Thermometry & Thermotherapy

Tuesday 13 May 2014

Rares V Salomir¹, Antje Kickhefel², Joerg Roland², Vincent Auboiroux^1,3, Arnaud Muller⁴, Christoph D Becker¹, and Patrick Gross^2
1Radiology, University of Geneva, Geneva, Switzerland, ²MR division, Siemens Healthcare, Erlangen, Germany, ³Clinatec/LETI, CEA, Grenoble, France,⁴NMR Unit, CHU Lyon Sud, Lyon, France

PRFS MR thermometry (MRT) is the generally preferred method for MR monitoring of the thermal ablation. Standard implementation with reference phase subtraction is highly sensitive to tissue motion and to external perturbation of the magnetic field. Previously described reference-less MRT was systematically applied on slice-per-slice basis, as a two dimensional problem. The purpose of the current work was to develop and validate a novel method for multi-planar reference-less PRFS thermometry using a linear spectral decomposition of the background phase on a base of spatial (3D) spherical harmonics. Accurate results were demonstrated on ex vivo samples and in sheep liver in vivo using MRgHIFU.

G. Wilson Miller^1,2, Kelsie F. Timbie², and Richard J. Price^1,2
1Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, United States, ²Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, United States

MR-ARFI (acoustic radiation force imaging) is a promising technique for visualizing the focal spot in MR-guided focused ultrasound without actually heating the tissue. We present here a new approach for generating sensitivity to the ARFI effect, based on a fluctuating-equilibrium (FE) balanced steady-state free-precession pulse sequence, that results in a magnitude difference (instead of a phase difference) between two oppositely encoded images. Our fluctuating equilibrium MR-ARFI technique is demonstrated in a gel phantom and in a living rat brain.

Misung Han¹, Serena J Scott^2,3, Eugene Ozhinsky¹, Vasant Salgaonkar², Peder EZ Larson¹, Chris J Diederich², Viola Rieke¹, and Roland Krug^1
1Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States, ²Radiation Oncology, University of California, San Francisco, San Francisco, CA, United States, ³Joint Graduate Group in Bioengineering, University of California San Francisco/Berkeley, San Francisco, CA, United States

High-intensity focused ultrasound is a new, noninvasive technique to ablate bone tumors and palliate pain. MR thermometry is frequently employed to ensure proper heat deposition to the targeted tumor and to prevent unwanted damage to healthy tissues. However, conventional MR thermometry based on the proton resonance frequency (PRF) shift of water is not suitable for monitoring temperature in cortical bone due to its short T2* relaxation time. In this work, we demonstrate the ability of 3D UTE imaging to assess T1 changes in cortical bone due to heating.

Urvi Vyas¹, Ethan M Johnson², John Pauly², and Kim Butts Pauly^1,3
1Radiology, Stanford University, Palo Alto, CA, United States, ²Electrical Engineering, Stanford University, Palo Alto, CA, United States, ³Bioengineering, Stanford University, CA, United States

CT-based imaging is currently used in transcranial MR-guided focused ultrasound surgery to correct for distortions in the location and shape of the beam’s focus due to heterogeneities of the cranium In this work, we compare bone contours segmented from CT and 3D UTE images. We use 3D ultrasound beam simulations to demonstrate the effect on the location and intensity of the focal zone using phase aberrations calculated from a cortical-only CT model and a UTE bone model. We find that correcting phase aberrations using the UTE model recovers 75% of the focal intensity at the focal (compared to the cortical CT model recovering 98%).

Eugene Ozhinsky¹, Maureen Kohi¹, and Viola Rieke^1
1Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States

In this study, we have implemented T2-based monitoring of near-field heating in patients, undergoing HIFU ablation of uterine fibroids using Insightec ExAblate system. In certain areas, near-field heating can reach 18°C and the tissue may experience sustained heating of more than 10°C for the period of 2 hours or more. This indicates a cumulative thermal dose that may cause necrosis. Our results show the feasibility and importance of measurement of near-field heating in subcutaneous fat.

E. M. Kardoulaki¹, R. R. A. Syms¹, I. R. Young¹, M. Rea², and W. M. W. Gedroyc^2
1Electrical and Electronic Engineering, Imperial College, London, United Kingdom, ²St. Mary's Hospital, London, United Kingdom

High SNR imaging with internal coil detectors has been verified and numerous designs have been proposed. Prior work employing them has shown improvements in controlling MR-guided high intensity focused ultrasound and RF ablations. Here we present results from a phantom-experiment conducted in a 3 T GE scanner to investigate the merits of substituting the 8-channel array coil -typically used during Nd:YAG laser liver interstitial thermal therapies (LITTs)- with a flexible micro-coil integrated on a commercially available laser ablation catheter.

Sherif G. Nour^1,2, Andrew David Nicholson^1,2, Tracy E. Powell^1,2, Melinda M. Lewis^3,4, and Viraj Master^4,5
1Radiology and Imaging Sciences, Emory University Hospital, Atlanta, GA, United States, ²Interventional MRI Program, Emory University Hospital, Atlanta, GA, United States, ³Pathology, Emory University Hospital, GA, United States, ⁴School of Medicine, Emory University, GA, United States,⁵Urology, Emory University Hospital, GA, United States

Interventional MRI technology has been used to guide and monitor renal ablation procedures because of its ability to provide online feedback on ablation progress and determine treatment endpoints based of individual tumor responses. The dissemination of this application of iMRI has been hampered by the cumbersome handling of cryoprobes/RFA probes and their cablings within the limited gantry space. We report a simple approach for interactive guidance and real-time monitoring of renal ablations performed entirely within an interventional MRI suite using a short introducing needle and a flexible laser fiber. The technique, safety, and short- and intermediate-term efficacy are discussed.

Matthias C. Roethke¹, Mathieu Burtnyk², Timur H. Kuru³, Maya Wolf¹, Gencay Hatiboglu³, Michele Billia⁴, Cesare Romagnoli⁵, Sascha Pahernik³, Joseph Chin⁴, and Heinz-Peter Schlemmer^1
1Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Profound Medical Inc., Toronto, Ontario, Canada, ³Urology, University Hospital Heidelberg, Germany, ⁴Urology, Western University UWO, London Health Sciences Center, London Victoria Hospital, Ontario, Canada,⁵Radiology, Western University UWO, London Health Sciences Center, London Victoria Hospital, Ontario, Canada

MRI-guided transurethral ultrasound ablation is a novel minimally-invasive treatment for localised prostate cancer, where a volume of thermal ablation is generated and shaped precisely to the prostate using MR-thermometry feedback control. A phase I safety and feasibility clinical trial was initiated, with 16 patients treated to-date and no cases of urinary incontinence or rectal injury. Median treatment time and prostate volume were 29min and 45ml. Spatial control of the ablation volume was -0.1±1.4mm (+0.5/-1.2ml), with good correlation to the non-perfused volume on post-treatment CE-MRI. At 1-month, median PSA reduced by 87% to 0.7ng/ml, with the nadir expected by 6 months.

Rajiv Chopra¹, Charles Mougenot², Aaron Boyes³, Robert Staruch³, Elizabeth Ramsay³, Mohamed Kazem³, Linda Sugar³, Masoom Haidar³, and Laurence Klotz^3
1UT Southwestern, Dallas, Texas, United States, ²Philips Healthcare, Toronto, Ontario, Canada, ³Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada

Five men have been treated for localized prostate cancer using transurethral ultrasound therapy, and whole mount pathology has been completed to assess the extent of thermal damage. For these cases, the temperature control accuracy and the treatment accuracy from comparison with histology are reported. Successful treatment to the prostate boundary has been observed, demonstrating the feasibility of this technique in prostates up to 71 cc in volume and with treatment radii up to 35 mm.

Joyce GR Bomers¹, Erik B Cornel², Christiaan O Overduin¹, Sjoerd FM Jenniskens¹, Christina A Hulsbergen - van de Kaa³, Fred Witjes⁴, and Jurgen J Fütterer^1
1Radiology, Radboud University Medical Center, Nijmegen, Gelderland, Netherlands, ²Urology, Ziekenhuisgroep Twente, Hengelo, Overijssel, Netherlands,³Pathology, Radboud University Medical Center, Nijmegen, Gelderland, Netherlands, ⁴Urology, Radboud University Medical Center, Nijmegen, Gelderland, Netherlands

Three patients with local prostate cancer underwent MR-guided focal laser ablation followed after three weeks by radical prostatectomy. Laser software, MR images and histopathologic specimens were used to assess the expected and actual size of the ablated region. The damage estimation maps of the laser software evidently overestimated the final ablation zone as seen in the histopathologic prostate images. The non enhancing area on the T1-weighted MR image gave a better indication of the final ablation zone.