Being naturally present in the human body, CO2 is the only 100% biocompatible contrast agent, meaning no adverse reactions, such as allergy, nephrotoxicity, and hepatotoxicity.<unk><unk>  is a negative contrast medium and it has a low radiopacity (while iodinated contrast media are defined as positive contrast media due to their high radiopacity). Contrast is caused by the different X-ray absorption coefficients between the tissue and the contrast agent. In the vascular imaging results produced using CO2, vessels look brighter rather than the surrounding tissues, because the contrast medium absorbs less X-ray radiations rather an iodine-based contrast medium, where the vessel are displayed in black. The CO2 does not mix with blood. At atmospheric pressure CO2 is in gaseous form and, when it comes out from the catheter, it forms a train of bubbles which displaces blood, causing a transient ischemia, in relation to the bloodstream (systolic pressure). When added together by DSA “stacking” software, the result is a composite diagnostic image of the frames.<unk><unk>  is highly soluble, allowing multiple injections without a maximum dosage (per procedure, while it is 100 mL per injection by the literature), but, in case of multiple injections, should be considered and adequate time interval between them, so to allow the gas to be expelled from the body. Compared with the oxygen, the most present gaseous substance in the body, CO2 is more than 20 times more soluble, meaning the possibility of injecting high quantities in the body. High compressibility and explosive delivery. More pressure is exerted to the gas, more its density increases, resulting in a decrease in gas volume and an increase in gas pressure. The effusion of the gas from the catheter orifice into a state of lower pressure, such as a blood vessel, leads to a sudden increase in the volume of the gas - the “explosive delivery” or “jet effect” - which could lead to an excessive stress in vessels walls. To avoid this, immediately prior to the injection of CO2, a flush is performed, injecting small amounts of CO2 to reduce gas compression and guarantee gas delivery at a steady flow rate. CO2 is 400 times less viscous than iodinated contrast medium, allowing its injection through devices with a very little inner lumen, as microcatheters, or, even, with other devices inserted in the catheter, as guidewires, balloons or as in atherectomy procedures. The low viscosity of CO2 makes it easy to pass through small vessels, visualizing tight stenosis, collaterals, small bleedings and endoleaks in AAA procedures. Expulsion: Once dissolved in the plasma, CO2 is transported to the lungs and removed in a single pass by the alveoli, favoring the possibility of performing multiple injections without complications (in healthy patients, meaning no severe COPD or significative POF, especially in presence of pulmonary embolism). Buoyancy is defined as the tendency of a body to float when submerged into a fluid. CO2 is lighter than blood and, therefore, floats above the bloodstream. The main advantage is represented by the simplicity of filling the more superficial (in transverse plane) vessels of the body, conversely the main disadvantage consists in a less ease of filling the deeper ones.
Carbon dioxide angiography
Intravascular fluorescence
Xenon gas MRI
Thorpe tube flowmeter
Radionuclide angiography
Indocyanine green angiography
Intravascular imaging
Perfusion scanning