After Susie Davis, 5, her brother Steve, 9, and their friend, 10-year-old Jimmy Larkin, filled bags with trick-or-treat loot from their Mount Vernon neighbors last night, they went to Mount Vernon Hospital and watched the goodies on television.

Strictly speaking, what the three crowded around wasn't a television set, but the images that moved across the fluoroscope monitor had their own fascination. On the screen was a parade of Halloween candy made transparent by X-rays and carefully monitored by radiology technologist Michael T. Myatt for bits of metal, glass or other evidence of tampering.

Mount Vernon was one of several area hospitals to offer free X-rays of Halloween candy last night.

Mount Vernon has checked treats for several years, a spokeswoman said. "When they started in on all the tricks people were pulling on the candy, that's when we started checking it," she said.

The fluoroscope will detect pieces of metal, needles and, occasionally, glass, radiologists said. But it cannot check for powder or liquid mixed or injected into candy.

Myatt and radiology technologist Betty McDowell said parents have become increasingly conscientious about bringing in their children's treats.

"It's very upper-middle class suburbia up here," said Mary Davis as her children peered at their candy -- splotches and squares in various shades of gray -- drift across the monitor screen. "You never think you would have problems like this."

Myatt donned a protective tunic, darkened the room and offered a play-by-play as the goodies passed the fluoroscope lens. "There's the Lifesavers. Those are the York peppermint patties over there," he narrated as the children giggled.

The Davis's candy checked out, as did Jimmy Larkin's and 4-year-old Christine McQueen's. Word of the fluoroscopy service "gets around fast," said Christine's mother, Jane.

William York and his 6-year-old son, William Jr., were among a cluster of about 10 persons waiting in the corridor. The younger York toted a plastic pumpkin stuffed to the stem with candy.

"We have a lot of neighbors, friends and relatives who wouldn't even let their kids go out for Halloween," said the elder York, "but I think kids should be able to do everything kids have done in the past."

McDowell herded in the next group. The service "is done free for the public," she said. "If they can take a few minutes to come in, it's well worth it."

Back toward the lobby, a man and a costumed child approached the receptionist, who started to inquire: "You're here to . . . . "

"For a little peace of mind," the father said.

By midnight, there were no reports from area hospitals of finding candy that had been tampered with.