Adac Laboratories, the largest U.S. maker of nuclear-medicine imaging equipment, said it expects to take a pretax charge of $7 million to $9 million for its fiscal fourth quarter ended Sunday as it increases its international sales force and discontinues a business. Milpitas-based Adac, which had revenue of $282.3 million last year, said it will fire an undisclosed number of employees as it tries to increase earnings in Latin America and Europe by cutting overhead and increasing its sales and support staff. Adac, which is eliminating its 2-year-old physician services business, is concentrating on expanding its nuclear-medicine imaging business. It already controls about half the U.S. market but wants more from overseas. Adac is expected to report earnings of 39 cents a share for the fourth quarter. Its shares fell 6 cents to close at $24.94 on Nasdaq.