When the Tour de France starts Saturday, some cyclists may as well wear targets on their backs. Anti-doping officials are boosting their arsenal and preparing to use it like never before at cycling's main event, with several riders out of the 180 in the cross-hairs already before the three-week race begins in Monaco. Focusing on suspicious competitors is one of the major innovations at this year's Tour, which is hoping to eradicate the doping scandals that have obliterated the sport's image in recent years. Pat McQuaid, the head of the International Cycling Union, says the race will be the most rigorously tested event in history. There will be about 520 doping tests. “(I'm) neither an optimist or a pessimist (that) it could be the year that we get no scandals,” he said in a phone interview Monday. “There's always an idiot out there who will try something.” In recent weeks, 50 riders likely to compete in the Tour have faced enhanced anti-doping tests. That includes team leaders, race favorites and an unspecified small number of riders with suspicious profiles, McQuaid said. The list of suspects has been drawn up based on the UCI's new “biological passport” program. In it, riders have provided blood or urine samples compiled in individual body chemistry profiles that anti-doping officials can compare to their race-day parameters. Any fluctuations from the athlete's known baseline levels could possibly be doping – in effect, searching for evidence of doping rather than individual illegal substances. McQuaid says the passport has acted as “a huge deterrent” to cheating. Levi Leipheimer, an American with the Astana team who has three race victories and four stage wins this year, said the passport suggests “they are tightening the net around doping and dopers.” “I think that's a great thing,” he said Monday on a conference call with reporters. “Maybe in the future we'll look back and say it improved from this date.” Among other new tactics, doping testers will indicate which riders they want to target as late as 15 minutes before the end of each stage – hoping to catch cheaters off-guard. Testers will also freeze riders' samples and store them, in the hope that if anti-doping checks are unable to turn up drug use today, maybe some day they will. McQuaid said that, as in years past, the stage winner and overall race leader will be automatically given doping tests after each stage, along with six other cyclists. The designer drug of choice in recent years has been the blood-booster EPO and – increasingly last year – an advanced version called CERA. Doping chiefs are also on the lookout for so-called blood doping – a practice in which riders extract their own blood, store it and inject it when needed. Such transfusions have been difficult to detect, but the top anti-doping official in France has said he expects a relevant test to be perfected.