Dumitru Mazilu

Assessment of Myocardial Microstructural Dynamics by In Vivo Diffusion Tensor Cardiac Magnetic Resonance.

BACKGROUNDnCardiomyocytes are organized in microstructures termed sheetlets that reorientate during left ventricular thickening. Diffusion tensor cardiac magnetic resonance (DT-CMR) may enable noninvasive interrogation of inxa0vivo cardiac microstructural dynamics. Dilated cardiomyopathy (DCM) is a condition of abnormal myocardium withxa0unknown sheetlet function.nnnOBJECTIVESnThis study sought to validate inxa0vivo DT-CMR measures of cardiac microstructure against histology, characterize microstructural dynamics during left ventricular wall thickening, and apply the technique in hypertrophic cardiomyopathy (HCM) and DCM.nnnMETHODSnInxa0vivo DT-CMR was acquired throughout the cardiac cycle in healthy swine, followed by in situ andxa0exxa0vivoxa0DT-CMR, then validated against histology. Inxa0vivo DT-CMR was performed in 19 control subjects, 19 DCM, and 13xa0HCMxa0patients.nnnRESULTSnIn swine, a DT-CMR index of sheetlet reorientation (E2A) changed substantially (E2A mobility ∼46°). E2A changes correlated with wall thickness changes (inxa0vivo r2xa0= 0.75; in situ r2xa0= 0.89), were consistently observed under all experimental conditions, and accorded closely with histological analyses in both relaxed and contracted states. The potential contribution of cyclical strain effects to inxa0vivo E2A was ∼17%. In healthy human control subjects, E2A increased from diastole (18°) to systole (65°; pxa0< 0.001; E2A mobilityxa0= 45°). HCM patients showed significantly greater E2A in diastole than control subjects did (48°; pxa0< 0.001) with impaired E2A mobility (23°; pxa0< 0.001). In DCM, E2A was similar to control subjects in diastole, butxa0systolic values were markedly lower (40°; pxa0< 0.001) with impaired E2A mobility (20°; pxa0< 0.001).nnnCONCLUSIONSnMyocardial microstructure dynamics can be characterized by inxa0vivo DT-CMR. Sheetlet function was abnormal in DCM with altered systolic conformation and reduced mobility, contrasting with HCM, which showed reducedxa0mobility with altered diastolic conformation. These novel insights significantly improve understanding of contractile dysfunction at a level of noninvasive interrogation not previously available in humans.

Robotic System for Transapical Aortic Valve Replacement with MRI Guidance

This paper reports our work on developing a robotic surgical system for transapical beating heart aortic valve replacement (AVR) under interactive real-time magnetic resonance imaging (rtMRI) guidance. Our system integrates a real-time MRI system, a compound MRI robot, as well as an interface for the surgeon to plan the procedure and manipulate the robot. The compound robot consists of a positioning module and a valve delivery module. A 5-DOF Innomotion positioning arm provides and maintains direct access to the native aortic valve. A newly developed 3-DOF robotic valve delivery module allows the surgeon to remotely control bioprosthetic valve delivery with MRI guidance. Preliminary evaluation of the parameters of the robotic system demonstrates it can provide sufficient capability to successfully assist the surgeon.

Transapical aortic valve replacement under real-time magnetic resonance imaging guidance: experimental results with balloon-expandable and self-expanding stents

OBJECTIVEnAortic valves have been implanted on self-expanding (SE) and balloon-expandable (BE) stents minimally invasively. We have demonstrated the advantages of transapical aortic valve implantation (tAVI) under real-time magnetic resonance imaging (rtMRI) guidance. Whether there are different advantages to SE or BE stents is unknown. We report rtMRI-guided tAVI in a porcine model using both SE and BE stents, and compare the differences between the stents.nnnMETHODSnA total of 22 Yucatan pigs (45-57 kg) underwent tAVI. Commercially available stentless bioprostheses (21-25 mm) were mounted on either BE platinum-iridium stents or SE-nitinol stents. rtMRI guidance was employed as the intraoperative imaging. Markers on both types of stents were used to enhance visualization in rtMRI. Pigs were allowed to survive and had follow-up MRI scans and echocardiography at 1, 3, and 6 months postoperatively.nnnRESULTSnrtMRI provided excellent visualization of the aortic valve implantation mounted on both stent types. The implantation times were shorter with the SE stents (60 ± 14s) than with the BE stents (74 ± 18s), (p=0.027). The total procedure time was 31 and 37 min, respectively (p=0.12). It was considerably easier to manipulate the SE stent during deployment, without hemodynamic compromise. This was not always the case with the BE stent, and its placement occasionally resulted in coronary obstruction and death. Long-term results demonstrated stability of the implants with preservation of myocardial perfusion and function over time for both stents.nnnCONCLUSIONSnSE stents were easier to position and deploy, thus leading to fewer complications during tAVI. Future optimization of SE stent design should improve clinical results.

Midterm results of transapical aortic valve replacement via real-time magnetic resonance imaging guidance

OBJECTIVEnPercutaneous valve replacements are presently being evaluated in clinical trials. As delivery of the valve is catheter based, the safety and efficacy of these procedures may be influenced by the imaging used. To assist the surgeon and improve the success of the operation, we have performed transapical aortic valve replacements using real-time magnetic resonance imaging guidance.nnnMETHODSnTwenty-eight swine underwent aortic valve replacement by real-time magnetic resonance imaging on the beating heart. Stentless bioprostheses mounted on balloon-expandable stents were used. Magnetic resonance imaging (1.5 T) was used to identify the critical anatomic landmarks. In addition to anatomic confirmation of adequate placement of the prosthesis, functional assessment of the valve and left ventricle and perfusion were also obtained with magnetic resonance imaging. A series of short-term feasibility experiments were conducted (n = 18) in which the animals were humanely killed after valve placement and assessment by magnetic resonance imaging. Ten additional animals were allowed to survive and had follow-up magnetic resonance imaging scans and confirmatory echocardiography at 1, 3, and 6 months postoperatively.nnnRESULTSnReal-time magnetic resonance imaging provided superior visualization of the landmarks needed. The time to implantation after apical access was 74 +/- 18 seconds. Perfusion scanning demonstrated adequate coronary flow and functional imaging documented preservation of ventricular contractility in all animals after successful deployment. Phase contrast imaging revealed minimal intravalvular or paravalvular leaks. Longer term results demonstrated stability of the implants with preservation of myocardial perfusion and function over time.nnnCONCLUSIONSnReal-time magnetic resonance imaging provides excellent visualization for intraoperative guidance of aortic valve replacement on the beating heart. Additionally, it allows assessment of tissue perfusion and organ function that is not obtainable by conventional imaging alone.

Pneumatic Actuated Robotic Assistant System for Aortic Valve Replacement Under MRI Guidance

We present a pneumatic actuated robotic assistant system for transapical aortic valve replacement under MRI guidance in a beating heart. This is a minimally invasive procedure that is currently performed manually inside the MRI bore. A robotic assistance system that integrates an interactive real-time MRI system, a robotic arm with a newly developed robotic valve delivery module, as well as user interfaces for the physician to plan the procedure and manipulate the robot, would be advantageous for the procedure. An Innomotion arm with hands-on cooperative interface was used as a device holder. A compact MRI compatible robotic delivery module was developed for delivering both balloon-expandable and self-expanding prostheses. A compact fiducial that can be placed close to the volume of interest and requires a single image plane was used for image-based robot registration. The system provides different user interfaces at various stages of the procedure. We present the development and evaluation of the components and the system in ex-vivo experiments.

Real-time Magnetic Resonance Imaging Guidance for Cardiovascular Procedures

Magnetic resonance imaging (MRI) of the cardiovascular system has proven to be an invaluable diagnostic tool. Given the ability to allow for real-time imaging, MRI guidance of intraoperative procedures can provide superb visualization, which can facilitate a variety of interventions and minimize the trauma of the operations as well. In addition to the anatomic detail, MRI can provide intraoperative assessment of organ and device function. Instruments and devices can be marked to enhance visualization and tracking, all of which is an advance over standard X-ray or ultrasonic imaging.

MRI-compatible hands-on cooperative control of a pneumatically actuated robot

MRI compatible robots are emerging as useful tools for image guided interventions. A shared control between a user and the MRI compatible robot makes it more intuitive instrument especially during setup phases of interventions. We present a MRI compatible, hands-on cooperative system using Innomotion robotic arm. An economic MRI compatible user input sensor was developed and its functionality was tested under typical application conditions. Performance improvement in phantom tasks shows promise of adding hands-on interface in MRI compatible robots.

MRI Compatible Robot Systems for Medical Intervention

Magnetic resonance imaging (MRI) is a non-invasive medical imaging tool that helps physicians diagnose and treat medical conditions. It offers excellent visualization of softtissue in any imaging plane without using of iodinated contrast agent or ionizing radiation. In addition to anatomical morphology, MRI can also provide functional information. With novel fast imaging technologies, MRI became an imaging tool for guiding and monitoring various interventions and biopsy procedures on various organs including the brain, breast, prostate, liver and spine (Jolesz, 1998, Melzer & Seibel, 1999). High performance magnetic field gradients, multi-channel receivers, and advanced reconstruction systems improve the clinical applicability of real time MRI procedures (Nayak et al., 2004, Bock et al., 2004, Guttman et al., 2003, Lederman, 2005). Modern scanners designed for the interventional environment can provide real-time images of acceptable quality in excess of 10 frames per second. As a result, real-time MRI (rtMRI) is becoming an attractive method for many minimally invasive cardiac interventions (Kuehne et al., 2003, Raval et al., 2006, Henk et al., 2005, McVeigh et al., 2006, Horvath et al., 2007). However the confined physical space of MRI scanner challenges medical intervention, even the magnets with open architecture provide only a limited working space, at the expense of image quality. The use of robots inside the MRI scanner is a very attractive solution: a robot manipulates the intervention instruments while MR images continuously give feedback of the position of the instruments which are controlled by the robot. MR compatible robotic systems have been researched and developed for prostate biopsy and brachytherapy (Chinzei et al., 2000, Krieger et al., 2005, Fischer et al., 2006, Stoianovici et al., 2007a), breast intervention (Kaiser et al., 2000, Larson et al., 2004), interventional spinal procedure (Hempel et al., 2003), neurosurgery (Masamune et al., 1995, Koseki et al., 2002), interventional liver therapy (Hata et al., 2005, Kim et al., 2002), and cardiac intervention (Li et al., 2008). Design of a system operating inside or close to the bore of a high field MRI scanner is of significant complexity. Due to the strong magnetic field of the MRI, standard materials, sensors and actuators cannot be employed. Due to the confined space of MRI bore, the mechanical design should be compact and simultaneously functional. In this chapter, we 22

Cardiac interventions under MRI guidance using robotic assistance

Transapical aortic valve replacement under MRI guidance in a beating heart is a recent minimally invasive technique that could benefit from a surgical assistant system. We present a robotic surgical assistant system that can precisely and repeatably deliver aortic valve prostheses. The surgical system consists of an imaging system, an Innomotion robotic arm, a 3-DoF valve delivery module and user interfaces. Interactive control allows the physician to remain in the loop and adjust the orientation and position using real-time MR feedback. The 3-DoF valve delivery module is developed to deploy both balloon-expandable and self-expanding stented prostheses. We use a new compact fiducial that can be placed close to the volume of interest and requires a single image plane for image based robot registration. We evaluate the MRI compatible valve delivery module for both types of prostheses. The accuracy for prosthesis delivery is about 0.8 mm and 1.5 mm, for self-expanding and balloon-expandable prostheses, respectively. Preliminary results in ex-vivo experimentation suggest that the robotic system can be translated into animal and clinical models.

A robotic assistant system for cardiac interventions under MRI guidance

In this paper we present a surgical assistant system for implanting prosthetic aortic valve transapically under MRI guidance, in a beating heart. The system integrates an MR imaging system, a robotic system, as well as user interfaces for a surgeon to plan the procedure and manipulate the robot. A compact robotic delivery module mounted on a robotic arm is used for delivering both balloon-expandable and self-expanding prosthesis. The system provides different user interfaces at different stages of the procedure. A compact fiducial pattern close to the volume of interest is proposed for robot registration. The image processing and the transformation recovery methods using this fiducial in MRI are presented. The registration accuracy obtained by using this compact fiducial is comparable to the larger multi-spherical marker registration method. The registration accuracy using these two methods is less than 0.62±0.50 deg (mean ± std. dev.) and 0.63±0.72 deg (mean ± std. dev.), respectively. We evaluated each of the components and show that they can work together to form a complete system for transapical aortic valve replacement.