Before your scan
Why You Have to Wait an Hour — After the Injection
The hour between your injection and the scanner is not administrative. What you do during it directly affects what your oncologist can see on the images.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026
- The wait is clinical — The radiotracer needs time to travel through your body and settle into cells before the scan can begin.
- Muscles compete with tumours — Any muscle you use during the wait absorbs the tracer — tracer that is then not available to show cancer.
- Talking affects head and neck scans — Speaking activates jaw and throat muscles in exactly the areas oncologists need to read.
- Staying warm is part of the protocol — Cold activates a type of body fat that absorbs tracer and creates confusing signals on the images.
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After the injection, the radiotracer needs time to travel through your body and be absorbed by cells. Cancer cells take it up faster than healthy cells — that difference is what the scanner reads. Moving your muscles during this wait draws the tracer into muscle tissue instead, which can obscure findings. Talking, walking and phone use all affect the images.
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What do you do — and not do — during the wait?
Receive the injection
A radiotracer — usually a glucose-like molecule — is injected through a cannula into a vein in your arm. You will not feel the tracer moving through your body. The cannula may be left in place until after the scan.
Move to the rest room
You go to a quiet, warm, dimly lit room and sit or lie in a recliner. The room is kept warm for a clinical reason: cold causes a type of body fat to absorb the tracer heavily and produce bright patches on the images that can be confused with disease.
Stay completely still
Do not get up to walk around. Muscles absorb glucose when they work, and the radiotracer follows glucose. Walking draws tracer into your leg muscles, leaving less available to highlight tumour tissue.
Do not talk
Jaw, tongue and throat muscles activate every time you speak. They sit in areas — the head and neck — that are often exactly what your oncologist is trying to read. Even brief conversations during the wait matter.
Keep your phone put away
Holding, scrolling or tapping a phone requires your hand and arm muscles to work continuously. Those muscles absorb tracer during the uptake period. If you want to listen to something, place the phone flat and untouched — and check first whether the centre allows it.
Wait to be collected
When the uptake period is complete, the radiographer will come to you. Do not assume the wait is over and go looking for them. The timing is set precisely, and starting the scan too early reduces image quality.
Go for the scan
You lie still on a table that moves slowly through the scanner. The scan itself is quiet. Stay as still as you were during the wait — movement during the scan affects image sharpness.
PET-CT Partner Centres
PET-CT Scan Centres in Hyderabad
CION offers PET-CT scans through 4 trusted partner PET-CT centres across Hyderabad, so you can choose the one closest to you. Call 18002028726 and we’ll guide you to the earliest available appointment.
PET-CT Centre — Punjagutta
PET-CT Centre — Himayatnagar
PET-CT Centre — Narayanaguda
These are partner diagnostic centres within the CION network. Toll-free booking: 18002028726.
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Why does moving your muscles affect what the scan shows?
The radiotracer behaves like glucose inside your body. Cancer cells consume glucose faster than most healthy cells — that difference is what makes them appear as bright spots on the images.
Muscles also need glucose to function. When you move during the uptake period, working muscles absorb tracer that would otherwise be available to mark tumour tissue. A small area of cancer that would have appeared clearly can become harder to distinguish from the tissue around it.
Talking activates the muscles of your jaw, tongue and throat. These create bright signals in the head and neck area — which is often exactly where your oncologist is looking for disease. Signals from muscle activity and signals from a tumour look similar on the scan, which is why speaking during the uptake period makes images harder to read.
Did you know?
When you feel cold, your body activates a type of fat called brown adipose tissue to generate heat. This fat absorbs the radiotracer intensely.
On the scan it appears as bright patches across the neck and upper chest — areas that are clinically important for many cancers. Staying warm during the uptake period is part of the imaging protocol, not a comfort measure.
Source: Society of Nuclear Medicine and Molecular Imaging (SNMMI) procedure guidelines
A whole-body PET-CT at CION is Rs 10,499 — among the lowest published prices in Hyderabad — with a free Rs 950 oncologist consultation to talk through your report. Indicative price, as of September 2026.
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Your next step
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Common questions
Frequently asked questions
What exactly is being injected — is it safe?
The injection is a radiotracer, most commonly a glucose-like molecule called FDG. It carries a small radioactive tag that the scanner detects. The radiation exposure is considered acceptable for diagnostic use and is in a range comparable to other medical imaging procedures. The tracer leaves your body through your urine within a few hours. If you want to know the specific tracer being used at your appointment, ask the radiographer when you arrive.
Can I listen to music on my phone during the wait?
Passive listening is lower risk than scrolling or tapping, but the phone should be placed flat and left untouched for the duration. Holding or interacting with it activates the muscles in your hands and arms, which then take up tracer during the uptake period. Some partner imaging centres prefer complete quiet during uptake and will tell you their preference. When in doubt, leave the phone aside entirely.
Does it really matter if I talk a little?
Yes, particularly for scans covering the head and neck. The muscles involved in speech are located in exactly the region your oncologist may be trying to read for disease. Bright spots from muscle activity and bright spots from a tumour are difficult to tell apart. Even a few minutes of conversation during the uptake period can produce signals that make the images harder to interpret with confidence. The quiet room exists for a clinical reason, not a comfort preference.
What if I need to use the bathroom during the wait?
Tell the staff — do not simply go on your own. You will likely be guided to the nearest bathroom, and the walk should be as short and calm as possible. Do not hold on uncomfortably; discomfort causes muscle tension, and a full bladder can also interfere with pelvic images. Some centres have guidance about flushing because the tracer passes into urine. The team plans for bathroom breaks and will help you manage it.
What happens if the wait is cut short?
Starting the scan before the tracer has fully distributed means less contrast between normal and abnormal tissue. Tumours that would have appeared clearly may be less visible, and in some cases the scan may need to be repeated. Partner imaging centres follow precise timing protocols for this reason. The wait is not shortened even when you feel ready, because feeling ready and the tracer being properly distributed are two different things.