CHICAGO — The chief executive of Chicago-based Mobile Doctors pleaded guilty today to charges that he fraudulently increased Medicare bills for in-home treatment that was shorter and less complicated than the claims indicated. DIKE AJIRI, 44, of Wilmette, admitted in a plea agreement that he personally altered patient files so that the now-defunct company could fraudulently bill several patient visits to Medicare at the highest possible level. The improper billing – known as “upcoding” – defrauded Medicare and the Railroad Retirement Board of approximately $1,854,000, according to the plea agreement.