Tuesday, August 09, 2005

Hui 4th week----Story of the pressure regulator..

I have been working on a regulating part for inflating cuffs for peripheral MRA. The cuff is placed around patient’s legs to prevent venous contamination and also movement during bolus chase using contrast agent. Currently the cuffs is hand-inflated. Leaking from connecting joints cause the pressure decrease slowly, which cause venous contamination (contrast agent flow into venous vessels) and leg movement which deteriorated images.

We need the output pressure to be stable 60mmHg (Around 1Psi) with error within 5 mmhg. Not many manufactures are making pressure regulators in such small range (most are for hundreds or thousands of Psi). After searching the internet and calling the manufactures many many times, I have had everything ordered last week.

We first intend to use the regulator with an oxygen tank that is available in every hospital and usually there is one just sit in the magnet room. Also there are oxygen outlets from the wall in the Weill Cornell Hospital.However to be safely used with the gas oxygen, all the parts have to be oxygen clean, which means suitable for use with pure oxygen. Only oxygen compatible greases can be used in oxygen-clean parts. Thus we need to make special order to ask the manufacure clean the part. However, it not only takes longer time, increase the expense, also requires that at least 10 pieces to be ordered. Fortunately we later found out that over at Columbia Hospital, they not only have oxygen but also have medical air outlets on the wall. Medical airs are just filtered air and must be much cheaper than oxygen (my guess). Even better!

Another consideration when picking the regulator and all the fittings is, they better are non-magnetic because there are a huge magnet in the scanning room. Although B decrease quickly with increased distance from the bore, it is safety requirement that no loose magnetic objects allowed in the scanning room and better anything in the room is nonmagnetic. So I was seeking for parts made from brass, aluminum, plastics, or non-magnetic stainless steal.

Thus I was able to test my non-oxygen-clean devices at Columbia. And it turns out to be great. The pressure is controlled precisely at 60mmHg. Leaking is compensated and legs are kept still.

Currently I am still optimizing the system. I just ordered a compact regulator with a compromised precise for test, and also trying to find non-magnetic alternatives for the knot, some screws in the regulator, which are magnetic.


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