** Shares of Healius rise as much as 6.5% to A$1.715, posting their biggest intraday percentage gain since Aug. 21

** Healthcare firm signs binding agreement to sell its diagnostic imaging arm, Lumus Imaging, to Affinity Equity Partners

** Says deal implies an enterprise value of A$965 mln ($657.65 mln)

** Says proceeds to be used to reduce debt, among others

** Stock almost flat this year, as of 0109 GMT

($1 = 1.4674 Australian dollars)

(Reporting by Rajasik Mukherjee in Bengaluru)

((Rajasik.Mukherjee@thomsonreuters.com;))