Stuff you always wanted to know about medical engineering, but were afraid to ask.

Hospital Hospitality

2007-05-03T17:38:00.000+10:00

It's nice to be appreciated for what you do.

If you manage a busy x-ray or medical imaging department, the last thing you want is equipment breaking down. Turning up on time and fixing the problem quickly reduces the inconvenience to a minimum. Stress levels tumble and staff quickly fall back into routine. Patients too, hate to be rescheduled.

So in the midst of turmoil, the engineer often arrives to hear "We're glad to see you". It's much nicer than "What took you so long?" If the problem can be diagnosed without a lot of fuss, much the better. If the fault is severe, honest communication is critical.
"Mr Manager, your equipment has a serious problem. It will need a new component that will take until tomorrow to arrive. I'll be back just as soon I have it. If there's any problem or delay I'll let you know straight away". So good, accurate information is essential so their timetable can be rescheduled. That information is then passed on to patients.

The engineer is an important part of a medical imaging department, even though he's not often seen. If I have a spare moment, I pay a visit to the department a couple of days after the service call to see that the equipment is behaving as his should.
This can create two responses. The manager has a momentary worried expression, wondering why you've called by, because he can't remember logging a service call.
"Just a quick visit to see if everything's still going all right" is generally enough to change the expression to relief. After that, it's nearly always appreciated that you cared enough to follow up your work.

It's a good ploy to turn up around morning or afternoon coffee break. Medical imaging staff know how to live well and bring cakes, pies and other niceties. Often you're invited to join in. It's also a simple gesture to bring along some goodies of your own to share.

Yes indeed. The little niceties of the workplace help make the difference between a great place to spend a portion of your day, or a place you turn up to.

Next time,

Parking Pains

2007-05-02T23:54:00.005+10:00

Finding a place to park is a pain.

Hospitals in major centres are easy to get to from every direction. The major hospitals are generally big; very big.
Staffing a big hospital needs the population of a large town. And staff need a place to park. So the car parks are big too.

The first shift of the day starts at around 7.00 am and staff start to arrive as early as 6.00. By the time I turn up, the sun is well above the yard arm and the car parks are full. So begins the spiral ascent. Level 1, not a hope. Level 2, about the same and so on up.

Reaching the seventh level, all hope of finding a space (all I need is one) is extinct. Your neck aches from swivelling back and forth looking for that elusive piece of bare concrete between two lines. Meanwhile, the customer has rung your office demanding to know why the engineer is late.

Consider that my expertise is not the only thing needed on site. The job needs tools, test equipment and parts as well. The prospect of descending those stairs in the tight stair wells, weighed down with the extra bits is enough to spoil lunch. Oh! That's right. You forgot lunch today. There's another load on the mind.

Forget about the lifts. They're so slow, you need to shave again before facing the customer! Besides, walking stairs is better for the cardiovascular system if you believe the experts.

There are rules in a car park, unwritten rules. For example, there are six other people looking for the only space in the whole complex. You spot the space at the same time as the other parker. So the first to indicate their intention, gets the space. I once almost broke my indicator switch in the rush to flick it on.
Don't you hate it when you see reversing lights in the rear view mirror? Someone's coming out just as you drive past.
Another rule; if you're turning into a space, smile and wave to the parker who missed out. Make sure not to look smug. You're likely to attract a finger salute.

And who pays the parking fee? Customer or company? Great relationships can be destroyed over who will pay for parking. In some city car parks though, it's cheaper to pay bail than pay for parking.

So if you know a better way of providing service to places with monster car parks, let me know. I'm sure there's a fortune to be made.

Next . . . Hospital hospitality.

Rotor for a Friend

2007-04-26T22:08:00.011+10:00

When I began my career in medical engineering, the company I worked for put all their engineers through extensive training. Training included a stint in an X-ray tube reloading facility.

We had the chance to repair x-ray tubes for CT scanners, cath labs and general x-ray rooms. The number one enemy of an X-ray tube is heat. Of all the energy that is pumped into a tube, 99% is converted to heat. The rest is X-radiation. The main problem is that the heat has to be carried away. But after many hours of enduring intense white-hot heat, the glass envelope just says "that's enough." The envelope then generally cracks and the vacuum inside the tube is lost. That's the end of the tube.

The part that cops the most heat, is the rotating anode, or rotor. It spins at very high speed and present a large surface area to the electron beam that produces the x-rays. Lots and lots of heat is generated. To cope with the punishment, the rotor is made of tungsten. It has a high melting point and doesn't stretch or expand too much. Good stuff, eh?

Tungsten is a dense metal. The shape and weight of a rotor feels strangely heavy in your hands. How a heavy rotor spins so freely holds a certain fascination too.

So where's all this leading too? On a previous training trip to the USA, I made friends with an engineer from Washington state. He was very interested in having a rotor for a paper weight on his desk. I transported one from Australia to the USA on a later training trip.
Passing through security at the airports was interesting to say the least. I had the most trouble in San Francisco. Security pulled me aside and asked many probing questions, mostly about who I was, what I was doing in the United States, could I pose a threat to national security? The security blokes were fascinated with the rotor. I'm sure they wondered about the dense object in their X-ray scanner.

My US mate was amazed that I'd remembered the rotor when I presented it to him. He really enjoyed the gift and it makes a nice conversation piece in his office.

Next time, Parking Pains

Electronix gone camping

2007-02-19T13:20:00.001+10:00

Our family recently took up camping, an extra-curricular activity involving the whole household.

To group the whole family is perhaps ambitious. I decided it would be good to take up again, and convinced the others of the excellency of the idea.
With the benefit of hindsight, it's worked out pretty well. We've had some great nights away.
A campfire on a balmy night, away from phone, TV and pressures, is somewhere close to paradise.
I resolved to make it enjoyable, especially for my wife. The idea of small creatures with six or eight legs, or long scaly ones with none, sets her thumbing through motel magazines that tout 4 or 5 stars.
That meant expending some dollars on a few creature comforts. Fair enough. Camping isn't fun when you wake up in the morning with bruised hips or spent the night shivering.

And what do you do when the sun is shining on the other side of the planet? Light is nigh on essential for enterprises like cooking, reading and just getting ready for sleep. Do we go for gas or batteries?
We cook with gas at home, so cooking with gas under the open sky is as natural as the smell of cow pasture. But lights?

When we were kids, my family did a lot of camping. The hiss of a gas lantern brings back memories. I loved to watch the big moths. They'd flutter drunkenly out of the grass, drawn magnetically to the light. They'd do a few reconnaissance loops around the lantern, then land on the hot cover of the lantern, exiting this life in a cloud of moth dust. Some would even make a tiny, satisfying 'tzeet' sound as they fried.
My brothers and I would watch breathlessly, in anticipation.
"Here comes another kamikaze. He's coming in . . . ooh! Another one down, captain."
The cane toads liked the moths too. A couple would be sitting quietly in the glow. I guess lightly roasted moth, gave a particular crunchy texture to their snack.

But I digress. Gas is OK, but battery power is the way to go. There's just so many uses for battery power. Having recently changed the battery sets out of a couple of mobile x-ray units, I had plenty to choose from.
These batteries are the big sealed lead-acid types. Plenty of grunt. Safe and clean; no toxic chemicals to worry about. No longer good for running x-ray equipment, they're ideal for new life in the great outdoors.

The boaties have the whole portable power business down pat. I picked up a battery box from the boating warehouse for very little money. Two batteries fitted in almost as if the box was made for it. By connecting them in parallel, I had a power supply capable of jump starting a small car.
And that's not as silly as it sounds!
Who knows when you (or a fellow traveller) might be stranded in need of a backup battery?!

Jaycar claim to be "number one for electronic kits". I checked out the claim and they're right. (Wander in sometime and wonder.)
I picked up an inverter kit to run a fluorescent light from a 12V battery. Works a treat! The fluoro just sips from the battery and gives hours of cool, white light. Even the moths are happy. They just fly around in ever increasing numbers without coming to mischief. (No animals are harmed in the making of our campsite.)
From another source, I found a battery charging kit. This trickle feeds the battery without over-cooking it. The battery pack just sits in the shed, being topped up whenever it needs it.
Off eBay, I picked up a small inverter that converts 12V to 240V. Fantastic for charging camera and CB radio batteries. It could even operate a laptop, but that's not the point of camping, is it?

Another very handy electronic device is an auxilliary battery switch. When connected to the car, it senses when the car battery is fully charged, then switches the car's alternator to charge the auxilliary battery. With a suitable plug, the battery pack can be left in the car or disconnected when we need to run our lights.
Warning! Never run the car battery flat when you're a long walk from home.

I fitted a couple of sockets. You know the ones. They're the same type used for cigarette lighters in most cars. When setting up camp, we plug in a little pump that blows up our air mattresses. When pulling down the camp, the same pump sucks the air out of the mattress, making it easy to fold and store.

That's all well and good, but how do you know the state of the battery after pressing it into so much useful service? A digital volt meter of course.
I found this on eBay as well, for a few bucks. Great little addition to the battery pack. Just press a small button and the meter reads out the battery volts. 13.8 volts; charging. 12.7V; operating. 12.3V; uh oh! Time for another feed of electrons. Neat!

My next project for the battery pack has zip to do with electronics. The pack is small but hideously heavy. A set of wheels and a retractable handle, like an aircraft carry-on bag, should prevent crushed vertebrae.

Next? Rotor for a friend.

Flash and bang.

2007-02-19T01:03:00.000+10:00

My next yarn was to be about flash and bang. Here it is as planned, if somewhat late.

An x-ray generator consumes a lot of energy to produce x-rays. Generally, the generator is connected directly to the building power source that supplies the energy that makes the mysterious rays. A power station right next to the hospital is ideal.

This is a bit technical, so stay with me.
First of all, a circuit in the generator charges a bank of high capacity capacitors. Sounds obvious but the capacitors are very dangerous when charged.
Following that circuit is a control section that releases the enormous energy stored in the capacitor. This is done by a device called an inverter.
The direct current released from the capacitor is inverted to a high frequency (15kHz) alternating current at about 350V. This is fed into very large transformer, that steps up the voltage to around 80 to 120 thousand volts (or 80,000 to 120,000V). That's a lot of volts, enough to make electrons jump across a gap inside a glass vacuum tube, slamming them into a tungsten anode with such force, that energy is released in the anode as x-rays.

I was called to investigate why no x-rays were being generated. I found the inverter devices in the generator were faulty, very faulty. The inversion is the job of six monster transistors. Two transistors had failed catastrophically, blown open by the in-rush of energy, popped like corn. I replaced the transistors, after having to import them from overseas. Two were gone, but I replaced all six. It was an old generator and parts are hard to find.

Having powered on the generator again, still no action and no x-rays.
I began to investigate the inverter control circuit. I probed the components with my volt meter. Suddenly, an intense flash dazzled me. The accompanying explosion slapped me to the floor. I sat dazed, everything a weird shade of yellow and all around, strangely quiet.

The next sensory experience was a concerned staff member who had rushed to see if I was OK.
"Are you OK?"
Like an idiot, I replied "Is who OK?"
As it turned out, even though the power was turned off, the capacitors were still in a state of charge. They dumped their walloping energy across my meter probes. I'd carelessly contacted exposed cables. Probes are usually made of brass, an excellent conductor. When a lot of current suddenly rushes out, brass probes turn to vapour. Mine vapourized with a blinding incandesence causing a violent expansion of super heated air, my own clap of thunder. I thank God it wasn't me who was crisped.

I looked at the time. 5.30PM.
"Enough for one day" I thought and pledged to wait until the capacitors were quiet and resting before disturbing them again.

Next time, electronics goes camping.

At it again

2007-02-19T00:53:00.000+10:00

This blog was going to be a mind exercise; an exercise in the discipline of writing a few words each day, just because I have something to say. It's for me you see. Nothing more.
Was it really June last year for the most "recent" post?

Like routine physical exercise, diet and other good habits, it seems I've a ways to go yet. Does arriving at work on time and getting the necessary things done, count?
How I admire the achievements of people who study to gain multiple degrees, sit on the boards of committees and corporations and still have time to raise a family.

There is obviously a level of drive blended with passion that fuels over-achievers. Friends tell me that I'm something of an over-achiever, so it's probably not a good thing to beat up on one's self in a public blog.

Let's see what I can achieve tomorrow.

Xray on de move, wit de fault.

2006-06-12T02:59:00.000+10:00

It reminds me of a riddle I used to ask my kids.
Make a 12 word sentence with these words. Defeat, deduct, defence, detail.
Answer: De feet of de duck go under de fence before de tail.

Honestly, I thought it was clever, even if the kids thought Dad had lost it.

This time, I had a mobile xray machine (xrays on de move) that had a drive fault (de fault). What a cow of a problem this was!
Turn the key, press the push bar and the machine would trundle away quite happily. After a while, it would hiccup, splutter (metaphorically) and roll to a stop, throwing up a Drive Fault message. The machine is very heavy as you would imagine. It carries a series of batteries, like car batteries, an xray generator, plus big drive motors to move the machine around.

Looking through the service manual gave some clues as to what the problem might be, what sections of the machine to look in and some tests to try.
None of this information was any good. Drive Fault error.

Fortunately, there is an identical machine in de hospital (oops) so I could swap parts between machines. The problem was in the push bar. It has miniature sensors that detect push pressure. That tells the drive logic to deliver battery power to the drive motors.

The push bar had been pushed one too many times and caused the sensors to fail.
A new push bar and presto, xrays on de move, widout de fault.

Next, a tale of flash and bang.

Over exposed - not enough ion

2006-06-12T02:36:00.001+10:00

An ion chamber is a little capsule of gas, about the size and thickness of a business card. When the gas is exposed to X-rays, it ionizes. That means some of the gas atoms have electrons knocked off them, creating an ion. The ion chamber has a high voltage applied across it.
Because the ion now has a positive charge (fewer electrons), it rushes toward the negative side of the chamber, created by the high voltage. A small electrical current is produced. We can take that current and measure it. When the ion chamber receives enough xrays, ie enough ionization, the measuring circuit tells the X-ray generator, "that's enough X-ray thanks" (measuring circuits don't say words, but you get the drift) and switches off the X-rays.

This is actually a very good thing. If you're having an X-ray taken, you want that X-ray to turn off when the X-ray film is properly exposed. That means the radiologist (doctor) gets a good view of your broken collar bone, lungs, skull or whatever, and you don't get ionized too much. Yep, you ionize too when exposed to X-rays. But don't worry. The amount of ionization is much, much less than the cosmic rays you're exposed to while flying in a plane.
So to make a good exposure, the ion chamber is placed in the X-ray beam, and it's adjusted to turn off the X-ray generator when it receives enough X-rays to make a good exposure on the film. The X-ray beam starts at the X-ray tube, then passes through you, then the ion chamber, then the film.

So I was called to investigate why films in this particular room were always dark, ie too much X-ray. You're way ahead of me here. You've probably already guessed that the ion chambers weren't working. Why was that? Because someone had unplugged the circuit that measures the current from the ion chamber. It wasn't me I promise.

So plugging the circuit back together fixed the problem.

Next, Xrays on de move, wit de fault.

Light's on, credit's good.

2006-06-12T01:49:00.000+10:00

Today, a ceiling suspended xray tube wouldn't lock into its central position.
To explain, in some general xray rooms, the xray tube (the part where the xrays originate) is suspended by rails from the ceiling. The tube can be moved in the X, Y and Z directions, that is, up/down, left/right, back/forwards.
To make it easy for the radiographer to make an xray film, the xray tube generally locks into a position that centres it over the film container, called a buckey. Centre of the film (and the patient) is then easy to locate, every time a film is exposed.

On this job, the central position lock didn't operate. My job is to find out why and fix it.
Using a ladder, I climbed up to a point where I could see if the index mechanism was actuating the lock. In many cases, it's simply a switch that operates as it passes a bump or groove in the suspension track. But not on this job.
I discovered that this particular room has a small infrared light beam, that reflects off a reflective dot stuck onto the suspension rail. As the light passes by the dot, a sensor next to the beam detects the reflected beam and triggers the lock for the centre of the buckey. A tiny little red light comes on at the sensor when it detects the beam. No little red light came on as the beam passed by the reflective dot. What gives?

What could I use as a mirror to test if the light beam was present. I needed a tiny little mirror about the width of a pencil. Where do you find one of those? I've seen one somewhere before. Aha! I remember that my American Express card has a very reflective strip on the back. And it was in my back pocket, saving a trip down the ladder.
Waving the credit card across the light beam . . . . clunk, the lock engaged. The little reflective dot had gone dull with age. Now how to fix it? Where could I find a bit of reflective something. No, my credit card has business most places except stuck to the suspension rail in an xray room.
A trip to the vending machine in the hallway; a packet of chewing gum with silver wrapper, a bit of sticky tape and viola, problem solved.

Now; if shining a light on my credit card could fix more problems. . . .

Next, Over exposed; not enough ion.