Studies with an angiographic injector of automatic flow-rate control design.

Abstract

With the growth of angiography as a branch of Radiology, several different types of pressure injectors have been developed to deliver contrast material rapidly into the vessels and the heart. Whether the injector is powered by an electric motor or by gas pressure, the operator can select the desired pressure to be delivered to the contrast medium in its syringe. The actual delivery rate of contrast media from the catheter into the vessel, then, is dependent on the internal bore and length of the catheter, on the viscosity of the contrast medium, and on the size of the connector or stopcock between the syringe and the catheter. Physical limitations of the system are imposed by the amount of pressure the injector can develop and by the strength of the catheter wall. The possibility of injuring tissue by the force of the jet or by the impaction of the tip and backlash movement of the catheter is the ultimate limitation of the injection procedure (4). To obtain the injection of a sufficient amount of opaque medium in a precise, short time-period one must know the capacity and characteristics of the injector, catheter and connections, and contrast medium. A previous study has shown that the best knowledge of flow-rate pressure relationships is obtained by pretesting the equipment in the laboratory under the same conditions as are to be used with the patient (3). It has been demonstrated that neither the Poiseuille formula for laminar flow or the Blasius formula for turbulent flow can be relied upon to predict rates of delivery of commonly used contrast media with a variety of catheters and injectors. The development of a new type of injector based on an automatic flow-rate control principle, has led to the expectation that a selected volume of one of several contrast media could assuredly be delivered through a variety of catheters. An evaluation was considered appropriate. Equipment and Methods A Viamonte-Hobbs injector, model 2000, was tested. The injector has two primary injection controls, one for the flow rate, with its scale graduated from 2.0 ml/sec. to 60 ml/sec.; and the other a timer, with its scale graduated from 0.2 second to 10 seconds. The two together determine the injection of a specific volume in a designated time. Additional features will not be considered here, but are well described elsewhere (6). The injector has a high-speed motor with a direct-coupled screw to drive the plunger into the barrel of the syringe. The syringe is of stainless steel and has a volume of 100 ml. The catheter was connected to the syringe with a Clay-Adams fitting. Injections were made through the catheter into a 100-ml graduated cylinder. An electric timer was used to verify the accuracy of the duration of the injection. Triplicate injections were made to check the reproducibility of performance.