Radiocontrast

Radiocontrast refers to substances used in radiologic imaging to increase the contrast between different tissues by altering the attenuation of X-rays. The most widely used are iodinated contrast agents for X-ray–based modalities such as CT and angiography, and barium sulfate for fluoroscopic and gastrointestinal studies. In addition, gadolinium-based agents are used to enhance magnetic resonance imaging (MRI), though they do not affect X-ray attenuation.

Iodinated contrast agents are water-soluble compounds administered intravenously or intra-arterially. They can be ionic (older) or nonionic, and may be high-osmolar, low-osmolar, or iso-osmolar. Nonionic low-osmolar and iso-osmolar formulations reduce adverse effects compared with older ionic preparations. Barium sulfate preparations are suspensions used for imaging the gastrointestinal tract, administered orally or rectally. They are not suitable for intravenous use due to the risk of embolism and poor absorption.

Safety and adverse effects: Allergic or hypersensitivity reactions can occur with iodinated contrast, ranging from mild symptoms such as warmth, nausea, or a metallic taste to rare but severe anaphylactoid reactions. Nephrotoxicity is a concern, particularly in patients with preexisting kidney disease, leading to contrast-induced acute kidney injury in some cases. Risk factors include reduced renal function, diabetes, dehydration, high or repeated doses, and concomitant nephrotoxic medications. Preventive measures include proper hydration, using the lowest effective dose, preferring low- or iso-osmolar agents, and checking renal function beforehand. In selected cases, premedication with corticosteroids and antihistamines may be considered. Gadolinium-based MRI contrast agents carry a risk of nephrogenic systemic fibrosis in patients with severe kidney impairment, so caution is advised in advanced CKD.

Radiocontrast use requires assessment of allergy history, kidney function, and imaging needs to balance diagnostic benefit with safety considerations.