Sherif Nour, Kareem Elfatairy, Debra Weber, Melinda Lewis, Viraj Master

Interventional MRI technology has been used to guide and monitor renal ablation procedures because of its ability to provide online feedback on ablation progress and determine treatment endpoints based of individual tumor responses. The field of Interventional MRI lacks the abundance of outcome data that provide the evidence for the added value of using MRI technology to guide interventions. We report the long-term efficacy data for interactive guidance and real-time monitoring of 46 renal ablation procedures performed entirely within an interventional MRI suite using a short introducing needle and a flexible laser fiber. 
 

Tobias Theis, Nicolas Behl, Erik Cressman, Armin Nagel, Sebastian Flassbeck, Aaron Kujawa, Peter Bachert, Mark Ladd, Florian Maier

Thermochemical ablation (TCA), a novel minimally invasive ablation therapy, was quantitatively evaluated using ²³Na MRI at 7T. In this study, eight TCA injection experiments were performed using eight ex vivo bovine liver phantoms. Normalization on the reference tubes and B₁-correction of the ²³Na images were performed to get quantitative values. This improved the maximum relative error of the estimated amount of substance by a factor of 3.6. The total injected amount was accurately determined. This study shows that quantitative ²³Na MRI provides detailed information about TCA injections, which is important for computational modelling of the method and cell damage prediction.

Junichi Tokuda, Kemal Tuncali, Ravi Seethamraju , Clare Tempany, Ehud Schmidt

We propose a new technique to delineate the area below the critical temperature in the frozen tissue during cryoablation using STIR UTE MRI. It relies on the temperature-dependency of the T1 in the frozen tissue. We demonstrated the technique in an ex vivo swine kidney sample using a 3T MRI scanner with a STIR PETRA sequence. To create a uniform temperature gradient, the sample was placed between dry-ice and warm bath, while UTE and STIR UTE images were being acquired. The STIR UTE image demonstrated hyper-intensity in the frozen area, relative to hypo-intensity in the UTE image.

Cyril Ferrer, Lambertus Bartels, Tijl van der Velden, Charles Mougenot, Chrit Moonen, Clemens Bos

During long hyperthermia procedures guided by MR thermometry, drift of the main magnetic field leads to systematic errors in PRFS measurements, compromising the required temperature monitoring. In this study we evaluated if interleaving acquisition of PRFS MRT with non-selective FID readouts using conventional receive coil elements allows for correcting the drift effects in PRFS thermometry. Automated field drift correction using interleaved non-selective FIDs allowed maintaining a precision and accuracy better than 1°C. This temperature precision would typically be required for controlling a hyperthermia procedure.

Ming Zhao , Ouri Cohen, Erez Nevo, R.Gilberto Gonzalez, Jerome Ackerman

As part of a project to develop MR-induced RF heating of a coagulable biomaterial for minimally invasive repair of vascular lesions, we investigate the relationship between the heat coagulation behavior and MR relaxation properties of egg white. This protein solution is a good model for the analogous behavior of human serum albumin solution, an optimal (but expensive) biomaterial for MR coagulation. We find that large changes in both T₂ and the width of the magnetization transfer spectrum clearly indicate the temperature at which the coagulation process occurs. T₂ and MT weighted MR images identify coagulated material in an aneurysm phantom. 

G. Salim, P. Baron, D.H.J. Poot, J.A. Hernandez Tamames, T. Drizdal, M.M. Paulides, S. Klein, G. Salim

In this work we illustrate the effect of changes in the transceive phase on the quality of MR thermometry in acqueous medium.  

Bryant Svedin, Allison Payne, Dennis Parker

A multi-echo pseudo-golden angle stack of stars sequence for use in free-breathing interventional procedures is evaluated in vivo with 5 healthy volunteers for use in MR thermometry in the breast. High spatial and temporal resolution (1.3 mm³, 1.43 s) is achieved through k-space filtering. PRF temperature, T2*, ρ (signal magnitude 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 library greatly improves temperature standard deviation compared to a single baseline reference.

Christopher MacLellan, David Fuentes, Sujit Prabhu, Ganesh Rao, Jeffrey Weinberg, John Hazle, R. Jason Stafford

Real-time damage estimates provided by Magnetic Resonance Temperature Imaging (MRTI) and appropriate thermal dose models can provide crucial feedback during of thermal ablation procedures. However, these models are not tailored to the post-treatment radiological endpoints that are used to verify the extent of the thermal lesion after therapy. A technique is developed to allow estimation of thermal dose model parameters through retrospective analysis of MRTI and post-treatment imaging. The feasibility of this technique is investigated in a protein coagulation phantom and clinical ablation data. 

Rebecca Weires, Will Grissom

Partial Fourier temperature mapping using the k-space hybrid algorithm is shown to be more accurate than conventional partial Fourier reconstruction, and the use of partial Fourier acquisition patterns improves the performance of the k-space hybrid algorithm. Undersampled partial Fourier acquisition with k-space hybrid reconstruction can be used to achieve highly accelerated, artifact-free temperature mapping with a robust Cartesian acquisition. Reconstruction is parallelized in the slice dimension and frequency-encoded dimension to achieve real-time volumetric EPI temperature mapping, without parallel imaging.

Jiachen Zhuo, Steven Roys, John Hebel, Erma Owens, Prashant Raghavan, Dheeraj Gandhi, Rao Gullapalli

The ventral intermediate nucleus (VIM) of the thalamus is a highly effective target for treatment of essential tremor (ET). Visualization of VIM is however challenging due to the lack of T1 or T2 MRI contrast between the various thalamic nuclei. In this study, we used synthesized MPRAGE images with varied inversion time (TI) (SynTI images) to visualize the VIM for pre-surgical planning in MRgFUS treatment of ET. Verification based on 24hr post-treatment lesion location on four patients showed good agreement from the identified VIM with lesion center. 

William Chu, Robert Staruch, Samuel Pichardo, Yuexi Huang, Merrylee McGuffin, Ruby Endre, Gregory Czarnota, Kullervo Hynynen

We present the updated results of our phase I trial that delivers mild hyperthermia using magnetic resonance-guided high intensity focused ultrasound (MR-HIFU) combined with radiation and chemotherapy in the treatment of locally recurrent rectal cancer. Participation in the study is based on careful consideration of patient and tumor factors. MR-HIFU mild hyperthermia was delivered in three sessions during a 17-day regimen. MR-HIFU mild hyperthermia was successfully delivered and the procedure was well tolerated. No adverse effects have been reported following the combined treatment to date.

Sara Johnson, Bryant Svedin, Allison Payne

MR-guided focused ultrasound (MRgFUS) ablation treatments can be improved with more accurate and faster treatment planning. In this study, a fast, automatic tracking coil system is employed to predict the ultrasound transducer focus for treatment planning purposes. The accuracy of the geometric focus predictions was assessed in vivo with a breast-specific MRgFUS device. This study reports a targeting accuracy of 3.1 ± 1.4mm, measured as the average Euclidean distance between the volumetric center of mass of thermal sonications and their predicted focal locations.

Eugene Ozhinsky, Vasant Salgaonkar, Chris Diederich, Viola Rieke

We have implemented a real-time MR thermometry-guided system for ultrasound hyperthermia delivery within user-defined regions and validated it in phantom experiments. It was based on the commercial ExAblate prostate transducer, RTHawk real-time MRI system and featured accelerated PRFS MR thermometry and automated steering of the ultrasound focus to ensure uniform heating of the entire region of treatment.

Yiyi Ji, Alexander Dunn, Michal Pham, Werner Hoffmann, Min-Chi Ku, Helmar Waiczies, Sonia Waiczies, Cyrille Boyer, May Lim, Thoralf Niendorf, Lukas Winter

Utilizing the RF pulses of the MR system for MR imaging, controlled RF heating and temperature monitoring with MRTh in an integrated system is appealing for MR guided thermal interventions. In this work, we demonstrate for the first time the applicability of our integrated system for targeted drug delivery using a pH- and thermoresponsive polymer. Upon RF heating to T>LCST, the polymers released 50% of its load in 30min, and 89% in 120min. Temperature monitoring with MRTh and external fiber optic temperature sensors were well correlated, with a deviation of 0.2-0.9°C. 

Solenn Toupin, Valéry Ozenne, Pierre Bour, Rainer Schneider, Matthieu Lepetit-Coiffé, Baudouin Denis de Senneville, Erik Dumont, Pierre Jaïs, Bruno Quesson

Cardiac MR thermometry provides a real-time monitoring of temperature distribution in myocardium during catheter-based radiofrequency ablation. One major challenge of this technique is the compensation of motion induced by the heart contraction and respiration. In this study, we propose to perform fast multi-slice proton resonance frequency (PRF) shift MR thermometry combined with a real-time slice following technique, based on active catheter tracking. Performance of this approach was evaluated in vitro on a moving agar gel phantom.

Yiyi Ji, Werner Hoffmann, Michal Pham, Celal Oezerdem, Helmar Waiczies, Thoralf Niendorf, Lukas Winter

An integrated RF heating system utilizes the MR spin excitation frequency together with dedicated RF antennas for controlled RF heating and MR imaging in an integrated system. Operating the MR power amplifier for both RF heating and MR imaging applications simultaneously requires customized transmit/receive (Tx/Rx) switches that can handle both high peak powers and high average powers. In this work we designed, built and evaluated a high power Tx/Rx switch for handle MRI and RF heating requirements.

Waltraud Buchenberg, Florian Wassermann, Martin Bruschewski, Sven Grundmann, Axel Krafft, Jürgen Hennig, Bernd Jung

MR thermometry (MRT) and MR velocimetry (MRV) allow to non-invasively measure temperature and velocity fields.  Therefore, they are well-suited to address medical questions; however, they can also be a valuable tool to study fluid flow and heat transfer phenomena in technical devices. Here, PRF temperature and velocity measurements were performed in a complex flow setup: a pin fin array consisting of multiple copper tubes which is frequently used in industrial processes for cooling purposes. MRV and MRT are excellent techniques to gain new insights into fundamental heat transfer phenomena and they greatly extend conventional tools for temperature and velocity measurements.

Jinchao Wu, Xing Wei, Jiafei Yang, Bingyao Chen, Zijing Dong, Shuo Chen, Kui Ying

A Bio-Heat Transfer (BHT) model enhanced PRF method was introduced to improve the temporal resolution and to recover the lost signal caused by the susceptibility of probe in microwave ablation. Simulation results of MR-guided microwave ablation performed in an agar phantom show that the proposed method can recover the temperature map with the largest error less than 2°C and increase the temporal resolution to 1s or 0.5s with adequate computing capacity.

Yuexi Huang, Ben Lucht, Rohan Ramdoyal, Samuel Guneseelan, Tyler Portelli, Ping Wu, Kullervo Hynynen

A flat focused ultrasound array of 13 cm in diameter with 4096 elements was manufactured in house with center-to-center element spacing of half-wavelength at the centre frequency of approximately 500 kHz. The design allows for a much wider steering range. Feasibility for thermal ablation and hyperthermia over large target volumes was demonstrated in animal studies.

Etsuko Kumamoto, Daisuke Kokuryo, Kagayaki Kuroda

MRgHIFU treatment for liver requires a tracking technique to “lock on” to the focal spot at the target tissue region during respiratory-induced motion for targeting and temperature imaging. Here, we proposed a target tracking technique using template matching methods. A pre-operative, multi-slice sagittal image series under natural slow breathing was acquired, and a database, including a three-dimensional translation and deformation behavior of the liver and the target, was constructed. Intra-operative target tracking was performed by acquiring a single sagittal slice. The experimental results were demonstrated the feasibility of the three-dimensional target tracking technique using a template matching methods.

Matthew Tarasek, Benny Assif, Eyal Zadicario, Desmond Yeo

Transcranial magnetic resonance (MR)-guided focused ultrasound (tcMRgFUS) has gained prominence as a technology for treating several brain pathologies. A typical FUS applicator has a large water bolus in direct contact with the patient’s head to provide (i) acoustic coupling to the patient, and (ii) a means to remove heat generated from acoustic absorption in the skull. These water bolus structures can lead to significant image artefacts. Here we use electromagnetic simulations to assess water bolus compartment designs that have different electrical properties. The goal is to downselect a design that produces improved B1+ homogeneity and SNR in a region of interest.

Cheng-Tao Ho, Chen-Hua Wu, Shih-Tsung Kang, Wen-Shiang Chen, Po-Hung Hsu, Hao-Li Liu, Chih-Kuang Yeh, Hsu-Hsia Peng

We aim to real-time monitor the signal intensity (SI) change of microbubbles in the presence of stable cavitation (SC) effect in a flowing phantom to comprehend the combining effects of SC and flow. Distinct reduced SI was observed, particularly in the focused ultrasound (FUS) focus and downstream regions, during transmitting FUS pulses. More substantial SI changes can be observed with increase of acoustic pressure. In this study, we verified the feasibility of using HASTE sequence to real-time monitor SI changes at the presence of SC effect of MBs in a flowing phantom.

Michal Pham, Yiyi Ji, Hendrik Paysen, Eva Oberacker, Till Huelnhagen, Thoralf Niendorf, Lukas Winter

Proton resonance frequency (PRF) shift temperature mapping is influenced by B0 field drift, temperature dependent electromagnetic property changes that alter phase velocity, alpha calibration and temperature dependent magnetic susceptibility changes. This work details PRF thermometry at 7.0T of a thermal MR setup. In a homogeneous agarose phantom PRF reading accuracy is within the accuracy of fiber optic sensor readings (0.29±0.21)°C. Temperature dependent magnetic susceptibility changes in pure fat lead to significant temperature reading errors. However, for more realistic thermal MR applications in the human brain (ΔT<10°C, volume fat fractions <10-20%), temperature reading accuracy is comparable to water-based samples.

Christiaan Overduin, Joyce Bomers, Michiel Sedelaar, Sjoerd Jenniskens, Jurgen Fütterer

We present a feasible and safe approach to perform transperineal MRI-guided focal cryoablation in patients with recurrent PCa after radiotherapy, with encouraging initial results.

H Michael Gach, Roger Nana, Clifford Robinson, Philip Cuculich, Rojano Kashani, Jeffrey Bradley, Michael Roach, James Dempsey, Sasa Mutic, Olga Green

Integrated MRI-guided radiotherapy (MRIgRT) systems perform simultaneous MRI acquisitions during radiation therapy to optimize the accuracy of dose delivery. Cardiac radiosurgery using stereotactic body radiation therapy (SBRT) is a promising new treatment option for cardiac arrhythmias. We imaged the heart with a novel ungated radial TrueFISP sequence on a 0.35 T MRIgRT system. The sequence is being developed for next generation SBRT. Image artifacts associated with the sequence were measured using a Medtronic implantable cardiac defibrillator (ICD) in hydrogel and extended 13 cm from its center. Thus, artifacts should not preclude MRIgRT for most patients with ICDs.

Jan Fritz, Wesley Gilson, Christoph Forman, Esther Ratihel, Mathias Nittka, Allan Belzberg

Interventional MR imaging at 3 Tesla benefits from high signal and affords visualization and subsequent targeting of submillimeter structures, but needle artifacts may be exaggerated. Optimized fast gradient echo- and turbo spin echo-based pulse sequences minimize in-plane signal displacement, but through-plane artifacts remain. Compressed Sensing Slice-Encoding Metal Artifact Correction (SEMAC) MRI has the ability to minimize through-plane displacement, and thus holds promise to improve the accuracy of device localization. We demonstrate the clinical feasibility of Compressed Sensing SEMAC TSE for interventional MR imaging at 3 Tesla and visualization of the needle artifact with high accuracy.

Martin Brady, Raghu Raghavan, Andrew Alexander, Walter Block

The hetergeneity of the brain makes designing a desired end drug distribution through pressurized catheters difficult.  We present a method to utilize real-time MR monitoring of a co-infused Gd tracer during initial stages of the infusion to derive a real-time 3D estimate of the velocity front. We also describe a new algorithm that uses the velocity front to provide surgical feedback on the likely final infusion distribution.

Samantha Mikaiel, Thomas Martin, Kyunghyun Sung, Holden Wu

Real-time visualization is crucial to the success of MRI-guided minimally invasive cancer interventions. We have developed golden-angle (GA) ordered radial integrated-SSFP (iSSFP), which can suppress banding artifacts associated with bSSFP while maintaining similar T₂/T₁ contrast. In this work, we further analyze the tissue contrast as well as passive visualization of interventional needles using GA radial iSSFP. In volunteer scans, we verify that GA radial iSSFP achieves T₂/T₁ tissue contrast similar to bSSFP while suppressing banding artifacts. With phantom scans we show that iSSFP reduced the size of the needle-induced signal void, versus that seen on bSSFP. These advantages of GA Radial iSSFP show its potential for improving real-time MRI-guided interventions.

Xinzhou Li, Samantha Mikaiel, James Simonelli, Yu-Hsiu Lee, Tsu-Chin Tsao, Holden H. Wu

MRI is capable of providing flexible soft tissue contrast and real-time guidance of interventions. Real-time information about the motion of tissues and devices is essential to provide feedback for physician and robotic control of MRI-guided interventions. In this work, a new motion prediction algorithm using MRI-based motion tracking and multi-rate Kalman filtering is proposed to provide accurate and real-time motion information. Experiments and simulations show that Kalman filtering with expectation maximization training and multi-rate data fusion is able to achieve low motion prediction error. This new algorithm has potential in providing real-time feedback information for MRI-guided interventions.

Alastair Martin, Philip Starr, Jill Ostrem, Paul Larson

MR guidance is increasingly being used to implant DBS electrodes.  The technique is extremely accurate and permits patients to be under general anesthesia during the procedure.  The incidence of complications during these procedures, however, has not been established.  We report on the incidence of hemorrhagic events during 231 surgical procedures (374 electrodes implanted).  The ability to detect hemorrhage intra-operatively is demonstrated and factors contributing to hemorrhage incidence are identified.  Total hemorrhage rates and symptomatic hemorrhage rates were found to be 2.4%/electrode implanted and 1.1%/electrode implanted respectively, which is comparable to conventional surgical approaches for DBS implantation.

Kareem Elfatairy, Christopher Filson, Omer Kucuk, Peter Rossi, Viraj Master, Sherif Nour

The use of multiparametric MRI for prostate cancer screening is challenged by the potential missing of clinically significant cancer in areas with no visible abnormalities. We randomly biopsied areas with no visible targets under direct MRI guidance. Out of 43 biopsied areas, negative predictive value for clinically significant cancers was 90.7% suggesting a very low potential for harboring clinically significant cancers and supporting the use of mpMRI in cancer screening and active surveillance. An extended biopsy approach including sampling of areas without visible MRI abnormalities may still need to be considered prior to focal therapy.

Sverre Langørgen, Brage Krüger-Stokke, Øystein Størkersen, May-Britt Tessem, Helena Bertilsson, Tone Bathen, Kirsten Selnæs

A retrospecive review of 34 patients who had been to former TRUS guided prostate biopsies, where there was a discrepancy between MRI reported tumor suspicious findings and histology. They were re-biopsied with MRGB. We could verify cancer in 14 of 24 patients with former negative or benign histology. We also upgraded 7 out of 10 patients from low-grade to intermidiate or high-grade cancer. In addition to finding former unknown cancers, we also found that the urologists settled with benign diagnoses from MRGB. They then decided to end investigations in these patients.

Matthew Restivo, Michael Hansen, Hui Xue, Adrienne Campbell-Washburn

 

Spiral imaging is appealing for MRI-guided interventions due to the need for high frame rate dynamic imaging and low RF power sequences to reduce RF-induced heating in metallic guidewires. Unfortunately, spiral images are susceptible to image distortions due to off-resonance which must be corrected. In this work, we implement a real-time interactive spiral sequence and a fast reconstruction in the Gadgetron that performs inline off-resonance correction that adapts to slice position and orientation changes. We show the effectiveness of our correction in both phantom and in-vivo volunteer images with reconstruction times that are approaching real-time.

 

Subashini Srinivasan, Amanda Wheeler, Brian Hargreaves, Bruce Daniel

Microsoft HoloLens provides the ability to visualize 3D holograms of preoperative MRI in addition to the physical environment. In this work we have developed a HoloLens application that aligns these preoperative holograms to the patient. The accuracy of perceiving these holograms was evaluated by presenting different shapes of holograms in random locations and comparing their positions to ground truth. The current set-up enables visualization and perception of holograms with a margin tolerance of < 6 mm.

Sébastien Roujol, Radhouene Neji, Henry Chubb, John Silberbauer, Tom Lloyd, Thomas Pohl, Rainer Schneider, Nick Kampa, James Harrison, Steven Williams, Rahul Mukherjee, Louisa O'Neill, John Whitaker, Matthew Wright, Tobias Schaeffter, Mark O'Neill, Reza Razavi

MRI shows promise for the guidance of electrophysiology (EP) procedures. MR-guided EP procedures require reliable catheter tracking capabilities. Passive catheter tracking enable positive or negative contrast visualization of the catheter in the MR-images using for example integrated ferromagnetic/paramagnetic materials or contrast agent. Positive contrast visualization remains challenging and often sensitive to imaging/post-processing parameters. Negative contrast techniques remain associated with confounding factors (i.e. any other signal void) which complicate visual catheter tracking. In this study, we sought to develop and evaluate a novel framework for passive catheter tracking with negative contrast combined with automatic tracking and enhanced visualization of the catheter.

Ellis Beld, Marinus A. Moerland, Jeroen Schuurman , Frank Zijlstra, Max A. Viergever, Jan .J.W. Lagendijk, Peter R. Seevinck

For MR-guided high-dose-rate (HDR) brachytherapy, an MR-compatible afterloader was developed, required for real-time HDR brachytherapy source tracking. This afterloader should be able to function well close to the MRI scanner. The functioning of both the MR-compatible afterloader and the MRI scanner, while operating simultaneously, was investigated. Source localization was performed by a phase-only cross correlation localization method. The results demonstrate that the afterloader was able to send the source to predefined source positions, while simultaneously performing MR imaging. Combined with high-temporal resolution imaging and fast reconstruction/post-processing, this study shows the feasibility of real-time source tracking for MR-guided HDR brachytherapy.

Michael Guttman, Susumu Tao, Aravindan Kolandaivelu, Sarah Fink, Henry Halperin, Daniel Herzka

Non-contrast-enhanced T1-weighted imaging has been demonstrated to be an effective technique for visualization of acute RF ablation lesions in the heart.  Current practice does not include any soft tissue visualization, which could lead to gaps or incomplete ablations and possible recurrence of symptoms.  We propose a T1-weighted sequence with long TI to increase contrast between normal and ablated myocardium.  Images are presented demonstrating the technique after ablations in the ventricles, left atrium and pulmonary vein.

Pim Borman, Clemens Bos, Sjoerd Crijns, Chrit Moonen, Bas Raaymakers, Rob Tijssen

Integrated MR-guided radiotherapy systems make it possible to monitor intra-fraction anatomy changes due to motion. A Simultaneous Multi-Slice (SMS) balanced SSFP sequence with interleaved stacks is used for dynamic imaging, where SMS is used to increase the spatial coverage without decreasing the frame rate. It is shown that SMS factors up to 4 are feasible without significant artifacts, for both orthogonal and parallel stacks.

Ieva Braškute, Clemens Bos, Roel Deckers, Lambertus Bartels

During Magnetic Resonance Imaging-guided High Intensity Focused Ultrasound (MR-HIFU) ablation of breast tumors, localization of the tumor during the treatment procedure is important for proper treatment planning. However, the use of a contrast agent during thermal ablation is preferably avoided for reasons of safety and practicality. We propose an image registration approach using pre-treatment eligibility CE and per-treatment non-CE breast MR scans, acquired with a dedicated mDixon-based tumor localization scan. We demonstrate the feasibility of our method in a volunteer study.

Danial Mir, Kareem Elfatairy, Debra Weber, Sherif Nour

Treatment of patients with metastatic liver disease requires accurate quantification of hepatic tumor burden and precise three dimensional localization. We demonstrate that intraprocedural MRI utilizing IV gadoxetate disodium (Eovist®) administration with controlled breath suspension under general anesthesia results in the detection additional hepatic metastatic deposits in 25% of cases, not appreciated on prior diagnostic imaging. In 88% of these cases this discovery led to a change in clinical management strategy that may have influenced patient outcomes.  

Mikayel Dabaghyan, Jose de Arcos, Raymond Kwong, William Stevenson, Jeff Schweitzer, Greg Olson, Ehud Schmidt

  Voltage Device Tracking (VDT), a method for catheter navigation, during MRI is explored. VDT utilizes multiple catheter electrodes that measure both the spatial location of the electrode and the ECG on the vessel wall (EGM) at that location. Electrode spatial-localization is performed by driving intermittent sinusoidal signals at kHz frequencies between surface electrodes, and measuring the signals received by the catheter. Large (>1V) signals (GIV), generated within the body by the MR gradients during a scan interfere with the much smaller (~10mV) tracking signals. We applied two approaches to remove GIVs, which allowed VDT visualization with <5% GIV contamination.

Andreas Reichert, Axel Krafft, Michael Bock

In MR-guided interventions passive markers serve as needle guides for percutaneous biopsies and can be followed automatically to visualize the planned needle trajectory. This is achieved by tracking techniques which acquire two cross-sectional Cartesian tracking images of a cylindrical marker to determine the position information. We show that the implementation of radially undersampled tracking images might be used to reduce the duration of percutaneous needle procedures by about 80%.

Felipe Godinez, Joseph Hajnal, Greig Scott, Ronald Mooiweer, Shaihan Malik

A method for measuring relative coupling between elements of a parallel transmit (PTx) array and conductive structures such as guidewires or braided catheters. The method relies on strong local enhancement of B1 fields close to conductors due to induced currents. Data acquired from single pulse-acquire measurements using very low flip angles is hence dominated by these induced current contributions. Coupling matrices for N-channel arrays can therefore be estimated using only N pulses; it is demonstrated that these are similar to those obtained from dedicated current sensors.

Matteo Maspero, Cornelis van den Berg, Frank Zijlstra, Hans de Boer, Gert Meijer, Max Viergever, Jan Lagendijk, Linda Kerkmeijer, Peter Seevinck

A novel approach aiming at automatic localization of gold Fiducial Markers (FMs) used in prostate radiotherapy to accurately perform patient positioning is presented and evaluated. The proposed method correctly detected 49/51 FMs in 17 patients when compared to FMs locations manually detected on MR. The spatial accuracy (median) and precision (STD) achieved were 0.2 mm, and 1.2 mm, respectively, when compared to relative FMs locations obtained with CT. When combined with a manual check, this approach could be a safe way to eliminate CT during radiotherapy planning, facilitating an MR-only workflow. 

Samantha Mikaiel, James Simonelli, Yu-Hsiu Lee, Xinzhou Li, Kyunghyun Sung, Tsu-Chin Tsao, Holden Wu

Motion is one of the main challenges in MRI, including interventional MRI. While many dynamic imaging and motion compensation techniques have been created, comparisons and validation are difficult, since it is difficult to reproduce in vivo motion for multiple experiments. This work proposes the design and development of a 1 Degree-of-Freedom hydrostatically actuated MRI-compatible motion platform, which can reliably reproduce programmed motion for dynamic MRI experiments.  

Jose de Arcos, Mikayel Dabaghyan, William Stevenson, Junichi Tokuda, Raymond Kwong, Ravi Seethmaraju, Jeff Schweitzer, Ehud Schmidt

We developed an intra-cardiac MRI (ICMRI) catheter to monitor heating during MRI-guided electro-physiological ablative procedures. ICMRI includes an imaging coil that expands within the cardiac chambers and a tetrahedral-shaped array of MR-tracking coils, intended to compensate for cardiac motion during the imaging process. In this study, we used real swine cardiac MR-tracking data, which may contain varying levels of positional uncertainty (noise), to develop algorithms that filter this noise, and thus do not distort the motional (translational/rotational) estimates, required for delivering non-blurred high-resolution intra-cardiac images. Our results show that submillimiter-error motion reconstruction is feasible under realistic levels of noise.

Jordy van Zandwijk, Frank Simonis, Robert Geelkerken, Robert Meerwaldt, Friso Heslinga, Bennie ten Haken

Low-field magnetic resonance imaging (lf-MRI) using super-paramagnetic iron-oxide (SPIO) nanoparticles as contrast agent seems to be a promising radiation free alternative to guide endovascular interventions in patients with critical limb ischemia (CLI). We propose an innovative workflow on how to deploy lf-MRI during such an intervention and investigate in phantoms the achievable contrast and resolution levels. The results showed that this combination of lf-MRI with SPIO contrast has potential to guide endovascular interventions, but that high quality pre-operative imaging might be required in deployment of this technique.

Thomas Lottner, Ali Özen, Simon Reiss, Timo Heidt, Axel Krafft, Lisa Besch, Klaus Düring, Constantin von zur Mühlen, Michael Bock

Active tracking or profiling coils mounted on catheters provide high signal. Other devices in the vicinity can alter the signal acquired by the catheters. The effects of guidewires on the signal from actively tracked catheters were investigated in phantom and in vivo. A standard metallic guidewire and a MR safe guidewire with a passive marker were introduced through the catheter and tested for different positions at the tip. The signal loss was substantial for both guidewires. When the metallic guidewire passed through the catheter tip, the signal was unstable, whereas the MR safe guidewire did not cause any distortions.