Report from ISET: MR catheter snakes its way toward FDA approval

January 31, 2007

Despite imaging advances for coronary artery disease, few clinically available tools can accurately characterize the lipid-rich core of vulnerable plaque. A company in Israel wants to change that with a disposable intravascular MR imaging device that entered clinical trials in the U.S. in January.

Despite imaging advances for coronary artery disease, few clinically available tools can accurately characterize the lipid-rich core of vulnerable plaque. A company in Israel wants to change that with a disposable intravascular MR imaging device that entered clinical trials in the U.S. in January.

The IntraVascular MRI catheter manufactured by TopSpin Medical incorporates all magnetic field sources and delivers 100-micron resolution of various plaque components, according to Dr. Ron Waksman, associate chief of cardiology at Washington Hospital Center in Washington, DC, who spoke at the International Symposium on Endovascular Therapy in Miami this week.

"Today, we look at plaque with CT angiography, catheter angiography, or intravascular ultrasound. None of those modalities gives us enough information about plaque composition to reliably identify vulnerable lesions," Waksman told Diagnostic Imaging.

The IVMRI catheter measures the apparent diffusion coefficient of the various components of the atherosclerotic vascular wall. Exploiting plaque's heterogeneous water diffusion properties, the technique shows decreased and isotropic water diffusion within the plaque compared with the fibrous cap and medial layer. This information allows clinicians to identify lesions that are at risk of rupture and to prescribe appropriate medical or therapeutic treatment, Waksman said.

The technology has been validated in preclinical studies on ex vivo human carotids, coronaries, and aortas and in in vivo rabbit aorta studies. About three dozen patients have been evaluated with the technology, including 29 from an earlier safety and efficacy trial in four centers in Europe and one in Israel.

Those centers have been joined by three U.S. sites for the latest study, TOP-IMAGE II, with a goal of enrolling 100 patients. The objective of the study is to assess the safety and functional performance of the device in risk-stratified patients. Researchers will evaluate plaques that are not associated with high-grade stenosis.

Primary endpoints are major adverse cardiac events at 24 hours, arterial dissection, and/or arterial perforation attributable to IVMRI. Secondary endpoints are system performance, major adverse cardiac events at 30 days, and incidence of unstable angina at 12 to 24 hours postprocedure.

Besides Waksman, U.S. investigators are Dr. Robert L. Wilensky, director of experimental interventional cardiology at the Hospital of the University of Pennsylvania, and Dr. Martin B. Leon, associate director of cardiovascular interventional therapy at Columbia University Medical Center.

Waksman cited several disadvantages of intravascular ultrasound, the gold standard for interventional cardiology imaging:

  • It cannot visualize vulnerable plaque cap.

  • It is not able to accurately image the area behind calcified regions.

  • It can't provide information about the activity of plaque and inflammation.

  • It has a very low sensitivity for detecting microcalcification areas of <0.05 mm and only 37% sensitivity for detecting plaque rupture.

"IVMRI allows us to know the amount of lipid in the plaque itself," he said.

TopSpin Medical initiated a study last year with the device for diagnosing, staging, and therapy guidance of prostate cancer. The study includes imaging of prostate glands dissected during prostatectomy from patients with prostate cancer and is being conducted in collaboration with Rabin Medical Center, Israel.

For more information from the Diagnostic Imaging archives:

Calcium score studies reveal noncalcified plaque

Intravascular technique shows clinical potential

Optical coherence tomography characterizes arterial plaque

Light-based imaging 'sees' thin fibrous cap