American Association of Physicists in Medicine
http://www.aapm.org/

American College of Radiology
http://www.acr.org/

American Society of Radiologic Technologists
https://www.asrt.org/

European Society of Radiology
http://www.myesr.org/intro.php

Image Gently
http://www.pedrad.org/associations/5364/ig/

Image Wisely
http://www.imagewisely.org/

Medical Imaging & Technology Alliance
http://www.medicalimaging.org/

Radiological Society of North America
http://www.rsna.org/

RadiologyInfo.org
http://www.radiologyinfo.org/

Society for Pediatric Radiology
http://www.pedrad.org/