SYSTEMS AND METHODS FOR DETECTING EXTRAVASATION

BY TISSUE FIRMNESS

FIELD OF INVENTION

[0001] The present invention relates generally to systems and methods for injecting a substance into a target blood vessel of a subject, and more particularly to systems and methods for automatically detecting extravasation of an injected substance into tissue surrounding the target blood vessel.

BACKGROUND

[0002] Substances may be injected into the blood vessels of people and animals for various reasons. For example, there are many different kinds of contrast media that are injected intravenously to enhance viewing of various internal soft tissue features in X-Rays, magnetic resonance images (MRIs) and other imaging techniques. Other injection media, such as chemotherapies, pharmaceuticals, and some radiopharmaceuticals (i.e., pharmaceuticals that are radioactive), are injected for various diagnostic and therapeutic purposes.

[0003] Any injection of a substance to a target blood vessel poses a risk of extravasation (sometimes referred to as infiltration), wherein some or ail of the injection medium is injected into the tissue surrounding the target blood vessel rather than the blood vessel itself. Extravasation may be caused by failure to properly position the tip of the injection needle inside the target blood vessel Extravasation may also result from physiological limitations on the ability of the blood vessel to withstand the increased pressure associated with the injection. The consequences of extravasation vary depending on the nature of the injection medium. For example, extravasation may cause severe discomfort for the subject, may cause tissue damage, and may result in permanent injury in severe cases. The consequences of extravasation can also depend on the amount of the injection medium that escapes into the tissue surrounding the vessel. Thus, it is desirable to use an automated extravasation detection system to monitor for extravasation.

[0004] One prior art method of monitoring for extravasation is by manually palpating the subject's tissue to detect any tissue swelling, which can be an indication of the presence of extravasated injection medium in the tissue. Various prior art automated extravasation detection systems are known. For example, optica!, thermal, pressure, ultrasound, and electrical impedance sensors have all been used to detect extravasation.

SUMMARY

[0005] One aspect of the invention is an extravasation detection system for monitoring injection of an injection medium into a subject to detect extravasation of the injection medium into tissue surrounding a target blood vessel in the subject. The system includes a tissue firmness sensing system operable to measure a tissue firmness of the subject and output a signal indicative of the tissue firmness. A processor is operable to receive the signal from the tissue firmness sensing system. The processor has one or more of instructions and circuitry for determining whether or not there is extravasation in the subject using the signal.

[0006] Another aspect of the invention is a method of monitoring for extravasation in a subject during injection of an injection medium into the subject. The method includes moving a probe so that the probe contacts the subject. A reaction produced by contact of the subject by the probe is sensed. A signal indicative of the reaction is output. The signal is used to automatically determine whether or not there is extravasation in the subject. One or more of the following is performed upon determining that there is likely to be extravasation in the subject: (a) the injection is automatically interrupted; and (b) an extravasation alarm system is activated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a schematic diagram of one embodiment of an extravasation detection system of the present invention;

[0008] FIG. 2 is a schematic diagram of one embodiment of a probe of the extravasation detection system illustrated in Fig. 1;

[0009] FIG. 3 is an enlarged schematic diagram of the probe illustrated in Fig. 2;

[0010] FIG. 4 is a schematic diagram similar to Fig. 3, illustrating the probe contacting a subject;

[0011] FIG. 5 is a graph illustrating outputs from a sensor indicative of a reaction to contact of the subject by the probe;

[0012] FIG. 6 is a basic schematic diagram illustrating the probe contacting tissue of the subject having increased firmness because of the presence of extravasated injection medium in the subject;

[0013] FIG. 7 is a schematic diagram of another embodiment of a electromagnetically driven probe suitable for use in the extravasation system shown in Fig. 1 ; and

[0014] FIG. 8 is a schematic diagram of the probe shown in Fig. 7 in the process of contacting a subject.

[0015] Corresponding reference characters refer to corresponding parts throughout the drawings.

DETAILED DESCRIPTION

[0016] Referring now to the drawings, one embodiment of an automatic injection system, generally designated 101, is illustrated schematically in Fig. 1 in the process of injecting an injection medium (not shown in Fig. 1 ) into a subject 102 with the aim of injecting the injection medium into a target blood vessel 103 in the subject. The subject 102 can be any organism having a vascular system, including a human or other animal.

[0017] As depicted in Fig. 1, injection system 101 includes a fluid delivery system, generally designated 105, for moving the injection medium along a fluid flow path 107 for injection into subject 102. In this particular embodiment, system 105 comprises an automated power injector 109, which is generally conventional except as noted. Injector 109 is a syringe pump and includes a reservoir 111 defined by a barrel 113 of the syringe for containing a supply of the injection medium and a motor 117 that drives a piston 119 in the barrel to expel the injection medium from reservoir 111 into the subject through an injection line 121 that is in fluid communication with the reservoir and subject 102 during the injection. Injection line 121 suitably comprises a needle 141 or other catheter having an outlet 175 that can be positioned in target blood vessel 103. Although fluid delivery system 105 shown in Fig. 1 includes a syringe pump, other types of injection mechanisms, including manual injection systems and power injectors can be used instead within the scope of the invention. Likewise, the flow path may have different configurations and lengths and be defined in different ways than shown in Fig. 1 within the scope of the invention.

[0018] The injection medium can be any flowable substance that is to be injected into target blood vessel 103. For example, the injection medium may be a contrast medium that is used to enhance contrast of features in an X-Ray, MRI, ultrasound or other imaging procedures. In another embodiment, the injection medium comprises a radioisotope (e.g., Technetium-99) for conducting any of various diagnostic and/or therapeutic procedures in the field of nuclear medicine. In another embodiment, the injection medium comprises a pharmaceutical (e.g., a chemotherapeutic substance).

[0019] Figure 1 illustrates injection system 101 in combination with one embodiment of an automatic extravasation detection system 131 of the present invention. Extravasation detection system 131 has a mechanical tissue firmness sensing system 133 operable to measure tissue firmness of subject 102 and output a signal indicative of the tissue firmness to a processor 161 that uses the signal to monitor for extravasation in the subject. Extravasation detection system 131 may be integrated with injector 109, e.g., via a substantially permanent connection 167 between processor 161 and motor 117 through which the processor controls operation of the motor. Alternatively, system 131 may be a separate unit that is connected to injector 109 or another part of the injection system or a stand-alone unit within the scope of

the invention. Tissue firmness sensing system 133 may be secured to subject 102 by any suitable means. For example, adhesive tape 135 is used to secure tissue firmness sensing system 133 to the subject in Fig. 1. It is contemplated that tissue firmness sensing system 133 may be secured to subject 102 in other ways (e.g., using an arm band (not shown) to hold it adjacent subject's arm 181) or be positioned adjacent the subject without being secured thereto within the scope of the invention.

[0020] One embodiment of tissue firmness sensing system 133 is shown in Figs. 2-4. This embodiment includes a probe 201 and a system 203 for moving the probe to contact {e.g. impact) subject 102 with the probe. For instance, the embodiment shown in Figs. 2-4 suitably includes a tapping system 203 that gently taps subject 102 with probe 201. Probe 201 suitably contacts subject 102 near outlet 175 of injection line 121 or within a few inches (a few centimeters) upstream of the outlet relative to blood flow in target blood vessel 103. When target blood vessel 103 is a vein in subject's arm 181, for instance, probe 201 suitably contacts subject's arm near outlet 175 of the injection line or at a location intermediate the outlet and the subject's shoulder.

[0021] In the embodiment shown in Figs. 2-4, tapping system 203 includes a pneumatic actuator 205 (such as a bellows, for example) operable to move probe 201 to tap subject 102 with the probe. As best understood in reference to Figs. 2 and 3, probe 201 in this embodiment is secured to a free end of a bellows 205. Bellows 205 is secured to a support 207 at a location on the bellows spaced from the free end (e.g., at an end of the bellows opposite the free end as shown in Fig 2). Support 207 engages subject 102 to maintain a suitable spacing between bellows 205 and subject 102. Bellows 205 can be expanded or contracted by adjusting the pressure inside the bellows (e.g., as set forth in U.S. Patent No. 5,181 ,452). Referring to Figs. 1 and 2, for instance, a fluid line 211 connects inside 213 of bellows 205 to a high or low pressure source (not shown) via a chamber 215 defined by support 207 and communicating with interior 213 of the bellows. There is also a vent 219 for equalizing pressure in chamber 215 with the ambient pressure. A pair of valves 221, 223 (e.g., solenoid valves as indicated in Fig. 2) controlled by processor 161 allow the processor to selectively open and close fluid line 211 and vent 219, thereby allowing the processor to selectively expand and/or contract bellows 205.

[0022] In general, the free end of bellows 205 moves away from subject 102 when the bellows contracts and moves toward the subject when the bellows expands. In one embodiment, fluid line 211 is connected to a low pressure (e.g., vacuum) source. In this embodiment, processor 161 opens valve 221 in fluid line 211 to suck fluid (e.g., air) from interior 213 of bellows 205, thereby causing bellows 205 to contract for moving (e.g., lifting) probe 201 away from subject 102. When bellows 205 has contracted, processor 161 closes valve 221 in fluid line 211 and opens valve 223 in vent 219 to raise the pressure in bellows

205, thereby causing the bellows to expand (e.g., due to elastic restoration force of the bellows and/or the weight of the probe assembly in combination with the pressure increase) and probe 201 to contact subject 102. When probe 201 contacts subject 102 it suitably exerts a force on the subject in the range of about 1 gram to about 100 grams. The foregoing process is suitably repeated (e.g., periodically during an injection) to contact subject 102 with the probe multiple times and take multiple tissue firmness measurements. In one embodiment, subject 102 is contacted with the probe up to five times. In another embodiment, subject 102 is contacted with the probe up to three times,

[0023] In another embodiment, fluid line 211 is connected to a high pressure source (e.g., above ambient pressure). In this embodiment, the processor opens valve 221 in fluid line 211 to increase the pressure in bellows 205, thereby expanding the bellows. The expanding bellows 205 exerts a force on probe 201 directed toward subject 102 and causes the probe to contact the subject. The elastic restoration force of bellows 205 may be sufficient to lift probe 201 assembly away from subject 102 when processor 161 closes valve 221 in fluid line 211 and opens valve 223 in vent 219, in which case the probe can be above the subject. Probe 201 can suitably be below subject 102 in this embodiment, in which case the weight of probe 201 helps contract bellows 205 when the high pressure fluid is vented from the bellows through vent 219.

[0024] Optionally, vent 219 may be replaced with another fluid line (not shown) communicating with a pressure source that is opposite (with respect to being a high or low pressure source) the pressure source communicating with fluid line 211 so that the pressure in bellows 205 can be alternately raised above and lowered below ambient pressure by operation of valves 221 , 223 to drive both expansion and contraction of the bellows.

[0025] Probe 201 is suitably slideably received in a housing 231 that moves with the free end of bellows 205. Housing 231 defines an opening 233 at the free end of bellows 205 through which probe 201 can extend to contact subject 102. As illustrated in Fig. 2, housing 231 is suitably secured to the free end of bellows 205 so that the housing extends into interior 213 of the bellows. Housing 231 seals opening 233 from interior 213 of bellows 205. Probe 201 is suitably biased toward a position in which the probe is completely within housing 231 (Fig. 3). In the illustrated embodiment, for example, probe 201 comprises an outer sheath 242 having an annular flange 241 extending radially outward toward an inner surface 243 of housing 231, Inner surface 243 of housing 231 has shoulder 245 facing in opposition to flange 241 on probe 201. A biasing member 247 (e.g., a spring) is positioned between flange 241 and shoulder 245 so that the biasing member exerts a force on probe 201 tending to hold the probe within housing 231.

[0026] Probe 201 defines a contact surface 251 for contacting subject 102. Contact surface 251 of the probe is suitably configured to avoid causing discomfort when it contacts

subject 102. Probe 201 illustrated in Figs. 2-4 has a rounded end, for instance, thereby defining a rounded contact surface 251. Contact surface 251 is suitably broad enough so that probe 201 does not pierce subject 102. In one embodiment the footprint of contact surface 251 , which is the area A1 (Fig. 3) included in a projection of contact surface 251 onto subject 102, has an area in the range of about 0.1 to 1 cm ² . Probe 201 suitably has a relatively small mass to facilitate avoiding damage or discomfort in subject 102 when the probe contacts the subject. For example, probe 201 suitably has a mass in the range of about 1 g to 100 g.

[0027] Extravasation detection system 133 has a sensor 261 operable to measure a reaction produced by the contact between subject 102 and probe 201 and output a signal indicative of the reaction to processor 161. Sensor 261 is suitably part of probe 201. In the embodiment illustrated in Figs. 3 and 4, for instance, sensor 261 is positioned in probe 201 , suitably near contact surface 251. Various sensors can be used within the scope of the invention. Sensor 261 illustrated in Fig. 4 is a force transducer for measuring a reaction force produced by the contact between subject 102 and probe 201. Force transducer 261 may include a piezoelectric material (e.g., PZT ceramic) that generates an electrical signal in response to external forces acting on the material. The electrical signal is suitably transmitted to processor 161 through a wire 263 or other suitable means (e.g., a wireless connection). In another embodiment, (not shown) the sensor is an accelerometer for measuring deceleration of the probe produced by contact between the subject and the probe. Acceleration (deceleration in this case) and force of impact are closely related and may be used as an indication of tissue firmness in substantially the same way. Although sensor 261 in the illustrated embodiment is part of probe 201, it is also contemplated that the sensor could be separate from the probe, such as a pressure sensor (e.g., a film type sensor) secured to the subject so that probe 201 contacts subject 102 indirectly via contact with the sensor.

[0028] Processor 161 has one or more instructions and circuitry for determining whether or not there is extravasation in subject 102 using signals it receives from sensor 261. The signal produced by sensor 261 when probe 201 contacts subject 102 is a pulse. The height of the peak and duration of the signal pulse produced by contact of subject 102 by probe 201 generally increase as the subject's tissue becomes firmer. In one embodiment of the invention, processor 161 uses the peak height and/or duration of the signal pulse received from sensor 261 to determine the tissue firmness of the subject during the injection.

[0029] In another embodiment, processor 161 is suitably operable to conduct an analysis of the signal received from sensor 261 that includes one or more of: (i) normalizing the signal to account for possible variations in a momentum of probe 201 as it contacts the subject and (ii) conducting a frequency domain analysis of the signal (e.g., by Fourier transform). Suitable systems and methods for conducing frequency domain analysis of the signal and normalizing the sensor signal are known in the field of testing structures by impact

(e.g., as described in PCT App. Pub. No. WO 98/40737 and U.S. Patent No.4,542,639, both of which are hereby incorporated by reference to the extent they are consistent with this disciosυre) and need not be described in more detail herein. As illustrated in Fig. 5, the momentum of probe 201 when it contacts subject 102 can influence the shape of the signal pulse independent of tissue firmness. If probe 201 has a relatively higher momentum when it contacts the subject, the resulting signal pulse 271 H may have a relatively higher peak height and shorter duration. On the other hand, if probe 201 has a relatively lower momentum when it contacts subject 102, the resulting signal pulse 271 L may have a relatively lower peak height. Normalizing the signal and/or frequency domain analysis of the signal make extravasation detection system 131 less susceptible to variations in the speed and/or momentum of probe 201 when it contacts the subject. One suitable way to normalize the signal pulse peak height is to divide the peak height by the area under the curve defined by the signal pulse. Another normalized signal pulse parameter is the square of the area under the curve divided by the momentum of probe 201 at impact with subject 102 wherein the momentum is equal to 14 MV ² (e.g., ¹ /z mass times the square of the velocity) and the area under the frequency spectrum of the signal pulse.

[0030] Whether or not processor 161 normalizes the signal and/or conducts frequency domain analysis of the signal pulse received from sensor 261 , the characteristics of the signal pulse can be calibrated (e.g., by testing tapping system 203 on substances having known properties) so that processor 161 can correlate characteristics of the signal pulse with a tissue firmness (e.g., expressed as bulk Young's modulus) of subject 102. The tissue firmness measured by extravasation detection system 131 during the injection is compared to one or more expected tissue firmness values to at least contribute to a determination by processor 161 as to whether or not there is extravasation in subject 102. For example, the measured tissue firmness may be compared to a tissue firmness of subject 102 measured before the start of the injection, a general threshold level of tissue firmness considered indicative of extravasation in a population having characteristics similar to the subject, and/or historical tissue firmness measurements. In general, if the tissue firmness exceeds a threshold value, processor 161 makes a determination that there is (or at least that there is a substantial risk of) extravasation in subject 102. In one embodiment, tissue firmness of the subject is the only information considered by processor 161 in making this determination. In other embodiments, processor 161 uses tissue firmness of subject 102 along with other information (e.g., other measurements taken by other sensors (not shown)) to make this determination.

[0031] To use system 101, a health care worker pierce's subject 102 with the needle with the aim of positioning outlet 175 in target blood vessel 103. Except as noted, injector 109 operates in substantially the same way as a conventional injector to inject the injection medium into subject 102.

[0032] In one embodiment, tapping system 203 suitably taps subject 102 (e.g., near outlet 175) before the injection begins to establish a baseline tissue firmness for subject 102. In the iilustrated embodiment, for example, processor 161 suitably opens and closes valve 221 in fluid line 211 and valve 223 in vent 219 to cause bellows 205 to expand and contract (e.g., in one of the ways described above depending on whether the fluid line is connected to a high or a low pressure source). Probe 201 moves toward subject 102 when bellows 205 expands. Bellows 205 continues to expand until the free end of the bellows contacts subject 102, as shown in Fig. 3. Contact with subject 102 limits further movement of the free end of bellows 205 and housing 231. However, probe 201 continues to move toward subject 102 because of its momentum, sliding in housing 231 toward the subject against the bias of biasing member 247 until contact surface 251 of the probe extends through opening 233 in housing 231 and contacts the subject. Then biasing member 247 pulls probe 201 back into housing 231 and the processor moves valves 221, 223 to collapse bellows 205. The process may be repeated to tap subject 102 with probe 201 multiple times.

[0033] When probe 201 contacts subject 102, sensor 261 senses a resulting reaction (e.g., an impact force and/or deceleration) and outputs a signal indicative thereof to processor 161. The processor analyzes one or more characteristics of the signal pulse such as pulse peak height, pulse duration, normalized pulse peak height, normalized pulse duration and/or frequency domain analysis of the signal pulse to correlate characteristics of the signal pulse with tissue firmness of subject 102. The tapping of subject 102 with probe 201 is optionally repeated one or more times before the injection, in which case an average of the tissue firmness measurements obtained thereby can be used as the baseline. It is also contemplated that the extravasation detection system can wait to begin tapping the subject with probe 201 until after the injection begins.

[0034] After injector 109 begins injecting the injection medium into subject 102, tapping system 203 periodically taps the subject with probe 201 in substantially the same manner described above. Each time probe 201 contacts subject 102, sensor 261 sends a signal to processor 161 indicative of the reaction (e.g., impact force). Processor 161 uses the signal to determine the tissue firmness of subject 102. Figure 6 is a schematic illustration of an arm 181 of a subject 102 experiencing extravasation. In particular a pool 281 of extravasated injection medium in subject 102 has increased the firmness of tissue 283 overlying the pool. Thus, when tapping system 203 taps tissue 283 with probe 201 , extravasation detection system 131 detects the increase in tissue firmness caused by the extravasation and thereby recognizes that there is extravasation in subject 102.

[0035] Extravasation detection system 131 is suitably operable (e.g., programmed) to activate an extravasation alarm system and/or automatically interrupt injector 109 if it detects extravasation in subject 102. The extravasation alarm system suitably comprises a visual

indicator (e.g., an LED 165 as shown in Fig. 1) and/or a noisemaking device (not shown) to alert health care workers to the extravasation. Processor 161 suitably controls (at least partially) operation of injector 109, such as by controlling supply of power to motor 117 through a power line 167 so the processor can stop the motor to interrupt the injection. In another embodiment, the processor suitably communicates (e.g., through an electrical line or wirelessly) with a control system in the injector to automatically interrupt the injection.

[0036] Figures 7 and 8 illustrate another embodiment of a tapping system 303 suitable for use in extravasation detection system 131 of injection system 101 described above. In contrast to tapping system 203 described above, which uses a pneumatic actuator 205 to move probe 201 , this embodiment of tapping system 303 has a solenoid actuator 305 for moving probe 201. In the illustrated embodiment, for instance, probe 201 is slideably mounted in a housing 231', which is similar to housing 231 described above in that it that it includes shoulder 245 that opposes flange 241 on the probe and defines opening 233 through which the probe extends to contact the subject. Probe 201 is also slidably mounted to housing 231 ' and biased to remain in the housing by biasing member 247 in substantially the same was described above. Housing 231' includes a ferromagnetic material 321 (e.g., iron) or other substance that can be accelerated by a magnetic field. Housing 231' is slideably mounted in a sheath 331 that includes an electromagnet 341 (e.g. a conductive coil that can be selectively energized by an electrical power source) controlled by processor 161. Support structure 207 holds sheath 331 in a desired position relative to subject 102 (e.g., spaced from or in contact with the subject) when the support is in engagement with the subject, substantially as described above for the bellows-based tapping system 203.

[0037] A biasing member 347 biases housing 231' to a first (retracted) position relative to sheath 331 (Fig. 7). In this position housing 231" and probe 201 are spaced from subject 102 and support 207 structure is in engagement with the subject. Housing 231' is moveable from its first position relative to sheath 331 to a second (extended) position relative to sheath (Fig. 8). In this position housing 231' is in contact with subject 102 and support structure 207 is in engagement with the subject, as shown in Fig. 8. Further, electromagnet 341 and ferromagnetic material 321 are arranged relative to one another so activation of electromagnet 341 produces an electromagnetic field that accelerates housing 231" (e.g., via attraction of the ferromagnetic material by the electromagnet) and probe 201 toward subject 102 to at least initiate movement of the housing from its first position to its second position.

[0038] The operation of injection system 101 and extravasation detection system 131 with solenoid-based tapping system 303 is substantially the same as described above, except for the operation of tapping system 303. Operation of tapping system 303 begins with housing 231' in its first (retracted) position, as shown in Fig. 7. Processor 161 initiates a tap of subject 102 with probe 201 by activating electromagnet 341. The activated electromagnet 341

generates a magnetic fieid that accelerates ferromagnetic material 321 toward subject 102 against the bias of biasing member 347, thereby accelerating housing 231' and probe 201 toward the subject along a path toward the second (extended) position of the housing. In one embodiment, processor 161 suitably deactivates electromagnet 341 before housing 231" has reached its extended position so that housing 231' and probe 201 are not influenced by the force of the magnetic field when they contact subject 102. In this embodiment, the momentum of housing 231 ¹ causes the housing to complete its movement to the extended position after electromagnet 341 has been deactivated. However, electromagnet 341 may remain energized until after probe 201 has tapped subject 102 within the scope of the invention.

[0039] Movement of housing 231' from its first position to its second position causes the housing and probe 201 move toward subject 102 until the housing contacts subject 102. Contact of subject 102 by housing 231 ' limits further movement of the housing. The momentum of probe 201 causes the probe to continue movement toward the subject, sliding in housing 23T against the bias of biasing member 247 until contact surface 251 extends through opening 233 and contacts (e.g., taps) subject 102. Sensor 261 in probe 201 senses a reaction to the contact of subject 102 by probe 201 , which is analyzed by processor 161 to assess tissue firmness of the subject and monitor for extravasation in the subject in substantially the same manner described above.

[0040] Although electromagnet 341 and ferromagnetic material 321 of embodiment illustrated in Figs. 7-8 are arranged so the electromagnet accelerates probe 201 toward the subject, the elements can suitably be arranged so that electromagnet 341 is energized to move probe 201 away from subject 102 (e.g., lifting the probe to a position above the subject) against the force of gravity and/or the force of a biasing member biasing probe 201 to remain in contact with subject 102 so that gravity and/or the biasing force cause the probe to tap subject 102 when the electromagnet is de-energized.

[0041] When introducing elements of the present invention or the preferred embodiments thereof, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of the elements. The terms "comprising", "including" and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0042] As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.