Moderators:

Three Dimensional Acute Radiofrequency Ablation Lesion Visualisation and Correlation with Electro-Anatomical Mapping System Ablation Points.

Benjamin R. Knowles¹, Dennis Caulfield¹, Aldo Rivaldi², Michael Cooklin², Jaswinder S. Gill², Julian Bostock², Reza Razavi¹, Tobias Schaeffter¹, Kawal S. Rhode^1
1Division of Imaging Sciences, King's College London, London, UK; ²Department of Cardiology, Guy's and St Thomas' NHS Foundation Trust, London, UK

Dingxin Wang¹, Ron Gaba², Robert Lewandowski², Robert Ryu², Kent Sato², Mary Mulcahy^3,4, Riad Salem^2,4, Reed Omary^1,4, Andrew Larson^1,4
1Departments of Radiology and Biomedical Engineering, Northwestern University, Chicago, IL, USA; ²Department of Radiology, Northwestern University, Chicago, IL, USA; ³Department of Medicine, Northwestern University, Chicago, IL, USA; ⁴Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, IL, USA

Transcatheter Intra-arterial Perfusion TRIP-MRI, using catheter-directed intraarterial (IA) contrast delivery, offers an objective method to intra-procedurally quantify tumor perfusion changes during TACE. The TRIP-MRI technique has previously been performed with 2D acquisitions in a combined clinical magnetic resonance/DSA unit (termed MR-IR unit) to monitor TACE. In this study, using a clinical MR-IR unit, we tested the hypothesis that 4D TRIP-MRI can be used to measure intra-procedural perfusion changes in liver tumors during TACE.

We report on our initial experience from 12 liver biopsies guided by a commercial stereotactic robotic system with six degrees of freedom in a closed-bore MRI scanner. Because the liver is subject to respiratory motion, (i) a preinterventional breathhold training with the patient was considered essential, and (ii) immediately after needle placement, the guiding sleeve had to be disconnected from the system to avoid liver injury. The device appears to provide a substantial benefit for biopsies with double oblique access paths. Most of the interventions could be performed without contrast media and the learning curve suggests a mean intervention time of less than one hour.

There is a need for methods to accurately manipulate instruments within closed MRI systems. During such procedures, it is useful to track deviations from the planned trajectory to minimize positioning error. This research focuses on using MRI-compatible sensors to measure strain on a standard biopsy needle. The sensors used are based on fiber Bragg grating (FBG) technology. FBG sensors produce wavelength shifts under various loads. Our results show that the FBG sensors do not produce image artifacts, and the sensor signals are not affected by the magnetic field.

Drilling under conventional X-ray guidance often leads to damage of the bone and cartilage, due to poor visualization and the complex anatomy of the ankle. We propose a passive, simple and inexpensive navigation concept, based on the cross-sectional nature of MRI for retrograde drilling of osteochondral lesions of the talus under MRI-guidance. For navigation, we used a custom-made MR-compatible drilling device. The passive navigation concept was fast and safe in practice. Saw cut specimens showed that the artificial lesion was hit in all cases. We conclude that our method is a viable alternative to conventional navigation concepts.

Shashank Sathyanarayana¹, Michael Schär^2,3, Meiyappan Solaiyappan², Paul Arthur Bottomley^1,2
1Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, USA; ²Radiology, Johns Hopkins University, Baltimore, MD, USA; ³Philips Healthcare, Cleveland, OH, USA

RF transmission and reception by modified miniature internal probes can intrinsically localize MRI signals to a sensitive “plane” locked to the probe-head, analogous to an endoscope. Here, intra-vascular “MRI endoscopy” is implemented in real-time at 3T in diseased human vessels in-vitro, and in a rabbit model of atherosclerosis in-vivo. Imaging at up to 4 frames-per-second can identify suspect lesions, with high-resolution (≥80µm) follow-up. Cine images from the rabbit aorta are rendered in 3D to visualize the advancing probe from its own perspective. MRI endoscopy offers the potential for fast high-resolution intravascular imaging of vascular pathology and morphology.

The success and safety of interventional magnetic resonance imaging (iMRI) procedures require conspicuous intravascular instruments that can be distinguished from surrounding tissues. We have developed an active two channel guidewire that incorporates individual channels to provide superior distal tip and whole shaft visibility simultaneously under real time iMRI. The guidewire visibility and handling were evaluated during in vitro phantom imaging and in vivo real-time MRI-guided vascular access experiments in swine. Also mechanical properties (torquability, tip flexibility, pushability) of the guidewire prototype were compared in several bench-top evaluations with representative 0.035” commercially-available guidewires.

An active tracking catheter using a semisolid rubber as signal source was constructed to be used for MRI-guided interventions in air-filled cavities of the body. Exploiting the short relaxation time of the material and providing suppression of interfering signals, a special tracking sequence and algorithm is shown. Results from phantom and animal experiments with a tracking catheter prototype are presented.

A View-Sharing Compressed Sensing Technique for 3D Catheter Visualization from Bi-Planar Views

Fast visualization of catheters is indispensable for MR-guided interventions. We propose a new method based on bi-planar imaging using two perpendicular 2D projection views. The two projection views are acquired rapidly by using a randomized view-sharing 1D phase encoding scheme allowing for accelerated recovery of the catheter shape using Compressed Sensing as well as measurement of organ motion. Furthermore, a new catheter design is proposed that allows for better shape recovery and robust tip tracking. The method was assessed on a simulation and its feasibility tested in an in-vivo.

Outer volume suppression (OVS) is performed in steady state sequences to restrict the field of view and thus, to accelerate the image acquisition. Without destroying the steady state, OVS is integrated in three different pulse sequences (FLASH, PSIF, trueFISP) which provide T1, T2-like and T2/T1 image contrast. With a 12.5% FOV restriction an update rate of 5 images/s could be achieved.