1.What is contrast agent? A contrast agent (also known as a contrast agent) is a diagnostic drug, the most important component of which is iodine. Iodine is characterized by its impermeability to X-rays, so it can be used to produce contrast in the distribution of iodine in the body when taking X-rays; or to make clear shadows of blood vessels and soft tissues that are not normally seen on X-rays to assist doctors in making reliable diagnoses. 2. Why is the use of contrast necessary? Some X-ray techniques, such as angiography, cannot be performed without the use of contrast media. In some techniques (e.g., CT), although contrast is not always necessary, the use of contrast will make the diagnostic image clearer and thus help the doctor make a more reliable diagnosis. 3.What types of iodine contrast agents are there? Generally, iodine contrast agents are divided into ionic and non-ionic contrast agents. Ionic contrast agents are divided into mono-acid monomers and mono-acid dimers according to their structure. The representative drugs are pantothenic glucosamine, etc. Ionic contrast agents have a high incidence of side effects and are poorly tolerated by the muscles. Non-ionic contrast agents can also be divided into monomer and dimer. Representative drugs include iopamidol, iotrexol, etc. Non-ionic contrast agents have a low incidence of side effects and are well tolerated by the body. The price of non-ionic contrast agents is much higher than that of ionic contrast agents. Contrast agents can also be classified according to the osmolarity of the drug, namely, hypertonic, hypotonic and isotonic. Isotonic drugs are well tolerated by the body. 4.What are the hazards after contrast agent injection? Generally speaking, contrast agents are safe for human body. However, due to individual differences in human body, some people may have some adverse reactions to contrast agents under certain circumstances, including allergic reactions and neurotoxicity, vascular toxicity, nephrotoxicity, etc., among which allergic reactions are the most common. Allergic reactions can be classified as mild, moderate or severe according to their severity. Generally speaking, all ionic contrast agents require allergy testing before use. Non-ionic contrast agents are relatively safe. According to the latest pharmacopoeia issued in China, these contrast agents do not require allergy testing before injection. However, there are some non-ionic contrast agents that still require allergy testing in their instructions for use. For those who have a history of iodine allergy, although it is not an absolute contraindication, great caution is needed when injecting. Therefore, for insurance purposes, doctors usually treat them as absolute contraindications and must have the patient sign an informed consent form. It should also be used with caution in the elderly and young children with high risk factors, in patients with bronchial asthma, cardiac or hepatic and renal insufficiency, hyperthyroidism, or when the patient’s serum creatinine exceeds 3 mg/dl. Generally, patients should be observed for 1 hour after contrast, as there are occasionally delayed allergic reactions. 5.What is contrast nephropathy? Contrast nephropathy refers to acute kidney injury caused by contrast, and is usually diagnosed by an increase in serum creatinine of more than 0.5mg/dl compared to the pre-contrast level, or an increase of 25% compared to the basal value. With the increasingly widespread use of contrast technology, contrast agents rank 2nd only to antibiotics in the etiology of acute renal failure due to drug toxicity. The prognosis of contrast nephropathy is generally good, most patients can return to normal renal function within a week after contrast, but some patients may have residual renal impairment and even need to enter maintenance hemodialysis or abdominal dialysis stage. The risk factors of contrast nephropathy include renal insufficiency, diabetes mellitus, congestive heart failure, insufficient effective blood volume, and application of high-dose contrast media, etc., while hypertension, advanced age (>65 years), and proteinuria (>2g/d) are regarded as secondary risk factors, among which pre-existing renal insufficiency combined with diabetes mellitus is the most important risk factor. 6.How to prevent contrast nephropathy? Contrast nephropathy can be prevented, the key is to do a good job of patient screening, ordinary patients generally do not need to worry too much, and high-risk patients consider whether they can be replaced by other examination methods (such as ultrasound, MRI, etc.). For high-risk patients who must have imaging, the causative factors should be actively corrected prior to imaging. The more recognized measures that can prevent the development of contrast nephropathy are hydration therapy (i.e., preoperative and postoperative administration of 0.9% saline for adequate rehydration) and the application of hypotonic or isotonic nonionic contrast agents. The effectiveness of other drugs (e.g., N-acetylcysteine, sodium bicarbonate, fenoldopam, prostaglandin E1, etc.) needs to be verified in large-scale randomized clinical controlled trials.