Iodinated contrast is the current gold standard for infrainguinal angiography imaging in patients without renal insufficiency and has also been used with intravascular Optical Coherence Tomography (iOCT) to improve image quality in human coronary arteries as well as carotid arteries. The current debate in the literature for iOCT medium is between iodinated contrast and dextran and CO2 may offer a superior method of iOCT imaging during lower extremity occlusive disease interventions.

The investigators hypothesize that the CO2 medium injection during iOCT data acquisition is feasible and will produce at least the same quality of imaging as that obtained with contrast or dextran without causing the problems of volume overload and renal toxicity seen with the two latter mediums.

Primary Outcomes Measured

• Quality: Cumulative number of clear image frame (CIF) through the entire 54mm length segment.
• Quantitative: Calculations of the area and diameter of each segment will be measured to determine if index of refraction has any effect between the three mediums to be tested.

The investigators expect to find little difference between all three iOCT mediums and hope to conclude that CO2 offers a superior side effect profile for iOCT imaging in the lower extremity arterial system.

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.

In addition to the benefits of patients with allergies and renal insufficiency, CO2 is extremely safe in a variety of arterial and venous applications. It is 20 times as soluble as room air and is expired through the lungs in a first-pass-type effect. The current contraindication to CO2 digital subtraction angiography is that the cerebral arterial circulation should never be exposed to CO2 because of possible neurotoxicity. Relative contraindications include use in the presence of a large arteriovenous shunt, with nitrous oxide anesthesia, and used cautiously in patients with chronic obstructive pulmonary disease.

Dextran has been used in the past in the critical care setting of human as a volume expander with the rare side effects of anaphylaxis and nephrotoxicity. It has also been used in human coronary arteries with iOCT as a blood displacement medium. Finally it has been used with iOCT in a proximal occlusion model. The main complaint in the final study was a burning sensation that lasted < 10s.

Iodinated contrast is the current gold standard for infrainguinal angiography imaging in patients without renal insufficiency and has also been used with iOCT to improve image quality in human coronary arteries as well as carotid arteries. The current debate in the literature for iOCT medium is between iodinated contrast and dextran and CO2 may offer a superior method of iOCT imaging during lower extremity occlusive disease interventions.

Inclusion Criteria:

• Age greater than or equal to 18 years
• English speaking
• Scheduled to undergo an infrainguinal angiogram and/or endovascular procedure as determined by a vascular surgery specialist
• Superficial Femoral Artery diseased segment

Exclusion Criteria:

• Acute or Chronic Renal insufficiency with Cr >1.5
• Chronic obstructive pulmonary disease
• Congestive heart failure (American Heart Association C lass III or IV)
• Acute limb ischemia, defined by a significant change in symptoms (one category on the Rutherford scale within the previous 14 days)
• Concurrent oral anticoagulant therapy that cannot be safely withheld

Adverse event data were collected throughout the entire study period. No observed adverse events occurred during the 30-day study period.

This was a single-center case series that was powered to detect only large differences in image quality. Subtle differences between the 3 liquid media may not have been appreciated despite analysis of over 10,000 individual frames.