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Friday, November 14, 2014

A failed quench circuit?

UPDATE: 23rd Feb 2015, courtesy of Tobias Gilk on Twitter

An article in Diagnostic Imaging claims to cover "everything you need to know about the GE MRI recall." Not sure about that, but it's a step in the right direction.

UPDATE: 19th Feb 2015, courtesy of Tobias Gilk on Twitter

The FDA has just ordered a recall of over 10,000 GE superconducting MRI systems worldwide. Some news articles here and here. Based on a quick read of the early reports it does look as if the Mumbai event precipitated the recall.

UPDATE: 20th Nov 2014, courtesy of Greg Brown on Twitter

It is being reported that the quench button was disabled by GE Healthcare engineers to the point that it was only usable by authorized personnel, presumably thus requiring a specific piece of kit that neither the hospital staff nor the first GE engineers to arrive on-site either possessed or perhaps even knew about. This story is set to run and run....


No doubt you've seen this news doing the rounds:

Two stuck to MRI machine for 4 hours

There was, of course, a huge procedural failure that allowed a large, magnetic oxygen cylinder into the MRI facility in the first place. No doubt the investigation will find ample blame to spread around. But the solution to the problem is rather simple: education/training coupled with standard operating procedures to nix the threat. As procedures go it's not especially difficult. (By comparison, over 34,000 people manage to get themselves killed on US roads every single year. Clearly, we can't drive for shit. Our procedures are severely wanting in this department.) And if you're ever in doubt as to whether an item can be brought safely into the MRI suite there is always - always! - someone you can go to for an expert opinion. In my facility no equipment is allowed through the door without that expert opinion being cast.

So let's shift to the part of this fiasco that really got my attention: the claim that the magnet quench circuit malfunctioned. From the second article, above:
"At a press conference on Wednesday, a day after this newspaper broke the story, senior officials of Tata Memorial-run Advance Centre or Treatment Research and Education in Cancer (ACTREC) in Khargar said that because a switch to disable the machine's magnetic field malfunctioned, it took engineers four hours to disengage the two employees - a ward boy and a technician -- stuck to the machine, when it should not have taken more than 30 seconds."

Then, later in the same article:
"Dr Gupta said the MRI machine was bought just four years back and its last periodic maintenance was carried out by GE engineers just six months back. "We were shocked. Despite several attempts to switch off the machine, we just could not disable it. Ideally, we should have removed both of our employees in 30 seconds, but they were stuck for four hours," he said.

Dr Gupta said that while ACTREC engineers had reached the spot within minutes of the mishap, they just could not switch off the machine. The manufacturer was informed immediately, but the GE engineer who arrived after an hour too could not turn the machine off. Nearly two-and-a-half hours after the incident, three more GE engineers arrived and replaced the existing electronic circuit with a new one and then switched off the machine."

So I asked my local service engineer - from Siemens, but I would wager large sums of money that I'd have got a similar response from any other vendor - what guarantees I have that my magnet will quench in the event I need to push the Big Red Button. Here is an edited version of his unequivocal response:

"Your rundown unit will work.  It is tested thoroughly every year, parts are tested daily, and parts are tested on the fly (always).

A magnet load simulator tool is connected (in place of the magnet) every year, and the quench circuits are tested into these loads to verify function.  Yes, we push the quench buttons every year. 

In case of power failure, there is a battery backup for the rundown unit.  The battery is load tested automatically every day at 2 AM to insure it is sustaining a proper charge and capacity (if it fails this test, the scanner will NOT SCAN!).

There is a small amount of current that is always applied through the quench and switch heaters in the magnet.  Seems like a scary concept, but it is shown not to produce enough heat to activate the heaters.  With this current applied, the voltage drop across the heaters is proportional to their resistance; if this value exceeds the allowed specification (too low or too high), you get an alarm.  You heard this alarm not too long ago when the switch/quench heater connecter was corroded/wet from condensation, and this resistance value was incorrect as a consequence.  So you got first-hand experience of what happens if the heaters aren’t connected with the correct resistance.  Further, this is also tested every year . . . we simulate high + low resistances with a tool for all three heaters in the magnet to check the monitoring circuits for proper function.

We even disconnect one of the ‘quench buttons’ to be sure the system gives an alarm reporting ‘too few buttons’.  Yes, even the presence of the switch being electrically connected is monitored.

These tests are monitored with a date/time stamp (file C:\MedCom\log\MsupHistory.log).  This data is transferred via remote connection to our server, and monitored by Erlangen (automated running script, I believe).  When the Siemens Magnet experts (not Oxford!) visit for magnet service, they also download this data from the magnet monitoring system.  If the logs show this test hasn’t been run within an approx 12 month interval, a service call is opened and an engineer is dispatched to check this immediately.

Again, your rundown unit will work.  The heaters are monitored and known to be connected with the correct resistance, the switches are monitored as being physically connected, the rundown unit ‘quenches’ a simulated magnet, and the battery backup is tested, and the monitoring circuits are all tested.  And we have a quality process in place to be sure these tests/functions are carried out."

I'm happy enough with this answer, but as someone who always likes backups for everything I still asked whether there was another way to quench the magnet, just in case. I was informed that there are other ways (and I already knew of one of them) but they are rather scary and not recommended for a variety of valid safety reasons. (Personnel safety, not magnet safety.)  They might be used in drastic cases, like perhaps if a fire destroys all the quench circuitry. But this is a very different scenario than trying to rescue someone stuck to the magnet. For everyday safety I am reassured that my quench circuit will activate if the button is depressed.

Whether or not GE was really at fault in Mumbai we shall learn eventually, I hope. (I have heard rumors that some sites like to bypass their quench circuit in order to avoid having the cost of recharging the magnet should the quench button get activated. Insert your own exclamations of disbelief here because I'm incredulous.) In the mean time, this sorry saga is an opportunity for all of us to review our own procedures and take the extra moments to ensure that we've done everything humanely possible to eliminate risks. There really is no excuse.