A device for measuring fluid pressure in the lumen of a syringe including a pressure transducer integrally mounted in the plunger of the syringe under the plunger tip, such that the force applied by the plunger to the fluid in the syringe is transmitted to the transducer and the resulting electronic signal is converted to a display value for aiding a physician. The general formula of these salts is X\u22123N+NHCH2CH2COOH where X\u2212 is an acid anion selected from the group of pharmaceutically acceptable acids. The apparatus further includes a detector coupled to the signal generator and configured to receive a combined signal at the injection point when coupled to the electronic signal path and determine an autocorrelation of the combined signal.