Michael Marx¹ and Kim Butts Pauly^2
1Electrical Engineering, Stanford University, Stanford, California, United States, ²Radiology, Stanford University, Stanford, CA, United States

Multiple-echo 2DFT SPGR was implemented for temperature monitoring, and compared with single-echo SPGR. It was found that performing a weighted average of individual echo temperature measurements gave significantly better temperature uncertainty than using least squares linear fitting to find B0 for each time point. Using the weighted average approach, combined temperature uncertainty matched expectations for a single readout of the same duration, and was close to achieving the upper bound on performance found by analyzing each echo’s uncertainty.

E. Brian Welch^1,2, Aliya Gifford^2,3, and Theodore F. Towse^2,4
1Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States, ²Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, ³Chemical and Physical Biology Program, Vanderbilt University, Nashville, TN, United States, ⁴Physical Medicine and Rehabilitation, Vanderbilt University, Nashville, TN, United States

This research demonstrates MRI-based thermometry in fat-water phantoms by explicitly modeling the temperature-dependent water peak frequency shift in the fat-water signal equation. Besides temperature monitoring of mixed fat/water tissue during interventional applications, this method is well suited for studying brown adipose tissue. The technique was tested on phantoms with nominal fat fractions of 0, 10, 20, 30, 40, 60 and 100 percent undergoing heating and cooling with validation using fiber optic temperature probes. MRI-based measurements followed closely the probe measurements except for areas with fat-water mapping errors or in phantoms with only one species, i.e. 0% or 100% fat.

Chang-Sheng Mei¹, Renxin Chu¹, Lawrence P Panych¹, and Bruno Madore^1
1Department of Radiology, Harvard Medical School, Brigham and Women's Hospital, Boston, MA, United States

Tissue damage is conventionally detected by thermal dose, which depends on heating history and can thus become fairly erratic in the presence of motion. The main purpose of this study was to detect tissue damage not only by thermal dose but also through changes in T2, in the presence of motion. We employed a dual-pathway sequence to simultaneously map temperature changes and T2 during focused ultrasound experiments that were performed in turn with or without motion. The presence of motion very much affected the phase-based temperature measurements but not nearly as much the magnitude-based T2 measurements.

Chang-Sheng Mei¹, Renxin Chu¹, W Scott Hoge¹, Lawrence P Panych¹, and Bruno Madore^1
1Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States

Field inhomogeneities may cause errors in the temperature values measured by the proton resonance frequency (PRF) method. The present work aims to further describe and avoid such errors. Field inhomogeneities were introduced on purpose by de-adjusting shim settings, and errors by as much as 26% were obtained on temperature measurements made as part of heating experiments in a gel phantom. Methods are introduced that enabled accurate temperature measurements to be obtained even in the presence of field inhomogeneities. More generally, the proposed approaches might be applicable to field-mapping methods beyond only PRF thermometry.

Peter T. Fwu¹, Jeon-Hor Chen^1,2, Yuting Lin¹, Wei-Ching Lin³, Po-Jung Tseng¹, Eddie Lin¹, and Min-Ying Lydia Su^1
1Tu & Yuen Center for Functional Onco-Imaging, Department of Radiological Sciences, University of California, Irvine, CA, United States, ²Department of Radiology, EDa Hospital and I-Shou University, Kaohsiung, Taiwan, ³Department of Radiology, China Medical University Hospital, Taichung, Taiwan

Regional hypothermia using endorectal cooling balloon (ECB) during prostatectomy surgery is proven capable of minimizing tissue inflammatory damages. In this work we analyzed 29 prostate MRI cases. The images were segmented to reconstruct a 3D anatomic model for each patient for simulating the cooling processes by using bioheat equation with finite element methods. Very reasonable results were obtained, suggesting feasibility of this approach. The temperature at neurovascular bundle(NVB) was strongly affected by the distance from the cooling balloon as well as the total venous blood volume. For patients with similar blood volumes, the temperature was linearly correlated with NVB-ECB distance.

Matthew Tarasek¹, Ruben Pellicer², Lorne Hofstetter¹, Jurriaan Bakker², Wouter Numan², Gyula Kotek², Eric Fiveland¹, Gavin Houston³, Gerard van Rhoon², Maarten Paulides², and Desmond Yeo^1
1MRI, GE global research, Niskayuna, NY, United States, ²Erasmus Medical Center, Netherlands, ³MRI, GE healthcare, Netherlands

MR thermometry (MRT) validation can be difficult in head and neck (H&N) hyperthermia treatments due to the nonlinear trajectory of H&N temperature (T) probe catheters. In this work, we utilize a previously developed spline-fitting technique to reconstruct the catheters in MR image coordinate space and present (i) an effective approach for T probe sensor localization in phantoms to mitigate T probe localization errors and (ii) provide a means of more accurate proton resonance frequency thermal coefficient characterization, which corrects for systematic over- or underestimation of temperature with MRT. Findings show that this method is beneficial for MRT validation.

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

During thermal therapies, measurements of the absolute temperature are needed to calculate the thermal dose. Deriving the absolute temperature directly from the water/fat(w/f) frequency difference has been proposed. The method assumes that the intra-voxel water and fat components experience the same magnetic field despite the fact that water and fat have slightly different magnetic susceptibilities. Here we investigate the influence of magnetic susceptibility distribution on the measured absolute temperature, both experimentally and with simulations. The results show a larger variation in measured temperature for a heterogeneous w/f distribution (15°C), such as the breast, than for a more homogenous distribution (5°C).

Feifei Qu¹, Amol Pednekar², Pei Hor^1,3, Claudio Arena⁴, Janie Swaab⁴, Debra Dees⁴, Brenda Lambert⁴, and Raja Muthupillai^4
1University of Houston, Houston, TX, United States, ²Philips Healthcare, Houston, TX, United States, ³Texas Center for Superconductivity, Houston, TX, United States, ⁴Diagnostic and Interventional Radiology, St. Luke's Medical Center, Houston, TX, United States

In this study, we sought to evaluate non-contrast imaging alternatives that can yield information regarding MR-HIFU treatment efficiency. In specific, we evaluate the following MR metrics for evaluating MR-HIFU treatment efficiency: (a) T2 maps (surrogate for edema), (b) Blood-flow fraction (f) maps (surrogate for tissue perfusion weighted imaging (PWI) or low b-value diffusion acquisition), and (c) ADC maps estimated from Diffusion Weighted Imaging (high b-value DWI as a surrogate for restricted diffusion). PWI (low ‘b’ value) is a non-contrast alternative to conventional NPV based estimation of MR-HIFU treatment efficiency. The blood-volume fraction map (f-maps) provide better delineation between treated and untreated regions than T2 map, or conventional ADC map, and is more insensitive to other confounding factors such as T2 changes after HIFU treatment

Kemal Tuncali¹, Xinyang Liu¹, William M Wells III¹, Stuart G. Silverman¹, and Gary P. Zientara^1
1Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States

The safety and effectiveness of percutaneous image-guided ablations can be improved if the procedure could be assessed quantitatively. Using MRI’s ability to depict both the tumor and the iceball during cryoablations, we developed a novel computerized tool that utilized fast automatic segmentation and registration methods to compute ablation metrics in MRI-guided cryoablations of renal cancer. The computer generated ablation metrics were compared to metrics calculated from manual segmentation of the tumor and the ablation zone in 24 hr MR images of same cases. Based on our experiments, the tool can provide accurate real-time quantitative assessment of key ablation metrics.

Eugene Ozhinsky¹, Vasant A. Salgaonkar², Chris J. Diederich², and Viola Rieke^1
1Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, ²Department of Radiation Oncology, University of California San Francisco, San Francisco, CA, United States

The goal of this project was to identify operational modifications, and assess the feasibility of delivering protracted MR-guided prostate hyperthermia with a commercial endorectal ablation array. Hyperthermia-specific sonications were imple-mented on ExAblate 2100 prostate phased array ablation system and performed on a tissue-mimicking phantom. Tem-perature monitoring was performed on a 3T MRI scanner using a spoiled gradient echo sequence. These experiments illustrate the ability to successfully employ hyperthermia specific beamforming to control the shape of energy deposition, to deliver long duration power output with the ExAblate 2100 prostate system, and to monitor the resulting heat generation with MR thermometry.

Nicolas Boulant¹, Alexandre Vignaud¹, Eric Giacomini¹, Benoit Larrat¹, Aurelien Massire¹, Alexis Amadon¹, Lynn Uhrig¹, and Michel Bottlaender^1
1Neurospin, CEA, Saclay, Ile de France, France

Measuring small temperature rises (<1 °C) in-vivo using MR thermometry is a challenging task given the required stability of the whole transmission-reception chain as well as the physiological noise spoiling the desired signal. We here report an experiment performed at 7T in-vivo on a baboon’s head where a non-local RF-heat generating system was separate from the MR scanner to provide high stability. Navigator free induction decays were used to correct for the DB0 variations induced by breathing and for the drift of the external field. Combined with the proton resonance frequency shift method, accuracy of ~0.1 °C could be obtained.

Jan Weis¹, Sebastien Murat², Francisco Ortiz-Nieto¹, and Håkan Ahlström^1
1Department of Radiology, Uppsala University Hospital, Uppsala, Sweden, ²The Dive Lab, Sydney, Australia

Temperature of the human brain is subject of change as a consequence of environmental conditions, pathological circumstances, drugs, etc. This study sought to demonstrate that human brain temperature can be down-regulated by breath-holding (apnea), which is a crucial component of neuroprotective reflexes known as the dive response. Brain temperatures of five volunteers were monitored by a phase-difference method. Apnea decreased brain temperature ca 1 °C in ca 70-80 seconds. The outcome of this study opens the possibility of devising new therapies that offer more effective neuroprotection in critically-ill patients (e.g., stroke, cardiac arrest, brain injury).

Joshua de Bever^1,2, Alexis Farrer^2,3, Henrik Odéen^2,4, and Dennis L. Parker^2,5
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 Bioengineering, University of Utah, Utah, United States, ⁴Department of Physics, University of Utah, Utah, United States,⁵Department of Radiology, University of Utah, Utah, United States

A 3D multi-contrast MRI pulse sequence is presented here as a novel method for performing Acoustic Radiation Force Imaging simultaneously with Proton Resonance Frequency thermometry. This could be used, for example, to safely localize the ultrasound focal in three dimensions before an MR guided Focused Ultrasound treatment while simultaneously measuring the induced temperature rise.

Jiming Zhang¹, Pei-Herng Hor¹, and Raja Muthupillai^2
1Physcs and Texas Center for Superconductivity, University of Houston, Houston, TX, United States, ²Diagnostic and Interventional Radiology, St. Luke's Medical Center, Houston, TX, United States

A high-intensity focused ultrasound system was used to cause a highly localized, broad-band mechanical excitation within a tissue mimicking phantom. We describe a frequency domain approach to resolve the resulting tissue displacement at various frequencies. A rheological model (Zener) fit the experimentally determined shear wave velocity dispersion well in the frequency range of 90-200 Hz.

Allison Payne¹, Joshua de Bever², Alexis Farrer³, Dennis Parker⁴, and Douglas Christensen^3
1Radiology, University of Utah, Salt Lake City, UT, United States, ²Computer Science, University of Utah, Utah, United States, ³Bioengineering, University of Utah, Utah, United States, ⁴Radiology, University of Utah, Utah, United States

The theory and validation of an MR-ARFI simulation technique is presented. The theory predicts the displacement due to the given force pattern along the axis of ultrasound beam propagation. Validation of the simulation technique is performed using a 3D spin echo segmented-EPI sequence with unbalanced-bipolar motion encoding gradients in homogeneous phantoms of varying stiffness. The simulations qualitatively match the experimental results for all tested phantoms. This computationally efficient simulation technique can be used to quantify the effects of ARFI for both MRgFUS treatment planning and assessment.

John M Pavlina¹, Tetiana Dadakova¹, Ali Özen¹, and Michael Bock^1
1Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany

In an endorectal high-intensity focused ultrasound (HIFU) treatment system the US transducer is surrounded by water to effectively couple the US energy into the adjacent prostate tissue. To provide temperature feedback during HIFU treatment, a local RF coil for the acquisition of temperature-sensitive MR data is required. This coil is in close proximity to the US transducer and is loaded by the dielectric US coupling medium. To optimize the SNR the embedded coils are often tuned within the magnet bore under tissue loading conditions which is impracticable for clinical applications. The purpose of this study is to determine the effect of the conductivity of the surrounding medium on coil performance to be able to predict the changes of the coil quality factor and the resonance frequency for correction. An RF surface coil in a HIFU system can become tedious to tune in match if the influence of the different loading conditions are not account for. In this work we analyzed the detuning of the coil using a simplified circuit model, which is able to account for the salient features of the coil behavior. This modeling concept allows for simple coil creation even in harsh conditions.

Ryan Alkins^1,2, Alison Burgess¹, Milan Ganguly¹, Giulio Francia¹, Robert Kerbel^1,2, Winfried S Wels³, and Kullervo Hynynen^1,2
1Sunnybrook Research Institute, Toronto, ON, Canada, ²University of Toronto, Toronto, ON, Canada, ³Chemotherapeutisches Forschungsinstitut Georg-Speyer-Haus, Frankfurt, Germany

Systemic treatments for breast cancer have limited success treating brain metastasis due to the blood-brain barrier (BBB). Here, we investigate the effects of repeated delivery of targeted NK-92 cells to brain metastases using MRI-guided focused ultrasound (MRIgFUS). Our data demonstrate that MRIgFUS enhances NK-92 cell translocation across the BBB. Repeated MRIgFUS and NK-92 cell treatments lead to reductions in tumour progression over time, particularly when the treatments are applied early during tumour growth. These data support the continued investigation of MRIgFUS-mediated cell delivery as a potential treatment option for metastatic brain tumours.

Samuel Pichardo^1,2 and Kullervo Hynynen^1
1Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, ²Electrical Engineering, Physics, Lakehead University, Thunder Bay, ON, Canada

This study presents preliminary in vivo results showing the feasibility of using Magnetic Resonance-guided High Intensity Focused Ultrasound (MRgHIFU) to perform ablative and hyperthermia interventions in the neck area. Six (6) experiments were performed for each intervention modality using an acute pig model. For hyperthermia, an automatic algorithm of the energy delivery was compared to an user-controlled approach for a 30-min delivery. The user-controlled approach was more successful to deliver a more controlled treatment. For the lesion experiments, a relatively high power (140W at 1.2 MHz) was required to induce 8-mm lesions in diameter.

Ricky Tong¹, K. Pallav Kolli¹, Chris Diederich², Vasant Salgaonkar², Viola Rieke¹, Eugene Ozhinsky¹, Maythem Saeed¹, Loi Do¹, Steve Hetts¹, and Mark Wilson^1
1Radiology, UCSF, San Francisco, CA, United States, ²Radiation Oncology, UCSF, San Francisco, CA, United States

Catheter-based high intensity ultrasound is a novel technology with the potential for precise thermal treatment delivery under real time imaging guidance. The potential advantages of this technology over other ablative therapies include dynamic 3-dimensional spatial control of energy deposition and greater penetration of delivered energy. In this study, a percutaneous MR compatible high intensity ultrasound catheter was used to ablate swine tissues in both ex-vivo and in-vivo settings. MR thermometry enabled us to monitor temperature changes during ablation. MR images defined the ablation site, which was confirmed with gross specimen and histology as irreversible thermal damage.

Jing Liu¹, Xuedong Yang¹, Rong Rong¹, Ying Zhu¹, Bilgin Keserci², Juan Wei³, Jianhua Zhang⁴, and Xiaoying Wang^1
1Radiology, Peking University, First Hospital, Beijing, Beijing, China, ²Philips Healthcare, Seoul, Korea, ³Philips Research China, Shanghai, China, ⁴Philips (China) Investment Co., Ltd, Beijing, China

Ktrans Maps from Dynamic Contrast Enhanced MRI shows potential in treatment guidance in MR-guided High Intensity Focused Ultrasound Treatment of Uterine Fibroids

Marlijne Elisabeth Ikink¹, Marianne J Voogt¹, Maurice AAJ van den Bosch¹, Robbert J Nijenhuis¹, Bilgin Keserci², Young-sun Kim², Koen L Vincken³, and Lambertus W Bartels^3
1Radiology, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, ²Radiology and Center for Imaging Science, Samsung Medical Center, Seoul, Korea, ³Radiology and Image Sciences Institute, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands

DWI and ADC-mapping have been suggested for evaluation of treatment results after MR-guided high-intensity focused ultrasound (MR-HIFU) ablation of uterine fibroids. In well-perfused tissues, the ADC is known to reflect not only the diffusion of water, but also information about the perfusion in capillaries. The aim of this study was to investigate the optimal combination of b-values on the ADC. It was found that the combination of low b-values (b = 0 and 200 s/mm²) allows the best differentiation between ablated fibroid tissue and untreated tissue immediately after volumetric MR-HIFU ablation of uterine fibroids.

Marlijne Elisabeth Ikink¹, Johanna MM van Breugel¹, Robbert J Nijenhuis¹, Marianne J Voogt¹, Maurice AAJ van den Bosch¹, Koen L Vincken², and Lambertus W Bartels^2
1Radiology, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, ²Radiology and Image Sciences Institute, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands

Diffusion-weighted MRI has been increasingly used to evaluate gynaecological tumors. Using the intravoxel incoherent motion (IVIM) approach, diffusion-weighted sequences can be used to measure both the molecular movement of water molecules and the microcirculation of blood in the capillaries. The diffusion coefficient (D) and perfusion fraction (f) of uterine fibroids were determined in relation with their signal intensity on T2-weighted (T2w) MRI. High-intensity (type 3) uterine fibroids were found to have a higher diffusion coefficient D than fibroids with a lower T2w signal-intensity. We were not able to demonstrate a significant difference in the perfusion fraction (f).

Matthew Bucknor¹, Viola Rieke¹, Loi Do¹, Sharmila Majumdar¹, Thomas Link¹, and Maythem Saeed^1
1University of California, San Francisco, San Francisco, CA, United States

Both experimental and clinical studies of MRgHIFU for focal bone lesions have demonstrated remodeling of bone in the weeks to months following MRgHIFU, in some instances with apparent new bone growth. The purpose of the current study was to clearly delineate patterns of bone remodeling following MRgHIFU in a porcine model, as a function of sonication energy. In our study, all higher energy ablations demonstrated evidence of new bone density along the cortex, with a subtle focus of osseous density at 3 weeks and a larger focus at 6 weeks. New bone density was not seen at lower energy ablations.

Piotr Walczak^1,2, Miroslaw Janowski^1,2, Jeff WM Bulte^1,2, and Monica Pearl^3
1Radiology, Johns Hopkins University, Baltimore, MD, United States, ²Institute for Cell Engineering, Johns Hopkins University, Baltimore, MD, United States, ³Interventional Neuroradiology, Johns Hopkins University, Baltimore, MD, United States

Efficient delivery of therapeutics to the brain parenchyma is highly desired for several disciplines, including regenerative medicine and oncology. Advances in interventional neuroradiology enable safe, super-selective catheterization of small intracranial vessels; however, methods for predicting and optimizing the perfused parenchymal territory remain uninvestigated. We used DSC-enhanced trans-catheter perfusion MRI with Feraheme to predict the perfusion territory prior to intra-arterial (IA) injection of mannitol for blood brain barrier disruption and stem cell delivery. DSC perfusion MRI was highly predictive. This method may aid in improving the efficacy and safety of IA delivery of therapeutics.

Marco Piccirelli¹, Oliver Bozinov², Jan-Karl Burkhardt², Roman Kocian³, Marian C. Neidert², Antonios Valavanis¹, Luca Regli², Athina Pangalu¹, and Jorn Fierstra^2
1Neuroradiology, University Hospital Zurich, Zurich, ZH, Switzerland, ²Neurosurgery, University Hospital Zurich, ZH, Switzerland, ³Anesthesiology, University Hospital Zurich, ZH, Switzerland

Cerebrovascular reserve capacity (CVR) is a useful clinical risk assessment tool for ischemia. Application to brain tumors has a very interesting potential due to the correlation between increased vascularity and tumor malignancy. Further, intraoperative CVR mapping should impact on patient management and guide surgical intervention, by assessing the effectiveness of surgery for brain tumors inducing vascular remodeling. We demonstrate the feasibility of CVR determination with MR during surgical tumor resection on 8 anesthetized patients and illustrate very different vascular responses to surgery. Such spatial information helps to better understand tumor hemodynamics and determine tumor borders.

Eugene G. Kholmovski^1,2, Ravi Ranjan², Sathya Vijayakumar^2,3, Joshua M. Silvernagel², and Nassir F. Marrouche^2
1UCAIR, Department of Radiology, University of Utah, Salt Lake City, Utah, United States, ²CARMA Center, University Of Utah, Salt Lake City, Utah, United States, ³Surgical Services Clinical Program, Intermountain Healthcare, Salt Lake City, Utah, United States

Development of MRI-guided electro-physiology procedures for atrial fibrillation ablations requires robust MRI techniques for intra-procedural evaluation of acute cardiac ablations. LGE-MRI has been used to visualize ablation related tissue changes but it requires contrast infusion limiting repeatability. In this study, we demonstrate that non-contrast T1-weighted technique can be used to visualize acute cardiac RF lesions.

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

Fluorine (¹⁹F) MRI combined with anatomic proton (¹H) MRI provides an effective method for in vivo cell tracking. Recently, 3T intravascular MRI (IVMRI) probes have been shown to provide high-resolution (sub-mm) in vivo imaging capabilities with local signal-to-noise ratios superior to conventional surface coils. Here, for the first time, using a 3T IVMRI probe designed for both ¹H and ¹⁹F MRI, we show high-resolution (in-plane: 0.2mm ¹H, 0.8mm¹⁹F) localization of perfluorooctyl bromide (PFOB) microcapsules in a porcine heart ex vivo. Localization is confirmed by CT imaging of the radio-opaque microcapsules.

Robert Xu^1,2, Prashant Athavale³, Adrian Nachman^4,5, and Graham Wright^1,2
1Dept. of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, ²Schulich Heart Research Program and Physical Science Platform, Sunnybrook Research Institute, Toronto, Ontario, Canada, ³Dept. of Mathematics, University of Toronto, Ontario, Canada, ⁴Edward S. Rogers Sr. Dept. of Electrical and Computer Engineering, University of Toronto, Ontario, Canada, ⁵Institute of Biomaterials and Biomedical Engineering, University of Toronto, Ontario, Canada

Traditional cardiovascular interventions are carried out under X-ray fluoroscopy guidance. However, due to the inherent lack of soft tissue contrast, it is often difficult to visualize the surrounding anatomical structures during the interventions. Alternatively, MR-guided interventions have been proposed in recent years to address this visualization problem via the use of realtime imaging or high-resolution prior roadmaps. Unfortunately, tradeoffs also exist for both of these approaches. Therefore, we propose to incorporate the advantages from both imaging acquisitions through alignment of the high-resolution prior roadmap to the dynamic realtime images via a novel multiscale registration framework.

Erin Girard¹, Tanja Kurzendorfer¹, Kevin Gralewski², Norbert Strobel³, and Yoav Dori^2
1Corporate Technology, Imaging and Computer Vision, Siemens Corporation, Princeton, New Jersey, United States, ²Cardiology, The Childrens Hospital of Philadelphia, PA, United States, ³Imaging and Therapy Division, Siemens AG, Healthcare Sector, Germany

Fusion of 2D x-ray images and 3D MRI datasets (XMRF) brings the MRI into the cath lab for online navigation and guidance during catheterization procedures. We present a new biplane method for XMRF using a prototype system and describe the accuracy of the resulting 2D roadmap (overlay) when rendered from an underlying, registered 3D MRI. We describe various visualization methods and demonstrate the clinical utility for complex congenital heart disease procedures.

Xiaoliang Zhang^1,2, Alastair Martin¹, Prasheel Lillaney¹, Aaron Losey¹, Yong Pang¹, Daniel Cooke¹, and Steven Hetts^1
1Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, ²UC Berkeley/UCSF Joint Bioengineering Program, San Francisco, CA, United States

It is technically challenging to design compact and sensitive, yet low SAR catheter RF coils for endovascular MR imaging. In this work, we investigate a catheter coil design technique based on transmission line resonator. The catheter coil is designed and constructed for vascular imaging at 1.5T. The imaging comparison between catheter coil and body coil demonstrate that the catheter coil has a significant SNR gain over the use of body coil at 1.5T.

Ouri Cohen¹ and Jerome L. Ackerman^1
1Department of Radiology, MGH/Athinoula A. Martinos Center for Biomedical Imaging, Massachussets General Hospital, Charlestown, MA, United States

Current treatment methods for intracranial aneurysms include surgical clipping or endovascular embolization with coils, particles or a coagulable material such as Onyx. These methods require either significant surgery or the introduction of foreign bodies into the patient and the risk of an immune reaction. Previous research has successfully shown the coagulation of tissue using radio frequency (RF) energy harvested from the MR scanner. We present an aneurysm treatment method proof-of-concept that consists of coagulation of Human Serum Albumin, a naturally occurring protein in the blood, using MR RF ablation.

Shashank Sathyanarayana Hegde¹, Yi Zhang^1,2, and Paul A Bottomley^2,3
1Radiology, Johns Hopkins University, Baltimore, Maryland, United States, ²Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland, United States, ³Radiology, Johns Hopkins University, Maryland, United States

High-resolution intravascular (IV) MRI is susceptible to degradation from physiological motion, and requires high frame-rates for true endoscopy. Traditional cardiac gating techniques are inefficient in scan-time usage and reduce the effective frame rate. Here, sparse ungated radial sampling is combined with motion correction using frame-by-frame projection shifting based on a singularity at the probe’s location, to provide reduced motion sensitivity with up to a four-fold effective increase in image acquisition speed. We demonstrate free-breathing ~200µm resolution in vivo intravascular MRI in rabbit aorta.

Maryam Etezadi-Amoli¹, Pascal Stang¹, Adam Kerr¹, John Pauly¹, and Greig Scott^1
1Electrical Engineering, Stanford University, Stanford, CA, United States

Previous work has demonstrated the feasibility of using a toroidal transceive coil at 1.5T for visualizing conductive interventional devices, such as guidewires and EP ablation catheters. Here we investigate some of the practical challenges of using this approach, such as its compatibility with projection imaging, behavior with longer device insertion lengths, and the effect on image quality when the interventionist touches the device. We also demonstrate the extendibility to higher field strengths and a non-phantom setting by acquiring images at 3T of an EP ablation catheter inserted in the esophagus of a pig cadaver.

William Dominguez-Viqueira¹, Chris Dey², Hirad Karimi^1,3, Jennifer Barry¹, and Charles H Cunningham^1,3
1Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada, ²Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada, ³Medical Biophysics, University of Toronto, Toronto, Ontario, Canada

Recently a novel susceptibility-based tracking device which can be mechanically turned ON and OFF was demonstrated for MR guided interventions. For this work, a new two-layer tracking element was designed, integrated into a 6F catheter with a lumen and demonstrated in-vivo. A novel tracking method was demonstrated in which the graphite layer was periodically moved every TR, creating a ghost of the catheter tip at precisely FOV/2 from the true location in projection images. In future work, an automated actuator will be designed and constructed to permit toggling of the device during rapid, short-TR projection images, enabling quick snap-to-slice functionality.

Nadège Corbin¹, Elodie Breton¹, Quentin Boehler¹, Laurent Barbé¹, Pierre Renaud¹, Michel de Mathelin¹, and Jonathan Vappou^1
1ICube, Université de Strasbourg, CNRS, Strasbourg, France

An all-in-one interventional Magnetic Resonance Elastography (MRE) system is developed in order to provide supplementary contrast based on biomechanical properties. Shear waves are generated inside the tissue with a piezoelectric needle driver. Induced waves are visualized in phase images acquired with an interactive real-time spoiled gradient echo sequence including motion sensitizing gradients with fractional encoding. An online inverse problem solver based on the local frequency estimation algorithm computes the elastogram in real-time. The complete interventional MRE system is successfully tested on a heterogeneous gelatin phantom with a total acquisition time of 2.15s per elastogram.

Labonny Biswas¹, Akram Kassay^1,2, Perry Radau¹, Kevan Anderson¹, and Graham Wright^1
1Sunnybrook Research Institute, Toronto, ON, Canada, ²University of Waterloo, ON, Canada

The use of the Leap Motion device and software for interventional MRI guidance through integration with visualization software has been investigated. Noise effects of the device were tested in the scanner room finding negligible decrease in SNR. Usability of gestures to control an imaging plane was evaluated in software, demonstrating ease of use in navigation of planes to targets. A feasibility test in the scanner allowed gesture-based control of real-time imaging planes by the operator in the scanner room.

Frank Zijlstra¹, Bo S. van Leeuwen², and Peter R. Seevinck^1
1Image Sciences Institute, UMC Utrecht, Utrecht, Netherlands, ²Dept. of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands

We propose a method for fast MRI needle tracking using Compressed Sensing, view-sharing and co-RASOR reconstruction of a 2D radial UTE acquisition. The method reconstructs positive contrast at the location of the needle at a high temporal resolution, as well an anatomical background image at a lower temporal resolution, but with increased spatial resolution. Results in a phantom show good needle contrast at 4x acceleration, resulting in about 4 frames per second for the needle image and about 1 frame per second for the background image.

Loïc Cuvillon¹, Elodie Breton¹, Jean-Baptiste Schell¹, Jean-Baptiste Kammerer¹, Daniel Gounot¹, Luc Hébrard¹, and Michel de Mathelin^1
1ICube, Strasbourg University - CNRS, Strasbourg, France

A 3D Hall sensor integrated circuit and its localization algorithm were designed for gradient-based localization of interventional instruments during MR-guided procedure. Dedicated bipolar gradients and synchronization signal were implemented in a multi-slice real-time interactive spoiled gradient echo sequence. The localization algorithm is based on a linear model of the gradient coil fields identified during a calibration procedure. Based on the calculated pose, two orthogonal slices are aligned in real-time on the main axis of the device. A position accuracy of 2 mm is achieved and free-hand motion is monitored. This integrated circuit 3D probe could be integrated inside surgical instruments.

Markus Neumann¹, Elodie Breton¹, Loic Cuvillon¹, and Michel de Mathelin^1
1ICube, Université de Strasbourg, Strasbourg, France

MR-guided percutaneous interventions require accurate scan plane positioning. A multi-modal tracking workflow is developed combining an MR-image based (passive marker) detection with an RGB-D sensor (active) approach for automatic scan-plane alignment in real-time. This work aims at combining the high frame rate of the RGB-D sensor with the precision of MR-image based tracking through dynamic data fusion using an Information filter. That workflow does not require an explicit registration step and is robust against missing data (e.g. marker detection failure in one modality). Promising experimental tracking results are obtained with free-hand motion.

Maryam Etezadi-Amoli¹, Christopher Ellenor¹, Pascal Stang¹, Adam Kerr¹, John Pauly¹, and Greig Scott^1
1Electrical Engineering, Stanford University, Stanford, CA, United States

We present a novel monopole-drive mechanism to allow RF ablations to be performed at the proton resonance frequency, without the need for a ground pad. The monopole driver consists of a high-Q shielded LC tank circuit that can be interfaced with classic RF ablation probes and also allows the probe to be used as a transmit-receive coil in the MRI scanner. Imaging results show successful probe visualization using power levels as low as 0.4W, and phantom heating tests indicate that temperatures exceeding 60^oC can be achieved in less than six minutes with 100W drive power.

Vincent O. Boer¹, Tijl van der Velden¹, Max Kohler², Chrit Moonen¹, Dennis W.J. Klomp¹, and Clemens Bos^1
1UMC Utrecht, Utrecht, Utrecht, Netherlands, ²Philips Medical Systems, Vantaa, Finland

Magnetic field drift compromises proton resonance frequency shift MR thermometry by adding a phase term over time which is misinterpreted as temperature change. For hyperthermia procedures, stable MR thermometry is needed over 10 minutes or more. Here, a field probe was used to independently measure field drift and compensate temperature mapping. In the upper legs of a volunteer, drift effects were reduced from 5.4°C to within well within 1°C over a 16 minute scan with full gradient system use. Results were comparable or better than compensation using the phase evolution in a user defined region of interest.

Yuval Zur¹, Benny Assif², Alex Volovick², and William Grissom^3
1GE Healthcare, Tirat Carmel, Israel, ²Insightec Ltd., Tirat Carmel, Israel, ³Biomedical Engineering, Vanderbilt University, Nashville, Tennesee, United States

The thermometry sequence used for Focused Ultrasound (MRgFUS) is multi slice gradient echo. Long TE gives higher temperature accuracy. To lengthen TE and reduce noise a low receiver bandwidth is used. However, lower bandwidth increases spatial shifts due to B0 inhomogeneity. For brain applications accuracy is mandatory so low bandwidth is not allowed. To overcome this we use a multi echo GRE sequence where N > 1 echoes are acquired in each TR. For each echo the bandwidth is high and therefore spatial shifts are low. The temperature signal to noise ratio (TSNR) is preserved by combining signals from all the echoes into a unified temperature image. Compared to the standard GRE sequence, the new sequence provides similar or higher TSNR with a 5 – 8 fold reduction in spatial shifts.

Tetiana Dadakova¹, Jan Gerrit Korvink^2,3, John Matt Pavlina¹, and Michael Bock^1
1Medical Physics, Department of Diagnostic Radiology, University Medical Center Freiburg, Freiburg, Germany, ²Department of Microsystems Engineering—IMTEK, University of Freiburg, Freiburg, Germany, ³Freiburg Institute of Advanced Studies—FRIAS, University of Freiburg, Freiburg, Germany

MR thermometry is an important tool to monitor efficiency and safety of different thermal treatment methods. Two temperature-sensitive MR parameters are used for temperature calculations: the proton resonance frequency shift (PRF) and the longitudinal relaxation time change (T1). A combination of these two methods might allow for a more precise temperature monitoring for example in fat where PRF techniques alone fail. In this work, simulations and analytical calculations for the optimal flip angle for combined PRF and T1 MR thermometry are presented.

Christopher MacLellan^1,2, David Fuentes^1,2, Florian Maier¹, Wolfgang Stefan¹, John D. Hazle^1,2, and R. Jason Stafford^1,2
1Department of Imaging Physics, University of Texas MD Anderson Cancer Center, Houston, Texas, United States, ²Medical Physics Program, University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas, United States

Monitoring thermal ablation procedures using multi-parametric MRI is primarily limited by post-processing time. Parallel GPU and CPU architectures were implemented to evaluate the feasibility of real time monitoring using a Prony algorithm and an iterative Steiglitz-McBride algorithm. Computation time decreased by roughly one order of magnitude for parallel CPU and two orders of magnitude for GPU. Both architectures finish processing in the time required to obtain one image. The Steiglitz-McBride algorithm showed greater accuracy at low SNR and should be implemented on GPU in the future.

Manivannan Jayapalan^1
1MR Software and Applications, GE Healthcare, Bangalore, Karnataka, India

Thermal monitoring in Magnetic Resonance guided Focused Ultrasound (MRgFUS) treatments is a crucial step where the phase images from MR images are used to get thermal maps. One of the widely used techniques is PRF shift technique that involves some form of image subtraction using a baseline pre-treatment image. Subject motion and tissue deformation due to coagulation can severely distort these techniques. Self-referenced methods [1] help to overcome this hurdle where the baseline phase in the region-of-interest (ROI) is estimated using the data available outside the hot zone (ROI) and subtracted with actual phase to get the thermal maps. In this work a new technique is described, where the baseline phase inside the ROI is estimated using the data acquired from two echos and their phase difference outside ROI. This method not only eliminates the need for baseline subtraction but also produces better results as the reference echo used in generating the model is acquired along same location

Seena Dehkharghani¹, Li Wei², Hui Mao¹, John N Oshinski¹, and Deqiang Qiu^1
1Radiology and Imaging Sciences, Emory University, Atlanta, GA, United States, ²Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, United States

The validity of single-voxel proton MRS techniques has been established for MR thermometry at discrete spatial positions. Multivoxel techniques may however permit the collection of spatial temperature gradients non-invasively, but have not been thoroughly evaluated for this purpose. We propose to compare standard 2D-multivoxel PRESS to single-voxel techniques in a phantom study of MR thermometry. As our preliminary experience has suggested vulnerabilities to chemical shift misregistration and limited MRS quality at excitation margins with standard multivoxel techniques, we further propose comparison with a more recently introduced semiLASER-localized CSI, offering theoretical benefits over 2D CSI in this phantom study.

Fulvio Zaccagna¹, Michele Anzidei¹, Fabrizio Boni¹, Luca Bertaccini¹, Alessandro Napoli¹, and Carlo Catalano^1
1Department of Radiological, Oncological and Pathological Sciences, University of Rome – Sapienza, Rome, Rome, Italy

Osteoid osteoma is a painful albeit benign bone lesion that usually affects younger subjects between 10 and 20 years of age. The most frequent symptom is localized bone pain that flares up nocturnally. Prompt relief is usually achieved with nonsteroidal anti-inflammatory drugs (NSAIDs). Once diagnosis has been established, conventional therapy options include surgery, pharmacological and/or percutaneous treatment. Minimally invasive therapies are increasingly the primary option at many centers. At present, radiofrequency (RF) ablation is the most popular of the various percutaneous techniques, with the percentage of patients reporting complete clinical success ranging between 85 and 98% at one year. Magnetic Resonance guided Focused Ultrasound (MRgFUS) is a non-invasive ablation modality that, due to the high acoustic energy absorption of cortical bone, may produce thermal damage to periosteal structures including nerves (i.e. periosteal neurolysis) and can potentially penetrate into the medullary bone, leading to coagulative necrosis of sub-cortical lesions. Our purpose was to investigate feasibility, safety, and clinical efficacy of MRgFUS in the treatment of painful osteoid osteoma.