Method of labeling proteins with technetium

A method of binding 99m technetium to fibrinogen to produce fibrinogen labeled with 99m technetium comprising the steps of:

• 1. reducing pertechnetate at a pH of about 11 to 12 by the addition thereto of a solution of acetic acid and stannous chloride in the presence of a base;
• 2. contacting the thus reduced pertechnetate with fibrinogen thereby labeling the fibrinogen with 99m technetium;
• 3. removing unbound technetium and technetium bound to molecules having a molecular weight less than 100,000, and in a second purification step;
• 4. removing all molecules having a molecular weight less than 300,000, thereby producing a product having about 90% or more of the 99m technetium bound to the fibrinogen.

A method of producing an injectable solution of 99m technetium labeled fibrinogen comprising the steps of:

• 1. reducing pertechnetate at a pH of about 11-12 by adding a solution of acetic acid and stannous chloride in the presence of a base;
• 2. dissolving lyophilized fibrinogen including buffer salts associated therewith in water yielding a fibrinogen solution;
• 3. mixing the fibrinogen solution of step (2) with the reduced pertechnetate of step (1) at ambient temperature for about 15 minutes;
• 4. lowering the pH of the solution of step (3) to a final pH of about 7-8 by the addition of an aqueous solution of sodium citrate and citric acid;
• and
• 5. removing fibrinogen degradation products and non-bound technetium, thereby producing an injectable solution of fibrinogen labeled with 99m technetium.