I'm Radioactive!

Actual sign in the hospital.  I am annoyed a bit by being referred to as "material"

Not long ago, I was radioactive.  I know, many reading this will want to point out that we’re all radioactive.  Stuff in our bones.  In our blood.  It radiates.  But that’s not what I’m talking about.

I was really radioactive.

Let’s back up a bit.  As I write this, I’m 61, and have a family history of clogged arteries, heart attacks, angioplasty, stents and bypass surgeries.  After reviewing this information and my own health situation with my doctor, she recommended that I get a “stress test”.  So I signed up for a “Nuclear Exercise Stress Test”, in the radiology department of my excellent local hospital.

A Nuclear Exercise Stress Test is a procedure that provides a comprehensive view of how your heart is working, in particular how it is working under stress.  It involves an obtaining an electrocardiogram (EKG), obtained under stress (a treadmill that is gradually inclined as the test progresses) to check the heart’s ability to manage high-work situations, and it involves a Gamma Camera.  That’s where the radioactivity comes in.

Gamma cameras are one of those “scanners” that you hear about, which use nuclear imaging technology to build and piece together many two-dimensional images to create a 3D image of your heart.  This is incredibly useful for determining if the heart is diseased or damaged in any way, or if it is suffering from not enough blood, or... just about any issue that it might have.

In order for the gamma camera to take these pictures, it needs there to be gamma rays coming from the body being imaged.  So, to give the camera something to work with, they made me radioactive.  Really radioactive.

The specific radioactive isotope that was used is a material called technetium 99m.  This is used because it emits gamma rays (remember, the camera needs that), and because it has a very short half-life (6 hours or so).  This means that it lasts long enough to provide gamma rays for the gamma camera to see, but not long enough to deliver anything close to a harmful dose of radiation to the patient.

Because technetium-99m is so short lived, none that was here when the world began is left – even the relatively long-lived isotopes of this element, with half-lives as log as 2.6 million years have decayed completely in the billions of years that our planet has been around.  And of course, anything with a 6-hour half-life is really long gone.  So, to get technetium-99m, we need to create it.

Wait.  Create it?

Yes, create it.  And to do this we need to fission (split) some atoms.  Bigger atoms than technetium.  And that usually requires a nuclear reactor these days.  What we actually create in the nuclear reactors, though is a precursor isotope of the element molybdenum, molybdenum-99 (AKA moly-99 for those of you who, like me, have trouble pronouncing “molybdenum”).  Moly-99 is (sometimes) what you get, about 6% of the time, when you split a uranium 235 atom.  Splitting atoms requires neutrons, and right now we use nuclear reactors to get those.  The Moly-99 created in these reactors (there are only a about a dozen of them in the world) makes its way through the supply chain to a distributor to the local hospital that will use it.  At that point, the technetium-99m can be stripped out chemically, and mixed with a pharmacological agent selected such that it will carry the technetium-99m to the organ(s) in the body that the technicians wish to observe with the gamma camera.

This is a “just in time” supply chain, of necessity.  The Moly-99 will decay away in a relatively short time and soon it will no longer be possible to extract any more technetium-99m from it.  At that point the vessel in which it was transported is returned to the facility that created it, where it is processed and ultimately “recharged” for the next customer.

Back to me.  On the day of my procedure, I checked in, and was handed off to a radiology technician.  He walked me through a waiting room in the radiology department, to a seat in a chair that was partially shielded from the rest of the waiting room by walls.  He had some stuff on the counter there, including a small, shielded container that has the technetium-infused solution that they would put into me.  This is when I got out my Geiger counter.

Wait.  A Geiger counter?

Yep, I brought my Geiger counter.  I had actually mentioned it to the technician on our way over.  His response was similar...

My counter, which I had turned on (the audio “clicking” was enabled) was reporting low-level, background radiation (there is always radiation around, from rocks, people, space etc.).  Just a couple of clicks per second, pretty tame, and normal.

The tech got out the solution and loaded it into his syringe, preparing to inject me.  At this point, my counter was a couple of feet away (in my other hand), but had livened up a lot once he opened the shielded container containing the technetium-99m.  He then told me, matter-of-factly, that “if that thing doesn’t go crazy now then it’s broke”.  Indeed, when I brought it over near the point in my right arm where he was injecting the solution, the clicks turned into a constant buzz.  Holy cow.  I was radioactive.

Here's the setup, used to inject a bit o' The Hot Stuff into me.  Twice.

Speaking of cows, it is my understanding that the container holding the Moly-99, when it is being prepared to extract the technetium-99m, is referred to as a “cow”, and extracting the technetium-99m is called “milking the cow”.  So, there you go.

I was then given a seat in the waiting room and we waited for the solution to make its way to the place we needed to image (my heart).  After about 35 minutes, the took me into the next room, where the gamma camera was waiting for me.

This is the gamma camera. I didn't catch the brand or model. You're slid in to be by those two boxes on the left and top, and then they rotate around you, a tiny bit at a time, for about 90 degrees.

The gamma camera is one of those imaging machines that goes around you, while you lie down.  In this case I had to lay still for about 15 minutes, while it snapped hundreds (I am imagining) of 2D images and feeding them to a back-end computer that would assemble them into a rotatable, detailed 3D image that would show the doctors what they needed to see.  This may have been the most difficult part for me – laying still for 15 minutes.  The camera machine consists of a platform to lay on, and a couple of big boxes that you slide under which contain the gamma detectors.  These boxes continuously are repositioned slightly during the procedure, to “take pictures” at all the necessary angles.  Fortunately, I was not “fully enclosed” in the machine as is required with some other types of medical scanning, so there was no risk of claustrophobia.

The stress and EKG part was next.  They took me over to another room with a treadmill and a heart monitor, shaved some chest hair (not much to do there) and stuck a bunch of electrodes onto me.  They put me to work with a specific heart rate target, and logged a bunch of data.  I was breathing pretty hard at the highest point but they did not have to cart me off to the OR like happened to my father.  I remember thinking that if I were riding my bike and I was working this hard, I’d slow down and get there later, for sure.

The EKG readout screen.  I'm sure this is all important.

Once done with the EKG I was taken back to radiology and they gave me another blast of technetium-99m and put me through the gamma camera routine again.  This provide them with more data, presumably to get insight into how my heart and the arteries feeding it were performing under stress.

That was it.  However, I had no end of fun over the next couple of days showing anyone around me how radioactive I was, using my handy Geiger counter and radioactive body.

Here's me, after I got home, in my "Melty" tee shirt, showing up with over 60 micro Sieverts per hour.

As predicted, I was back to normal levels within a couple of days.  With a six hour half-life, the amount of material left after 24 hours is significantly lower, but still easily detectable.  After 48 hours it was still a bit high, but not by much. In three days I was back to normal, and my unusually-high radioactivity had come to an end.

48 hours later, almost back to background levels

Around my house, the "going rate" for my Geiger count seems to hover around about 0.5 micro Sieverts, so even after a couple of days of decay, I was still 10 times hotter than stuff around me.  I'm happy to report that I no longer set off my Geiger counter, but it was sure fun while it lasted.

Oh, and the results?  The EKG picked up a little blip at my highest heart rate while on the treadmill (which my doctor said not to worry about), but all the imaging showed that everything's clear, and operating well.  Happy ending!