In this version you will find a few improvements in length measurements:
-imager pixel spacing is used when available (which is often the case for XA images)
-US calibrated regions support (length or other parameters such as time, velocity, depending on the region)
-support for manual length calibration
-other small improvements
Download here:
http://www.radiantviewer.com/startdownload.php?f=rc
And here's the updated manual section:
http://www.radiantviewer.com/betamanual/index.html?length.htm