PET Scan Procedure Step-by-Step: What to Expect on Scan Day

A first-time PET scan is unfamiliar to most patients in a way that an X-ray or even an MRI is not. The combination of an IV injection, a one-hour waiting period in a quiet room, and a scanner that looks unfamiliar can be unsettling without a clear preview. This article walks through the entire day, hour by hour, and answers the questions most often raised at check-in.

Day Before: Fasting and Diet Rules

For a standard FDG PET-CT (the most common type), the day before involves dietary preparation:

• 24 hours before: avoid strenuous exercise (muscle FDG uptake increases otherwise)
• 6–12 hours before: nothing to eat. Plain water is allowed and encouraged.
• No sugary drinks, juice, sports drinks: even small amounts of carbohydrates elevate blood glucose and reduce image quality
• No chewing gum in the last hour
• Take regular medications with sips of water unless told otherwise. Diabetic patients on insulin or oral hypoglycemics need specific instructions — typically hold morning insulin and breakfast, do not skip metformin entirely without checking.
• Bring an updated medication list including supplements

For specialized PET scans (cardiac sarcoid, brain dementia), the prep is more elaborate and given to you in writing at booking.

Arrival and Check-In (30 Minutes)

You arrive at the imaging center, typically 30–60 minutes before the scheduled scan:

1. Registration: identity verification, paperwork, consent
2. Vitals: weight, height, blood pressure
3. Blood glucose check: a finger-stick blood sugar — must be under approximately 200 mg/dL (11 mmol/L) for FDG. Higher levels reduce tumor visibility because tumor cells compete with circulating glucose for the FDG tracer.
4. Brief interview: any recent surgery, infections, biopsy, chemotherapy or radiation in the last 4–6 weeks (all affect interpretation)
5. Pregnancy check: for any woman who could be pregnant, a serum or urine pregnancy test

Wear loose, comfortable clothing without metal zippers or snaps over the area being scanned. The scanner will require you to remove metal-containing items (belt, jewelry, dentures if metal-containing). Some centers provide a gown.

Tracer Injection: What It Feels Like

A small IV catheter is placed in your arm, usually the antecubital fossa (inner elbow). The radioactive tracer — typically 8–15 mCi of F-18 FDG for an adult, calibrated to your weight — is injected over 10–30 seconds. A saline flush follows.

What it feels like: the IV stick itself, identical to any blood draw. The injection itself is painless. No warm flush, no taste, no nausea — unlike CT contrast. You will not feel "radioactive."

The IV stays in place during the uptake phase in case any post-scan medication is needed (rare).

The Uptake Phase: 60-Minute Wait

After injection, you rest quietly in a designated room for approximately 60 minutes while the tracer circulates and accumulates in metabolically active tissue.

Rules during uptake:

• Stay still and relaxed — talking, chewing gum, or unnecessary movement can increase FDG uptake in muscles (jaw, throat, hand) and confuse the image
• No phone calls, reading aloud, or vocal activities
• Warm environment — many centers heat the room to prevent brown adipose tissue activation (cold triggers brown fat to consume glucose)
• No food, drink — water sips only
• Bathroom break before scanning is encouraged to empty the bladder

You can listen to quiet music, scroll your phone silently, or rest with eyes closed. Sleep is fine. Some centers have warm blankets.

On the Scanner: 20-30 Minutes

When uptake is complete:

1. Bathroom break: void the bladder (FDG is excreted in urine; emptying improves pelvic image quality)
2. Position on the scanner table: lying flat on your back, arms above your head for whole-body scans (sometimes arms at sides for head/neck-focused studies)
3. Imaging starts: the table moves slowly through the scanner ring. The PET ring is short (~70 cm) — much less claustrophobic than MRI. You can see daylight from either end.
4. Scan duration: 20–30 minutes for a whole-body scan (skull base to mid-thigh). Brain-only or cardiac scans run 15–25 minutes.
5. Stay still and breathe normally: brief breath-holds may be requested at the start and end of the scan to align the CT portion

The scanner is silent compared to MRI — soft mechanical hum and the table movement, no banging. Many patients find it easier than MRI.

For questions about your specific scan type before booking, our team can help.

After the Scan: Hydration and Precautions

After scanning is complete:

1. IV removed: the catheter is taken out with a small bandage
2. Hydration encouraged: 1–2 liters of water in the next 4–6 hours to clear residual tracer via the urine
3. Avoid close contact with pregnant women, infants, and young children for the first 6 hours — out of caution, even though the absolute radiation is low
4. Normal activity resumes immediately; driving is fine
5. Diet: eat normally; many patients eat a large meal right after the scan, having fasted for 12+ hours

The F-18 isotope has a 110-minute half-life. After about 10 half-lives (~18 hours), essentially all radiation has decayed. By the next day you are no longer "radioactive."

Results Timeline and Report Pickup

Standard timelines vary by center:

• United States, hospital-based: report finalized in 24–72 hours; sent to ordering physician
• United States, freestanding imaging center: same-day to next-day
• United Kingdom NHS: 1–2 weeks
• United Kingdom private: 2–5 business days
• Mainland China (top tier): 24–48 hours; written report in Chinese, English on request

A copy of the report and image disc (DICOM) should be available for the patient on request. For international patients, top Chinese centers can email both directly.

Travel Day Planning for International Patients

For patients flying in for a PET-CT:

• Day 1: arrival, hotel check-in
• Day 2: pre-scan consultation; review prior imaging; receive prep instructions
• Day 3: prep day (fast 6 hours before scan)
• Day 4: scan day (half-day)
• Day 5: results review with specialist
• Day 6: departure (or earlier if results are time-flexible)

Airport security in many countries (US TSA, EU, China) can detect residual radiation up to 24–48 hours post-scan. Carry a copy of the report or a letter from the imaging center to explain.

Frequently Asked Questions

Can I take my medications before the scan?
Yes, with sips of water, unless instructed otherwise. Insulin and oral hypoglycemics need specific timing — discuss with your physician.

Will the IV hurt?
Roughly the same as any blood draw. The tracer itself is painless.

What if I am claustrophobic?
PET scanners are much shorter (~70 cm long, open ends) than MRI machines. Most claustrophobic patients tolerate them well. Mild sedation is possible if needed.

Can I bring someone with me?
A companion can be present in the waiting room. During injection and uptake, only the patient is in the prep area (radiation safety). For pediatric scans, a parent may be allowed.

How long do I stay radioactive?
F-18 has a 110-minute half-life. After ~18 hours, essentially all activity has decayed. Brief precautions (distance from young children and pregnant women) apply only for the first 6 hours.

Does insurance cover PET-CT?
In the US, Medicare and most commercial insurers cover PET-CT for confirmed or suspected cancer, infection, or specific cardiac/neurological indications. Screening PET-CT in asymptomatic patients is rarely covered. Self-pay cash prices typically $3,500–6,500.

Need Help Booking?

SinoCareLink can pre-book your PET-CT at a top Chinese hospital, send detailed prep instructions in English, translate reports, and arrange airport pickup. Contact us for a free consultation.