The DMX (Digital Motion X-ray) is a x-ray in real time. It represents the next evolution of normal x-rays and combines digital with optical technology. It offers patients the advantage of scanning the spine in extreme positions and in real time. DMX is carried out under normal weight bearing, while standing or sitting and is used to diagnose ligament damages that normal static x-rays miss.
There are no scientific publications about the safety of this technique and the radiation exposure is not clear. Most information I could find online are from the manufacturer of DMX.
Every x-ray comes with a radiation exposure, but DMX seems to have a significant higher amount which is why some doctors highly argue against it. On the other hand other physicians support the usage especially for the detection of ligamentous injuries of the cervical spine.