Abstract:
A method of preventing extravasation of contrast agent during a computed tomography injection. An automatic injector device facilitates ease of accomplishing the method. The method includes establishing the absence of extravasation using an absorbable injectate, such as saline, prior to injecting the contrast agent. The device includes a computerized injector head capable of switching between two injectates without physical human intervention. The device is controlled by a remote operating panel located in a control room that is protected from X-ray radiation. The device includes various software driven safety features that prevent the occurrence of unsafe conditions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority from U.S. Provisional Application Serial No. 60/294,471 filed on May 30, 2001 and entitled CT INJECTOR SYSTEM, incorporated by reference herein in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Computed tomography (hereinafter “CT”) is a medical procedure whereby an X-ray imaging machine is used to take cross-sectional images of a patient. The source of the X-rays is placed on one side of the body while an array of detectors is placed on the other side. The X-rays pass through the body and are read by the detectors on the other side. The signals received by the detectors are sent to a computer which compiles the data to create images. The detectors and X-ray source may be rotated around the body, while the body is being translated axially, to create a plurality of layered images.  
           [0003]    CT differs from traditional X-ray imaging in that a computer is used to first “record” the image. Often, a contrast agent providing radiopaque contrast is injected into the patient intravenously to greatly enhance the images. Because the nature of CT is more like a continuous “movie” rather than a snapshot-like traditional X-ray, the flow and efficacy of the contrast agent may be monitored during the procedure.  
           [0004]    Using radiopaque contrast agents for CT procedures, however, involves complications. For example, extravasation, the unintentional delivery of an injectate into the tissue surrounding the targeted vein or artery, can be a serious complication when injecting a radiopaque contrast agent during a CT procedure. These contrast agents are relatively thick solutions that are not easily absorbed by human tissue. Thus, whereas extravasation of an easily-absorbed solution, such as saline, is of relatively minor consequence, extravasation of a CT contrast agent can be a painful mishap often requiring an invasive, surgical removal procedure called a fasciotomy.  
           [0005]    Extravasation occurs whenever the tip of the percutaneous needle is not located in the target vein and injectate is nonetheless delivered through the needle. There are various causes of extravasation. One cause involves a technician or nurse missing the lumen of the target vein, or passing completely through the vein with the needle tip, during introduction. Another cause involves the jetting force of the injectate creating a rearward, resultant force on the needle, pushing the needle out of the vein, or pushing the vein away from the needle tip until the tip is no longer in the lumen. Extravasation may also be caused by the jet force of the injectate eroding through the wall of the vessel.  
           [0006]    Manual control of the injection flow rate by a skilled technician would effectively minimize extravasation caused by excessive jetting force. However, as previously mentioned, contrast agent continues to be injected into the vein during a CT procedure. A technician manually injecting the agent would thus be exposed to repeated, and cumulatively harmful, doses of X-ray radiation.  
           [0007]    The need for precise control over the flow rate of CT contrast agent, along with the hazards of repeated exposure to X-ray radiation, has illuminated the need for the development of a computer controlled, automatic injector system. The applicants have developed a somewhat similar system for use in angiographic procedures. This system is described in U.S. Pat. No. 6,099,502, filed Oct. 24, 1997, and U.S. patent application Ser. No. 09/542,422, filed Apr. 4, 2000, both of which are incorporated herein by reference in their entireties.  
           [0008]    Angiograms are similar to CT scans in that the same contrast agent is used to form an X-ray image. However, angiograms do not share many of the complications of CT scans. Angiograms involve the introduction of a long catheter into the aorta through an entry in the groin. The catheter is threaded through the aorta to the target site, such as the heart or brain, and used to deliver a larger volume of injected contrast agent in a short time. The goal is to create a slug of contrast agent that occupies substantially the entire lumen of the target site in order to form an image of the targeted vascular system. Once the agent is injected, a series of traditional X-rays are taken. If it is determined that more X-rays are needed, another slug of contrast agent is injected. Thus, extravasation is much less likely to happen as the catheter is positioned deep within the aorta and the location of the distal end is established before the agent is introduced. Further, there is sufficient time between the introduction of the agent and the taking of the X-rays for the attending physician and technicians to leave the X-ray room.  
           [0009]    The aforementioned injector system was developed because technicians were unable to achieve the necessary injectate flow rate manually. However, this system is unsuitable for CT agent introduction. In addition to being too large, it requires the technician to be present in the X-ray room during operation.  
           [0010]    It would be desirable to develop an automated injector system tailored to the unique needs of CT. Such a system would optimally provide remote operation, redundant safeguards against uncontrolled agent introduction, and the ability to alternate between two injectates. A need for a method of injecting a radiopaque contrast agent that reduces the risk of contrast agent extravasation is also needed.  
         SUMMARY OF THE INVENTION  
         [0011]    In one aspect of the present invention, there is a method of injecting a contrast agent that minimizes the extravasation of the agent. The method involves the use of a preliminary injection of an easily absorbable liquid, such as saline, to establish the absence of extravasation.  
           [0012]    While the preliminary injection of saline is being administered, the technician monitors the injection site by palpation for signs of extravasation. If extravasation is present, the technician repositions the needle and repeats the process of injecting saline and monitoring for signs of extravasation. Because saline is readily absorbed by the body, the extravasation of saline is much less painful and less likely to cause scarring than the extravasation of contrast. Thus, if extravasation occurs while injecting saline, a fasciotomy is typically unnecessary.  
           [0013]    Once it is confirmed that extravasation is not present, the needle or catheter is held in place and fluidly connected to a supply of contrast agent. The contrast agent is introduced at a flow rate that may be approximately equal to that of the saline, thereby minimizing the possibility of extravasation caused by the jetting force of the injectate. Once the desired quantity of contrast agent has been administered, it is preferable to inject a second quantity of saline. Doing so flushes the introduction site of contrast agent, thereby reducing pain and preventing any inadvertent extravasation during needle extraction. Doing so also increases the patency of the contrast agent. It has been determined that providing such a saline boost following the agent allows a smaller dose of the expensive contrast agent to be used without sacrificing image quality. Additionally, this boost injection ensures that the intended dosage of contrast agent is actually delivered to the patient by flushing the remainder of the contrast bolus from the tubing connected to the percutaneous needle.  
           [0014]    In order to present an environment in which a patient may receive a CT agent while being exposed to X-ray radiation, without the need for an attending technician, another aspect of the present invention is an automatic injector system. The system includes a remote operating panel which may be located in a radiation-free control room, adjacent to the room where the patient is located. The system generally comprises a mechanical linear actuator controlled by a computerized operating system. The linear actuator is operably connected to a plunger within a syringe to either force fluid from the syringe or draw fluid into the syringe. An operating system controlling the automatic injector system is enabled by software programs that allow a technician to input flow rates and quantities.  
           [0015]    The linear actuator includes a plunger rod that is preferably magnetically coupled to the plunger. A magnetic coupling between the plunger rod and the plunger is advantageous over a traditional “snap fit” connection, commonly used in other automatic injector devices. This “snap fit” arrangement is found on systems wherein automatic engagement and disengagement of the plunger with the plunger rod is desirable to prevent contaminating the syringe pumping chamber and to simplify the operation of the injector system. In some situations, it is desirable to damage or destroy the connection portion of the plunger to prevent syringe reuse. As a result of the unsnapping and/or destruction of the connection, particles may remain in the connection area and cause problems during subsequent interconnections. Magnetically coupling the actuator to the plunger provides a connection which is broken cleanly and, lacking interlocking componentry, is not susceptible to clogging or other interference.  
           [0016]    Another advantage of providing a magnetically coupled, actuator-plunger relationship is that a connection is established without requiring any connection force. One problem often encountered with automatic injectors using snap connections is that the force necessary for engagement is too high, while the force necessary for disengagement is too low. With snap connectors it may be difficult to maintain the plunger in a fixed position relative to the pumping chamber because the plunger may be driven forward during the engagement procedure. Additionally, it may be difficult to maintain the plunger in an engaged position with the plunger rod when the plunger rod is retracted. Instances where a connection is either never achieved, or not achieved until the plunger has reached the distal end of the syringe, are not uncommon. A magnetized plunger rod connects to a ferrous or magnetic plunger coupling with a zero, if not a negative, connection force.  
           [0017]    Preferably, the magnetic connection employs rare earth neodymium iron boron magnets. Rare earth magnets are strong enough and small enough to maintain contact with the plunger while the plunger is being withdrawn to draw fluid into the syringe. A stack of such magnets may be used to increase the power of the magnetic field.  
           [0018]    The performance of the magnetic connection is further enhanced by using an advanced plunger design with the syringe. The plunger includes a lip seal that prevents fluid within the syringe from leaking out, prevents contaminants and air from entering the syringe, and assists the gripping power of the magnets by reducing the friction between the inner walls of the syringe and the sides of the plunger. A thin ridge or lip is oriented radially outward and is angled forward from the leading edge of the side of the plunger. Upon the application of force from the injector actuator to the plunger assembly, the fluid pressure within the syringe increases. This increase in pressure forces the lip into closer contact with the internal surface of the syringe bore. The contact force between the lip and the syringe bore is directly proportional to the fluid pressure, reinforcing the seal between these surfaces with increasing pressure.  
           [0019]    This lip seal may be used in combination with standard seal “bumps” that protrude radially around the circumference of the plunger assembly. A second lip seal, rearward of the first lip seal and angled rearward rather than forward, may be used to more effectively prevent the ingress of air into the syringe bore when the plunger is being withdrawn during a fill operation.  
           [0020]    Notably, the existence of one or more of these lip seals greatly reduces the area of contact between the plunger and the bore compared to more conventional syringe designs. This reduction in contact area corresponds to a reduction in friction and thus enhances the performance of the magnetic connection between the plunger rod and the plunger.  
           [0021]    Another aspect of the present invention provides an injectate delivery device that enables a technician or automated injector to easily switch between two different solutions using a common percutaneous introducer such as a needle or catheter. The device is preferably constructed and arranged for insertion into the aforementioned automatic injector system.  
           [0022]    In one aspect of the delivery device, there are provided two separate syringes fluidly connected to the percutaneous needle or catheter with a fluid communications network. The network has one or more valves directing the fluid toward the lumen of the needle or catheter. This device reduces the possibility that the needle or catheter will be inadvertently displaced from the target vein when switching injectates.  
           [0023]    Preferably, the device further includes connections to fluid supplies, and associated valves, such that one syringe may be filled with a liquid without affecting the operation of the other syringe. This device may be embodied using material that will result in a disposable, single-use device, or using a combination of materials such that portions of the device are reusable.  
           [0024]    The valve network provided with the various embodiments of the injectate delivery device is constructed and arranged to automatically port a pressurized liquid to the introducing catheter. Manually actuated valves are either minimized or completely replaced, thus eliminating the potential for operator error and allowing the fluids to be alternated remotely.  
           [0025]    Alternatively, there is provided a similar delivery device that provides only one syringe. Similar in design and construction to the two-syringe embodiment, this less expensive embodiment is ideally situated to applications where only one injectate is necessary. If necessary, this embodiment may be used to alternate injectates by switching the supply reservoir from which the device is drawing injectate.  
           [0026]    Another aspect of the automatic injector system is a computerized operating system. The computerized operating system includes a remote operating panel located in an adjacent room, shielded from X-ray radiation. Because the present invention pertains to a computerized machine performing a medical procedure in the absence of immediate human contact, redundant safety measures are needed. A variety of safety features are thus incorporated into the present invention to preserve, or improve upon, the standards of safety exercised when contrast agents are injected manually.  
           [0027]    The present invention includes components located in the vicinity of the patient, and remote components, located in an adjacent control room, that are used by physicians to operate and monitor components in the patient room. In addition to the components described above, the patient room also includes an injector head. As used herein, “injector head” generally refers to a computer controlling a motor connected to a linear actuator or plunger rod. As mentioned above, the linear actuator is operably attached to the plunger such that the plunger may be moved back and forth within the syringe. In the embodiment providing two syringes, the injector head preferably includes two motors and two linear actuators, controlled by the computer. Alternatively, the injector head includes one motor alternatingly engageable to two linear actuators.  
           [0028]    The components in the control room include a monitor, such as a liquid crystal display (LCD) touch monitor, and a computer with a power supply. The computer communicates with and controls the injector head from the control room. Having introduced the basic components of the system, it is now possible to briefly summarize the basic safety features relating to the injector head of the present invention.  
           [0029]    One aspect of the injector head of the present invention includes a watchdog computer program for ensuring all safety-critical computer programs or “tasks” that are supposed to be running during an injection operation are doing so without error. Computer-controlled, safety-critical medical devices must ensure that if the computer processor becomes inoperable for any reason, the system can be shut down in a manner that will not harm the patient or operators of the device. Electronic watchdog circuits that require the software to signal the watchdog circuit at a predetermined time interval are known. However, in a multitasking operating environment, it is possible that the task responsible for signaling the watchdog circuit remains operational while a separate task pertaining to patient safety becomes inoperable in a manner undetected by the electronic watchdog circuit. Thus, this watchdog program includes a code segment that monitors signals from each of the safety-critical tasks, either by passively receiving “operation normal” signals from the tasks, if they are so programmed to send these at predetermined intervals, or by requesting or pulling such signals from the tasks. The program also includes a code segment that verifies that such an “operation normal” signal has been received from each and every one of the designated safety-critical tasks. In other words, the program repeatedly performs a “roll call” at a predetermined interval.  
           [0030]    This code segment, herein referred to as the “watchdog task” then sends a reset signal to a watchdog timer code segment. The watchdog timer code segment is a timer that runs continuously, beginning from zero, whenever it is reset. A shutdown code segment sends a shutdown signal to a motor shutdown logic circuit, discussed below, whenever the timer reaches a predetermined elapsed time. Thus, the watchdog computer program generates a shutdown signal unless it is verified that each of the safety tasks is operating normally during the predetermined interval.  
           [0031]    One of the critical safety tasks monitored by the watchdog task is an interprocessor communications link task run by the microprocessors of the injector head and the remote operating panel. The two microprocessors communicate with each other via an acceptable communication link. The processors send messages to each other at predetermined intervals, verifying that they are operating normally. When it is established that the processors are operating normally, an operation normal signal is sent to the watchdog task, as described above.  
           [0032]    Another aspect of the injector head of the present invention is a safety circuit that includes the aforementioned motor shutdown logic circuit. This safety circuit provides a degree of redundancy to the watchdog computer program. A plurality of comparators, each having a first input line, a second input line, and an output line are provided. The first input line of each comparator receives a voltage signal from a sensor measuring a selected operating parameter of the automatic injector system. Examples of such parameters include: plunger speed, plunger position, and motor torque, for both the saline and the contrast agent plungers and/or motors.  
           [0033]    The second input line is preferably connected to a digital-to-analog converter which takes an inputted limit on one of the parameters, converts it to an analog signal, and sends it to the comparator. The comparator compares the signal from the first line to that of the second line. If the difference exceeds a predetermined threshold, the comparator sends a signal to the motor shutdown logic circuit. Thus the motor logic circuit is able to receive signals from any of the comparators and from the watchdog timer. The motor logic circuit is also connected to a relay electrically connecting the motor of the injector head to a power supply. The motor logic circuit is designed to trip the relay when it receives a signal from any of the comparators or the shutdown code segment.  
           [0034]    Another safety feature of the injector head includes a computer program to control the flow rate created by the plunger being forced through the syringe by the motor. The computer program is embodied on a computer readable medium executable by a computer and generally comprises a velocity loop and a pressure loop. The velocity loop is a code segment capable of comparing data representative of actual plunger speed to a predetermined speed setting. The pressure loop is a code segment capable of comparing data representative of actual motor load to a predetermined motor load limit.  
           [0035]    The velocity loop and the pressure loop work together to ensure the safe delivery of the contrast agent and/or saline to a patient. The velocity loop maintains the flow rate of the fluid within a predetermined range so that the contrast agent flow rate is high enough to be effective, but not excessive causing internal trauma, such as extravasation. The pressure loop monitors the load on the motor, becomes active at a selected setting, and prevents the load from exceeding the selected setting by a predetermined amount. Motor load is representative of pressure on the plunger. If a blockage were to occur in the fluid path, for example, the flow rate could be decreased. The velocity loop would note that the plunger speed has decreased and would send a signal to increase the motor speed. However, the presence of the blockage would result in an increased load condition on the motor, and an increase in pressure within the syringe. The pressure loop thus either shuts the system down or slows the motor speed if the motor load exceeds the selected setting by a predetermined amount. These loops are preferably software programs but may be solid state circuits or even mechanical feedback devices.  
           [0036]    Because the automatic injector is driven by at least one microprocessor, the system must be capable of storing the data and software used for executing the application. It would be desirable to have the capability to install software after the device has been assembled. This capability facilitates ease of manufacture and allows immediate field upgrades without significant down time. Thus, it is preferable to provide the software and data storage capability on a modular memory card, such as CompactFlash™. The CompactFlash™ mass storage device is a card which can be unplugged and replaced through an access point on the injector device. Using a CompactFlash™ removable mass storage device for storing application software, calibration data, and device usage data, provides the ability to both download and retrieve the software and data from the injector using a connected computer, and to physically remove and replace the CompactFlash™ card with the data on it.  
           [0037]    The microprocessor may be configured for connection to the Internet or an intranet, thereby allowing a physician in a remote location to program various injector parameters. Remote connectivity could also be used for manufacturer troubleshooting without requiring a technician to make an on-site service call. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]    [0038]FIG. 1 is a flow chart that describes a method of preventing contrast agent extravasation of the present invention;  
         [0039]    [0039]FIG. 2 is a perspective view of an automatic injector system of the present invention;  
         [0040]    [0040]FIG. 3 a  is a plan cutaway view of the syringes and fluid network of the present invention;  
         [0041]    [0041]FIG. 3 b  is a plan cutaway view of the catheter connector of the present invention;  
         [0042]    [0042]FIG. 3 c  is a perspective view of a preferred embodiment of the syringes and fluid network of the present invention;  
         [0043]    [0043]FIG. 4 is a plan view of an injector head of the present invention;  
         [0044]    [0044]FIG. 5 is an elevation view of a plunger of the present invention;  
         [0045]    [0045]FIG. 6 is a section view of the plunger of FIG. 5 taken generally along lines  6 - 6 ;  
         [0046]    [0046]FIG. 7 is a rear perspective view of a linear actuator assembly of the present invention;  
         [0047]    [0047]FIG. 8 is a front perspective view of a linear actuator assembly of the present invention;  
         [0048]    [0048]FIG. 9 is a side elevation sectional view of the linear actuator assembly of FIG. 8 taken generally along lines  9 - 9 ;  
         [0049]    [0049]FIG. 10 is an enlarged view of the circled area bearing assembly  122  of FIG. 9;  
         [0050]    [0050]FIG. 11 is a diagram of the basic components of the automatic injector system of the present invention;  
         [0051]    [0051]FIG. 12 is a data flow diagram of the injector head operation of the present invention;  
         [0052]    [0052]FIG. 13 is a flow diagram of the watchdog feature of the present invention;  
         [0053]    [0053]FIG. 14 is a logic flow diagram of the safety circuit of the present invention;  
         [0054]    [0054]FIG. 15 a  is a perspective cutaway view of a docking plate equipped with a syringe lock assembly of the present invention;  
         [0055]    [0055]FIG. 15 b  is a perspective view of an alternative docking plate of the present invention; and,  
         [0056]    [0056]FIG. 16 is a flow diagram of the velocity loop and pressure loop of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0057]    Method of Preventing Extravasation  
         [0058]    [0058]FIG. 1 shows a flow diagram of the method of preventing extravasation  10  of the present invention. Beginning at  12 , an injection site is located by the attending health professional and prepared for injection at  14  using appropriate cleaning techniques. The needle or catheter is inserted at  16  to establish fluid communication between the needle or catheter and the targeted lumen of the patient.  
         [0059]    At  18 , a supply of saline is fluidly connected to the needle or catheter and, at  20 , a quantity of saline is injected into the patient at a predetermined flow rate that may be approximately equal to the desired flow rate of the eventual contrast agent injection. It is preferred that the flow rate of the saline injection be at least as great as the planned flow rate of the contrast agent. Doing so ensures that extravasation complications caused by jetting forces will be revealed prior to the introduction of the contrast agent. While the saline is being injected, the attending professional is constantly monitoring by palpation, and visually, at  22 . If extravasation is suspected, the professional halts the injection at  24  and repositions the needle at  26 . The process then repeats back to step  20  whereby saline is injected and palpation is resumed at  22 .  
         [0060]    If extravasation is not detected at  22 , the attending professional aligns or connects the radiopaque contrast agent to the needle or catheter at  28 . At  30 , the contrast agent is injected at the preferred flow rate. The flow rate of the contrast agent is chosen for maximum contrast effect. The flow rate of the saline is chosen based on the flow rate of the agent. While contrast agent is being injected, and imaging is occurring, the attending professional preferably leaves the patient room to minimize his or her exposure to radiation.  
         [0061]    Upon completion of the contrast agent injection at  30 , the saline supply is again connected to the needle or catheter at  32 . At  34 , a quantity of saline is injected in order to clear the needle, flush the contrast agent away from the injection site, and increase the efficacy of the contrast agent.  
         [0062]    Automatic Injector System  
         [0063]    The present invention includes an automatic injector system that greatly enhances the method  10 , described above. The method  10  included two steps,  28  and  32 , where the inserted needle or catheter had to be connected to different fluids. The automatic injector system of the present invention allows this realignment to be performed remotely. The system also provides precise control over the flow rate at which the injectates are administered.  
         [0064]    Referring now to FIG. 2, there is shown a preferred embodiment of the automatic injector system  40  of the present invention. The system  40  generally includes an injector head  42  operably attached to at least one, preferably two, syringes  44 . The syringes are attached to a fluid communications network  46 . All of the aforementioned components are located in the patient room  48 . In an adjacent control room  50 , the system  40  also includes a remote operating panel  52 . Each of these components will now be discussed in detail.  
         [0065]    Syringes and Fluid Communication Network  
         [0066]    The syringes  44  are connected to the patient with the fluid communication network  46 , as best shown in FIGS. 3 a - 3   c . The fluid communications network  46  is a series of valves and tubes. Syringe connector valves  54  connect the distal ends  56  of the syringes  44  to both supply tubes  58  and to cross tubes  60 . The supply tubes  58  lead to supply connectors  62  and the cross tubes  60  lead to a common shuttle valve  64 . The shuttle valve  64  is a three-way valve allowing fluid to flow from either cross tube  60  into a common tube  66 . The common tube  66  leads to a catheter connector  68 , which is designed to be attachable to a standard catheter via a port  70 . Additionally, the catheter connector may have a medicament port (not shown) that provides a site for injecting fluids other than saline and contrast agents. This medicament port may also be used as an attachment point for an air column detector.  
         [0067]    [0067]FIG. 3 b  shows the catheter connector  68  in greater detail. A coupling  69  removably couples the connector  68  to the common tube  66 . A plug  71  biased closed by a spring  73  allows fluid flow in only one direction by requiring the pressure created by the syringe  44  to overcome the force of the spring  44 .  
         [0068]    The supply connectors  62  are attachable to containers  72  (FIG. 2), one of which preferably contains saline and the other preferably contains contrast agent. Because the two-syringe system is designed to allow an attending professional to remotely alternate between the injection of saline and a contrast agent, for ease of explanation, the components carrying saline are labeled “a”, and the components carrying contrast agent are labeled “b”, throughout the Figures.  
         [0069]    The container  72   a , then, contains a supply of saline solution. The saline solution is loaded into the syringe  44   a  by pulling the plunger  74   a  away from the distal end  56   a , thereby creating a negative pressure within the syringe chamber  76   a . A close look at the syringe connector valve  54   a  reveals a plug  78   a  held in place against a shoulder  80   a  by a biasing mechanism, preferably a spring  82   a . Alternatively, the plug  78   a  is buoyant, such that the buoyancy of the plug constitutes the biasing mechanism. When the negative pressure created in the syringe chamber  76   a  is sufficient to overcome the force of the spring  82   a , the plug  78   a  is pulled toward the syringe  44   a , compressing the spring  82   a , and allowing the saline to flow between the plug  78   a  and the shoulder  80   a  and into the syringe chamber  76   a . Once the syringe  44   a  is filled with a sufficient quantity of saline, the plunger  74   a  is stopped, thereby causing the negative pressure created in the chamber  76   a  to subside as the saline continues to fill the chamber  76   a . The spring  82   a  quickly overcomes the effects of the negative pressure, and reseats the plug  78   a  against the shoulder  80   a.    
         [0070]    When the saline in the chamber  76   a  is to be injected into the patient, the plunger  74   a  moves toward the distal end  56   a  of the syringe  44   a , creating a positive pressure in the chamber  76   a . The plug  78   a  prevents the saline from reentering the supply tube  58   a . The saline instead is forced into the cross tube  60   a  toward the shuttle valve  64 .  
         [0071]    The shuttle valve  64  also uses a plug and shoulder arrangement. To accept fluid from either the saline supply tube  60   a  or the contrast agent supply tube  60   b , the shuttle valve has a plug  84   a  on its saline side which acts against a shoulder  86   a , and a plug  84   b  on its contrast agent side which acts against a shoulder  86   b . The two plugs  84   a  and  84   b  are held apart by a spring  88 . The shuttle valve  64  connects the two cross tubes  60   a  and  60   b  to the common tube  66 . Note that the shuttle valve  64  is designed to insulate the common tube from any negative pressure forces arising in the cross tubes  60  when either of the syringes  44  are being filled.  
         [0072]    Continuing with the saline injection explanation, when the saline is forced into the cross tube  60   a  with sufficient pressure to overcome the spring  88 , the plug  84   a  is displaced from the shoulder  86   a  and the saline is allowed to pass around the plug  84   a . The saline, however, is blocked from passing around the other plug  84   b , which is seated, now with even greater force, against its respective shoulder  86   b . Thus the saline is forced into the common tube  66 , through the catheter connector  68  and into the patient via the needle or catheter.  
         [0073]    The construction of the components on the contrast agent side of the fluid network  46  are virtually identical to those on the saline side, just described. The design of the syringe connector valves  54  and the shuttle valve  64  allow both syringes to be filled simultaneously and allow fluid from either syringe  44  to be injected alternately without requiring any alignment adjustments. The valves are aligned automatically based on the fluid forces in the network  46 .  
         [0074]    The fluid network  46  preferably includes a plurality of connectors  89  (FIG. 3 c ). These connectors are placed between the various other components and allow the components to be replaced and rearranged. For example, the connectors  89   a  and  89   b  on either side of the shuttle valve  64  can be used to replace the shuttle valve  64  with a mixing valve (not shown) useable to mix the fluids from the two syringes  44  together. Additionally, the connector  69  can be used to disconnect the network  46  from one patient and use it on another patient without presenting sterility issues.  
         [0075]    Injector Head  
         [0076]    Referring to FIG. 4, the injector head  42  includes one plunger rod  90  per syringe  44 , an actuator assembly having one or more motors  110  arranged to move the plunger rods  90 , and a local control panel  94 . Each plunger rod  90  is connected to the plunger or wiper  74  of the syringe  44 . Preferably, the plunger rod  90  includes a magnet or magnetic stack  96  at its distal end that magnetically connects the plunger rod  90  to a ferrous metal insert  98  in the dry side of the plunger  74 . Using a magnetic connection between the plunger rod  90  and the plunger  74  is advantageous because it exerts no resistive force when a connection is being made. Neodymium iron boron (NIB) magnets, also known as rare earth magnets, provide sufficient strength to remain attached to the ferrous metal insert  94  when drawing a negative pressure on the syringe  44  during filling. A greater magnetic field may be obtained by using a stack of such magnets.  
         [0077]    The performance of the connection between the magnet  96  and the ferrous metal insert  98  is enhanced by the design of the plunger  74 . FIGS. 5 and 6 show a preferred plunger  74 . The plunger  74  has a conical end  100  that substantially matches the shape of the distal end  56  of the syringe  44 . The plunger  74  also has an annular lip  102  angled forward that extends from the sidewall  104  of the plunger in both a forward and an outward direction. The lip  102  is shaped to create an inner surface  106  against which fluid pressure can act to press the lip  102  against the inner sidewall of a syringe  44 , thereby improving the seal between the syringe and the plunger. This improved seal reduces the amount of friction between the plunger  74  and the syringe  44 , thereby enhancing the performance of the connection between the magnet  96  and the ferrous metal insert  98 . Friction is further reduced by providing a rear ridge  108 . This ridge  108  also acts against the inner wall of the syringe  44 , thereby ensuring that the plunger  74  remains centered within the syringe  44  and also prevents air from seeping past the annular lip  102  when the plunger  74  is being withdrawn, such as when the syringe  44  is being filled. The ridge also prevents the entire sidewall  104  from contacting the inner wall of the syringe  44 , thus reducing the friction between the plunger  74  and the syringe  44 . It may be desired to provide a ridge  108  which has the same shape as the lip  102 , and faces rearward, to further enhance the seal between the ridge  108  and the syringe  44  when the plunger is being withdrawn.  
         [0078]    Each of the plunger rods  90  is moved by a linear actuator assembly  92 . FIGS.  710  present detailed views of the linear actuator assemblies  92 . The assembly  92  converts rotational motion from the motor  110  into linear motion imparted to the plunger rod  90 . The motor  110  is mounted on a rear plate  112 . The shaft  114  of the motor  110  is attached to a motor gear  116  that is rotatably connectable to a plug screw gear  118  with a pulley, belt  119 , reduction gear or the like. The plug screw gear  118  is fixed to a plug screw  120  and imparts rotation thereto.  
         [0079]    The plug screw  120  is supported by a bearing assembly  122 , the details of which are shown in FIG. 10. The bearing assembly  122  also prevents the plug screw from moving axially, relative to the rear plate  112 . On the external side  128  of the rear plate  112 , the bearing assembly  122  preferably includes a pair of angular contact bearings  124  separated by a spacer washer  126 , all held in place against the external side  128  of the rear plate  112  by a lock nut  130  and a lock nut washer  132 . On the internal side  134  of the rear plate  112 , the bearing assembly  122  includes an axial bearing  136  surrounded by two axial bearing washers  138 . One of the axial bearing washers  138  acts against the internal side  134  of the rear plate  112  while the other axial bearing washer  138  acts against a shoulder  140  of the plug screw  120 .  
         [0080]    The plug screw  120 , thus rotates with the motor  110 . To impart linear motion to the plunger rod  90 , the plug screw  120  is threaded and carries a plug nut  142  that is attached to the plunger rod  90 . The plug nut  142  is attached to a guide flange  144  that slides along a tie rod  146  by way of a guide flange bearing  148 . The tie rod  146  prevents the plug nut  142  and guide flange  144  from rotating with the plug screw  120 , thereby forcing linear movement as the internal threads of the plug nut  142  necessarily interact with the external threads of the plug screw  120 . The tie rod  146  is preferably one of four tie rods  146  that connect the rear plate  112  to a front plate  150 .  
         [0081]    The rearward end of the plunger rod  90  is attached to, and supported by, the plug nut  142 . Near the front plate  150 , the plunger rod  90  is supported by a linear bearing  152  that is attached to the front plate  150 . The plunger rod  90  slides through the linear bearing  152  as the rod  90  linearly advances and returns. In addition to the linear bearing  152 , the plunger rod  90  also slides through a rod wiper seal  154 , which is forward of the linear bearing  152 , and prevents dust from being picked up by the plunger rod  90  while in a forward position, from entering the housing  156  (FIG. 2) of the linear actuator assembly.  
         [0082]    The plunger rod  90  is hollow and surrounds the plug screw  120 . The forward end of the plunger rod  90  contains the magnet or magnetic stack  96  that is secured to the end of the rod  90  with an end plug  158 . The stack is contained within a thin ferrous end cap  160  that is shaped to be received by the dry side  162  of the plunger  74 , best seen in FIG. 6. The dry side  162  of the plunger is lined with the ferrous metal insert  98  that is configured to mate with the end cap  160 .  
         [0083]    Referring again to FIGS.  7 - 9 , it is shown that the front plate  150  is mounted to a docking plate  164 . The docking plate  164  includes two receiving grooves  166  for receiving the syringes  44 . Note the docking plate  164  is arranged to accept two linear actuator assemblies  92 .  
         [0084]    The plunger rod  90  is sized such that when it is in the fully retracted position, as shown in FIG. 9, the forward end of the end cap is flush with the back face  168  of the receiving groove  166 . This allows a fresh syringe  44  to be slid into place prior to a procedure or midway through a procedure, if necessary. Securing the syringes  44  to the docking plate  164  by sliding them into place, instead of screwing or otherwise twisting them into place, is preferred because any twisting motion imparted to the syringe may twist the fluid communication network  46 . Locking the syringes  44  into the grooves  166  is accomplished with a syringe lock assembly  250 .  
         [0085]    One embodiment of the syringe lock assembly  250  is best shown in FIG. 15 a . The lock assembly  250  includes two engagement members  252  pivotally attached to the docking plate  164  with pivot pins  254 . The engagement members  252  are spaced apart from the back face  168  of the docking plate  164  such that the flange  234  of the syringe  44  (FIGS. 3 a  and  3   b ) is held between the engagement members  252  and the back face  168 . Preferably, the flange  234  includes a plurality of détentes  235  to add rigidity and strength to the flange  234 . The engagement members  252  are connected together with linkages  256 . The linkages  256  serve to move the engagement members  252  around the pivot pins  254  from an open position  258  to a locked position  260 . In FIG. 15, the syringe lock assembly  250  on the left is shown in the open position  258  while the syringe lock assembly  250  on the right is shown in the locked position  260 .  
         [0086]    Looking at the syringe lock assembly  250  in the open position  258 , it can be seen that the linkages  256  fold inward, partially occluding the hole  262  in the docking plate  164 , through which the plunger rod  90  passes. When the syringe  44  is slid into the groove  166  and over the hole  168 , the flange  234  of the syringe  44  passes under the engagement members  252  and eventually contacts the linkages  256 . The flange  234  pushes the linkages upward, forcing the upper portions  264  above the pivot pins  254  apart, thus causing the lower portions  266  below the pivot pins  254  together. The engagement members  252  are shaped such that when the lower portions  266  come together, the engagement members  252  substantially surround the syringe  44 , above the flange  234 , thereby holding the syringe  44  in place. Furthermore, when fully engaged, the linkages  256  pass slightly beyond alignment with each other, thereby creating an affirming snap engagement into the locked position  260 . One or more stops  272 , attached to either the docking plate  164  or integral with the linkages  256 , prevent the linkages  256  from travelling past alignment to the extent that the linkages  256  begin to pull the upper portions  264  of the engagement members  252  together.  
         [0087]    A release pin  268  passes through the docking plate  164  and engages the linkages  256  when the pin  268  is pressed. Depressing the pin  268  moves the linkages  256  downward, pulling the upper portions  264  of the engagement member  252  together, and forcing the lower portions  266  apart. The pin  268  also pushes the linkages  256  into the flange  234  of the syringe  44 , thereby forcing the syringe  44  out of the syringe lock assembly  250 . A biasing mechanism, such as a spring  270 , biases the pin  268  toward an inactive position, thereby preventing an accidental disengagement of the syringe  44 .  
         [0088]    Another embodiment of a syringe locking device  251  is shown in FIGS. 2 and 4 and in detail in FIG. 15 b . The syringe locking device  251  is mounted on the same or similar docking plate  164 . It employs one catch  253  associated with each groove  166 . The catch  253  is an upwardly biased protuberance having an angled edge  255  that allows the catch  253  to be pressed downwardly when the flange  234  of the syringe  44  passes over the catch  253 . A substantially vertical edge  257  prevents the syringe  44  from retreating out of the groove  166  once the syringe  44  is fully inserted into the groove  166  and the catch  253  has snapped back into an engaged position. A release button  259  allows the operator to depress the catch  253  so that the syringe  44  may be removed.  
         [0089]    Referring back to FIGS. 4 and 7- 9 , there is shown a linear position sensor  170 . The linear position sensor  170  includes a stationary rod  172  and a position detector  174  that rides on the guide flange  144  in close proximity to the stationary rod  172 . The position sensor  170  further includes a communications port  176  for relaying position data to the local control panel  94 . The operation of the position sensor  170  will be discussed in more detail below. Acceptable position sensors include magnetostrictive position sensors such as Temposonics® commercial sensors manufactured by MTS® Systems Corporation at Cary, N.C.  
         [0090]    As shown diagrammatically in FIG. 11, the injector head  42  also includes a local control panel  94 . The local control panel is basically a computer  178  with an interface  180  for manipulating the software programs that control the motors  110 . A transceiver (not shown) operably connected to the computer  178  allows the injector head  42  to communicate with the remote operating panel  52 .  
         [0091]    The injector head  42  is shown in the patient room  48 . A communications link  184  is established between the transceiver (not shown) inside the injector head  42  and the computer  178 , which is located in the control room  50 . Preferably, there is a computer  178  in both rooms. The computer  178  in the patient room  48  is considered part of the injector head  42 . The injector head  42  also receives direct current power from a power supply  186  (shown as integral with the computer  178 ) via a grounded power line  188 . A pendant  232  is also located in the patient room  48 . The pendant  232  is a tethered on/off switch attached to the local control panel  94 . The pendant  232  allows the operator to turn the system  40  on and off while verifying proper fluid flow using the method  10 .  
         [0092]    Also located in the control room  50  is the remote operating panel  52  that establishes a communications link  190  with the computer  178 . The remote operating panel  52  preferably includes a touch monitor  190 . Both the remote operating panel  52  and the power supply  186  have power mains  192  that receive alternating current power from outlets in the control room  50 .  
         [0093]    Injector Head Operation  
         [0094]    The overall data flow operation of the injector head  42  is diagrammed in FIG. 12. The diagram introduces many of the safety features of the present invention. An overview explanation of FIG. 12 will be followed by a detailed analysis of these features.  
         [0095]    Beginning with the processor  178 , it can be seen that data flows to and from the other components in the system via a peripheral component interconnect (PCI) bus interface  194  that includes memory designated to store logic and act as a buffer  196 . The computer  178  is also in electronic communication with the touch monitor  190  of the remote operating panel  52 . The computer sends the appropriate commands via the communications link  184  to the local control panel  94  (FIGS. 2 and 4).  
         [0096]    The PCI bus interface  194  provides the interconnect for all of the various components to communicate with each other. Starting at the top of the diagram and working clockwise it can be seen that data  197  is received by the buffers  196  from the safety comparators  198 . These comparators are part of a software-based safety feature that automatically set a safety limit at a predetermined margin, e.g. on the order of 10%, above a parameter entered by the operator. The buffered data  202  that the comparators monitor originates as data  200   a  and  200   b  obtained from sensors on the motors  110   a  (saline) and  110   b  (contrast agent). Data  200   a  and  200   b  first undergoes digital/analog conversion and buffering at  204 . The data  200   a  and  200   b  includes motor torque and position and is measured or computed by sensors that will be discussed in more detail below. If the buffered data  202  exceeds 110% of the entered parameters, the safety comparator  198  may send a signal  206  that disables the power  208  to the motors by tripping the motor power relay  210 .  
         [0097]    In addition to providing buffered analog data  202  to the safety comparators  198 , the digital/analog conversion and buffering process  204  supplies digital data  212  directly to the buffers  196 . This digital information  212  pertaining to the motors  110  is used by the computer  178  as feedback on whether the motors  110  are performing as expected. If the computer  178  determines adjustments need to be made, digital commands  214  are converted to analog signals at  204  and sent as commands  216  to the appropriate servo amplifiers  218 , which then send corrected direct current power to the motor  110 .  
         [0098]    In addition to the sensors providing the torque and secondary position data  200  from the motors  110 , the motors also have quadrature encoders  182  (FIG. 14) providing primary position data  220  for plunger velocity control. This data  220  is also received by the processor  178  via the buffers  196 . Like the sensors, these encoders  182  will be discussed in detail below.  
         [0099]    To prevent a computer problem, such as a single circuit failure, from adversely affecting the operation of the motors  110 , a watchdog timer  222  is provided that receives reset signals  224  from the processor  178  via the PCI bus interface  194 . The watchdog timer  222  is part of a watchdog safety feature that will be discussed individually. The timer  222 , like the comparators  198 , is able to send a motor power shutdown signal  226  to the motor power relay  210 .  
         [0100]    Other sensors and devices  228  may also provide inputs  230  to the computer  178  via the buffers  196 . Examples of such inputs  230  include: air column alert, manifold position, travel limits, and pendant commands. An air column detector may be fashioned to the catheter connector  68  such that if an air column develops in the line leading to the catheter, the motors  110  may be stopped to prevent injecting air into the patient. Manifold position and travel limits are obtained from the linear position sensor  170 . The individual safety features and components will now be discussed. Watchdog Feature  
         [0101]    Referring to FIG. 13, the watchdog feature  236  of the present invention is diagrammed. The watchdog feature  236  includes the aforementioned watchdog timer circuit  222  and motor power relay  210 , and also includes a watchdog task  240  that monitors a plurality of safety-critical tasks  238 . The watchdog feature  236  is a software-driven safety feature that ensures all of the software tasks  238 , deemed safety-critical, are operating normally. The safety-critical tasks  238  are those programs or subprograms that operate continuously during an injection and could adversely affect safety if they malfunction.  
         [0102]    The watchdog task  240  is a code segment that takes “roll call”. At a predetermined interval, it determines if all of the safety-critical tasks  238  are operating normally. It preferably does this passively, requiring that each of the tasks  238  “check in”. If all of the tasks  238  report a normal operating status within the predetermined interval, the watchdog task sends a timer reset signal  224  to the watchdog timer circuit  222  resetting the timer  222  to zero. The watchdog timer circuit  222  is a timer circuit that continually runs or advances until a predetermined time is achieved. Once the predetermined time is achieved, the timer circuit sends the motor power shutdown signal  226  to the motor power relay  210 , tripping the relay  210  and cutting power to the motors  110 . As long as the watchdog task  240  sends reset signals  224  to the watchdog timer circuit  222  before the timer circuit  222  reaches the predetermined time, the timer circuit will not send the motor power shutdown signal  226  to the motor power relay  210 .  
         [0103]    Interprocessor Communications Link  
         [0104]    One of the safety-critical tasks  238  is an interprocessor communications link  244  (FIG. 11). The interprocessor communications link is signal sent over the communications link  184  between the processors  178  of the injector head  42  and the remote operating panel  52 . The two microprocessors  178  communicate with each other by sending pings back and forth at a predetermined interval. These pings indicate that each processor  178  is operating normally. At each interval, if normal operations have been confirmed, a corresponding signal is sent to the watchdog task  240  that the watchdog task  240  acknowledges as one of the necessary signals for a successful roll call before resetting the watchdog timer  222 .  
         [0105]    Further safety may be provided by encoding the pings between the microprocessors  178 . Changing the code at each interval according to a predetermined schedule may prevent one of the processors  178  from sending a false positive ping.  
         [0106]    Quadrature Encoders  
         [0107]    The motors  110  are equipped with quadrature encoder  182  (FIG. 14). Quadrature encoder  182  are known sensors that include a stationary pickup in operable proximity to two flags, such as magnets, on a moving (in this case rotating) part. The flags are 90 degrees apart on the rotor of the motor  110  to create two sine waves or digital “square wave” pulse signals that are 90 degrees out of phase and distinguishable from each other. By monitoring the digital pulse signals, rotor speed and position can be calculated from the frequency of the pulses and the total number of the pulses, respectively. By monitoring two sets of pulses that are out of phase, rotor direction can be determined by detecting which wave is leading the other wave. Summing the number of pulses in one direction, and subtracting from the total the pulses occurring while the rotor is traveling in the opposite direction, the linear position of the plunger rod  90  can be calculated.  
         [0108]    As noted in FIG. 12, digital quadrature encoder data  220  is generated by each motor  110  and sent to the processor  178  via the buffer  196  and PCI bus interface  194 . The processor  178  makes the calculations to determine the position and velocity of the plunger rod  90 . Notably, if a computer problem results in a loss of the flag count, rod position can no longer be calculated unless the rod  90  is moved to a zero position and the counter is reset.  
         [0109]    Analog Data  
         [0110]    Also introduced in FIG. 12, analog data  200  pertaining to motor torque and plunger rod position flows to the safety comparators  198  and to the processor  178 . The analog position data is obtained from the linear position sensor  170 , shown in FIG. 9 and described above. This analog position data provides safety redundancy to the digital position data generated by the processor  178  using inputs from the quadrature encoder  182  on the motors  110 . The linear position sensor  170  senses absolute position and, therefore, does not have to be reset.  
         [0111]    The analog torque data is simply a measure of the current draw by the motors. Current draw provides an accurate indication of resistance to rotation. An increase in current draw, for any given flow rate, may be indicative of a problem such as a clog in the fluid communication network  46 , a mechanical problem within the motor  110 , or the possibility that the end of the catheter has abutted against the interior wall of the vessel into which it is inserted.  
         [0112]    Safety Circuit  
         [0113]    [0113]FIG. 14 shows an embodiment of the overall safety circuit  242  used by the computer  178  to prevent unsafe conditions. Limits  214  pertaining to torque and plunger rod position for both motors  110   a  and  100   b  are entered into the computer  178  and are stored in the buffer  196  (FIG. 12). When summoned, the limits  214  pass through the digital to analog converters  204  so they may be read by the analog comparators  198 . The comparators  198  compare actual readings for torque (current draw) and rod position (read from the linear position sensor  170 ) to the converted limits and feed digital (true/false) results to a status buffer  282 . The comparators  198  are programmed to add a predetermined percentage or constant to the inputted limit to allow for inaccuracies in the system, thereby preventing unwanted false shutdowns. The status buffer is in data flow communication with a shutdown logic program  280 , detailed below. The status buffer  282  may be the same buffer as buffer  196 .  
         [0114]    In addition to the output from the comparators  198 , the shutdown logic program  280  receives inputs via buffer  282  from the frequency counter and magnitude comparator  284 . The frequency counter measures the encoder  182  pulse frequency by recording the amount of time between pulses (the period of the pulses). The period is inversely proportional to the frequency of the pulses and the flow rate of the injectate. The magnitude comparator detects when this frequency has exceeded a predetermined set point value. The digital output of the frequency counter  284  is stored in the status buffers  282  for use by the computer  178  to monitor the speed and positions of the plungers  74 .  
         [0115]    The shutdown logic program  280  operates by monitoring the results from the comparators  198  and shutdown signals  226  from the watchdog timer  222 . If the shutdown logic program  280  receives a signal from any of the comparators  198  indicating that a limit has been exceeded, or a signal  226  from the watchdog timer  222  indicating that one of the safety-critical tasks has encountered an error, a trip signal is sent to the motor relay  210 , cutting power to both motors  110 .  
         [0116]    Velocity Loop/Pressure Loop Program  
         [0117]    [0117]FIG. 16 is a flow chart of how the computer  178  maintains the desired injectate flow rate during an injection. To maximize the efficacy of the contrast agent, an optimal volume of contrast agent must be flowing through the area of the body being imaged. Thus, a predetermined flow rate is maintained using motor speed. However, if the motor is hindered from rotation, such as due to a clog or a mechanical malfunction, the motor speed should be decreased to prevent harm to the patient or equipment. The program  286  charted in FIG. 16 maintains a desired flow rate without exceeding an upper pressure limit.  
         [0118]    The velocity loop/pressure loop program  286  begins at  288  with the operator entering the desired injectate flow rate and upper pressure limit. At  290  the computer  178  calculates the motor speed that corresponds to the desired flow rate based on the cross-sectional area of the syringe  44 , the pitch of the plug screw  120 , and the reduction ratio of the motor gear  116  to the plug screw gear  118 . The computer also adds a tolerance around the computed motor speed to generate an acceptable velocity range, V R . The computer has preset upper absolute limits on velocity and change in velocity, V A , and torque and change in torque, T A . For simplicity, the absolute velocity limit and limit on change in velocity are both denoted as V A . The same convention is true for torque and change in torque.  
         [0119]    Next, at  292 , the computer  178  calculates the upper torque limit T L  based on the inputted upper pressure limit. The operator, when selecting the upper pressure limit, considers the viscosity of the fluid. The pressure limit should be set higher for more viscous liquids for a given flow rate. The computer  178  allows for resistance to flow due to the friction inherent in the mechanical system  40 . Torque, as discussed above, is calculated as a function of motor current draw.  
         [0120]    At  294  the injection begins. At  296 , as a liquid is being injected, the computer  178  receives continuous velocity readings from the quadrature encoder  182  (FIG. 14) of the operating motor  110 . The computer  178  is also receiving torque data representing the current drawn by the operating motor  110 . The computer  178  is not only noting the velocity V and the torque T, but also the rate of change of velocity and torque.  
         [0121]    At  298 , the computer  178  first checks to ensure the absolute limits on velocity and change in velocity, V A , are not exceeded. Exceeding these limits, V A , indicates a probable hardware or software failure resulting in an inability to control the motor. Thus, if V A , is exceeded, the computer sends a trip signal at  300 , which trips the motor power relay  210 .  
         [0122]    At  302 , the computer  178  checks to ensure the absolute limits on torque and change in torque, T L , are not exceeded. If exceeded, the computer sends the trip signal  300  to the motor power relay  210 . Excessive torque and an abrupt change in torque are indicative of a clog or mechanical failure and warrant a shutdown signal.  
         [0123]    At  304 , the computer  178  is comparing the actual torque T to the computed torque limit T L . If the actual torque T exceeds the limit, the motor speed is reduced at  306 .  
         [0124]    At  308 , if the torque limit T L  is not exceeded, the computer  178  determines whether the actual velocity V is within the acceptable velocity range, V R . If it is, the injection continues at the present motor speed and computer continues to monitor torque T and velocity V at  296 . If the velocity V is not within the acceptable velocity range V R , the computer  178  determines whether the velocity V is too high or too low at  310 . If the velocity V is too low, the motor speed is increased at  312 . If the velocity V is too high, the motor speed is decreased at  306 .  
         [0125]    This program  286  operates independently from the circuit  242 . Thus, an overtorque situation could result in a shutdown generated by circuit  242 , or by the program  286 . However, controlling torque by decreasing motor speed is performed only by the program  286 . Importantly, the independence of these two programs,  286  and  242 , provides a degree of redundancy to the safety of the operation of the system  40 .  
         [0126]    Modular Memory  
         [0127]    To provide enhanced flexibility, and minimize downtime in the event of software problems, the above programs and buffers may be provided on a modular memory card  245 . Referring to FIG. 2, it can be seen that a mass storage device in the form of a modular memory card  245 , such as CompactFlash™, is provided on both the local control panel  94  and the remote operating panel  52 . The modular memory cards  245  can be unplugged and replaced through an access point on the injector device. Using these cards  245  to store application software, calibration data, and device usage data, provides the ability to both download and retrieve the software and data from the injector using a connected computer, and to physically remove and replace the cards  245  containing data.  
         [0128]    The foregoing description addresses embodiments encompassing the principles of the present invention. The embodiments may be changed, modified and/or implemented using various types of arrangements. Those skilled in the art will readily recognize various modifications and changes that may be made to the invention without strictly following the exemplary embodiments and applications illustrated and described herein, and without departing from the scope of the invention, which is set forth in the following claims.