U.S. patent number 3,701,345 [Application Number 05/076,491] was granted by the patent office on 1972-10-31 for angiographic injector equipment.
This patent grant is currently assigned to Medrad, Inc.. Invention is credited to Marlin S. Heilman, Donald Jones, Rudolph J. Kranys.
United States Patent |
3,701,345 |
Heilman , et al. |
October 31, 1972 |
ANGIOGRAPHIC INJECTOR EQUIPMENT
Abstract
An angiographic injector control system for delivering a
controlled volume of injection fluid is described. The injector has
a motor driven piston for ejecting fluid from a syringe cartridge
contained within a pressure jacket. The drive motor is operated in
accordance with a command voltage corresponding to an incremental
position of the injector piston, the command position signal also
corresponding to the volume of fluid to be ejected from the
cartridge. This command position voltage signal is compared to an
actual position voltage to produce an error signal for operating
the drive motor, whereby the syringe piston follows the position
command signal. Volume selector means produce a volume signal
corresponding to a desired maximum volume of fluid to be ejected;
this volume signal is compared to the sum of the position command
increments, producing a stop signal when the position command
signal equals or exceeds the volume limit signal. Thus, the
injector control system regulates the injection of fluid by sensing
and controlling the position of the injector piston.
Inventors: |
Heilman; Marlin S. (Gibsonia,
PA), Kranys; Rudolph J. (Pittsburgh, PA), Jones;
Donald (Churchill, PA) |
Assignee: |
Medrad, Inc. (Allison Park,
PA)
|
Family
ID: |
22132372 |
Appl.
No.: |
05/076,491 |
Filed: |
September 29, 1970 |
Current U.S.
Class: |
600/432;
128/DIG.1; 604/121; 422/926; 604/66; 604/67; 604/155 |
Current CPC
Class: |
A61M
5/14546 (20130101); A61B 6/504 (20130101); A61M
5/172 (20130101); B01L 3/0227 (20130101); G05D
7/0676 (20130101); A61B 6/481 (20130101); A61M
5/14566 (20130101); Y10S 128/01 (20130101) |
Current International
Class: |
A61B
6/00 (20060101); A61M 5/172 (20060101); A61M
5/145 (20060101); A61M 5/168 (20060101); B01L
3/02 (20060101); G05D 7/06 (20060101); A61b
006/00 (); A61m 005/00 (); A61m 005/20 () |
Field of
Search: |
;128/2R,2A,2.5F,2.5R,215,218R,218A,DIG.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truluck; Dalton L.
Claims
What is claimed is:
1. An injection system for producing a controlled volume of
injection fluid for use in angiography comprising:
a. an injector including syringe means for said fluid, piston means
connected to said syringe and movable along a linear path for
ejecting said fluid from said syringe means, conduit means for
connecting said syringe means to a patient, and a drive motor for
moving said piston; and
b. control means for said injector, said control means including
command means for producing a command signal which is a function of
the desired injector piston position, sensing means for producing a
position signal which is a function of the actual injector piston
position along its path, and means for comparing said command and
actual position signals to produce a resultant signal for operating
said drive motor, whereby said piston is advanced along said path
to its command position to eject said controlled volume of
fluid.
2. The injector system of claim 1 wherein said sensing means is a
potentiometer driven by said injector to produce said position
signal.
3. The injector system of claim 2 wherein said control means
further includes means for selecting the volume of fluid to be
injected by said injector, and means for regulating the operation
of said drive motor to terminate an injection after said selected
volume has been injected.
4. The injector system of claim 3 wherein said means for regulating
the operation of said drive motor includes a comparison means
responsive to a first signal corresponding to the selected volume
and to said position signal, said position signal corresponding to
incremental movement of said drive motor, said comparison means
producing an output when the position signal is equal to or greater
than said first signal.
5. The injector system of claim 4 wherein said control means
further includes a disarm circuit for said injector, the output
from said comparison means being effective to trigger said disarm
circuit and stop said drive motor.
6. The injector system of claim 1 wherein said command means
includes means for selecting a predetermined command function, and
integrator means for integrating said command function to produce
said command signal.
7. The injector system of claim 1 wherein said control means
further includes means for selecting a maximum injector pressure in
said syringe and means for regulating the operation of said drive
motor to limit said injector pressure to the selected value.
8. The injector system of claim 7 wherein said means for limiting
said injector pressure includes means for producing a signal
proportional to the actual torque of said drive motor, comparing
said torque signal to a signal proportional to said selected
injector pressure and producing a resultant pressure limit signal
for regulating said drive motor.
9. The injection system of claim 8 wherein said means for producing
a signal proportional to the actual torque of said drive motor
comprises a resistor in series with said motor.
10. The injector system of claim 8 wherein said means for selecting
a maximum injector pressure further includes actual means
responsive to said signal proportional to the actual torque of said
drive motor for displaying the torque in terms of injector
pressure.
11. The injector system of claim 5, further including fault
detector means responsive to malfunctions in said injector for
triggering said disarm circuit to stop said drive motor.
12. The injector system of claim 1, wherein said resultant signal
for operating said drive motor is an error signal proportional to
the difference between the instantaneous value of said command
signal and the incremental position of the injector piston, the
instantaneous value of said position signal being proportional to
said incremental position.
13. The injector system of claim 1, further including means for
producing a volume selector signal which may be varied to select a
desired displacement of said piston, means responsive to said
actual position signal for establishing a signal proportional to
the initial location of said piston, and means for comparing said
initial location signal, actual position signal and volume selector
signal and for producing a volume limiting signal when the
difference between said initial location signal and said actual
position signal equals said volume selector signal, said volume
limiting signal terminating an injection after said selected volume
has been injected.
14. The injector system of claim 13 wherein said means for
establishing said signal proportional to the initial location of
said piston comprises a memory circuit for storing the position
signal at the start of an injection.
15. The injector system of claim 14, wherein said means for
producing a volume selector signal comprises a digital switch
array.
16. The injector system of claim 1 wherein said control means
further includes an arm/disarm circuit for said injector drive
motor, said arm/disarm circuit being operable to establish and to
interrupt the armature current of said motor.
17. The injector system of claim 16 wherein said control circuit
further includes means for generating a volume limit signal, and
means within said arm/disarm circuit responsive to said volume
limit signal for terminating the operation of said injector after a
predetermined amount of fluid has been ejected from said syringe
means.
18. The injector system of claim 1, wherein said control circuit
further includes pressure limit means for limiting the armature
current of said motor.
19. The injector system of claim 18, said pressure limit means
comprising means for producing an actual pressure signal
proportional to the actual armature current in said motor, pressure
selector means for producing a selected pressure signal
proportional to the desired maximum armature current, and
comparator means for producing a pressure limit signal proportional
to the difference between said actual pressure signal and said
selected pressure signal, said pressure limit signal modifying said
resultant signal for regulating the operation of said drive
motor.
20. The injector system of claim 17 wherein said means within said
arm/disarm circuit responsive to said volume limit signals
comprises a volume limit switch, said volume limit switch serving
to terminate the operation of said injector and permitting
subsequent injection cycles in a multiple inject mode.
21. The injector system of claim 17 wherein said means within said
arm/disarm circuit responsive to said volume limit signals
comprises a disarm switch to terminate the operation of said
injector and preventing subsequent injection cycles to thereby
establish a single inject mode.
22. The injector system of claim 21 wherein said arm/disarm circuit
further includes an arm switch, a master relay, and a volume limit
switch in series with said disarm switch and with a start switch,
closure of all said arm/disarm circuit switches and consequent
energization of said master relay being required for operation of
said injector.
23. The injector system of claim 22 wherein said arm/disarm switch
further includes a safe circuit in series with the armature of said
drive motor, said safe circuit being controlled by said master
relay, whereby said arm/disarm circuit regulates the operation of
said drive motor.
24. The injector system of claim 22, further including fault
detector means responsive to malfunctions in said injector for
opening said disarm switch, thereby to disable said drive
motor.
25. The injector system of claim 24, wherein said fault detector
means includes overrate sensing means responsive to the speed of
said drive motor, said overrate sensing means producing a fault
output for disabling said motor when said motor exceeds a
predetermined speed.
26. The injector system of claim 1 wherein said means for producing
a command signal comprises a digital switch array having adjustable
switch contacts for selecting a desired command signal level.
27. The injector system of claim 1, wherein said means for
producing a command signal comprises a source of variable voltage,
whereby said command signal varies in accordance with a preselected
program to produce a desired command signal function.
28. The injector system of claim 27, wherein said source of
variable voltage comprises an array of potentiometers connectable
to a common line, and means for sequentially connecting said
potentiometers to said line, whereby said variable voltage is a
step function corresponding to the settings of said
potentiometers.
29. The injector system of claim 28 wherein said means for
sequentially connecting said potentiometers to said common line
comprises clock-driven counter means having a plurality of outputs,
each output being energized in sequence to connect a corresponding
potentiometer to said common line.
30. The injector system of claim 29, further including means for
synchronizing said counter means with an electrocardiogram, whereby
said command signal function is initiated at a selected time.
31. The injector system of claim 30, further including counter
means for counting the number of times said command signal function
is generated, said counter means producing an output signal after a
predetermined count is reached to terminate operation of said drive
motor.
32. The injector system of claim 1, further including fault
detector means responsive to malfunction in said injector for
stopping said drive motor.
33. The injector system of claim 32, wherein said fault detector
means includes overrate sensing means responsive to the speed of
said drive motor, said overrate sensing means producing a fault
output for disabling said drive motor when said drive motor exceeds
a predetermined speed.
Description
BACKGROUND OF THE INVENTION
This application relates, in general, to the medical science of
angiography, and more particularly to the injection equipment for
use therein.
Angiography is the science of producing human body radiographs
outlining vascular structures by means of contrast media fluid
injections into the appropriate vascular areas. The contrast media
is placed in an appropriate injection apparatus and forced through
a long, thin tube (catheter) in such a way that the contrast media
enters the blood stream at the appropriate time and place for the
radiograph or angiogram. Early injection apparatus was designed to
allow the operator to preset the driving force or pressure level
necessary to propel the contrast media through the catheter.
However, catheters vary greatly in their resistance to contrast
media flow and it was found to be extremely difficult to control
injection rates by presetting an injection pressure. Thus, the
prior application of Heilman et al., Ser. No. 567,643, filed July
25, 1966, issued as U.S. Pat. No. 3,623,474, on Nov. 30, 1971, and
entitled Angiographic Injection Equipment, proposed the use of a
rate or speed indicating feedback signal from the injector motor
for comparison with a selected command rate signal to produce a
rate error signal. This rate error signal was then used to control
the injector motor speed, and thus the injection pressure. The
result of this prior control system was that the injector pressure
automatically adjusted, within the pressure range available, to
match actual injection rates with selected command injection rates
regardless of varying catheter resistances; if increased flow
resistance tended to slow the motor, the speed sensing mechanism
would produce a larger error signal in an attempt to speed up the
motor. This, in turn, increased the pressure to compensate for the
flow resistance, thus tending to maintain the desired rate of
injection.
Although the system described in the foregoing application presents
a distinct improvement in the angiographic art, there are
disadvantages of using a speed, velocity, or injection rate signal
to control the injection rate. It has been found that one of the
most significant factors in obtaining accurate angiograms is
regulation of the volume of fluid injected, and a primary
disadvantage of a rate control system is the difficulty of
controlling the volume of contrast media injected. If a rate
feedback control mechanism is used, the volume of contrast media
injected is determined by setting an injection timer since,
provided the injection rate is constant and controlled, the
injection volume would equal the product of the injection time and
rate. However, experience has shown that even with a rate feedback
mechanism it is easy to get a low injection rate during some part
of the injection cycle, particularly if one uses an excessively
resistive catheter. Such a catheter may require the injector to
deliver more pressure than it has at its command, and as a result
there is a low injection rate. When this occurs, there would also
be a low injection volume, since the injection timer would stop the
injection before the system could compensate for the volume lost
during the low rate period.
A second disadvantage to velocity feedback is the difficulty of
measuring velocity over a wide range. Rate feedback measurements
normally are obtained from a tachometer connected to the injector
drive motor, with the output voltage corresponding to the velocity
of fluid flow. Angiography typically requires rates from 1 to 40
milliliters per second, whereas lymphography, which is the
injection of contrast media into the body's lymphatic system, may
require a rate of several milliliters per hour. If both injections
are to be accomplished by the same machine, the variations in the
amplitude of the tachometer output signal would be exceedingly
large, and extremely difficult to measure accurately. At the lower
end of the scale the voltage would approach zero and be
indistinguishable from noise and interference, resulting in errors
and inaccuracies.
In practice, the angiographer uses connector tubing between the
injector and catheter which is partially within the patient's body,
and this tubing produces another problem in successful angiography,
for the tubing generally has a lower bursting pressure than does a
catheter. Angiographers may inadvertently rupture this connector
tubing or even, in extreme circumstances, the catheter itself if
they place high resistive catheters on an injector and ask for a
high injection rate. As alluded to above, if the catheter prevents
the flow from reaching the selected value, the rate feedback system
will produce a large error signal, and the injector will respond by
developing the maximum pressure possible. This maximum pressure
condition can present a serious hazard to the patient.
Finally, since angiograms generally show a static X-ray photograph
of some vascular structure filled with contrast media, multiple
films can show the progress of contrast media as it flows through
the vessel. With prior methods, however, there was no simple way to
estimate the actual rate of blood flow through a particular artery
in question. It is well known, of course, that as blood is passing
through the heart, it has a discontinuous, or non-linear flow
pattern due to valve closure. If pathology exists, there may be
reverse flow through the heart valves or flow from one chamber to
another through a defective interchamber wall. The arterial system
of the human body receives pulses of blood from the heart and
immediately absorbs this output by expansion of the aorta, which is
the first portion of the arterial system. The further out the
arterial system blood travels, the less pulsatile both blood
pressure and flow become. Blood flowing in and around the heart is
synchronous with the electrocardiogram (the electrical signal that
initiates the heart action) and the heart valve closure, the latter
being detectable by sounds (phonocardiograms) eminating from the
heart.
If, then, the injection of the contrast media can be synchronized
with heart pulses, more accurate and meaningful measurements of
blood flow can be obtained; for example, the distal resistance to
the flow could be estimated and this information would be useful in
the functional evaluation of arteriosclerosis.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an
improved method of controlling an angiographic injector, whereby
reliance on rate measurements for injection control is
eliminated.
A further object of the present invention is to provide an improved
angiographic injector which is position controlled to overcome the
problems inherent in rate controlled devices.
Another object of the invention is the provision of a position
control system for an injector, wherein a position command signal
is compared to an actual position signal to provide an error signal
which operates the injector, whereby a preselected volume of fluid
is injected.
Still another object of the invention is to provide a
position-controlled injector which will accurately inject a
preselected volume of fluid in spite of variations in injection
rate or pressure.
It is another object of the invention to provide a position
controlled injector which is pressure and volume limited to prevent
injury to the patient receiving the injection.
Another object of the invention is to provide a safe, efficient and
accurate angiographic injector having a motor drive which is
position controlled, the motor being energizable only when
specified conditions exist.
A further object of the invention is the provision of a motor
driven injector which is position controlled, the motor circuit
including arm-disarm networks which provide safety interlocks
responsive to volume injected, pressure of injection, overrate, and
the like.
It is another object of this invention to provide an injector
having pressure indicator means so that the angiographer will know
how much pressure he is using with a particular catheter choice and
injection setting. It is a further object of this invention to
provide a control means for the angiographer to place a maximum
pressure development capability on the injector.
Another object of the invention is to match contrast media flow
from an injector with the blood flow of a patient receiving the
injection by synchronizing the contrast media injection with the
patient's heart cycles. The injection rate may be continuous,
discontinuous, linear, or non-linear.
Another object of the invention is to automatically and positively
disarm the mechanism once the injection has taken place to prevent
inadvertent repetition of the injection cycle.
Briefly, the present invention overcomes the disadvantages of the
prior art by the use of what may be termed a position control
system for an angiographic injector having a motor-driven syringe
plunger. The position control system utilizes a feedback voltage
signal corresponding, not to the syringe plunger velocity, but to
the injector syringe plunger position, this feedback signal being
generated by a potentiometer mechanically driven by the syringe
motor, and thus movable with the syringe plunger. Prior to
injection, the actual position of the plunger is sensed and this
position is used as a zero reference value for the injection,
whereby an accurate measure is obtained for each in a series of
injections. Independently, voltages proportional to the desired
injection volume, pressure limits, and the desired rate are preset
by the operator. Upon initiation of the injection, a command signal
is generated which provides incremental position signals for
comparison with the potentiometer position sensor. Any difference
between selected and measured positions produces an error signal
which is amplified and provides the motor armature current. This
armature current is limited by the pressure limit voltage to
prevent the motor from building up excessive power. The
potentiometer also feeds a comparator circuit for comparing actual
volume injected, which is proportional to the position of the
plunger, with a selected volume limit; when the limit is equalled
or exceeded, the comparator produces an output which disarms the
motor circuit. If the injector is operating in a single inject
mode, disarming the circuit prevents further operation of the
device until it is reset. A multiple inject mode is also provided
which permits repetitive operation of the selected injection cycle
without disarming the circuit.
In one embodiment of the invention, the position command signal may
be generated by a selected direct current value; in another
embodiment the command function may be variable in a selected
manner to produce a variable injection. Further, the injection may
be synchronized with the heart pulses of the patient receiving the
injection.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects, features, and advantages of the invention
will become apparent to those skilled in the art from the following
description of a preferred embodiment thereof, taken in conjunction
with the accompanying drawings, in which:
FIG. 1 is a block diagram of the control logic for the subject
injector;
FIG. 2 is a block diagram of a variable function generator which
may control the injection function of the subject injector;
FIG. 3 is a schematic diagram of a digital switch shown in FIG.
1;
FIG. 4 is a graphical representation of a volume limited injection
compared to a time limited signal;
FIGS. 5 and 6 are schematic diagrams showing the injection control
circuitry of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to a detailed consideration of the drawings, there is
illustrated in FIG. 1 a control system for an angiographic injector
wherein the operator of the injector system may select a precise
volume of contrast media or equivalent material to be delivered to
a patient. It will be understood that the contrast media is
conventionally delivered to selected locations through a suitable
catheter, where X-ray exposures are to be made at timed
intervals.
Considering first the structure of an injector device, shown
generally at 10, which is suitable for use with the control system
to be described, it will be seen that the injector mechanism is
constructed for lightness and compactness, without sacrificing the
required power, and thus is driven by a direct current permanent
magnet motor 12 preferably having a printed circuit armature 14.
The shaft 16 of the motor is drivingly coupled to a threaded screw
shaft 18 which thus rotates with the motor armature 14. Threaded
engaging shaft 18 is a ball nut 20 which is prevented from rotating
by pin 22, but which is free to move axially along shaft 18, the
pin sliding in a guide slot 24 formed in a guide bar 26 and
supported in the housing 28 of the injector 10. At the forward end
of the guide slot 24 is a microswitch 27 which detects the
forwardmost movement of the pin 22 and closes to provide an output
signal. The microswitch function will be explained in detail in the
description of the control circuitry.
The axial movement of ball nut 20 in response to rotation of the
threaded shaft 18 converts the rotary motion of the motor 12 to a
linear motion. Ball nut 20 is connected to a piston tube 30 which
moves with the ball nut along shaft 18. The outer end of the tube
is supported, during its linear motion, by an oil seal 32 secured
in an opening 34 at one end of the housing 28. Piston tube 30 abuts
directly against a piston head supporting member 36, which, in
turn, provides mechanical support for a rubber piston cap 38. A
syringe, or cartridge, 40 is mounted on the injector housing 28 by
means of an internally threaded nut 42 adapted to engage external
threads on the end of the housing 28. Nut 42 has a centrally
located aperture 44 which receives the syringe in a seal member 46
to permit an airtight fitting on the end of the housing. A flange
portion 48 is provided on the end of the syringe which faces the
housing to facilitate a tight seal between the sealing members 34
and 46 when nut 42 is tightened. The other end of the syringe 40
forms a conduit 49 which is adapted for connection to a suitable
catheter (not shown) through which fluid may flow for injection
into a patient during operation of the injection.
The internal diameter of the syringe and the external diameter of
piston 36 are selected to provide the clearance required to permit
a flange edge 50 of the rubber piston cap 38 to seal the interior
of the syringe. It will be apparent that different sizes of
syringes will require pistons having varying diameters, but the
construction of this mechanism is such that various sizes are
easily connected to the injector drive mechanism. The aperture in
nut 42 is sufficiently large to permit larger syringes than the one
illustrated, while smaller diameter syringes with sufficiently
large flanges can be used with this equipment as well. Piston
member 36 in cap 38 may be driven in the forward direction (toward
the right as viewed in FIG. 1) by piston tube 30 without any
mechanical connections being made between the piston and the tube.
This arrangement is often used where it is essential to prevent
reversal of the motion of the piston. As an alternative, piston 36
may be connected to piston tube 30 by means of a screw 52 to permit
both forward and reverse driving of the piston. It will be apparent
that forward motion of the piston will expel fluid or any other
matter within the syringe 40, such as contrast media 54. If the
piston is attached to the piston tube 30, reverse driving can be
used to fill the syringe with the desired amount of contrast
material while the syringe is attached to the injector drive
mechanism. To this end, a suitable motor reversing switch (not
shown) may be provided in the control circuits to be shown.
The broken-away portion of motor 12 illustrates, in addition to the
armature 14, the arrangement of the permanent magnet 56. In
operation, direct current is commutated to the armature conductors,
and the resultant alternating magnetic field interacts with the
stationary magnetic field of the permanent magnet to produce the
torque on shaft 16. The use of a printed circuit armature permanent
magnetic torque motor allows for a maximum power for a minimum size
and makes practical a hand-held injector much smaller than
conventional electro-mechanical injectors.
A gear train consisting of a first gear 58 mounted on motor shaft
16 and a corresponding gear 60 drives a potentiometer 62 to provide
a direct measurement of shaft rotation, and thus of the location of
ball nut 20. Since the potentiometer is mechanically geared to the
drive train of the injector via gears 58 and 60, and the syringe is
mechanically connected to the ball nut which is driven by the drive
shaft of the motor, the voltage appearing on the wiper arm of
potentiometer 62 will correspond to the plunger position. When an
injection is to take place, the voltage level representing the
actual position of the piston plunger is sensed and registered in
an initial position memory circuit 72 through lines 70 and 73. The
memory circuit 72 acts as a zero reference for any subsequent
injection so that a selected volume can be injected from any
starting point of the syringe plunger, the starting point being
represented by the existing potentiometer output. This memory
circuit permits a selected volume to be injected upon demand,
without requiring the circuit to start from the beginning each time
an injection cycle is required.
The desired volume for the injection is set in an injection volume
selection unit 74 and a corresponding signal is applied to a volume
comparator 76 in the form of a volume reference signal on line 78.
The voltage representing the position of the potentiometer 62 at
the start of an injection is also applied to the comparator 76 in
the form of an output on line 80 from the memory circuit 72. The
memory voltage signal plus the selected volume signal, when summed
in the comparator 76 provide a target position signal which
corresponds to the location of the injector plunger after it has
moved from its starting location and injected the selected volume
of fluid. The incremental movements of the potentiometer which
correspond to the injection of contrast media, and thus to rotation
of the syringe drive motor, are also fed into the comparator 76 by
way of lines 70, 73, 79 and 81. When the signal level received from
the potentiometer, or the sum of the position increments of the
syringe plunger movement, is equal to or greater than the desired
volume signal selected on line 78 plus the memory signal, the
comparator 76 produces an output on line 82. This output signal
indicates that the plunger has moved from its initial position
sufficiently far to inject the selected volume of fluid; therefore,
the output is fed by way of line 82 to an automatic arm-disarm
circuit 84 to terminate the injection. By making this control
circuit sensitive to position rather than to a rate of fluid flow,
it is assured that the desired volume of contrast media is ejected
from the syringe even if the desired injection rate is not
achieved, or is only partially achieved.
Logic circuitry for controlling and monitoring the rate of
injection is also shown in FIG. 1, this circuitry serving to
provide a command function for the injector motor so that the
injection will at least tend to take place at a preselected rate,
it being understood that the starting and stopping functions of the
device are regulated by a volume, or position, control. The logic
circuitry, which is shown in detail in FIG. 3, includes a digital
switch 90 with outputs 91, 92 and 93 which may be selected by
switch 94 to provide a desired rate signal. The digital switch
illustrated herein produces a direct current voltage of desired
level, which voltage corresponds to the desired rate of injection,
for example, in cubic centimeters per unit time. It has also been
found desirable, on occasion, to modify the rate of injection
during the course of an injection cycle, and to this end an
additional line 96 is shown for selector switch 94. Line 96, as
will be explained, may be supplied with a selectively variable
voltage function which, when selected, will cause the drive motor
to follow a corresponding rate function. If desired, this function
may be synchronized with the heart beat of the patient receiving
the injection, thereby providing further control over the
injection, as is described in detail in FIG. 2. In any event, the
injection control system is capable of operating with any constant
rate or variable rate command function selected, with the
successful completion of the injection being dependent on the
movement of the plunger from one position to the next, rather than
on the rate at which the piston moves and the fluid is
injected.
The function selected by selector switch 94 is fed into an
integrator 100 to produce a position command signal which is to be
followed by the syringe motor. The integrator 100 integrates the
function selected by switch 94 and produces the position command
signal on line 102. In the case of a d.c. voltage function, the
output of the integrator will be a negative-going ramp, while a
variable function will produce a more complex signal. The output
from the integrator is fed to a position comparator 104, this
output providing a position command function for the injector
plunger for each instant in time. A second signal is fed to the
comparator from the potentiometer 62 through lines 70 and 105, the
signal on line 105 corresponding to the actual instantaneous
position of the injector plunger. When the two input signals to
comparator 104 are equal, the syringe plunger is at the location
dictated by the command signal; when the two signals are not equal,
the position comparator 104 produces an error voltage on line 106
which is proportional to the difference between the two incoming
signals. The error voltage on line 106 is fed into a power
amplifier 108 which provides a corresponding armature current by
way of line 110 to motor 12 to either speed up or slow down the
motor.
It will be seen that if the motion of the syringe plunger is
impeded during an injection cycle, the drive motor can be slowed,
causing the actual position of the motor (plunger) to fall behind
that which is dictated by the command signal. A large error signal
can then be generated, increasing the motor torque and the pressure
of the injection. If the flow impedance is momentary, its release
will cause the motor to speed up in an attempt to "catch up" to the
command signal; if the impedance is not released, the error signal
will continue to increase. Either condition, if allowed to exist
for an appreciable length of time, can result in serious injury to
the patient, and thus the present system provides several safety
systems. An overrate sensitive network responds to sudden increases
in motor speed to shut off the injector if the speed increases
outside predetermined limits, the network providing an offset to
accommodate normal transient variations. Similarly, a settable
pressure limit network responds to the injector pressure to
modulate, and thus limit, the motor armature current, thereby
effectively preventing excessive pressure conditions.
The overrate sensitive network includes a rate monitor circuit 116
which receives the output from the potentiometer 62 by way of lines
70, 79 and 117 and modifies it for comparison with an input on line
118 which corresponds to the selected rate of the injection. When
the input on line 117 is appreciably larger than the selected
command rate value on line 118, the rate monitor circuit 116 will
trigger the arm-disarm circuit 84 through line 119 and terminate
the injection. A suitable difference between the actual rate on
line 117 and the desired rate on line 118 is required before the
injector will be disarmed so that normal transient conditions will
be ignored and the circuit will operate upon failure of the
equipment, or in emergency situations.
As mentioned above, microswitch 27 detects the forwardmost position
of the syringe plunger. When all of the contrast media 54 has been
injected and the plunger reaches this position, a signal from the
microswitch 27 is generated on line 124 which triggers the
arm-disarm circuit 84 to positively terminate the injection and
prevent further operation of the system.
To monitor pressure conditions in the injector, a sampling
resistance 130 is connected in series with a safe circuit 132 in
the armature circuit of motor 12 by way of line 133. The current
through this resistor establishes a voltage proportional to the
motor current which, in turn, is proportional to injection pressure
when a torque motor is used. Under normal operating conditions,
safe circuit 132 which may, for example, be a power transistor in
series with the armature circuit, is a short circuit (i.e., is
closed) and allows the motor armature current to pass through
resistor 130 to ground to establish the sampling voltage. Since the
voltage across resistor 130 is proportional to the actual injection
pressure, this voltage is referenced by way of lines 134 and 135 to
a pressure comparator 136 and by way of lines 134 and 137 to a
pressure indicator 138. The pressure indicator 138 preferably
comprises a plurality of lamps corresponding to various pressure
levels, with the pressure voltage being operative to illuminate a
lamp corresponding to the pressure at which the motor is running.
The pressure comparator 136 compares the actual pressure of the
injector with a selected pressure limit voltage on line 140 which
is derived from a pressure selector 142. Selector 142 permits the
operator to preset a maximum injector pressure, and if the pressure
signal on line 135 exceeds the limit voltage on line 140, the
pressure comparator 136 provides an error voltage on line 144
corresponding to the magnitude of this difference. The pressure
limit error voltage on line 144 is fed to the input of the motor
power amplifier in opposition to any position comparator signal
that would tend to increase the motor current. Thus, the pressure
comparator limits the injector pressure to the preselected value by
preventing the motor armature current from increasing.
If it is desired to provide a capability in the present injector
for operating at a controlled, variable rate during the course of a
single injection, a suitable function generator may be provided, as
indicated above. One such function generator is illustrated in FIG.
2 as providing an output of selectable waveform on line 96.
Turning now to FIG. 2, a function generator 148 consists of ten
manually settable sliding potentiometers 150 - 159, each connected
between a positive reference voltage and ground. The wiper arm of
each potentiometer is connected through a corresponding one of
electronic switches 160 - 169 to a common output line 170, the
switches being normally open. A clock circuit 172 closes successive
ones of switches 160 - 169 in a sequential fashion, each switch
feeding its particular selected potentiometer voltage to the common
line for a predetermined period of time, in this example, 100
milliseconds. Capacitance is generally added to common line 170 to
get a smoothing effect during sequencing. As the clock sweeps the
switches 160 - 169, closing each in turn, a stepped output voltage
appears on line 170, each step corresponding in amplitude to the
selected value of the connected potentiometer. It will be seen that
if each potentiometer is set at the same level, a selected d.c.
voltage will appear on the line; by setting the potentiometers at
different values, any desired waveform may be generated.
In some circumstances it may be desired to correlate the generation
of the command function with the heart pulses of the patient, and
for this purpose each cycle of the waveform may be triggered by a
signal derived from an electrocardiogram 174 in the following
manner. The waveform corresponding to the heartbeat is fed from the
electrocardiogram 174 to a QRS trigger 176 by way of line 177. The
QRS trigger will trigger the injection at a selected slope along
the electrocardiogram waveform by producing a triggering pulse
which is conducted through line 178 to a variable delay 180 which
will delay the triggering pulse with the contraction of the
patient's heart. This delay differs with the individual involved so
that different intervals will be selected for different patients.
Once the triggering pulse passes through the variable delay, it is
conducted through line 182 to a monostable circuit 184 having two
outputs only one of which is on at a particular instant. In the
normal mode of operation for the monostable circuit 184 output line
185 is in the on state and output line 186 is off. When output line
185 is on, a binary counter 187 is energized to receive and count
pulses received from clock 172; the off condition of line 186
permits the clock to run freely. The counter 187 drives a binary to
decade counter 188 which produces output signals sequentially on
lines 190 - 199 to energize each of switches 160 - 169 in turn.
When the output line 185 is in the off state, the binary counter
187 and the decade counter 188 are de-energized and automatically
reset. At the start of an injection, the inject button is pushed
and a start signal is fed into the monostable circuit through line
200 to switch circuit 184 to its unstable state. This turns output
line 185 off, resetting the counters, and turns output line 186 on,
which inhibits the clock from running. In otherwords, the pulse on
line 200 is a resetting pulse which sets all the counter values to
zero. A second pulse is then needed to trigger the monostable
circuit back into its normal operating mode and this pulse is
provided by the QRS trigger 176. In this manner, it can be seen
that the electrocardiogram triggers the generation of the injection
command function waveform. The injection function can be varied
simply by varying the values of the potentiometer 150 - 159 and can
be triggered in synchronism with the electrocardiogram. This output
function is conducted through lines 170 and 96 to one of the
terminals of selection switch 94.
The synchronizing of the injection with the electrocardiogram can
be viewed graphically by feeding the function output on line 170
through an integrator 201 where the function is integrated and
conducted by way of line 202 into one of two information channels
on a multiplexer single gun display tube 203. The waveform of the
electrocardiogram may be fed to the second information channel of
tube 203 by way of line 204, this input being derived either
directly from the electrocardiogram output or from a microphone 205
which can be placed over the patient's heart.
Although it is usual to provide only a single injection of a
preselected quantity of contrast media, it may be desirable to
provide, instead, a series of injections, for example, of lesser
quantities of fluid, in synchronism with successive heartbeats. The
present invention provides such operation by a digital switch 206,
which is settable to a selected number of successive injections.
The switch is connected through a binary counter 207 and a binary
to decade counter 208 which may be identical to units 187 and 188.
If, for example, three injections are desired, the digital switch
206 is set to the number 3 and the injection cycle will repeat
itself with each successive heartbeat until the number of
injections totals three. The digital switch 206 will then produce a
stop command signal on line 209 which is fed to the disarm circuit
84, simulating a volume limit signal and turning the injector
off.
The function generator described and illustrated is, then, a means
to selectively produce a linear, a non-linear, or a discontinuous
flow rate command signal which may be synchronized with the
patient's electrocardiogram. The injection would be discontinuous
if one of the potentiometers 150 - 159 were set at zero and
adjacent potentiometers had a flow setting.
Turning now to a more detailed consideration of the control
circuitry of the present invention, FIG. 3 is illustrative of a
preferred form of the digital switch 90 which produces the constant
function for the injection rate selection. A stable reference
voltage is divided into nine equal parts by a first series of
precision resistors 210 - 218 connected between the reference and
ground. The first divider provides a voltage corresponding to a
tens value; a second divider comprising resistors 210' - 218' is
used for units, and is similarly constructed. A precise digitized
voltage for a desired number of tens or units may be chosen by the
operator by selecting the desired detented position 220 - 229 and
230 - 239 on numbered digital switches. The selection is made by
positioning arms 240 and 242, respectively, in the appropriate
position. The tens and units outputs from arms 240 and 242 are
conducted through lines 244 and 246, respectively, through pairs of
scaling resistors 247 - 248, 249 - 250, and 251 - 252 which
appropriately scale the value of the voltage to a flow rate per
second, per minute, or per hour. The selection of appropriate
scales can then be made by arm 94 by connecting it to one of the
output lines 91, 92 or 93 to obtain a d.c. voltage level
corresponding to a desired flow of injection fluid, for example, in
milliliters per unit time.
Although the digital switch 90 provides a rate function as a
command for the operation of the syringe, this rate function in the
present system serves primarily as a position target for the drive
motor operation, since no time limit is set for regulating the
duration of the injection. Thus, the rate signal provided by switch
90 is essentially an incremental position signal, commanding the
motor to shift the position of the syringe piston a specified
distance (volume) per unit of time. The distinction between this
position control and the rate control of the prior art is
illustrated in the graph of FIG. 4, wherein the volume of fluid
injected is plotted along the ordinate axis and the injection time
is plotted along the abscissa. Line A represents a selected
injection rate of 30 milliliters per second. If the injection were
time limited to, e.g., 1 second, the desired volume would be
injected if no unexpected flow resistance were encountered, and the
prior art devices could function properly. If, however, the
operator had selected a more restrictive catheter, if unexpected
resistance to flow were encountered, or if a catheter were used
that could withstand only limited pressure, the actual flow rate
might be considerably below the selected value, as indicated by
line B. Safety factors such as pressure limiting circuits of the
type disclosed herein might also reduce the flow by limiting the
allowable pressure that could be developed by the motor. If under
these circumstances the prior art rate control systems were used, a
time limit of one second would result in a considerable reduction
in the amount of fluid actually injected; as indicated by line B of
FIG. 4, the actual injection might be only 15 milliliters. On the
other hand, the present invention provides injections which are
volume limited rather than time limited so that the probability of
a satisfactory angiogram is much improved due to the fact that the
desired volume of contrast media is injected even though the rate
might be less than desired. In the graph of FIG. 4, Y represents
the end of an injection which is volume limited, while point Z
represents a time limited injection having an underrate injection
due to a restrictive catheter or a catheter that could withstand
only limited pressure.
FIG. 5 and FIG. 6 show schematically the circuit components of the
control system shown in FIG. 1. In FIG. 5, the signal on line 73 is
a voltage which is derived from potentiometer 62, and thus
corresponds to the position of the injector plunger. Under
non-inject conditions, the voltage from the potentiometer 62 is fed
through line 73 to the position memory circuit 72, which includes
resistor 250 and a switch 252 which is one of the five switches
controlled by the master relay to be described. All of the switches
denoted as being operable by the master relay will be shown in
their non-inject mode, and when injection is to take place, the
master relay will switch all five of these controlled switches to
the opposite position, or their inject mode. Therefore, during
non-inject conditions the voltage from the potentiometer travels
through line 73, resistor 250, switch 252 and an inverting
amplifier 254 having a bypass resistor 255 to charge a memory
capacitor 256. This capacitor thus takes on a charge proportional
to the voltage produced by the potentiometer so that each injection
cycle will be measured from the actual position of the injector.
Note that when the injection is to take place the master relay will
move switch 252 from contact point 258 to contact point 259. The
capacitor 256 is connected to ground through a relay contact switch
262, 263 during non-injection modes, allowing the capacitor to
accumulate a charge. However, switch 262 will move from contact
point 263 to contact point 264 when the inject mode begins, thereby
completing a bypass around amplifier 254 by way of the capacitor.
Therefore, during injection, a completely closed loop exists
involving the amplifying inverter 254, the memory capacitor 256,
switch 262, and switch 252. During the inject mode, the reference
voltage from the potentiometer is no longer applied to the memory
capacitor 256 and normally the capacitor 256 would begin to
discharge. However, should the capacitor begin to discharge, say by
3 volts, this change would be automatically fed back through
switches 262 and 252 to the input of the inverter 254 where the -3
volt input would be inverted into a +3 volt output and fed back
into the capacitor 256. The initial position memory circuit 72
will, therefore, memorize (retain) the voltage from the
potentiometer corresponding to the position of the injector plunger
immediately prior to the start of an injection. This initial
position voltage is added to any incremental position changes
required by the selected volume of fluid to be injected so that the
final position of the injector will be that which is required to
inject the selected volume. This initial position voltage memorized
by the circuit 72 is fed into the comparator 76 by way of line 80
and the actual position voltage corresponding to incremental
movements of the piston, and thus, of the potentiometer 62 during
the injection is fed to the comparator 76 through lines 79 and 81.
The actual position voltage is applied to one input of a summing
amplifier 264 through line 265, the signal appearing at the summing
amplifier as a positive voltage. The output of the digital switch
74, by which the operator may select the desired volume to be
injected, is connected to the second input of the summing amplifier
by line 78, this voltage appearing at the summing amplifier as a
negative voltage. When the algebraic total of the signal voltages
applied to the summing amplifier 264 goes positive, indicating that
the position of the plunger has reached the position within the
syringe which requires injection of the selected volume of fluid,
an output is produced on line 267 which pulses the disarm circuit
84 and terminates the injection. The digital switch 74 may be of
the type shown in FIG. 3 for the injection rate selection.
Termination of the injection is accomplished by the volume limit
circuit as follows. The pulse output from the comparator circuit 76
is fed through line 267, diode 272 and line 82 into the automatic
arm-disarm circuit 84. Note that when the injection has been
instigated by depressing the start switch pushbutton 269, a clamp
is placed across the summing amplifier 264 by way of diode 268,
switch contact 269' and resistor 270. The clamp formed by these
components prevents recycling of the injector after the volume
limit has been reached. Since only a positive voltage on line 267
will cause diode 272 to conduct and operate circuit 84, any slight
fluctuation in the positive voltage on line 265 could cause line
267 to once again go negative, remove the terminate signal and
recycle the injector. Therefore, when a positive voltage appears on
line 267, the comparator is clamped by feeding the signal back
through diode 268, pushbutton switch contact 269', and resistor 270
to the input of the summing amplifier 264. This causes the input on
line 265 to become more positive, thereby insuring that the summing
amplifier output on line 267 will remain positive and keep the
arm-disarm circuit 84 energized until such a time as the start
injection button 269 has been released.
FIG. 5 also shows the schematic representation of the automatic
arm-disarm circuit 84. As shown, the output signal on line 82 from
the volume limit comparator 76 is fed through line 274 to volume
limit switch 276 which opens upon reception of the signal to shut
off the motor. Switch 276 is connected in series with the master
relay 278 which controls five relay contacts in the control
circuitry, and in series with normally open contact 269" of the
start injection button. An arm switch 280, which typically is an
SCR, is also connected in series with the master relay, and
requires a pulse input to fire it into conduction. Once the arm
switch 280 has been pulsed, it will continue to conduct until the
circuit is disarmed; i.e., until the ground connection for the arm
circuit is opened. The resetting of arm switch 280 to its off, or
non-conductive, condition is accomplished by disarm switch 282,
also in series with the master relay and the arm switch. The disarm
switch 282 typically is a two transistor switch which is normally
closed (conductive) but which opens when a signal input is present
on any one of its input lines 284, 119, or 124. The disarm switch
282 resets the arm switch 280 to its non-conductive state by
opening the series circuit and removing the ground connection 283
from the SCR.
The present control system provides a capability for either single
cycle operation, where the start switch is closed, a selected
volume of fluid is injected, and the system shuts down, or for a
multiple cycle mode, where the system automatically recycles to
inject repeatedly the selected volume. The single or multiple modes
may be selected by operating one or the other of the mode
pushbuttons 286 or 287. When a single injection is desired, the
single mode button 287 is depressed, closing its corresponding
contacts 288 and 290, while leaving contacts 292 of the multiple
mode switch 286 open. Closure of contact 290 applies a positive
bias voltage to arm switch 280 by way of line 291 so that this
latter switch is enabled. Thereafter, closure of the start button
269 will apply a further positive bias to the second input of the
arm switch 280 form the volume limit switch 276, and through master
relay 278, causing the arm switch to close. This completes the
circuit through the master relay to energize that relay and start
the injector operation. One arm switch 280 is closed, the volume
limit switch and the start switch may both be opened to stop the
injection (by de-energizing relay 278) without disarming the
circuit.
Closure of contact 288 of the single mode pushbutton 287 completes
a circuit from the volume comparator circuit 76 by way of lines 82
and 284 to the disarm switch 282, whereby upon receipt of an output
from the volume comparator circuit both the volume limit switch 276
and the disarm switch 282 are opened. This shuts down the injector
and prevents it from recycling even if switch 276 should
reclose.
If a series of injections is required, the multiple mode switch 286
is depressed, closing its contacts 292, while leaving switch 287
open. Again, this provides a positive bias to arm switch 280
through line 291, whereby switch 280 may be closed to permit
energization of master relay 278 and consequent operation of the
injector. As before, when the selected volume has been injected,
comparator 76 will produce an output on line 82 which will open the
volume limit switch 276; however, this signal will not disarm the
circuit because contacts 288 are open. When switch 276 opens,
master relay 278 opens to stop the injection, memory circuit 72
acquires a voltage equal to the voltage on potentiometer 62, and
comparator 76 again sees a voltage difference between the
potentiometer and the volume selector 74. This removes the output
from comparator 76, switch 276 closes, relay 278 is energized, and
a second injection cycle occurs. This cycle recurs under these
conditions until the start switch 269 is released, or until some
other signal disarms the circuit. Such a signal might be provided
by the forward limit switch 27, which produces a signal on line 124
when the syringe plunger reaches its forward limit, by the rate
monitor circuit 116, or by a suitable counter circuit which may be
provided to limit the number of cycles. Such a counter is
illustrated in FIG. 2 in conjunction with the electrocardiogram
synchronizing circuit, where counter 207 counts the number of
cycles initiated by the synchronizing circuit. The counter operates
in conjunction with a digital switch 206 to produce an output
signal on line 209 when a selected number of cycles have occurred.
As shown in FIG. 5, the signal on line 206 is applied directly to
the disarm circuit 282 so that when the last cycle is complete, a
simulated volume limit signal will be applied to the disarm
circuit, disabling circuit 84.
The schematic of FIG. 6 shows the circuitry for the pressure and
the position control portions of the present system. The digital
switch 90 for injection rate selection with its outputs 91, 92 and
93 is once again shown, along with its positive bias supply which
is connected to the resistor arrays of the switch by way of contact
294 of the master relay 278. This contact supplies the bias voltage
which provides the selected injection rate signal on one of the
outputs 91, 92 or 93 when injection is initiated by closing start
switch 269 to energize relay 278. Also shown is lead 96 which may
carry a variable waveform such as the electrocardiogram function
described above. Switch 94 may be operated to select either a
constant or a variable rate function from one of the four output
lines 91, 92, 93 or 96. The injection rate function selected by
switch 94 is conducted through a resistor 300 into the integrator
circuit 100 by way of line 302. The integrator circuit 100 consists
of an integrating amplifier and shunt capacitor 304 which produces
a position command signal by integrating the function received on
line 302. This position command signal, which appears on output
line 102, is a negative going signal; in the case of a d.c. input
voltage, the output signal will be a linear ramp waveform, while a
variable input will produce a more complex output. The negative
going voltage on line 102 is then summed with a positive going
voltage from potentiometer 62 by way of line 105.
When the summation of the voltages on lines 102 and 105 is
negative, it indicates that the actual position of the syringe
piston is lagging behind the command position, and the comparator
104 produces an output in the form of an error voltage on line 310.
This error voltage is conducted through an amplifying unit 312, a
switch contact 314 of the master relay 278 (FIG. 5), and line 106
to a high gain amplifier 316 and the power amplifier 108. Although
switch 314 is shown in its lower, or non-inject condition, it will
be understood that the switch will move to the upper contact to
complete the circuit through line 106 when injection occurs. The
amplified error voltage is then used to control the power amplifier
and thereby regulate the amplitude of the armature current fed to
the motor 12 by way of line 110. If, however, the sum of the
voltages on lines 102 and 105 is positive, a positive input will
exist at the input terminal of comparator 104 and no error voltage
will be produced; therefore, no armature current will be conducted
to motor 12 through the amplifying unit. By the use of high gain
amplifiers, the motor will respond to very small error signals, and
the syringe plunger will closely follow the position signal
generated by the integrator 100. This method of controlling the
motor insures that the actual position of the injector plunger is
slightly behind the desired position selected by the command signal
on line 102.
As has been explained, it occasionally happens that a large error
signal is generated in the system, because back pressure in the
injector has severely slowed the motor or even stalled it, because
of some fault in the control system, or for some other reason. If
the error is large enough, it will cause a very high armature
current to flow in the motor, thereby greatly increasing the
pressure developed by the injector. If this condition is relieved
suddenly, the motor will tend, in the present system, to speed up
well above the selected rate value in order to "catch up" to the
command position being generated, instead of merely resuming the
command rate, as would occur in rate controlled systems. If care is
not taken, this excess speed can cause an excessive flow of
contrast media, and endanger the patient; thus, the present system
provides the overrate monitoring circuit 116 shown in FIG. 6. As
illustrated, this circuit receives the potentiometer voltage
carried on line 117 where the voltage is fed to a differentiator
320 in which the incremental position signal is converted into a
rate signal. The differentiated signal is inverted and amplified in
amplifier 321, so that a negative going signal is produced at
output line 322. This rate signal is a d.c. level which represents
the actual rate at which the motor is moving the piston, and it may
be compared to the desired rate signal level selected by digital
switches 90 and 94 and conducted through line 118 to one input of a
comparator 324. An offset is provided so that the actual and
selected rates may differ by a predetermined amount. This limited
overrate is provided by means of a predetermined voltage which is
applied to the second input of comparator 324. This offset voltage
is produced by a voltage divider consisting of a resistor 325 and a
diode 326, the junction of which is connected to the second input
of the comparator through a resistor 327. When the difference
between the actual and selected injection rates equals or exceeds
the offset voltage, the comparator produces an output signal on
line 328 which is fed through a diode 329 and through line 119 to
the disarm switch 282 (FIG. 5) to disable the injector. This offset
insures that normal fluctuations in motor (and injector) speed will
not cause the comparator to disarm the injector circuits.
The output of the comparator 324 is also applied to a lamp driver
330 which serves to turn indicator lamp 332 on in the event of an
overrate condition. When the lamp driver is on, the output of
comparator 324 is fed back to its input through diode 329, line
336, a normally closed rate monitor reset button 338, line 334, and
resistor 327 to hold the comparator output positive. This will keep
the driver, and thus the lamp, turned on until the feedback path is
opened by depressing button 338.
A second safety factor is included in the rate monitoring circuit
116 and is designed to detect failure of the potentiometer 62. In
connecting the position sensing potentiometer to the injector, a
minimum voltage output for the potentiometer is established when
the syringe plunger is fully withdrawn from the syringe barrel. As
an example, a minimum setting of 250 millivolts may be selected.
If, then, the output of the potentiometer ever drops substantially
below this value, it is an indication that the potentiometer has
failed. Such an occurrence during an injection would endanger a
patient, for it would result in a very high error signal at
comparator 104. Because of the offset discussed above, the overrate
circuit would not respond immediately to such a fault in the
system, although as the motor speed increased under this condition
it would eventually terminate the injection. To provide a quicker
response to this condition, the potentiometer voltage is applied by
way of lines 117 and 339 to a comparator 340. A reference voltage
derived from a voltage divider 341, 342 is also applied to the
comparator, this reference source providing a negative voltage of
approximately 200 millivolts. The summation of the inputs from the
potentiometer and the reference voltage divider would always be
positive during non-failure conditions, since the potentiometer
would provide a positive voltage in excess of 250 millivolts.
Therefore, only upon failure of the potentiometer could the
summation of the voltages at the comparator become negative, and
when this occurs, comparator 340 immediately produces an output on
line 343 which is conducted by way of lines 336 and 119 to the
disarm switch 282.
Also illustrated in FIG. 6 are the pressure responsive circuits
136, 138 and 142. As mentioned previously, the armature current of
motor 12 flows from power amplifier 108, through line 110, motor
12, line 133, safe circuit 130 and sampling resistor 132 to ground.
This current is proportional to the torque of motor 12 and thus is
proportional to the pressure being exerted by the motor on the
injection fluid. This current can be conducted through the safe
circuit 132, which may typically be a power transistor, only when
the start inject button 269 has been closed to energize the master
relay 278 which in turn closes its corresponding contact 345. When
switch 345 is closed, line 346 is connected to a source of supply
by way of line 126 and the normally closed contact 347 of the
forward motion limit switch 27 (FIG. 1). This latter contact
remains closed until the syringe plunger reaches the end of its
path, at which time contact 347 is opened and contact 348 is
closed. When the latter contact closes, a positive voltage is
applied by way of line 124 to operate the disarm switch 282 and
terminate the injection. Closure of master relay contact 345 causes
the safe circuit to conduct, whereby the motor armature circuit is
closed, and the motor can be operated; de-energization of the
master relay, then, will serve to disable the motor by opening safe
circuit 132.
The motor current passing through resistor 130 develops a voltage
across the resistor which is proportional to the pressure developed
by the injector; this measured pressure signal is fed through
amplifier 350 where the signal is increased before it is fed into
the pressure comparator 136 by way of line 135. The second input to
the comparator 136 is provided by way of line 140 from pressure
limit selector 142. The pressure selector 142 may be similar to the
selectors described previously, having a movable arm 354 which is
connected to any one of 10 outputs from a resistive voltage
divider. In this case, each output voltage corresponds to a
specific pressure, and the selected voltage is also applied to the
input of comparator 136. The actual pressure signal on line 135 is
negative since amplifier 350 also has inverted the signal, while
the pressure limit signal on line 140 is positive; these two
signals are summed at comparator 136. When the sum of the two
signals is negative, which indicates that the motor is operating at
a pressure higher than that permitted by selector 142, an amplifier
355 in the comparator will produce an amplified error signal output
indicating the motor is operating over maximum pressure. Since the
comparator 355 also inverts the signal, a positive output will be
produced on line 356 which is proportional to the amplitude of the
overpressure condition.
The pressure limit signal on line 356 is then used to limit the
pressure buildup in the injector by limiting the amplitude of the
position error signal on line 106, which signal, as has been
described, regulates the motor power amplifier. This limiting
effect is obtained by feeding the positive pressure limit signal to
the input of amplifier 316 in common with the negative error signal
on line 106. The limit signal counteracts the position error signal
and limits it to a value which will produce no more than the
selected pressure in the injector, for the larger the pressure
error, the larger will be the pressure limit signal.
In summary, the operation of the control circuit of the present
invention under both modes of operation can be described. Prior to
injection, the master relay 278 has not been energized and
therefore switches 252, 262, 294, 314 and 345 are all in the
position shown in the drawings. The desired injection volume is
preselected in digital switch 74 while the desired maximum pressure
is set in pressure selector 142. The rate function for producing a
position command signal is selected by setting the digital switch
90 to the desired tens and units values, and by setting switch arm
94 to obtain the desired unit time. The single or multiple
injection mode is then selected by switches 286 and 287. At this
time, safe circuit 132 is an open circuit, preventing operation of
the injector. If the multiple inject mode switch 286 is selected,
the number of injections can be regulated by a suitable counter,
such as digital switch 206 by selecting the appropriate number; if
such a counter is not included in the circuit, the number of cycles
is manually controlled by start button 269. Capacitor 256 in
initial position memory circuit 72 is charged to the preinjection
potentiometer voltage. The SCR in arm switch 280 is receiving an
input through one of the two switch contacts 290 or 292 but still
requires the closing of switch 269 to pulse it into conduction.
Therefore, switch 280 is not armed prior to starting the
injection.
When start button 269 is depressed to start the injection, the SCR
in arm switch 280 is pulsed into conduction and will continue to
conduct until such a time as disarm switch 282 opens and removes
the ground terminal for arm switch 280. Master relay 278 is
energized and shifts switches 294, 252, 262, 314 and 345 to the
position opposite that which is shown in the drawings. The closing
of switch 294 connects a source of supply for the injection rate
selection circuit 90 while the closure of switches 252 and 262
connects capacitor 256 in a loop through inverting amplifier 254.
The closing of switches 252 and 262 therefore memorizes the voltage
corresponding to the initial position of the potentiometer. When
switch 314 closes, it connects the output from the position
comparator 104 to the power amplifier 108 controlling the motor 12,
while the closing of switch 345 provides a base current for the
power transistor in safe circuit 132 causing the safe circuit to
close the motor armature circuit through sampling resistor 130.
When switch 294 connects the bias voltage to rate switch 90, the
selected injection rate function is fed directly into integrator
304 to start the generation of the integrated position command
signal. The integrator 304 produces a position command signal which
is immediately and continuously compared to the potentiometer
signal on line 105 by comparator 104 and when the signal on line
105 is less than the signal on line 102 the comparator 104 produces
an output in the form of an error signal to the power amplifier
108. The power amplifier 108 in turn responds to this signal to
modulate the armature current to the motor 12, increasing its
torque to speed up the motor until the signal on line 105 balances
the signal on line 102. However, to make sure that excessive
pressure is not developed by motor 12 in an attempt to equalize the
signals on line 105 and 102, a maximum pressure for motor operation
is selected by pressure selector 142. The maximum pressure selected
is then compared with a signal proportional to the pressure at
which the motor is operating, the latter signal being obtained
across resistor 130 by way of amplifier 350. When the pressure at
which the injector is operating is slightly greater than the
maximum pressure set by switch 142, an output from comparator 136
is produced which subtracts from the position comparator output on
line 106 to prevent further increase of the motor pressure. The
circuits will continue to function in this manner until a stop
command is given.
Several conditions can exist in the injector system, any one of
which can stop the injection. The first condition involves the
termination of a single, successful injection involving no system
malfunctions or safety failures in the equipment. In this case, the
volume which is to be injected into the patient is selected by
digital switch 74 and fed into comparator 78 as a reference
voltage. The actual volume being injected is detected by
potentiometer 62 since the position of the injector plunger is
proportional to the amount of fluid displaced, and thus injected.
This value is fed into comparator 76, indicating the amount of
contrast media which has already been injected. When the amount of
contrast media that has been injected is equal to or greater than
the amount desired to be injected, the selected volume signal will
become equal to or slightly less than the measured value, and the
comparator 76 produces an output on line 82 which passes through
the closed switch contacts 288 and directly to the disarm switch
282, opening switch 282, removing the ground contact from the
arm-disarm circuit 84, and terminating the injection.
If multiple injections are desired, switch contacts 288 will be
open, inhibiting passage to the disarm switch of the comparator
output on line 82 and thus requiring a different type of volume
limit control. Since a pulse on line 82 cannot operate the disarm
switch to disable the control circuitry during multiple injections,
the pulse on line 82 will travel through line 274 to the volume
limit switch 276. This also occurs during single injection although
its effect is overridden by the disarming of the circuitry. When
the volume limit switch 276 is pulsed, it opens and de-energizes
the master relay 278 which in turn opens switches 294, 252, 262,
314 and 345. However, note that switch 280 is still armed since its
ground has not been removed. Therefore, to produce multiple
injections it is necessary only to hold down the start injection
switch 269, and recycling will automatically take place. The first
part of the recycling has already been completed since the volume
limit switch has opened and caused the master relay 278 to
de-energize. The master relay 278 has opened its switch contacts
and switch contact 294 has removed the reference voltage from the
injection rate selection switch. Switches 252 and 262 have opened
and memory capacitor 256 is charging to a voltage representing the
present position of the potentiometer, and switch 314 has shifted,
producing a feedback pulse to reset the integrator 304. Switch 345
is open, causing safe circuit 132 to open, which action, combined
with the movement of switch 314, removes all error voltages from
the operating circuit of the motor 12. With switches 252 and 262 in
the position shown in the drawing, the input to the comparator 264
on line 265 has been eliminated by the cancelling effect of the
inverter 254, which produces a voltage equal and opposite to the
potentiometer voltage. Since the value of the voltage on line 265
must be greater in magnitude that the value of the voltage on line
78 for the comparator 264 to produce an output on line 267, the
disappearance of a voltage on line 265 will eliminate the output on
line 267 which provides through lines 82 and 274 the pulse
necessary to keep the volume limit switch 276 open. Therefore,
shortly after the master relay 278 has been de-energized, the
volume limit switch 276 will close once again, to energize the
master relay which, in turn, will once again close the five
switches 294, 252, 262, 314, and 345. Therefore, complete recycling
of the control system will occur and multiple injections will
continue, under normal conditions, until either switch 269 is
released, the syringe limit switch is reached, or a counter such as
digital switch 206 in FIG. 2 reaches the number selected therein.
The digital switch 206 is shown as one means of stopping the
injection after a predetermined number of injections have occurred.
However, it will be obvious that a counter of any type may be
placed in the circuitry which is capable of pulsing the disarm
circuit after a predetermined number of injections have taken
place.
It will be noted that repetitive injection cycles may also be
accomplished when the injector is in the single inject mode, merely
by releasing the manual start button prior to injecting the
selected volume of fluid. In this case, the master relay is
de-energized by opening switch contacts 269", again without
operating the disarm switch. Therefore, when the start switch is
reclosed, the cycle will be repeated in the manner described
above.
The various safety factors provided in the circuits of the present
invention which are also capable of terminating the injection have
been described above, but may be briefly summarized as follows. The
overrate circuit 116 compares the desired injection rate, which is
referenced to the circuit by line 118, to the actual injection
rate, which is the differentiated output from the potentiometer. An
offset is constructed in the rate monitor circuit 116 so that the
actual rate at which the motor is running must be a predetermined
percentage higher than the rate selected for the motor to run
before a fault condition exists and the circuit is triggered to
pulse the disarm switch 282. The comparator 324 compares the actual
rates with the desired rates and triggers the disarm circuit when
the actual rate is significantly higher.
A circuit is also included to detect failure of the potentiometer
62. This involves setting up a minimum voltage at which the
potentiometer can operate. If the voltage produced by the
potentiometer is significantly lower than its predetermined minimum
output value, the comparator 340 will sense this faulty condition
and disarm the control circuitry through line 119, without waiting
for an overrate condition to appear.
When the injector plunger has reached the maximum limit of its
forward travel, indicating that all of the contrast media within
the injector syringe has been ejected, the microswitch 27 provides
a signal by way of line 124 to the disarm circuit.
An improved angiographic injector control system has thus been
described and illustrated. The system controls the volume of
contrast media which is injected into a patient by regulating the
position of the injector plunger in accordance with a position
command signal and a volume limit signal. The system is capable of
synchronizing the injections to correspond to the heartbeat of a
patient or to any other linear or irregular function program.
Suitable circuitry for detecting and responding to malfunctions of
equipment has also been described and illustrated although it will
be understood that modifications and additions to this circuitry
can be made without departing from the true spirit and scope
thereof. Many counters or regulating circuits for limiting the
number of injections to take place can be developed as well as
different means for producing an irregular function to operate the
injector. Therefore, it is desired that such modifications and
additions be recognized and that the injector and control system of
the present invention be limited only by the following claims.
* * * * *