A lung PET scan takes about 20 to 30 minutes of actual imaging time, but you should expect to spend 2 to 3 hours at the facility from arrival to departure. Most of that time is spent waiting quietly after the radioactive tracer injection, not inside the scanner itself.
The Full Timeline at the Facility
Your visit breaks down into several distinct phases, and understanding each one helps set expectations for the day.
When you arrive, staff will check you in, confirm your fasting status, and measure your blood sugar with a finger prick. You’ll change into a gown and have an IV line placed for the tracer injection. This check-in and prep phase typically takes 15 to 30 minutes.
After the tracer is injected, you enter the longest stretch of the visit: the uptake period. You’ll rest quietly in a chair or on a bed for about 60 minutes while the tracer travels through your bloodstream and collects in metabolically active tissues, including any areas of concern in your lungs. Guidelines recommend an uptake window of 55 to 75 minutes. During this time, you’ll be asked to avoid talking, reading on your phone, or moving around, since muscle activity can pull the tracer away from the areas your doctor needs to see.
The actual scan comes next. You’ll lie on a narrow table that slides through a ring-shaped scanner. For a combined PET-CT scan, which is the standard approach for lung imaging, the process runs about 20 to 30 minutes. PET-MRI scans, used less commonly, take closer to 45 minutes. Once imaging is done, you’re generally free to leave right away.
What Happens Inside the Scanner
The scanner itself is open on both ends, so it feels less enclosed than a traditional MRI tube. You’ll need to lie still and may be asked to hold your breath briefly at certain points. For lung scans specifically, breathing motion can blur the images because your lungs expand and contract with each breath. Some facilities use a technique called respiratory gating, which synchronizes the imaging with your breathing cycle. Studies show this adds little to no extra time, with gated whole-body scans completing in about 21 minutes on average.
You won’t feel anything from the scan itself. There’s no noise like an MRI, and the tracer injection feels like a standard IV. Some people find the hardest part is simply lying still for the duration.
Preparation Before You Arrive
Your prep starts the night before or several hours ahead of your appointment. You’ll need to fast for at least 4 to 6 hours before the tracer injection. Morning appointments are common because you’ll naturally be fasting from the night before. If your scan is in the afternoon, you’ll need to stop eating at least 4 hours prior.
Blood sugar matters for this scan. The tracer used in lung PET scans is a sugar-based compound, and high blood glucose can compete with it, reducing image quality. Staff will check your levels before proceeding, and scans generally go ahead when blood sugar is under 200 mg/dL. If you have diabetes, your care team will give you specific instructions about managing your medication and meals beforehand. Elevated fasting glucose is actually common among lung cancer patients, so don’t be surprised if staff pay close attention to this step.
You’ll also be asked to avoid strenuous exercise for 24 hours before the scan, since physical activity affects how the tracer distributes in your body.
Newer Scanners Are Getting Faster
If your facility uses a newer digital PET-CT system, your time inside the scanner may be shorter than the traditional estimates. Digital detectors are more sensitive than older technology, which means they can capture the same quality images in less time. Recent data from facilities using the latest generation of scanners show scan times reduced by up to 33 to 40% compared to conventional systems. For some protocols, individual imaging positions dropped from 3 minutes down to 2 minutes each.
These faster scans also use less radioactive tracer, which means a lower radiation dose. You won’t always know in advance what type of scanner your facility operates, but if speed is a concern, it’s worth asking when you schedule.
After the Scan
Once imaging wraps up, there’s no formal recovery period. The tracer decays naturally and leaves your body through urine over the next several hours. Drinking plenty of water after your scan helps flush it out faster. Most people return to normal activities, including eating, immediately after leaving the facility.
If you’re around young children or pregnant individuals, some guidelines suggest limiting prolonged close contact for a few hours after the scan, since your body does emit a small amount of radiation until the tracer clears. Your technologist will let you know if any specific precautions apply.
Results typically aren’t available the same day. A specialist reads the images and sends a report to your ordering physician, which usually takes 1 to 3 business days depending on the facility.