Bryant Svedin¹ and Dennis L. Parker^1
1University of Utah, Salt Lake City, UT, United States

A multi-echo pseudo-golden angle stack of stars sequence is investigated for use in MR thermometry. High spatial and temporal resolution is achieved through k-space filtering. PRF temperature, T2*, ρ (signal magnituade at TE = 0), respiration correction and fat/water separation are simultaneously measured. Use of a pseudo-golden angle increment allows for the removal of phase (and therefore PRF temperature) artifacts due to changing k-space sampling between reconstructed time points. k-Space sampling based phase reference greatly improves temperature standard deviation. FUS heating experiments are performed while simulating respiration artifacts.

Michael Marx¹, Pejman Ghanouni¹, and Kim Butts Pauly^1
1Radiology, Stanford University, Stanford, CA, United States

Multi-slice thermometry was developed that overcomes several limitations of single-slice 2DFT thermometry in MR-guided focused ultrasound brain treatment. Using multiple-echo spiral imaging provides much greater imaging performance, which was applied to improved focal spot localization and to improved ablation monitoring. High-resolution higher-precision multi-slice focal spot localization can shorten treatment time and improve patient safety. High-speed high-precision focal spot monitoring, combined with full-brain monitoring and 3-dimensional focal spot characterization during ablations can improve treatment guidance and feedback while also improving patient safety. The new sequences were validated both in vivo and in a phantom within a clinical transducer.

Jeremy Tan^1,2,3, Adam C. Waspe^1,2, Charles Mougenot⁴, Kullervo Hynynen^1,5, James M. Drake^1,2, and Samuel Pichardo^3,6
1University of Toronto, Toronto, ON, Canada, ²Hospital for Sick Children, Toronto, ON, Canada, ³Thunder Bay Regional Research Institute, Thunder Bay, ON, Canada, ⁴Philips Healthcare, Toronto, ON, Canada,⁵Sunnybrook Research Institute, Toronto, ON, Canada, ⁶Electrical Engineering, Lakehead University, Thunder Bay, ON, Canada

Accurate thermometry during abdominal high-intensity focused ultrasound is severely compromised by motion and susceptibility artifacts. A hybrid artifact correction method has been developed using principal component analysis as a multi-baseline method and projection onto dipole fields as a near-referenceless approach. The hybrid algorithm was tested using free-breathing porcine and human subjects and achieved an average temperature stability and precision of 0.31 (±0.22) °C and 1.18 (±0.94) °C, respectively in the kidney.

Pierre Bour^1,2, Fabrice Marquet², Fanny Vaillant², Valery Ozenne², Solenn Toupin^2,3, Matthieu Lepetit coiffe³, Erik Dumont¹, and Bruno Quesson^2
1IGT, PESSAC, France, ²IHU-LIRYC, PESSAC, France, ³Siemens Healthcare, Saint-Denis, France

HIFU cardiac stimulation may enable diagnostic and therapeutic applications such as noninvasive electrophysiological exam, emergency care and temporary stimulation. In-vivo proof of concept of HIFU cardiac stimulation has already been done on pig. We propose here a first proof of feasibility to monitor the displacement induced by acoustic radiation force impulse (MR-ARFI) during contactless stimulation ex-vivo, on a beating pig heart model. ARFI displacement maps will be used for precise localization of the depolarization source and a quantification of displacement will be done during refractory (contraction) and non-refractory (resting time) period. 

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

Using focused ultrasound and MR acoustic radiation force imaging (MR-ARFI), the mechanical properties of tissues can be interrogated.  Changes to tissue properties, for instance before and after a MR guided focused ultrasound thermal therapy, could help evaluate treatment success. This abstract presents a novel method for measuring acoustic radiation force simultaneously with proton resonance shift thermometry. This would enhance the safety of MR-ARFI, and provide additional temperature information that may indicate when, and at what temperature, a tissue property change occurred. Temporal resolution was enhanced by a factor of 5 by employing a temporally constrained reconstruction algorithm.

Misung Han¹, Wenwen Jiang², Roland Krug¹, Peder Larson^1,2, and Viola Rieke^1
1Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States, ²Joint Graduate Program in Bioengineering, University of California, San Francisco/Berkeley, San Francisco, CA, United States

High-intensity focused ultrasound (HIFU) is a promising, noninvasive technique to ablate bone tumors and palliate painful bone metastases. During HIFU treatment, temperature mapping is desirable for proper heat deposition to targeted bone regions. Even though conventional PRF-based thermometry cannot be applied for cortical bone due to its short T2 relaxation time, it was demonstrated using 3D UTE imaging can be used to measure T1 changes due to heating. In this work, we accelerated 3D UTE imaging by combining parallel imaging and compressed sensing and compared calculated T1 changes due to heating with those from fully sampled data.

Elena Kaye¹, Sebastien Monette², Majid Maybody³, Stephen B Solomon³, and Amitabh Gulati^4
1Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, United States, ²Comparative Pathology, Sloan Kettering Institute, New York, NY, United States, ³Radiology, Memorial Sloan Kettering Cancer Center, New York, NY, United States, ⁴Anesthesiology, Memorial Sloan Kettering Cancer Center, New York, NY, United States

The main goals of this preclinical study were to determine whether direct MRgFUS ablation of the lumbar MB nerve leads to functional changes and to study the extent of the thermal damage to the targeted and adjacent tissues, including neurologic structures. We found that direct FUS ablation of the lumbar MBN achieves thermal necrosis of the targeted nerve with minimal thermal damage of the adjacent bone and muscle tissue. The extent of the cellular changes in bone is limited to a few millimeters with no changes in the spinal cord, confirming the protective effects of spine bone rapidly attenuating the ultrasound. No functional changes were observed.

Qiyuan Tian^1,2, Max Wintermark², Kim Butts Pauly², Diane Huss³, W. Jeffrey Elias⁴, and Jennifer A. McNab^2
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Radiology, Stanford University, Stanford, CA, United States, ³Physical Therapy, University of Virginia, Charlottesville, VA, United States,⁴Neurosurgery, University of Virginia, Charlottesville, VA, United States

We retrospectively studied 13 essential tremor patients treated with MRI-guided focused ultrasound. The purpose was to demonstrate the value of using diffusion MRI tractography to help localize the ventral intermediate (Vim) nucleus of the thalamus (the treatment target). Tractography between the thalamus and hand-knob region of the motor cortex was consistent from subject-to-subject and followed the expected anatomy. The thalamic voxels with high tractography streamline counts qualitatively matched the location of Vim as depicted on the Schaltenbrand-Wahren Atlas. A trend was found towards better treatment outcome scores with higher pre-treatment probabilistic tractography streamline counts within the visualized MRgFUS treatment-induced lesion.

William Chu¹, Robert Staruch², Samuel Pichardo^3,4, Yuexi Huang⁵, Charles Mougenot⁶, Matti Tillander⁷, Max O. Köhler⁷, Mika Ylihautala⁷, Merrylee McGuffin¹, Gregory Czarnota¹, and Kullervo Hynynen^5
1Radiation Oncology, Sunnybrook Health Science Centre, Toronto, ON, Canada, ²Philips Research, Cambridge, MA, United States, ³Thunder Bay Regional Research Institute, Thunder Bay, ON, Canada, ⁴Electrical Engineering, Lakehead University, Thunder Bay, ON, Canada, ⁵Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, ⁶Philips Healthcare, Toronto, ON, Canada, ⁷Philips Healthcare, Vantaa, Finland

We present the first results of a Phase I trial that includes delivery of mild hyperthermia using magnetic resonance-guided high intensity focused ultrasound (MR-HIFU) combined with radiation and chemotherapy in the treatment of locally recurrentrectal cancer.  MR-HIFU mild hyperthermia was delivered in three sessions (day 1, 8 and 15) during a 17-day treatment protocol (total dose 30.6 Gy combined with fluropyrimidine-based chemotherapy). MR-HIFU mild hyperthermia was successfully delivered and the procedure was well tolerated by the patient. No adverse effects have been reported 3 months after the treatment.

Juan C. Camacho^1,2, Nima Kokabi¹, Tracy E. Powell², and Sherif G. Nour^1,2
1Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA, United States, ²Interventional MRI Program, Emory University Hospital, Atlanta, GA, United States

The objective of this study is to present outcomes of MRI-guided laser ablation for early stage renal cell carcinomas and to describe associated prognostic factors in a consecutive cohort of patients with relative long-term longitudinal follow-up. A prospective cohort of patients presenting with pathology-confirmed RCC underwent MRI-guided biopsy and subsequent laser ablation. Twenty-four consecutive patients presenting with 35 RCC were recruited. Follow-up MRI imaging was obtained in all cases with a median follow-up period of 20 months. Of the different analyzed prognostic factors, R.E.N.A.L nephrometry score was the only one predicting the incidence of complications.