Health Library / Scans & imaging
PET-CT scan in Lucknow: who needs one, and how to prepare
· 6 min read · Lucknow
A PET-CT is usually ordered at a difficult moment — during a cancer workup, to see whether treatment is working, or to check whether disease has returned. It is also one of the least explained scans, and preparing for it wrongly can mean the scan has to be repeated.
This is what it does and, more practically, exactly what is asked of you beforehand and why.
What it shows that a CT alone does not
A CT shows structure — where things are and what size they are. PET shows activity. A small amount of radioactive tracer, usually a glucose analogue called FDG, is injected, and tissue that is metabolically busy takes up more of it and lights up.
Combining the two in one machine puts the activity onto the anatomy: not just that there is a lump, but whether it is metabolically active, and whether anything else in the body is. That is why it is used for staging, for assessing treatment response, and for finding recurrence — questions structure alone cannot answer.
It is not a general screening test for healthy people. Metabolically active does not mean cancer — infection and inflammation light up too — which is why it is read by specialists in the context of the whole case.
Preparation, and why it is strict
Because the tracer is a glucose analogue, blood sugar competes with it. High blood sugar at the time of injection genuinely degrades the scan, which is why the preparation is about sugar rather than merely about fasting.
- Fast for around six hours — plain water is allowed and encouraged
- No sugary drinks, juice, sweets or chewing gum, and no intravenous glucose
- Avoid strenuous exercise for about 24 hours — working muscle takes up tracer and obscures the picture
- If you have diabetes, follow the specific instructions given at booking; insulin timing matters and must be planned with the centre
- Tell the centre if you are pregnant or breastfeeding, and dress warmly — being cold activates brown fat, which takes up tracer
The appointment, and afterwards
Allow two to three hours in total. After the injection there is a quiet uptake period of roughly an hour where you rest without moving or talking much — movement and muscle activity affect the images. The scan itself then takes around twenty to thirty minutes.
Afterwards you can generally eat and return to normal activity. The tracer decays quickly and is cleared in urine, so you will be advised to drink plenty of water. As a precaution you will usually be asked to keep some distance from infants and pregnant women for the rest of the day; the centre will give you specific guidance.
At Charak, PET-CT sits alongside gamma camera, CT, MRI and pathology at Chowk, and is reported by nuclear medicine physicians.
This article is general health information, not a diagnosis or a treatment plan. Test results are read alongside your symptoms and history — please discuss yours with your doctor. See our disclaimer.
