Thermotherapy, HIFU & Preclinical Interventions
Tuesday 4 May 2010
Room A4 13:30-15:30 Moderators: Dennis L. Parker and Viola Rieke

13:30 244.

Velocity Navigator Triggering for Motion Compensated PRF Thermometry - not available
Florian Maier1, Axel Joachim Krafft1, Jürgen W. Jenne2,3, Rüdiger Dillmann4, Wolfhard Semmler1, Michael Bock

1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 2Clinical Cooperation Unit Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 3Mediri GmbH, Heidelberg, Germany; 4Institute of Anthropomatics, Karlsruhe Institute of Technology, Karlsruhe, Germany

Proton resonance frequency shift thermometry is sensitive to motion. Artifacts are caused by tissue displacement and susceptibility changes. In this work, a novel navigator technique for triggering MR thermometry image acquisition is presented. Non-velocity and velocity encoded navigator signals were acquired without lengthening of TR. Based on the phase variation of non-encoded values and the estimated velocity, trigger events were generated. The measurements indicate that the proposed triggered segmented EPI pulse sequence allows for motion compensated thermometry of periodically moving tissue.

13:42 245.

Fat-Referenced MR Thermometry in Heterogeneous Tissue Using IDEAL
Lorne Hofstetter1, Desmond Teck Beng Yeo2, Cynthia Davis2, Thomas K. Foo2
GE Global Research, Niskayuna , NY, United States; 2GE Global Research, Niskayuna, NY, United States

Time-varying, non-temperature dependent phase changes affect the accuracy of conventional phase difference proton resonance frequency shift (PRFS) temperature mapping in the breast.  We demonstrate a fat-referenced PRFS technique capable of correcting for this phase variation. This new approach reduced temperature measurement error in the left breast by a factor of 3.6 and in the right breast by a factor of 2.5 when compared to conventional phase difference techniques (n = 1).

13:54 246

The Effects of Spatial Sampling Choices on MR Temperature Measurements
Nick Todd1, Josh De Bever2, Urvi Vyas3, Allison Payne4, Dennis L. Parker5
Physics, University of Utah, Salt Lake City, UT, United States; 2Robotics, University of Utah, Salt Lake City, UT, United States; 3Bioengineering, University of Utah, Salt Lake City, UT, United States; 4Mechanical Engineering, University of Utah, Salt Lake City, UT, United States; 5Radiology, University of Utah, Salt Lake City, UT, United States

MR temperature maps are necessarily a discrete representation of a physical quantity that is continuously varying in both space and time. The HIFU focal spot size can be smaller than the imaging voxel dimensions.  Due to averaging effects, it is likely that different choices for the sampling grid location, voxel size, and scan time will lead to variations in the measured temperature distribution. In this abstract we present simulation and experimental results quantifying the effects of the sampling scheme on maximum temperature and thermal dose, and show the effects of zero-filled-interpolation post-processing on the measured maximum temperature and thermal dose.

14:06 247.  

Reference-Less PRFS MR Thermometry Using a Thin Open Border and the Harmonic Functions Theory: 2D Experimental Validation
R Salomir1, M Viallon1, Joerg Roland2, Sylvain Terraz1, Denis Morel3, CD Becker1, P Gross2
1Radiologie, Hopital Universitaire de Genève, Geneva, Switzerland; 2Siemens Medical Solutions, Erlangen, Germany; 3Anesthesiology, University Hospitals of Geneva, Geneva, Switzerland

A new method for reference-less MR thermometry is described based on the fundamental theoretical frame of harmonic functions. The method was implemented for a thin open border and validated for 2D situation with HIFU heating in phantoms and in vivo rabbit thigh, and also with baseline acquisition in volunteers liver. Measurement accuracy in liver under free breathing was as good as 0.5°C for 0.3 seconds temporal resolution. The method is insensitive to periodic or accidental motion, tissue expansion or drift, and to external perturbation from interventional device.

14:18 248.

Hybrid Multi-Baseline and Referenceless PRF-Shift Thermometry
William A. Grissom1,2, Andrew B. Holbrook3, Viola A. Rieke2, Michael Lustig1, Juan A. Santos1, Aravind Swaminathan, Michael V. McConnell, Kim Butts Pauly2
1Electrical Engineering, Stanford University, Stanford, CA, United States; 2Radiology, Stanford University, Stanford, CA, United States; 3Bioengineering, Stanford University, Stanford, CA, United States

We introduce a new temperature estimation method that is a hybrid of multi-baseline and referenceless methods. From multi-baseline methods the hybrid method inherits the ability to estimate temperature in the presence of rapidly-varying background anatomical phase. From referenceless methods the hybrid method inherits robustness to smooth main field shifts during thermal therapy. The method is demonstrated in the heart and liver.

14:30 249

MRI Monitoring of Skull-Base Heating in Transcranial Focused Ultrasound Ablation
Yuexi Huang1, Junho Song1, Kullervo Hynynen1,2
1Sunnybrook Health Sciences Centre, Toronto, ON, Canada; 2Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada

In transcranial focused ultrasound ablation, the heating of the outer skull surface has been reduced by a hemispherical design of phased-array transducers and active cooling of the skull surface with water circulation. However, the potential heating of the skull base has not been brought into much attention. In this work, experiments were performed with a MR-guided transcranial focused ultrasound system on a full human skull sample to investigate the heating of the skull base. MR thermometry was applied to measure the temperature change of the phantom adjacent to the skull base. The distance of the foci to the bone was varied to measure a safety margin for avoiding significant skull base heating.

14:42 250

Temperature Measurement Nearby an Iceball Using the Proton Resonance Frequency Method: Recalculation of Susceptibility Artifacts
Antje Kickhefel1, Rares Salomir2,3, Jörg Roland4, Patrick Gross4, Fritz Schick5, Clifford R. Weiss

1Eberhard-Karls-University Tübingen , Tübingen,  Baden-Württemberg, Germany; 2University Hospitals of Geneva, Switzerland; 3 University Hospitals of Geneva; 4Siemens Healthcare, Erlangen, Germany; 5Eberhard-Karls-University Tübingen, Tübingen,  Baden-Württemberg, Germany; 6Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, United States

The study demonstrates that susceptibility artifacts in GRE phase image induced by ice ball can be corrected allowing the PRF method to be used to monitor the near zero temperature during cryoablation. Susceptibility artifacts were corrected in post-processing. First the susceptibility contrast between frozen and melted meat was determined and second the magnetic perturbation was calculated using a convolution filter in the k-space. The susceptibility artifacts were fully corrected. In conclusion, using an in-line post processing system, this method could be applied during clinical MR-guided cryotherapy, and allow for the non-invasive monitoring of near zero temperatures.

14:54 251

PRF Based MR-Thermometry on Abdominal Organs: A Pragmatic Comparison of Referenceless Vs Multi-Baseline
Baudouin Denis de Senneville1, Sébastien Roujol1,2, Chrit Moonen1, Mario Ries1
Laboratory for Molecular and Functional Imaging: From Physiology to Therapy, CNRS/ University Bordeaux 2, Bordeaux, Aquitaine, France; 2LaBRI, CNRS/ University Bordeaux 1, Talence, Aquitaine, France

Reliable temperature and thermal-dose measurements using PRF based MR-thermometry for MR-guided ablation therapy on abdominal organs require a robust correction of artefacts induced by the target displacement through an inhomogeneous and time-variant magnetic field. The presented study combines the two most promising candidates for this role, the multi-baseline and the referenceless method, with a real-time in-plane motion correction which permits thermal-dose calculations and evaluates the practical aspects of both methods in an ex-vivo RF-ablation and an in-vivo high-intensity focused ultrasound ablation of a porcine kidney.

15:06 252.

Quantitative Perfusion Analysis for Transcatheter Intraarterial Perfusion MR Imaging
Dingxin Wang1, Johnathan Chung2, Robert Lewandowski2, Richard Tang2, Rachel Klein2, Reed Omary1,3, Andrew Larson1,3

1Departments of Radiology and Biomedical Engineering, Northwestern University, Chicago, IL, United States; 2Department of Radiology, Northwestern University, Chicago, IL, United States; 3Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, IL, United States

In this study, we presented a new quantitative TRIP-MRI perfusion analysis approach, and evaluated its efficacy in a gel perfusion phantom and in rabbits with VX2 liver tumors during TAE. Our results successfully evaluated the efficacy of this proposed perfusion analysis method for TRIP-MRI datasets in the perfusion phantom, and demonstrated the use of quantitative TRIP-MRI to monitor reductions in liver tumor perfusion during TAE.

15:18 253

MR-Based Dosimetry of  166holmium-Loaded Microspheres for Internal Radiation Therapy Treatment Planning
Peter Roland Seevinck1, Tim C. de Wit2, Gerrit Hendrik van de Maat1, Maarten A.D. Vente3, Mattijs Elschot3, Mark Konijnenberg4, Johannes F.W. Nijsen3, Chris JG Bakker1,2
Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; 2Dept. of Radiology, University Medical Center Utrecht, Utrecht, Netherlands; 3Dept. of Nucleair Medicine, University Medical Center Utrecht, Utrecht, Netherlands; 4Research and Development, Mallinckrodt Medical BV, Covidien, Petten, Netherlands

The potential of MRI for dose calculations of Holmium-166 loaded microspheres to enable MR-based treatment planning of transcatheter radioembolization of hepatic malignancies was investigated. MRI and SPECT experiments were conducted using an anthropomorphic agarose gel phantom containing tumor-simulating gel samples with known amounts of 166Ho-PLLA-MS. Excellent agreement was observed both qualitatively and quantitatively when comparing MR-based to SPECT-based dose maps to reference data obtained with a dose calibrator. In conclusion, MR-based dosimetry of 166Ho-PLLA-MS was demonstrated to be feasible, indicating the potential of MR-based dosimetry for planning, guidance and evaluation of transcatheter radioembolization treatment of hepatic malignancies with 166Ho-PLLA-MS.



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