Abstract:
A micro-injection pump for angiography and micro-intervention procedures comprises first and second linear traverses each have a pusher element movable by stepper motor drive for controlling discharge from a respective micro-syringe engaged by the pusher element. The first micro-syringe preferably contains a volume of a soluble contrast medium, and the second micro-syringe preferably contains a volume of an insoluble contrast medium. Fluid discharged by the micro-syringes is directed to a bifurcated micro-droplet generator having a straight primary passage and an obliquely merging tributary passage. Insoluble contrast medium from the second micro-syringe flows through a micro-sized injection needle extending partially and coaxially within the primary passage to a termination point just downstream from where the tributary passage joins the primary passage. Soluble contrast medium from the first micro-syringe passes through the tributary passage to provide a flow field surrounding the injection needle for shearing off discrete same-sized boluses from the terminal tip of the injection needle at regular frequency in coordination with a predetermined motion profile of the first and second linear traverses. Motion control of the linear traverses is possible using LABVIEW® virtual instrumentation software arranged to communicate with a 2-axis indexer control connected to first and second motor indexers for driving the stepper motors of the linear traverses. Linear potentiometers on the linear traverses, rotary encoders connected to the motors, a flowmeter, and pressure transducers indicate motion and flow parameters of the system in real-time to provide a feedback loop in the system so that a desired media delivery waveform is realized.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent application Ser. No. 60/213,319 filed Jun. 22, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to the field of controlled injection devices used to inject contrast media for angiography and therapeutic fluids for micro-intervention, and more particularly to a high-pressure micro-injection pump capable of injecting precise micro-liter fluid volumes into the vasculature and accurately controlling the velocity, acceleration, and timing of the injected fluid volumes. The present invention finds particular application in the field of high-speed pulsed digital subtraction angiography (DSA).  
           [0004]    2. Description of the Related Art  
           [0005]    Devices for controlled injection of radiopaque dye into the bloodstream through micro-catheters are known from the art of angiography for evaluation of blood flow patterns. U.S. Pat. No. 3,623,474 describes an angiographic injector system having automatic syringe drive means controlled by a programmable command signal, such that an operator may select an injection flow rate. The actual flow rate is monitored and a feedback signal is generated to maintain the desired flow rate regardless of flow attenuating factors such as catheter internal diameter, catheter length, contrast medium viscosity, and flow path configuration. The described system includes a rate trip circuit for preventing delivery of excessive flow to the patient should the control system fail. An improved angiographic control system by the same inventors is disclosed in U.S. Pat. No. 3,701,345, wherein syringe position follows a position command signal with the guidance of a syringe position feedback signal. U.S. Pat. No. 3,812,843 teaches an apparatus for injecting contrast media either sequentially at two different rates or at one rate, depending upon flow requirements. Where two different rates are selected, the duration of each can be specified.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    It is therefore an object of the present invention to provide a micro-injection pump capable of delivering precise micro-liter fluid volumes into the vasculature and accurately controlling the velocity, acceleration, and frequency of the injected fluid volumes.  
           [0007]    It is another object to provide a micro-injection pump with a graphic motion control interface that is simple to use.  
           [0008]    It is a further object of the present invention to provide a micro-injection pump with motion and flow sensing devices for providing real-time feedback to the motion control system to correct delivery parameters to follow a desired waveform.  
           [0009]    It is a further object of the present invention to provide a micro-injection pump that is compatible with a variety of syringes and micro-catheters commonly in use.  
           [0010]    A micro-injection pump formed in accordance with a preferred embodiment of the present invention generally comprises first and second linear traverses each having a syringe holder for holding respective first and second micro-syringes, and a carriage-mounted pusher element for engaging a plunger of the associated micro-syringe. The first micro-syringe preferably contains a volume of a soluble contrast medium, and the second micro-syringe preferably contains a volume of an insoluble contrast medium. Each linear traverse includes a stepper motor for allowing very accurate control of the position, velocity, and acceleration of the traverse carriage.  
           [0011]    Fluid discharged by the micro-syringes is directed to a bifurcated micro-droplet generator having a straight primary passage and an obliquely merging tributary passage. More specifically, insoluble contrast medium from the second micro-syringe flows through a micro-sized injection needle extending partially and coaxially within the primary passage to a termination point just downstream from where the tributary passage joins the primary passage. Soluble contrast medium from the first micro-syringe is routed through the tributary passage to provide a flow field surrounding the injection needle, thereby providing shear force to separate discrete same-sized boluses from the terminal tip of the injection needle at regular time intervals in coordination with a predetermined motion profile of the first and second linear traverses.  
           [0012]    Motion control of the linear traverses is possible using LABVIEW® virtual instrumentation software arranged to communicate with a 2-axis indexer control connected to first and second motor indexers for driving the stepper motors. Linear potentiometers mounted on the traverses, rotary encoders connected to the stepper motors, a flowmeter, and pressure transducers indicate motion and flow parameters of the system in real-time to provide a feedback loop in the system so that a desired media delivery waveform is realized. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the preferred embodiments taken with the accompanying drawing figures, in which:  
         [0014]    [0014]FIG. 1 is a perspective view of a micro-injection pump formed in accordance with a preferred embodiment of the present invention;  
         [0015]    [0015]FIG. 2 is a top plan view of the micro-injection pump shown in FIG. 1, with syringe plungers in a ready position;  
         [0016]    [0016]FIG. 3 is a partial top plan view similar to that of FIG. 2, with syringe plungers in a discharged position;  
         [0017]    [0017]FIG. 4 is a partially sectioned detail view taken generally along the line  4 - 4  in FIG. 1 showing a micro-droplet generator of the present invention; _  
         [0018]    [0018]FIG. 5 is a schematic view illustrating initial formation of a liquid bolus of insoluble contrast medium by the micro-droplet generator shown in FIG. 4;  
         [0019]    [0019]FIG. 6 is a schematic view similar to that of FIG. 5 illustrating separation and conveyance of a liquid bolus of insoluble contrast medium;  
         [0020]    [0020]FIG. 7 is a schematic system diagram showing currently preferred hardware connections of the present invention;  
         [0021]    [0021]FIG. 8 is a screen capture of a LABVIEW® front panel showing a Contrast Injector virtual instrument (VI) for operating the micro-injection pump of the present invention;  
         [0022]    [0022]FIG. 9 shows a first of three main LABVIEW® graphical object-based software sequence frames associated with the Contrast Injector VI, wherein the first frame comprises an initializing and homing configuration routine for the Contrast Injector VI;  
         [0023]    [0023]FIG. 10A shows a second of three main LABVIEW® software sequence frames associated with the Contrast Injector VI, wherein the second frame comprises a main sequence structure associated with the Contrast Injector VI depicted with blank schematic representations of independent sequences ( 2 ) through ( 6 ) illustrated fully in subsequent figures;  
         [0024]    [0024]FIG. 10B fully shows LABVIEW® software sequences ( 2 ) and ( 3 ) represented schematically in FIG. 10A;  
         [0025]    [0025]FIG. 10C fully shows LABVIEW® software sequence ( 4 ) represented schematically in FIG. 10A;  
         [0026]    [0026]FIG. 10D fully shows LABVIEW® software sequences ( 5 ) and ( 6 ) represented schematically in FIG. 10A;  
         [0027]    [0027]FIG. 11 shows a third of three main LABVIEW® software sequence frames associated with the Contrast Injector VI, wherein the third frame comprises a shut down routine for the Contrast Injector VI;  
         [0028]    [0028]FIG. 12 is a screen capture of a LABVIEW® front panel showing a Profile Tracker virtual instrument (VI) for operating the micro-injection pump of the present invention according to a predefined injection flow profile chosen by the user;  
         [0029]    [0029]FIG. 13 shows a first of three main LABVIEW® software sequence frames associated with the Profile Tracker VI, wherein the first frame comprises an initializing and homing configuration routine for the Profile Tracker VI;  
         [0030]    [0030]FIG. 14A shows a second of three main LABVIEW® software sequence frames associated with the Profile Tracker VI, including a Trace Option alternative case control structure shown in its true condition, a second of three sequence sub-frames nested in the Trace Option alternative case control structure, and an inner alternative case control structure nested in the second sequence sub-frame shown in its true condition;  
         [0031]    [0031]FIG. 14B shows the Trace Option alternative case control structure shown in FIG. 14A, however in its false condition;  
         [0032]    [0032]FIG. 14C shows a first of three sequence sub-frames nested in the Trace Option alternative case control structure shown in FIG. 14A;  
         [0033]    [0033]FIG. 14D shows a third of three sequence sub-frames nested in the Trace Option alternative case control structure shown in FIG. 14A;  
         [0034]    [0034]FIG. 14E shows the inner alternative case control structure nested in the second sub-frame sequence shown in FIG. 14A, however in its false condition; and  
         [0035]    [0035]FIG. 15 shows a third of three main LABVIEW® software sequence frames associated with the Profile Tracker VI, wherein the third frame comprises a shut down routine for the Profile Tracker VI. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]    Referring initially to FIGS.  1 - 3 , a micro-injection pump  10  of the present invention is shown as comprising a first linear traverse  12  operable along a first axis  12 A, and a second linear traverse  14  operable along a second axis  14 A. First linear traverse  12  includes a track  12 B and a carriage  12 C mounted on track  12 B for back and forth driven motion along first axis  12 A. A stepper motor  12 D is located at a front end of first linear traverse  12  and connected to carriage  12 C via a drive coupler  12 E and drive shaft (not shown). Carriage  12 C supports an upstanding pusher element  12 F which is axially movable with the carriage relative to a stationary syringe holder  12 G provided near the front of first linear traverse  12 . Travel limit switches  12 H are also provided. Likewise, second linear traverse  14  includes a track  14 B, carriage  14 C, stepper motor  14 D, drive coupler  14 E, pusher element  14 F, syringe holder  14 G, and limit switches  14 H in similar arrangement.  
         [0037]    As can be seen, syringe holder  12 G on first linear traverse  12  holds a first micro-syringe  16  preferably filled with an amount of a soluble contrast medium  18 . First micro-syringe  16  includes an axially movable plunger  16 A having a distal end  16 B engaged by pusher element  12 F. Syringe holder  14 G on second linear traverse  14  holds a second micro-syringe  20  which, for evaluation and intervention applications, may be filled with an amount of an insoluble contrast medium  22  such as ETHIODOL® available from Savage Laboratories of Melville, N.Y. Second micro-syringe  20  includes an axially movable plunger  20 A having a distal end  20 B engaged by pusher element  14 F. First and second micro-syringes  16  and  20  are in flow communication with a micro-droplet generator  28  by way of catheter tubes  24  and  26  respectively coupled to the outlet ports of micro-syringes  16  and  20 . Micro-droplet generator  28  feeds a micro-catheter  29  in flow communication with the vasculature of a patient.  
         [0038]    Micro-droplet generator  28  is shown in detail in FIGS.  4 - 6 . Micro-droplet generator  28  includes a bifurcated junction member  30  upstream from a reducer  32  threadably joined thereto. Junction member  30  includes a tributary port  30 A fed by first micro-syringe  16  via catheter tube  24  and closable valve  25 , an inlet port  30 B fed by second micro-syringe  20  via catheter tube  26 , and an outlet port  30 C opposite inlet port  30 B. Inlet port  30 B is connected for flow communication with outlet port  30 C by a straight primary passageway  30 D, and tributary port  30 A is connected for flow communication with primary passageway  30 D by a tributary passageway  30 E forming an acute angle with primary passageway  30 D. A narrow injection needle  34  extends partially within primary passageway  30 D from inlet port  30 B to a region just downstream from the junction of tributary passageway  30 E with primary passageway  30 D. Clearance is provided between the outer wall of injection needle  34  and the inner wall defining primary passageway  30 D to allow fluid to occupy the intervening space. For example, in the preferred embodiment primary passageway  30 D has an inner diameter of 2.00 mm. An adjustable sealing coupler  36  normally provides a fluid tight seal about injection needle  34 , and can be loosened to bleed the system such that fluid that is free of air bubbles occupies the intervening space. Based on the above arrangement of micro- 161  droplet generator  28 , it is apparent from FIGS. 5 and 6 that flow of soluble contrast medium  18  within primary passageway  30 D about injection needle  34  exerts a shear force upon boluses  22 A of insoluble contrast medium  22  forming at the tip of the injection needle, thereby separating and conveying each bolus for travel through a reducer  32  connectable to a micro-catheter  29  by a leur lock  31 . By controlling the motion of linear traverses  12  and  14 , a series of same-sized boluses  22 A having identifiable velocity and acceleration characteristics can be released at a desired regular frequency.  
         [0039]    In accordance with the present invention, micro-liter precision for injection volumes and accurate control of dosage velocity and acceleration are achieved by computerized motion control of first and second linear traverses  12  and  14  actuating micro-syringes  16  and  20 , respectively. Linear traverses  12  and  14  can be controlled according to any predetermined profile to achieve necessary delivery parameters. The schematic system diagram of FIG. 7 illustrates the currently preferred hardware arrangement for micro-injection pump  10 . Stepper motor  12 D is connected to a first motor indexer drive  46  by lead  48 , and stepper motor  14 D is connected to a second motor indexer drive  50  by lead  52 . First and second indexer drives  46  and  50  are, for example, Parker Compumotor Zeta 4 drives having respective motor drive ports  54  and  56  to which leads  48  and  52  are connected. A  2 -axis indexer control  58  is linked for serial communications with a central processing unit  60  via an RS232 cable  62 . In keeping with the present example embodiment, indexer control  58  is a Parker Compumotor 6200 controller with dual axis capability, and RS232 cable  62  is linked to an auxiliary port  64  of indexer control  58 . The indexer control board includes a Drive  1  port  66  connected by cable  68  to an indexer port  70  on first motor indexer drive  46 , and a Drive  2  port  72  connected by cable  74  to an indexer port  76  on second motor indexer drive  50 . Indexer control  58  further includes a limit switch port  78  to which limit switches  12 H and  14 H can be connected by leads  80  and  82 .  
         [0040]    Hardware is preferably installed for providing feedback information to computer  60  describing system variables. A pair of linear potentiometers  84  and  86  are matched with first and second linear traverses  12  and  14 , respectively, for tracking position, velocity, and acceleration information with regard to each traverse in real time. A suitable linear potentiometer for the example system described herein is a Type HLP190/SA1/150/6K available from Penny &amp; Giles Controls Limited. In addition to linear potentiometer feedback, two rotary encoders  85  and  87  are also employed for position, velocity, and acceleration feedback with respect to first and second linear traverses  12  and  14 . Encoders  85  and  87  are attached to corresponding drive motors  12 D and  14 D via a flexible shaft connection. A suitable encoder for the example system described herein is a model C150/152/153 distributed by Dynamic Research Corp, having a resolution of 8000 counts per revolution. A pair of pressure transducers  88  and  90 , available for example from Validyne of Northridge, Calif., monitor fluid pressure as fluid exits first and second micro-syringes  16  and  20 , respectively. In addition, a flowmeter  92  is preferably installed to measure flow rates for each micro-syringe. The model T206 flowmeter available from Transonic Systems Inc. of Ithaca, N.Y. can perform this function.  
         [0041]    User interface and control of the micro-injection pump of the present invention is currently configured using LABVIEW® virtual instrumentation software available from National Instruments Corporation. FIG. 8 is a screen capture of a Contrast VI front panel  100  showing a virtual control screen for operating micro-injection pump  10 . Contrast Injection front panel  100  includes a home button  102  for running a home positioning routine, a start button  104 , a stop button  106 , and an escape button  108 . A quit button  110  is also provided for exiting from front panel  100 . A two-axis graphical display  112  reports theoretical and measured flow rates in real time for first and second micro-syringes  16  and  20 , with corresponding digital readouts  114  and  116  preferably being provided as well. Stepper motors  12 D and  14 D can be assigned “soft” travel limits in the clockwise and counter-clockwise directions using digital controls  118 A,  118 B and  118 C,  118 D, or using their corresponding pointers  119 A,  119 B and  119 C,  119 D on bar graphs  121  and  123 , respectively. Bar graphs  121  and  123  provide a visual indication of the individual syringe volumes injected by first micro-syringe  16  and second micro-syringe  20 , measured in cubic centimeters, with the scale of each bar graph being dependent upon the chosen syringe size. Corresponding digital displays  122  and  124  also report the injected volumes for the respective syringes in digital format. In addition, two pairs of LED indicators  120 A,  120 B and  120 C,  120 D illuminate when the traverse has crossed the associated soft limit setting.  
         [0042]    Controls for first linear traverse  12  include a syringe size selector  126  and a velocity knob control  128 . A digital flow rate control terminal  130  shows the flow rate in cc/sec based on the selected syringe size and velocity, and can be used to directly choose a desired flow rate and thus set a corresponding velocity. Likewise, controls associated with second linear traverse  14  include a syringe size selector  132 , a velocity knob control  134 , and a digital flow rate control terminal  136 . A predetermined time delay for starting motion of second linear traverse  14 , if desired, is selectable at delay control portion  138  of front panel  100 . A hardware trigger button  139  (Digital Trigger Enable) is also provided to enable synchronized injections with ECG and angiographic equipment. Below hardware trigger button  139  is a profile tracker button  140  (Profile Tracker Enable) which is used to call the Profile Tracker VI software. Upon depression of this button, execution of the Contrast Injector VI software is suspended while the Profile Tracker VI software is loaded and run. A Profile Tracker front panel, described below, stays in the foreground until the user exits from the Profile Tracker front panel, at which time the Contrast Injector front panel  100  will come to the foreground and re-engage. Finally, a linear traverse direction toggle  141  and a soft limit enable toggle  142  allow further control of microinjection pump  10 .  
         [0043]    FIGS.  9 ,  10 A- 10 D, and  11  are directed to three main sequence frames of the Contrast Injector VI. FIG. 9 shows a first frame  144  containing a motor controller initializing routine and a homing configuration routine. Home configuration blocks  146  and  148  determine the velocity, acceleration, and deceleration of the homing routines for first linear traverse  12  and second linear traverse  14 , respectively. Additionally, there is a parameter precision “sub-VI”  145  which is preferably used to specify a three decimal place level of precision on all numbers sent to the motor controller  58 , thereby improving communications performance. Motion scaling sub-VIs  147  and  149  are issued to scale position, velocity, and acceleration parameters for the specified motors.  
         [0044]    FIGS.  10 A- 10 D show a second frame  150  containing a main sequence structure of the Contrast Injector VI software. A main “while loop”  152  contains six independent sequence frames ( 1 )-( 6 ), an alternative case structure ( 7 ), and sub-VIs  151  for stopping the program and halting motor motion. Sequence ( 1 ) takes in velocity information from the velocity knob controls  128  and  134 , scales the data and sends the information to the motor controller. Sequence ( 1 ) also provides a direction sub-VI  153  for setting the travel direction of both linear traverses. Sequence ( 2 ), best seen in FIG. 10B, acquires, scales, and plots position and velocity (volume and flow rate) ascertained by linear potentiometers  84  and  86  affixed to the linear traverses  12  and  14 . Sequence ( 3 ), also shown in Fig. 10B, is used to scale slider bars  121  and  123 , which indicate volumes injected for each syringe pump, and also to scale the appropriate soft limit controls. Sequence ( 4 ) shown in Fig. 10C enables and disables both the delay timer and the hardware trigger. Within this sequence are two nested alternative case structures  154  and  156 . The outer most case structure  154  enables or disables the hardware trigger by checking the hardware trigger button  139  on the front panel. If the hardware trigger is engaged, the system can be started by clicking on the start button  108  or by reading a transistor transistor logic (TTL) digital input high, acquired from controller  58 . This is especially useful when injections need to be synchronized with an angiographic run or with the cardiac cycle. The inner case structure  156  enables or disables the second linear traverse delay timer. Referring now to FIG. 10D, sequence ( 5 ) is used to scale and set “soft” limits. Sequence ( 6 ) checks the software limits&#39;status and sends pass/fail information to LED indicators  120 A- 120 D on Contrast Injector front panel  100 . The final structure in while loop  152  (FIG. 10A) is an alternative case structure ( 7 ) used to call a secondary program, namely the Profile Tracker VI mentioned above.  
         [0045]    [0045]FIG. 11 shows a third frame  160  of the Contrast Injector VI for shutting down the apparatus. Inputs to an enable motor drive sub-VI  162  are changed to disable the motor drives, and a close device sub-VI  164  is executed for shutting down the virtual instrumentation.  
         [0046]    [0046]FIG. 12 shows a front panel  200  of the Profile Tracker VI software mentioned above. The Profile Tracker program is utilized during injection of embolic agents, and has the capability of injecting a single syringe of fluid at a variable rate. The user predetermines the rates of injection by selecting a predefined injection flow profile from a Profile Menu presented by a drop down text box  201 . The user can also run new and unique profiles with the system by selecting “user defined profile” in the aforementioned drop down menu. The user needs only to create a profile data set in “.txt” format and in units of cc/sec, and load the data set into the program. Similar to the Contrast Injector VI front panel  100 , the Profile Tracker VI front panel  200  has motion control buttons including a home button  202 , a start button  204 , a stop button  206 , and a quit button  210 . A syringe size/loading control panel  212  includes a drop down menu  214  from which a user can select one of a plurality of standard and user-programmable syringe sizes, and a load toggle  216  for moving carriage  14 C and pusher element  14 F into proper position for loading and unloading syringes.  
         [0047]    The Profile Tracker VI includes a proportional plus integral plus derivative (P.I.D.) feedback control loop to ensure proper tracking of specified injection flow profiles. The P.I.D. VI controls are placed in a “PID Parameter Settings &amp; Gain Scheduling” panel  220 . These controls allow the user to tune the P.I.D. controller. The graph  228  plots the predetermined profile data in solid white line and the Profile Trackers VI&#39;s real time actual flow profile data in colored circles. There are four basic steps to using the Profile Tracker VI: first, load a desired syringe; second, select the corresponding syringe size; third, choose a preferred injection flow profile from profile menu  201 ; and fourth, select “Start Profile Tracker” button  203  when ready.  
         [0048]    Reference is now made to FIG. 13, which illustrates a first frame  230  of three main sequence frames of the Profile Tracker VI. First frame  230  includes a motor controller initializing routine and homing configuration routine. Home configuration sub-VIs  232  and  234  determine the velocity, acceleration and deceleration of the homing routines for first linear traverse  12  and second linear traverse  14 , respectively.  
         [0049]    FIGS.  14 A- 14 E show a second frame  240  containing a main sequence structure of the Profile Tracker VI. Within second sequence frame  240  is a main while loop  242  used to run the program until the quit button  210  on front panel  200  has been depressed (see lower right corner of FIG. 14A). The while loop  242  contains a file selector sub-VI  244  which is used to retrieve a predetermined injection profile or allows the user to search for a specific file. Data and trace graph attribute nodes  246  and  248  respectively ensure that the data graph and the real time trace graph have the same scaling. There is also a linear potentiometer sub-VI  250  and a velocity scaler sub-VI  252  in the main while loop  242 . A motor engage control sub-VI  254  has an alternate case structure  256  adjacent to it in order to enable resetting or unlatching of the start button  204  after it has been depressed.  
         [0050]    Attention is now directed to alternate case structure  260 , sequence sub-frame  262 , alternate case structure  264 , and while loop  266  located in nested arrangement at the right side of second frame  240 . The outer most alternate case structure  260  is a Trace Option case structure used to determine if the profile trace program should be initiated, as determined by the Start Profile Tracker button  203  located on the front panel  200 . If button  203  is “ON”, Trace Option case structure  260  executes according to the “true” condition as depicted in FIG. 14A. If button  203  is “OFF”, Trace Option case structure  260  executes according to the “false” condition as depicted in FIG. 14B. The execution of inner alternate case structure  264  is likewise determined by Start Profile Tracker button  203 , with a “false” condition of case structure  264  being shown in FIG. 14E. The nested sequence sub-frame  262 , which is the second in a series of three sub-frames  261 - 263 , serves to dump the data from a selected injection profile file to the P.I.D. control loop and to designate a time base for the data to be read and moves to be executed. FIG. 14C shows first sequence sub-frame  261  which functions to clear the feedback history data of the trace graph  228 . FIG. 14D shows third sequence sub-frame  263  programmed to ask the user if he or she would like to run another profile by bringing up a pop up window with yes and no buttons. This function is disengaged when the user clicks quit button  210 . Third sub-frame  263  also unlatches both Start Profile Tracker button  203  and stop button  206 .  
         [0051]    A third frame  270  of the three main sequence frames of the Profile Tracker VI is shown in FIG. 15, and is similar to the third frame  160  of Contrast Injector VI  160 . Third frame  270  shuts down the apparatus by changing inputs to an enable motor drive sub-VI  272  to disable the motor drives and by executing a close device sub-VI  274  for closing down the virtual instrumentation.  
         [0052]    As will be appreciated from the above description, the micro-injection pump of the present invention maintains accurate flow rates under high pressure loading. In preliminary testing, a micro-injection pump as described above demonstrated the capability to deliver 1.0±0.1 microliters at high pressure up to  20  atmospheres. Micro-injection pump  10  is compatible with a an assortment of syringes and micro-catheters commonly used in micro-intervention procedures. While not described above, it is of course advisable to provide safety features, such as automatic shut-off and alarm features, to prevent serious complications in the event of a system malfunction.  
         [0053]    Benefits of the present invention include improved quantitative measurements of blood flow patterns, more precise transit time estimates, and greatly improved visualization of complex hemodynamics associated with arteriovenous malformations.