The disabled 60-year-old driving a royal blue Chevy Malibu on New Hampshire's Spaulding Turnpike didn't look like an emissary of Al Qaeda.

But there was something menacing coming from his car.

On his way home last month after receiving a PET scan at Portsmouth Regional Hospital, Michael Rosenthal noticed a State Police sport utility vehicle driving next to him and the trooper inside staring at him strangely. The trooper then sped in front of Rosenthal, slowed down, and pulled behind him.

"I was in the granny lane, driving on cruise control, taking my time, when all of a sudden I looked over and I saw this trooper with a puzzled look," said Rosenthal, a former New York City police officer who lives in East Wakefield, N.H. "When he put on his blue lights and pulled me over, I knew it wasn't a normal traffic stop."

The trooper, Bill Burke, walked over to Rosenthal, but the State Police veteran didn't ask for his license or registration. Instead, he had an all-too-knowing, Big Brotherlike question.

"Were you in contact with any radioactivity today?" he asked.

Rosenthal began to wonder whether his veins were glowing from the chemicals injected for the scan.

"I thought it was an odd question, like I was on 'Candid Camera,' " Rosenthal said.

He asked Burke why he was asking the question, and the trooper explained that he carries a radioactivity sensor and that something in Rosenthal's car set off the alarm.

"It's very rare that you get them going off for a vehicle going by," said Sergeant John Begin of State Police Troop G, which monitors radioactive waste in commercial vehicles passing through New Hampshire. "I can only think of three or four cases."

Rosenthal registered a six on the sensor's scale, which goes from one to nine, with nine the highest amount of radioactivity.

Begin said that about 30 New Hampshire troopers carry the sensors, which are the size of a bulky cellphone and can detect radioactivity as far away as 100 feet. New Hampshire bought the radiation-detecting equipment, called Mini rad-Ds and made by D-tect Systems, with a grant from the US Department of Homeland Security before the 2004 Democratic National Convention in Boston as part of efforts to prevent attacks on the city.

On the side of the turnpike that Nov. 21, Rosenthal explained to Burke that he had just come from having a positron emission tomography scan, which requires an injection of short-lived radioactive isotopes to identify any unhealthy cellular activity. The isotopes can remain in the body for as long as 18 hours, and patients are advised to keep their distance from others for that period.

"I told him I was surprised his equipment could detect the radioactivity in my body," Rosenthal said.

But Burke didn't take Rosenthal's word for it. He asked him to prove it.

"I was very lucky that I had the documents with me from the hospital," he said. "After that, he was satisfied and sent me on my way."

Like hospitals around the country, Portsmouth Regional does hundreds of scans a week. Nancy Notis, a hospital spokeswoman, said Rosenthal's case is the first time they've heard of a patient being pulled over for emitting radioactivity.

As a result, she said, the hospital is reviewing whether to alert patients that they could be stopped by police.

Despite his delay getting home, Rosenthal said he is happy to know the police are on the prowl for terrorists.

"It made me feel good in one respect - that our money is going to good purposes," he said.

David Abel can be reached at dabel@globe.com.

© Copyright 2008 Globe Newspaper Company.