Magnetic resonance in pediatric and adolescent neuroimaging. With improved availability and a practical understanding of the principles of utilization, MRI will continue to replace CT and US in pediatric neuroimaging, just as it has impacted upon the more invasive modalities. In general, US remains the procedure of choice for screening of fetal and infant CNS abnormalities, and CT continues as the principal screening modality beyond infancy and especially for acute, emergent presentations. MRI has now emerged as a primary option for screening as well as for more definitive assessment of many intracranial and most intraspinal conditions. 