Method and apparatus for injecting a substance into the bloodstream of a subject

A method of injecting a substance into the blood stream of a subject, so that a concentration of said substance in the blood stream of said subject increases linearly with time making said concentration follow a predetermined function of time, comprising the steps of:

• (a) providing a signal proportional to the concentration of said substance in the blood stream of said subject;
• (b) connecting said signal into a feedback loop to control the rate of injection of said substance;
• and,
• (c) injecting said substance at said controlled rate.

An apparatus for the injection of a radiopharmaceutical into the bloodstream of a subject, such that the concentration of said radiopharmaceutical in the bloodstream increases linearly over a period of time making said concentration a predetermined function of time and thus a known quantity for any given time, comprising:

• (a) means for the injection of said radiopharmaceutical into the bloodstream of said subject, said injection means being driven by a servo motor;
• (b) means for measuring the concentration of said radiopharmaceutical in the bloodstream of said subject that permits this measurement to be carried out in a time that is short compared to the radioactive and biological-lives of said radiopharmaceutical;
• (c) means for generating a function of the time elapsed after the beginning of the injection of said radiopharmaceutical, which function reflects the half-life of said radiopharmaceutical and the physiological parameters effecting disposition of said radiopharmaceutical, said function serving as a reference for the desired concentration of said radiopharmaceutical in the bloodstream of said subject;
• (d) means for comparing the concentration of said radiopharmaceutical in the bloodstream of said subject with said function and generating an error signal proportional to the variation of said concentration from said function;
• and
• (e) means for controlling the rate of injection by said injection means in response to said error signal.