Before your scan
Cold Weather, Shivering and Brown Fat: — Why You Are Asked to Stay Warm
The instruction to stay warm before a PET scan sounds minor. It is not. Cold temperatures switch on a type of tissue in your neck and shoulders that absorbs the scan tracer the same way a tumour does. If that happens, the scan may be harder to read or may need to be repeated.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026
- Tissue, not a tumour — Brown fat is normal tissue that becomes active in the cold. It is not cancer and it is not dangerous.
- It looks like cancer on the scan — Active brown fat absorbs the PET tracer the same way a tumour does, making the image harder to read.
- Cold is the trigger — Even mild cold — an air-conditioned room or a cold drink — can switch brown fat on during preparation.
- Warmth prevents it — Staying warm in the hours before your scan, and throughout the waiting period, is the main way to stop this.
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Brown fat is heat-generating tissue in your neck, shoulders and spine. Cold temperatures switch it on, and when it is active it absorbs the PET tracer the same way a tumour does. Staying warm before your scan prevents this interference. SNMMI and EANM guidance identifies cold exposure as the main avoidable cause of brown fat artefact.
CION offers PET-CT in Hyderabad from Rs 10,499 — among the lowest published prices in the city, with no hidden charges. Indicative price, as of September 2026.
What is brown fat and why does it show up on a PET scan?
Brown fat is a type of fatty tissue found mainly in the neck, shoulders, and the area alongside the spine. Its job is to burn energy and produce heat — it is the body's way of warming itself when it senses cold.
A PET scan uses a glucose-like tracer to find areas of the body that are using more energy than usual. Tumours consume a great deal of energy, which is why they show up brightly. Active brown fat consumes energy in the same way, and on the scan image the two can look almost identical.
This is not a flaw in the scan. It is a normal biological response to cold being detected by a highly sensitive machine. Preventing cold from reaching you before and during the scan is the only reliable way to prevent this interference.
How to stay warm before your PET scan
Plan your clothing the night before
Wear warm, full-length layers on the day of your scan. Bring an extra layer even if the weather feels mild — waiting and preparation areas are often air-conditioned, and even a brief temperature drop can be enough to activate brown fat.
Avoid cold drinks during your fasting period
Cold liquids can lower your core temperature enough to switch brown fat on. Unless your team has given you specific instructions, drink only water at room temperature during the fasting period. If you have diabetes or any condition that affects fasting, confirm the approach with your treating team before the scan day.
Tell the booking team if you feel the cold easily
Some people are more prone to brown fat activation — including people who are thin, younger adults, and people who feel anxious before procedures. Mentioning this at booking allows the team to take extra steps on the day.
Use the warm room and blankets during the uptake period
Scanning centres following accredited protocols keep the preparation room warm and have blankets available during the uptake period. Use them. If you feel cold and no blanket has been offered, ask for one.
Tell the radiographer immediately if you feel cold or shiver
The period after the injection — while the tracer is being taken up by the body — is the most critical time. If you feel cold or shiver at any point during this period, tell the team straight away rather than waiting to see if it passes.
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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What happens if brown fat is still visible on your scan?
When brown fat uptake appears on a scan, the radiologist who reads the images will note it. Its pattern is often recognisable — symmetrical, in the known locations, appearing on both sides at once — and experienced readers can usually separate it from suspicious findings.
If the uptake is extensive or falls in an area being closely evaluated, your team may recommend a repeat scan. This is not a worrying result. It means the image in that region was not clear enough to give a confident answer, and a cleaner image is needed.
A repeat scan is avoidable in most cases. Following the warm preparation steps consistently is what makes the difference.
How does cold affect your PET scan if you do not stay warm?
| Feature | Warm preparation | Cold-affected preparation |
|---|---|---|
| Brown fat activity | Minimal or switched off | Activated — absorbs tracer alongside the tumour signal |
| Appearance on scan | Not visible, or faint and easy to dismiss | Bright, symmetrical uptake in the neck and shoulders |
| Scan readability | Fully readable, reported with confidence | Regions of uncertainty; possible missed or misread findings |
| Result on the day | Report issued after one visit | Possible need for a repeat scan |
| Action needed from you | None beyond standard preparation | Return visit, repeat fasting, repeat tracer injection |
PET-CT at CION starts from Rs 10,499 — among the lowest published prices in Hyderabad — across 4 partner centres in Banjara Hills, Punjagutta, Himayatnagar and Narayanaguda. Indicative price, as of September 2026.
Explore 92 more Preparing For and Having Your Scan Safely topics
Preparing for Your Scan
- A Printable PET-CT Preparation Card
- Can I Drink Water Before a PET-CT Scan?
- Can I Have a PET-CT Scan During My Period?
- Can I Take My Regular Medicines Before a PET-CT Scan?
- Can You Reschedule a PET-CT Scan?
- Cold Weather, Shivering and Brown Fat: Why You Are Asked to Stay Warm
- Fasting Before a PET-CT Scan: How Long and Why
- How to Prepare for a PET-CT Scan: The Complete Checklist
- Preparing a Very Elderly or Frail Person for a PET-CT
- Preparing a Wheelchair-Bound or Bedridden Patient
- Preparing for a PSMA, DOTATATE or FAPI PET-CT
- Should I Avoid Exercise Before a PET-CT Scan?
- Smoking, Alcohol and Caffeine Before a PET-CT Scan
- What Happens If You Break the Fast by Mistake?
- What to Carry to Your PET-CT Appointment
- What to Eat the Day Before a PET-CT Scan
- What to Wear to a PET-CT Scan
- Why Your Kidney Function Test Is Needed Before a PET-CT
Contrast, Cannula & Procedure Safety
- Can You Have a PET-CT If You Are on Blood Thinners?
- Can You Have a PET-CT Through a Port or PICC Line?
- Contrast Allergy and PET-CT: What to Declare
- Contrast Reaction Symptoms: What to Watch For
- Contrast and Kidney Function: The Creatinine Rule
- Infection Risk and Hygiene at a Scan Centre
- Is Contrast Used in a PET-CT Scan?
- Metformin and Contrast: What Is the Rule?
- Side Effects of a PET-CT Scan
- The Cannula: Bruising, Pain and Difficult Veins
- Tracer Leakage at the Injection Site (Extravasation)
- What If You Feel Unwell During the Scan?
Diabetes & Blood Sugar for PET-CT
- A Diabetic Patient's PET-CT Day Plan
- Best Appointment Time for a Diabetic PET Scan
- Can Diabetics Take Their Tablets Before a PET Scan?
- Does Diabetes Change Your SUV Reading?
- Fasting Safely With Diabetes Before a Scan
- Insulin and PET-CT: Timing Rules
- Newly Diagnosed Diabetes Found Before a Scan
- PET-CT Scan With Diabetes: The Complete Preparation Guide
- PET-CT With Steroid-Induced High Sugars
- What Blood Sugar Level Is Needed for a PET-CT Scan?
- What Happens If Your Sugar Is High on the Day?
- What to Eat the Day Before if You Have Diabetes
Radiation Safety & After-Scan Precautions
- Are You Radioactive After a PET-CT Scan?
- Being Around Pregnant Women After a PET-CT Scan
- Can I Hold My Child or Grandchild After a PET-CT Scan?
- Can a PET-CT Scan Cause Cancer?
- Cumulative Radiation From Repeated Scans
- Do You Need Precautions After a PSMA or DOTATATE Scan?
- Do You Need Separate Utensils or a Separate Toilet After a PET-CT?
- How Long Does the Tracer Stay in Your Body?
- How Long Should You Avoid Close Contact After a PET-CT?
- How Many PET-CT Scans Are Safe in a Year?
- How Much Radiation Is in a PET-CT Scan?
- Is PET-CT Radiation Different From Radiotherapy?
- Is the Radiation From a PET-CT Scan Dangerous?
- PET-CT Radiation Compared With CT, X-Ray and Natural Background
- Radiation Safety at Home After Your Scan: A Family Checklist
- Radiation Safety for Staff and Attendants at the Centre
- Simple Steps to Clear the Tracer Faster
- Travelling Home After a PET-CT Scan: Public Transport and Airports
Scan Day: What Actually Happens
- Can Someone Stay With Me During the Scan?
- Can You Drive Yourself Home After a PET-CT Scan?
- Can You Have Sedation for a PET-CT Scan?
- Can a PET-CT Scan Be Done on the Same Day as Other Tests?
- Contrast in a PET-CT Scan: When It Is Used and Why
- Eating and Drinking After Your PET-CT Scan
- How Long Does a PET-CT Scan Take?
- Is a PET-CT Scan Painful?
- Is a PET-CT Scanner Closed Like an MRI? Claustrophobia Explained
- The Tracer Injection: Does It Hurt?
- What Happens If the Scan Cannot Be Completed?
- What If You Cannot Lie Still or Have Tremors?
- What to Expect Immediately After the Scan
- Why Was My Scan Repeated or Extended on the Day?
- Why You Have to Wait an Hour After the Injection
- Your PET-CT Scan Day: What Happens, Step by Step
Special Populations
- Breastfeeding and PET-CT: How Long to Pause
- PET-CT Scans for Children: A Parent's Guide
- PET-CT With Kidney Disease or on Dialysis
- PET-CT With a Pacemaker, Stent or Metal Implant
- PET-CT for Claustrophobic Patients
- PET-CT for Patients Who Cannot Lie Flat
- PET-CT for Patients With Anxiety or Panic Disorder
- PET-CT for Patients With Dementia or Confusion
- PET-CT for Patients With Incontinence or a Catheter
- PET-CT for Patients With a Stoma
- PET-CT for Patients on Long-Term Steroids
- PET-CT for Very Elderly or Frail Patients
- PET-CT for Very Heavy Patients: Weight and Bore Limits
- PET-CT for Wheelchair and Bedbound Patients
- PET-CT in Pregnancy: Why It Is Avoided
- Sedation and Fasting for a Child's PET Scan
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Common questions
Frequently asked questions
Will the radiologist know it is brown fat and not cancer?
Usually, yes. Brown fat uptake has a recognisable pattern — it is symmetrical, it appears in the known locations of the tissue, and it tends to show on both sides of the neck and shoulders at once. Experienced nuclear medicine radiologists are trained to identify it. The difficulty arises when the uptake falls in or near an area where cancer is being evaluated, or when it is unusually extensive. In those cases, a repeat scan with better warm preparation gives a cleaner image and a more confident answer.
Does it matter if I shiver only briefly in the waiting room?
It can. Brown fat activation does not require prolonged cold. Brief shivering during the uptake period — which lasts well over an hour — can be enough to switch the tissue on. The period after the injection is when it matters most. If you shiver at any point during this time, tell the radiographer rather than waiting to see if it settles. The team can take additional warming steps to reduce the effect.
Am I more likely to have brown fat problems than other patients?
Some people are more prone to it than others. Brown fat is more active in younger people, in people who are thin, and in people who feel anxious before medical procedures — because anxiety raises adrenaline, which is one of the signals that activates brown fat. If you know you feel the cold easily, or if you tend to be anxious before scans, mention it at booking. Your team can arrange additional warming measures before you arrive.
Is brown fat itself something to be worried about as a finding?
No. Brown fat is normal tissue. Its presence in your neck and shoulders is not a sign that something is wrong with you, and it is not cancer. The issue is entirely about the quality of the PET scan image — active brown fat absorbs the tracer and creates a signal that can interfere with reading the images accurately. Once the scan is over, brown fat activity has no bearing on your health or your diagnosis.
Will being cold before I arrive affect the scan, or only the waiting period?
Both matter. Brown fat can be switched on by cold exposure before you arrive — a cold journey, sitting in an air-conditioned vehicle, or wearing insufficient clothing on the way to the centre. Once activated, it takes time to settle, which is why preparation guidance covers the hours before the scan, not just the time inside the building. Dressing warmly for the journey, and not only for the waiting room, is part of the preparation.