Mac users interested in Irad dicom viewer generally download:
iRad is a DICOM viewer exclusively written for MacOSX.
The application features fast OpenGL graphics, uncompressed, JPEG, and RLE color and grayscale DICOM images supported, multi-images view with series synchronization, references lines and autohoming for comparing series, distance, point, and ROI measurements, oval, rectangular, and polygon selection tools.
