Miles E. Olsen¹, Ethan K. Brodsky¹, Jonathan A. Oler², Marissa K. Riedel², Eva M. Fekete², Ned H. Kalin², and Walter F. Block^1
1Medical Physics, University of Wisconsin - Madison, Madison, WI, United States, ²Psychiatry, University of Wisconsin - Madison, Madison, WI, United States

We present a technique for rapidly aiming interventional devices during prospective stereotaxy procedures. Our approach enables accurate computational determination of trajectory guide orientation and the true physical pivot point of frameless stereotaxy guides that mount on the skull.

 

Historically, these neurosurgical tasks require minutes per iterative cycle consisting of: scan, interpret image, adjust aim, repeat – or no intraoperative imaging at all, relying on preoperative images registered to stereotactic frame coordinates. Our rapid technique (~5 FPS) is closer to the clinician’s preferred responsiveness of optical tracking of devices in the OR (~30 FPS).

Alastair Martin¹, Paul Larson², Nadja Levesque², Jill Ostrem³, and Philip Starr^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

Hardware infection incidence for DBS implantations performed in a diagnostic MR suite is reported.  A total of 164 DBS procedures were performed in movement disorder patients resulting in six (3.7%) hardware related infections.  Two infections occurred within the first 10 cases and led to a change in sterile practice.  Over the last 154 cases four (2.6%) infections have been reported and all were associated with implantation of the IPG controller, which is done in a separate surgical procedure 1-3 weeks after DBS implantation.  Infection risk when implanting DBS electrodes in a diagnostic MR suite is comparable to conventional OR procedures.   

Nicolas G.R. Behl¹, Armin M. Nagel^1,2, Erik N.K. Cressman³, Reiner Umathum¹, David Fuentes⁴, R. Jason Stafford⁴, Peter Bachert¹, Mark E. Ladd¹, and Florian Maier^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Diagnostic and Interventional Radiology, University Medical Center Ulm, Ulm, Germany, ³Interventional Radiology, M. D. Anderson Cancer Center, Houston, TX, United States, ⁴Imaging Physics, M. D. Anderson Cancer Center, Houston, TX, United States

Thermochemical ablation (TCA) is a novel minimally invasive ablation approach. Acetic acid and sodium hydroxide are injected simultaneously and mix and react directly before entering the tissue. The exothermal reaction releases heat that is used for thermal ablation. For a detailed characterization of TCA injection, 4D ²³Na-data with reasonable temporal resolution are required. In this work, a compressed sensing approach was applied to acquire 4D ²³Na-data of injections with high spatial and good temporal resolution.

Philippa Krahn^1,2, Venkat Ramanan², Labonny Biswas², Nicolas Yak², Kevan Anderson², Jennifer Barry², Sheldon Singh³, Mihaela Pop^1,2, and Graham A Wright^1,2
1Medical Biophysics, University of Toronto, Toronto, ON, Canada, ²Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, ³Cardiology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada

Here we explored an efficient imaging protocol for visualizing both the edema (reversible) and necrosis (irreversible) regions of myocardial injury in RF lesions. Using an MR-guided catheter system, we performed ablation in swine, immediately followed by T₁-based imaging (IR-SSFP) and T₂ mapping (T₂-prepared SSFP) for lesion characterization. The areas of edema segmented from IR-SSFP images and T₂maps were visually similar and showed good correlation. IR-SSFP is known to visualize lesion cores at a specific TI--selecting an additional TI which emphasizes edema, we successfully demonstrated that both regions could be visualized by a single IR-SSFP acquisition.

Solenn Toupin^1,2, Matthieu Lepetit-Coiffe², Pierre Bour¹, Valery Ozenne¹, Baudouin Denis de Senneville³, Rainer Schneider⁴, Kimble Jenkins⁵, Arnaud Chaumeil¹, Pierre Jais¹, and Bruno Quesson^1
1IHU-LIRYC, Bordeaux, France, ²Siemens Healthcare, Saint Denis, France, ³Mathematical Institute of Bordeaux, Bordeaux, France, ⁴Siemens Healthcare, Erlangen, Germany, ⁵MRI Interventions, Irvine, CA, United States

The visualization of lesion formation in real time is one potential benefit of carrying out radiofrequency ablation (RFA) under magnetic resonance (MR) guidance in the treatment of ventricular arrhythmia. In this study, we propose a real-time MR thermometry method to visualize online the temperature distribution in the myocardium during catheter-based RFA. An echo-navigated sequence is used with slice tracking to compensate respiratory-induced through-plane motion and allow all image orientation. The method was evaluated during free breathing in 5 healthy volunteers and during RF delivery on the left ventricle (LV) of a sheep in vivo.

Robert Xu^1,2 and Graham Wright^1,2
1Medical Biophysics, University of Toronto, Toronto, ON, Canada, ²Schulich Heart Research Program, Sunnybrook Research Institute, Toronto, ON, Canada

The objective of this study is to explore the use of a rapidly updated dynamic motion model to correct for respiratory motion induced errors during MRI-guided cardiac interventions. The motivation for the proposed technique is to improve the accuracy of MRI guidance by taking advantage of the anatomical context provided by the high-resolution prior images and the respiratory motion information present in a series of real-time MR images. To achieve this goal, the proposed dynamic motion model is updated continuously, and is used to predict the motion estimate for realigning the prior volume with the real-time images during an intervention.

Axel Joachim Krafft^1,2,3, Simon Reiss², Andreas Reichert², Michael Vogele⁴, and Michael Bock^2
1German Cancer Consortium (DKTK), Heidelberg, Germany, ²Radiology – Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ³German Cancer Research Center (DKFZ), Heidelberg, Germany,⁴iSYS Medizintechnik GmbH, Kitzbuehel, Austria

Minimally invasive interventions highly benefit from imaging guidance during instrument positioning and monitoring of therapeutic progress. MRI with its unique soft tissue contrast and ability for functional imaging is ideally suited for interventional guidance. To enable and facilitate minimally invasive interventions in closed-bore high-field MR systems with small bore diameters that severely limit patient access, we propose a novel, versatile assistance system in combination with passive instrument tracking. The system was studied in a systematic phantom experiment during needle procedures, and a mean targeting accuracy of less than 2 mm was achieved (mean procedure time: 6.5 min). 

Yuxin Zhang¹ and William A Grissom^2
1Biomedical Engineering, Tsinghua University, Beijing, China, People's Republic of, ²Biomedical Engineering, Vanderbilt University Institute of Imaging Science, Nashville, TN, United States

Signal loss induced by ablation probe prevents accurate temperature monitoring where the thermal dose is highest. To address this problem, a dual echo sequence with z-shimming is proposed to recover the signal and an associated penalized likelihood approach is applied to estimate a single temperature map from both echoes. Phantom experiments were conducted to validate the effect of the proposed sequence. Evident signal recovery is shown in the magnitude images and temperature maps with heating. Standard deviation maps with no heating are presented to reflect the large reduction in uncertainty over time with dual-echo z-shimmed thermometry.

Nadège Corbin¹, Jonathan Vappou¹, Pramod Rao¹, Benoit Wach¹, Laurent Barbé¹, Pierre Renaud¹, Michel de Mathelin¹, and Elodie Breton^1
1ICube-University of Strasbourg, Strasbourg, France

MR-guided percutaneous thermal ablations are currently monitored by MR thermometry. However, no information related to intrinsic property changes of the tissue is available during the procedure. The feasibility of monitoring in vivo thermal ablations by simultaneous Magnetic Resonance Elastography (MRE) and MR-thermometry is demonstrated in this work. The interventional MRE system includes a needle MRE driver, a respiratory triggered gradient-echo sequence with motion encoding and an online reconstruction method that provides elasticity and temperature measurements in real-time.  Changes in elasticity and temperature occurring during laser thermal ablation are successfully measured in vivo over 20 minutes thanks to this interventional MRE system.

Junichi Tokuda¹, Kemal Tuncali¹, Lisanne Kok^1,2, Vincent M Levesque ¹, Ravi T Seethamraju ³, Clare M Tempany¹, and Ehud J Schmidt^1
1Department of Radiology, Brigham and Women's Hospital, Boston, MA, United States, ²Eindhoven University of Technology, Eindhoven, Netherlands, ³Siemens Healthcare, Boston, MA, United States

We tested the feasibility of R2*-based temperature mapping using a PETRA UTE sequence to determine the “kill zone” within an ice ball in the kidney during MRI-guided renal cryoablation. R2*-maps were calculated from dual-echo PETRA images acquired during six renal cryoablation cases, and converted to temperature maps using R2*-temperature calibrations performed in swine kidneys. We compared ablation volumes estimated from (a) the -20°C boundary on the temperature maps; (b) the signal void on intra-procedural T2-weighted images; and (c) post-ablation contrast-enhanced MRI as the “gold standard”. Results show that R2*-based temperature maps provided a reliable lower limit of the kill-zone volume.