Detecting Unstable Lesions in High-risk Patients: The Single-use, IntraVascular MRI (IVMRI) Catheter

What is the IntraVascular MRI (IVMRI) catheter? We have all heard about the wonderful things that can be done with MRIs in cardiology. The problem is that these scanners are bulky and expensive, and it is very hard to imagine cath labs transforming into MRI suites. TopSpin has developed a way to allow MRI to be done in the cath lab, using only a catheter and a small console. Instead of sending your patients for an MRI scan, you can slide a miniature MRI scanner over the guidewire and with very high resolution, image the moderate lesion that you’re not sure about. The IntraVascular MRI (IVMRI) catheter is designed to give interventional cardiologists a tool to identify lipid laden regions of the vascular wall.* Do you envision use of this catheter as one more tool in the invasive cardiology "arsenal," or do you feel it may one day replace certain devices/catheters currently in use? We do envision use of this catheter as an additional important tool in the invasive cardiology "arsenal," which will enable the cardiologist to characterize plaque composition and geometry. This clinical need is not met by currently available devices, and thus at present, diagnosis and treatment are focused in lesions that are severely stenotic, while intermediate or modestly stenotic plaques that may be prone to rupture or erosion (i.e., vulnerable plaque) are left behind. Nevertheless, plaque rupture with subsequent thrombus formation has been demonstrated to be the underlying cause of the majority of acute coronary syndromes. How does use of this catheter offer an improvement over a standard IVUS catheter? IVUS images are very hard to interpret and can rarely give the most important differentiation between lipid and fibrotic plaque composition.* The advantages of MRI as an imaging technology are well-recognized by the medical community. MRI’s sensitivity to the chemical characteristics of tissue components makes it the modality of choice for tissue characterization and differentiating soft tissues. However, the extent of MRI scanners has been limited by their high cost and size (compared with ultrasound systems, for example), the limited ability to operate on the patient while performing MRI and the complexity of the imaging procedure. The IVMRI catheter developed by TopSpin Medical enables the performance of local high-resolution MR imaging using magnetic field sources, which are integrated in the catheter itself, so that images can be obtained without the external MRI setup. More specifically, the IVMRI catheter is highly sensitive to the diffusion properties of the artery walls, and hence lipid-rich plaques can easily be detected using diffusion coefficient measurements. TopSpin did not need to prove MRI can differentiate lipid from fibrotic lesions. MRI has been known to be able to do that for years. We simply miniaturized the $2M scanner to a size of a catheter. Will the cardiologist be able to perform/interpret this test, or will the MRI staff have to be available (similar to IVUS)? Cardiologists will be able to both operate the IVMRI catheter and interpret the image. The IVMRI catheter system is specifically designed for that purpose and enables easy operation. The images obtained by the IVMRI catheter are much simpler and easier to interpret than images obtained by conventional MRI scanners. Can you describe your first-in-man clinical trial, TOP IMAGE: CORONARY? The purpose of the TOP IMAGE: CORONARY study is to assess the safety and performance of the IVMRI catheter system during diagnostic coronary artery catheterization procedure. It is a prospective, multi-centre, non-randomized, open label study conducted in Europe, and includes patients undergoing angiographic evaluation due to suspected coronary artery disease of native vessels. The first two sites are in Germany: The Universitatskliniken des Saarlandes in Homburg (Saarland) with Dr. Benno Hennen and the Herzzemtrum in Siegburg with Professor Eberhard Grube. We expect trial results to be presented in mid-2004. Can you describe some the results from your initial clinical cases? Preliminary data from our initial clinical cases shows that the introduction of the IVMRI catheter to the coronary arteries is safe and the procedure is well-tolerated by the patients. According to the physicians, the procedure is easy and takes about five minutes overall. This was the first time that MRI images were obtained in human patients with no external magnets and there were no detectable motion artefacts. MR images of the vessel walls reveal parameters similar to the ones measured in our human ex-vivo coronary and aorta studies. You mentioned that there were no detectable motion artefacts with use of the catheter. Can you explain why that’s an issue for cardiac MRIs? Motion artefacts are a major source of problems in cardiac MRI. The combination of heartbeat and ventilation during the acquisition of the MR image deteriorates the quality of the image. Thus, the resolution of the current state-of-the-art cardiac MRI scanners is 300 to 500 microns (0.3 to 0.5 millimeter). In order to achieve high resolution, the IVMRI catheter is stabilized vis-a -vis the arterial wall by a gentle inflation of low pressure (up to 1 atmosphere) side-balloon. The resolution of the current IVMRI catheter is 100 microns (0.1 millimeter) which is about 3 to 5 times better than cardiac MRI scanners. What is the estimated cost per procedure for the IVMRI catheter versus a standard cardiac MRI? How does the IVMRI compare in price per procedure to IVUS? Since the IVMRI catheter is not available for sale as yet, I cannot currently answer that question. What is the size (diameter) of the working catheter and what guide catheter sizes will be needed? The current IVMRI catheter used in the first clinical trials is 5.5F and is compatible with 8F guide catheter. The next-generation IVMRI catheter currently under development is 5F and will be compatible with a 7F guide catheter. Is it configured as a monorail or as an over-the-wire system? The current IVMRI catheter used in the first clinical trials is configured as an over-the-wire system. The next generation IVMRI catheter is configured as a rapid exchange system. What is the estimated time necessary to investigate and evaluate a coronary artery? Estimated procedure time for investigating one or two lesions in a coronary artery with the IVMRI catheter is around five minutes. How many vessels should be investigated at one time if the suspected vessel does not show a problem? The IVMRI catheter is intended to investigate intermediate or mildly stenotic plaques that should be selected by the cardiologist using an angio image. Thus, it should be the cardiologist’s decision as to how many lesions to investigate. Can this device be used on patients with existing permanent pacemakers or cardiac defibrillators? Currently patients with existing permanent pacemakers or cardiac defibrillators are excluded from IVMRI catheter use in the clinical trials since we have not evaluated their effect by preclinical or clinical testing. Is there special training that someone in the lab needs in order to interpret the images they will see with this catheter? The IVMRI catheter system is designed to present much simpler images than conventional MRI scanners and is easy to operate. Thus, the training of cardiologists to operate the catheter system and interpret images is minimal and the learning curve is expected to be very fast. *Caution: TopSpin IVMRI system is not available for sale in the US. Currently conducting clinical trials to evaluate safety and efficacy. Eyal Kolka discloses an employment affiliation with TopSpin Medical, Inc.

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