Patent Description:
In many medical diagnostic and therapeutic procedures, a physician or trained clinician injects fluid into a patient. For example, a physician may inject saline and/or an imaging contrast medium into a patient to help improve the visibility of internal body structures during one or more X-ray/CT imaging, MRI imaging, or other imaging procedure. To inject the saline and/or contrast medium, the clinician may use a manual injection syringe or may, alternatively, use a powered fluid injection system. A catheter is coupled to the manual injection syringe or injection device and is used to inject the saline and/or contrast medium into the patient (such as into a vessel in the patient's hand or arm). The contrast medium and saline are provided from separate sources, such as bags, bottles, or syringes, and, in certain cases, may be mixed together before injection into the patient. However, several problems may develop during use of certain capacitive pressure injection systems and syringes, including spikes in fluid flow rates, extravasation and/or infiltration, saline or contrast medium contamination during injection due to backflow of the fluids, real-time injection ratio inaccuracies, or kick-back in catheter tubes that are inserted into patients.

Extravasation and infiltration are often characterized as an accidental infusion of an injection fluid, such as a contrast medium (extravasation) or saline (infiltration), into tissue surrounding a blood vessel rather than into the blood vessel itself. Extravasation and infiltration can be caused, for example, by a fragile vascular system, valve disease, inaccurate needle placement, sudden changes in fluid flow, or patient movement resulting in the injected needle being pulled from the intended vessel or pushed through the wall of the vessel.

Additional extravasation and/or infiltration issues may occur when using both a contrast medium and saline for a procedure. As shown in <FIG>, initially, no pressure is applied to the contrast medium <NUM> or saline <NUM>, resulting in no flow through the fluid injector system. As shown in <FIG>, pressure is then applied to the contrast medium <NUM> resulting in a pressure build up and initial backflow of contrast medium <NUM> into the saline <NUM> at point A. As a result, the flow rate of the contrast medium <NUM> may be reduced due to the effect of backflow and expansion in the contrast medium <NUM> bag or syringe and saline <NUM> bag or syringe due to the injection fluid pressure. Further, the saline <NUM> bag or syringe may expand depending on the particular capacitance of the saline <NUM> bag or syringe. As shown in <FIG>, the flow rate and pressure of the contrast medium <NUM> may continue to increase, thereby stabilizing the pressure in the injector system. As shown in <FIG>, due to the higher viscosity of the contrast medium <NUM>, the pressure applied to the saline <NUM> must be increased further until resistance to the flow of the saline <NUM> drops and the saline <NUM> is directed into the contrast medium <NUM> flow at point B. Until the saline <NUM> reaches a pressure that is substantially similar to the contrast medium <NUM>, the saline <NUM> stores pressure energy during the contrast medium <NUM> injection. When the saline <NUM> piston begins immediately after the contrast medium <NUM> injection stops, however, the flow rate of the saline <NUM> increases rapidly (higher than the flow rate programmed for the saline <NUM>) due to the stored pressure energy (capacitance), sending an increased amount of saline <NUM> to mix with the contrast medium <NUM>. This increased flow rate or flow spike can cause a rapid fluid acceleration in the catheter. The syringes or bags of the injector system will begin to deflate as the pressure within the syringes or bags decreases due to the uniform flow of contrast medium <NUM> and/or saline <NUM>. The rapid increase in flow rate for the saline <NUM> creates a transition to turbulence that causes the resistance to slightly rise again, causing oscillations in the flow. Eventually, a stable flow rate is reached at a lower equilibrium pressure. However, due to the initial backflow and increased pressure in the fluid injector system, an increased injection pressure and/or flow rate of contrast medium <NUM> or saline <NUM> may be experienced. Attempts were made to detect and avoid extravasation. <CIT> describes a multi-fluid injection system that is designed to sense when extravasation occurs by detecting a change in fluid level in tissue during injection of a first fluid (saline) and to stop the injection of a second fluid (contrast). This reduces discomfort to the patient and waste of contrast. <CIT> utilizes an extravasation sensor that transmits electromagnetic energy into the subcutaneous tissue of the patient and measure the resulting signal to determine a change of fluid level in the muscle tissue surrounding a blood vessel. The flow rate of the injection of the first fluid can be increased or decreased if the initial flow rate is insufficient to determine whether extravasation has occurred. If extravasation is detected, then injection of the first fluid (saline) is halted and injection of the second fluid (contrast) is prevented. <CIT> does not describe a method or processor configured to adjusting at least one of a first flow profile of the first flow rate and a second flow profile of the second flow rate to dampen a transient increase in the overall flow rate during a transition between delivering one of the first fluid and the second fluid to delivering the other of the first fluid and the second fluid.

With further reference made to <FIG> and the injection process described above, also due to the initial backflow and increased pressure in the fluid injector system, accurate flow rates of contrast medium <NUM> and saline <NUM> are not always provided to the patient. Accurate flow rates of the contrast medium <NUM> and saline <NUM> may be achieved in average. However, for short periods of time until the system achieves steady state, the flow rates may be ramping, slowing down, peaking, and may not be particularly precise. In one scenario, the contrast medium <NUM> injection may be followed by the saline <NUM> injection, which causes a saline <NUM> overrate to the patient. In another scenario, a dual flow simultaneous injection of the contrast medium <NUM> and the saline <NUM> may cause inaccurate ratios of the contrast medium <NUM> and saline <NUM> until the system stabilizes.

An additional factor that may contribute to the problem of inaccurate fluid mixing ratios is the backflow of fluid that occurs in injections where the viscous contrast medium <NUM> is injected at a higher ratio than the less viscous saline <NUM>. In such a scenario, before a uniform fluid flow is established, the fluid pressure of the more viscous contrast medium <NUM> that is injected at a higher ratio may act against the fluid pressure of the less viscous saline <NUM> that is injected at a lower ratio to force the contrast medium <NUM> to reverse the desired direction of flow. After injection, pressures equalize and the fluid injection system achieves a steady state operation where the contrast medium <NUM> and saline <NUM> are injected at a desired ratio. However, in small volume injections, steady state operation may not be achieved prior to the completion of the injection process and the fluid mixing ratio of contrast medium <NUM> and saline <NUM> being delivered to the patient may not be accurately achieved. Thus, even though a desired ratio of contrast medium <NUM> and saline <NUM> may be <NUM>% contrast medium <NUM> to <NUM>% saline <NUM>, the actual ratio due to backflow of contrast medium <NUM> into the saline <NUM> may be higher. This problem is further compounded with an increase in injection pressure. In one particular example of a fluid injector system, the syringes are typically always pointing upwards and are used for multiple patients throughout an entire day. Therefore, contrast medium <NUM> may backflow into the saline syringe and sink to the bottom of the saline syringe. By the time multiple patients have been treated and multiple injections have been performed, the saline syringe may be substantially filled with contrast medium thereby contaminating and reducing the amount of the saline fluid <NUM>.

An additional complication with known multi-fluid injector systems is a kickback or rapid movement of the catheter in the patient's body as a result of the erratic flow of the contrast medium or saline. In many known multi-fluid injector systems, the saline and contrast medium tubing is connected to a catheter that is used for injecting the fluids into the patient. However, due to the backflow of the saline and/or contrast medium and the rapid acceleration of contrast medium or saline into the fluid line of the multi-fluid injector system during fluid transitions, the catheter may at least partially kick-back or otherwise change position within the patient vasculature. Fluid accelerations may be caused by nozzle effects in the catheter and rapid increases in flow rate during contrast medium-to-saline transitions. The nozzle on the catheter may accelerate the fluid from a lower flow rate in the tubing of the catheter to an increased flow rate exiting the catheter. The transition from a contrast medium injection to a saline injection causes a rapid flow rate increase. The force imparted to the catheter may cause undesired movement of the catheter. Complications related to extravasation and infiltration, inaccurate fluid mixing ratios, and catheter kickback and rapid movement may include unnecessary pain and discomfort to the patient. There is a current need for a system that provides accurate flow rates of saline and/or contrast medium to a patient, thereby reducing the risk of extravasation and/or infiltration. There is also a current need for a catheter design that reduces kickback and rapid movement of the catheter during injection of a fluid into a patient's blood vessel.

In view of the foregoing, a need exists for an improved fluid delivery system for fluid delivery applications in medical diagnostic and therapeutic procedures. There is an additional need in the medical field for a fluid delivery system that provides a more precise and efficient flow rate or ratio of fluids during initial injection procedures compared to existing fluid delivery systems. Existing fluid delivery systems do not always provide accurate flow rates or mixing ratios of the desired fluids resulting in the risk of extravasation and/or infiltration. There is a current need for a fluid delivery system that allows an individual to quickly and accurately provide the necessary flow rate or ratio of fluids to a patient. To accomplish these objectives, the present invention provides a multi-fluid injection system according to claim <NUM>. Any features defined by the independent claim are required to form an embodiment of the invention, even if referred to in the following description as optional.

The features and characteristics of the fluid injection system, as well as the methods of operation and functions of the related elements of structures and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claim with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the disclosure. As used in the specification and the claim, the singular form of "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

For the purposes of the description hereinafter, spatial orientation terms, if used, shall relate to the referenced example as it is oriented in the accompanying drawings, figures, or otherwise described in the following detailed description. However, it is to be understood that the examples described hereinafter may assume many alternative variations and examples. It is also to be understood that the specific systems illustrated in the accompanying drawings, figures, and described herein are simply exemplary and should not be considered as limiting.

Referring to the drawings in which like reference characters refer to like parts throughout the several views thereof, several systems and methods are provided for reducing incidences of infiltration and/or extravasation, reducing the occurrence of spikes or sudden changes in fluid flow rates during an injection procedure, ensuring accurate flow rates and mixing ratios of fluids are delivered to the patient, and reducing kickback and rapid movement of a catheter during a transition from one injected fluid to another fluid. In a typical multi-fluid injection procedure, an injection fluid, such as a contrast medium, is delivered from a contrast medium source to the patient using a powered or manual injector. The injected contrast medium is delivered to a desired site in a patient's body through a catheter inserted into the patient's body, such as the arm. Once the contrast medium is delivered to the desired site, the area is imaged using a conventional imaging technique, such as computed tomography (CT), angiography imagining, magnetic resonance imaging (MRI), or other imaging or scanning technique. The contrast medium becomes clearly visible against the background of the surrounding tissue. However because the contrast medium may comprise toxic substances, it is desirable to reduce contrast dosing to the patient, while maintaining an effective contrast amount necessary for accurate imaging. By supplementing an overall contrast medium delivery procedure with saline, the saline flushes the contrast medium to the area of interest and additional hydration of the patient occurs automatically and aids the body in removing the contrast medium. In addition to improved patient comfort level and less toxicity, introduction of saline at clinically significant pressures and flow rates also allows higher flow rates to be achieved at lower pressure settings on the injector.

In one example, as shown in <FIG>, a fluid injector <NUM> (hereinafter referred to as "injector <NUM>"), such as an automated or powered fluid injector, is adapted to interface with and actuate at least one syringe <NUM>, each of which may be independently filled with a medical fluid, such as contrast medium, saline solution, or any desired medical fluid. The injector <NUM> may be used during a medical procedure as described herein to inject the medical fluid into the body of a patient by driving a plunger <NUM> of the at least one syringe <NUM> with at least one piston (not shown). The injector <NUM> may be a multi-syringe injector, wherein several syringes <NUM> may be oriented in a side-by-side or other arrangement and include plungers <NUM> separately actuated by respective pistons associated with the injector <NUM>. In examples with two syringes arranged in a side-by-side relationship and filled with two different medical fluids, the injector <NUM> may deliver fluid from one or both of the syringes <NUM>. The injector <NUM> has a control mechanism <NUM> for controlling operation of at least one operating parameter of injector <NUM>, such as the injection pressure, volume, and/or flow rate of fluid delivered from at least one of the syringes <NUM>.

The injector <NUM> has a housing <NUM> formed from a suitable structural material, such as plastic or metal, that encloses various components for delivering fluid from the syringes <NUM>. The housing <NUM> may have various shapes and sizes depending on a desired application. The injector <NUM> includes at least one syringe port <NUM> for connecting the at least one syringe <NUM> to respective piston elements. In some examples, the at least one syringe <NUM> includes at least one syringe retaining member for retaining the syringe <NUM> within a syringe port <NUM> of the injector <NUM>. The at least one syringe retaining member operatively engages a locking mechanism provided on or in the syringe port <NUM> of the injector <NUM> to facilitate loading and/or removal of the syringe <NUM> to and from the injector <NUM>.

At least one fluid path set <NUM> may be fluidly connected with the at least one syringe <NUM> for delivering medical fluid from the at least one syringe <NUM> to a catheter, needle, or other fluid delivery device (not shown) inserted into a patient at a vascular access site. Fluid flow from the at least one syringe <NUM> may be regulated by a fluid control module. The fluid control module may operate various pistons, valves, and/or flow regulating structures to regulate the delivery of the medical fluid, such as saline solution and contrast medium, to the patient based on user selected injection parameters, such as injection flow rate, duration, total injection volume, and/or ratio of contrast medium and saline. An example of a suitable front-loading fluid injector <NUM> that may be modified for use with the above-described system including at least one syringe <NUM> and at least one syringe interface loading and releasable retaining of the at least one syringe <NUM> with the fluid injector <NUM> described herein with reference to <FIG> is disclosed in <CIT>; <CIT>; and <CIT>. Another example of a multi-fluid delivery systems that may be modified for use with the present system is found in <CIT>; <CIT>; <CIT>; and <CIT>.

To enable effective simultaneous flow delivery of first and second injection fluids, such as contrast and saline, substantially equal pressure must be present in each delivery line. In a powered injection systems described herein, in a dual flow mode it is desirable to actuate the plunger elements substantially simultaneously in simultaneous flow delivery applications to equalize the pressure in each line. Alternatively, in a single flow mode, one plunger element is actuated to deliver the desired fluid while the other plunger element is held in place. If the injector is operated with differential pressure in each delivery line of the fluid path set, fluid in the lower pressure line may be stopped or reversed until sufficient pressure is achieved in the lower pressure line to enable flow in a desired direction. This time delay could reduce the image quality. The fluid in the lower pressure side may also begin to store fluid pressure energy against the fluid in the higher pressure line. As the stored fluid pressure energy in the lower pressure side continues to build, the lower pressure will eventually achieve the same pressure as the higher pressure fluid as it exits into the catheter tubing. Due to the stored fluid pressure energy in the lower pressure side, the flow rate of the lower pressure fluid can rapidly accelerate into the catheter tubing, particularly when the pressure in the high pressure fluid is reduced.

As shown in <FIG> and <FIG>, when delivering contrast medium and, subsequently, saline solution to a patient's blood vessel, a spike or sudden increase in an overall flow rate of fluid exiting the catheter may be experienced during a flow transition between the contrast medium and the saline. In one example, an overall flow rate through the catheter is understood to be the combined flow rate of the first fluid (in one example, saline solution) and the second fluid (in one example, contrast medium) exiting from the catheter. In one example, in which there is no flow of contrast medium through the catheter, the overall flow rate is equal to the flow rate of the saline solution. In another example, in which there is no flow of saline solution through the catheter, the overall flow rate is equal to the flow rate of the contrast medium. In another example, in which there is flow of saline solution and contrast medium through the catheter, the overall flow rate is equal to the combined flow rates of the saline solution and the contrast medium. Therefore, a fluid system may have a first flow rate corresponding to the flow rate of the first fluid, a second flow rate corresponding to the flow rate of the second fluid, and an overall flow rate corresponding to the combination of flow rates of the first and second fluids. As shown in <FIG> and <FIG>, as the contrast medium is initially directed through the catheter, the overall flow rate of the system equals the flow rate of the contrast medium and gradually increases to a desired steady-state flow rate. In <FIG>, in one example, the desired overall flow rate exiting the catheter is <NUM>/s. Once a sufficient volume of contrast medium has been directed through the catheter and into the patient's blood vessel, a volume of saline solution is subsequently directed through the catheter to flush the contrast into the patient. As the delivery of the more viscous contrast medium transitions to the delivery of less viscous saline solution from the catheter, a sudden spike or increase in the overall flow rate is experienced in the system. As shown in <FIG>, this spike or increase in the overall flow rate lasts for a specified duration and increases the overall flow rate of the system to a flow rate greater than the desired overall flow rate. As shown, the overall flow rate may increase to <NUM>/s, which is <NUM>/s higher than desired for the injection protocol. Therefore, it is an object of the present disclosure to dampen the sudden spike or increase in the overall flow rate exiting the catheter, for example by reducing the height of the spike and/or the duration of the spike, by adjusting a flow profile of the saline solution and/or the flow profile of the contrast medium during a transition between the delivery of the contrast medium to the delivery of the saline solution. Several different methods and arrangements for dampening the increase in overall flow rate exiting the catheter and reducing the duration of the increased overall flow rate are described below.

As shown in <FIG>, in a system delivering only saline solution to a patient, there is no sudden spike or increase observed in the overall flow rate exiting the catheter when switching from one saline syringe to another. In fact, the system may experience a slight temporary decrease in the overall flow rate exiting the catheter. As shown in <FIG>, the difference in viscosity of the contrast medium used in the system compared to that of the saline (Δ-Viscosity) may also affect the severity of the sudden spike or increase in the overall flow rate exiting the catheter. For example, a contrast medium with a higher viscosity (e.g., <NUM> cP) may contribute to a larger spike or increase in the overall flow rate exiting from the catheter than a contrast medium with a lower viscosity (e.g., <NUM> cP). As shown in <FIG>, the desired overall flow rate of the fluid exiting from the catheter may also affect the severity of the sudden spike or increase in the overall flow rate exiting the catheter. For example, a higher desired overall flow rate (e.g., <NUM>/s) may contribute to a larger spike or increase in the overall flow rate exiting from the catheter than a lower desired overall flow rate (e.g., <NUM>/s).

Further, the fluid mixing ratio of contrast medium-to-saline may become inaccurate due to the stored fluid pressure energy in the lower pressure saline syringe or line. The contrast medium may be injected at a significantly higher ratio relative to saline, such as <NUM>% contrast medium to <NUM>% saline injection protocol. The flow reversal may be exacerbated at high injection pressures. In small dosage injections at a high injection pressure, flow reversal may effectively stop the delivery of saline such that up to <NUM>% contrast medium is injected, rather than the desired <NUM>% contrast medium to <NUM>% saline ratio. Similar inaccuracies may occur at various other injection protocols, including, but not limited to <NUM>% contrast medium to <NUM>% saline ratio.

The above-described situation of flow reversal during powered injections at high contrast medium-to-saline ratio may occur at least in part due to injection system capacitance. Total system capacitance (also referred to as compliance or the ability to store a fluid volume and/or hydraulic energy) represents the amount of suppressed fluid (i.e., backflow volume) that is captured in the swelling of the fluid injector system components or compression of fluid injector system components, such as the fluid lines and/or syringe(s) due to pressure applied to a medical fluid during an injection process. Total system capacitance is inherent to each fluid injection system and depends on a plurality of factors, including injector construction, mechanical properties of materials used to construct the syringe, plunger, pressure jacket surrounding the syringe, fluid lines delivering the contrast medium and saline to a flow mixing device, size or surface area of the syringe, plunger, pressure jacket, compression or deflection of syringe injector components, etc. The amount of back or reverse flow increases when the relative speed difference between the two plungers is large, the simultaneous fluid flow is through a small restriction, the speed of the total fluid injection is large, and/or the viscosity of the fluid is high. The back or reverse flow can prevent different ratios of simultaneously delivered fluid from occurring in certain injections, which can be a detriment for two-syringe type fluid injector systems.

In general, capacitance is directly correlative to injection pressure and inversely correlative to volume of contrast medium and saline in the syringes. For example, in one example, capacitance during an injection at <NUM> psi with <NUM> of contrast medium and saline remaining in certain medical injector syringes is around <NUM>. In another example, the capacitance volume can be from about <NUM> to about <NUM>. Capacitance is also a function of the ratio at which the first and second injection fluids, such as contrast and saline, are injected. At a <NUM>%-<NUM>% ratio, where contrast and saline are injected in equal amounts, backflow volume is minimized because the capacitance on the contrast medium side is equal to the capacitance on the saline side of the fluid injection system such that substantially equal pressures are present in each delivery line. Backflow may occur in situations where first and second injection fluids are delivered through long fluid conduits. However, as the injection ratio of contrast and saline changes, backflow volume increases corresponding to the increase in the ratio.

With reference to <FIG>, capacitance in a particular injector system can occur in several different locations during an injection procedure of the system. In particular, in one example, the catheter tubing <NUM> of the system may experience swelling and/or compression during an injection procedure, which can affect the flow rates of the fluids through the tubing <NUM>. In another example, the catheter <NUM> itself may experience swelling and/or compression during an injection procedure, which can affect the flow rate of the fluid exiting the catheter <NUM>. In another example, the syringe <NUM> of the injector system may experience swelling and/or compression during an injection procedure. The swelling of the syringe <NUM> may occur in the form of radial expansion and/or axial expansion of the syringe <NUM>. In another example, the syringe interface <NUM> may experience swelling and/or compression during an injection procedure. The syringe interface <NUM> is the connection between the syringe <NUM> and the injector system. In one example, the syringe interface <NUM> may include locking mechanisms, O-rings or other sealing members that can experience swelling and/or compression during the injection procedure. In another example, locking features <NUM> on the syringe, such as flanges or lugs may compress or bend under the applied pressure. In another example, a piston head <NUM> in the injector system may experience swelling and/or compression during an injection procedure, for example if there is mechanical play between the piston head <NUM> and the corresponding syringe plunger. Due to the forces exerted by and on the piston head <NUM>, compression forces may create swelling in the piston head <NUM>. In another example, the piston <NUM> may experience bending, torqueing, swelling and/or compression during an injection procedure. Due to the forces exerted by and on the piston <NUM>, compression forces may create swelling in the piston <NUM> and corresponding reduction in piston length. In another example where a polymeric cover <NUM> is provided on piston head <NUM> or syringe plunger assembly, the polymeric cover <NUM> may experience swelling and/or compression during an injection procedure. In another example, a strain gauge cap <NUM> positioned in the injector system on an end of piston <NUM> may experience swelling and/or compression during an injection procedure. Although the strain gauge cap <NUM> is configured to stretch to measure strain in piston <NUM>, the injection procedure may create additional swelling and/or compression in the strain gauge cap <NUM>. One or more of these or other factors (such as compression of the medical fluid or gas bubbles therein) may contribute to the overall capacitance volume of an injector system. Depending on the type of injection procedure or system, all of these factors may contribute to overall capacitance of the injector system or only a subset of these factors may contribute to overall capacitance of the injector system. The value of the contribution of each factor may differ from other factors.

While several different factors that can affect the overall flow rate or an individual flow rate of one of the fluids in the injector system have been described, it is also contemplated that other factors may also affect these flow rates. The state of the particular flow of fluid through the injector system and the particular flow transition physics (laminar versus turbulent flow) during fluid mixing, fluid flow past fluid path components, and exiting from the catheter into the patient's blood vessel, the temperature of the contrast medium may increase the viscosity of the contrast medium, and the higher flow rates for cardiac CT and other advanced imaging applications may also affect these flow rates.

Solutions to the problem of reducing backflow to compensate for system capacitance, for example in a high contrast medium-to-saline ratio, and thereby reducing undesired spikes in fluid flow rates and providing more accurate mixing ratios of fluids to the patient are described herein. In all of the examples described herein, a fluid flow profile of at least one of a first fluid <NUM> and a second fluid <NUM> is adjusted based on a function of the flow rate of one of the first fluid <NUM> and the second fluid <NUM> to minimize or dampen the spike or increase in the overall flow rate of fluid exiting from the catheter during a transition between delivering one of the first fluid <NUM> and the second fluid <NUM> to delivering the other of the first fluid <NUM> and the second fluid <NUM>.

In one embodiment, one solution for improving (i.e., reducing) the overall capacitance of the injector system is to increase the stiffness of one or more of the components of the injector system subject to capacitance, to reduce swelling and/or compression in the one or more components. In one example, the stiffness of one of the catheter tubing <NUM>, the catheter <NUM>, the syringe <NUM>, the syringe interface <NUM>, the piston head <NUM>, the piston <NUM>, the polymeric cover <NUM>, and the strain gauge cap <NUM> may be increased to reduce swelling and/or compression in the components of the injector system. In another embodiment, a pressure jacket may be placed around an outer surface of syringe <NUM> to reduce radial swelling under injection pressure.

The various embodiments described herein may be applied to injection procedures including simultaneous injection of fluid from two or more syringes or, alternatively, to reduce pressure and fluid flow spikes associated with transition from one fluid to another fluid during sequential injection of two or more fluids from two or more syringes, for example when transitioning from a contrast injection to a saline injection, or vice versa.

As shown in <FIG>, due to the additional time that is needed for the correct pressure to be achieved in the less viscous first fluid <NUM>, various embodiments of the methods herein include delaying or ramping the application of pressure to the second fluid <NUM> until the pressure of the first fluid <NUM> has reached a predetermined pressure. This predetermined pressure may be a low equilibrium pressure that provides a smooth flow rate of fluid through the fluid injection system. In one example, the second fluid <NUM> may be more viscous than the first fluid <NUM>. In one example, the second fluid <NUM> may be contrast medium and the first fluid <NUM> may be saline. As shown in <FIG>, initially, pressure may be applied to the first fluid <NUM> via a plunger <NUM> until the pressure of the first fluid <NUM> has reached the predetermined pressure. As shown in <FIG>, after the first fluid <NUM> has reached the predetermined pressure, the same predetermined pressure may be applied to the second fluid <NUM> via a plunger <NUM>, resulting in the first fluid <NUM> and the second fluid <NUM> having a substantially similar flow rate through the fluid injection system. This system and method reduces the rapid increases in first fluid <NUM> pressure through the fluid injection system, which often causes erratic flow and inaccurate volumes of the first fluid <NUM> and the second fluid <NUM> being injected in the patient. By allowing the pressure of the first fluid <NUM> to reach a predetermined pressure before the second fluid <NUM>, the first fluid <NUM> and the second fluid <NUM> can reach the same predetermined pressure at substantially the same time. The predetermined pressure will be dependent upon several factors, including, among others, the diameter of the catheter that is used to inject the first fluid <NUM> and the second fluid <NUM> into the patient, the viscosity of the first fluid <NUM> and the second fluid <NUM>, the capacitance of the first fluid <NUM> and the second fluid <NUM> syringes and overall capacitance of the injector system, and/or the inner diameter of the tubing used to deliver the first fluid <NUM> and the second fluid <NUM> to the catheter. It is also contemplated that this fluid injection system may be automated with the use of a controller <NUM> that controls the actuation of each of a pair of motors <NUM>, <NUM> that are configured to move the pair of plungers <NUM>, <NUM> that are used to apply pressure to the first fluid <NUM> and the second fluid <NUM>. In this example, the controller <NUM> may be programmed to delay applying or ramping the application of pressure to the second fluid <NUM> until the first fluid <NUM> has reached the predetermined pressure. The controller <NUM> may be a processor configured to store several different protocols for injection procedures based upon one or more of predetermined pressures for the fluid injection system, syringe volumes, catheter, the first fluid <NUM> type and/or volume to be delivered, the second fluid <NUM> type and/or volume to be delivered, flow rates of the first fluid <NUM> and/or the second fluid <NUM>, system capacitance, fluid temperature, tubing type and/or diameter, and/or patient depending on the procedure. In one example, a user of the fluid injection system may input this identifying information into the controller <NUM>, which will calculate the proper predetermined pressure to apply to the first fluid <NUM> and the second fluid <NUM> during the injection procedure to minimize pressure and flow spikes at fluid transitions. In an alternative example, the first fluid <NUM> may be more viscous than the second fluid <NUM>. In this example, the process described above in reference to <FIG>, would be switched to apply an initial pressure to the second fluid <NUM> before applying pressure to the first fluid <NUM>. It is also contemplated that the first fluid <NUM> and the second fluid <NUM> may have substantially equal viscosities. In this example, equal pressures may be applied to the first fluid <NUM> and the second fluid <NUM> at the outset of the process.

With reference to <FIG>, another method for reducing undesired spikes in fluid flow rates and providing more accurate fluid mixing ratios with the fluid injection system is described. A first fluid <NUM> and a second fluid <NUM> may be provided in a fluid injection system in which plungers <NUM>, <NUM> driven by motors <NUM>, <NUM> apply pressure to the first fluid <NUM> and the second fluid <NUM>, respectively. In one example, the second fluid <NUM> may be more viscous than the first fluid <NUM>. The second fluid <NUM> may be contrast medium and the first fluid <NUM> may be saline. A controller <NUM> may be operatively connected to the motors <NUM>, <NUM> to control the rate of pressure applied to the first fluid <NUM> and the second fluid <NUM> by the plungers <NUM>, <NUM>. The controller <NUM> may be programmed to apply pressure to the first fluid <NUM> based on the pressure that is being applied to the second fluid <NUM>. As the second fluid <NUM> is pushed through the fluid injection system, the controller <NUM> may correspondingly change the pressure applied to the first fluid <NUM> by the plunger <NUM>. For example, if a certain pressure is being applied to the second fluid <NUM> by the plunger <NUM>, the controller <NUM> may instruct the plunger <NUM> to apply a proportionally larger pressure to the first fluid <NUM> to compensate for the resistance of the more viscous second fluid <NUM>. Using the controller <NUM> in this manner, the first fluid <NUM> and the second fluid <NUM> may flow through the fluid injection system at substantially equal flow rates, thereby minimizing any erratic flow in the fluid injection system. In another example, the first fluid <NUM> may be more viscous than the second fluid <NUM>. In this example, the process described above in reference to <FIG>, would be switched to apply a proportionally larger pressure to the second fluid <NUM> in comparison to the pressure applied to the first fluid <NUM>. It is also contemplated that the first fluid <NUM> and the second fluid <NUM> may have substantially equal viscosities. In this example, equal pressures may be applied to the first fluid <NUM> and the second fluid <NUM> at the outset. For example, in certain embodiments a more viscous fluid may be diluted with a less viscous fluid, or vice versa, so that the Δ-Viscosity between the two injected fluids is minimized. Δ-Viscosity may also be reduced by heating a fluid having a higher viscosity, for example to a temperature close to body temperature, prior to the injection procedure.

In another example, after pressure has been applied to the first fluid <NUM> and the second fluid <NUM>, the flow rate of each fluid <NUM>, <NUM> is measured. In the event the flow rates are not equal to one another, the fluid injection system may pause or hold the injection procedure, or pause injection or one or both fluids, to allow both fluids <NUM>, <NUM> to achieve a steady-state pressure to reduce any stored energy in the fluid injection system. In one example, as the flow rates of the fluids <NUM>, <NUM> are being measured, in the event it is determined that the flow rate of first fluid <NUM> is not equal to the flow rate of the second fluid <NUM> the fluid injection system can pause or hold the injection procedure while pressure is applied to either the first fluid <NUM> or the second fluid <NUM> to equalize the flow rates of the fluids <NUM>, <NUM>. In another example, the overall flow rate of the fluid exiting the catheter is measured during the injection procedure. The information regarding the overall flow rate is sent as real-time feedback information to the controller <NUM> to permit the controller <NUM> to adjust the pressures applied to the first fluid <NUM> and/or second fluid <NUM> to equalize the flow rates through the fluid injection system to ensure a consistent overall flow of fluid is exiting from the catheter into the patient's blood vessel. As shown in <FIG>, in one example, a sensor <NUM>, for example an ultrasonic mass flow rate sensor or other suitable flow rate sensor, is used to measure the overall flow rate in real-time of at least one of the first fluid <NUM> and second fluid <NUM> through the system. It is contemplated that the sensor <NUM> can be placed a various positions within the system. It is also contemplated that more than one sensor <NUM> is used to measure the overall flow rate of at least one of the first fluid <NUM> and the second fluid <NUM> at different positions in the system. In one example, the sensor <NUM> is a sensor that clips onto the exterior of the fluid path set <NUM> to the catheter. In another embodiment, the flow rate sensor may be internal and located within the fluid flow path. It is contemplated, however, that other flow rate sensing technologies could be used and alternative mounting scenarios could be used to position the sensor <NUM> on the fluid path set <NUM>. The sensor <NUM> provides a real-time feedback loop to the controller <NUM> to control one or more of the injection parameters based on the overall flow rate measured by the sensor <NUM>. In other embodiments, such a sensor arrangement could also be used with peristaltic systems and other continuous flow injector systems. In another example, an air sensor <NUM> is provided in line with the sensor <NUM> to measure the air content in the fluid flowing through the fluid path set <NUM>. The information measured by the air sensor <NUM> may also be fed back to the controller <NUM> to control one or more of the injection parameters. For example, pressure applied to a plunger for a first viscous fluid <NUM> may be ramped down and pressure applied to a plunger of a second less viscous fluid <NUM> may be ramped up or one or more other fluid injection parameters may adjusted as appropriate so that the real-time feedback from a flow sensor indicates that the flow rate of the fluid exiting a catheter is substantially constant, for example not varying by more than <NUM>/sec, <NUM>/sec, <NUM>/sec, <NUM>/sec, <NUM>/sec, or even <NUM>/sec during transition from the first fluid <NUM> to the second fluid <NUM>.

As further shown in <FIG>, a check valve <NUM> may also be provided in the fluid injection system. The check valve <NUM> may be positioned in-line with the tubing of the first fluid <NUM>. Using this check valve <NUM>, the first fluid <NUM> will only flow into the second fluid <NUM> flow until a predetermined pressure is achieved by the first fluid <NUM>. The predetermined pressure may be substantially equal to the desired flow rate pressure of the second fluid <NUM>. The check valve <NUM> may be chosen based on the desired predetermined pressure. With the use of the check valve <NUM>, the second fluid <NUM> is not permitted to flow back into the tubing of the first fluid <NUM>, thereby reducing the expansion of the second fluid <NUM> syringe and/or first fluid <NUM> syringe under the extra pressure. In the example where the first fluid <NUM> is less viscous than the second fluid <NUM>, the check valve <NUM> may be positioned in-line with the tubing of the first fluid <NUM> to prevent the first fluid <NUM> from opening the check valve <NUM> until a predetermined pressure has been applied to the first fluid <NUM>. According to this example, capacitance build up in the first syringe <NUM> is reduced by eliminating any component from the pressure applied to the second fluid <NUM>.

In a similar fashion, as shown in <FIG>, a check valve <NUM> may be provided in-line with the tubing of the second fluid <NUM> portion of the fluid injection system. Similar to the check valve <NUM> on the first fluid <NUM> portion, the check valve <NUM> may be configured to control the flow of the second fluid <NUM> through the fluid injection system based on a desired predetermined pressure for the fluid injection system. The check valve <NUM> may be chosen according to the desired predetermined pressure. Using this system and method, the controller <NUM> may control the amount of pressure applied to the first fluid <NUM> and the second fluid <NUM> via the motors <NUM>, <NUM> and plungers <NUM>, <NUM>. The controller <NUM> may monitor the pressures of the first fluid <NUM> and the second fluid <NUM> and adjust the plungers <NUM>, <NUM> accordingly to maintain equal pressures in the fluid injection system. Using the check valve <NUM> on the second fluid <NUM> portion of the fluid injection system, the peak pressure values in the fluid injection system can be significantly lowered. Using this arrangement, the pressure of the first fluid <NUM> can reach a predetermined pressure, while the check valve <NUM> does not release the second fluid <NUM> until the predetermined pressure on the second fluid <NUM> is also achieved, thereby reducing the amount of second fluid <NUM> that backflows into the first fluid <NUM> portion of the fluid injection system. In one example, the first fluid <NUM> may be brought to the predetermined pressure and then the second fluid <NUM> may be subsequently pressurized to be released through the check valve <NUM>. It is contemplated that the controller <NUM> can be programmed to initiate these pressurization procedures. In the example where the first fluid <NUM> is more viscous than the second fluid <NUM>, the check valve <NUM> may be positioned in-line with the tubing of the second fluid <NUM> to prevent the second fluid <NUM> from opening the check valve <NUM> until a predetermined pressure has been applied to the second fluid <NUM>.

As shown in <FIG>, it is also contemplated that the fluid injection system may include a check valve <NUM> on the first fluid <NUM> portion of the fluid injection system and a check valve <NUM> on the second fluid <NUM> portion of the fluid injection system. In this arrangement of the fluid injection system, fluid pressure from the non-active portion of the fluid injection system may be eliminated or isolated until the active portion of the fluid injection system reaches the same fluid pressure. For example, fluid pressure from the second fluid <NUM> may be eliminated or isolated in the fluid injection system until the fluid pressure of the first fluid <NUM> reaches a predetermined pressure or an equal pressure to the second fluid <NUM>. The check valves <NUM>, <NUM> may be chosen based on the desired predetermined pressure of the first fluid <NUM> and the second fluid <NUM>. Using this arrangement, the first fluid <NUM> and the second fluid <NUM> are not mixed together in the fluid injection system until each fluid has reached the predetermined fluid pressure. A controller <NUM> may also be used in this arrangement to control the pair of motors <NUM>, <NUM> that actuate the plungers <NUM>, <NUM> that apply pressure to the first fluid <NUM> and the second fluid <NUM>. The controller <NUM> may be pre-programmed with information regarding the threshold pressures for the check valves <NUM>, <NUM>, and user input on information on the first fluid <NUM> and second fluid <NUM> may be used to coordinate the proper pressures applied by the plungers <NUM>, <NUM> to the first fluid <NUM> and the second fluid <NUM>. In another example, the check valves <NUM>, <NUM> may be high crack pressure check valves configured to reduce or essentially eliminate the backflow in the fluid injection system. The high crack pressure check valves <NUM>, <NUM> may be check valves that allow flow in one direction with a relatively low pressure drop. The high crack pressure check valves <NUM>, <NUM> may have a high opening or cracking pressure that may be above or near the maximum operating pressure of the fluid injection system. One example of such a high cracking pressure valve may include a spool valve having an internal sliding element that can block fluid flow. The valve may include a resistive force element, such as a spring or a pressurized bladder, to resist the movement of the sliding element. By providing the high crack pressure check valves <NUM>, <NUM> with a high cracking pressure, no fluid may continue to flow or dribble out of the two syringes into the fluid path and possibly the patient until the requisite pressure balance is achieved in the fluid injection system. In another example, the open position of the check valves <NUM>, <NUM> can be adjusted so that the check valves <NUM>, <NUM> are partially open to control the flow of fluid through the check valves <NUM>, <NUM>. The check valves <NUM>, <NUM> may be adjusted manually or automatically by the controller <NUM>. Based on the flow rates of the first fluid <NUM> and/or the second fluid <NUM>, the check valves <NUM>, <NUM> can be partially opened, fully opened, or closed to achieve a desired flow rate of the fluid <NUM>, <NUM> through the check valve <NUM>, <NUM>.

As shown in <FIG> and <FIG>, another method of reducing undesired spikes in fluid flow rates in and providing accurate fluid mixing ratios to the patient is through the use of an over-travel and fast-controlled reverse pull of the plunger <NUM> within the first fluid <NUM> syringe to at least partially compensate for any undelivered first fluid <NUM> in the fluid injection system due to capacitance volume of the system. In this arrangement, the second fluid <NUM> may be more viscous than the first fluid <NUM>. The over-travel position and fast-controlled reverse pull of the plunger <NUM> may be calculated according to the amount of potential stored volume in the first fluid <NUM> syringe based on the desired fluid pressure and the plunger <NUM> position at the end of the first fluid <NUM> injection procedure. To determine the length of over-travel for the plunger <NUM> needed to receive the desired volume of the first fluid <NUM>, the following equation is used to calculate the plunger <NUM> over-travel distance, as identified in <CIT>: <MAT>.

To receive the desired volume of the first fluid <NUM> from the fluid injection system, the plunger <NUM> must be over-traveled the same amount and then the plunger <NUM> is pulled back in reverse to compensate for release of the capacitance volume of the first fluid <NUM> syringe.

With reference to <FIG>, upon activation of the controller <NUM>, the motor <NUM> is activated to drive the plunger <NUM>, which causes transition of the plunger <NUM> from a first initial position P1plunger (shown in dashed lines) to a second extended position P2plunger, thereby advancing the plunger <NUM> a corresponding delivery distance D1plunger. As the plunger <NUM> is transitioned across the delivery distance D1plunger, a pre-set volume of the first fluid <NUM> is delivered from the interior of the first fluid <NUM> syringe to a downstream location. During delivery of the first fluid <NUM> from the interior of the syringe to the downstream location, the syringe swells and the system otherwise increases in capacitance volume as described herein, in such a manner that it is radially displaced from its initial configuration. As the plunger <NUM> is advanced longitudinally within the syringe to dispel liquid from the interior of the syringe, the first fluid <NUM> imparts an axial force to the wall of the syringe.

As shown in <FIG>, in order to account for the under-delivery of fluid from the interior of the syringe due to the swelling of the syringe and other capacitance effects, the plunger <NUM> can be programmed to over-travel a sufficient longitudinal distance to compensate for system capacitance, such as the expansion of the syringe when under resulting axial pressure. In order to over-travel a specified longitudinal distance, the motor <NUM> is actuated by the controller <NUM>, which causes further transition of the plunger <NUM> from the second extended position P2plunger (shown in dashed lines) to a third over-travel position P3plunger, thereby advancing the plunger <NUM> a corresponding delivery distance D2plunger. As the plunger <NUM> is transitioned across the delivery distance D2plunger, a pre-determined volume of the first fluid <NUM> is delivered from the interior of the syringe to the downstream location to compensate for the under-delivery of fluid from the interior of the syringe as a result of the capacitance volume of the first fluid <NUM> syringe during transition from the first initial position to the second extended position.

Once forward longitudinal movement of the plunger <NUM> within the syringe is ceased, the plunger <NUM> may be rapidly driven back in order to compensate for the increased pressures within the fluid injection system resulting from the over-travel of the plunger <NUM>. In order for the plunger <NUM> to retract to the retracted position, the controller <NUM> activates the motor <NUM>, which causes transition of the plunger <NUM> from the third over-travel position P3plunger to the retracted position, thereby retracting the plunger <NUM> a corresponding retraction distance. This rapid backwards retraction of the plunger <NUM> relieves the swelling of the syringe and depressurizes the system. In one example, the rapid back-drive of the plunger <NUM> can be on the order of about <NUM>/s to <NUM>/s, for example <NUM>/s. This depressurization of the system allows the linear travel of the plunger <NUM> to coincide with the actual commanded location, irrespective of capacitance volume. In the example where the first fluid <NUM> is more viscous than the second fluid <NUM>, the process described above in reference to <FIG> and <FIG> would be switched to apply an over-travel and fast-controlled reverse pull of the plunger <NUM> within the second fluid <NUM> syringe to compensate for any undelivered second fluid <NUM> in the fluid injection system. It is also contemplated that the first fluid <NUM> and the second fluid <NUM> may have substantially equal viscosities. In this example, equal pressures may be applied to the first fluid <NUM> and the second fluid <NUM> at the outset of the process.

In typical fluid injection systems with saline and contrast medium fluids, the contrast medium has a higher viscosity than the saline. Due to this difference in viscosity, it is often difficult to apply the correct pressure to each fluid to achieve a uniform pressure between the two fluids to create a smooth flow of the mixture of the two fluids to the downstream location or sequential flow of the fluids without a flow spike at the fluid transition. As described herein, the higher viscosity of the contrast medium may cause backflow in the fluid injection system and/or swelling of the syringes holding the saline and/or contrast medium. Therefore, in one embodiment of the disclosure, the saline used in the fluid injection system may be replaced with an alternative fluid that has similar properties to saline but has a higher viscosity to substantially match the higher viscosity of the contrast medium. In one example, the saline may be replaced with a Ringers Lactate solution, which has a viscosity similar to blood or low viscosity contrast mediums. The pressure required to deliver the Ringers Lactate solution through the fluid injection system is higher than saline, which leads to a smaller difference between the pressure to move the Ringers Lactate solution and that needed to move the more viscous contrast medium resulting in lower spikes or jumps in the flow rates of the two fluids. The Ringers Lactate solution will also have a higher density than saline, which will reduce the density exchange between the Ringers Lactate solution and the contrast medium.

As shown in <FIG>, in another example of the present disclosure, the second fluid <NUM> syringe may be designed with a lower capacitance (stored volume under pressure) than conventional syringes to reduce the effect of backflow into the second fluid <NUM> syringe. In one embodiment, the first fluid <NUM> may be more viscous than the second fluid <NUM>. In an embodiment, a pressure jacket <NUM> may be provided around the outer surface of at least the second fluid <NUM> syringe to restrict the swelling in at least the second fluid <NUM> syringe due to backflow of second fluid <NUM>. By providing the pressure jacket <NUM>, the outer circumferential surface of the second fluid <NUM> syringe is reinforced, thereby limiting the amount of expansion or swelling in the second fluid <NUM> syringe. The pressure jacket <NUM> is configured to lower the capacitance of the second fluid <NUM> syringe, which results in a more accurate volume of the second fluid <NUM> being provided at the downstream location. The pressure jacket <NUM> may be made from a hard, medical-grade plastic, composite, or metal to provide the sufficient rigidity to the second fluid <NUM> syringe. It is also contemplated that an additional pressure jacket <NUM> may be provided around the outer circumferential surface of the first fluid <NUM> syringe. The pressure jacket <NUM> will assist in also lowering the capacitance of the first fluid <NUM> syringe, thereby providing more accurate volumes of the first fluid <NUM> at the downstream location. In the example where the second fluid <NUM> is more viscous than the first fluid <NUM>, the pressure jacket <NUM> may be provided on the first fluid <NUM> syringe and the additional pressure jacket <NUM> may be provided on the second fluid <NUM> syringe.

With reference to <FIG>, additional methods for reducing undesired spikes in fluid flow rates in the fluid injection system are described. In <FIG>, an obstruction member <NUM> may be provided in the second fluid <NUM> syringe to increase the fluid pressure of the second fluid <NUM> through the second fluid <NUM> syringe. In this example, the first fluid <NUM> may be more viscous than the second fluid <NUM>. In one example, the obstruction member <NUM> may include an opening <NUM> configured to increase the fluid pressure of the second fluid <NUM> based on the desired fluid pressure through the fluid injection system. In one example, the opening <NUM> may be circular. However, it is contemplated that alternative shapes for the opening may be used, along with additional openings in the obstruction member <NUM>. The obstruction member <NUM> is configured to increase the fluid pressure of the second fluid <NUM> so the second fluid <NUM> tubing of the fluid injection system does not decompress during the fluid injection process. Further, the increased fluid pressure of the second fluid <NUM> will decrease the amount of backflow that is directed to the second fluid <NUM> syringe, which may expand or swell the second fluid <NUM> syringe. The increased pressure of the second fluid <NUM> may be substantially equal to the pressure of the first fluid <NUM>. In the example where the second fluid <NUM> is more viscous than the first fluid <NUM>, the obstruction member <NUM> may be provided in the first fluid <NUM> syringe to increase the fluid pressure of the first fluid <NUM> through the first fluid <NUM> syringe.

Similar to the obstruction member <NUM> used in <FIG> to obstruct the flow of the second fluid <NUM> through the second fluid <NUM> syringe, in another example of the disclosure the second fluid <NUM> syringe may include a reduced inner diameter to create a similar obstruction. As shown in <FIG>, the inner diameter of the second fluid <NUM> syringe has been reduced from a larger diameter (shown in dashed lines) to a smaller diameter to increase the fluid pressure of the second fluid <NUM> through the fluid injection system. The inner diameter of the second fluid <NUM> syringe may be reduced in only a portion of the second fluid <NUM> syringe or the inner diameter of the second fluid <NUM> syringe may be reduced along the entire length of the second fluid <NUM> syringe. Similar to the obstruction member <NUM>, the reduced inner diameter of the second fluid <NUM> syringe is configured to increase the fluid pressure of the second fluid <NUM> so the second fluid <NUM> tubing of the fluid injection system does not decompress during the fluid injection process. Further, the increased fluid pressure of the second fluid <NUM> will decrease the amount of backflow that is directed to the second fluid <NUM> syringe, which may result in the expansion or swelling of the second fluid <NUM> syringe. The reduced inner diameter will also assist in bringing the pressure of the second fluid <NUM> to a substantially equal pressure as the first fluid <NUM>. In the example where the second fluid <NUM> is more viscous than the first fluid <NUM>, the inner diameter of the first fluid <NUM> syringe may be reduced to create a similar obstruction.

With reference to <FIG>, another method of reducing undesired spikes in fluid flow rates is described. In this example, the first fluid <NUM> may be more viscous than the second fluid <NUM>. In this example, an external restriction member <NUM> may be provided around at least a portion of the outer circumferential surface of the second fluid <NUM> syringe. The external restriction member <NUM> may be cylindrical in shape. However, it is contemplated that alternative shapes and sizes may be used with the second fluid <NUM> syringe. The external restriction member <NUM> may define an aperture through which the second fluid <NUM> syringe may be inserted. The external restriction member <NUM> may be provided via a friction-fit on the second fluid <NUM> syringe to control the flow rate of the second fluid <NUM> through the second fluid <NUM> syringe. The external restriction member <NUM> may reduce the swelling or expansion of the second fluid <NUM> syringe due to any backflow into the second fluid <NUM> syringe, thereby reducing the capacitance of the second fluid <NUM> syringe. The external restriction member <NUM> may apply pressure to the outer surface of the second fluid <NUM> syringe, thereby restricting the flow of the second fluid <NUM> through the second fluid <NUM> syringe. Pressure may be applied by the external restriction member <NUM> by decreasing the diameter of the aperture defined by the external restriction member <NUM>. It is also contemplated that the pressure applied by the external restriction member <NUM> may be controlled by the controller <NUM>. The controller <NUM> may be programmed to adjust the pressure applied by the external restriction member <NUM> and the diameter size of the aperture defined by the external restriction member <NUM> based on the fluid pressures in the fluid injection system, the capacitance of the second fluid <NUM> syringe and the first fluid <NUM> syringe, the catheter size, and the viscosities of the second fluid <NUM> and the first fluid <NUM>, among other factors. The controller <NUM> may also be programmed to adjust the diameter size of the aperture defined by the external restriction member <NUM> based on the timing of the fluid injection procedure. In the example where the second fluid <NUM> is more viscous than the first fluid <NUM>, the external restriction member <NUM> may be provided around a portion of the outer circumferential surface of the first fluid <NUM> syringe.

With reference to <FIG>, another method of reducing undesired spikes in fluid flow rates is described. In this example, the second fluid <NUM> may be more viscous than the first fluid <NUM>. This method includes the use of an equalizing flow valve <NUM> to monitor and control the flow rates of the first fluid <NUM> and the second fluid <NUM>. The equalizing flow valve <NUM> may be positioned in the fluid injection system at a location where the first fluid <NUM> tubing and the second fluid <NUM> tubing connect with one another. The equalizing flow valve <NUM> may monitor the flow rates of the first fluid <NUM> and the second fluid <NUM> and adjust an orifice defined by the equalizing flow valve <NUM> to maintain the desired delivery flow rates of the two fluids. In one example, the equalizing flow valve <NUM> may be connected to a controller <NUM>, which also actuates the motors <NUM>, <NUM> that drive the plungers <NUM>, <NUM> in the fluid injection system based on real-time feedback readings from equalizing flow valve <NUM>. Using the controller <NUM> with the equalizing flow valve <NUM>, the pressure applied by the plungers <NUM>, <NUM> can be adjusted according to the flow rates of the two fluids through the equalizing flow valve <NUM>. The controller <NUM> may be programmed to read the flow rates of the two fluids through the equalizing flow valve <NUM> and adjust the pressure applied by the plungers <NUM>, <NUM> accordingly to ensure that the second fluid <NUM> and the first fluid <NUM> have substantially equal pressures. Alternatively, the controller <NUM> and/or equalizing flow valve <NUM> may be pre-programmed according to the types of fluids used in the fluid injection system, fluid volumes, syringe features, catheter size, the capacitance of the fluid injection system, and/or the desired flow rates of the two fluids, which information may be stored in the controller <NUM>. An operator may manually input the information regarding the fluid injection system into the controller <NUM>, which will assist in adjusting the plunger <NUM>, <NUM> pressure and/or the equalizing flow valve <NUM> accordingly to obtain the desired flow rates of the two fluids.

With reference to <FIG>, another method of reducing undesired spikes in fluid flow rates is described. In this example, the first fluid <NUM> may be more viscous than the second fluid <NUM>. According to this embodiment, during operation of the fluid injection system, an operator will likely know the pressures that are to be applied by the plungers <NUM>, <NUM> and the volume of the first fluid <NUM> and the second fluid <NUM> in the fluid injection system. By determining the capacitance of the second fluid <NUM> syringe, the operator can adjust the plunger <NUM> of the second fluid <NUM> syringe accordingly to account for the extra stored volume of the second fluid <NUM> due to the capacitance of the second fluid <NUM> syringe. Using this method, the plunger <NUM> may be pulled back from the second fluid <NUM> syringe equal to a capacitance volume of the second fluid <NUM> syringe, which will reduce the pressure to zero in the second fluid <NUM> syringe. The second fluid <NUM> may then be injected at the desired flow rate without experiencing any swelling or expansion in the second fluid <NUM> syringe. It is also contemplated that the plunger <NUM> may be pulled back by an instruction from the controller <NUM>. Based on information regarding the fluid injection system, such as, fluid viscosities, catheter size, capacitance of the second fluid <NUM> syringe, and/or the volume of fluid in the fluid injection system, the controller <NUM> may be programmed to pull the plunger <NUM> from the second fluid <NUM> syringe in an amount equal to the capacitance volume of the second fluid <NUM> syringe. For example, if the second fluid <NUM> syringe capacitance is <NUM>, the plunger <NUM> may be pulled from a starting position P1 (shown in dashed lines) to a new position P2 to compensate for the extra volume that will be stored in the second fluid <NUM> syringe during the fluid injection procedure. In the example where the second fluid <NUM> is more viscous than the first fluid <NUM>, the process described above with reference to <FIG> may be used with the first fluid <NUM> syringe.

According to an embodiment, in a similar method, a test injection procedure using the first fluid <NUM> and second fluid <NUM> may be performed before the actual diagnostic phase, using the same flow rates as will be used from the diagnostic injection procedure. A pressure measurement of the first fluid <NUM> phase is obtained during the test injection procedure, which gives an indication of the expected pressure for the programmed flow rate under the current tubing and patient conditions. This measured pressure value is recorded and used during the diagnostic injection procedure to modify the flow rate of at least one of the first fluid <NUM> and the second fluid <NUM> to modify the flow rate and fluid flow profile of at least one of the first fluid <NUM> and the second fluid <NUM> to compensate for capacitance in the injector system. In one example, the flow rate modification is achieved by temporarily changing a pressure limit of one of the fluids <NUM>, <NUM> in an adaptive flow algorithm used by a controller <NUM> to control the pressures of the fluid injection system. In another embodiment, a series of flow algorithms may be programmed into a controller <NUM> or processor based on set of pre-programmed injection protocols. Alternatively, one or more algorithms may be determined and programmed into the controller <NUM> that utilize various system parameters for a specific injection setup and protocol, such as, for example, fluid volumes and types, temperature, syringe volumes and types, desired flow rates, target organ or body part for imaging, patient information, etc., where the algorithms utilize the various parameters to calculate and appropriate injection protocol for the injection procedure.

With reference to <FIG>, another embodiment of a method of providing more accurate mixing ratios is described. During current multi-fluid injection procedures, a spike in saline flow rate may occur when the fluid passing through the catheter suddenly changes in viscosity, for example during a transition from contrast to saline, resulting in a drop in the pressure at the restriction point of the catheter. During this period of pressure drop, any fluid stored in the compliance of a disposable set or system capacitance holding the fluid is released through the catheter. As shown in <FIG>, contrast medium is initially directed through the catheter. After the contrast medium has been injected, the saline is injected and begins to flow through the catheter. A transition period occurs when the flow rate of the contrast medium begins to decrease through the catheter and the flow rate of the saline begins to increase through the catheter. During this transition period, the viscosity of the fluid flowing through the catheter suddenly and quickly changes, which results in a spike of the saline flow rate through the catheter. Due to the short transition period that occurs during the switch between injecting the contrast medium and injecting the saline, an increased drop in pressure is created, which causes an increased saline flow rate spike in the fluid exiting the catheter.

As shown in one embodiment in <FIG>, by extending the transition period between injecting the contrast medium and injecting the saline, a more gradual viscosity/pressure gradient may be achieved during the injection procedure. With this extended transition period, the same volume of fluid is released over a longer period of time, so the average flow rate magnitude of the saline spike is reduced. The flow rate of the contrast medium is gradually and slowly reduced, while the flow rate of saline is gradually and slowly increased. The change in viscosity of the fluid through the catheter is gradual, resulting in a decreased drop of the pressure in the catheter. The extended transition period may be achieved in such a manner that does not increase the volume of contrast medium that is delivered during the injection procedure and does not degrade the efficacy of the injection procedure. It is also contemplated that non-linear or non-continuous extended transition periods could be used, which would result in less impact to the image taken of the patient, and taking advantage of the fluid dynamics of the fluid injection system. In other embodiments, real-time fluid flow rate measurements in a feedback loop to a processor may allow the processor to adjust the contrast and saline flow rates appropriately to minimize any spike in fluid flow rate during transition from one fluid to another.

In another example, the viscosity of the first fluid <NUM> or the second fluid <NUM> is adjusted to minimize or dampen the spike or increase in the overall flow rate during a transition between delivering one of the first fluid <NUM> and the second fluid <NUM> to delivering the other of the first fluid <NUM> and the second fluid <NUM>. In one example, a volume of the first fluid <NUM> is added to the second fluid <NUM> to dilute the overall viscosity of the second fluid <NUM>. Since the first fluid <NUM> has a lower viscosity, the first fluid <NUM> will dilute the second fluid <NUM> and reduce the overall viscosity of the second fluid <NUM>. In another example, the viscosity of the first fluid <NUM> is increased to match the viscosity of the second fluid <NUM>. By equalizing the viscosities of the fluids <NUM>, <NUM>, the transition of flow between the delivery of one of the first fluid <NUM> and the second fluid <NUM> and the delivery of the other of the first fluid <NUM> and the second fluid <NUM> does not create such a large spike or increase in the overall flow rate exiting from the catheter.

With reference to <FIG>, several methods are described for reducing undesired spikes in fluid flow rates by using several different catheter designs to control the erratic flow of fluid to the patient's blood vessel. The following methods are configured to reduce the amount of kick-back or pull out the catheter experiences when the erratic flow of the contrast medium is delivered through the fluid injection system.

As shown in <FIG>, one method of reducing kick-back in the catheter <NUM> is to provide a rigid member <NUM> along the longitudinal length of the catheter <NUM>. In one example, the rigid member <NUM> may be a wire. The rigid member <NUM> may be attached to the outer surface of the catheter <NUM> or embedded in the walls of the catheter <NUM>. The rigid member <NUM> may be configured to stiffen the catheter <NUM> from bending during injection of the erratic fluid from the fluid injection system. By stiffening the catheter <NUM> with the rigid member <NUM>, the catheter <NUM> may be less likely to kick-back or pull out of the injection site when the erratic flow is delivered through the catheter <NUM>. By reducing the kick-back of the catheter <NUM>, the catheter <NUM> may be less likely to extend into the surrounding tissue of the patient.

As shown in <FIG>, another method of reducing kick-back in the catheter <NUM> is to provide a sheath or braided member <NUM> on an outer circumferential surface of the catheter <NUM>. The sheath <NUM> may extend along the length of the catheter <NUM> or may only be provided on a distal end of the catheter <NUM>. In one example, the inner diameter of the sheath <NUM> may be substantially equal to the outer diameter of the catheter <NUM> so that the catheter <NUM> may fit within the sheath <NUM>. The sheath <NUM> may be made of stainless steel wire interlaced together, nylon, Kevlar, spectra fiber, or any other suitably flexible material that is safe to insert into a patient's blood vessel. Initially, before injection of fluid through the catheter <NUM>, the sheath <NUM> and catheter <NUM> are substantially deflated within the patient's blood vessel (<FIG>). As fluid is injected through the catheter <NUM>, the fluid expands the inner diameter of the catheter <NUM> to permit fluid to flow therethrough (<FIG>). As the catheter <NUM> expands against the inner diameter of the sheath <NUM>, the sheath <NUM> also begins to expand. The catheter <NUM> expands until the catheter <NUM> and the sheath <NUM> have expanded to their respective maximum outer diameters. The outer diameter of the sheath <NUM> may be substantially equal to an inner diameter of at least a portion of a blood vessel so that the outer diameter of the catheter <NUM> is constrained by the sheath <NUM> to keep the catheter <NUM> from expanding to a diameter larger than the diameter of a blood vessel. By keeping the outer diameter of the catheter <NUM> smaller than the blood vessel, the fluid exiting the catheter <NUM> remains coaxial with the catheter <NUM>. Since the inner diameter of the catheter <NUM> expands slowly under pressure when initially deflated, the jetting velocity and acceleration of the fluid through the catheter <NUM> is reduced, which also reduces any kick-back or rapid movement of the catheter <NUM> in the patient's blood vessel. Further, as sheath <NUM> expands against the inner wall of at least a portion of the patient's blood vessel, the sheath <NUM> may be secured to the inner walls to stabilize catheter <NUM> within the blood vessel or may seal the needle hole entrance in the blood vessel, thereby reducing the risk of rapid movement of the catheter.

As shown in <FIG>, another method of reducing kick-back in the catheter <NUM> is to provide a split tip <NUM> on the distal end of the catheter <NUM>. The split tip <NUM> may define an aperture <NUM> through which the fluid may be delivered to the patient. As shown in <FIG>, the split tip <NUM> may be configured to remain in a closed position in which the aperture <NUM> also remains closed. In this example, the split tip <NUM> will not open until a predetermined or sufficient pressure is provided by the fluid in the catheter <NUM>. With reference to <FIG>, upon reaching this predetermined pressure, the aperture <NUM> of the split tip <NUM> will open and allow the fluid to be delivered into the patient's vein. The split tip <NUM> assists in reducing the erratic flow of the fluid that is permitted to exit from the catheter <NUM>. The fluid is unable to exit into the patient's vein until the predetermined pressure is achieved, which stabilizes the fluid in the catheter <NUM> before injection into the patient. It is also contemplated that different shapes and number of apertures in the split tip <NUM> may be utilized to improve the stability of the catheter <NUM>.

As shown in <FIG>, similar to the split tip <NUM> of <FIG>, another method of reducing kick-back in the catheter <NUM> includes providing an over-molded tip <NUM> on the distal end of the catheter <NUM>. The over-molded tip <NUM> may be configured to overlap the distal end of the catheter <NUM>. The over-molded tip <NUM> may be configured to open and allow the fluid to exit the distal end of the catheter <NUM> upon the fluid reaching a predetermined or threshold pressure. As shown in <FIG>, the over-molded tip <NUM> is configured to remain closed during use of the catheter <NUM>, until a certain pressure is obtained by the fluid. Once the fluid pressure has increased to the threshold pressure, the over-molded tip <NUM> will open and move away from the opening of the distal end of the catheter <NUM> (as shown in <FIG>), thereby permitting the fluid to exit into the patient's blood vessel. The over-molded tip <NUM> assists in reducing the erratic flow of the fluid that is permitted to exit from the catheter <NUM>. The fluid is unable to exit into the patient's vein until the predetermined pressure is achieved, which stabilizes the fluid in the catheter <NUM> before injection into the patient. It is also contemplated that different shapes of the over-molded tip <NUM> may be utilized to improve the stability of the catheter <NUM>.

With reference to <FIG>, another method of reducing kick-back in the catheter <NUM> includes tapering the inside diameter of the catheter <NUM> to allow more steady flow of fluid through the catheter <NUM>. In one example, the inner diameter may start at a smaller dimension at a proximal end <NUM> of the catheter <NUM>. In this example, the inner diameter will taper or increase outwardly to the distal end <NUM> of the catheter <NUM>, which will have a larger inner diameter than the proximal end <NUM>. By tapering the inner diameter in this fashion such that the proximal end has a smaller diameter, a reduction in the proximal hoop stress on the catheter <NUM> tubing at the proximal end <NUM> of the catheter <NUM> is achieved, and a reduction in the kick-back or rapid movement of the catheter <NUM> by lowering the acceleration of the fluid as it exits the catheter <NUM> may be achieved. It is contemplated that the catheter <NUM> may begin to taper at different locations along the length of the catheter <NUM>. However, proximal end <NUM> of the catheter <NUM> will always have a smaller inner diameter than the distal end <NUM> of catheter <NUM>. It is contemplated that the dimensions of the inner diameter at proximal end <NUM> and distal end <NUM> may vary in catheter <NUM>.

With reference to <FIG>, another method of reducing kick-back in the catheter <NUM> includes providing a balloon tip <NUM> on an end of the catheter <NUM>. The balloon tip <NUM> may be made from a flexible material so the balloon tip <NUM> can be stretched. The balloon tip <NUM> may be inflatable and deflatable based on the amount of fluid that is directed through the balloon tip <NUM>. The balloon tip <NUM> may be provided on the distal end <NUM> of the catheter <NUM>. As shown in <FIG>, when fluid is not being provided through the catheter <NUM>, the balloon tip <NUM> is deflated and rests in the blood vessel <NUM> of the patient on the distal end <NUM> of the catheter <NUM>. As shown in <FIG>, upon fluid being injected through the catheter <NUM>, the balloon tip <NUM> is inflated by the liquid and is directed out of the balloon tip <NUM> via an aperture <NUM>. When fluid is directed through the balloon tip <NUM>, the balloon tip <NUM> is expanded to substantially the same inner diameter size as the blood vessel <NUM>. The balloon tip <NUM> may assist in centering the flow of the liquid through the blood vessel <NUM>. The balloon tip <NUM> may also anchor the catheter <NUM> to the inner walls of the blood vessel <NUM> to seal any puncture holes in the blood vessel <NUM> from leaking any injected fluid into the surrounding tissue. This sealing feature is particularly advantageous when the catheter <NUM> punctures through both walls of the blood vessel <NUM> and is then slightly pulled back into the blood vessel <NUM>. The balloon tip <NUM> will assist in sealing any accidental punctures in the blood vessel <NUM> walls to reduce any contrast medium or saline leaking into the surrounding tissue.

Claim 1:
A multi-fluid injection system (<NUM>) configured to maintain an overall flow rate during a sequential delivery of at least two fluids to a patient's blood vessel, the system (<NUM>) comprising:
a processor configured to control the multi-fluid injection system to:
deliver at least a first fluid into the patient's blood vessel at a first flow rate;
deliver at least a second fluid into the patient's blood vessel at a second flow rate; characterized in that
the processor is configured to adjust at least one of a first flow profile of the first flow rate and a second flow profile of the second flow rate to dampen a sudden increase or spike in the overall flow rate during a transition between delivering one of the first fluid and the second fluid to delivering the other of the first fluid and the second fluid, wherein the first fluid has a higher viscosity than the second fluid, and wherein
the processor is further configured to control the multi-fluid injection system to increase a transition time between delivering one of the first fluid and the second fluid and delivering the other of the first fluid and the second fluid; or
the processor is further configured to control the multi-fluid injection system to delay the delivery of one of the first fluid and the second fluid until the other of the first fluid and the second fluid reaches a predetermined flow rate; or
the processor is further configured to control the multi-fluid injection system to over-deliver a predetermined volume of at least one of the first fluid and the second fluid during delivery of at least one of the first fluid and the second fluid.