Fixed versus rotating gantry – making an informed choice

Reliability – performance – service 

These are the three key areas to evaluate when upgrading explosives detection systems (EDS) from single or multi-view X-ray to computed tomography (CT) technology.  This is a costly, long-term investment so it is critical to make informed decisions and choices – and there is a difference between marketing positioning and field-tested results.

For example, what about fixed versus rotating data acquisition (also referred to as fixed or rotating gantry).  Mechanical rotation is a mature technology which has been used in medical applications for over 20 years. Significant advances in bearing design have increased equipment lifespan far beyond the replacement cycles typically found in security screening.  Static gantry supporters will often highlight vibration issues in rotating gantries but this does not prove a key issue in the field.  In fact, rotating gantries with a single X-ray source have been proven to deliver a much higher level of availability and reliability than static systems.

Let’s elaborate on the comparison.

One light source vs many

In rotating gantry CT EDS systems, a single X-ray tube, detector arrays and the power supplies are rotated around the object to produce the CT image. The X-ray tube is essentially a high-powered light bulb emitting photons as X-rays, rather than as visible light.

To create CT imagery, a fixed gantry CT EDS generates a fan beam of X-rays using multiple X-ray sources (“sparse view”); or a much more complicated X-ray with hundreds or even thousands of source points (“many view”). This design increases complexity and adds X-ray tubes in order to simulate what can be achieved by rotating a single tube. In addition, the fixed construction makes changes or future upgrades challenging.

The problem with X-ray tubes

From an engineering perspective, the most troublesome aspect of any X-ray screening system is the X-ray tube itself. The components with the highest failure rates in CT EDS systems tend to be associated with X-rays (tubes, as well as the detectors and power supplies).   However, this is not  related to whether the gantry is fixed or rotating, but due to high use during continuous screening operations averaging 20+ hours per day. This becomes a problem for fixed gantries as they rely on dozens (and in some cases hundreds of tubes) which can potentially fail – versus a rotating system which relies on just one tube.

Ask the right questions

In the end, the best way to make a decision is to go on-site and ask questions. Go and see systems which have been operating in a live environment over a period of time and request data on performance, uptime and failure points.   Ask if the machines can be serviced in the field. When a system goes down, how long will it be out of operation? Are spare parts available on-site or nearby? What is the response time for the supplier’s trained technicians and service personnel?

With all the relevant information to hand, you will be ready to make informed choices for your particular operation and will have a system which should last for 15 years or more.

Harald Jentsch
Head of Baggage Handling Solutions
Harald Jentsch
Head of Baggage Handling Solutions
Harald is currently Head of Baggage Handling Solutions for Smiths Detection. In this role he is working closely with divisions like Sales, Products and Technology and Marketing to develop the overall strategy of the business. It includes very close customer interaction to develop the strategic guidelines for the Baggage Screening but also adjacent businesses like Air Cargo and Passenger Screening. Harald’s previous roles in Smiths Detection were mainly in Product Management to guide and develop networking and advanced checkpoint solutions and various activities in roles close to Sales and Business Development.