Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2001-04-03
2003-02-18
Mendez, Manuel (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S154000, C417S044200
Reexamination Certificate
active
06520930
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to injectors, injector systems and control of injectors and injector systems, and, especially, to injectors, injector systems and injector control for use in medical procedures in which a fluid is injected into a patient.
In many medical diagnostic and therapeutic procedures, a physician or other person injects a patient with a fluid. In recent years, a number of injector-actuated syringes and powered injectors for pressurized injection of fluids such as contrast media have been developed for use in procedures such as angiography, computed tomography, ultrasound and NMR/MRI. In general, these powered injectors are designed to deliver a preset amount of contrast media at a preset flow rate.
To ensure the safety of the patient, the operation of a powered injector should be carefully controlled. For example, it is desirable not to exceed a certain fluid pressure during an injection procedure. In addition to potential hazards to the patient (for example, vessel damage) and potential degradation of the diagnostic and/or therapeutic utility of the injection fluid, excessive pressure can lead to equipment failure. For example, because of the potential of cross-contamination between patients, the syringe and tubing used to carry fluid to a patient are typically changed on a per-patient basis. Such disposable syringes and other fluid path components (sometimes referred to collectively as a “disposable set”) are typically fabricated from plastics of various burst strengths. If the injector causes pressure in the fluid path to rise above the burst strength of a disposable fluid path element, the fluid path element will fail.
In controlling system or injection pressure, current injectors use motor current as an indication of system pressure. This technique has inherent accuracy problems, as there are many variables between the parameter being measured (motor current) and the parameter of interest (fluid pressure). These include, for example, measurement inaccuracies, motor torque constant variation, motor variation with temperature, frictional effects in the drive train, and frictional effects in the syringe. In general, any control algorithm must allow for such errors and must make a conservative estimate of fluid pressure to prevent actual fluid pressure from reaching a hazardous value.
Current systems typically predefine a conservative pressure (that is, motor current) control value. As the preset pressure control level is reached, such injectors begin to slow down the flow rate of injection in an effort to stop the build up pressure. At that point, an injector system that was originally intended to servo control the volume and flow rate of the injection fluid begins to servo control pressure. The inaccuracies inherent in using motor current to derive pressure result in a compliant system, and the operation of the servo in that state is oscillatory. Pressures in excess of desirable limits can occur, resulting in potentially hazardous operation of the injector.
In addition to problems of control with current injector systems, many such systems lack convenience and flexibility in the manner in which the injector systems must be operated. In that regard, the complexity of medical injection procedures and the hectic pace in all facets of the health care industry place a premium on the time and skills of an operator.
It is thus very desirable to develop injectors exhibiting improved operative control as well as injectors exhibiting improved ease of use.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides an injector for use in injecting a fluid in a medical injection procedure. The injector includes a drive mechanism to pressurize the fluid; a sensor to measure a variable that is proportional to fluid pressure (that is, a direct or indirect measurement of fluid pressure); and a pressure monitor (for example, including hardwired circuitry and/or software) in communication with the sensor and the drive mechanism to stop the injection procedure when the sensor measures a value of the variable that corresponds to a pressure hazard limit.
Preferably, the pressure monitor further limits power input to the drive mechanism to a power limit once the variable reaches a value that corresponds to a power limiting pressure that is below the pressure hazard limit. In this manner, the pressure hazard limit should never be reached. If, however, the power limiting feature fails, the injector terminates the injection procedure once the pressure hazard limit is reached.
The drive mechanism may, for example, receive power from a motor. In this embodiment, the sensor can, for example, measure motor current. The pressure monitor can limit the motor current to a value corresponding to the power limiting pressure. The power limit is typically predetermined or preset for the injector in this embodiment.
In another embodiment, a more direct and accurate manner of measuring fluid pressure than measuring motor current is used. In one embodiment, for example, the sensor measures force exerted upon a component of the drive mechanism or an injector component in connection with the drive mechanism. In general, the sensor can measure force upon any component of the injector that bears a load proportional to the fluid pressure. Particularly in the case that a force sensor (for example, a strain gauge) or pressure transducer is used to measure fluid pressure, setting of the power limit during injector use and periodic auto-recalibration are facilitated.
In another aspect, the present invention provides an injector for use in injecting a fluid in a medical injection procedure including: a drive mechanism to pressurize the fluid; a sensor to measure a variable that is proportional to fluid pressure; and a pressure monitor in communication with the sensor and the drive mechanism to limit power input to the drive mechanism to a power limit once the variable reaches a value that corresponds to a power limiting pressure.
In a further aspect, the present invention provides an injector system for use in injecting a fluid in a medical injection procedure including a drive mechanism to pressurize the fluid and a control mechanism to control flow rate of the fluid and volume of the fluid injected. The injector further includes a sensor including a force transducer providing a measure of fluid pressure and a pressure monitor in communication with the sensor and the drive mechanism to stop the injection procedure when the sensor measures a pressure corresponding to a pressure hazard limit. The pressure monitor also preferably limits power input to the drive mechanism to a power limit when the sensor measures a pressure corresponding to a power limiting pressure. As discussed above, the power limiting pressure is less that the pressure hazard limit.
In another aspect, the present invention provides an injector system for use in injecting a fluid in a medical injection procedure including a drive mechanism to pressurize the fluid and a control mechanism to control flow rate of the fluid and volume of the fluid injected (typically on the basis of flow rate and volume setting input by the user of the injector using a data entry mechanism as known in the art). The injector also includes a safety system including a sensor (for example, a force transducer) to provide a measure of fluid pressure. The safety system also includes a pressure monitor in communication with the sensor and the drive mechanism. The pressure monitor is adapted to override settings of the control mechanism and stop the injection procedure when the sensor measures a pressure corresponding to a pressure hazard limit. Moreover, the pressure monitor is adapted to override settings of the control mechanism to limit power input to the drive mechanism to a power limit when the sensor measures a pressure corresponding to a power limiting pressure, the power limiting pressure being below the pressure hazard limit. In general, the power limit is preferably the power being supplied to the drive m
Bates Richard A.
Critchlow Richard G.
Doiron Robert J.
Mishler David A.
Uram Martin J.
Bartony, Jr. Henry E.
Bradley Gregory L.
Han Mark
Medrad Inc.
Mendez Manuel
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