Thermometry & Thermotherapy

Wednesday, 3 June 2015

Tetiana Dadakova¹, Ali Caglar Özen¹, Axel Joachim Krafft¹, Jurgen Fütterer², Martijn Hoogenboom², Jürgen Walter Jenne³, Erik Dumont⁴, Christakis Damianou⁵, Jan Gerrit Korvink⁶, and Michael Bock^1
1Department of Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²Department of Radiology and Nuclear medicine, Radboud University Medical Center, Nijmegen, Netherlands, ³Fraunhofer MEVIS, Bremen, Germany, ⁴Image Guided Therapy, Pessac, France, ⁵Department of Electrical Engineering, Computer Engineering and Informatics, Cyprus University of Technology, Limassol, Cyprus, ⁶Department of Microsystems Engineering (IMTEK), University of Freiburg, Freiburg, Germany

High intensity focused ultrasound (HIFU) under MR guidance allows for pre-treatment planning, post-treatment assessment and real-time temperature monitoring during treatment in ablative hyperthermia of tumors. In addition to heating, HIFU causes micrometer transient displacements in the tissue, which is most pronounced at the focal spot. The displacement can be visualized with MRI (acoustic radiation force imaging, ARFI) using motion encoding gradients. The time-dependency of the displacement can be described by an overdamped harmonic oscillator model, which has two parameters: the maximum tissue displacement ∆x, and the rise time τ. The rise time is related to the mechanical tissue properties, and its quantification is needed for modelling of the tissue response during ARFI, and to distinguish tissues based on their stiffness. In this work we developed a method to quantify τ from MR-ARFI data. To assess whether tissue stiffness changes with heating, τ was calculated in 4 regions of a porcine muscle ex vivo phantom, which received different thermal doses.

Yuval Zur^1
1GE Healthcare, Tirat Carmel, Israel

MR guided Focused Ultrasound treats noninvasively many brain disorders. The skull bone in the brain induces significant distortions of the ultrasonic wave field. It is necessary to measure the acoustic field and correct it. This field is measured with Acoustic Radiation Force Imaging (ARFI) where the ultrasound induced tissue displacement, in conjunction with a gradient generates a phase shift which is read by EPI. In this abstract we describe a new ARFI sequence based on Fast Spin Echo. The new sequence is artifact free and is not affected by b0 field inhomogeneity. In addition the phase sensitivity is higher than EPI ARFI.

Joshua Thomas de Bever^1,2, Henrik Odéen^2,3, and Dennis L. Parker^2,4
1School of Computing, University of Utah, Salt Lake City, Utah, United States, ²Utah Center for Advanced Imaging Research, Salt Lake City, Utah, United States, ³Department of Physics, University of Utah, Salt Lake City, Utah, United States, ⁴Department of Radiology, University of Utah, Salt Lake City, Utah, United States

A 3D method for characterizing the dynamic response of tissue due to acoustic radiation force is tested. This 3D MR-ARFI technique can provide valuable information about the state of tissue elastic properties and assist with phase correction algorithms for beam focusing through aberrating tissue environments such breast and skull.

Jiming Zhang¹, Amol Pednekar², Pei-Herng Hor³, and Raja Muthupillai^1
1Diagnostic and Interventional radiology, CHI St Lukes' Health, Houston, TX, United States, ²Philips Healthcare, TX, United States, ³Physics, University of Houston, Houston, TX, United States

Magnetic resonance acoustic radiation force imaging (MR-ARFI) has been used to either localize the focal spot during high intensity focused ultrasound (HIFU) surgery or measure tissue viscoelasticity from temporally tracking the shear wave propagation initialize by acoustic radiation force (ARF) by an impulse excitation of HIFU. In addition to the mechanical effect of ARF, its thermal effect will potentially result in temperature increase during the MR-ARFI acquisition and may cause tissue damage in vivo study due to the repeat application of HIFU pulse. The results from the tissue mimicking gel phantom demonstrate the associated temperature rise and accumulated thermal dose during the acquisition of tracking shear wave propagation.

Eugene Ozhinsky¹, Vasant A. Salgaonkar², Chris J. Diederich², and Viola Rieke^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

We implemented and evaluated an MR Thermometry feedback control system for hyperthermia therapy using a commercially available prostate ablation system.

Robb Merrill¹, Henrik Odeen¹, Emilee Minalga¹, J. Rock Hadley¹, Dennis Parker¹, and Allison Payne^1
1Radiology, University of Utah, Salt Lake City, UT, United States

This work describes an MRgFUS system for conducting ultrasound procedures on large animals on a Siemens 3T MRI scanner. A craniotomy was performed on a pig to provide unobstructed passage of ultrasound during treatment. A seven-channel phased array RF coil was used for ultrasound guidance and MR thermometry. A multi-axis adjustment mechanism suspended the ultrasound transducer above the prone animal, and allowed for a treatment envelope covering the majority of the brain volume. Two brain locations were targeted and heating was successfully observed, verifying the ultrasound focus position. The system can be easily adapted to other animals and anatomy.

Sharon L Giles¹, Jessica M Winfield², Ian Rivens³, David J Collins², Gail R ter Haar³, and Nandita M deSouza^2
1MRI Unit, Royal Marsden Hospital, Sutton, Surrey, United Kingdom, ²CRUK Cancer Imaging Centre, The Institute of Cancer Research, Sutton, Surrey, United Kingdom, ³Therapeutic Ultrasound, The Institute of Cancer Research, Sutton, Surrey, United Kingdom

This study assesses the utility of DWI for detecting tissue changes during MRgHIFU by evaluating repeatability of ADC measurements and ADC changes after sonication in n=7 lamb legs. Measurements were made in soft tissues immediately adjacent to bone. Imaging appearances were macroscopically compared with dissected tissues. The coefficient of variation for repeat ADC measurements was 1.0% and the degree of ADC change increased with increasing power of sonications. A 20% sustained increase in ADC produced visible lesions on dissection, unapparent on T1- or T2-W imaging, making DWI a potential tool for monitoring damage during MRgHIFU in bone applications.

Samuel Pichardo^1,2, Justin Lee³, and Kullervo Hynynen^4
1Thunder Bay Regional Research Institute, Thunder Bay, ON, Canada, ²Electrical Engineering & Physics, Lakehead University, Thunder Bay, Ontario, Canada, ³Odette Cancer Centre, Toronto, Ontario, Canada, ⁴Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada

We propose to use Magnetic resonance image (MRI) guided high intensity focused ultrasound (MRgHIFU) as an adjuvant therapy to radio-therapy for the treatment of recurrent head and neck tumours. A previous pre-clinical study using a porcine model showed the importance of artifacts in MR-based temperature calculation and a method was developed and tested to compensate this source of noise. This paper presents the first results of using this method in a clinic context with patients with primary cancer in the neck area.

Jia Liu¹, Bilgin Keserci², Juan Wei³, Queenie Chan⁴, Yu Zhang⁵, Rong Rong¹, and Xiaoying Wang^1
1Radiology, Peking University First Hospital, Beijing, Beijing, China, ²Philips Healthcare, Seoul, Korea, ³Philips Research China, Shanghai, China, ⁴Philips Healthcare, Hong Kong, China, ⁵Philips Healthcare, Beijing, China

Multiple b-values DWI scan was performed on all 23 patients before and 6 months after HIFU ablation of fibroids using 3.0 T MR acquisition systems. For all b-values no larger than 100 s/mm2 and 200 s/mm2, mono-exponential model was used to calculate the diffusion coefficient respectively. For all b-values, bi- exponential IVIM model was used to calculate D, D* and f. Fibroids diffusion increased apparently accompanied with less microcirculation perfusion 6 months after HIFU treatments. IVIM MR imaging may serve as a valuable tool in emphasizing such diffusion and perfusion changes by using all b-values and/or low b-values no larger than 100 s/mm2.

Patrick Winter¹, Matthew Lanier¹, Ari Partanen², and Charles Dumoulin^1
1Radiology, Cincinnati Children’s Hospital, Cincinnati, OH, United States, ²Clinical Science MR Therapy, Philips Healthcare, Andover, MA, United States

MRI-guided HIFU (MR-HIFU) allows non-invasive ablation of deep tissues. MR-HIFU could be used to treat obesity and diabetes by heating body fat. Conventional MR thermometry methods cannot monitor temperature changes in fat. Instead, we used T2 mapping to evaluate the effects of HIFU on fat at 1.5T. Whole body heating experiments showed that fat T2 increased by 3.3 ms for every °C of heating. Immediately after HIFU, the T2 at the target increased by 17.7 ms, corresponding to 42.4 °C. A clear therapeutic effect was observed ten days after MR-HIFU, with rats losing 7.5 ± 1.2 % body weight.

Maythem Saeed¹, Loi Do¹, Mark W Wilson¹, and Roland Krug^1
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, Ca, United States

This swine study aimed to demonstrate the perfusion deficits, as an early indicator, of successful thermal MRg-HIFU ablation. Kidneys (n=12) were ablated after minimizing diaphragm motion using rocuronium injection and breath-hold. Saturation recovery-GRE was used after ablation to monitor regional perfusion in ablated, viable and aortic blood to obtain perfusion data. This study shows the potential of perfusion imaging as an early indicator of successful ablation. Thermal MRg-HIFU causes loss of vascular and cellular integrity. The severity of injury is dependent on the energy used. Thus, the used energy must be optimized in the kidney for future translation to clinic.

Chenchen Bing¹, Joris Nofiele¹, Robert Staruch^1,2, Yonatan Chatzinoff¹, Michele Harbeson³, Danny Maples³, Jerry Malayer³, Samuel Pichardo⁴, Ashish Ranjan³, and Rajiv Chopra^1
1Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ²Clinical Sites Research Program, Philips Research North Amarica, Briarcliff Manor, NY, United States, ³Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, United States, ⁴Thunder Bay Regional Research Institute, Thunder Bay, ON, Canada

Temperature-sensitive drug carriers are able to induce a fast release of active drugs in the target region, which will solve the problem of causing systemic toxicity during traditional chemotherapy. An MRI-compatible high-intensity focused ultrasound (MR-HIFU) system was developed to perform localized hyperthermia in rodent models. This MR-HIFU system can conduct precise-controlled thermal therapies to allow heat-mediated drug delivery in small animal models. Feasibility and performance of the system is well evaluated with phantom and in-vivo experiment.

Waltraud B. Buchenberg¹, Florian Wassermann², Sven Grundmann², Bernd Jung³, and Robin Simpson^1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²Center of Smart Interfaces, Technische Universität Darmstadt, Darmstadt, Germany, ³Institute of Diagnostic, Interventional and Pediatric Radiology, University Hospital, Bern, Switzerland

There is a need in thermo-fluidic disciplines to measure temperature distributions in flowing liquids, for example to investigate heat transfer for performance improvement of devices. Although primarily used for medical applications, MR thermometry (MRT) has the potential to provide these measurements. This work applied MRT to investigate temperature distributions in a heat exchanger using different flow rates, demonstrating that MRT can provide high-quality 3D measurements of temperature fields in such setups. Collaboration with thermo-fluidic engineers can also benefit the medical community, for example through the investigation into MR compatible materials that could be used in medical devices.

Yuval Zur^1
1GE Healthcare, Tirat Carmel, Israel

MR guided Focused Ultrasound (MRgFUS) is used to treat noninvasively many brain disorders. Currently gradient echo (GRE) is used for thermometry imaging using the PRF shift. In this work we present a new thermometry sequence which is based on Fast Spin Echo. It is shown that this sequence is not sensitive to field inhomogeneity, provides higher temperature signal to noise ratio, and acquire 3 slices simultaneously during heating.

David O. Brunner¹, Simon Gross¹, Lars Kasper¹, Bertram J. Wilm^1,2, Christoph Barmet^1,2, and Klaas P. Pruessmann^1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, ²Skope Magnetic Resonance Technologies LLC, Zurich, Switzerland

Temperature mapping based on the temperature dependence of the chemical shift of water protons offers high sensitivity, however it is also subject to many confounds. Mainly drifts in the magnetic fields have to be corrected for in order to achieve high accuracy. Therefore field monitoring based on an array of 16 temperature stabilized NMR field probes is used to reconstruct phase based temperature maps for field drifts up to 3^rd order in space. Sub-degree accuracy was achieved even in the presence of comparably strong dynamic field perturbation in-vitro in comparison to fluoroptic temperature reference probes.

Hans Weber¹, Daehyun Yoon¹, Valentina Taviani¹, Kim Butts Pauly^1,2, and Brian A Hargreaves^1
1Radiology, Stanford University, Stanford, California, United States, ²Bioengineering, Stanford University, Stanford, California, United States

Within this study, we propose a technique for MR thermometry close to metal. The technique utilizes a multispectral imaging approach and the temperature dependency of the T1 relaxation time. Within a phantom experiment, initial feasibility is demonstrated by tracking the T1 change close to a metal implant during heating.

Atsushi Shiina¹, Kenji Takahashi², Jiro Nakano³, and Kagayaki Kuroda^1
1Graduate School of Engineering, Tokai University, Hiratsuka, Kanagawa, Japan, ²Department of Orthopaedic Surgery, Nippon Medical School, Bunkyo, Tokyo, Japan, ³School of Information Science and Technology, Tokai University, Hiratsuka, Kanagawa, Japan

Feasibility of MR temperature imaging for joint cartilage using conventional water proton resonance frequency technique was demonstrated. Laser heating experiments with cartilage samples in vitro excised from porcine knee joints showed clear temperature elevation images of the thin cartilage region of 1-2 mm thickness. The temperature coefficient of the water proton resonance frequency was -0.0108 ppm/degree C. These results may be a first step to apply the noninvasive temperature imaging technique for thermally induced pain-relief for a patient with osteoarthritis.

Yuxin Hu¹, Shuo Chen², Bingyao Chen³, Jiafei Yang³, Xing Wei³, Shi Wang², and Kui Ying^2
1Tsinghua University, Beijing, Beijing, China, ²Engineering Physics, Tsinghua University, Beijing, China, ³Department of Orthopedics, First Affiliated Hospital of PLA General Hospital, Beijing, China

High speed and temperature accuracy are required in MR thermometry. While parallel imaging can speed up the acquisition, the corresponding reconstruction usually requires significant computation, especially when large coil arrays are used. This work evaluates the feasibility of direct virtual coil (DVC) for MR thermometry on bone tumor thermotherapy, in which parallel imaging and coil combination are combined into one step to reduce reconstruction time. It has been demonstrated that DVC can achieve similar temperature mapping accuracy compared to traditional parallel imaging method under different acceleration factors while it can be about twice faster.

Henrik Odéen^1,2, John Roberts¹, Joshua de Bever^1,3, and Dennis L Parker^4
1Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, Utah, United States, ²Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah, United States, ³School of Computing, University of Utah, Salt Lake City, Utah, United States,⁴University of Utah, Salt Lake City, Utah, United States

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Changjun Tie¹, Chao Zou¹, and Xin Liu^1
1Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China

Most referenceless MR thermometry methods use a large and fixed ROI to ensure to contain the whole heated region. However, the heated region is unknown and hard to estimate before heat occurs. The large ROI also compromises the accuracy in some measurements. This work proposes to use adaptive size of ROI for real-time referenceless thermometry. The size of ROI is decided by the size of heated region, which is measured from previous temperature map. The results would increase the accuracy of referenceless methods and improve the automation of referenceless thermometry for real-time monitoring.

Jochen Keupp¹, Steffen Weiss¹, Jaakko Tolo², Holger Gruell^3,4, and Edwin Heijman^3
1Philips Research, Hamburg, Germany, ²Philips Healthcare, Helsinki, Finland, ³Philips Research, Eindhoven, Netherlands, ⁴Eindhoven University of Technology, Eindhoven, Netherlands

MR guided high-intensity focused ultrasound (MR-HIFU) is establishing as a new treatment option for various diseases that elegantly combines two non-invasive technologies. Near-field ultrasound heating of the skin and heat accumulation in the subcutaneous fat layer can become problematic due to the low thermal conductivity of fat. Currently, temperature mapping based on the proton resonance frequency shift (PRFS) is applied during clinical MR-HIFU treatment. However, reliable PRFS temperature maps can only be acquired in non-adipose tissue, while fat tissue requires different temperature mapping techniques like e.g. based on T2-mapping. Simultaneous temperature monitoring would be desirable in separate FOVs, like the adipose far field and non-adipose tumor regions. We here propose to use an acquisition technology which quickly interleaves a PRFS (gradient-echo) and a T2 (dual spin-echo) sequence on the level of individual repetitions with microsecond latency. Feasibility was demonstrated in a model setup using ablation conditions on a clinical MR-HIFU system.

Candace C. Fleischer^1,2, Deqiang Qiu³, Xiaodong Zhong⁴, Hui Mao³, John N. Oshinksi³, Xiaoping Hu^1,2, and Seena Dehkharghani^3
1Biomedical Imaging Technology Center, Emory University, Atlanta, GA, United States, ²Biomedical Engineering, Emory University, Atlanta, GA, United States, ³Radiology and Imaging Sciences, Emory University Hospital, Atlanta, GA, United States, ⁴MR R&D Collaborations, Siemens Healthcare, Atlanta, GA, United States

Current brain thermometry methods are costly and highly invasive. Chemical shift imaging (CSI) is a promising technique for non-invasive thermometry utilizing temperature-dependent chemical shift differences between water and N-acetylaspartate. The current standard using a PRESS sequence with automated shimming suffers from poor spatial resolution and chemical shift artifacts. We present a CSI protocol for thermometry with quantitative improvements to shimming and spectral quality in vitro and in vivo: a semiLASER spectroscopy sequence with GRE Shim. Combining the semiLASER advanced voxel localization with a more homogenous magnetic field from GRE Shim will be beneficial for thermometry and other applications of CSI.

Jonathan Scalera¹, Gary P. Zientara², and Kumal Tuncali^1
1Brigham and Women's Hospital, Boston, MA, United States, ²US Army Research Institute of Environmental Medicine, Natick, MA, United States

MRI-guided cryoablation is a minimally invasive treatment for renal cell carcinoma for eligible patients. Currently, intra-procedural monitoring of these procedures relies on a subjective assessment of tumor margins and proximity to critical structures by the interventionalist. Quantitative, computerized methods of monitoring and measuring ablation performance in real-time has the potential to improve the safety and success of these procedures. We developed an integrated, real-time intra-procedural monitoring software and determined its feasibility and functionality for cryoablation procedures.

Dong-Hyun Kim^1,2, Ken Zhao¹, Daniele Procissi¹, Andrew Gordon¹, Weiguo Li¹, and Andrew C Larson^1,2
1Department of Radiology, Northwestern University Feinberg School of Medicine, Chicago, IL, United States, ²R.H. Lurie Cancer Center, Chicago, IL, United States

Nanoparticles mediated photo thermal ablation and MR temperature mapping

MR-Guided Inteventions

Wednesday, 3 June 2015

Nicholas Whiting¹, Jingzhe Hu^1,2, and Pratip Bhattacharya^1
1Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, Houston, TX, United States, ²Department of Bioengineering, Rice University, Houston, TX, United States

While visualizing the movement of catheters during endovascular interventions is typically accomplished using x-ray fluoroscopy, there are many potential advantages to developing MRI-based approaches that will allow for three-dimensional imaging of the tissue/vasculature interface while monitoring other physiologically-relevant criteria, without exposing the patient or clinician team to potentially harmful ionizing radiation. In this educational session, we will discuss the various benefits and current limitations of MRI-guided catheter tracking, as well as open a dialogue as to how we can improve this technique and allow large-scale adoption of MRI-guided catheter tracking that may benefit patients and clinicians alike.

Feng Zhang¹, Zhibin Bai¹, Yaoping Shi¹, Jianfeng Wang¹, Longhua Qiu¹, Yonggang Li¹, and Xiaoming Yang^1
1Radiology, University of Washington, SEATTLE, WA, United States

Systemic chemotherapy has limited therapeutic effect on pancreatobiliary cancers due to the insufficient drugs delivered to the tumors. To address this problem, we successfully developed a technique of using interventional magnetic resonance imaging (MRI) to guide intrabiliary agent delivery into pig common bile duct (CBD) walls with a newly-designed MR compatible needle-integrated balloon catheter system.

Clifford R. Weiss¹, Daniel M. O'Mara², Paul A. DiCamillo², Di Xu³, Wesley D. Gilson⁴, Daniel A. Herzka³, and Jonathan S. Lewin^2
1Vascular and Interventional Radiology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States, ³Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, MD, United States, ⁴Siemens Healthcare USA, Baltimore, MD, United States

Low-flow vascular malformations (venous and lymphatic) are traditionally treated using ultrasound and fluoroscopy guided percutaneous sclerotherapy. However, certain lesions are particularly difficult to visualize and/or treat using these modalities. Real-time MR-guided intervention may serve as a safer alternative with better visualization of surrounding critical soft tissue structures and with less or no exposure to ionizing radiation. We present here our experiences with targeting and treating low-flow vascular malformations using real-time MR imaging.

Olivia Garandeau¹, Maxime Bories¹, Fabrice Marquet¹, Remi Dubois², Pierre Jais³, and Bruno Quesson^1
1IHU Liryc/CRCTB Inserm U1045, University of Bordeaux, Pessac, Aquitaine, France, ²IHU Liryc/CRCTB Inserm U1045, ESPCI Paris Tech, Pessac, Aquitaine, France, ³CHU bordeaux, Pessac, Aquitaine, France

Catheter exploration, key procedure for cardiac arrhythmia diagnosis and treatment, could benefit from MRI guidance and procedure monitoring. In this work, we present a homemade MR compatible 3D and real-time catheter navigation device based on electric field detection. The system was validated in vitro providing catheter positions with a maximum error of 5.5 mm at 25 frames per second. In vivo feasibility was also demonstrated in a swine model. Such work opens perspectives for catheter guidance and 3D slice tracking during MR exam enabling real-time visualization of the targeted area and respiratory motion correction.

Prasheel Lillaney¹, Aaron D Losey¹, Alastair J Martin¹, Bradford RH Thorne¹, Leland B Evans¹, Vincent Malba¹, Maythem Saeed¹, Ronald Arenson¹, and Steven W Hetts^1
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States

This study evaluates the in vivo performance of the magnetically assisted remote controlled (MARC) catheter in a renal embolization model using MR image guidance. The MARC catheter is navigated through the aorta and into the origin of the renal artery at which point embolic spheres (100 to 300 uM in size) are delivered through the catheter into the kidney. The intervention is repeated using X-ray guidance and performance parameters are compared between the two imaging modalities.

Samantha Mikaiel^1,2, Rashid Yasin³, Samuel Ross⁴, M. Wasil Wahi-Anwar¹, James Simonelli³, David Lu², Kyung Sung^1,2, Tsu-Chin Tsao³, and Holden H. Wu^1,2
1Biomedical Physics, University of California Los Angeles, Los Angeles, CA, United States, ²Radiological Sciences, University of California Los Angeles, Los Angeles, CA, United States, ³Mechanical and Aerospace Engineering, University of California, Los Angeles, CA, United States, ⁴Santa Monica College, Santa Monica, CA, United States

In this work, we present a new robotic system prototype based on hydrostatic actuation that enables 3-degree-of-freedom (DOF) remote control of interventional devices inside the scanner bore under real-time MRI guidance. We observed negligible effects on MR image artifact, SNR, and distortion. We also demonstrated the feasibility of our new robotic system for 3-DOF control and to achieve needle placement within 1.6 mm of defined targets under real-time MRI guidance. Our new MRI-compatible robotic system can potentially provide physicians continuous access to patients during real-time MRI-guided interventions with improved visualization and accuracy.

Mahamadou Diakite¹, Steve Roys¹, Yeongjin Kim², Taehoon Shin¹, Mark J Simard³, Jaydev P Desai², and Rao P Gullapalli^1
1Center for Metabolic Imaging and Therapeutics, Depart. of Diagnostic Radiology and Nuclear Medicine, University of Maryland, School of Medicine, Baltimore, MD, United States, ²Mechanical Engineering, University of Maryland, College Park, MD, United States, ³Neurosurgery, University of Maryland, School of Medicine, Baltimore, MD, United States

Real-time tracking and navigation is important for effective use of surgical robotic devices with multiple degrees-of-freedom, and especially ones that have multiple end effector functions including cauterization. The goal of this study is to develop a real-time MRI system for tracking and visualizing the interventional device using a passive magnetic sensor and a closed-loop control algorithm. Its technical feasibility is demonstrated on a phantom.

D. Adair^1,2, K. S. Gomes³, Y. P. Starreveld^3,4, Z. H.T. Kiss³, and D. G. Gobbi^1,4
1Calgary Image Processing and Analysis Centre, Calgary, Alberta, Canada, ²Biomedical Engineering, University of Calgary, Calgary, Alberta, Canada, ³Clinical Neuroscience and Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada, ⁴Atamai Inc., Calgary, Alberta, Canada

Framed stereotaxic surgery remains the most accurate and precise method for targeting deep-brain stimulation (DBS) but lacks effective planning software. We developed a novel tool (Tactics) for a clinical study on DBS in treating depression. Targeting was performed with both Tactics and a stereotactic frame and a mean software accuracy of 0.7 mm was calculated, demonstrating a high level of accuracy. The system is open-source and can be extended to include other functional and electrophysiological mapping data. Tactics has demonstrated to be both effective and intuitive and has been adopted by an ongoing clinical study as their standard tool.

Alastair J Martin¹, Krystof Bankiewicz², John Bringas², Chad Christine³, Marin Thompson², Janine Beyer², and Paul Larson^2
1Radiology and Biomedical Imaging, UCSF, San Francisco, CA, United States, ²Neurological Surgery, UCSF, San Francisco, CA, United States, ³Neurology, UCSF, San Francisco, CA, United States

MR guidance is used to monitor convection enhanced delivery of a novel gene therapy agent (AAV2-hAADC) in patients with Parkinson’s disease. The therapeutic is infused bilaterally into the putamen and targeting is performed with intra-operative MR guidance. Two infusions are performed in each putamen in order to maximize coverage of the anatomic structure. Continuous infusion monitoring with MR imaging revealed sub-optimal distributions such as reflux along the cannula tract and shunting along vascular channels. Detection of these effects permitted adjustments to infusion strategy, including changing cannula depth and aborting ineffective infusions.

Alexandre Bigot¹, Maxime Latulippe¹, Charles Tremblay¹, and Sylvain Martel^1
1Nanorobotics Laboratory, Polytechnique Montreal, Montreal, Quebec, Canada

Magnetic Resonance Imaging scanners have the potential to control endoscopic capsules for gastrointestinal (GI) examination. The correct imaging and detection of small abnormal tissues along the GI tract require fine adjustment of the capsule position and of the capsule angle. We therefore demonstrate that gradients can generate eddy currents in a small coil and therefore induce a torque on a small capsule. With time-varying magnetic field below stimulation levels, a 2.5-cm capsule rotates from 35° to 0° (aligned with B0) in less than 20 seconds. This work may open the way to the development of MR actuated endoscopic capsules.

Florian Maier¹, Erik N. K. Cressman², Moritz C. Berger¹, David Fuentes³, R. Jason Stafford³, Christopher J. MacLellan³, Reiner Umathum¹, and Armin M. Nagel^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Interventional Radiology, The University of Texas MD Anderson Cancer Center, Houston, TX, United States, ³Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, United States

Thermochemical ablation (TCA) provides a novel concept in minimally invasive ablative procedures in which two reactive solutions, such as acetic acid and sodium hydroxide, release heat as they react prior to entering the tissue as sodium acetate (NaOAc) solution. Besides thermal damage, additional damage is caused by the hyperosmolar environment after injection. In this work, ²³Na MRI is used to image NaOAc distributions to provide more detailed insight for effective delivery. ²³Na MRI of TCA injections will facilitate a platform for the design and optimization of applicators as well as development and validation of computational models, and progress towards clinical translation.

Shashank Sathyanarayana Hegde¹, Li Pan², Guan Wang^1,3, Martin Radvany¹, Yingli Fu¹, and Dara L Kraitchman^1
1Radiology, Johns Hopkins University, Baltimore, Maryland, United States, ²Siemens Healthcare, Baltimore, Maryland, United States, ³Electrical and Computer Engineering, Johns Hopkins University, Maryland, United States

We developed and characterized an internal probe at 3T designed for interchangeable ¹H and ¹⁹F use. The internal probe demonstrated increased signal-to-noise ratio with respect to a conventional ¹⁹F surface coil for structures deeper than 2 cm from the surface. ¹⁹F imaging of ~7.5mL of a 10-fold dilution (e.g., 5 mg/ml) of fluorouracil (5-FU) was possible in 2 minutes. Multinuclear MRI of perfluorooctyl bromide (PFOB) microcapsules was performed in tissue samples ex vivo and a rabbit thigh in vivo. High-resolution (0.2 mm ¹H and 0.8 mm ¹⁹F in-plane) MRI of PFOB capsules was possible and was concordant with cone beam computed tomography (CT) imaging of the radiopaque microcapsules.

Alex Luk¹, Yuting Lin², David Thayer³, Seunghoon Ha⁴, and Gultekin Gulsen^1
1UC Irvine, Irvine, California, United States, ²Harvard Medical School, Massachusetts, United States, ³UC Irvine Medical, Irvine, California, United States,⁴UC Irvine, Irvine, california, United States

Diffuse optical imaging is advantageous in enhancing tumor diagnosis by providing functional information but suffers from low resolution. We combined MR thermometry and diffuse optical tomography and built the first prototype photo magnetic imaging system. It provides in-vivo functional information with MR resolution and helps to monitor different optical contrast agents such as Indocyanine green. A finite element based forward simulation of the laser induced temperature change map has been compared with PMI measurements. The forward simulation accurately estimates the temperature tomography collected by MR thermometry. By solving the inverse problem with multiple wavelengths, we will be able to reconstruct MR resolution tomography of different chromophores concentrations.

Jan Fritz¹, Margaret W Arnold², Holly Grunebach², Kendall Likes², Jonathan S Lewin¹, and Ying W Lum^2
1Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, United States,²Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, United States

Neurogenic thoracic outlet syndrome is often caused by brachial plexus compression in the scalene triangle and costoclavicular space. As such, scalene muscles are the principle target for intramuscular diagnostic and therapeutic injections. MRI guidance offers cross-sectional imaging with high soft tissue contrast, absence of ionizing radiation, and the ability to visualize injectants without a contrast agent. We describe a technique of 3 Tesla MR-guided scalene muscle injections, which combines high accuracy, a favorable safety profile, the absence of ionizing radiation, and the ability to accurately visualize the injectant without the need of a contest agent.

Ellis Beld^1,2, Marinus A. Moerland¹, Job G. Bouwman², Frank Zijlstra², Jan J.W. Lagendijk¹, Max A. Viergever², and Peter R. Seevinck^2
1Department of Radiotherapy, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, ²Image Sciences Institute, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands

Image guidance is of great importance in high-dose-rate (HDR) prostate brachytherapy. A robotic MR-guided HDR brachytherapy treatment is being developed and one of the aims is real-time tracking of the HDR source. In this study, localization of an HDR brachytherapy source was performed retrospectively, by simulating the artifact of the source in a gradient echo image and matching the simulated artifact to the experimental image by means of phase-only cross correlation. Furthermore, it was investigated to what extent the localization depends on the materials of the interventional devices.

S. Ghose¹, J. Mitra¹, D. Rivest Henault¹, A. Fazlollahi¹, P. Stanwell², P. Greer³, P. Pichler³, J. Fripp¹, and J. Dowling^1
1Australian e-Health Research Centre, CSIRO Digital Productivity Flagship, Herston, QLD, Australia, ²University of Newcastle, NSW, Australia, ³Department of Radiation Oncology, Calvary Mater Newcastle Hospital, NSW, Australia

Gold seeds or fiducials implanted in the prostate prior to radiation treatment are frequently used to enable the rigid registration of the two modalities required for the transfer of the prostate contours from MRI to CT. An automatic efficient detection method for the fiducials from MRI is necessary to automate the procedure. This work proposes Gaussian mixture modeling (GMM) and spectral clustering based methods for fiducial candidate selection and a similarity score based fiducial detection. The proposed approach detects fiducials with an accuracy of 95% when compared to the manual detection.

Justin Y.C. Lau^1,2, Jennifer Barry², and William Dominguez-Viqueira^2
1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, ²Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada

The feasibility of locating a controllable device, with susceptibility effects that can be turned ON and OFF, in the presence of motion is examined in the common iliac artery of a porcine model. A 2D fast spoiled gradient echo sequence was modified with a phase-encoding scheme that acquires odd k-space lines first, followed by a pause to allow manual toggling of the susceptibility effect before the acquisition of even k-space lines. Despite severe motion artifacts, the device was located unambiguously in vivo. Further optimization of the sequence allowed in vitro location of both the device and a clinical balloon catheter in less than 5 seconds.

Robert D Darrow¹, Mark Schneider², Eric W Fiveland¹, Xiaofeng Liu¹, and Ileana Hancu^1
1Global Research Center, GE, Niskayuna, New York, United States, ²NDI Ascension, Shelburne, Vermont, United States

Many factors can contribute to an inaccurate MR-guided breast biopsy. The lack of real-time visualization of tool advancement towards the biopsy site increases the time to perform the biopsy, and likely contributes to the false negative rate. In this work, we have acquired preliminary evidence, indicating breast immobility during the procedure. Secondly, we have shown that electromagnetic (EM) tracking in the strong fringe field of 3T MRI magnets is feasible. Retrofitting breast biopsy tools with EM sensors could enable real time visualization of tool advancement towards the lesion, hence significantly increase the accuracy and decrease the time needed for breast biopsy procedures.

Yulia Shcherbakova¹, Cornelis A.T. van den Berg¹, Jan J.W. Lagendijk², Chrit T.W. Moonen², and Lambertus W. Bartels^1
1Imaging Division, University Medical Center, Utrecht, Utrecht, Netherlands, ²Imaging Division, University Medical Center, Utrecht, Netherlands

Rapid quantitative imaging is very important for planning and guidance of MRI-guided oncological therapy. The normal liver tissue and metastases have different T1 and T2 relaxation times and their ratio T1/T2 , which makes these parameters relevant quantitative imaging biomarkers. Conventional T1 and T2 mapping techniques are relatively time-consuming, which has led to the development of promising rapid techniques, such as DESPOT1 and DESPOT2. However, in practice, even at 1.5T, electromagnetic fields are imperfect, which may influence the accuracy and precision of quantitative imaging techniques. In this study we have investigated the impact of B1 field inhomogeneity on the performance of 3D DESPOT1 and DESPOT2 methods and demonstrated that DESPOT1 method is sensitive to B1 field inhomogeneity, even at 1.5T. A 5% error in nominal flip angle significantly influences the calculated T1 value and leads to a 10% error in the observed T1 value. However, the T2 estimates are minimally affected, when T2 is calculated using non-B1 corrected T1 values. Thus, the influence of B1 deviations on T2 mapping is negligible, so, B1 field correction for T2 mapping based on DESPOT2 method, is not required.

Jijun Han¹, Shuai Song¹, and Bensheng Qiu^1
1University of Science and Technology of China, Hefei, Anhui, China

Carbon fiber needle for MRI-guided radiofrequency ablation

Thomas Boyd Martin^1,2, Holden Wu¹, Danny JJ. Wang³, and Kyung Sung^2
1Biomedical Physics Interdepartmental Program, University of California Los Angeles, Los Angeles, California, United States, ²Radiological Sciences, University of California Los Angeles, Los Angeles, California, United States, ³Neurology, University of California Los Angeles, Los Angeles, California, United States

MRI has great potential to provide an improved ability 1) to track the needle position, 2) to distinguish diseased from healthy tissue and 3) to monitor treatment effect for image guidance procedures. Balanced-SSFP (bSSFP) offers good T2/T1 tissue contrast and is a fast imaging technique that minimizes patient motion, but severe needle induced banding artifacts are present. Gradient Spoiled (GRE) and RF-Spoiled Gradient-Echo (SPGR) sequences decrease needle-induced artifacts, but result in lower soft tissue contrast. This study demonstrates a special case of a GRE sequence, integrated-SSFP (iSSFP), that reduces needle induced banding artifacts from bSSFP, while maintaining similar T2/T1 contrast.

Ying Dong¹, Guoxi Xie², and Jim Xiuquan Ji^1
1Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, United States, ²Paul C. Lauterbur Research Center for Biomedical Imaging, Chinese Academy of Sciences, Shenzhen, Guangdong, China

Interventional devices normally show as dark features (negative contrast) on MRI. Several methods have been proposed to generate positive-contrast device images in interventional MRI. These methods generally rely on the off-resonance effects due to the device’s high susceptibility, which highlight the surrounding areas instead of the devices themselves. Recently, we developed a novel method to generate positive contrast images of small devices such as brachytherapy seeds by direct susceptibility mapping. Technical advances of the method are reported here on imaging of medium/large devices such as biopsy needles on 3T systems.

Hirad Karimi^1,2, William Dominguez-Viqueira², and Charles H Cunningham^1,2
1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, ²Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada

Performing catheter and needle-based interventional procedures under MRI guidance remains a promising area, where the extra soft tissue contrast can be used to improve outcomes in certain procedures. Passive tracking with susceptibility effects offers an easy-to-make and cost efficient method for tracking interventional devices, however difficulty locating devices when they are out-of-slice, or in projection images, is a major drawback. Laser-induced demagnetization of metal films has been used in magneto-optic devices. In this abstract, the possibility of using laser-induced demagnetization to modulate the susceptibility artifact from Ni nanoparticles in MR-images was investigated, making the artifact “flicker� and enabling detection in projection images.

Simon Reiß¹, Axel Joachim Krafft^1,2, Klaus Düring³, Constantin von zur Mühlen⁴, and Michael Bock^1
1Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²German Cancer Consortium (DKTK), Heidelberg, Germany, ³MaRVis Medical GmbH, Hannover, Germany, ⁴Department of Cardiology and Angiology I, University Heart Center Freiburg, Germany

The white marker phenomenon has been proposed for passive localization in MR-guided interventions. A positive contrast of interventional devices is generated by dephasing background signal while preserving signal in the proximity of the device by unbalanced gradient schemes, and has been implemented in FLASH and bSSFP sequences. In this work, we compare these sequences to optimize the white marker signal of small platinum markers and an MR-compatible guidewire. Our results indicate that the bSSFP sequence is optimally suited to generate high contrast even for small paramagnetic objects which could be used for the localization of vascular scaffolds.