actually Radiant viewer displays length measurement tags with this format:

“mm size (number of pixel)” i.e. 20.8 mm (24.9 px)

So if you try to do vertebral morphometry (either on an X-ray or an MR image) you will encounter some issues...

As you can see from the screenshot:
http://simplest-image-hosting.net/jpg-0-morphometry

length measures do overlap over each other mostly because of the “pixel number” information after the mm size information.

I suggest to get rid of the pixel size info in the measure tag and to display just mm...

doing this would probably prevent overlap of tags and avoid annoying crowding over the images.

Moreover i think that pixel size information is probably unnecessary, if not useless, since when you measure a lesion or a vertebral height, you just really wanna know how many mm is it...

IMHO nobody really cares about how many pixels is it (whose number is always variable and depends on the acquisition matrix of your image)

Do you think that is possible to remove the pixel size information on display or at least to make it optional?

You're probably right, I think that only millimeters will be left as default units.
Other solution would be an automatic repositioning of labels.

I think pixel should be removed at all...
think about giving a clinician a key image with size expressed in mm and pixels... it could confuse them.

regarding label position, I thonk the best thing would be make them movable...

in Siemens MRI and CT software once you draw a lenght measuse, you can then move the label in the place you desire, in order to avoid crowding

the only situation where I would leave pixel measurement on the labels is when you deal with curved MPRs from CT or MRI, in which length measures in mm are unreliable because of the distortion of the images

actually in these cases Radiant already shows just pixel size with no mm measure,