Understanding SUV values on PET scans
I am starting this new topic to have a conversation on understanding the SUV values on your PET scan results. When an area lights up it is given an SUV value number, what do the numbers mean? Is there a scale for the numbers? I read that anything over 2.0 is suspicious for malignancy. But how high can the numbers go? Does the higher the number, the stronger the area "lit up", means anything?
I had a repeat PET recently (have only had 3 PETS in my 4 years of MBC) and my SUV for my liver (Yes I have liver mets) was 21. My PET at diagnosis 4 years ago said the SUV in the liver was 8.4 and 5.7 (done at a different facility with a different radiologist).
So is the liver more active now?
At what number is the oncologist concerned? Does the onc look at the SUV values or take much stock in them?
Thoughts....
Comments
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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
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BSandra- I know nothing about all this imaging stuff. My PET from 2017 diagnosis says " Approximately 4.8cm AP x 5.8cm transverse hypermetabolic hypodense lesion with a maximal SUV 8.4 " and then also describes the smaller lesion in the liver with a "maximal SUV 5.7" . This latest PET says this about the liver lesions " The most avid lesion located.... SUV max of 21.5 " No where on either PET report does it say anything about "SUV mean".
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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
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Candy, thanks for starting this thread, I am sure many useful information will be shared, looking forward...
A question for you, in your pet report, the radiologist mentioned any baselines? I had only one pet, and it analyzed based on the 2 baselines (edit to add:Baseline mediastinal blood pool activity, and Baseline hepatic activity) I was told these 2 baselines are given based on circulation of cancer cells in individual blood and the liver function, so any suv between these 2 means tumors are under control ie medication is working, as opposed to higher than those baselines.
BSandra, thanks for the radiology pixel analysis, very informative post.
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Snow-drop-- The only thing maybe mentioned on the 2 page report about this is where it says " The patient's fasting blood glucose level....After IV administration of FDG, noncontrast CT images were obtained.... The mean liver SUV (reported for quality control purposes) is 2.6."
Nothing about "baselines"
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This made me curious, I've never paid attention to the SUV values before.
here's what I could glean from my own reports -
First PET scan before having any treatment- the SUV max in my breast tumor was “over 27"
The SUV of each bone lesion is not mentioned, probably because there are so many? Not sure.
I'm thinking those SUV numbers are recorded somewhere though, even if not written in the final report.
After the Taxol phase of treatment, I had my second PET. Most bone lesions were no longer hypermetabolic except a few in my spine which were described as “barely above baseline osseous metabolism" - Itake that to mean each organ has a normal level of metabolism, the cancer cells or lesions will show a higher rate than baseline. The only SUV number mentioned was for one lesion at 3.2 peak SUV.
So I would guess a normal SUV for bone is some number less than three. Not sure if normal or baseline for liver would be similar.
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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)
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