Final answer:
The ARRT provides post-primary certifications in specialized areas of radiologic technology, which require candidates to be registered in a relevant supporting discipline first.
Step-by-step explanation:
The American Registry of Radiologic Technologists (ARRT) offers various post-primary certifications for individuals who wish to specialize in certain areas after their initial certification. To be eligible for post-primary certification, candidates must already be registered with the ARRT in the appropriate supporting discipline. These certifications allow technologists to demonstrate their qualifications in advanced practice areas such as mammography, computed tomography (CT), magnetic resonance imaging (MRI), and others, enhancing their career opportunities and expertise within the field of radiologic technology.