Patent Document

FIELD OF THE INVENTION  
       [0001]     The present invention relates to injectors for injecting fluid into patients.  
       BACKGROUND OF THE INVENTION  
       [0002]     In a variety of medical procedures a fluid is injected into a patient for the purpose of diagnosis or treatment. For example, a contrast media fluid is injected into a patient to improve computed tomography (CT), angiographic, ultrasound, or magnetic resonance imaging (MRI) procedures. During such procedures, there are typically time periods where a contrast injector is connected to a patient, but procedural preparations delay the injection of the contrast media fluid. Since no fluid is flowing through the injection site during the delay, if the delay is long enough, blood at the injection site may begin to coagulate or clot. If a significant blood clot forms within the fluid path, the injection of contrast media fluid may be hindered.  
         [0003]     One approach to keep the vein open before the main injection begins, is to slowly drip the contrast media. However, this wastes contrast media, which, as used in MRI procedures, is very expensive. To prevent this premature and undesirable restriction or closure of the fluid path, without waste of contrast media, some injector systems include a second syringe, which is typically filed with a saline solution. During the time period when no contrast fluid is being injected, these injectors will intermittently dispense small bursts of saline into the fluid path.  
         [0004]     There are, however, a number of problems associated with the use of a second syringe filled with saline. First, the addition of a second syringe can significantly increase the cost and complexity of the injector. Second, technologists are forced to set up two syringes with two different fluids, connecting Y-tubing instead of a single line tube, and must go through a more involved air purging process to rid both syringes and the Y-tubing of air. Y-tubing also is typically more expensive than a single line tube, thus also increasing the cost to the consumer. Finally, an imaging suite has to order and stock extra syringes for saline use and must dispose of additional medical waste after the saline syringes are used.  
         [0005]     Accordingly, there is a need to simply and cost effectively keep a vein open during procedures without the use of a second syringe and a saline drip solution.  
       OBJECTS OF THE INVENTION  
       [0006]     It is an object of the invention to keep the fluid path open during intravenous contrast injector procedures without injecting saline from a separate syringe. It is further an object of the invention to keep a fluid path open during imaging procedures in a simple and cost effective manner, and with a relatively simple and cost effective device.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention provides a method for keeping a patient&#39;s vein open during an intravenous contrast injector procedure without the use or injection of a saline solution from a separate syringe. The present invention also provides and an injector adapted to incorporate this method. The injector includes a controller having a programable software module to allow an operator to configure the injector to push some contrast media fluid through an injection site and then retract a plunger drive ram. A syringe is adapted to allow a patient&#39;s blood pressure to push the syringe plunger back towards its starting position, thus enabling a patient&#39;s blood to pass back through the injection site.  
         [0008]     Alternatively, the syringe is adapted with an elastic plunger which as it enlarges and contracts facilitates fluid communication through the injection site. Additionally, the plunger drive ram can be adapted to pull as well as push the plunger thereby causing fluid to gradually flow back and forth through the injection site. The cycle of advancing the plunger drive ram with a drive motor and allowing the syringe plunger to retract is repeatable, as needed, to discourage blood coagulation or clotting. Of significance, the present invention does not require the use of saline or a separate syringe containing a flush medium to keep the fluid path open.  
         [0009]     The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the brief description thereof. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0011]      FIG. 1  is a partial environmental view of an injector for injecting fluids from a syringe into a patient in accordance with one embodiment of the present invention.  
         [0012]      FIG. 2A  is a diagrammatic partial cross-sectional view of the injector of  FIG. 1  showing a syringe injecting fluid into a patient&#39;s blood stream.  
         [0013]      FIG. 2B  is a diagrammatic partial cross-sectional view similar to  FIG. 2A  showing a patient&#39;s blood stream pressure pushing a syringe plunger back towards a drive ram.  
         [0014]      FIG. 2C  is a diagrammatic partial cross-sectional view similar to  FIG. 2A and 2B  showing the injector after the patient&#39;s blood pressure has returned the syringe plunger back to its general starting position at or near the position of the retracted drive ram.  
         [0015]      FIG. 3A  is a diagrammatic partial cross-sectional view of an alternative embodiment of the injector of  FIG. 1 , showing a syringe injecting fluid into a patient&#39;s bloodstream.  
         [0016]      FIG. 3B  is a diagrammatic partial cross-sectional view similar to  FIG. 3A  showing the elastic plunger in a contraptive state when the plunger drive ram is withdrawn.  
         [0017]      FIG. 3C  is an enlarged view of a portion of  FIG. 3B  showing the plunger in its retracted state, and showing in phantom the position of the plunger in its extended state.  
         [0018]      FIG. 4A  is a cross-sectional view of an alternative embodiment of the injector shown in  FIG. 3A  showing the plunger in its extended position.  
         [0019]      FIG. 4B  is a cross-sectional view similar to  FIG. 4A  showing the elastic plunger in its retracted position.  
         [0020]      FIG. 5A  is a cross-sectional view of an alternative embodiment of the injector shown in  FIG. 4A  showing the syringe plunger in its extended position.  
         [0021]      FIG. 5B  is a cross-sectional view similar to  FIG. 5A  showing the plunger in its retracted position.  
         [0022]      FIG. 6  is a diagrammatic partial cross-sectional view of an alternative embodiment of the injector shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Referring to the Figures, and to  FIG. 1  in particular, a Magnetic Resonance Imaging (MRI) system  10  is shown in accordance with the principles of the present invention although the invention is applicable to all other imaging and injector using environments. The MRI system  10  includes an MRI injector  12  which is attached via a connector  14  to a tube  16  which is in turn attached to a catheter.  18  by another connector  20 . The catheter  18  enters a patient  22  at an injection site  24 . While  FIG. 1  illustrates the injection site  24  on an arm  26  of a patient  22 , the injection site  24  could also be located on other parts of a patient&#39;s anatomy. For example, in some MRI procedures, it may be desirable to locate the injection site  24  in a patient&#39;s groin area (not shown). Additionally, while  FIG. 1  shows a portion of a human patient&#39;s anatomy, the MRI system  10  of the present invention could also be used on animal subjects. Finally, nothing prevents the present invention from being used for procedures other than MRIs. The present invention may be utilized whenever a fluid path into a blood vessel is desired to be kept open without the use of a second injection syringe.  
         [0024]     The MRI injector  12  comprises a controller  28  which is operatively connected to a drive motor  30  which is used to mechanically advance or retract a plunger drive ram  32 . The controller  28  and the drive motor  30  are typically electrically powered by AC current, but could also be battery powered or otherwise powered by DC current.  
         [0025]     The controller  28  controls the cycles of advancing and retracting the plunger drive ram  32  via programmable software. Accordingly, an MRI technician may set the rate at which the plunger drive ram  32  is advanced, the amount of time the plunger drive ram  32  remains at its extended position, the rate at which it retracts, and the amount of time the plunger drive ram  32  remains at its retracted position before beginning the cycle again. The settings that the technician chooses may vary depending on the properties of the fluid  34  that is being injected, the physical characteristics of the patient  22 , the size of the MRI injector  12 , the size and length of the tubing  16 , the estimated delay time before beginning the main injection, or any other like factors. Typically, the cycle of advancement and retraction will be repeated as needed until the MRI technologist starts the main contrast injection or terminates the cycle.  
         [0026]     While the controller  28  may be preprogrammed to control the plunger drive ram  32  vis-a-vis the drive motor  30 , the MRI technician may at anytime override the controller  28  or manually operate the MRI injector  12 . Thus, while the plunger drive ram  32  will normally be advanced programmably as part of an injection procedure, the MRI technician may manually advance and retract the drive ram  32 .  
         [0027]     In addition to preprogramming or manually controlling the cycles of the plunger drive ram  32 , the MRI system  10  may also incorporate pressure, fluid flow, or other like sensors and feedback control circuitry whereby the cycling of the plunger drive ram  32  is real time optimized based on the existing and possibly changing biological or mechanical conditions.  
         [0028]     When the plunger drive ram  32  is advanced, it makes contact with and pushes the syringe plunger/pusher  36  forward within an interior fluid compartment  40  of a syringe  42 . The fluid compartment  40  contains the fluid  34  that will be injected into the patient  22 . As the syringe plunger/pushrod  36  is pushed forward, the head  44  of the syringe plunger/pushrod  36  pushes the fluid  34  forward and ultimately causes some fluid  34  to pass through the injection site  24  and into the patient  22 . In MRI procedures, this fluid  34  is a contrast agent or a contrast medical fluid, however, any suitable medical fluid could be used for other procedures.  
         [0029]      FIGS. 2A, 2B  and  2 C further illustrate the process of the present invention which is performed by the injector in a keep vein open operative mode, or manually by the technician, before, after, or during a pause in a programmed injection procedure. This process involves sequential injection and withdrawal of fluid to/from the patient. Specifically,  FIG. 2A  shows the plunger drive ram  32  in contact with the syringe plunger/pushrod  36  and pushing the syringe plunger/pushrod  36  forward, whereby some amount of contrast agent  34  passes through the injection site  24  and into a patient&#39;s bloodstream  46 . In the preferred embodiment, there is typically about 0.1 to 1 milliliter (mL) of contrast fluid  28  that is pushed through the injection site  24  by the syringe plunger/push rod  36 . The pressure that is needed to inject fluid into the vein, while dependent on several factors, such as flow rate, tube length, and contrast agent  34  viscosity, will generally be less than 20 psi for typical applications.  FIG.2B  shows the plunger drive ram  32  being retracted from contacting the syringe plunger/pushrod  36 . As shown, once the plunger drive ram  38  is retracted, due to the patient&#39;s blood pressure, blood  48  from a patient&#39;s bloodstream  50  flows back through the injection site  24  and forces the fluid  34  to push the syringe plunger/pushrod  36  back towards the plunger drive ram  38 . The contrast injector syringe  42  is adapted in a preferred embodiment to allow a patient  22  with a blood pressure of between about 50 to about 200 mm—Hg to move the syringe plunger/pushrod  36  back towards the plunger drive ram  32 . Given a patient&#39;s blood pressure of about 50 to about 200 mm—Hg, the pressure pushing the contrast agent back through the catheter  18  is about 1 to about 4 psi. In this blood-pressure-return step, about 0.1 to 1 milliliter (mL) of a patient&#39;s blood  48 , blood  48  mixed with other fluid  34 , or even just the fluid  34 , flows back through the injection site  24  due to the patient&#39;s own blood pressure.  
         [0030]      FIG. 2C  shows the end of the cycle when blood  48 , from a patient&#39;s bloodstream  52 , has flowed back towards the MRI injector  12  and caused the syringe plunger/pushrod  36  to move back to or near to its starting position which may be against or near the plunger drive ram  32 . The injector then repeats the injection of a small amount of contrast and retraction of the ram as shown in  FIGS. 2A and 2B . By repeating such cycles, flow is maintained in the catheter without substantial consumption of contrast media. It should be noted that the patient&#39;s blood pressure may not fully return the syringe plunger/pushrod to the initial position shown in  FIG. 2A  after a brief injection as shown in  FIGS. 2B and 2C . In such a case, the subsequent brief injection of the desired amount of fluid may require advancement of the plunger by the injector during the second injection to a position that is more advanced than the position reached in the first injection. A pressure sensor on the injector may be advantageously used to determine whether and at what position the syringe plunger/pushrod  36  has engaged ram  32  as a consequence of the blood-pressure-return step. If an incomplete plunger return is achieved in the blood-pressure-return step, small amounts of contrast media may be consumed in the keep-vein-open procedure of the present invention, due to incomplete return of the plunger under influence of the patient&#39;s blood pressure, and a subsequent additional advance to inject the desired volume into the patient&#39;s vein. However, the amount of contrast media consumed in this manner will be substantially less than is the case in prior methods in which no blood-pressure-return step is implemented. The important point is not where the syringe plunger/pushrod  36  is finally pushed back to but rather simply that blood  48  or a blood  48  and other fluid  34  mixture or even pure fluid  34  flows back and forth through the area(s) likely to experience clotting problems, preventing clotting with reduced loss of contrast media.  
         [0031]      FIGS. 3A-3C  show an alternative embodiment of the injector  54 .  FIG. 3A  shows the injector  54  with the plunger/pushrod  56  in its extended position. This occurs when the plunger drive ram  32  advances or pushes against the plunger  56  and moves it forward in the barrel  58  of the syringe  54 . As the plunger  56  advances, the volume of the fluid chamber  60  decreases.  
         [0032]     The plunger  56  contains a plunger head  62  which pushes the fluid  34  into a tube  16  during the injection process. As shown, the head  62  is comprised of an elastic material, such as rubber, which allows it to elastically expand or advance and elastically contract or retract. The head  62  expands or stretches when the stretcher  64  pushes against it. The stretcher  64  can be a pin, a rod, a bar, a shaft, or the like. As shown in  FIG. 3B , the end  64   a  of the stretcher  64  is proximally located to the drive ram  32  and is positioned so as to make contact with the drive ram before the drive ram contacts the flange  66  of the plunger  56 . As the drive ram  32  moves forward, the pressure in the syringe  54  and the friction of the plunger  56  within the barrel  58  allows the distal end  64   b  of stretcher  64  to depress or enlarge or stretch the head  62  even before the plunger moves forward. Similarly, when the drive ram  32  is retracted, as shown in  FIG. 3B , the head  62  elastically contracts or returns to its initial or relaxed starting position. Thus, as shown in  FIG. 3C , the expansion and contraction of the head  62  adjusts the volume of the fluid chamber  60 .  
         [0033]     In operation, the drive ram  32  will advance the plunger  56  forcing fluid  34  through an injection site. During this push cycle, the stretcher  64  enlarges or expands the head  62 . When the drive ram  32  is retracted, the head stretcher  64  also withdraws, allowing the head  62  to elastically relax and return to its original or contracted position. The return of the head  62  to its contracted position increases the volume of the fluid chamber  60  which draws fluid and/or blood back through the injection site. The drive ram  32  can continue to advance against the head structure  62  and withdraw, allowing the cycle of the expansion and contraction of the head  62  to continue as needed to facilitate fluid communication back and forth through the injection site. The volume of fluid displacement can be controlled and predetermined by the length of the stretcher  64 .  
         [0034]      FIGS. 4A and 4B  illustrate an alternative embodiment where the plunger  68  pushes against the head  62  to create the deformation or expansion of the head  62 . As shown, a backer plate  70  is sandwiched between the head  62  and the plunger  68  and helps to maintain the integrity of the seals  72  that prevent the fluid  34  from leaking out of the barrel  58  of the injector  54 . Here, as the plunger  68  advances, the head  62  is forced forward or away from the rigid backer plate  70 . This movement as shown in  FIG. 4B , decreases the volume of the fluid chamber  60 . When the plunger is allowed to relax, the head  62  returns to its relaxed position against the rigid backer plate  70 . This increases the volume of the fluid chamber  60  and draws a small amount of fluid and/or blood back through the injection site.  FIGS. 5A and 5B  show another alternative embodiment that operates as the embodiment shown in  FIGS. 4A and 4B , but without a rigid backer plate  70 .  
         [0035]     Another alternative embodiment of the present invention is shown in  FIG. 6 . In this embodiment, the plunger  80  is attached to the drive ram  32 . A gripper or other like mechanism could be used to connect the plunger  80  with the drive ram  32 . In this embodiment, the retraction or withdrawal of the drive ram  32  increases the volume of the fluid chamber  60  and draws a small amount of fluid and/or blood back through the injection site. The drive ram  32  can advance and retract as often as required, to push and pull blood and/or fluid through the catheter and the injection site.  
         [0036]     In all of the embodiments of the present invention, the drawing of blood and/or fluid back through the injection site is done in such a way, as to not adversely extract oxygen out of the blood. Typically this means a gradual pulling of the blood. In addition, all the various seals and connectors of the system are secured and sealed so as to prevent oxygen from entering the system during the injection and/or withdrawal cycles. Finally, while the present invention has been illustrated with the initial cycle being the advancement of fluid into a catheter or through an injection site, the first cycle of the system could equally be the reception of blood and/or fluid through an injection site or a catheter.  
         [0037]     While the present invention has been illustrated by description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspect is, therefore, not limited to the specific details, representative system, apparatus, and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant&#39;s general inventive concept.

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