TRADITIONAL POSTER - ismrm

Poster Sessions
1827. MRgRFA: Physical Model and First Order Correction of PRFS Thermometry Corrupted by Magnetic
Susceptibility-Mediated Cavitation’s Effects
Rares Salomir 1 , Magalie Viallon 1 , Sylvain Terraz 1 , Christoph D Becker 1
1 Radiologie, Hopital Universitaire de Genève, Geneva, Switzerland
MR thermometry based on the proton resonance frequency (PRF) method (1) has gained good acceptance for guiding RF ablation of liver tumors (2). Major
artifacts in the PRFS thermometry have recently been reported related to per-operatory changes of the tissue bulk susceptibility during RF heating (3). They
are originating from gas bubbles formation, known as white cavitations’ artifacts in US imaging. We propose here a theoretical description of the effects and
a first order correction that confirm the source of the spatially related errors in temperature maps and TD during power application.
1828. MR Thermometry in Moving Objects Using a Novel Referenceless and User-Independent Approach
Bruno Madore 1 , Renxin Chu 1 , Chang-Sheng Mei 1,2 , Lawrence P. Panych 1
1 Radiology Department, Brigham and Women's Hospital, Harvard Medical School , Boston, MA, United States; 2 Department of
Physics, Boston College, Chestnut Hill, MA, United States
MR thermometry in moving organs is a challenging application, as fairly subtle temperature-induced changes must be accurately measured in the presence of
often much larger motion-induced changes. A novel approach at doing so is proposed here, which is both referenceless (does not require a baseline reference
image) and user-independent.
1829. Air Susceptibility Effects on Proton Resonance Frequency Temperature Mapping
Markus Nikola Streicher 1 , Andreas Schäfer 1 , Dimo Ivanov 1 , Robert Turner 1
1 Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
MR thermometry is usually based on the temperature dependence of the proton resonance frequency (PRF), thus any magnetic field changes might be
misinterpreted as temperature changes. Here we report on the effects of changes of susceptibility of surrounding air on the magnetic field inside an object.
When the air was heated by 46 ºC, its susceptibility changed from χ air = 3.6×10 -7 to χ air = 2.7×10 -7 , inducing an apparent additional temperature change of
1.9°C inside the object. For a more realistic surrounding air temperature increase of 10°C this could result in an error of 0.75°C.
1830. Real-Time MR-Thermometry and Dosimetry for Interventional Guidance on Abdominal Organs
Sébastien Roujol 1,2 , Mario Ries 1 , Bruno Quesson 1 , Chrit Moonen 1 , Baudouin Denis de Senneville 1
1 laboratory for molecular and functional imaging: from physiology to therapy, CNRS/ University Bordeaux 2, Bordeaux, Aquitaine,
France; 2 LaBRI, University Bordeaux 1, Talence, Aquitaine, France
A computationally efficient pipeline for 2D motion compensated PRF-thermometry and thermal dose measurements on moving abdominal organs is
presented. The method is designed to address both, inter-scan and intra-scan artifacts by applying high frame-rate MRI coupled with a real-time image
processing. The proposed MR-thermometry method was evaluated in both liver and kidney of 11 healthy volunteers and achieved a precision of less than 2
°C in 70 % of the pixels. The ability to perform MR-Thermometry and Dosimetry in-vivo was demonstrated on one HIFU-heating experiment on a porcine
kidney.
1831. A Self-Reference MR Thermometry Method Utilizing the Phase Gradient
Jason A. Langley 1,2 , Qun Zhao 1,2
1 Department of Physics and Astronomy, The University of Georgia, Athens, GA, United States; 2 Bioimaging Research Center (BIRC),
The University of Georgia, Athens, GA, United States
A modified self-reference MR thermometry method is presented in this abstract. We circumvent the phase unwrapping procedure in the self-reference MR
thermometry procedure by utilizing the phase gradient to estimate the baseline phase map. In the method proposed in this abstract, the phase map is modeled
as a 2D polynomial. The components of the gradient of the model are then fitted to the components of the phase gradient using 2D weighted least squares.
The proposed procedure is evaluated using two simulated MR thermometry data sets.
1832. First Clinical Experience with Navigated RF Ablations of the Liver in a Closed-Bore 1.5T MRI
Daniel Seider 1 , Harald Busse 1 , Nikita Garnov 1 , Gregor Thörmer 1 , Susann Heinig 1 , Tim Riedel 1 , Thomas
Kahn 1 , Michael Moche 1
1 Diagnostic and Interventional Radiology, Leipzig University Hospital, Leipzig, Germany
MRI is well suited to guide percutaneous interventions of liver lesions that are hardly visible with ultrasound or CT. Dedicated open MR systems are often
used because they provide good patient access. This work presents first clinical experience with a new navigation solution that was used during RF ablation
of liver tumors in a standard closed-bore scanner environment. After a special breathhold training, even double oblique access paths could be realized. RFA
probe and thermally induced lesion could be reliably visualized with a VIBE sequence. While technical efforts are higher the times for needle placement and
thermal ablation are comparable to those under CT guidance.
1833. Highly Accelerated Temperature Mapping Using Nonlocal Regularized Parallel Imaging
Sheng Fang 1 , Xinyi Pan 1 , Kui Ying 1
1 Department of Engineering Physics, Tsinghua University, Beijing, China
Model-based MR thermometry method based on the proton resonance frequency shift (PRFS) can effectively improve the temperature estimate accuracy of
conventional phase different method. However, its temporal resolution need be improved for real-time temperature monitoring. To solve the problem, we
applied highly accelerated PI to temperature mapping and used nonlocal regularization that extracts the prior from the acquired data themselves to stabilize
the reconstruction. The method was demonstrated using whipping cream phantom. The results show that the nonlocal regularization can effectively increase
the temporal resolution of PRFS while avoiding the introducing the bias to quantification, due to its data-driven property.