[Joan M]

Hi Patty,

Glad to see that you're doing well and can't blame you for wanting to the best follow-up you can.

PET/CT and CT scan are really two different tecnologies.

Each has it's good and bad points and sometimes it can be hard to determine which is best.

The CT uses a contrast medium and can "see" nodules as small as 2-3 mm, for example, (there are 10 mm in 1 cm, and 1 cm is about 0.34, or about a third of, an inch). On the other hand, although the CT scan can see a nodule that small, it might not be able to identify it as benign or malignant. However, such a nodule can then be followed. (In the case of cancer, a CT scan can be done for the chest, abdomen and pelvis, for example. They're done in one setting, but there will be three separate reports.)

On the other hand, a PET scan doesn't really "see" anything but rather measures metabolic activity of glucose, which rapidly metabolizes in cancer (and in other types of) cells. A "nodule" will "light up" on the screen at about 1 cm to be sure if there's a potential problem, and the probability of it lighting up below that size, even if it's malignant, decreases as the size of the nodule decreases (as in a linear relationship).

The PET is a nuclear test. It does not use the same "contrast" as a CT scan, which uses iodine. The PET instead uses a nuclear isotope (FDG 18, or something like that). Sometime a reports states, "no FDG avid areas," if nothing lit up.

The CT had been eventually added to the PET to give position to the whole PET scheme. It adds a better view of the liver, lungs, etc. to better pinpoint any problems.

Which is better?

Case in point (you decide): In May 2006 I had a PET/CT, which is whole body for everybody (meaning the organs and bones from the upper neck to the middle of the thighs). The scan was clean.

In May 2007 the scan was repeated and it revealed a 9 mm malignant nodule in the left lung which was eventually removed by a wedge resection. It recurred a year later in April 2008 as residual from the surgery and I had radiofrequency ablation to attend to that this past August.

When the 9 mm nodule was noted in 2007, my onc asked the facility where the PET/CT was done to determine whether that nodule had been there in the PET/CT of 2006, and it was, as a 5 mm nodule. But because the scan was a nuclear scan it was too small to light up and therefore it was never noted.

It's difficult to say whether this was standard of care, meaning that perhaps another facility may have noted the nodule in the CT part of the report even though it didn't light up on PET.

Joan