SURGICAL INSTRUMENT WITH INJECTION NEEDLE AND RETRACTABLE SHEATH

A surgical instrument includes a housing (20), a syringe carriage (40), a movable handle (25), a shaft (30), a needle sheath (50), and a needle (60). The syringe carriage is operably coupled to the housing and configured to couple to a syringe. The movable handle is movable relative to the housing and operably coupled to the syringe carriage to distally advance the syringe carriage. The shaft extends distally from the housing and defines a lumen. The needle sheath extends through the lumen of the shaft, defines a lumen, and is movable relative to the shaft between an extended condition and a retracted condition. The needle extends through the lumen of the needle sheath and is configured to operably couple to a syringe coupled to the syringe carriage.

FIELD

This disclosure is generally related to surgical instruments and, more particularly, to surgical instruments including an injection needle and a retractable sheath for covering and uncovering a distal end of the injection needle and a surgical robotic catheter unit with an injection needle and retractable needle sheath.

BACKGROUND

Injection of drugs in robotic procedures has been accomplished by use of a long needle catheter which is typically used with an available grasper unit. Working with these catheters is somewhat challenging as the protruding catheter needle poses safety risks to users and inadvertent tissue sticks inside the patient. An additional challenge is posed when passing the catheter needle through a laparoscopic port that contains pressure seals inside.

With growing use of indocyanine green (ICG) in near infrared (NIR) imaging as a local injection for marking or mapping tissue anatomy such as lymphatic drainage, the utility of these simple catheters becomes even more problematic. Any ICG lost from the needle will be detected by the NIR imaging camera and, as this leaked ICG spreads, its ability to mark or map tissue is lost. Additionally, providing precise injection for transversus abdominis pain (TAP) blocked under direct visualization by the surgeon provides cost effective alternative uses of ultrasound by the anesthesiologist as a separate procedure. Finally, tumescent infiltration and hydrodissection are frequently used methods to separate tissues and tissue planes using various solutions of anesthetic, epinephrine, dye, and saline. The ability to monitor pressure and total injection amounts enhances patient safety.

SUMMARY

This disclosure is directed to a surgical instrument including an injection needle and a retractable sheath for covering and uncovering a distal end of the injection needle and a surgical robotic catheter unit with an injection needle and retractable needle sheath.

In accordance with aspects of the disclosure, a surgical instrument includes a housing, a syringe carriage, a movable handle, a shaft, a needle sheath, and a needle. The syringe carriage is operably coupled to the housing and configured to couple to a syringe. The movable handle is movable relative to the housing and operably coupled to the syringe carriage to distally advance the syringe carriage. The shaft extends distally from the housing and defines a lumen. The needle sheath extends through the lumen of the shaft, defines a lumen, and is movable relative to the shaft between an extended condition and a retracted condition. The needle extends through the lumen of the needle sheath and is configured to operably couple to a syringe coupled to the syringe carriage. A distal end of the needle is covered by the needle sheath when the needle sheath is in the extended condition and the distal end of the needle is uncovered by the needle sheath when the needle sheath is in the retracted condition.

In an aspect, the surgical instrument includes a lever operably coupled to the needle sheath and slidably coupled to the housing. The lever is configured to selectively move the needle sheath between the extended condition and the retracted condition.

In an aspect, the surgical instrument includes a seal coupled between an outer surface of the needle and an inner surface of the needle sheath forming a fluid-tight seal therebetween when the needle sheath is in the retracted position and forming a fluid seal when the needle sheath is in the extended condition. In an aspect, the fluid-tight seal is arranged such that when the needle sheath is fully extended the fluid-tight seal is distal of the needle tip and closes the needle sheath to fluid loss.

In an aspect, the surgical instrument includes a fluid port extending from the housing and in fluid communication with the lumen of the needle sheath.

In an aspect, a proximal end of the needle includes a luer lock for coupling to a distal end of the syringe.

In an aspect, the syringe carriage includes a gear rack and the movable handle is operably coupled to a pinion gear such that movement of the movable handle causes rotation of the pinion gear and linear translation of the gear rack of the syringe carriage. The movable handle and the pinion gear may be in ratchet engagement with each other.

In an aspect, the surgical instrument includes a kick-back assembly configured to bias the syringe carriage in a proximal direction. The kick-back assembly includes an adjustable kick-back lever, a kick-back stop including a tooth operably coupled to the gear rack of the syringe carriage, and a spring disposed between the adjustable kick-back lever and the kick-back stop. The adjustable kick-back lever is configured to selectively adjust the length of travel for the proximal bias back at the end of each injection.

In another aspect of the disclosure, a surgical instrument includes a housing, a syringe carriage, a syringe, a movable handle, a shaft, a needle sheath, a lever, and a needle. The syringe carriage is operably coupled to the housing and houses the syringe which stores a fluid therein. The movable handle is movable relative to the housing and is operably coupled to the syringe carriage to distally advance the syringe carriage and expel the fluid from the syringe. The shaft extends distally from the housing, and defines a lumen. The needle sheath extends through the lumen of the shaft, defines a lumen, and is movable relative to the shaft between an extended condition and a retracted condition. The lever is operably coupled to the needle sheath and is configured to move the needle sheath. The needle extends through the lumen of the needle sheath and is operably coupled to the syringe to deliver the fluid from the syringe.

In an aspect, a distal end of the needle is covered by the needle sheath when the needle sheath is in the extended condition and the distal end of the needle is uncovered by the needle sheath when the needle sheath is in the retracted condition.

In an aspect, the surgical instrument includes a seal coupled between an outer surface of the needle and an inner surface of the needle sheath forming a fluid-tight seal therebetween when the needle sheath is in the retracted position and forming a fluid seal when the needle sheath is in the extended condition. In an aspect, the fluid-tight seal is arranged such that when the needle sheath is fully extended the fluid-tight seal is distal of the needle tip and closes the needle sheath to fluid loss.

In an aspect, the surgical instrument includes a fluid port extending from the housing and in fluid communication with the lumen of the needle sheath.

In an aspect, a proximal end of the needle includes a luer lock for coupling to a distal end of the syringe.

In an aspect, the syringe carriage includes a gear rack and the movable handle is operably coupled to a pinion gear such that movement of the movable handle causes rotation of the pinion gear and linear translation of the gear rack of the syringe carriage. The movable handle and the pinion gear may be in ratchet engagement with each other.

In an aspect, the surgical instrument includes a kick-back assembly configured to bias the syringe carriage in a proximal direction. The kick-back assembly includes an adjustable kick-back lever, a kick-back stop including a tooth operably coupled to the gear rack of the syringe carriage, and a spring disposed between the adjustable kick-back lever and the kick-back stop. The adjustable kick-back lever is configured to selectively adjust the length of travel for the proximal bias back at the end of each injection.

In another aspect of the disclosure, a surgical instrument includes a housing, a syringe carriage operably coupled to the housing and configured to couple to a syringe, a movable handle movable relative to the housing and operably coupled to the syringe carriage to distally advance the syringe carriage, a shaft extending distally from the housing and defining a lumen, a needle sheath extending through the lumen of the shaft, and a kick-back assembly configured to bias the syringe carriage in a proximal direction. The needle sheath defines a lumen configured to receive a needle therethrough and is movable relative to the shaft between an extended condition and a retracted condition.

In accordance with yet another aspect of the present disclosure, a robotic surgical catheter unit includes a catheter head assembly, a microtube coupled to the catheter head assembly and a guidewire. The catheter head assembly includes a housing, a grasper tab extending from the housing, an injection needle extending distally from the housing, a retractable sheath moveable relative to the injection needle between an extended condition and a retracted condition, a check valve disposed within the housing, and a resilient member disposed within the housing and configured to bias the retractable sheath to the extended condition. The microtube is operably coupled to a proximal portion of the housing and configured to couple to a fluid supply. The guidewire is operably coupled to the retractable sheath and configured to control movement of the retractable sheath between the extended condition and the retracted condition.

DETAILED DESCRIPTION

In this description, the term “proximal” is used generally to refer to that portion of the device that is closer to a clinician, while the term “distal” is used generally to refer to that portion of the device that is farther from the clinician. Further, the term “clinician” is used generally to refer to medical personnel including doctors, nurses, and support personnel.

The disclosure describes a needle injection instrument, with a retractable sheath covering a needle, that includes a pump handle that provides limited and precise dosing with each squeeze of the handle. In use, the needle is covered by the retractable sheath as it is passed through a laparoscopic port and brought into close approximation to a target injection point. The retractable sheath may then be pulled back exposing the needle for immediate insertion into the target tissue with little risk of losing imaging elsewhere in the abdomen. The pump handle then enables the user to inject a precise amount of fluid (e.g., ICG solution) from the syringe while maintaining visual attention to the injection sight. Once the intended volume of fluid (e.g., ICG solution) is injected by number of counts of pumps of the handle, the retractable sheath is extended toward the tissue pushing the tissue off of the needle and covering the needle as it clears the tissue surface reducing the likelihood of any loss of fluid (e.g., ICG solution) into the abdomen or surgical area.

The disclosed surgical instrument10is designed in a manner that it can be operated with one hand, injects very small volumes of fluid at predetermined volumes for each actuation of the handle, has a shielded needle for trocar pass-through and has drip prevention features in the form of automatic drawback and a pierceable membrane at the end of the needle sheath. The needle covering (e.g., needle sheath) may be spring operated in one direction, for example distally biased to cover the needle.

FIGS.1-7illustrate an exemplary surgical instrument10in accordance with the disclosure. The surgical instrument10includes a housing20, a syringe carriage40configured to house a syringe45, and a movable handle25operably coupled to the syringe carriage40to distally advance the syringe carriage40. A shaft30defining a lumen32extends distally from the housing20and a needle sheath50extends through the lumen32of the shaft30. The instrument may also include a lever55extending through a slot21defined through the housing20and operably coupled to the needle sheath50for moving the needle sheath50relative to the housing20. The needle sheath50defines a lumen52and is movable relative to the shaft30between an extended condition and an approximated condition. A needle60extends through the lumen52of the needle sheath50and operably is coupled to the syringe45to deliver fluid from the syringe45. A distal end60bof the needle60is covered by the needle sheath50when the needle sheath50is in the extended condition and the distal end60bof the needle60is uncovered by the needle sheath50when the needle sheath50is in the retracted condition.

The lever55is coupled to the needle sheath50(e.g., at a proximal portion of the needle sheath50) and is slidable relative to the housing20. The lever55is selectively slidable by a user to move the needle sheath50between the extended condition, where the needle sheath50covers the distal end60bof the needle60, and the retracted condition, where the needle sheath50does not cover the distal end60bof the needle60. In an aspect, the lever55is biased toward one direction. A seal53is positioned at a distal end of the needle sheath50which is pierceable by the needle60as the needle sheath50is moved toward the retracted condition. The seal53may assist in limiting fluid ingress during use and prevents fluid egress when the needle60is shielded by the needle sheath50(e.g., when in the retracted condition). The fluid-tight seal is arranged such that when the needle sheath50is fully extended, the fluid-tight seal is distal of the needle tip and closes the needle sheath50to fluid loss.

A fluid port54extends from the housing20for connection to a vent or suction device (not shown). The fluid port54is in fluid communication with the lumen52of the needle sheath50, thereby forming a fluid path between an outer surface of the needle60and the inner surface of the needle sheath50when the needle60is positioned through the lumen of52of the needle sheath50. The fluid port54may capture fluid escaping from the residual pressure in the needle60or the injected tissue. The surgical instrument10may also include a shut-off to the fluid port54extending from the housing and in communication with the lumen52of the needle sheath50such that when the needle sheath50is retracted proximally the fluid port54is closed. For example, a proximal end of the needle sheath50may end in a compartment and when positioned all the way proximally (e.g., in the retracted-most position) blocks the fluid port54from the compartment to the luer of the fluid port54to prevent the flow of fluid therethrough.

A proximal end of the needle60includes a luer lock64for coupling to a distal end of a syringe45secured to the syringe carriage40. The syringe45is configured to house fluid (e.g., drugs, imaging fluids, etc.) for delivery through the needle60into a target site upon actuation of the syringe carriage40to which the syringe45is coupled. In particular, the syringe carriage40is coupled to the movable handle25in a rack and pinion arrangement such that when the movable handle25is moved toward a fixed handle (not shown) of the housing20, or otherwise actuated, the syringe carriage40moves a plunger (not shown) of the syringe45thereby causing fluid to expel from the syringe45and through the needle60. Each actuation of the movable handle25causes a precise predetermined dose of fluid to be delivered from the syringe45.

The syringe carriage40includes a gear rack40gdefined along its bottom surface which is meshingly engaged with a pinion gear25grotatably controlled by movement of the movable handle25. In one aspect, the pinion gear25gis coupled to the movable handle25in a ratchet engagement. Movement of the movable handle25causes rotation of the pinion gear25gwhich, in turn, causes longitudinal translation of the gear rack40g.

With particular reference toFIGS.5and6, the surgical instrument10may also include a kick-back assembly80configured to bias the syringe carriage40in a proximal direction or otherwise prevent drippage of fluid from the distal end60bof the needle60(e.g., after fluid is delivered therefrom). The kick-back assembly80may be selectively adjustable (e.g., by a user) to adjust the distance the kick-back withdraws the syringe carriage40. The kick-back assembly80includes an adjustable kick-back lever81extending through the housing20and selectively adjustable by a user, a kick-back stop84rotatable relative to the housing20about a pivot point20p, and a spring82. The kick-back stop84includes an arm83on one side of the pivot point20pand a tooth85on the other side of the pivot point20p. The spring82is positioned between the kick-back lever81(e.g., along a camming surface of the kick-back lever81) and the arm83of the kick-back stop84and provides a biasing force against the arm83of the kick-back stop84. The tooth85of the kick-back stop84is operably coupled to the gear rack40gof the syringe carriage40. The adjustable kick-back lever81is configured to selectively adjust the travel of the spring82against the arm83of the kick-back stop84to, in turn, adjust the distance the syringe carriage40can be withdrawn proximally.

The surgical instrument10is illustrated as a manually actuatable surgical instrument, but it is appreciated that surgical instrument10may be an electrically powered surgical instrument including an electrically powered handle assembly that may support one or more batteries (not shown). It is envisioned that the disclosed aspects could also be incorporated into a surgical instrument that is configured for use with a robotic system that does not include a handle assembly, or to a surgical instrument including a manually actuated handle assembly.

Turning toFIGS.8-10, a surgical robotic system1000with a robotic surgical catheter unit having an injection needle and a retractable sheath for covering the injection needle will now be described. The surgical robotic system1000includes a surgical console, a control tower, and one or more movable carts having a surgical robotic arm coupled to a setup arm. The surgical console receives user input through one or more interface devices, which are interpreted by the control tower as movement commands for moving the surgical robotic arm. The surgical robotic arm includes a controller, which is configured to process the movement command and to generate a torque command for activating one or more actuators of the robotic arm, which would, in turn, move the robotic arm in response to the movement command.

With reference toFIG.8, a surgical robotic system1000includes a control tower200, which is connected to all of the components of the surgical robotic system1000including a surgical console300and one or more robotic arms400. Each of the robotic arms400includes a surgical instrument, for example, a stapler, grasper, forceps, catheter head unit1500, or any other surgical instrument removably coupled thereto. Each of the robotic arms400is also coupled to a movable cart600.

The surgical instrument is configured for use during minimally invasive surgical procedures. In embodiments, the surgical instrument may be configured for open surgical procedures. In embodiments, the surgical instrument may be an endoscope, such as an endoscopic camera510, configured to provide a video feed for the user. In further embodiments, the surgical instrument may be an electrosurgical forceps configured to seal tissue by compressing tissue between jaw members and applying electrosurgical current thereto. In yet further embodiments, the surgical instrument may be a surgical stapler including a pair of jaws configured to grasp and clamp tissue while deploying a plurality of tissue fasteners, e.g., staples, and cutting stapled tissue.

One of the robotic arms400may include the endoscopic camera510configured to capture video of the surgical site. The endoscopic camera510may be a stereoscopic endoscope configured to capture two side-by-side (i.e., left and right) images of the surgical site to produce a video stream of the surgical scene. The endoscopic camera510is coupled to a video processing device560, which may be disposed within the control tower200. The video processing device560may be any computing device as described below configured to receive the video feed from the endoscopic camera510, perform image processing based on the depth estimating algorithms, and output the processed video stream.

The surgical console300includes a first display320, which displays a video feed of the surgical site provided by camera510disposed on the robotic arms400, and a second display340, which displays a user interface for controlling the surgical robotic system1000. The first and second displays320and340may be touchscreens allowing for displaying various graphical user inputs.

The surgical console300also includes a plurality of user interface devices, such as foot pedals360and a pair of handle controllers380aand380bwhich are used by a user to remotely control robotic arms400and any surgical instrument(s) coupled thereto.

The control tower200includes a display230, which may be a touchscreen, and outputs on the graphical user interfaces (GUIs). The control tower200also acts as an interface between the surgical console300and one or more robotic arms400. In particular, the control tower200is configured to control the robotic arms400, such as to move the robotic arms400and the corresponding surgical instrument, based on a set of programmable instructions and/or input commands from the surgical console300, in such a way that robotic arms400and the surgical instrument execute a desired movement sequence in response to input from the foot pedals360and the handle controllers380aand380b.

Each of the control tower200, the surgical console300, and the robotic arm400includes a respective computer210,310,410. The computers210,310,410are interconnected to each other using any suitable communication network based on wired or wireless communication protocols. The term “network,” whether plural or singular, as used herein, denotes a data network, including, but not limited to, the Internet, Intranet, a wide area network, or a local area networks, and without limitation as to the full scope of the definition of communication networks as encompassed by the present disclosure. Suitable protocols include, but are not limited to, transmission control protocol/internet protocol (TCP/IP), datagram protocol/internet protocol (UDP/IP), and/or datagram congestion control protocol (DCCP). Wireless communication may be achieved via one or more wireless configurations, e.g., radio frequency, optical, Wi-Fi, Bluetooth (an open wireless protocol for exchanging data over short distances, using short length radio waves, from fixed and mobile devices, creating personal area networks (PANs), ZigBee® (a specification for a suite of high level communication protocols using small, low-power digital radios based on the IEEE 122.15.4-2003 standard for wireless personal area networks (WPANs)).

The computers210,310,410may include any suitable processor (not shown) operably connected to a memory (not shown), which may include one or more of volatile, non-volatile, magnetic, optical, or electrical media, such as read-only memory (ROM), random access memory (RAM), electrically-erasable programmable ROM (EEPROM), non-volatile RAM (NVRAM), or flash memory. The processor may be any suitable processor (e.g., control circuit) adapted to perform the operations, calculations, and/or set of instructions described in the present disclosure including, but not limited to, a hardware processor, a field programmable gate array (FPGA), a digital signal processor (DSP), a central processing unit (CPU), a microprocessor, and combinations thereof. Those skilled in the art will appreciate that the processor may be substituted for by using any logic processor (e.g., control circuit) adapted to execute algorithms, calculations, and/or set of instructions described herein.

The surgical robotic catheter unit1500can be operated remotely and via a user interface of a robotic console controlled by a surgeon. The user interface is customizable per the user's needs. The robotic catheter unit1500is configured to inject very small volumes of fluid (e.g., ICG), has a shielded needle for trocar pass through, and has drip prevention features, for example in the form of a check valve, and a pierceable membrane at the end of its needle sheath. The needle covering may be spring operated in one direction (for example, distally).

The robotic catheter unit1500includes a catheter head assembly1510(FIG.9) and is coupled to a syringe pump1200(FIG.8) via a double lumen micro tube1250. The catheter head assembly1510includes a housing1580with a grasper tab1582extending outwardly from a side of the housing1580and a retractable sheath1550extending distally from the housing1580and movable relative to the housing1580. A distal portion of a guidewire1275is operably coupled to the retractable sheath1550such that when the guidewire1275is pulled proximally, the retractable sheath1150also moves proximally (e.g., retracted). An injection needle1560is in fluid communication with the micro tube1250, extends distally from the housing1580and may be at least partially disposed within the housing1580. A resilient member1570(e.g., a spring mechanism) and a check valve1590are disposed at least partially within the housing1580. The resilient member1570is configured to bias the retractable sheath1550distally, that is, to a position where the retractable sheath1550covers at least a distal end of the injection needle1560. The retractable sheath1550is also connected to a guidewire1275, which when pulled proximally, in turn pulls the proximal side of the retractable sheath1550relative to the injection needle1560to uncover the distal end of the injection needle1560.

The check valve1590is placed in the catheter head assembly1510so that it can open when sufficient pressure is applied otherwise it will not allow fluid to pass through, thereby preventing any dripping of fluid from the catheter head assembly1510(e.g., to inside the abdominal body cavity).

The grasper tab1582of the catheter head assembly1510is dimensioned such that it can be easily held by a grasper unit (e.g., grasper unit1600inFIG.10). In particular, the shape form and size of the grasper tab1582is configured to be easily grasped by a variety of robotic grasper units, for example, a grasping device coupled to a robotic arm or a hand-held grasping device held by an operator.

A distal portion of the double lumen micro tube1250is connected to a proximal portion of the housing1580of the catheter head assembly1510and directly to the injection needle1560. A proximal end the double lumen micro tube1250is configured to be connected to a fluid supply, for example a syringe connected to a syringe pump1200(FIG.8). One tube of the double lumen micro tube1250is used to pass the fluid from a syringe in the syringe pump1200to the injection needle1560. The other tube of the double lumen micro tube1250may be used to carry the guidewire1275for controlling movement of the retractable sheath1550.

The syringe pump1200and mechanisms for controlling the positioning of the guidewire1275are coupled to, and controlled by, the robotic control tower200for providing precise dosage delivery by the syringe pump1200and for providing precise control of the movement and position of the guidewire1275to control the position of the retractable sheath1550over the injection needle1560. At the surgical console300, the user interface provides data corresponding to the position of the retractable sheath1550, the injection pressure, and the total injected volume for the procedure and for the current injection (as some injectables may have a limited total dose).

In an aspect, the injection pressures are derived from a force on the syringe pump1200or, for more precision, an inline sensor (not shown) attached to the micro tube1250(e.g., at the syringe pump1200or at any portion of the catheter head unit1500). The injection pressure may be further refined by subtracting the opening pressure of a valve (e.g., check valve1590) through which the injectable passes. The opening pressure may be determined dynamically by the system or as predetermined calibration value.

Automated feedback on the pressure provides a more precise determination of the injection location. For example, the algorithms may be based on an injection rate and back-pressure values since the volume of fluid is being absorbed into the tissue particularly avoiding vessels where fluid back-pressure will be particularly low or solid tissue, where the fluid pressure will rise quickly. In other areas, the injection volume and/or back-pressure may be tied to the camera view providing correlation of volume, pressure, and observed tissue bulge.

During operation, the catheter head assembly1510can be inserted into the abdominal body cavity by a small push force through a 10 mm trocar unit. While inserting the catheter head assembly1510, the retractable sheath1550is covering the injection needle1560so that it may be safely placed inside the body cavity without damaging trocar pressure seals and without injuring internal organs. The catheter head assembly1510can be navigated to the intended surgical area and positioned within the body cavity by a robotic or surgical grasper unit (e.g., by a surgical/robotic grasper inserted into another trocar unit different from the one in which the catheter head assembly1510is inserted through).

Once the catheter head assembly1510reaches the injection target, tissue, or vessel, the retractable sheath1550can be pulled back by the guidewire1275which will expose a sharp distal end of the injection needle1560. The injection needle1560is further guided into the tissue by a grasper unit1600(FIG.10) grasping the grasper tab1582of the catheter head assembly1510. Once the injection needle1560is inserted, the syringe pump1200can be operated to pass the required amount of solution to the intended tissue. Solutions may include, for example, solutions used for tumescent surgery, local injection of fluorophores (ICG) or anesthetic solutions, or any other injectable. Once the injection of fluid is complete, the injection needle1560can be pulled back by the grasper unit1600grasping the grasper tab1582and the retractable sheath1550can be controlled and/or biased to cover the injection needle1560. Additionally, or alternatively, the tissue may be pushed from the injection needle1560by deploying the retractable sheath1550and/or enabling the deployment of the retractable sheath1550(e.g., by releasing the guidewire1275). The check valve1590will operate based on the set pressure and will not allow fluid coming from the micro tube1250to drip out of the tip of the injection needle1560.

The disclosed catheter unit assists to reduce ICG lost from the needle and does not reduce the quality of the NIR imaging camera and system, thereby improving its ability to mark or map the tissue. Additionally, the design of the catheter unit reduces safety risks to users and inadvertent tissue sticks inside the patient. Additionally, the disclosed catheter unit reduces the risk of damaging laparoscopic ports that contain pressure seals inside when the catheter unit is passed through the port. The disclosed catheter unit is compatible with robotic platforms and is easily customizable to meet user needs by using a syringe pump and an ECU unit. This system can be operated remotely and improves the current standard of care for catheter injection needles. The total amount of fluid injected over time may be monitored by the system to assure safe and accurate dosing. The back-pressure provides automated feedback to ensure that the injected solution is going into the correct location, not solid tissue (high pressure) or a vessel (low pressure).