In 1997, Medical Instrumentation Diagnostics Corporation (MIDCO) filed a patent infringement lawsuit against Elekta for alleged infringement of US Patent No. 5,398,684 (the '684 patent), which claims an apparatus and method for acquiring images from different imaging sources, converting the images into a selected format and displaying them on a single device. MIDCO claimed that three Elekta medical products infringed the apparatus claims in the '684 patent. MIDCO did not pursue infringement of any method claims in the '684 patent, and the US District Court for the Southern District of California dismissed the method claims without prejudice at Elekta's request. After a jury verdict of infringement, the Federal Circuit reversed because the patent specification did not disclose software for digital-to-digital image conversions. As a result, the Federal Circuit found that a means-plus-function claim limitation for image conversions was limited to analog-to-digital conversions. The Federal Circuit reversed the infringement finding because Elekta's accused products did not perform analog-to-digital conversions. On remand, the district court refused to allow MIDCO to revive the dismissed method claims, and that decision was summarily affirmed by the Federal Circuit in 2005.

In 2009, MIDCO licensed the '684 patent to Brain Life. In July 2010, Brain Life filed suit against Elekta and other defendants for infringement of the '684 patent's method claims. Brain Life alleged infringement by four Elekta medical products:

The district court granted summary judgment that Brain Life's claims were barred by the MIDCO litigation because:

After Elekta's dismissal, the case proceeded against the other defendants. In a claim construction order, the district court held that the '684 patent's method claims were broader because they covered digital-to-digital conversions (unlike the apparatus claims that were limited to analog-to-digital conversions).

The Federal Circuit explained that claim preclusion bars relitigation of claims that were or could have been brought in the earlier case. To apply claim preclusion in a patent case, the accused product must be essentially the same as the accused product from the earlier case. Applying this standard, the court held that claim preclusion bars Brain Life's allegations of infringement concerning alleged infringements that predated the MIDCO case's final judgment. However, the court held that claim preclusion does not preclude Brain Life's claims for infringements occurring after the MIDCO final judgment. The court found that claim preclusion should not apply to these claims because MIDCO could not have sought damages for future infringements that had not yet occurred.

The court noted that issue preclusion bars parties from relitigating claims or facts that were fully, fairly and actually litigated in an earlier suit between them. The Federal Circuit found that issue preclusion did not bar Brain Life's claims because:

The Kessler Doctrine provides that when an accused infringer obtains a final judgment of non-infringement, the accused products acquire the status of non-infringing devices and the patent owner is barred from asserting that they infringe in a second lawsuit. Unlike claim preclusion, the doctrine immunizes infringing acts that occur after the earlier case's final judgment. The Federal Circuit observed that its past reliance on the Kessler Doctrine has been "sparse" and that the doctrine's continuing viability may be questionable based on modern developments in defensive estoppel law. Nevertheless, the court found that the Kessler Doctrine precluded Brain Life's claims against the three Elekta products involved in the MIDCO litigation because MIDCO could have pursued the method patent claims in the earlier case and the accused products are materially similar. The court found that the Kessler Doctrine did not apply to the ERGO++ product because it was not accused of infringement in the MIDCO suit.

Because claim construction, issue preclusion and the Kessler Doctrine did not preclude Brain Life's claims against the ERGO++ product, the Federal Circuit reversed and remanded the case for further proceedings.