Optical Imaging Measurement of Intravascular Solution Efficacy Trial

Peripheral artery disease (PAD) affects anywhere from 8-12 Million people in the United States. Many of these people go on to develop claudication, rest pain, and tissue loss. During the workup for these disease states many imaging modalities are conducted including Pulse Volume Recording, Duplex Ultrasound, Angiography, and IVUS, but an emerging catheter based imaging has been developed that may supplement the current modalities used.

Intravascular optical coherence tomography (iOCT) is based on near-infrared light system. The light reflects off plaque and other objects within vessels and the signals are processed into a series of axial images (A-scans) at different positions along the artery to generate a two-dimensional dataset (B-scans). These images are created at an extremely fine resolution of 10-15 μm, which has allowed iOCT to be used in many research settings including PAD and coronary artery disease. OCT has been approved for clinical use in the coronary territory by the FDA in May 2010. Since then many centers have been using iOCT in the daily clinical practice. However, it's still not widely in the clinical management of patients with PAD. There is hope that the high resolution capabilities of iOCT may help before and after an intervention to predict outcomes or correct errors in stent deployment.

The iOCT procedure for lower extremity PAD is fairly straightforward. An introducer is placed into the femoral artery. After which a wire is placed past the lesion of interest and the iOCT catheter is inserted. The catheter is then attached to an automated pullback device. Next an optical medium is needed to displace the erythrocytes. Due to the high resolution of the iOCT this is necessary for a cleaner image to analyze. At the time of injection of the optical medium a sensor triggers the catheter to be withdrawn (distal to proximal) at anywhere from 10-25 mm/sec. The images are captured and processed and arterial plaque can be characterized.

The greatest strength of the iOCT catheter is its high resolution images but the problem is that the imaging signal is substantially attenuated by blood. In order to remedy this complication techniques such as proximal balloon occlusion and continuous infusion of a fluid have been used to acquire improved iOCT images. In the continuous infusion methods, different mediums have been injected such as contrast, dextran, and even an oxygen-carrying substitute in hopes of improving decreasing the attenuation by blood.

In order the overcome the attenuation of red blood cells during iOCT imaging, we are proposing a novel approach involving CO2 injection to clear the erythrocytes. Currently CO2 is used as medium for digital subtraction angiography in patients with renal insufficiency and was first used in humans by Hawkins in 1982. The other alternative for angiography, iodinated contrast medium, is nephrotoxic and thus is avoided in these patients for fear of exacerbating the patient's acute or chronic problem. Another group where CO2 angiography is employed is history of a contrast allergy. Although this technique is usually used under these circumstances, Kerns et al reports conducting CO2 angiography in as high as 20% of their patients with abdominal and lower extremity studies.