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Background
Contrast agent selection and dosing presents unique challenges in children. The need to limit radiation exposure in pediatric imaging often goes hand in hand with shifts to alternate modality utilization, as contrast-enhanced CT has given way to ultrasound and MRI for many clinical indications. Recent COVID-related shortages of Iohexol, concerns over gadolinium retention in children, and 2022 FDA recommendations related to concerns of hypothyroidism for children under 3 years old exposed to iodine-based contrast media have emerged as recent topics of interest to radiologists.

Educational Goals / Teaching Points
1. Discussion of contrast dosing, different agents, modality optimization, and premedication regimens for children will be described. 2. Current consensus related to gadolinium will be reviewed, including strategies to avoid unnecessary contrast utilization in pediatrics. 3. Ultrasound contrast agents and their applications will be reviewed. 4. The new gadolinium-based contrast agent (GBCM) gadopiclenol will be included. 5. Recent statements from the American College of Radiology will be described and discussed.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Pediatric contrast dosing, contrast agents and premedication regiments discussed. Infants and smaller children are less likely to tolerate the fluid shifts potentially inherent to higher osmolality contrast agents compared to adults. Smaller caliber catheters required for children affect injection rates and timing of imaging. The Bedside Schwartz equation is recommended to estimate GFR using serum creatinine. Gadolinium retention, safety implications of macrocyclic versus linear, and recommendations discussed. Contrary to some myths, there is no association between gadolinium administration and sickle cell crisis. Ultrasound contrast agents and their safety profiles will be reviewed. Contrast-enhanced voiding sonography can eliminate the radiation associated with traditional VCUG while sparing iodinated contrast. Evidence demonstrates that ultrasound can identify appendicitis even in obese children, potentially eliminating the need for contrast-enhanced CT and representing one strategy to mitigate the recent iodinated contrast shortage. Gadopiclenol is a recently approved macrocyclic Group II GBCM for use in patients over 2 years old that has increased kinetic stability and relaxivity compared to current contrast agents, allowing for decreased gadolinium content. Recent American College of Radiology statements will be discussed, including those related to decreased supplies of iodinated contrast and the 2022 statement disagreeing with many of the tenets put forth by the FDA with respect to hypothyroidism. The evidence basis for the safety of IV iodinated contrast is included.

Conclusion
Radiologists face multiple issues related to contrast in the pediatric population. Appropriate selection of modality, agent, and dose is crucial to modern radiology.