X-ray scanners are complex systems which combine multiple technologies and are part of a wider overall security ecosystem. Selecting the right x-ray scanner requires careful consideration of the scanner’s operational environment, what items will be scanned, and what threats are expected. This article explores five key factors for security professionals to consider when selecting an x-ray scanner.

1.Tunnel Size

Security professionals must be cognizant of what their scanner will be used to scan, specifically the size of potential scanned items. The expected size of scanned items will determine the size of the scanner, because x-ray scanners come in a wide range of sizes from tunnels designed for small bags to freight scanners for a tractor-trailer.

Most x-ray scanners have their tunnel size in their name. For example, the Astrophysics XIS-6040™ has a tunnel that measures 60cm by 40cm, making it easy to determine the size for each scanner.

Astrophysics categorizes x-ray scanners by their tunnel size and general use, as shown below:

• Mail and Small Parcel: 53.3 cm x 35.8 cm – 65.7 cm x 45.1 cm
• Checkpoint: 60 cm x 40 cm – 75.6 x 55.2 cm
• Hold Baggage: 58.4 x 78.3 cm – 100 cm x 100 cm
• Cargo: 58.4 x 78.3 cm – 181.1 cm – 180.5 cm
• Mobile: 100 cm x 100 cm – 101.6 x 81.4 cm
• Vehicle & Freight: 305 cm x 320 cm – 375 cm  x 500 cm

2. Generator Power 

X-ray generators are the energy source for scanners. Understanding the specific scanning use case is vital to selecting the proper x-ray generator. Systems that are too powerful for their use case will be unnecessarily expensive, but systems that are too weak will not scan effectively and will fail to penetrate dense potential threat objects. The machine must be matched to the intended application.

X-ray scanners generate x-rays via high voltage generators that pass that voltage through an x-ray tube. That tube generates x-rays via the excitation of particles that strike a target, emitting x-rays in the direction that the tube is pointed. The power of these generators determines how much radiation the x-ray tube emits. For larger and thicker scan items more x-rays are required and thus a higher power generator is required.

Generators are measured in electron-volts (eV), which essentially measures the kinetic energy of electrons as they move through a vacuum tube. However, since the electron-volt is such a small unit, x-ray generators are always in kilo-electron-volts (keV) and high-power x-ray generators may even be in mega-electron-volts (meV).

Astrophysics offers multiple generator ratings at 90, 160, 180, 200, 320kV and 450keV for small to medium sized generators. Each of the previously mentioned categories corresponds to a range of appropriate generator ratings. Typically, generators range from 160-180kV for checkpoint scanners, 200-320kV for conventional cargo systems, and up to 450keV for the Astrophysics Multi-View CT™. Vehicle scanners can be either 450keV for cars and passengers vehicles, and from 6.0-7.5meV for freight scanners.

 

3. Image Quality

Image quality is critical to x-ray scanner performance.X-ray scanners are only as effective as the quality of their imaging. The inspection process, despite a myriad of image manipulation functions and automation programs, still relies upon the ability of an analyst to review the image and identify threats. If an x-ray manufacturer produces low quality images that are blurred or pixelated, it will be challenging, if not impossible, for analysts to screen effectively and identify threats and contraband. 

Image quality can be broadly determined from the following attributes:

• Contrast: The contrast in an image is the ability to differentiate light and dark areas which, in the case of x-ray scanners, means the ability to differentiate two areas of close but not identical density.
• Spatial Resolution: Spatial resolution refers to the ability of a system to separate similar items that are adjacent. If two items of similar density and material are very close to each other, a poorly performing machine may tend to combine the distinct items into a single detail in the scan image. Spatial resolution is often stated as the minimum distance between two wires suspended in air at which a system can differentiate the wires in an image. Thus, a lower spatial resolution is more desirable.
• Noise: Noise is a general term to refer to undesired photons that are detected in the image. High noise can make an image appear grainy or blurry. There cannot be no noise in an image, but reducing noise is key to good image quality.
• Sharpness: Sharpness is the edge resolution in an image. High sharpness means crisp edges that are easily defined, whereas low sharpness means that edges of details are blurry and may blend.

4. Service 

Service quality is important to consider for maintenance of an x-ray scanner. Scanning machines are complex, often require difficult to acquire components for repair, and are necessary as part of a larger security regime. The quality of a service contract is determined by the following qualities:

• Mean Time Between Failures (MTBF): The MTBF refers to the expected time between major failures that would shut down operation of the system. This will be based on past installations and field testing of the system. A higher MTBF means that the machine will fail less over a given time period.
• Mean Time to Repair (MTTR): The MTTR refers to the expected time between the failure of a critical system component and the completion of repairs by a repair technician. This includes response period, travel time of the technician, diagnostic time, sourcing of parts, and time for repairs. A lower MTTR means that repairs are completed faster, and the machine returns to operation earlier.
• Spare Parts Availability: A good service organization will maintain spare parts inventories that are readily available for repairs anywhere that a system is installed. Many critical components of an x-ray scanner have long lead times from the manufacturers, so the x-ray scanner manufacturer should maintain an inventory of these components so repairs can be completed quickly.
• Remote Service Capabilities: Remote service allows a service organization to diagnose problems remotely by communication with the customer, and perhaps guide customer personnel through basic repairs if possible. A service organization should maintain remote service capabilities to ensure timely and quality repairs.
• Preventative Maintenance: A good preventative maintenance schedule ensures that the machine does not break down due to neglect or easily preventable problems. Service organizations should have a regular preventative maintenance schedule and should ensure that such repairs are completed with minimal involvement of the customer.
• Training: A service organization should have a comprehensive training program for operators of the systems, inspection personnel, and local service technicians. Central service techs who work at the manufacturer’s headquarters might be far remote from the scanner’s installation site, so the ability to train local technicians ensures time repairs.

5. Total Cost of Ownership

The final factor may seem obvious, but it encompasses multiple aspects of acquiring, running, and maintaining an x-ray system. Ensuring maximum product value with minimal lifetime costs requires a holistic review of the below:

• Purchase Price
• Personnel Requirements
• Training Costs
• Product Reliability
• Service Warranty

A scanner that is less expensive upfront, but fails frequently, has slow service support and significant downtime, or requires costly generator replacements, has nowhere near the value and low total cost of ownership of an effective, well-maintained scanner. It is critical to evaluate the total cost of ownership, along with the tunnel size, generator power, imaging quality, and service to determine exactly which x-ray scanner is best for your security mission.

Astrophysics is the Manufacturer of Choice

Headquartered in California, USA, Astrophysics is a premier x-ray manufacturer with over 20 years of experience and ISO certified manufacturing to the highest American quality standards. Astrophysics systems are known for high image quality, reliable performance, and ease of use. We also offer extensive integration, all inclusive service contracts with guaranteed response times, and are known for our “solutions-focused” service delivery system to go above and beyond for our customers.

Looking to purchase x-ray equipment? Have questions? Email our experts at sales@astrophysicsinc.com or call us directly at (909) 598-5488 for more information.