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Preparing for an FDG or Amyloid PET Scan: A Caregiver’s Step-by-Step Guide

A PET scan can feel daunting, but knowing what to expect helps you and your loved one stay calm and prepared. This guide covers the two main types of PET scans used in dementia evaluation—FDG-PET and amyloid PET—and explains the very different prep steps for each. You’ll find concrete actions, exact phrases to use, and tips for navigating the imaging center with confidence. You’ve got this, and we’re here to walk you through every step.

Key points

  • Know which type of PET scan is scheduled—FDG or amyloid—because the preparation is completely different.
  • For FDG-PET: fasting is required, and the patient needs a quiet, dark room after the injection.
  • For amyloid PET: no fasting is usually needed, and the waiting period is more flexible.
  • Practice lying still at home before the scan to reduce anxiety.
  • Pack a comfort kit with familiar items and a snack for after the scan.
  • Ask the imaging center ahead of time about their policies on caregivers in the room.
  • Discuss costs and insurance coverage before the day of the scan.

Why a PET scan? What does it show?

A PET scan is a special imaging test that looks at how the brain is working, not just its structure. There are two main types used in dementia evaluation. An FDG-PET scan measures how well brain cells are using sugar (glucose) for energy. In Alzheimer’s disease, certain brain regions show a pattern of reduced activity, called hypometabolism, especially in the temporal, parietal, and posterior cingulate areas. In Lewy body dementia, the pattern is different—it often shows reduced activity in the back of the brain, including the occipital cortex, which is the visual processing center. This difference in the pattern of hypometabolism helps doctors distinguish between types of dementia. An amyloid PET scan, on the other hand, looks for sticky protein clumps called amyloid plaques, which are a hallmark of Alzheimer’s disease. The tracer used in this scan binds to amyloid plaques, and the result is simply ‘positive’ or ‘negative’—meaning the plaques are either present or not. Both scans are powerful tools, but they answer different questions.

How are FDG and amyloid PET scans different in preparation?

The preparation for these two scans is very different, and it’s crucial to know which one your loved one is having. For an FDG-PET scan, the patient needs to have a quiet, dark room for about 30 minutes after the tracer is injected. This is because the brain’s activity during that time will affect the scan results—if the patient is talking, listening to music, or even just thinking actively, it can change where the tracer goes and make the results harder to read. For an amyloid PET scan, there is no such requirement. The amyloid plaques are already there, so the patient can be in a normal, lit room and can talk or listen to music during the waiting period. The waiting time after the injection also differs: for FDG, it’s typically 30–60 minutes; for amyloid, it can range from 30 to 130 minutes, depending on the specific tracer used at your imaging center. Both scans involve lying still in the scanner for about 10–20 minutes, but the prep beforehand is what really matters.

What happens during the scan itself?

For both types of PET scans, the process starts with an IV line placed in the arm. The radioactive tracer is injected through this IV. Then comes the waiting period, which varies by scan type as described above. After the waiting period, the patient is positioned on the scanner table. They need to lie very still for the duration of the scan, which is usually 10 to 20 minutes. The scanner itself is a large, doughnut-shaped machine, and the table moves slowly through it. The patient may hear clicking or whirring sounds. Some imaging centers allow a caregiver to stay in the room during the scan, but policies vary—some will say yes, others will say no. It’s best to ask ahead of time and not to take it personally if they say no. The scan itself is painless, but the stillness can be challenging for someone with dementia. Knowing this in advance lets you prepare your loved one and yourself.

General caregiving information, not medical advice. Check medications and major care changes with your clinician.

Step-by-step

  1. Call the doctor or imaging center to confirm whether the scan is FDG-PET or amyloid PET, and ask for specific prep: fasting, caffeine, alcohol, tobacco, and which medications are allowed that morning.

  2. For FDG-PET: after the tracer injection, the patient needs a quiet, dark room for 30 minutes. Bring a sleep mask and earplugs. For amyloid PET: the waiting period is flexible; bring a book or tablet.

  3. Dress the patient in loose-fitting clothes with no metal (e.g., sweatpants and a soft t-shirt). Leave jewelry, watches, and glasses at home.

  4. Pack a bag: a snack and water for after the scan, a list of medications and allergies, a copy of the doctor's order, and a phone charger.

  5. Practice a 'stillness drill' at home a few days before: have the patient lie still for 5–10 minutes with a timer, and praise them. This reduces anxiety and prevents blurry images.

  6. Arrive 15–20 minutes early. Tell staff about mobility issues, anxiety, or trouble staying still. Ask about a mild sedative if appropriate.

  7. During the scan, if allowed in the room, stand by the patient's head, hold their hand, and speak calmly. If not allowed, ask staff to call you as soon as it's done.

  8. After the scan, offer a snack and water. Ask when results will be ready (usually a few days to a week, read by a nuclear medicine specialist and sent to the neurologist).

What not to do

  • Don't assume all PET scans are the same. Always confirm whether it's FDG-PET or amyloid PET—prep differs significantly.

  • Don't let the patient eat or drink anything except water before an FDG-PET. If they accidentally eat, call the imaging center immediately.

  • Don't keep the patient awake or active during the FDG-PET waiting period. Falling asleep is helpful.

  • Don't argue if staff say you can't be in the scan room. Ask to be nearby or to be called when the scan ends.

  • Don't forget to ask about cost and insurance coverage. Amyloid PET may not be covered by Medicare; FDG-PET coverage varies.

  • Don't skip the stillness drill. Even a few minutes at home reduces movement during the scan, avoiding repeat scans.

Practical tools

  • Two-Scan Checklist

    On paper or phone, list: scan type, date, time, fasting required (yes/no), quiet dark room needed (yes/no), waiting time after injection, and items to bring. Check off each item.

  • Reassuring Phrases for Your Loved One

    Say: 'We're going to a place where they take pictures of your brain. You'll get a small poke in your arm, then we'll rest. Then you'll lie on a soft table and stay still for a few minutes. I'll be right with you.' Avoid words like 'test' or 'procedure' if they cause anxiety.

  • Comfort Kit Bag

    Pack: a soft blanket, favorite small comfort object, sleep mask, earplugs or noise-cancelling headphones, water bottle, snack (for after scan), medication list, allergies list, and doctor's order. Label the bag with the patient's name.

  • Stillness Drill Timer

    Use a kitchen or phone timer. Practice lying still for 5 minutes, then 10. Say: 'Let's be very still until the timer beeps. You're doing great!' Gradually increase duration.

Discuss with your clinician

Ask your doctor: ‘Is an FDG-PET or an amyloid PET scan the right test for my loved one’s specific symptoms and suspected diagnosis?’

Ask your doctor: ‘Are there any medications my loved one should stop taking before the scan? For example, some medications can affect brain activity and may need to be paused for an FDG-PET.’

Ask your doctor: ‘What are the risks of the radioactive tracer? Are there any side effects I should watch for?’

Ask your doctor: ‘If the scan shows amyloid plaques, what does that mean for treatment options? Are there anti-amyloid medications like lecanemab or donanemab that might be appropriate?’

Ask your doctor: ‘If the scan is negative for amyloid but symptoms suggest Alzheimer’s, what are the next steps?’

Ask your doctor: ‘For Lewy body dementia, would a different test, like a dopamine transporter SPECT scan (DaTscan), be more helpful?’

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