EBME Forums Forums Maintenance Spare Parts CD 38 collimator

Hi has anyone removed a Picker CD 38 collimator, type R20MC? I have a unit in a vet clinic and the collimator "catches" as it is rotated. The manual does not include the collimator.

With a machine that old, Phil, you should count yourself lucky if that's the least of your worries!

But the problem you mention should be easy enough to identify by inspection ... slight damage, or simply worn out!

You may be able to improve matters (mechanically), but without seeing the thing it's difficult to be sure.

But ... how good are the radiographs? And does the collimator ... er, collimate (accurately)?

The output is fine as is the field size and alignment.

The problem is dropping the collimator slowly to allow inspection. I suspect there are leaded fingers inside which are some how catching during rotation, but I have no drawings to refer to.

Yes; maybe some "grit" (or similar) in there.

If you're there alone (without an extra pair of hands), try resting the tube and collimator on something (pillow, chair ... whatever is available) before releasing the collimator.

Sounds like a screwdriver job, Phil.

No problem with the mechanics, just hoped someone had actually disassembled the device or had collimator drawing of what is inside.

Yes; I had gathered that. But either way you'll need to open it up to clear (clean, most likely) the fault.

So you'll know soon enough, Phil.

Trouble is, later on (after re-fitting) you'll probably need to fiddle about getting the alignment right again.

Those old collimators - or Light-Beam Diaphragms, as we used to call them - (and probably even the current ones) were much of a muchness. I have opened up a few in my time, but (again) that was all a long time ago now. You just need to be carefull.

In fact, Phil, I wish I were there with you!

Morning, It's difficult to tell or remember it but going back to basics,

- you say rotation - is this internal leaves/iris or whole body rotation on the flange?

Hope you don't mind me saying but to build on Geoff's comment, to inspect the collimator action, you can compensate the weight of the collimator to allow inspection of the leaves by putting similar weighted lead-rubber aprons on the arm but also tie a rope incase they fall off (covering my back here).

BW Ian

I suspect "whole body rotation" ... but Phil isn't on site until Friday, apparently; hopefully all shall be revealed then. How about some photos, Phil?

If things are nice and quiet there, he should be able to quickly assess the situation just by putting an ear to the collimator whilst rotating it and (or) twiddling the knobs. Also by physically rotating the tube (if need be) and peering through the bottom of the collimator whilst twiddling away.

BTW Phil, you might want to check (and maybe change) the lamp whilst you're at it. If so, you'll need to carry one with you (might save another journey).



Meanwhile Ian, your sound advice reminds me of the time I single-handedly changed (removed, and swapped it with a "known good" one) an x-ray tube on a major Philips unit - without ropes, nor any other (safety) aids. Not in the UK, I hasten to add. But anyway, "don't try this at home, folks"!

Of course, I was much younger (not to mention, stronger) back then.

Phil should be OK with just the collimator, though. If removal proves to be necessary, it's just a matter of being able to "catch it" when the final screw is released! A job for two pairs of hands, you might say - but hardly any weight involved (the normal locking lever should suffice to hold the tube in position).

Geoff, not been on for a while so hi

Old fart time - I realise you're reminiscing but I wouldn't advocate any practices without safety tie off's etc - one engineer had his jaw broken by an old spring-balanced film changer that he didn't restrain.

I know what it was like then - I have much worse skeletons in my cupboard BTW.

On topic - will keep an eye out for the reply.

Is it on a CAT scanner?