Understanding SUV values on PET scans

Dear Candy, as I understand from any imaging technique, there should be different SUV values, i.e. SUVmax for highest pixel (small group of pixels, i.e. 1 or 4?) in the image, then SUVmean for defined area (area defined by radiologist which he recognizes as tumor?). So these are very different, as larger tumors might be very heterogeneous and SUVmax can be very high in just one small part of the tumor, whereas I think SUVmean is more important - it shows the average/mean uptake value. I think in another thread you stated SUVmax values from your PET scan, so what are the SUVmean ones - I think they might be much more important? I am not a PET expert, I just know how general imaging techniques and analyses work...

Saulius

Dear Candy, as I said, a tumor can be, for example, 50x50 pixels in the image, and only 1(!) pixel might have SUVmax, others can have very low SUVs, which would theoretically mean that that 1/50x50 = 1/2500 of the tumor is very active, so basically, very simply speaking, tumor is dead. This is why SUVmax is not very indicative. Just a radical example but imaging in radiology works this way, this is why SUVmax is a strange indicator, which should be explained in more detail, or other values should be used... Could others probably comment on this too? Saulius

It seems to me that my radiologists describe the background uptake in places without tumors, and compare that to the uptake in tumors. They give numbers, but they also simply use descriptive terms such as "mild uptake" etc. I would be very careful about interpreting the scan report, candy, because reading PET scans is complex. My *guess* is that higher uptake would mean a more active cancer, as the higher uptake of the radioactive glucose by cancer cells is what makes PET scans work. BUT it seems many factors can affect the numbers. I think you are stuck with trying to speak to a radiologist or oncologist about it. With that caution in mind, here is some info I found:

"The cut off between benign and malignant lesion/nodule is in the SUV range of 2.0-2.5. PET sensitivity and specificity decreases with lesions smaller than 7 mm." (https://radiopaedia.org/articles/standard-uptake-value?lang=us)

"Standardized uptake value (SUV) is a semiquantitative measurement of uptake in tissue. Many factors affect the SUV, including accuracy of dose calibration, time between injection and imaging (dose to scan time), patient weight (changes are common in oncology patients), motion artifacts, and blood glucose levels. Many interpreting physicians give SUV values, while some prefer to read qualitatively based on visual comparison with blood pool or liver. Some literature, in particular lymphoma staging systems, is prompting F-18 FDG PET readers to give SUV values so that interpretations can be more standardized and more confidently direct clinical decision-making.

Occasionally, the SUV can be much more intense or much less intense than expected. If this occurs, the reader can measure the SUV of the liver or blood pool, which allows for internal consistency for metabolic activity within a particular patient. Generally, the SUV of the normal liver is between 2 and 5; if it is outside of this range, the values entered for SUV calculation during image acquisition can be checked, as they are likely erroneous." (https://www.sciencedirect.com/topics/medicine-and-dentistry/standardized-uptake-value)