UK: Experts Told How Not To Approach Obviousness In X-Ray Scanning Patent Case

American Science & Engineering Inc's (AS&E's) patent to a covert X-ray van has been found to be valid (not obvious) by Mr Justice Arnold in the High Court of England & Wales, following a challenge made by Rapiscan Systems Limited (Rapsican). Rapiscan had infringed the patent.

Mr Justice Arnold's decision of 11 April 2011 in American Science & Engineering Inc v Rapiscan Systems Ltd [2016] EWHC 756 (Pat) is available here.


AS&E brought proceedings against Rapiscan for infringement of its European Patent (UK) number 1,558,947, entitled "X-ray backscatter mobile inspection van" (the "Patent"). Rapiscan conceded that if the Patent was valid then it had infringed it; however Rapiscan asserted that the patent was invalid for lack of inventive step.

Common general knowledge and the skilled team

It was agreed that the patent was addressed to a team engaged in developing X-ray scanning systems, which would be headed by a physicist skilled at designing X-ray imaging systems.

At the relevant time (2002), there was only a small community of manufacturers. The USA being the leading national market and the market driver in terms of development, the global security scanning market was US-centric: a skilled person in the field working in the Western world would be interested in developments in that market and aware of the interest in obtaining mobile detection systems.

The 'common general knowledge' included an understanding of the physics of X-rays, as well as of scanning and security systems in existence at the time and used, for example, in airports and ports. Much of the judgment (paragraphs 9-64) is dedicated to explaining the technology.

The Patent

The Patent claimed "an inspection system for inspecting an object comprising an enclosed conveyance" with a number of features, including the following:

  1. "the detector module is contained entirely within the body of the enclosed conveyance while the conveyance is in motion during the course of inspection"; and
  2. "characterised in that the system further comprises a relative motion sensor for generating a relative motion signal based on a relative motion of the enclosed conveyance and the inspected object".

In practice, the advantage of the claimed arrangement was that it enabled a mobile x-ray scanner to be used for covert imaging (i) with the vehicle moving past the target - in "drive-by" mode, (ii) with the vehicle stationary as the target moves past it - in "drive-past" mode, and also (iii) with the vehicle overtaking the target while both are in motion.

Was the Patent obvious?

By the trial, the substantive issues between the parties had narrowed to whether the claims of the Patent, and in particular integers (f) and (g) were obvious in light of one piece of prior art, "Swift". Swift  was a paper published in the proceedings of a well-attended industry conference.  It described a prototype of AS&E's marketed 'MobileSearch' system.

Claim feature (f)

Swift stated that the closet doors of the described system were "opened and secured" during scanning. This, said Arnold J, meant that claim feature (f) was not disclosed by Swift.

Was claim feature (f) nevertheless obvious? In the judge's view it would be sufficient to bring Swift within this aspect of the claim to re-design it to operate with the doors shut. In effect, this would involve changing the system described in Swift into a covert system.

However, on the evidence, the judge thought this depended upon hindsight. A 'throwaway' suggestion to such effect in another article in a trade journal did not address the practicalities of doing so. For example, one would need not simply to shut the doors, but to replace them with non-attenuating material in order to obtain a useful image.

Claim feature (g)

As regards feature (g), Swift did not require a relative motion sensor because it operated at two fixed speeds. Rapsican contended that it would be obvious to incorporate one into the system described by Swift i.e. for use in a drive past mode, but the judge disagreed. In doing so he referred to a number of arguments made by AS&E, including that:

  • Swift made no mention of the possibility of a drive-past mode; in fact it taught away;
  • there were no mobile drive-past backscatter systems in operation at the relevant time;
  • the Swift system did not lend itself 'naturally' to such a mode; and
  • Rapsican's case amounted to cherry-picking one particular feature of a system that was within the common general knowledge (Mobile VACIS) and then combining that with Swift while ignoring both a key aspect of Mobile VACIS and a proposal in Swift.

The judge therefore concluded that converting Swift into a drive-past system was only obvious with hindsight.

Features (f) and (g) combined

Further, even if the steps from Swift to features (f) and (g) were individually obvious, Arnold J considered that the combination was not. There were plenty of obvious avenues for development of Swift, some of which were flagged in the paper itself, but changing the whole method of operation of the system in order to reach the claimed invention was far removed from these, and it was only with hindsight that the necessary changes could be seen as relatively simple.

Secondary evidence

Arnold J noted that he found "modest support" for his conclusion that claim 1 was not obvious in the 'secondary' evidence. In particular, nobody had come up with the claimed invention in the six years following Swift; and the evidence of Rapiscan's response to the commercial success of AS&E's commercial vehicles which implement the invention also supported this finding.

Short shrift was given to Rapiscan's arguments that the six-year interval between the publication of Swift and AS&E's patent filing was explained by AS&E having patent protection for relevant systems (i.e. reducing the incentive for third parties to develop such systems).

The judge also disagreed with Rapiscan's contention that the burden lay on AS&E to refute this. It was "plain" that the burden lay upon Rapiscan to prove the existence and relevance of facts they relied on; and the burden had not been met.

Expert evidence - asking the right question

Arnold J was critical of the instructions given to both experts. Both had been instructed to consider the person skilled in the art and the common general knowledge, then to consider the prior art relied upon by Rapiscan, and only then to consider the Patent. But there were, nevertheless, differences in the way the parties' respective approaches had been structured.

AS&E's expert was asked to consider obvious developments of the prior art before being shown the Patent. This resulted in criticism that he had failed to address whether the differences between Swift and the Patent constituted steps which would have been obvious to the person skilled in the art.

In contrast, Rapiscan's expert was only asked to consider obviousness after being shown the Patent. While this avoided the difficulty of AS&E's approach, Rapiscan's approach resulted in its expert appearing not to have understood the importance of trying to avoid hindsight.

Comment: how should expert witnesses be instructed to proceed in an obviousness challenge?

Previously, in Medimmune v Novartis ([2011] EWHC 1669 (Pat)), Arnold J noted that the correct approach for the lawyers instructing the experts (in that case) to take was to ask the expert to consider, first, the prior art, then the priority documents and then the patent. This enabled the expert to form and express his opinions on the prior art without knowledge of the invention, and on the priority documents without knowledge of the patent.

In the present case, which was concerned just with an obviousness challenge, the approaches taken by the parties' representatives when instructing their respective expert witnesses would appear to have been consistent with the judge's earlier guidance. Nevertheless, both approaches were criticised without a solution being spelt out by the judge. Rapiscan's approach, of asking its expert only to consider the question of obviousness after being shown the patent, appeared to receive the greater criticism.

So how should expert witnesses be asked to proceed when retained in the context of an obviousness challenge?

The correct question for the expert to be asked to consider in the context of an obviousness dispute is whether, viewed without any knowledge of the claimed invention, the differences constituted steps which would be obvious. The expert must understand the importance of trying to avoid hindsight.

AS&E's approach, of asking its expert to consider obvious developments before showing him the patent, had the "advantage" of enabling the expert to consider obvious developments of the prior art free from knowledge of the patent, and so would seem the better course, but this alone is not enough. It would seem advisable for the expert then to be asked to consider whether the differences between the prior art and the claimed invention constituted steps which would have been obvious to the person skilled in the art, whether or not they occurred, in fact, to him.

In more complex disputes, where issues of priority, added matter, sufficiency and/or multiple challenges to validity arise (or are contemplated), very careful consideration must be given to the order in which documents are first put to an expert witness.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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