The FBI arrested 46 doctors and nurses across the country this week in the largest Medicare fraud bust ever.

In total, 243 people were arrested in 17 cities for allegedly billing Medicare for $712 million worth of patient care that was never given or unnecessary.

In one of the most egregious cases, owners of a mental health facility in Miami billed tens of millions of dollars for psychotherapy sessions based on treatment that was little more than moving patients to different locations, said Attorney General Loretta Lynch.

Four people are charged for mass-marketing a talking glucose monitor and sending the devices to Medicare patients across the country who didn't need or request them. They billed Medicare for the devices and received more than $22 million.

In some cases health care providers paid kickbacks to fraudsters who could get their hands on Medicare patients' personal information. They would then use that info to bill Medicare for bogus care.

Sometimes fraudsters, known to the Feds as "patient recruiters," will go to places like homeless shelters and soup kitchens and offer money to those who would share their Medicare patient numbers, a Department of Justice spokesman said.

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A Los Angeles doctor is charged for allegedly billing $23 million for 1,000 power wheelchairs and home health services that were not medically necessary and often not provided. And in a Florida case, a health care provider received $1.6 million from Medicare for prescription drugs that were never purchased and never dispensed, said Lynch.

The FBI analyzed billing data to find areas in the country where there is a high potential for fraud.

"In these cases, we followed the money and found criminals who were attracted to doctors offices, clinics, hospitals and nursing homes in search of what they viewed as an ATM," said FBI Director James B. Comey.

The DOJ's Medicare Fraud Strike Force team led the investigations. Since 2007, it has charged 2,300 people who have falsely billed the Medicare program for more than $7 billion. In recent years, the team has expanded from two cities to nine, thanks to an additional $350 million in funding from the Affordable Care Act.