What Is Backscatter And Millimeter Wave Detection? (TSA Scanners)
Backscatter scanners use low-energy, ionizing X-rays to form an image from radiation scattered back by the body and objects on it. Millimeter-wave scanners use reflected, non-ionizing radiofrequency energy instead. TSA retired backscatter passenger scanners in 2013; U.S. airport body scanners now use millimeter-wave technology and show officers a generic outline with areas to check.
Planning: Identify the Scanner Technology and Its Purpose
A body scanner is a security tool, not a medical test. The key distinction is the type of energy it uses: backscatter systems use X-rays, while millimeter-wave advanced imaging technology (AIT) uses radiofrequency energy. Both are designed to help find objects concealed under clothing, but neither guarantees that every object will be found.
People often use “body scanner” as if it names one device. It does not. The technology matters because the two systems work in different ways and have different safety rules. TSA retired its passenger backscatter scanners in 2013. TSA airport AIT screening now uses millimeter-wave scanners.
Both kinds of scanner aim to find items that may need further inspection. A scan result is not a medical diagnosis, proof that a particular object is present, or proof that no object is present. The officer may need to resolve an alert using other screening steps.
What does a TSA scanner look for?
A TSA scanner checks for items on or near the body that may be hidden under clothing. It does not identify every item by name, and it is not designed to assess a person’s health. If the system flags an area, an officer may carry out additional screening to resolve it.
In practice, an alert means that a spot needs attention, not that the system has confirmed a prohibited item. Clothing folds, personal items, and medical devices may affect screening. Follow the officer’s instructions and explain relevant concerns before the scan.
How Backscatter and Millimeter-Wave Scanners Work
Backscatter and millimeter-wave systems form screening results from different kinds of energy. Backscatter measures low-energy X-rays scattered back from the body or objects. Millimeter-wave AIT measures radiofrequency energy reflected from the body and nearby objects. The distinction matters: X-rays are ionizing radiation, while millimeter waves are non-ionizing radiofrequency energy.
Backscatter X-ray screening
Backscatter is a type of X-ray imaging. The system directs a low-energy X-ray beam at a person and measures radiation that scatters back. Differences in the returned signal can help reveal objects beneath clothing.
Because it uses X-rays, backscatter involves ionizing radiation. “Ionizing” means the energy can remove electrons from atoms. TSA retired its passenger backscatter scanners in 2013, so they are not the technology used for current TSA airport AIT screening.
Millimeter-wave AIT screening
Millimeter-wave AIT sends radiofrequency energy toward the person and measures what reflects back. This energy is non-ionizing and does not produce an X-ray image. TSA systems use automated target recognition to show a generic outline and mark areas that an officer may need to resolve.
“Non-ionizing” describes the type of energy; it does not mean that every exposure in every setting is automatically risk-free. Equipment and exposure conditions remain subject to applicable rules. AIT is also not a medical scan and cannot reliably identify every object.
| Feature | Backscatter passenger scanner | TSA millimeter-wave AIT |
|---|---|---|
| Energy used | Low-energy X-rays | Radiofrequency energy |
| Energy type | Ionizing radiation | Non-ionizing |
| What the system measures | X-rays scattered back | Radiofrequency energy reflected back |
| Image or result | X-ray-based image | Generic outline with areas flagged |
| TSA passenger screening status | Retired in 2013 | Used for current TSA AIT screening |
Access and Clearances: Passenger Options and Accommodations
Screening procedures can depend on the airport, the equipment, and a passenger’s needs. Tell the officer before screening if a medical device, mobility limit, or other concern could affect how you stand or move. If you cannot or do not wish to use AIT, ask the officer about available alternatives; additional screening may be required.
Medical devices, implants, and mobility needs
Do not assume a scanner will identify, distinguish, or clear a particular implant. A device may affect the scan or lead to follow-up screening. Tell the officer about the device and ask how to proceed. If you need help standing, raising your arms, or moving through screening, explain that before the scan begins.
A scan cannot confirm that an implant is safe, diagnose a health condition, or replace guidance from a clinician or device maker. If you are unsure how airport screening may affect a specific device, ask the relevant medical professional before travel.
Choosing an alternative to AIT
If you do not want to go through the scanner, tell the officer and ask what screening options are available. TSA procedures may include a pat-down or other checks. The exact steps can vary, so do not assume that opting out means you can skip screening.
A practical sequence is simple:
- Identify the screening process from posted signs or by asking an officer.
- Share medical or mobility concerns before screening.
- Follow the instructions for AIT or the alternative offered.
- Ask the officer what further screening is needed if the system flags an area.
Execution: How AIT Screening Works
Millimeter-wave AIT screening is a short security process, not a diagnosis. The passenger follows posted directions, the scanner gathers reflected radiofrequency signals, and automated target recognition generates a generic outline. If the system flags an area, an officer carries out the next screening step under TSA procedures.
The details of equipment and instructions may vary by checkpoint. In general, passengers are directed where to stand and how to position themselves. The system processes the scan and identifies areas that may need resolution. It does not provide a reliable, item-by-item inventory of everything a person carries.
If there is an alert, follow the officer’s direction. An alert alone does not establish what caused it. The officer may use additional screening to determine whether the area needs further attention. Do not treat a clear result as a guarantee that no object is present.
Representative screening scenarios
These examples describe common types of situations, not specific documented incidents or guarantees about how a checkpoint will respond.
- A medical implant is present: Tell the officer before screening. The device may affect the result, and the officer can explain the next step.
- A mobility limitation affects the standard position: Explain the limitation before the scan. Ask what accommodation or alternative screening is available.
- The system flags an area: Follow the officer’s instructions for additional screening. The flag is a prompt for resolution, not a diagnosis.
- A passenger declines AIT: Ask the officer about the available alternative and any extra steps. Screening still applies.
Verification: Safety References, Results, and Follow-Up
U.S. rules address X-ray cabinet-system emissions and radiofrequency exposure limits, but they apply to equipment and exposure conditions. They are not a blanket promise that every device or scan is risk-free in every circumstance. For a passenger, the practical step is to identify the scanner type, follow instructions, and raise specific concerns with the officer.
What the federal references cover
21 CFR 1020.40 addresses emissions from cabinet X-ray systems. It is relevant to equipment that uses X-rays, such as backscatter systems, but it does not make a millimeter-wave scanner an X-ray device.
47 CFR 1.1310 sets radiofrequency exposure limits. It is relevant to radiofrequency sources, including millimeter-wave systems. The rule concerns exposure limits and conditions; it should not be read as a claim that all exposure in all circumstances has zero risk.
These references help distinguish the regulatory framework for the two energy types. They do not allow a passenger to infer the exact performance or safety of a specific scanner from its name alone. If you have a concern about a device or an exposure, ask airport staff about the equipment and process in use.
What a scan result can and cannot tell you
AIT can flag areas that need a closer check, but it is not a medical tool and does not identify every object with certainty. A clear screen is not a guarantee that no item is present. A flag is not proof that an item is prohibited.
The most useful way to read a result is as one part of a screening process. Officers may use follow-up steps when needed. Cooperate with those directions, and ask for clarification if you do not understand what is being requested.
Frequently Asked Questions
These answers cover the core differences between backscatter X-ray scanners and millimeter-wave TSA screening. Procedures can vary, so follow airport signs and officer instructions for the screening in front of you.
Is a TSA body scanner an X-ray machine?
Current TSA AIT passenger scanners use millimeter-wave radiofrequency energy, not X-rays. TSA retired its passenger backscatter X-ray scanners in 2013.
What is backscatter in airport security?
Backscatter is an X-ray method that measures low-energy radiation scattered back from the body or objects on it. It is an ionizing-radiation technology.
What is millimeter-wave detection?
It is a screening method that sends radiofrequency energy toward a person and measures the reflected energy. TSA AIT uses it to flag areas for officer review.
Does millimeter-wave screening use ionizing radiation?
No. Millimeter-wave energy is non-ionizing radiofrequency energy. That distinction does not mean every device or exposure is risk-free in all conditions.
Do current TSA scanners show officers a detailed body image?
TSA AIT uses automated target recognition to display a generic outline and mark areas that may need resolution, rather than showing a detailed passenger image.
Can a TSA body scanner detect every concealed object?
No. Neither technology is a reliable way to identify every object. Officers may use additional screening if an area is flagged or needs review.
Can a scanner identify or clear a medical implant?
Do not assume that it can. Tell the officer about the implant before screening and follow the instructions given.
Can I decline millimeter-wave AIT?
Ask the officer about the available alternative. TSA procedures may involve a pat-down or other additional screening.
What does an AIT alert mean?
It means the system marked an area for resolution. It does not, by itself, prove what caused the alert or confirm that an item is prohibited.
Which safety rules relate to these scanners?
21 CFR 1020.40 addresses cabinet X-ray system emissions. 47 CFR 1.1310 addresses radiofrequency exposure limits. The rules apply to equipment and exposure conditions, not as a guarantee of zero risk in every situation.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
