Medical fluid injector having watchdog circuit

Details Medical fluid injector having watchdog circuit Medical fluid injector having watchdog circuit

1999-11-22

2001-07-03

Kennedy, Sharon (Department: 3763)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

C128SDIG001

Reexamination Certificate

active

06254572

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to injectors for injecting fluid into animals.
BACKGROUND OF THE INVENTION
In many medical environments, a medical fluid is injected into a patient during diagnosis or treatment. One example is the injection of contrast media into a patient to improve CT, Angiographic, Magnetic Resonance or Ultrasound imaging, using a powered, automatic injector.
Injectors suitable for these and similar applications typically must use a relatively large volume syringe and be capable of producing relatively large flow rates and injection pressures. For this reason, injectors for such applications are typically motorized, and include a large, high mass injector motor and drive train. For ease of use, the motor and drive train are typically housed in an injection head, which is supported by a floor, wall, or ceiling mounted arm.
The injection head is typically mounted on the arm in a pivotal manner, so that the head may be tilted upward (with the syringe tip above the remainder of the syringe) to facilitate filling the syringe with fluid, and downward (with the syringe tip below the remainder of the syringe) for injection. Tilting the head in this manner facilitates removal of air from the syringe during filling, and reduces the likelihood that air will be injected into the subject during the injection process. Nevertheless, the potential for accidentally injecting air into a patient remains a serious safety concern.
In addition to the injection head discussed above, many injectors include a separate console for controlling the injector. The console typically includes programmable circuitry which can be used for automatic, programmed control of the injector, so that the operation of the injector can be made predictable and potentially synchronized with operations of other equipment such as scanners or imaging equipment.
Thus, at least part of the injection process is typically automatically controlled; however, the filling procedure, and typically some part of the injection procedure, are normally performed by an operator, using hand-operated movement controls on the injector head. Typically, the hand-operated movement controls include buttons for reverse and forward movement of the injector drive ram, to respectively fill and empty the syringe. In some cases, a combination of buttons is used to initiate movement of the ram or to control ram movement speed. The injector head also typically includes a gauge or display for indicating injection parameters to the operator, such as the syringe volume remaining, for the operator's use when controlling the injector head. Unfortunately, operators have found it cumbersome to use the hand-operated movement buttons and to read the injector head gauges and displays, for several reasons, not the least of which is the necessary tilting of the injector head between the upward, filling position to the downward, injection position, changing the positions of the hand-operated movement buttons relative to the operator, and at some tilt angles rendering the gauges or displays difficult to read.
In many applications, it is desirable to use an injector with multiple different syringe sizes. For example, it may be desirable to use a smaller syringe for pediatric use than for adult use. To facilitate the use of different syringe sizes, injectors have been constructed with removable face plates, where each of the various face plates is configured for a particular syringe size. Typically, the injector is able to adjust injection parameters by detecting which face plate is mounted to the injector, for example using a magnetic detector mounted to the front surface of the injector housing to detect the presence or absence of a magnet in the face plate. Unfortunately, the necessity of incorporating a magnetic detector into the outer housing of the injector head increases the complexity and expense of manufacturing the injector head.
SUMMARY OF THE INVENTION
In accordance with the invention, improvements are made on these various aspects of the operation of the typical injector.
In particular, an injector in accordance with the invention features an air bubble detection system positioned adjacent the tip of the syringe for detecting the presence of air in the tip of the syringe. This detection system, which is electrically connected directly to the control circuitry in the injector, permits the injector to detect air in the tip of the syringe, and if air is detected, to halt any prospective or ongoing injection. Since air is detected prior to exit from the syringe and before passage through the tubing leading to the patient, rather than at some intermediate point along the tubing, the injector is more likely to detect air early enough to prevent or halt the injection before the air reaches the patient.
In the specific disclosed embodiment, the air detector generates a light beam and directs this light beam into the tip of the syringe, where it is reflected from the inner wall of the syringe tip and returned into a detector. Other methods of air detection, such as ultrasonic air detection, may also be performed by a detector mounted at the syringe tip with similar advantage, and are encompassed within the scope of the invention.
Another aspect of this feature of the injector is the structure of the syringe tip, which includes an outwardly-projecting transparent section positioned for mechanical coupling to the source of light in the air detector, to facilitate light coupling into the syringe tip for reflection from the inner wall of the tip and return to the detector. This outwardly-projecting section forms a lens for focusing light impinging upon the syringe tip so that this light properly reflects through the interior of the syringe tip.
The injector in accordance with the present invention also features a hand-operated fill/expel control which facilitates operator control of the injector. The control includes a lever movable between home, forward, and reverse positions, where movement of the lever to the forward position causes the injector to move the plunger drive ram forward to expel fluid from the syringe, and movement of the lever to the reverse position causes the injector to move the plunger drive ram in reverse to draw fluid into the syringe.
In specific embodiments, the lever is mounted on a pivot, and biased to the home position by return springs positioned on opposite sides of the lever. Rotation of the lever away from the home position progressively bends the springs at increasing angles of lever rotation. A detector, specifically a rotary potentiometer, detects the angle of rotation of the lever, so that this angle can be used to control the speed of motion of the plunger drive ram. Using this structure and control, the relative position of the lever, and (if desired) the return torque applied by the springs to the lever, can be made roughly proportional to the flow rate of fluid into or out of the syringe, providing the operator with intuitive feedback on the operation of the injector. Alternatively, the injector may control the injection pressure produced by the injector in response to the angle of rotation of the lever, to provide the operator with feedback on the injection pressure being applied.
As a safety feature, in the disclosed specific embodiment, the return springs and lever are elements in an electrical circuit which produces a movement control signal. The central processing unit controlling the injector responds to this signal by displaying a fault message, or rendering the hand-operated movement control inoperative, if one of the springs breaks, so that in such a case the injector will not respond to unintentional displacement of the lever away from the home position which might result from breakage of a spring.
As an aid in filling the syringe, an additional detent spring is positioned relative to the lever in order to alter the return torque applied to the lever when the lever is rotated more than a given angle away from the home position. The result is a “detent” that can be identified

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