In Vivo Contrast Imaging of Rat Heart with Carbon Dioxide Foam

Widely used classical angiography with the use of iodine contrast agents is highly problematic, particularly in patients with diabetes mellitus, cardiac and pulmonary diseases, or degree III or IV renal insufficiency. Some patients may be susceptible to allergic reaction to the iodine contrast substance. The intravenous injection of a bolus of CO₂ (negative contrast) is an alternative method, which is, however, currently only used for imaging blood vessels of the lower limbs. The aim of our project was to design and test on an animal model a methodology for injecting the CO₂ foam which would minimize the possibility of embolization of the brain tissue and heart infarction, leading to their damage. This is important research for the further promotion of the use of CO₂, which is increasingly important for endovascular diagnosis and treatment, because carbon-dioxide-related complications are extremely rare. CO₂ foam was prepared by the rapid mixing in a 2:1 ratio of CO₂ and fetal bovine serum (FBS)-enriched Dulbecco's Modified Eagle Medium (DMEM). Freshly prepared CO₂ foam was administered into the catheterized rat tail vein or cannulated rat abdominal aorta and inferior vena cava (IVC). CO₂ foam was compared with commercially available microbubbles (lipid shell/gas core). The rat heart in its parasternal long axis was imaged in B-Mode and Non-linear Contrast Mode before/during and after the contrast administration. Samples of the brain, heart and lungs were collected and subjected to histological examination. The non-linear contrast imaging method enables the imaging of micron-sized gas microbubbles inside a rat heart. The significantly shorter lifetime of the prepared CO₂ foam is a benefit for avoiding the local ischemia of tissues.