OCT makes for a better angioplasty balloon

Charles T. Troy, charley.troy@photonics.com

Coronary angioplasty is performed a million times a year in the US to help patients with clogged arteries relieve angina. A main component of the procedure is a balloon.

Now, with the goal of improving balloon deployment, researchers at the Industrial Materials Institute of the National Research Council of Canada and at the Centre for Intelligent Machines at McGill University in Montreal have investigated a technique that combines a deployment tester with an optical coherence tomography system. Their approach holds the potential to greatly improve angioplasty.

They reported their work in the August 2010 online edition of the Review of Scientific Instruments, which is published by the American Institute of Physics.

The investigators integrated an intravascular optical coherence tomography (IVOCT) probe into a computerized balloon deployment system to monitor the inflation process. The minimally invasive instrument provides detailed cross-sectional imaging of the artery wall. Thanks to the development of swept-source optical coherence tomography, IVOCT has evolved rapidly in the past few years. Studies have shown its clinical relevance for the diagnosis of atherosclerosis and for monitoring the results of percutaneous coronary interventions.

Shown are cross-sectional images demonstrating how balloon inflation in a three-layer phantom mimics a coronary artery. The images reveal various levels of balloon inflation pressure: a) a partially folded balloon without pressure; b) a partially inflated balloon; c) an inflated balloon; and d) an OCT probe rotating withina balloon (no phantom). The red dot indicates where the light beam exits the probe. Note: Imaging is performed with IR light, but visible light is coupled in the system to ease identifying probe location. Courtesy of Guy Lamouche.

OCT enables imaging over a depth of a few millimeters in a tissue or material. By performing a custom pullback – rotation and translation – of a catheter OCT probe in a balloon, the scientists can obtain precise measurement of the diameter and thickness of entire balloons. The diameter can be estimated by an external camera or a laser scanner, and the burst pressure can be characterized by a balloon deployment tester.

“Balloon rupture has been reported in different articles,” said Guy Lamouche, a research officer at the National Research Council of Canada. “Although it does not occur frequently, the outcome can be fatal. We haven’t identified any major problem in the current angioplasty balloons. Nevertheless, the manufacturing process and testing of this product are continuously being improved, and we propose an apparatus to ease the development process and to ensure optimal performances.”

The researchers used the LMS-100, a laser measurement system from Interface Catheter Solutions of Laguna Niguel, Calif., and the LSM-9506, a laser scan micrometer from Mitutoyo, for characterization of compliance, burst pressure and the diameter of the balloon inflated in air. The system readings contained errors when the balloons were inflated in water. A hydraulic pressure tester, the HP-3070, also from Interface Catheter Solutions, performed leak, burst, compliance, fatigue and cycle life testing.

The IVOCT probe comprises a single-mode fiber enclosed within a spiral metallic tube in the proximal region and within a polymer tube in the distal region. At its tip, light is focused by a gradient index lens and redirected at 90° by a right-angle prism. The optical components are enclosed in a metallic ferrule.

“Combining OCT with a balloon deployment system provides an improved platform for angioplasty balloon development and can also be used in the development of next-generation minimally invasive devices for percutaneous – through the skin – coronary interventions,” Lamouche said.

“It’s now possible to monitor balloon inflation within an artery phantom (model) or an excised artery to assess the efficiency of innovative balloon angioplasty or stent deployment procedures.”