Kontrastid

Kontrastid, or contrast media, are substances used in medical imaging to enhance the visibility of internal structures. By altering tissue contrast in radiography, computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound, they help distinguish normal from abnormal tissues and delineate anatomy.

The main categories are iodinated contrast media (ICM) for X-ray and CT, gadolinium-based contrast agents (GBCA) for MRI, and ultrasound microbubble contrast agents. Iodinated media are used for intravenous or oral administration and are available in ionic and nonionic forms; modern formulations are typically low-osmolar. GBCA are given intravenously to shorten relaxation times and improve MRI signals. Microbubble agents are gas-filled spheres injected intravenously to enhance vascular and organ imaging in ultrasound. In some protocols, oral or rectal contrast such as barium sulfate or iodinated solutions supports gastrointestinal visualization.

Administration depends on modality and clinical need. ICMs are common in CT and radiography; GBCA in MRI; microbubbles in selected ultrasound studies. Mechanisms include radiopacity for X-ray/CT, magnetic relaxation effects for MRI, and acoustic enhancement for ultrasound.

Safety considerations include the risk of hypersensitivity reactions and nephrotoxicity with iodinated media, and, for certain gadolinium agents, a risk of nephrogenic systemic fibrosis in people with significant kidney impairment. Rare adverse events include extravasation, warmth or nausea during injection, and, less commonly, anaphylaxis. Prior to contrast use, clinicians assess allergy history and renal function, and hydration or premedication may be used in at-risk patients.

Contrasts significantly improve diagnostic accuracy in neuroimaging, oncology, vascular, and GI imaging, and ongoing research seeks safer agents and more individualized use.