Volcano (NSDQ:VOLC) and St. Jude Medical (NYSE:STJ) are at it again, battling in a courtroom once more over fractional flow reserve technology used to measure arterial blood pressure.

Volcano sued St. Jude in a Delaware federal court this week, alleging infringement of a pair of patents covering aspects of its PrimeWire FFR device by St. Jude’s competing PressureWire Certus and Aeris devices.

The technology covered by the patents was invented by researchers at Volcano’s corporate predecessor, Cardiometrics, the lawsuit alleges, saying Douglas Corl, Robert Obara and John Ortiz "were the first to invent a pressure sensing guide wire that uses a solid state pressure sensor."

The 2 patents, both covering technology for an "Ultra Miniature Pressure Sensor," issued March 5 to Volcano, according to court documents.

"St. Jude monitors the prosecution of Volcano’s pending patent applications," according to the lawsuit, which accuses the St. Paul-based medical device company of willfully infringing the patents.

The 2 medical device companies are bitter rivals with a long history of legal wrangling over FFR devices. Last October Volcano won a round when a Delaware jury ruled that 2 Volcano FFR patents don’t infringe St. Jude Medical and deeming a pair of St. Jude patents invalid.