A CT scan shows shape; a PET scan shows activity. Combined in one machine, they answer the question that decides treatment: is this lump metabolically alive, and is anything else in the body lit up too? Understanding what the numbers in the report mean — and what they cannot mean — prevents a great deal of unnecessary fear.
What you'll read
How the scan works
You receive an injection of a sugar molecule labelled with a small amount of radioactive tracer, most commonly FDG. Cells that consume a lot of sugar — including most cancer cells — take it up faster than their neighbours, and the scanner maps where it accumulates. The CT taken at the same time supplies the anatomy, so the report can say not only that something is active but exactly where it sits.
Preparing for the appointment
- Fast for about six hours; water is allowed and encouraged.
- Avoid exercise for 24 hours — working muscles absorb the tracer and blur the picture.
- Tell the team if you are diabetic: blood sugar has to be in range for the scan to be readable.
- Expect to rest quietly for about an hour after the injection before scanning begins.
- The whole visit takes two to three hours; the scan itself is around 20 – 30 minutes.
What SUV numbers mean
SUV — standardised uptake value — measures how much tracer a spot holds compared with the average across your body. A higher number means more metabolic activity, and SUVmax is simply the brightest pixel in that area. It is a useful ruler, not a diagnosis: there is no universal threshold above which a finding is cancer.
SUV is most valuable as a comparison over time. If the same lesion measured 12 before treatment and 3 afterwards, on the same type of scanner and with the same protocol, that fall is meaningful evidence of response. Comparing an SUV from one hospital with an SUV from another is far less reliable.
Why not every bright spot is cancer
Inflammation consumes sugar too. Infection, a healing surgical wound, recent radiotherapy, arthritis, an active thyroid, brown fat on a cold day and even a recent injection site can all light up. Conversely some tumours barely take up FDG at all — certain slow-growing prostate cancers, some kidney cancers, low-grade lymphomas and mucinous tumours can look almost normal on PET.
Questions to ask about your report
- Does this scan change my stage, and therefore my treatment?
- Is any finding uncertain enough to need a biopsy rather than an assumption?
- Was the scan compared side by side with my previous imaging?
- If treatment has started, was the timing right — scanning too soon after chemotherapy or radiotherapy can mislead.
- Can I have the images in DICOM format for a second opinion?
Frequently asked questions
Is a PET-CT dangerous because of the radiation?
The dose is comparable to a few years of natural background radiation and is justified when the result changes management, which in cancer staging it usually does. The tracer clears from the body within hours; drinking water helps.
Can a PET-CT tell whether a tumour is benign or malignant?
Not definitively. It measures activity, and activity has several causes. Only a biopsy and the pathologist's microscope establish the diagnosis; PET-CT tells the team where to biopsy and what else to look at.
How much does a PET-CT cost?
In the United States a whole-body PET-CT is commonly billed between $3,000 and $8,000. At accredited hospitals in İstanbul the same study with an English report is typically $500 to $1,200, and it is often bundled into a diagnostic package with the consultation and blood work.
Want your scan reviewed by a second radiologist?
Send the images in DICOM format with the report. A radiologist and an oncologist will review them together and tell you whether the stage and the plan still hold.