Henrik Odéen^1,2, Nick Todd², Mahamadou Diakite^1,2, Allison Payne², and Dennis L. Parker^2
1Physics and Astronomy, University of Utah, Salt Lake City, Utah, United States, ²Radiology, University of Utah, Salt Lake City, Utah, United States

Three different k-space subsampling schemes were implemented in a 3D segmented EPI sequence for temperature measurements using the PRF shift method. The three schemes were evaluated by HIFU heating through a skull imbedded in an agar gel phantom. It is shown that sampling schemes with sequential sampling in the phase encode direction perform well, whereas sampling schemes with centric sampling underestimate temperatures, due to temperature induced frequency shifts resulting in a blurring effect of the focal spot.

Changqing Ye¹, An Jing², Yan Zhuo¹, Rong Xue¹, and Jing Chen^1
1State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, Beijing, China,²Siemens Mindit Magnetic Resonance Ltd., Shenzhen, Guangzhou, China

For ultra-high field imaging, many sequences are limited by the increased RF energy deposition, conventionally quantified by Specific Absorption Rate (SAR) which is an indirect estimation method, causing lack of subject¡¯s safety guarantee or unnecessary scan limitations. In this work, we present a PRF-based MR thermometry method to supervise temperature increased by the RF energy deposition directly with real-time temperature measurement with a very high precision (<0.1¡æ) within a very short time (2 s). This method might be used to monitor temperature change in subjects directly, which would be especially useful for ultra-high field imaging.

Feiyu Chen¹, Xiaoying Cai¹, Xinwei Shi¹, Shuo Chen², Enhao Gong³, Kui Ying², and Shi Wang^2
1Department of Biomedical Engineering, Tsinghua University, Beijing, China, ²Department of Engineering Physics, Tsinghua University, Beijing, China, ³Electrical Engineering, Stanford University, Stanford, CA, United States

Phase information is significant in temperature mapping using proton resonance frequency shift (PRFS) method. Acceleration methods can be applied to reconstruction in order to shorten the imaging duration and accomplish real-time temperature mapping. A method to improve the accuracy of phase reconstruction in dynamic scans is proposed in our research. Compressed Sensing with nonlinear filters such as median filter and k-t FOCUSS are combined in our method. Phantom experiments have demonstrated that the proposed method is a promising tool for real-time temperature monitoring using PRFS method.

Pooja Gaur¹ and William A. Grissom^2
1Chemical and Physical Biology, Vanderbilt University, Nashville, Tennessee, United States, ²Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, United States

Real-time volumetric MR thermometry is desirable for several applications of MR-guided focused ultrasound. We propose a constrained temperature reconstruction method that estimates temperature changes directly from k-space data. Because we fit an image model comprising fully-sampled baseline images to the accelerated k-space data, temperature maps containing aliasing artefacts are removed from the solution space, and high acceleration factors can be achieved without temporal regularization that sacrifices temporal resolution. The method is demonstrated in 2D simulations and experiments. The method will readily extend to 3D, where it will enable accurate real-time volumetric thermometry at a high frame rate.

Feiyu Chen¹, Enhao Gong², Shuo Chen³, Xinwei Shi¹, Feng Huang⁴, Shi Wang³, and Kui Ying^3
1Department of Biomedical Engineering, Tsinghua University, Beijing, China, ²Electrical Engineering, Stanford University, Stanford, CA, United States, ³Department of Engineering Physics, Tsinghua University, Beijing, China, ⁴Philips Healthcare, Gainesville, FL, United States

MR thermometry based on proton resonance frequency shift (PRFS) is a promising method for noninvasive temperature measurement. In this method, phase differential information is highly needed during the acquisition and reconstruction process. Previous research has demonstrated that the correlation between different scans could be used for reconstruction from under-sampled data. Based on this demonstration, a method for accelerated temperature mapping using sharable information from reference scans is proposed in our research. Phantom experiments have demonstrated the accuracy and feasibility of our new framework in comparison with previous parallel imaging methods and parallel¨CCS methods.

Baudouin Denis de Senneville^1,2, Chrit T.W. Moonen², and Mario Ries^2
1IMB, UMR 5251 CNRS/University Bordeaux 1/INRIA, Talence, Gironde, France, ²Imaging Division, UMC Utrecht, Utrecht, Netherlands

For the continuous monitoring of High Intensity Focused Ultrasound interventions using real-time Magnetic Resonance thermometry, a volumetric observation of the temperature in the near- and far-field would be preferable. Here, a continuous volumetric MR-temperature monitoring is obtained as follows: 1) The targeted area is continuously scanned by a multi-slice sequence; 2) Measured data and a priori knowledge of 3D data derived from a forecast based on a physical model are combined using a Kalman filter. A quantitative analysis of the accuracy of the method is presented when applied to different temperature increases and when applied with different spatial resolutions.

Peng Wang¹ and Orhan Unal^1
1Medical Physics, University of Wisconsin - Madison, Madison, Wisconsin, United States

MRI-guided RF ablation is a promising method for the treatment of atrial fibrillation. Proton resonance frequency (PRF) shift MR thermometry, which has been the method of choice, is sensitive to motion. In this work, a new method utilizing information from catheter-embedded tip tracking coils and Linear Phase Model (LPM) is proposed to synthesize reference phase images for motion correction. This method utilizes 2D multi-slice acquisition to facilitate volumetric temperature monitoring of the target region. The proposed method offers advantages in the case of irregular through-plane motion and reduced computation.

Tao Wan¹, B.Nicolas Bloch², Shabbar Danish³, and Anant Madabhushi^1
1Case Western Reserve University, Cleveland, OH, United States, ²Boston University School of Medicine, Boston, MA, United States, ³University of Medicine and Dentistry, New Jersey, New Brunswick, NJ, United States

The purpose of this work is to co-register pre- and post-ablation MRI images for laser-induced interstitial thermal therapy (LITT) of neurological disorders, in order to build an improved model for therapy planning and evaluating imaging related treatment changes in terms of MRI markers for LITT. Despite being a promising treatment option for multiple brain diseases, the effect of LITT on the focal site is currently unknown. The objective of this work is to develop a learning based fiducial driven registration method (LeFiR) for accurately registering pre- and post-LITT brain images. The localized nature of deformation induced by LITT can be well captured and precisely aligned to pre-LITT image via a supervised learning scheme. The identified optimal landmark set is utilized to drive a thin-plate spline (TPS) image registration. The LeFiR method was performed to register pre- and post-LITT brain MR images for treating glioblastoma multiforme (GBM) and epilepsy with LITT. By using LeFiR, more accurate and robust registration results can be achieved according to two registration experiments performed on brain MRI for GBM and epilepsy. The local deformation induced by the LITT procedure can be better captured and recovered by the identified landmark fiducials than simply uniformly picking landmarks. Given that only spatial information is used to determine landmark locations, the LeFiR method has the potential to be adopted in various clinical applications for the purpose of registering different image modalities.

Baudouin Denis de Senneville^1,2, Mario Ries², and Chrit T.W. Moonen^2
1IMB, UMR 5251 CNRS/University Bordeaux 1/INRIA, Talence, Gironde, France, ²Imaging Division, UMC Utrecht, Utrecht, Netherlands

Thermotherapies can now be guided in real-time using magnetic resonance imaging. This technique is gaining importance in interventional therapies for abdominal organs. An accurate on-line estimation and characterization of organ displacement is mandatory to prevent misregistration and correct for motion related thermometry artifacts. Here we describe the use of a Principal Component Analysis to detect spatio-temporal coherences in the physiological organ motion and to characterize in real-time the complex organ deformation. During hyperthermia, incoherent motion patterns could be discarded, which enabled improvements in the compensation of motion related errors in thermal maps, as well as in the motion estimation robustness.

Nick Todd¹, Mahamadou Diakite², Allison Payne², and Dennis L. Parker^1
1Radiology, University of Utah, Salt Lake City, Utah, United States, ²Physics, University of Utah, Salt Lake City, Utah, United States

The goal is to simultaneously measure temperature changes in aqueous and adipose tissues to properly monitor MR-guided HIFU treatments of localized breast cancer. To achieve this, we have developed a 2D multi-echo hybrid PRF/T1 sequence which measures PRF changes in water-based tissues and T1 values in fat-based tissues. The precision of the technique was evaluated by imaging four female volunteers in our developed breast-specific MRgHIFU system.

Nick Todd¹, Mahamadou Diakite², Allison Payne², and Dennis L. Parker^1
1Radiology, University of Utah, Salt Lake City, Utah, United States, ²Physics, University of Utah, Salt Lake City, Utah, United States

We present a sequence for simultaneous measurement of PRF, T1, and T2*. The additional information provided by T1 and T2* may be helpful for assessing tissue damage during MR-guided thermal therapies. These properties are analyzed as a function of thermal dose during ex vivo HIFU heating of turkey muscle.

Shuo Chen¹, Xinwei Shi², Feiyu Chen², Karen Ying³, and Shi Wang^3
1Engineering Physics, Tsinghua University, Beijing, China, ²Biomedical Engineering, Tsinghua, Beijing, China, ³Engineering Physics, Tsinghua, Beijing, China

A new Spectrum Based/Least-Square PRFS hybrid method for MR temperature mapping is proposed, which can measure temperature in water-only and water-fat mixed tissues simultaneously. In water-only region, the accuracy of temperature measurement is improved by modifying traditional PRFS method with least square fitting. In addition, fat frequency calculated in water-fat mixed voxels is utilized to eliminate B0 field drift effect in PRFS method. The proposed method was validated in phantom experiment.

Mie Kee Lam¹, Martijn de Greef¹, and Lambertus W. Bartels^2
1Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands, ²University Medical Center Utrecht, Utrecht, Netherlands

In the application of MR-guided High Intensity Focused Ultrasound (MR-HIFU) to organs in the abdomen, the near-field area is at risk of undesired heat accumulation. Therefore, there is a need for a temperature mapping technique that can visualize the cumulative near field heating effects of subsequent sonications. In this work we show the potential of using multi-gradient echo (mGE)-based absolute MR thermometry at the subcutaneous fat-muscle interface for the assessment of the thermal build-up in the near-field area.

Paul Baron¹, Roel Deckers¹, Martijn de Greef¹, Job G. Bouwman¹, Chris J.G. Bakker¹, and Lambertus W. Bartels^1
1University Medical Center Utrecht, Utrecht, Utrecht, Netherlands

During MR-guided high intensity focused ultrasound (MR-HIFU) ablation of fat-containing tissues like the human breast or liver, heat induced susceptibility changes may give rise to local field disturbances, leading to errors in PRFS thermometry of the water-based tissues. A correction method is presented that combines the initial uncorrected measured temperature change with a thermal model to estimate the field disturbance and thus correct for these errors. The feasibility is shown in a porcine adipose tissue and ethylene glycol gel phantom. The maximum temperature error decreased from 3°C before correction to less than 1°C after the correction.

Linus Willerding¹, Simone Limmer¹, Martin Hossann^1,2, Anja Zengerle¹, Maximilian F. Reiser³, Rolf D. Issels^1,2, Lars H. Lindner^1,2, and Michael Peller^3
1Department of Internal Medicine III, University Hospital of Munich, Ludwig-Maximilians University, Munich, Germany, ²CCG Tumor Therapy through Hyperthermia, Helmholtz Zentrum München, German Research Center for Environmental Health, Munich, Germany, ³Department of Clinical Radiology, University Hospital of Munich, Ludwig-Maximilians University, Munich, Germany

Efficacy of systemically applied anti-cancer drugs is limited by insufficient selectivity and thus dose is limited by side effects. To improve the effectiveness of chemotherapy, thermosensitive liposomes (TSL) in combination with hyperthermia are used to target and trigger the release of chemotherapeutics. With MRI contrast agent loaded TSL (CA-TSL) were used for visualisation. Here we present a newly developed setup for MR-monitoring of laser-based hyperthermia in a rat model with CA-TSL for optimized visualisation of content release.

Anil Shetty¹, Hiroumi Kitajima^2,3, Tracy E. Powell^2,3, Michael A. Bowen^2,3, and Sherif G. Nour^2,3
1Visualase Inc, Houston, Texas, United States, ²Department of Radiology and Imaging Sciences, Emory University Hospital, Atlanta, Georgia, United States, ³Interventional MRI Program, Emory University Hospital, Atlanta, Georgia, United States

This report demonstrated the feasibility of percutaneous laser ablation for hepatic tumors with real-time MRI monitoring within a dedicated “interventional MRI” suite. The online feedback of the ablation, along with combination of multiple fibers and pullbacks, allowed creation of large ablation volumes. The real-time monitoring, along with automatic shutoff mechanism with triggering of safety limits, protected adjacent critical structures. Advantages of using MR guided laser ablation include ability to ablate lesions which are in locations that are difficult to access and ability to ablate lesions which are only conspicuous on certain MR weighted sequences.

Joyce GR Bomers¹, Eva Rothgang^2,3, Christiaan G. Overduin¹, Jörg Roland³, Jelle O. Barentsz¹, and Jurgen J. Füttterer^1,4
1Radiology, Radboud University Nijmegen Medical Centre, Nijmegen, Gelderland, Netherlands, ²Center for Applied Medical Imaging, Siemens Corporation, Corporate Research, Baltimore, Maryland, United States, ³Siemens Healthcare, MR, Erlangen, Bayern, Germany, ⁴MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, Overijssel, Netherlands

The clinical feasibility and time efficiency of an integrated workflow for MR-guided transrectal laser treatment and real-time treatment monitoring were tested. Furthermore, temperature stability at 3T in prostate cancer patients using a fast gradient echo (GRE) echo planar imaging (EPI) sequence was evaluated.

Matthew Tarasek¹, Lorne Hofstetter¹, Ruben Pellicer², Jurriaan Bakker², Wouter Numan², Gyula Kotek², Eric Fiveland³, Gavin Houston⁴, Gerard van Rhoon², Maarten Paulides², and Desmond Yeo^1
1MRI, GE Global Research, Niskayuna, NY, United States, ²Erasmus Medical Center, Rotterdam, Netherlands, ³MRI, GE Global Research Center, Niskayuna, NY, United States,⁴GE Healthcare, Rotterdam, Netherlands

Validation of MR thermometry (MRT) for RF hyperthermia in a head and neck clinical setup requires accurate co-registration of the inserted temperature probes to MRT data. Here, we explore the use of MR imaging techniques and 3D spline fitting for probe localization. In addition, we investigate how uncertainty in the localization affects the registration of probe and MRT readings. Findings show that a maximum operator-dependent temperature probe placement variability of 2mm along the catheter length accounts for at most a ±0.5 degree temperature uncertainty in the MRT maps.

Sébastien Murat¹, Jan Weis¹, Francisco Ortiz-Nieto¹, and Håkan Ahlström^1
1Department of Radiology, Uppsala University Hospital, Uppsala, Sweden

Controversy exists as to whether humans are capable of brain-cooling under any circumstances. Based on previous animal experiments, evidence of brain cooling was sought during controlled breath-holding. MR phase-difference method was used for measurement of human brain temperature changes during breath-hold. Brain temperature promptly decreased by ca 1 °C in 1 min. Indications are that humans can invoke extreme brain cooling to lower metabolic rate. The study opens-up new in-roads for potentially treating a wide range of critical illnesses (e.g., stroke, cardiac arrest, brain injury) avoiding the limitations of therapeutic hypothermia.

Xinyang Liu¹, Kemal Tuncali¹, William M. Wells, III¹, and Gary P. Zientara^1
1Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States

MRI-guided cryoablation provides direct visualization of the target tumor and iceball. Visual assessment of therapy progress during the freezing cycle can be challenging, though. Nonetheless, real-time quantitative assessment of ablation is needed to ensure safety and effectiveness. We developed software that includes methods for: (1) automatic cryoprobe localization, able to detect multiple inserted probes (in 3D) from pre-freeze MRI; and, (2) automatic iceball segmentation, guided by the labeled probes, that can extract 3D iceball configuration from periodic MRI scanning during the freezing cycle. Both methods showed good accuracy when applied to five cases of 3T MRI-guided cryoablation of kidney tumors.