View Full Version : X-Ray System/Patient Collision

James R Harvey
08-14-1992, 11:05 AM
Comments to
Jonathan Jacky - University of Washington, Seattle, Washington 98195

It appears from Jon's comments that a tremendous responsibility is left to
the operator as to the prevention of collision between a system and the
patient. I've asked before if systems can collide with patients or if
patient tables can strike the floor or other system components and the
answer I often receive is "we would never do that; that's dumb!" That's
right but it still happens.

I suppose the difference is what you are trying to achieve: Collision
Avoidance or Collision Detection. Clearly, Collision Avoidance is the
better approach but it leaves open the issue of liability. On the other
hand, Collision Detection recognizes the fact that collisions will occur
and attempts to prevent serious injury. I think it also makes the system
more user friendly in that "false detections" are reduced.

As for a ring around the image intensifier or x-ray tube, these do not
protect the system/patient against possible collisions between other
components, such as the inside of the c-arc of some systems. Also, what
happens when the user has arm boards, IV poles and the like in the

I would seem that the most "fail-safe" method should be used. This appears
to eliminate software methods of collision avoidance.

As for a deadman switch, there was a very recent FDA Recall on a system
that had about 3 seconds of coast after the deadman was released.
According to the FDA, this violates the regulations. Granted, 3 seconds
seems like a long time but what is reasonable? Could the FDA require
something like 0.5 seconds? On large systems, this could require many amps
of motor current. After all, you don't stop a freight train on a dime.

For a while, it seemed the industry was working toward having everything
counterbalanced. This may reduce the forces available from the drive
system but does nothing for the inertia. In fact, a counterbalanced system
appears to have twice the intertia as a non-counterbalanced system.

As for the mentioned protective mechanisms (mechanical stops, deadman,
detection rings, etc.), these are required by UL 187, IEC-601 and CDRH 21
CFR. Even with all of these, collisions still occur. The industry seems to
be working toward more sophisticated methods.

Is anyone aware of what these are?