What’s a PET scan?

Posted by: KLM on: October 28, 2010

• In: Cancer | Medical Info
• 9 Comments

In the image above, you can see the lower parts of the head, with the armpits next to it (they make you lie with your arms up so your armpits are by your ears).

The test I got is called a PET/CT  scan.  This combination test  is a relatively new procedure dating back to 2000,  although the CT and PET scans alone date back to the 1970’s.

This test is used primarily in oncology screening – to search for metastasis or signs of spreading.  For me, we will see it as we are looking for confirmation that only my lymph nodes are problematic.

For the CT scan, one drinks barium to define the GI tract. For the PET scan they inject a variation of glucose that they can track in the body.

The put you on a table that passes back and forth through a doughnut of equipment until the right data has been collected.

Each test shows different things. The composite image clearly shows the most biologically active areas of the body. Cancer cells will be the brightest.

What’s it like to get the PET/CT scan?

There are a surprising number of instructions for this test.  They ask the patient to refrain from exercising the day before and to avoid air conditioners.  I asked the technician about these requirements.  The tracer material is a variant of glucose.   All cells will absorb some glucose.  When we are cold and after exercise, our muscles work harder to absorb glucose.  More energy warms us.  After exercise, the muscles need to restock on glucose for the next time.  If our muscles take up the tracer, they will reduce the contrast in the image and also leave less of the substance in the blood for any cancer cells to absorb – so they may not glow as brightly.

The other requirement is dietary – an attempt to restrict sugars and carbohydrates for many hours before the test so that the cells will be thrilled to see some glucose and readily absorb it from the blood.

As I wrote before, we were in the process of cooking spaghetti for dinner when I read the handout for the test.  It is best to eat protein, dairy products and vegetables and avoid juices, fruits, breads, pasta, potatoes and rice.

The next morning, I was allowed to drink water.  I didn’t find out until later it is OK to take normal medicines.  I drank hot water in the morning which felt a wee bit like coffee or tea.

I took the metro to the test.  It was a small, relatively unmarked building where I had to press to buzzer to gain entry.  This is a private clinic, and it differentiates itself by its decor – natural stone floors,  beautifully arranged array of magazines to appeal to the wealthier customers – devoid of the check-out stand celebrity gossip variety of reading materials.

After five years with a public health system, I’ve grown accustomed to medical facilities which focus funds toward treatments rather than ambiance.  All the fancy stuff was nice, but it doesn’t really matter – I just want the test done without having to pay to much for it.

The first step was my medical history – they want a full list of surgery dates and treatments and information about past broken bones etc.  They asked about medicines, antibiotices and things like aches and pains – trying to garner enough information to accurately interpret what they see.

My oncologist told me he was not telling them about my biopsy results. He wanted to see if they would identify it.  If they detect it, we can have more confidence that everything is actually clean inside me.

The technician asked if I’d had any biopsies.  I wasn’t sure how to answer to the question – since I liked the doctor’s strategy.  I also wanted to be truthful.  So I said there had been an axillary biopsy, but said that I did not yet have the results.  He was OK with that.

There were lockers with keys to put my stuff and a bookcase filled with thick terry cloth hospital gowns and thick white bathrobes for decency.  I have to admit this part was nice – although here, I was wearing stuff that would  easily fit  a six foot man.  Once bulked up in all this finery, I was whisked off to be weighed and measured.

The amount of tracer they give you is based on your height and weight.

I was lead to a little private room with a chair that looks just like the ones in the chemo lounge – a big easy chair with a foot rest that comes up.   The technician started looking for a good vein.  The third time he tapped a vein, it worked right.  My veins are small and not so easy to work with – it flustered the guy to have to keep trying to find a reasonable vein.

The shot of tracer looks strange – the syringe is covered in a thick layer of lead to protect anyone handling it.   As he slowly fed the 3 inches of liquid into my veins, I noticed a sign on the wall.  “Tell us if you are traveling soon!”  I had to ask about their interest in my vacation plans.

There is enough radioactivity in my veins to freak out the guards at the US/Canada border or the airport.  Especially for heavier people, it can take a week or more for the radiation levels to drop to undetectable levels.  More than one person has been hauled off for interrogation after a PET test.

Before I was left alone for an hour, the technician handed me a “Big Gulp” size glass of barium to drink.  It is white and tastes like an orange soda without being sweet.   It is unoffensive, and because I hungry, it did not bother me to drink.

He came back with a second helping of barium 15 minutes before the test began.

A PET/CT scanner

A short walk took me to the big machine.  I’m getting used to the look of these machines, most follow similar designs.

My job was to hold still and not move for 30 minutes.  I got into as comfortable position as I could with my arms above my head and my knees over a triangle bolster to support them.

The machine moved me through it and then slowly brought me back to the original location.  It would move about a foot, then sit there for like five minutes, then move again.

I could breath normally – there was no holding my breath like happened with the CT scanner at the hospital.  At times I worried I might have to cough. Other times pains started in my knees, but the discomfort would subside.

The PET/CT machine is nearly silent compared to an MRI or the CT scanner.  He played music for me – to bad it was some variation of country music, not my favorite.

A half our later, I was back getting dressed.  As I left, I was handed a CD of the scan. The report will be faxed to my doctors on Friday.  I like the certainty of knowing when the results are ready.

I was told to drink lots of water over the next few days to flush out the tracer and the barium.  Other than that, there were no real side effects.  I felt a little weird all day, but thinking of two days with no naps, the news and a morning with no food, I could not really blame the odd feelings on the chemicals.

On the way to the subway, I grabbed small coffee and visited the one pastry store I passed on my way.  The idea of an Asian bakery was kind of scary – I’ve never been much impressed by Chinese desserts I’ve tried.  I knew I needed to eat – so I picked a cream filled sponge cake, hoping for something Twinkie like.  I was pleasantly surprised – it was appropriate and nicely executed.  I was secretly hoping for a good American jolt of sugar,  but I live in Montreal, where other flavors matter.  I wouldn’t go out of my way to get this again, but it was something I would definitely pick again in similar circumstances.

As tests go – the PET/CT is a pretty easy one. It takes about three hours.  I was glad I brought something to read.