Åsmund Kjørstad¹, Fabian Temme¹, Jens Fiehler¹, and Jan Sedlacik^1
1Neuroradiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany

Targeted temperature management is a treatment that seeks to reduce and control the body temperature. We demonstrate a novel localized cooling technique using high flow cold air applied nasally and orally to the airways by monitoring the brain temperature using gradient echo phase imaging at 3T. 2 healthy volunteers were investigated, with one subject being scanned twice and the other once. A significant temperature reduction (p<0.05) was seen in the inferior frontal lobe in all three experiments with an average cooling effect of -0.33°C. This demonstrates the feasibility of our proposed high flow cold air system. 

Juan Camilo Plata¹, Sam Fielden², Bragi Sveinsson³, Brian Hargreaves⁴, and Craig Meyer^2
1Bioengineering, Stanford University, Las Vegas, NV, United States, ²Biomedical Engineering, University of Virginia, Charlottesville, VA, United States, ³Electrical Engineering, Stanford University, Palo Alto, CA, United States, ⁴Stanford University, Palo Alto, CA, United States

Early detection of thermal lesions generated using MR-guided focused ultrasound systems is critical for treatment feedback. Irreversible changes in the apparent diffusion coefficient (ADC) have been previously shown to be an early indicator for loss of viability in the prostate. Due to poor image quality using standard diffusion weighted imaging strategies inside the focused ultrasound system, radiologists rely on T2-weighted fast spin echoes (FSE) for lesion detection. T2-weighted changes due to lesion formation develop more slowly than  ADC changes. We propose using a diffusion-weighted steady state sequence for early detection of thermal lesions inside the focused ultrasound system.

Fuyixue Wang¹, Zijing Dong¹, Shuo Chen², Bingyao Chen³, Jiafei Yang³, Xing Wei³, Shi Wang², and Kui Ying^2
1Department of Biomedical Engineering, Tsinghua University, Beijing, China, People's Republic of, ²Key Laboratory of Particle and Radiation Imaging, Ministry of Education, Medical Engineering and Institute, Department of Engineering Physics, Tsinghua University, Beijing, China, People's Republic of, ³Department of Orthopedics, First Affiliated Hospital of PLA General Hospital, Beijing, China, People's Republic of

Real time thermometry is desirable for thermal therapy such as microwave ablation to ensure patient safety. MR temperature imaging using proton resonance frequency (PRF) shift technique can provide temperature maps during the treatment. In this work, we proposed a novel reconstruction framework that estimates temperature changes from undersampled k-space with a few fully sampled k-space points. Simulation studies, phantom heating experiments and human experiments were performed to validate the proposed method. The proposed method can provide temperature images with relatively high accuracy and short reconstruction time at a reduction factor of 4 in presence of motion.

Fuyixue Wang¹, Zijing Dong¹, Haikun Qi², Shi Wang³, Huijun Chen², and Kui Ying^3
1Department of Biomedical Engineering, Tsinghua University, Beijing, China, People's Republic of, ²Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China, People's Republic of, ³Key Laboratory of Particle and Radiation Imaging, Ministry of Education, Medical Engineering and Institute, Department of Engineering Physics, Tsinghua University, Beijing, China, People's Republic of

Real time MR temperature imaging during thermal therapy is beneficial for monitoring and controlling the treatment in clinical applications. In this work, we explored correlations in the temporal dimension of temperature imaging and proposed a novel method, temporal weighted sliding window SPIRiT using motion-insensitive golden angle radial sampling, to achieve real time temperature imaging. Through simulation studies and phantom heating experiments, we validated the ability of the proposed method to obtain temperature images with relatively high temperature accuracy at a reduction factor of 8.

Pooja Gaur¹, Xue Feng², Samuel Fielden², Craig H Meyer², Beat Werner³, and William A Grissom^1
1Vanderbilt University, Nashville, TN, United States, ²University of Virginia, Charlottesville, VA, United States, ³University Children's Hospital, Zurich, Switzerland

Accelerated temperature imaging is desirable to improve spatiotemporal coverage during MR-guided focused ultrasound procedures in the brain. Circulating water prevents skull overheating, but also creates signal variations that disrupt correlations between images collected before and during treatment (which are relied on to overcome undersampling artifacts), leading to errors in temperature measurements. We propose a spatially-segmented iterative reconstruction method, which applies the k-space hybrid model to reconstruct temperature changes in the brain and a POCS method to reconstruct the image in the water bath. Separately reconstructing brain and water bath signal results in lower temperature error when undersampling k-space.

Christiaan G. Overduin¹, Jurgen J. Fütterer^1,2, and Tom W.J. Scheenen^1
1Radiology, Radboud University Medical Centre, Nijmegen, Netherlands, ²MIRA Institute for Biomedical Engineering and Technical Medicine, University of Twente, Enschede, Netherlands

Our study assessed the feasibility and accuracy of 3D ultrashort TE (UTE) MR thermometry to dynamically track temperatures across frozen tissue during cryoablation on a clinical MR system at 3T. We demonstrated 3D UTE imaging to achieve measurable MR signal from frozen tissue down to temperatures as low as -40°C within a clinically realistic time-frame (~1min) and with sufficient spatial resolution (1.63mm isotropic). Using a calibration curve, we could derive 3D MR-estimated temperature maps of the frozen tissue, which showed good agreement with matched temperature sensor readings on statistical analysis.

Fuyixue Wang¹, Zijing Dong¹, Bingyao Chen², Jiafei Yang², Xing Wei², Shi Wang³, and Kui Ying^3
1Department of Biomedical Engineering, Tsinghua University, Beijing, China, People's Republic of, ²Department of Orthopedics, First Affiliated Hospital of PLA General Hospital, Beijing, China, People's Republic of, ³Key Laboratory of Particle and Radiation Imaging, Ministry of Education, Medical Engineering and Institute, Department of Engineering Physics, Tsinghua University, Beijing, China, People's Republic of

Thermal therapies such as microwave ablation require temperature imaging with high temporal resolution to calculate thermal absorption and evaluate the curative effects of the ablation. Thus, acceleration techniques of data acquisition for MR temperature imaging using PRF shift technique are desirable. In this work, we explored the low rank property of k-t space in dynamic MR temperature imaging and proposed a novel fast reconstruction method AscLR with an ascending-threshold low rank constraint. Through simulation studies and microwave heating experiments, we validated the ability of the proposed method to provide relatively accurate temperature estimation at a reduction factor of 8.

Tomoya Kimura¹, Atsushi Shiina¹, Kenji Takahashi², and Kagayaki Kuroda^1,3
1Course of Electrical and Electronic Engineering, Graduate School of Engineering, Tokai University, Hiratsuka, Japan, ²Department of Orthopaedic Surgery, Nippon Medical School, Tokyo, Japan, ³Center for Frontier Medical Engineering, Chiba University, Chiba, Japan

Temperature dependence of T1 of tissue water in the porcine knee joint cartilage in vitro was examined at 9.4T in comparison with that of the water proton resonance frequency. The absolute value of T1 at each temperature between room temperature and 60^oC was reproducible. Hysteresis was negligible during heating and cooling processes. The correlation coefficient with temperature was higher than 0.998, and hence that with water proton chemical shift was also high (>= 0.996). The temperature coefficient was 1.28%/^oC at 30^oC for heating and 1.24%/^oC for cooling. These results suggested that T1 is a favorable index for thermometry of the knee joint cartilage under thermal therapies.

 

Yuan Zheng¹, Michael Marx¹, G. Wilson Miller², and Kim Butts Pauly^1
1Radiology, Stanford University, Stanford, CA, United States, ²Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, United States

We have developed a novel MR-ARFI technique that makes use of transition band balanced steady-state free precession (bSSFP). Due to the strong dependence of image phase on the motion-encoded phase, this technique improves the sensitivity of MR-ARFI measurements over commonly used spoiled sequences. The proposed technique also features high speed, as an ARFI contrast image can be acquired in a few seconds. With its high speed and high sensitivity, the bSSFP-ARFI technique could be useful in confirming/calibrating the HIFU focal spot before thermal ablation treatment.

Kexin Deng¹, Yuxin Zhang¹, Yu Wang¹, Bingyao Chen², Xing Wei², Jiafei Yang², Shi Wang³, and Kui Ying^3
1Biomedical Engineering, Tsinghua University, Beijing, China, People's Republic of, ²Department of Orthopedics, First Affiliated Hospital of PLA General Hospital, Beijing, China, People's Republic of, ³Key Laboratory of Particle and Radiation Imaging, Ministry of Education, Department of Engineering Physics, Tsinghua University, Beijing, China, People's Republic of

The temperature dependency of susceptibility, especially for fat, could introduce errors in temperature estimation. To address this problem, a hybrid model integrated with susceptibility change induced phase is proposed to reduce the phase error. Simulation was conducted to validate the proposed model and a water-fat phantom was made and heated to illustrate the effect of susceptibility-induced phase error correction. The proposed model shows more accurate temperature estimation near the water-fat interface both in simulation and phantom heating experiment. 

Cyril J Ferrer¹, Lambertus W Bartels¹, Marijn van Stralen¹, Chrit T.W Moonen¹, and Clemens Bos^1
1University Medical Center Utrecht, Utrecht, Netherlands

Magnetic Resonance Imaging-guided High Intensity Focused Ultrasound has recently been suggested as an alternative treatment modality for pancreatic cancer that is non-invasive, and may be suited for treatment in cases where surgery is not an option. However, using proton resonance frequency shift based thermometry in this area is highly challenging, because of motion and air in the digestive tract near the pancreas. We have shown experimentally that patient preparation by filling the stomach and duodenum with juice can be a pragmatic solution for more precise temperature monitoring during MR-HIFU therapy particularly in the head of the pancreas. 

Charles Mougenot¹, Samuel Pichardo^2,3, Steven Engler^2,4, Adam Waspe^5,6, Elodie Constanciel⁵, and James Drake^5,6
1Philips Healthcare, Toronto, ON, Canada, ²Thunder Bay Regional Research Institute, Thunder Bay, ON, Canada, ³Electrical Engineering, Lakehead University, Thunder Bay, ON, Canada, ⁴Computer Science, Lakehead University, Thunder Bay, ON, Canada, ⁵Hospital for Sick Children, Toronto, ON, Canada, ⁶University of Toronto, Toronto, ON, Canada

Algorithms have been developed that use Magnetic Resonance Acoustic Radiation Force Imaging (MR-ARFI) to maximize the intensity at the focal point of a high intensity focused ultrasound beam in order to compensate for tissue related phase aberrations. A combination of two methods is proposed to achieve refocusing using a clinically acceptable acquisition time at 3T. Compensation of three aberrators inducing a relative intensity of 95%, 67.4% and 25.3% were successfully evaluated in a phantom to retrieve a relative intensity of 101.6%, 91.3% and 93.3% in 10 minutes or 103.9%, 94.3% and 101% in 25 minutes.

Johanna Maria Mijntje van Breugel¹, Martijn de Greef², Charles Mougenot³, Maurice AAJ van den Bosch², Chrit CW Moonen², and Mario AAJ Ries^2
1Radiology, University Medical Center Utrehct, Utrecht, Netherlands, ²University Medical Center Utrehct, Utrecht, Netherlands, ³Torontp, Canada

Hypothesis: MR-ARFI can be deployed in the kidney as an alternative for the thermal test shot at low power.

The employed respiratory gated MR-ARFI sequence in combination with a 450 W excitation tone-burst is sensitive enough to exceed the noise level and to clearly display the focal point of the HIFU beam. Both at 450W and at 1000W the displacement due to the radiation force coincided with the location of the temperature rise due to thermal ablation at equivalent power. Hence, radiation force in combination with a pencil beam navigator to compensate for respiratory motion is a reliable indicator of the location of the thermal lesion and might be an alternative to the low power thermal test shot in highly perfused organs such as the kidney.

Yuan Zheng¹, Michael Marx¹, Rachelle R. Bitton¹, and Kim Butts Pauly^1
1Radiology, Stanford University, Stanford, CA, United States

We have demonstrated a method for shear wave elasticity imaging (SWEI). A shear wave was generated by a short focused ultrasound (FUS) pulse, and was tracked by collecting images with different delays (t_delay) between the FUS pulse and bipolar motion-encoding gradients (MEG). The time-of-flight (TOF) at each pixel was determined by the zero-crossing of the image phase as a function of t_delay. Based on the TOF map, a shear wave velocity map was generated in polar coordinates. 

Korel Dursun Yildirim¹, Engin Baysoy¹, Zahid Sagiroglu², Çagla Özsoy¹, Ozgur Kocatürk¹, and Senol Mutlu^2
1Biomedical Engineering, Bogaziçi University, Institute of Biomedical Engineering, Istanbul, Turkey, ²Electrical and Electronics Engineering, Bogaziçi University, Institute of Graduate Studies in Science and Engineering, Istanbul, Turkey

In this study, A Novel method and system were devoloped for developing clinical grade active devices dedicated to interventional MRI procedures. Before prototype fabrication, according to desired component dimensions, component values were simulated. With the exact dimensions used in simulations, component prototypes were fabricated via conductive ink as component material. Finally, simulation results and banch top measurements of component values were compared and reliability of simulation results were comfirmed.

T. Stan Gregory¹, Ehud Schmidt², John Oshinski³, and Zion Tsz Ho Tse^1
1College of Engineering, The University of Georgia, Athens, GA, United States, ²Radiology, Brigham and Women's Hospital, Boston, MA, United States, ³Radiology, Emory University Hospital, Atlanta, GA, United States

Magnetic Resonance Imaging (MRI) is increasingly becoming the preferred diagnostic and interventional imaging modality for a variety of diseases.  Despite the increasing clinical merit, practical implementation of these procedures in the clinic is oftentimes limited due to the high risk associated with these patient groups and the subsequent need for advanced physiological monitoring for each patient to be cleared for MRI imaging and interventional workflows.  The presented method for beat-to-beat SV and continuous aortic flow monitoring within the MRI bore based on Magnetohydrodynamic Voltages (VMHD) induced onto 12-lead Electrocardiograms (ECG), enables MR imaging and MRI-guided interventional procedures for these patients. 

Reza Madankan¹, Wolfgang Stefan¹, Christopher MacLellan¹, Samuel Fahrenholtz¹, Drew Mitchell¹, R.J. Stafford¹, John Hazle¹, and David Fuentes^1
1Imaging Physics, MD Anderson Cancer Center, Houston, TX, United States

Compressive sensing and sparse image reconstruction has received significant attention and has demonstrated potential in reduction of acquisition times. However, in many methods, under-sampling strategies are heuristically chosen and empirically validated. This often leads to a relatively larger number of k-space samples than needed for a particular application. The presented work develops a mathematically rigorous and quantitative methodology for k-space under-sampling with respect to model-based reconstruction of MR thermometry. The key idea of the proposed approach is to detect the useful samples of k-space in order torefine the model, and then the refined mathematical model is utilized to reconstruct the image.

Yuxin Zhang¹, Kexin Deng¹, Shuo Chen², Bingyao Chen³, Xing Wei³, Jiafei Yang³, Shi Wang², and Kui Ying^2
1Biomedical Engineering, Tsinghua University, Beijing, China, People's Republic of, ²Key Laboratory of Particle and Radiation Imaging, Ministry of Education, Department of Engineering Physics, Tsinghua University, Beijing, China, People's Republic of, ³Department of Orthopedics, First Affiliated Hospital of PLA General Hospital, Beijing, China, People's Republic of

The proposed Kalman ?ltered Bio Heat Transfer Model Based Self-adaptive Hybrid MR Thermometry, abbreviated as KalBHT hybrid algorithm, introduced the BHTE model to synthesize a window on the regularization term of the hybrid algorithm, which leads to a self-adaptive regularization both spatially and temporally with change of temperature. Further, to decrease the sensitivity to accuracy of the BHTE model, Kalman ?lter is utilized to update the window at each iteration time. Besides, the BHTE model is able to interpolate temperature maps during the acquisition and reconstruction of the next MR image to make real time temperature monitoring possible. To investigate the effect of the proposed model, phantom microwave heating experiment and in-vivo experiment with heating simulation were conducted in this study.

Tongxin Chen¹, Fuyixue Wang¹, Zijing Dong¹, Haikun Qi², Shi Wang³, Huijun Chen², and Kui Ying^3
1Department of Biomedical Engineering, Tsinghua University, Beijing, China, People's Republic of, ²Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China, People's Republic of, ³Key Laboratory of Particle and Radiation Imaging, Ministry of Education, Medical Engineering and Institute, Department of Engineering Physics, Tsinghua University, Beijing, China, People's Republic of

Radial sampling is sensitive to trajectory errors and can cause image distortions. To investigate the effect of trajectory errors on temperature imaging, we first evaluated the use of Trajectory Auto-Corrected Image Reconstruction (TrACR), a method to reconstruct radial images without trajectory errors, for radial temperature imaging. Then, we examined the feasibility of TrACR with only one calibration on dynamic temperature imaging based on the assumption that gradient errors are time-invariant. Through phantom heating experiments, we validated that both of the TrACR and the single-calibration TrACR can correct the errors of normal and golden angle radial sampling and provide improved temperature accuracy.

Steven Engler^1,2, Charles Mougenot³, Jochen Keupp⁴, Steffen Weiss⁴, Edwin Heijman⁵, and Samuel Pichardo^1,6
1Thunder Bay Regional Research Institute, Thunder Bay, ON, Canada, ²Lakehead University, Computer Science, Thunder Bay, ON, Canada, ³Philips Healthcare, Toronto, ON, Canada, ⁴Philips Research, Hamburg, Germany, ⁵Philips Research, Eindhoven, Netherlands, ⁶Lakehead University, Electrical Engineering, Thunder Bay, ON, Canada

Temperature changes can be assessed in non-adipose tissue using proton resonance frequency shift MR-thermometry methods based on gradient-echo sequences, and in adipose tissue using apparent T2-mapping MR-thermometry methods based on multi-echo fast spin-echo sequences. It has been previously demonstrated that these sequences can be interleaved to simultaneously monitor temperature in all tissues. In this study we show the feasibility of controlling the sequence duty-cycle of the aforementioned interleaved scanning technique on-demand in order to dynamically change the temporal resolution of the two interleaved scans in response to actual temperature changes and the stage of the hyperthermia application.

Henrik Odéen¹, Scott Almquist², Joshua de Bever¹, and Dennis L Parker^1
1Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT, United States, ²School of Computing, University of Utah, Salt Lake City, UT, United States

Thermal model based reconstruction of subsampled MR temperature data for focused ultrasound applications rely on acoustic and thermal parameters that are often analytically determined from a pre-treatment sonication. In this work we combine a thermal model based reconstruction method with ultrasound beam simulations to determine the specific absorption rate in order to avoid potentially damaging the tissue during a pre-treatment sonication. Proof-of-concept experiments are performed in a homogenous gelatin phantom and a gelatin phantom embedded with a plastic skull. The temperature estimations using US modeling show the same accuracy as those using a pre-treatment sonication.

Henrik Odéen¹, Bradley Bolster², Eun Kee Jeong¹, and Dennis L Parker^1
1Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT, United States, ²Siemens Healthcare, Salt Lake City, UT, United States

Measurements of changes in signal intensity and T1 relaxation time with temperature has been suggested for temperature monitoring in cortical bone during MR guided focused ultrasound treatments. In this study we compare changes in signal intensity, T1, and T2* with temperature using a 3D ultrashort echo time pulse sequence and a 2D gradient recalled echo pulse sequence with short TE. The effects of T1 and T2* change with temperature counteract each other making the change in signal intensity small, and therefore T1 and T2* appears to have the greatest sensitivity to changes in temperature.

Mingming Wu¹, Matthew Tarasek², Axel Haase³, and Silke Lechner-Greite^4
1IMETUM, Technische Universität München, Garching, Germany, ²GE Global Research, Niskayuna, NY, United States, ³Technische Universität München, Garching, Germany, ⁴GE Global Research, Garching, Germany

Inversion Recovery prepared bSSFP sequence is used to quantify T1 and PRFS simultaneously based on a phase sensitive bSSFP readout. This technique allows for temperature mapping in both adipose and aqueous tissues at the same time. The feasibility of this method is shown with means of a cooling down experiment of a heterogeneous phantom. B0 drift correction is performed based on neighboring voxels in the fatty tissue.

Yi Chen^1,2, Filip Sobczak¹, and Xin Yu^1,2
1Research Group of Translational Neuroimaging and Neural Control, High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany, ²Graduate School of Neural Information Processing, University of Tuebingen, Tuebingen, Germany

A key challenge of the fiber optic-mediated multi-model fMRI methodologies is locating the fiber tip accurately and precisely to target  deep brain nuclei. The requirement of precision is only several hundreds of microns in the animal brains. In this work, a multi degree of freedom robotic arm was developed with the use of step motors. The setup is in compatible with 14.1T MRI scanner. This MRI-guided robotic arm provides visually monitored fiber insertion to reduce the position error significantly in the perfused rat brain.

Thiele Kobus^1,2, Yongzhi Zhang², Natalia Vykhodtseva², and Nathan McDannold^2
1Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, Netherlands, ²Radiology, Brigham and Women's Hospital, Boston, MA, United States

We studied the treatment effect of HER2-targeting antibodies in combination with MR-guided focused ultrasound (FUS) to disrupt the blood-brain barrier in a breast cancer brain metastasis model. Tumors were implanted in rats and animals either received no treatment, six weekly treatments with antibodies, or six treatments of the antibodies combined with FUS-mediated BBB disruption. MR was used to guide the treatments and monitor tumor volume. 4/10 animals in the FUS+antibody-group responded to the treatment, but none of the other animals did. We could not explain with our results why only some of the FUS+antibody-animals responded and this requires further investigation. 

Michaela A U Hoesl¹, Peter R Seevinck¹, Matteo Maspero¹, Gert J Meijer², Jan J W Lagendijk¹, Bas W Raaymakers¹, and Cornelis A T van den Berg^1
1Center of Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands, ²Radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands

Pseudo-CT (pCT) generation for Head and Neck region based on ultrashort echo time and radial under sampling is investigated in order to reach a clinical acceptable time frame for image acquisition. Two different UTE sequences, a 3D radial “kooshball” and a 3D radial “stack-of-stars” k-space acquisition are compared for image acquisition and pCT result using tissue classification and bulk density assignment. The results suggest that radial undersampling is feasible and thus results in a time frame of clinical relevance of 3 min for image acquisition plus 1 min for post-processing pCT generation.

Esther Kneepkens¹, Adriana Fernandes², Klaas Nicolay³, and Holger Grüll^3,4
1Biomedical NMR, Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands, ²Universidade de Lisboa, Lisbon, Portugal, ³Eindhoven University of Technology, Eindhoven, Netherlands,⁴Philips Research, Eindhoven, Netherlands

The aim of this study was to investigate the potential of Fe(III) N-succinyl deferoxamine (Fe-SDFO) as a safe T₁ contrast agent  for encapsulation in temperature sensitive liposomes (TSLs) in order to visualize drug release from TSLs when using Magnetic Resonance-guided High Intensity Focused Ultrasound (MR-HIFU).  Two TSLs were developed that contained either Fe-SDFO or doxorubicin. Both TSLs showed suitable release and stability characteristics in vitro.  An in vivo proof-of-concept study was carried out in tumor-bearing rats treated with MR-HIFU. Treated tumors showed an increase in R₁ and future work aims to correlate the R₁change with tumor drug concentrations.

Xiao Chen¹, Rou Li¹, Changjun Tie¹, Xiaoqing Hu¹, Xiaoliang Zhang^2,3, Chao Zou¹, Xin Liu¹, Hairong Zheng¹, and Ye Li^1
1Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, CAS, Shenzhen, China, People's Republic of, ²Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, ³UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, United States

Due to MRI’s unique capability of providing accurate, non-invasive and real-time target localization and temperature monitoring, MRI guided high intensity focused ultrasound (HIFU) has been a critical modality for imaged guided thermal therapy. We propose a 3 channel ultrasound compatible rat array to obtain high resolution and homogeneous rat brain images at 3T for temperature monitoring. Phantom and in-vivo imaging experiments in temperature mapping demonstrate the capability of the proposed array to provide homogenous and high SNR images and temperature map in the whole rat brain at 3T, which provides the possibility to perform MRI guided HIFU treatment in-vivo.

Navid Farr¹, Yak-Nam Wang², Samantha D’Andrea³, Frank Starr², Ari Partanen⁴, Kayla Gravelle³, Donghoon Lee⁵, and Joo Ha Hwang^1,3
1Department of Bioengineering, University of Washington, Seattle, WA, United States, ²Applied Physics Laboratory, University of Washington, Seattle, WA, United States, ³Department of Medicine, University of Washington, Seattle, WA, United States, ⁴Philips Healthcare, Andover, MA, United States, ⁵Department of Radiology, University of Washington, Seattle, WA, United States

Pancreatic cancer has one of the lowest survival rates because current therapies are ineffective. Dense stromal tissue and poor vascular perfusion limits drug penetration and uptake into the tumor. Growing evidence suggests that hyperthermia in combination with temperature sensitive liposomal drug delivery can lead to increased organ perfusion and drug extravasation resulting in high local drug concentration. We performed MR-guided heating methods that enable accurate and precise spatial and temporal control of heating. Enhanced drug delivery was achieved to treat pancreatic tumors using Magnetic Resonance-guided High Intensity Focused Ultrasound (MR-HIFU) in conjunction with a heat triggered drug delivery system. 

Cornel Zachiu¹, Nicolas Papadakis², Mario Ries¹, Chrit Moonen¹, and Baudouin Denis de Senneville^1,2
1Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands, ²Institut de Mathématiques de Bordeaux, Bordeaux, France

Current methods for real-time MR-guided HIFU and EBRT interventions in moving organs rely on an algorithm that is sensitive to gray-level intensity variations from other sources than motion. In this work, an improved real-time tracking algorithm with increased robustness to such effects is proposed and experimentally compared to the existing methods. Results have shown a notable improvement in the quality of the motion estimates when the proposed method was used, while maintaining real-time capabilities. Our method was shown to be potentially beneficial for MR-guided HIFU and EBRT interventions in the abdomen, where cardiac activity might become problematic for current approaches.

Sharon L Giles¹, Matthew Brown², Jessica M Winfield¹, David J Collins³, Ian Rivens⁴, John Civale⁴, Gail R ter Haar⁴, and Nandita M deSouza^1
1CRUK Cancer Imaging Centre, The Royal Marsden Hospital NHS Foundation Trust and The Institute of Cancer Research, London, United Kingdom, ²Anaesthetic Department, The Royal Marsden Hospital NHS Foundation Trust, London, United Kingdom, ³CRUK Cancer Imaging Centre, The Institute of Cancer Research, London, United Kingdom, ⁴Therapeutic Ultrasound, The Institute of Cancer Research, London, United Kingdom

This study assessed intraprocedural DWI for detecting extra- and intra-osseous tissue change during MRgHIFU treatment of bone metastases by comparing appearances with post-procedural and Day-30 DWI and T1-W contrast-enhanced image appearances. Change in image appearances for n=9 patients was assessed by 2 observers assigning a consensus score where 0=no, 1=mild, 2=moderate and 3=striking change. Extra-osseous DWI changes were more conspicuous than intra-osseous DWI changes, but were less striking than immediate post-procedural contrast-enhanced changes. However, intra-procedural DWI changes significantly correlated with post-procedural and Day-30 DWI and contrast-enhanced changes, suggesting that intra-procedural DWI can provide an indicator of subsequent extra-osseous tissue damage.

Steven P Allen¹, Luis Hernandez-Garcia², Charles A Cain¹, and Timothy L Hall^1
1Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States, ²fMRI Lab, University of Michigan, Ann Arbor, MI, United States

We estimate the R2 relaxation rate and the apparent diffusion coefficient at 7T in a variety of in vitro tissues and tissue mimicking phantoms after they have been subjected to homogenization by ultrasonic cavitation (histotripsy). The estimated R2 rate of these lesions decreases with increased treatment so long as the lesions are made in materials with high iron content. When lesions are made in brain tissue or phantoms with low iron content, the R2 rate remains unperturbed by homogenization. The apparent diffusion coefficient increases with increasing treatment for all tissues and phantoms.

Eugene Ozhinsky¹, Matthew D. Bucknor¹, and Viola Rieke^1
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States

Desmoid tumors are benign but locally aggressive soft tissue tumors that arise from fibroblast cells. Focused ultrasound has shown promising results in reduction of tumor volume without significant side effects. Post-treatment contrast enhanced MR imaging allows assessment of the non-perfused volume (NPV), the gold standard assessment of the quantity of tumor ablation. However, safety concerns regarding heating of tissue after gadolinium injection prevent further treatment following the NPV assessment. We have shown that T2 mapping can be used to visualize the extent of ablation with focused ultrasound and be used as a predictor of NPV without the need for contrast injections.

Bjorn Stemkens¹, Rob HN Tijssen¹, Jan JW Lagendijk¹, and Cornelis AT van den Berg^1
1Department of Radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands

Geometric accuracy is vital for MR-guided radiotherapy.  In this study we quantify the geometric fidelity of a retrospectively sorted 4D-MRI and 2D MS cine-MR acquisition, which serve as input for a motion model for dose accumulation mapping and tumor tracking. A linearly moving MRI-compatible motion phantom was used to quantify the positional error in the 4D-MRI and 2D MS acquisitions using a range of user-defined motion trajectories.  Geometrical errors were found to be smaller than the voxel or pixel size.

Peter Roland Seevinck¹, Frank Zijlstra¹, Jouke Smink², Sascha Krueger³, Frebus Jan van Slochteren^4,5, Steven A.J. Chamuleau⁴, Max A Viergever¹, and Marinus Adriaan Moerland^1
1Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands, ²Philips Healthcare, Best, Netherlands, ³Innovative Technologies, Philips Research Laboratories, Hamburg, Germany, ⁴Department of Cardiology, University Medical Center Utrecht, utrecht, Netherlands, ⁵ICIN, Utrecht, Netherlands

The Co-RASOR imaging technique for high temporal resolution passive device visualization was implemented in the interventional Suite software package. This facilitates MRI-guided device tracking by combining high temporal resolution color overlays on top of high spatial resolution 3D roadmaps. Titanium needles were accurately depicted in two orthogonal planes with 2.5Hz framerate, facilitating easy freehand needle targeting.  The ability to adapt crucial Co-RASOR reconstruction parameters, including the off-resonance value, during the intervention was demonstrated to provide unprecedented flexibility and robustness in device visualization.