyzed MR images/histology and wrote the manuscript; Krug R performed the ablation and MR imaging and involved in manuscript editing; Do L achieved and analyzed the images, prepared the figures and involved in manuscript editing; Hetts SW and Wilson MW provided vital advices and were also involved in manuscript editing.
Institutional review board statement: Departmental Scientific Merit Approval.
Institutional animal care and use committee statement: This study received approval from Institutional Animal Care and Use Committee.
Conflict-of-interest statement: All investigators have no conflict-of-interest.
Data sharing statement: The authors are solely responsible for the data.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Maythem Saeed, PhD, Professor, Department of Radiology and Biomedical Imaging, School of Medicine, University of California San Francisco, 185 Berry Street, Suite 350, Campus Box 0946, San Francisco, CA 94107-5705, United States. msaeed@ucsf.edu
Telephone: +1-415-5146221 Fax: +1-415-3539423
Received: June 26, 2015
Peer-review started: July 7, 2015
First decision: September 11, 2015
Revised: October 23, 2015
Accepted: November 13, 2015
Article in press: November 17, 2015
Published online: March 28, 2016
Abstract

AIM: 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 cm3 for single sonication 3000J, 0.50-0.84 cm3, for double 3000J, 0.75-0.78 cm3 for single 4400J and 0.12-2.65 cm3 for double 4400J) and at postmortem (0.23-0.52 cm3, 0.25-0.82 cm3, 0.45-0.68 cm3 and 0.29-1.80 cm3, 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.

CONCLUSION: 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.

Keywords: Magnetic resonance-guided high intensity focused ultrasound, Renal ablation, Magnetic resonance imaging, Microscopy, High intensity focused ultrasound

Core tip: Renal carcinoma constitutes the majority of kidney malignancies. The gold standard procedure for treatment of renal carcinoma remains surgical excision. However, in a large number of patients, surgical excision is precluded by increased perioperative risk due to medical comorbidities. Recent innovations in the field of thermal ablation procedures and real-time imaging have accelerated the development of magnetic resonance-guided high intensity focused ultrasound (MRg-HIFU). This study showed that contrast enhanced magnetic resonance imaging (MRI) provides good assessment of renal ablation created noninvasively by MRg-HIFU. The volume and depth of ablated tissue depends on the applied energy and number of sonications. Histopathology demonstrated coagulation necrosis and vascular damage in the ablated tissue and confirmed the volume of damage seen on contrast enhanced MRI.