Automatic Injection Devices

CHAPTER OBJECTIVES

After completing this chapter, the reader will be able to perform the following:

Identify the need for automatic injection devices

List the basic components of an automatic injector

List and describe the advantages of a detachable injector head

List and describe the advantages of dual syringe capacity

Define the concept of flow rate

Identify the factors that affect the flow rate

Explain the injectors that are used for computed tomography (CT) and magnetic resonance imaging (MRI)

Many special radiographic procedures require an injection of contrast medium under specific controlled conditions. Performing these injections by hand would make it difficult to maintain a consistent flow rate. Maintenance of a sufficient dilution of contrast agent in the blood is also difficult to achieve with an injection made by hand.

Angiography requires the delivery of a specific amount and concentration of contrast agent to the target area. As the contrast agent enters the bloodstream, it is diluted. This dilution effect is dependent on several factors, such as the injection site, size of the vessel, and type and iodine concentration of the contrast agent. The target site determines the speed (rate of flow) of the injection. Vessel size also affects the concentration of the contrast agent. The larger the vessel, the greater the flow rate must be to maintain the proper concentration of contrast medium so that the desired anatomic features can be visualized radiographically. In some procedures, flow rates of 30 to 40 ml of contrast material per second are not uncommon.^* These injections must be performed with a mechanical device in order to achieve consistency in the flow rates. The flow rate is controlled by many factors, such as the viscosity of the contrast medium, catheter length, catheter diameter, and injection pressure. The flow rate or injection speed can be increased or decreased by varying any of these parameters.

Most current injectors are designed for operation as either high- or low-pressure injectors, thereby broadening their usefulness in many types of angiographic procedures. The Medrad Avanta injector (Fig. 3-1, A) is a multimodality system that can be utilized in the cardiac and angiography arena as well as for larger vessels and peripherals. The Medrad Avanta is capable of injecting contrast material in variable mode at low flow rates and low pressures, fixed mode at high flow rates and high-pressure injections, and fixed mode for saline flushing. Dedicated automatic injection systems such as the Medrad Stellant CT injection system and Spectris Solaris EP MRI injector are also available (see Fig. 3-1, B and C). These systems can be configured with options specific to each of their respective modalities.

FIGURE 3-1 Medrad contrast delivery systems. A, Medrad Avanta Injection System, B, the Medrad Stellant CT Injector, and C, the Medrad Spectris Solaris EP MRI Injector System.

AUTOMATIC INJECTORS

Basic Components

All automatic injectors have certain components in common; each is equipped with a control panel, syringe, heating device, and high-pressure mechanism.

Control Panel

Each of the automatic injection devices has a control panel that is used to set the parameters of the injection sequence (Fig. 3-2). Depending on the unit and the optional equipment purchased, the control panel will appear more or less intricate. The injector systems are equipped with a touch screen display for ease of programming. Almost all of the units available are digitally controlled and ergonomically designed for ease of use. Some of the systems allow the control panel to be removed from the unit and taken to the control area during the procedure.

The controls and indicators present on the control panel vary with the type of options available with the system. These controls are clearly marked for ease of operation. In the Medrad ProVis Mark V injector the control panel is segmented and sequenced to guide the setup procedure. The system’s rotating and tilting console is easily read in a variety of lighting situations and throughout a range of distances. The Angiomat Illumena injector is also equipped with a tilting and rotating console that allows for viewing from a wide variety of angles.

Many of the systems come equipped with optional electroluminescent displays. This type of display can be easily read from a variety of angles and under a wide range of lighting conditions. Some of the systems also have graphical user displays for easy setup and system monitoring. The EmpowerCT provides a number of voice prompts (spoken cues) that can quickly alert the operator to potential problems.

Each of the systems is supplied with an instruction manual that should be referred to if questions concerning operation or troubleshooting arise. The manufacturers also make available product manuals and technical assistance on their websites.

The main type of high-pressure mechanism used on automatic injectors is the electromechanical system. This is simply an electric drive motor connected to a jackscrew that drives the piston into or out of the syringe. Figure 3-5 depicts a simplified version of an electromechanical high-pressure device. The high-pressure mechanisms of modern automatic injectors have several safety features built into them. The Medrad ProVis injector can prevent injections from exceeding their preset volume, flow rate, and pressure. There is also a mechanical stop that physically limits the injection volume to a preset amount. In the case of an electrical malfunction, the injection would still be limited by the device, which is not dependent upon electricity to function.