The Securities and Exchange Commission (SEC) has announced an emergency action to freeze the assets of a Las Vegas-based firm and its sole owner charged with perpetrating a Ponzi scheme against thousands of investors primarily living in Japan. The SEC alleges that Edwin Fujinaga and his company MRI International raised more than $800 million from investors who were told that their money would be used to buy accounts from U.S. medical providers with outstanding balances to collect from insurance companies.   They purchased no such accounts in reality, and merely used investor money to pay the principal and interest due to earlier investors in typical Ponzi fashion.