Method for counting and locating surgical sponges

Abstract

A method for counting and retrieving surgical sponges using a surgical sponge management system. Potential duplicate sponges are identified based on a unique identifier from an RFID tag and a received signal strength indicator (RSSI) value. The RSSI value from the second detection can be compared to an RSSI threshold. If the RSSI value is equal to or greater than the RSSI threshold, a duplicate sponge notification is presented on a display interface. The RSSI threshold can be a fixed value or can be based on sponge type or tag type. A scan-specific RSSI threshold can be based on the RSSI value and / or the transmission frequency associated with the first detection of the sponge being counted out. The methods disclosed herein can provide for excluding two or more subsets of surgical sponges from a search for surgical sponges using an RFID scanner.

Description

[Technical Field]

[0001] Priority claims This application claims priority to and the full benefit of U.S. Provisional Patent Application No. 63 / 424,601, filed November 11, 2022, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] During surgical procedures, it is essential to have an accurate inventory of surgical sponges that are "counted in" for use in the surgical field and those that are "counted out" before the end of the surgical procedure. Medical personnel follow strict procedures due to the risks associated with inadvertently leaving surgical sponges in the patient. Traditionally, medical personnel have relied on manually counting surgical sponges, but manual counting requires handling and exposure to contaminated surgical sponges and is prone to human error. Recently, surgical sponges have been fitted with radiopaque markers, bar codes, and / or wireless transponders, such as radio frequency identification (RFID) tags, to facilitate wireless electronic counting of surgical sponges using a data reader.

[0003] The RFID tag can uniquely identify each surgical sponge. Instances exist where a user may unintentionally or intentionally present a surgical sponge to a data reader that has already been counted out. The system can be configured to provide a notification or alert that a duplicate sponge has been presented. One exemplary manner in which this is done is disclosed in commonly owned U.S. Patent Application Publication No. 2022 / 0246288, published August 4, 2022, the contents of which are incorporated herein by reference in their entirety. The notification can help a user recognize that they have unintentionally mishandled a sponge (e.g., presented sponge A to the data reader and counted out, placed sponge B in a counting or collection bag, and then re-presented sponge A to the data reader).

[0004] In instances where a data reader detects sponges that have already been counted out but are only gathered relatively close to the data reader, duplicate sponge notifications can be annoying to the user. In other words, the user does not actually present the duplicate sponges to the data reader, but the data reader detects sponges gathered nearby. In these instances, the duplicate sponge notifications may not represent “true duplicate” sponges being counted out, and repeated notifications may be unwarranted. A similar problem may arise in virtual count-in situations, where the detected sponges are not “true count-out” sponges. Certain systems may use a data reader at a lower power level when counting out surgical sponges to prevent unwarranted duplicate notifications. However, doing so may make it more difficult for the data reader to detect sponges the user wants to count out. The user may undesirably need to move items closer to the data reader, improve alignment, and / or make other time-consuming changes to reliably count out sponges. Thus, there is a need in the art to provide duplicate sponge notifications in a more accurate manner without disrupting surgical workflow.

[0005] Electronic counting of surgical sponges beneficially notifies the user whether there are any surgical sponges remaining counted in, and if so, the sponges need to be searched or located. Existing systems can provide alerts to guide the user toward sponges to be located. However, there are instances where a user may have counted in several sponges but would like to locate only a subset of these sponges, and in particular, a specific subset of these sponges. Thus, there is a further need in the art to provide a means to locate specific sponges while excluding others from the search. Summary of the Invention

[0006] The present disclosure is directed to a surgical sponge management system for managing an inventory of surgical sponges during a surgical procedure, thereby preventing surgical sponges from being left behind in a patient. An aspect of the present invention is a system that includes means for detecting duplicate surgical sponges based not only on the RFID tag but also on the received signal strength indicator (RSSI) value from the RFID tag. This allows a sponge to be placed closer to the reader without being detected as a duplicate. Thus, the system can use higher power for counting operations without resulting in undue duplicate sponge notifications. In one embodiment, the system indicates to the user that a sponge is a duplicate if it is detected with an RSSI value equal to or greater than a predetermined RSSI threshold or a scan-specific RSSI threshold. For example, one or more RSSI values ​​can be associated with a tag type. In another example, one or more RSSI values ​​detected when a sponge is first counted out can be used to determine a scan-specific threshold. In addition to the RSSI value, the scan-specific threshold can be based on the transmit frequency associated with the first detection of the sponge being counted out and / or the nominal frequency response spectrum of the tag type. The scan-specific RSSI threshold can be correlated to the frequency hopping of the reader. Scan-specific RSSI thresholds can take into account that tags respond differently to different frequencies based on, for example, the orientation and distance between the tag and the reader.

[0007] Thus, a method for counting surgical sponges using a sponge management system in a surgical procedure includes: an RFID scanner detecting a first detection of an RFID tag on a first one of the surgical sponges. A unique identifier stored on the RFID tag is received by a processor (or two or more processors). The first surgical sponge is identified by the processor as having been counted out of the surgical procedure. The RFID scanner detects a second detection. The second detection can be a detection of the RFID tag on the first surgical sponge or another RFID tag on a second one of the surgical sponges. A response signal of the unique identifier or another unique identifier is received by the processor. If the unique identifier associated with the second detection matches the unique identifier associated with the first detection, the first surgical sponge is identified by the processor as a candidate duplicate sponge. A received signal strength indicator (RSSI) value as an indication of the power level of the response signal from the second detection of the RFID tag is determined by the processor. If the RSSI value meets a predetermined RSSI threshold, a duplicate sponge notification is presented on a display interface indicating the candidate duplicate sponge is a duplicate sponge.

[0008] Another method for counting surgical sponges using a sponge management system in a surgical procedure includes an RFID scanner detecting a first detection of an RFID tag on a first one of the surgical sponges. A unique identifier stored on the RFID tag is received by a processor. The first surgical sponge is identified by the processor as having been counted out of the surgical procedure. The RFID scanner detects a second detection of the RFID tag on the first surgical sponge or detects another RFID tag on a second one of the surgical sponges. A response signal of the unique identifier or another unique identifier is received by the processor. If the unique identifier associated with the second detection matches the unique identifier associated with the first detection, the first surgical sponge is identified by the processor as a potential duplicate sponge. A received signal strength indicator (RSSI) value is determined by the processor as an indicator of the power level of the response signal from the second detection of the RFID tag. A tag type or sponge type is determined by the processor based on the unique identifier associated with the second detection. A predetermined RSSI threshold associated with the tag type or sponge type is accessed from a database. If the RSSI meets a predetermined RSSI threshold, a duplicate sponge notification is presented on the display interface indicating that the duplicate sponge candidate is a duplicate sponge.

[0009] Yet another method for counting surgical sponges using a sponge management system in a surgical procedure includes an RFID scanner detecting a first detection of an RFID tag on a first one of the surgical sponges. A unique identifier stored on the RFID tag is received by a processor. A first received signal strength indicator (RSSI) value is determined using the processor as an indication of the power level of a response signal from the first detection of the RFID tag. The first surgical sponge is identified as having been counted out of the surgical procedure using the processor. The RFID scanner detects a second detection of the RFID tag on the first surgical sponge or another RFID tag on a second one of the surgical sponges. A response signal of the unique identifier or another unique identifier is received by the processor. When the unique identifier associated with the second detection matches the unique identifier associated with the first detection, the first surgical sponge is identified as a potential duplicate sponge using the processor. A second RSSI value is determined using the processor as an indication of the power level of a response signal from the second detection of the RFID tag. If the second RSSI value meets a scan-specific RSSI threshold, a duplicate sponge notification is presented on the display interface indicating that the duplicate sponge candidate is a duplicate sponge.

[0010] Yet another method for counting surgical sponges using a sponge management system in a surgical procedure includes: an RFID scanner detecting a first detection of an RFID tag of a first one of the surgical sponges; a response signal of a unique identifier stored on the RFID tag is received by a processor; the processor determines whether the first surgical sponge has not been counted into the surgical procedure or another surgical procedure based on the unique identifier; a received signal strength indicator (RSSI) value as an indication of the power level of the response signal from the detection of the RFID tag is determined using the processor; the processor compares the RSSI value with an RSSI threshold and, if the RSSI value is equal to or greater than the RSSI threshold, identifies the first surgical sponge as virtually counted into the surgical procedure; unique identifiers of the remaining surgical sponges from the bundle associated with the first surgical sponge that has not been counted into the surgical procedure are accessed from memory; the processor identifies the remaining surgical sponges as being counted into the surgical procedure; and a display interface presents an inventory of the surgical sponges. The first surgical sponge in the bundle is identified as being counted out, and the remaining surgical sponges in the bundle are identified as being counted in.

[0011] Another aspect of the present disclosure is the ability to exclude certain sponges from a search for surgical sponges via guidance from the reader. In one example, the sponges to be excluded can be scanned. In another example, the sponges to be excluded can be selected on a user interface.

[0012] Thus, a method for retrieving surgical sponges using a sponge management system is provided. Input is received from a user on a display interface locating fewer than all of two or more of the surgical sponges that remain counted in. An RFID tag of at least one of the surgical sponges to be the surgical sponge to be discarded is detected using an RFID scanner. A unique identifier stored on the RFID tag is received by a processor. The surgical area is scanned using the RFID scanner. Two or more of the surgical sponges that remain counted in are detected by the RFID scanner. Feedback is provided by the RFID scanner to guide the user to the location of at least one of the two or more of the surgical sponges that remain counted in. The processor causes the RFID scanner to not provide feedback regarding the discarded surgical sponge based on the unique identifier of the discarded surgical sponge.

[0013] Another method for retrieving surgical sponges using a sponge management system includes a display interface that receives a first input from a user locating fewer than all of two or more of the surgical sponges that remain counted in. A second input is received from the user on the display interface that includes at least one of the surgical sponges that will be an excluded surgical sponge, and a unique identifier stored on an RFID tag is received by a processor. The surgical area is scanned with an RFID scanner. Two or more of the surgical sponges that remain counted in are detected by the RFID scanner. Feedback is provided by the RFID scanner to guide the user to the location of at least one of the two or more of the surgical sponges that remain counted in. The processor causes the RFID scanner to not provide feedback regarding the excluded surgical sponge based on the unique identifier of the excluded surgical sponge.

[0014] Yet another method of searching for surgical sponges using a sponge management system includes a display interface receiving a first input from a user locating fewer than all of two or more of the surgical sponges that remain counted in. An RFID tag of at least one of the surgical sponges to be the surgical sponge to be excluded is detected using an RFID scanner. A unique identifier stored on the RFID tag is received by a processor. A second input including at least one of the surgical sponges to be excluded is received from the user on the display interface. The unique identifier stored on the RFID tag is received by the processor. The display interface displays the excluded surgical sponge as being included again in the search based on the second input. An RFID scanner scans an area of ​​the surgical procedure where two or more of the surgical sponges that remain counted in are detected by the RFID scanner. The RFID scanner provides feedback to guide the user to the location of at least one of the two or more surgical sponges that remain counted in. The processor causes the RFID scanner to not provide feedback regarding the excluded surgical sponge based on the unique identifier of the excluded surgical sponge. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view of a surgical sponge management system. [Figure 2] FIG. 1 is a perspective view of a bundle of surgical sponges. [Figure 3] It is a surgical sponge. [Figure 4] 1 is a plot of return signal strength indicator (RSSI) values ​​versus transmission frequency for several RFID tags. [Figure 5] 10 is a screenshot of a display interface for implementing a method for excluding one or more surgical sponges from a search. [Figure 6]10 is a screenshot of a display interface for implementing a method for excluding one or more surgical sponges from a search. [Figure 7] 10 is a screenshot of a display interface for implementing a method for excluding one or more surgical sponges from a search. [Figure 8] 10 is a screenshot of a display interface for implementing a method for excluding one or more surgical sponges from a search. [Figure 9] 1 is a flow chart of a method for counting surgical sponges. [Figure 10] 1 is a flow chart of a method for retrieving a surgical sponge. DETAILED DESCRIPTION OF THE INVENTION

[0016] FIG. 1 illustrates a surgical sponge management system 10 including a stand 12, an electronic subsystem 14, and a dispenser assembly 15. The stand 12 includes a wheeled base 18 for moving the surgical sponge management system 10 within a medical facility. The stand 12 may include a main support 19 coupled to and extending upwardly from the base 18. The dispenser assembly 15 is configured to store and ergonomically dispense a sponge sorter 34 and surgical drapes. At least one arm 17 is movable from a non-deployed position to a deployed configuration in which the arm 17 extends outward, as shown in FIG. 1. The arm 17 is configured to support the sponge sorter 34. The sponge sorter 34 may be hung or suspended from the arm 17, and surgical sponges 32 may be received in pockets of the sponge sorter 34, most often after being counted out of a surgical procedure.

[0017] The electronic subsystem 14 is supported by a main support 19. The electronic subsystem 14 includes a module base 20, a display interface 22, and a data reader 24. The module base 20 can include a mount 26, to which the display interface 22 is removably coupled. The display interface 22 can be a tablet that displays a graphical user interface (GUI). The tablet can include the processor 16, or alternatively, the tablet can provide wireless connectivity to a remote resource, such as a hospital network or Internet server, for remote processing. The module base 20 can define a cradle 28 configured to removably couple with the data reader 24. The illustrated embodiment shows the cradle 28 to be a recess sized to receive and support the data reader 24.

[0018] Data reader 24 is configured to be used as a handheld device or while supported by cradle 28, and is configured to seamlessly transition between configurations. More particularly, when supported by cradle 28, surgical sponge 32 can be brought close to data reader 24 for data reader 24 to detect a unique identifier associated with a tag associated with sponge 32. If bringing the surgical sponge close to data reader 24 is not feasible or otherwise desirable, data reader 24 can be efficiently removed from cradle 50 and activated in proximity to tag 30 associated with the surgical sponge.

[0019] As used hereinafter, data reader 24 refers to an RFID scanner 24 configured to detect tag 30 associated with sponge 32. RFID scanner 24 includes physical components and operating software for generating interrogation signals and receiving responses to the interrogation signals. The physical components may include a signal-generating transmitter and a signal receiver or transceiver, as disclosed, for example, in commonly owned International Patent Application Publication No. WO 2021 / 041795, published March 4, 2021, and commonly owned International Patent Application Publication No. WO 2021 / 097197, published May 20, 2021, each of which is incorporated herein by reference in its entirety. Exemplary tags other than RFID tags are disclosed in commonly owned International Patent Application Publication No. WO 2017 / 112051, published June 29, 2017, each of which is incorporated herein by reference in its entirety. Similarly, other wireless detection technologies may be implemented, particularly those in which the strength of a response signal from an interrogation signal can be determined.

[0020] Referring now to FIG. 2 , a bundle 36 of surgical sponges 32 is shown. The bundle 36 may include a master tag 38 that stores identification data associated with the bundle 36. The data may include the number of sponges 32 in the bundle 36 and / or a unique identifier for each of the sponges 32 contained therein. As used herein, a surgical sponge 32 may be any absorbent article, including, but not limited to, a laparotomy pad, gauze, towel, zipper, etc. Additionally, as an alternative to surgical sponges, it should be understood that the subject matter of the present disclosure may be modified for use with non-absorbent surgical articles, including implants, clips, staples, or surgical instruments. For example, commonly owned U.S. Patent Application Publication No. 2019 / 0000589, published January 3, 2019, which is incorporated herein by reference, discloses embodiments in which scannable and human-readable elements are disclosed on forceps and suture needles.

[0021] Each sponge 32 may include an absorbent body 40 and a tag 30 coupled to the body 40. The tag 30 may be incorporated, adhered, or encapsulated within a layer of the body 40 and / or positioned near an edge or corner of the surgical sponge 32. As used hereafter, tag refers to an RFID tag 30 that is detectable by the RFID scanner 24. The RFID tag 30 may include a capacitor and an antenna (not shown) that receives power from the RFID scanner to charge the capacitor of the RFID tag 30. The RFID tag 30 may have an integrated circuit, which may have readout capabilities, carrier frequency modulation capabilities, and a read-only memory portion with burn-in code. The RFID tag 30 may operate at frequencies below the megahertz (MHz) range, in the MHz range, or above the MHz range. Exemplary frequencies can include approximately 13.35-14.15 MHz (high frequency), 850-950 MHz (ultra-high frequency), or 2.45-2.55 GHz (microwave frequency), among others.

[0022] The RFID tag 30 facilitates counting and identification of the sponges 32. The RFID tag 30 can further facilitate locating the sponges 32 within the surgical field. The RFID tag 30 includes a unique identifier for the sponge 32 on which the RFID tag 30 is attached. The identification scheme can include a serial number or other identifier that is unique or assigned only to a corresponding one of the sponges 32. For example, the RFID tag 30 can be manufactured with a tag identification (TID) assigned by the manufacturer of the tag integrated circuit (TIC). The TID is typically stored in a one-time writeable memory location, also known as a read-only memory location, on the TIC. Thus, each sponge 32 includes an RFID tag 30 that stores a unique identifier, i.e., a sponge ID (see FIG. 7). In addition to the sponge ID, other identifiers can include tag type, size, weight, manufacturing date, expiration date, and other information about the sponge 32. Other features of the identification scheme are disclosed in the aforementioned U.S. Patent Application Publication No. 2022 / 0246288.

[0023] The RFID tag 30 communicates the unique identifier by transmitting an electromagnetic signal or wave corresponding to the unique identifier. The processor 16 may be configured to evaluate the strength of the response signal received from the RFID tag 30 and assign a value indicative of the strength of the received signal response. In other words, the system 10 reports the power level of the backscattered response signal relative to the power level of the initial transmission signal from the RFID scanner 24. The response signal strength indicator (RSSI) value may be used to evaluate the quality of the response within the interrogation zone of the RFID scanner 24.

[0024] The data is transmitted to processor 16, from which system 10 manages an inventory of sponges 32 during a surgical procedure. In particular, processor 16 can be configured to identify sponges 32 as having been counted in or counted out based on detection of RFID tags 30 with RFID scanner 24. Display interface 22 updates and provides an inventory identifying the types and quantities of sponges 32 that have been counted in, as well as the types and quantities of sponges 32 that have been counted out (see FIG. 5).

[0025] As described above, in instances where a surgical sponge 32 that has already been counted out is again presented to the RFID scanner 24, the system 10 can be configured to provide a duplicate sponge notification. The system 10 of the present disclosure facilitates such functionality by preventing unwarranted duplicate sponge notifications. Such enhancement is achieved without requiring adjustment of the power level of the RFID scanner 24 and / or requiring additional action from the user. The system 10 includes a non-transitory computer-readable medium storing instructions configured to be executed by the processor 16 to implement the methods disclosed herein.

[0026] The method may assume that the surgical sponge 32 has already been counted into the surgical procedure. Referring to FIG. 9 , the method (100) includes using the RFID scanner 24 to detect a first detection of the RFID tag 30 of a first one of the surgical sponges 32 (step 102). The response signal is received by the processor 16. In other words, the RFID scanner 24 transmits a response signal backscattered from the interrogation signal to the processor 16. The response signal from the first detection includes a unique identifier. The unique identifier stored in the RFID tag 30 is transmitted to and received by the processor 16. A first RSSI value may be determined as an indication of the power level of the response signal (step 104). Based on the unique identifier received from the first detection, the processor 16 identifies the first surgical sponge as having been counted out of the surgical procedure (step 106). The processor 16 may cause the inventory displayed on the display interface 22 to be updated accordingly. The method includes detecting, with RFID scanner 24, a second detection of RFID tag 30 on the first surgical sponge 32 or detecting another RFID tag 30 on a second one of the surgical sponges 32 (step 108). In other words, the user unintentionally or intentionally presents to RFID scanner 24 a sponge 32 that has already been counted out, or presents another surgical sponge 32 that remains counted in.

[0027] Upon the second detection, another response signal is received by processor 16, which includes either the same unique identifier from the first detection or a different unique identifier associated with the surgical sponge 32 that remains counted in. If a unique identifier is not associated with the surgical sponge 32 that remains counted in, processor 16 determines that the second surgical sponge is not a duplicate, and the inventory displayed on display interface 22 is updated accordingly. However, if the unique identifier from the second detection matches the unique identifier from the first detection, processor 16 may identify the first surgical sponge as a potential duplicate sponge (step 108).

[0028] The method includes using processor 16 to determine an RSSI value from a second detection of RFID tag 30 (step 110). The RSSI value is compared to an RSSI threshold to be described. If the RSSI value is equal to or greater than the RSSI threshold, processor 16 identifies the duplicate sponge candidate as a duplicate sponge (i.e., a "true duplicate"). A duplicate sponge notification may be presented on display interface 22 indicating to the user that the presented sponge is a duplicate sponge (step 116). However, if the RSSI value is equal to or less than the RSSI threshold, processor 16 identifies the duplicate sponge candidate as not a duplicate sponge. In either case, no duplicate sponge notification is presented on display interface 22.

[0029] Because the RSSI value increases as the sponge approaches the RFID scanner 24, the comparison of the RSSI value to the RSSI threshold effectively requires that a "true duplicate" sponge be within the sponge presentation zone sufficiently close to the RFID scanner 24. Thus, unless the user actually presents a duplicate sponge to the RFID scanner 24, a display sponge notification is unlikely to be presented to the user. By way of example, with reference to FIG. 1 , five surgical sponges may have been counted into a surgery. Two of the surgical sponges were counted out and placed in the sponge sorter 34, as shown. Depending on the power level of the RFID scanner 24, the RFID scanner 24 may still detect the presence of these sponges 32 in the sponge sorter 34, which may be within a distance of one, two, or three feet from the RFID scanner 24. Response signals from these sponges 32 are transmitted to the processor 16, which may therefore identify the surgical sponges 32 as potential duplicate sponges. However, at these distances, the RSSI value associated with further detection of the surgical sponges 32 may be below the RSSI threshold. Thus, typically, system 10 will ignore these surgical sponges 32 as duplicates, even though they are close enough to be detected. Continuing the example, later in the surgery, these sponges 32 (along with other surgical sponges that remain counted in) may be removed for weighing to determine blood loss and returned to the area of ​​system 10. Perhaps the user mishandled the sponges 32 and placed the wrong sponge in sponge sorter 34. If the user brought one of the two surgical sponges 32 close enough to (e.g., adjacent to or touching) RFID scanner 24, the RSSI value may be high enough to meet or exceed the RSSI threshold. System 10 will identify the potential duplicate sponge as a duplicate sponge and present a notification to the user on display interface 22. The above example is merely illustrative; other clinical scenarios may better reflect clinical conditions and result in duplicate sponges being presented to RFID scanner 24.

[0030] The RSSI threshold can be a predetermined threshold, and the second RSSI value is compared to the predetermined RSSI threshold (step 112). In one variation, the RSSI threshold can be a fixed value common to all sponge types. The RSSI value and threshold can be expressed in decibel-milliwatts (dBm), with a more negative value indicating a weaker response signal and therefore a greater distance from the RFID scanner 24. For example, the RSSI threshold can be a value in the range of approximately −10 to −50 dBm. The predetermined RSSI threshold can be selected to create a sponge presentation zone of a desired size so that sponges other than those brought close enough to the RFID scanner 24 are not considered duplicate sponges. In other words, the sponge presentation zone can be considered a virtual sphere centered at the RFID scanner 24, and the RSSI threshold is selected to prevent sponges outside the virtual sphere from being considered duplicate sponges. In one example, the RSSI threshold can be selected so that the virtual sphere does not extend to the sponge sorter 34 when the arm 17 is positioned in the deployed configuration.

[0031] The system 10 may be compatible with multiple RFID tag types, which may apply to several different sponge types. These differences may affect the RSSI values ​​detected during countout activities. Thus, in certain embodiments, the RSSI thresholds may be based on the tag type of the RFID tag 30. More specifically, an RFID tag 30 that is an ultra-high frequency (UHF) may have a first RSSI threshold, an RFID tag 30 that is a high frequency (HF) may have a second RSSI threshold, and an RFID tag 30 that is a low frequency (LF) may have a third RSSI threshold. Similarly, the RSSI thresholds may be based on the sponge type. For example, the following table lists non-limiting examples of sponge types (e.g., dimensions, layers, etc.) along with associated RSSI thresholds:

[0032] [Table 1]

[0033] The RSSI threshold associated with the tag type or sponge type may be stored in a database that can be accessed by the processor 16. Additionally or alternatively, certain tag types, sponge types, and / or other surgical article types may not have an RSSI threshold, in which case a duplicate notification may be presented when the RFID scanner 24 detects the RFID tag 30 (and if the article had previously been counted out).

[0034] In certain embodiments, the RSSI threshold may be scan-specific, and the second RSSI value is compared to the scan-specific RSSI threshold. More specifically, the scan-specific RSSI threshold may be associated with one or more RSSI values ​​detected when the sponge 32 is first counted out (i.e., by the first detection). Thus, the exemplary method may include determining the scan-specific RSSI threshold based on the first detection. The processor 16 determines a second RSSI value as an indication of the power level of the response signal from the second detection of the RFID tag. The second RSSI value is compared to the scan-specific RSSI threshold. If the second RSSI value is equal to or greater than the scan-specific RSSI threshold, the processor 16 determines the duplicate sponge candidate to be a duplicate sponge. A duplicate sponge notification is presented on the display interface 22 (step 116).

[0035] The scan-specific RSSI threshold can be based on the first unique identifier. For example, the sponge ID can be correlated with or encoded with data including the scan-specific RSSI threshold that is transmitted to the processor 16 using the first response signal. The processor 16 can be configured to store the data and apply it later. Alternatively, the processor 16 can be configured to provide a fixed or variable offset to the data correlated with the sponge ID. Similarly, the scan-specific RSSI threshold can be based on the first RSSI value or its fixed or variable offset. For example, if the RSSI value from the first detection of the RFID tag 30 is −35 dBm, the processor 16 can establish the scan-specific RSSI threshold as −35 dBm or as −25 dBm with a fixed offset of 10 dBm.

[0036] In certain embodiments, the scan-specific RSSI threshold can be based on the frequency emitted by the RFID scanner 24 during the first detection and / or the frequency emitted by the RFID scanner 24 during the second detection. FIG. 4 shows a plot of RSSI values ​​across a frequency range for several tags. As can be seen from the plot, for each tag, the RSSI value varies across the frequency range. To reduce reader interference, the RFID scanner 24 can be configured to "frequency hop," i.e., emit interrogation signals at different frequencies in a near-continuous or sequential manner. In particular, systems using UHF signals emit signals in a predetermined frequency band, and the frequency band is changed throughout use. The RFID scanner 24 can hop randomly or in a predetermined sequence. Because frequency hopping occurs rapidly, when the surgical sponge 32 is presented to the RFID scanner 24, the system 10 may detect the surgical sponge 32 at multiple frequencies, each frequency associated with a different RSSI value. Thus, even if the distance and orientation between the sponge 32 and the RFID scanner 24 remain constant, the RSSI value may vary significantly depending on the frequencies associated with the first and second detections of the RFID tag 30.

[0037] The method may include the processor 16 receiving an emission frequency associated with a first detection of the RFID tag 30 and determining a scan-specific RSSI threshold based on the emission frequency. The scan-specific RSSI threshold may be based on a first RSSI value, or a fixed or variable offset thereof, associated with the emission frequency. By way of example, with continued reference to FIG. 4 , a first detection (diamond icon) of a Type 3 RFID tag 30 occurs at approximately 950 MHz, and the first RSSI value is −35 dBm. The processor 16 may establish a scan-specific RSSI threshold of −35 dBm, or −20 dBm with a fixed offset of 15 dBm. The scan-specific RSSI threshold may apply to a second detection within a frequency band, or may apply to all frequencies within the operating range of the RFID scanner 24.

[0038] Alternatively, the system 10 can establish a scan-specific RSSI threshold from an emission frequency associated with a first detection of the RFID tag 30 and an emission frequency associated with a second detection of the RFID tag 30. Based on the tag type, sponge type, and / or unique identifier transmitted to the processor 16, the memory can store calibration data (e.g., the “curves” of the plot in FIG. 4 ) including RSSI values ​​across a range of oscillation frequencies. For example, based on the first RSSI value and emission frequency in the first detection, the processor 16 can identify a curve for the tag type or sponge type. The scan-specific RSSI can be established as the corresponding RSSI value of that tag type, or a fixed or variable offset thereof. Next, based on the emission frequency in the second detection, the scan-specific RSSI threshold is referenced and compared with the second RSSI value. Thus, in some respects, the scan-specific RSSI threshold of this embodiment can “jump” in a manner corresponding to frequency hopping.

[0039] Extending the above example, where the first detection of tag 30 (Type 3) occurs at approximately 950 MHz and the first RSSI value is −35 dBm, the second detection of tag 30 occurs at approximately 900 MHz. Because the tag type has a stronger response at 900 MHz for the curve associated with the tag type, the scan-specific RSSI threshold may be offset from the first RSSI value by −15 dBm. In such an embodiment, the scan-specific RSSI threshold may be based on a frequency adjustment factor. Again, the scan-specific RSSI threshold may apply when the second detection is within the same frequency band, including the oscillation frequency, or for all frequency bands.

[0040] The methods described herein can advantageously reduce instances in which a duplicate sponge notification is presented to a user when it is otherwise unwarranted. To the extent that a duplicate sponge notification is presented on display interface 22, the method includes receiving a user input to suppress the notification. The method can include receiving an input on display interface 22 in response to the duplicate sponge notification to suppress further duplicate sponge indications for the first surgical sponge. Additionally or alternatively, the input can include suppressing further duplicate sponge indications for all subsequent surgical sponges.

[0041] The methods described herein can also reduce instances of unintentional "virtual" count-in of a surgical sponge 32 (and other sponges 32 in a bundle 36) by ensuring that the surgical sponge 32 being detected by the RFID scanner 24 has an RSSI value equal to or greater than an RSSI threshold. Existing systems, such as those sold under the trademark SurgiCount+ by Stryker Corporation (Kalamazoo, Michigan), allow users to "virtually" count-in a bundle 36 of surgical sponges 32 when a single "unknown" sponge is presented and counted out. As used herein, an "unknown" sponge is a surgical sponge 32 that has not been counted in a surgical procedure and for which there is no indication from its unique identifier that the surgical sponge 32 was used in another procedure. Omissions to count-in a surgical sponge 32 may be due to emergency patient care or human error. As a result, surgical sponges 32 in a bundle 36 may become scattered throughout the surgical field, making it impractical to count-in the surgical sponges 32 in the usual manner. Virtual count-in addresses this issue by counting in surgical sponges 32 from a bundle 36 that contained one of the surgical sponges 32 being counted out. For example, bundle 36 may include sponge A, sponge B, and sponge C. If sponge B is virtually counted in during count-out, sponges A and C will be counted in and sponge B will be counted out.

[0042] Despite its advantages, the virtual count-in process may cause the display interface 22 to switch modes or screens in an undesirable or unexpected manner if the surgical sponge 32 is simply detected from a staging or storage area near the system 10, leading to confusion or annoyance. Therefore, the present disclosure addresses such drawbacks by including a method in which the virtually counted-in surgical sponge 32 is compared to an RSSI threshold. The method includes detecting, using the RFID scanner 24, the detection of the RFID tag 30 of a first one of the surgical sponges 32 in the bundle 36, and a response signal of a unique identifier stored in the RFID tag 30 is received by the processor 16. Based on the unique identifier, the processor 16 determines that the first surgical sponge 32 is not being counted into the surgical procedure or another surgical procedure. In other words, the processor 16 can access the memory of the RFID tag 30 and / or compare the sponge ID to a database of sponges previously used in the surgical procedure. The method includes using the processor 16 to determine an RSSI value as an indication of the power level of the response signal from the detection of the RFID tag 30. The processor 16 compares the RSSI value to an RSSI threshold. The RSSI threshold may be a predetermined RSSI threshold and / or a scan-specific RSSI threshold, according to any of the embodiments disclosed and described herein. The processor 16 may identify the first surgical sponge 32 as virtually counted into the surgical procedure if the RSSI value is equal to or greater than the RSSI threshold. If the surgical sponge 32 is virtually counted in, the method includes accessing from memory unique identifiers of the remaining surgical sponges 32 from the bundle 36 associated with the first surgical sponge 32 that is not counted into the surgical procedure. The processor 16 may identify the remaining surgical sponges 32 as being counted into the surgical procedure. The inventory may be presented on the display interface 22. The first surgical sponge 32 of the bundle 36 is identified as being counted out, and the remaining surgical sponges 32 of the bundle 36 are identified as being counted in.

[0043] As mentioned above, the functionality of the RFID tag 30 also facilitates locating sponges 32 in or around the surgical field. The inventory displayed on the display interface 22 may show several surgical sponges 32 that remain counted in. The locations of some of these surgical sponges 32 may be known, while others may be unknown (i.e., "lost sponges"). The SurgiCount+ system described above facilitates guiding the user to the lost sponges. The RFID scanner can operate in a "search mode" in a handheld configuration, providing visual and audio feedback as the RFID scanner moves around the surgical field.

[0044] While the search mode is useful for locating lost sponges, it may be desirable to exclude other surgical sponges that remain checked in from the search. In other words, the user may wish to search for lost sponges, but not sponges whose location is known (i.e., not lost sponges). Exemplary clinical scenarios include adjusting inventory during personnel changes or body cavity closures, and / or keeping "cleaning" sponges. The surgical sponge 32 may not be lost, but may simply be lying on a table next to the surgical field, for example.

[0045] The system 10 of the present disclosure advantageously provides for the exclusion of certain surgical sponges 32 from a search, and does so in an intuitive manner as described, while minimizing disruption to surgical workflow. FIG. 10 depicts a method (200) for searching or locating surgical sponges 32 using the system 10, an exemplary embodiment of which is described with simultaneous reference to FIGS. 5-8. At least two surgical sponges 32 remain counted in. The inventory of FIG. 5 shows all five surgical sponges 32 remain counted in. The method includes receiving input from a user on the display interface 22 locating the surgical sponges 32 that remain counted in. FIG. 6 depicts a GUI displayed on the display interface 22 with a "Find Sponges" indicator selected. In instances where more than one surgical sponge 32 remains counted in, a prompt (not shown) may be presented on the GUI asking whether any of the surgical sponges 32 should be excluded from the search. The method includes receiving input from a user on display interface 22 to locate less than all of two or more of the surgical sponges 32 that remain counted in (step 202). For example, the step may include responding affirmatively to a prompt question. In contrast, if the question is answered negatively, the search mode workflow may continue as known.

[0046] In certain embodiments, a user can scan surgical sponges 32 to be excluded from the search. As shown in FIG. 6, the GUI can instruct the user to remove the RFID scanner 24 from the cradle 50. The method can include using the RFID scanner 24 to detect at least one RFID tag 30 among the surgical sponges 32 that represents the excluded surgical sponge, and the unique identifier stored on the RFID tag 30 is received by the processor 16 (step 204). For example, the user can scan surgical sponges 32 on a table next to the surgical field. The surgical sponges 32 can be scanned simultaneously or, preferably, individually and / or at a lower power level (e.g., approximately 14 dBm). The processor 16 causes a GUI on the display interface 22 to list the excluded surgical sponges. FIG. 8 shows two of the excluded surgical sponges 32, along with their sponge type and unique identifier (e.g., sponge ID). Thus, a subset of the surgical sponges 32 is identified to be excluded from the search. If the exclusion is erroneous or otherwise, the user can rescan the surgical sponge 32 and then update its status on the list or remove it from the list. Additionally or alternatively, an indication on the display interface 22 may be selectable to re-include the surgical sponge 32 in the search.

[0047] In certain embodiments, a user can select surgical sponges 32 to exclude from the search. The GUI can present a list of surgical sponges 32 that have been counted in (and not counted out) to a surgical procedure. The list can include, among other information, sponge type, sponge ID, and / or scan-in time. Additionally or alternatively, a search function can be provided that allows a user to search for one or more of the surgical sponges 32 based on sponge type, scan-in time, etc. The method receives a second input from the user on the display interface 22, including at least one of the surgical sponges to be an excluded surgical sponge, and the unique identifier stored on the RFID tag is received by the processor 16 (step 206). The second input can be a selection of a sponge type such that all surgical sponges 32 of that sponge type are treated as excluded surgical sponges. The second input can be a selection of a time range such that all surgical sponges counted in within that time range are treated as excluded surgical sponges. The second input can be associated with any sponge characteristic common to two or more of the surgical sponges 32.

[0048] Based on the second input, the list on the GUI can be updated accordingly (e.g., the status column in FIG. 7). The display interface 22 can provide an alert if the unique identifier of the surgical sponge to be excluded does not match any of the unique identifiers of the surgical sponges previously counted in the surgical procedure. In other words, if the user somehow scans for exclusion a surgical sponge 32 that has not been counted in, an alert can be displayed on the GUI. Additionally, the display interface 22 can provide an alert if the user scans or selects all surgical sponges 32 to be excluded from the search.

[0049] The method includes using RFID scanner 24 to scan an area of ​​the surgical procedure where two or more of the surgical sponges that remain counted in are detected by RFID scanner 24 (step 208). FIG. 8 illustrates guidance provided by the GUI to do this, with RFID scanner 24 activated and moved within or around the surgical field. RFID scanner 24 provides feedback to guide the user to the location of at least one of the two or more of the surgical sponges that remain counted in (step 210). Processor 16 causes the RFID scanner to not provide feedback regarding the excluded surgical sponge based on the unique identifier of the excluded surgical sponge (step 212). The feedback can be audio (e.g., a beep that increases in frequency as RFID scanner 24 approaches the missing surgical sponge), visual (e.g., a flashing light that increases in frequency as RFID scanner 24 approaches the missing surgical sponge), tactile or haptic, etc. When the RFID scanner 24 moves near or around the excluded surgical sponge, no output is provided from the RFID scanner 24 .

[0050] The above disclosure is not intended to be exhaustive or to limit the invention to any particular form. The terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations are possible in light of the above teaching, and the invention may be practiced otherwise than as specifically described.

Claims

1. 1. A method for counting surgical sponges in a surgical procedure using a sponge management system having a radio frequency identification (RFID) scanner, a processor, and a display interface, wherein each of the surgical sponges includes an RFID tag that stores a unique identifier, the method comprising: detecting a first detection of the RFID tag of a first one of the surgical sponges with the RFID scanner, wherein the unique identifier stored on the RFID tag is received by the processor; identifying, with the processor, the first surgical sponge as having been counted out of the surgical procedure; detecting, with the RFID scanner, a second detection of the RFID tag of the first one of the surgical sponges or another RFID tag of a second one of the surgical sponges, wherein a response signal of the unique identifier or another unique identifier is received by the processor; using the processor to identify the first surgical sponge as a potential duplicate sponge if the unique identifier associated with the second detection matches the unique identifier associated with the first detection; determining, with the processor, a received signal strength indicator (RSSI) value as an indication of the power level of the response signal from the second detection of the RFID tag; If the RSSI value meets a predetermined RSSI threshold, presenting a duplicate sponge notification on the display interface indicating that the duplicate sponge candidate is a duplicate sponge; A method comprising:

2. The method of claim 1 , further comprising not presenting the notification on the display interface if the RSSI value is below the predetermined RSSI threshold.

3. 3. The method of claim 1 or 2, wherein the predetermined RSSI threshold is based on a tag type or a tag type, and optionally, the tag type is one of ultra-high frequency (UHF), high frequency (HF), and low frequency (LF) of radio frequency energy.

4. The method of claim 3 , further comprising: not providing a predetermined RSSI threshold for a preselected tag type or a preselected surgical item.

5. 1. A method for counting surgical sponges in a surgical procedure using a sponge management system having a radio frequency identification (RFID) scanner, a processor, and a display interface, wherein each of the surgical sponges includes an RFID tag that stores a unique identifier, the method comprising: detecting a first detection of the RFID tag of a first one of the surgical sponges with the RFID scanner, wherein the unique identifier stored on the RFID tag is received by the processor; identifying, with the processor, the first surgical sponge as having been counted out of the surgical procedure; detecting, with the RFID scanner, a second detection of the RFID tag of the first one of the surgical sponges or another RFID tag of a second one of the surgical sponges, wherein a response signal of the unique identifier or another unique identifier is received by the processor; using the processor to identify the first surgical sponge as a potential duplicate sponge if the unique identifier associated with the second detection matches the unique identifier associated with the first detection; determining, with the processor, a received signal strength indicator (RSSI) value as an indication of the power level of the response signal from the second detection of the RFID tag; determining, with the processor, a tag type or a sponge type based on the unique identifier associated with the second detection; accessing from a database a predetermined RSSI threshold associated with said tag type or said sponge type; If the RSSI value meets the predetermined RSSI threshold, presenting a duplicate sponge notification on the display interface indicating that the duplicate sponge candidate is a duplicate sponge; A method comprising:

6. The method of claim 5 , wherein different predetermined RSSI thresholds are associated with at least two different tag or sponge types.

7. 1. A method for counting surgical sponges in a surgical procedure using a sponge management system having a radio frequency identification (RFID) scanner, a processor, and a display interface, wherein each of the surgical sponges includes an RFID tag that stores a unique identifier, the method comprising: detecting a first detection of the RFID tag of a first one of the surgical sponges with the RFID scanner, wherein a response signal of the unique identifier stored on the RFID tag is received by the processor; determining, with the processor, a first received signal strength indicator (RSSI) value as an indication of the power level of the response signal from the first detection of the RFID tag; identifying, with the processor, the first surgical sponge as having been counted out of the surgical procedure; detecting, with the RFID scanner, a second detection of the RFID tag of the first one of the surgical sponges or another RFID tag of a second one of the surgical sponges, wherein a response signal of the unique identifier or another unique identifier is received by the processor; using the processor to identify the first surgical sponge as a potential duplicate sponge when the unique identifier associated with the second detection matches the unique identifier associated with the first detection; determining, with the processor, a second RSSI value as an indication of the power level of the response signal from the second detection of the RFID tag; If the second RSSI value meets a scan-specific RSSI threshold, presenting a duplicate sponge notification on the display interface indicating that the duplicate sponge candidate is a duplicate sponge; A method comprising:

8. 8. The method of claim 7, further comprising: determining, with the processor, the scan-specific RSSI threshold value based on the first RSSI value and, optionally, a fixed offset of the first RSSI value.

9. receiving, at the processor, a transmission frequency associated with the first detection of the RFID tag by the RFID scanner; determining, with the processor, the scan-specific RSSI threshold based on the emission frequency; The method of claim 8 further comprising:

10. accessing calibration data for the RFID tag including RSSI values ​​over a frequency range based on the emission frequency of the first detection; determining, with the processor, the scan-specific RSSI threshold based on an offset from the second RSSI value at an emission frequency of the second detection; The method of claim 9 further comprising:

11. The method of claim 9 , wherein the processor determines the scan-specific RSSI threshold based on a nominal frequency response spectrum of the RFID tag type.

12. 12. The method of claim 8, further comprising applying the scan-specific RSSI threshold only if the emission frequency of the second detection is in the same frequency band as the emission frequency of the first detection.

13. The method of claim 12 , further comprising utilizing the scan-specific RSSI threshold for all frequency bands.

14. 14. The method of any one of claims 1 to 13, further comprising receiving an input on the display interface in response to the notification to suppress further duplicate sponge notifications for the first surgical sponge.

15. 15. The method of any one of claims 1 to 14, further comprising receiving an input on the display interface in response to the notification to suppress further duplicate sponge notifications for all subsequent surgical sponges.

16. 1. A method for retrieving counted-in surgical sponges during a surgical procedure using a sponge management system having a radio frequency identification (RFID) scanner, a processor, and a display interface, wherein each of the surgical sponges includes an RFID tag that stores a unique identifier, the method comprising: receiving an input from a user on the display interface to locate less than all of the two or more of the surgical sponges that remain counted in; detecting, with the RFID scanner, the RFID tag of at least one of the surgical sponges representing a rejected surgical sponge, and the unique identifier stored on the RFID tag is received by the processor; scanning an area of ​​the surgical procedure with the RFID scanner where the two or more of the surgical sponges that remain counted in are detected by the RFID scanner; providing feedback using the RFID scanner to direct the user to the location of at least one of the two or more of the surgical sponges that remain counted in, wherein the processor causes the RFID scanner to not provide the feedback regarding the excluded surgical sponge based on the unique identifier of the excluded surgical sponge; A method comprising:

17. detecting the RFID tag of the rejected surgical sponge with the RFID scanner; displaying the excluded surgical sponges on a display interface as being re-included in the search; and 17. The method of claim 16, further comprising:

18. receiving a second input on the display interface selecting the excluded surgical sponge; displaying the excluded surgical sponges on a display interface as being re-included in the search; and 20. The method of claim 17, further comprising:

19. 20. The method of claim 18, further comprising using the display interface to provide instructions to remove the RFID scanner from a cradle of the sponge management system, the step of providing instructions occurring after the step of receiving the input and before the step of detecting the RFID tag.

20. 1. A method for retrieving counted-in surgical sponges during a surgical procedure using a sponge management system having a radio frequency identification (RFID) scanner, a processor, and a display interface, wherein each of the surgical sponges includes an RFID tag that stores a unique identifier, the method comprising: receiving a first input from a user on the display interface locating less than all of two or more of the surgical sponges that remain counted in; receiving a second input from the user on the display interface including at least one of the surgical sponges that is a rejected surgical sponge, the second input being received by the processor with the unique identifier stored on the RFID tag; scanning an area of ​​the surgical procedure with the RFID scanner where the two or more of the surgical sponges that remain counted in are detected by the RFID scanner; providing feedback using the RFID scanner to direct the user to the location of at least one of the two or more of the surgical sponges that remain counted in, wherein the processor causes the RFID scanner to not provide feedback regarding the excluded surgical sponge based on the unique identifier of the excluded surgical sponge; A method comprising:

21. 21. The method of claim 20, wherein the step of receiving the second input further comprises receiving a selection of a sponge type, and all surgical sponges of that sponge type are treated as the excluded surgical sponges.

22. 21. The method of claim 20, wherein the step of receiving the second input further comprises receiving a selection of a time range, wherein all surgical sponges counted in within the time range are treated as the excluded surgical sponges.

23. 23. The method of any one of claims 16-22, further comprising receiving, on the display interface, a search input for a search query including one of the unique identifier, a time range in which the surgical sponge was counted in, a tag type, and a sponge type.

24. 24. The method of any one of claims 16 to 23, further comprising providing an alert on the display interface if the unique identifier of the surgical sponge to be excluded does not match one of the unique identifiers of the surgical sponges previously counted in the surgical procedure.

25. The method of any one of claims 16 to 24, further comprising providing an alert on the display interface if all surgical sponges are identified as excluded.

26. 1. A method for retrieving counted-in surgical sponges during a surgical procedure using a sponge management system having a radio frequency identification (RFID) scanner, a processor, and a display interface, wherein each of the surgical sponges includes an RFID tag that stores a unique identifier, the method comprising: receiving an input from a user on the display interface to locate less than all of the two or more of the surgical sponges that remain counted in; detecting, with the RFID scanner, the RFID tag of at least one of the surgical sponges representing a rejected surgical sponge, and the unique identifier stored on the RFID tag is received by the processor; receiving a second input from the user on the display interface including at least one of the excluded surgical sponges, wherein the unique identifier stored on the RFID tag is received by the processor; displaying, on a display interface, the excluded surgical sponge as being re-included in the search based on the second input; and scanning an area of ​​the surgical procedure with the RFID scanner where the two or more of the surgical sponges that remain counted in are detected by the RFID scanner; providing feedback using the RFID scanner to direct the user to the location of at least one of the two or more of the surgical sponges that remain counted in, wherein the processor causes the RFID scanner to not provide feedback regarding the excluded surgical sponge based on the unique identifier of the excluded surgical sponge; A method comprising:

27. 1. A method for counting surgical sponges in a surgical procedure using a sponge management system having a radio frequency identification (RFID) scanner, a processor, a memory, and a display interface, the surgical sponges being arranged in bundles and each including an RFID tag storing a unique identifier, the method comprising: detecting, with the RFID scanner, the detection of the RFID tag of a first one of the surgical sponges in the bundle, wherein a response signal of the unique identifier stored on the RFID tag is received by the processor; determining, with the processor, based on the unique identifier, that the first surgical sponge has not been counted into the surgical procedure or another surgical procedure; determining, with the processor, a received signal strength indicator (RSSI) value as an indication of the power level of the response signal from the detection of the RFID tag; using the processor to compare the RSSI value to an RSSI threshold; using the processor to identify the first surgical sponge as being virtually counted into the surgical procedure if the RSSI value is greater than or equal to the RSSI threshold; accessing from the memory unique identifiers of the remaining surgical sponges from the bundle associated with the first surgical sponge that has not been counted into the surgical procedure; identifying, with the processor, the remaining surgical sponges as being counted into the surgical procedure; presenting an inventory of the surgical sponges on the display interface, wherein the first surgical sponge of the bundle is identified as being counted out and the remaining surgical sponges of the bundle are identified as being counted in; A method comprising:

28. 28. The method of claim 27, wherein, according to any of the disclosed and described implementations, the RSSI threshold is a predetermined RSSI threshold and / or a scan-specific RSSI threshold.

29. A sponge management system comprising the RFID scanner, the display interface, and the processor configured to perform the method of any one of claims 1 to 28.

30. A non-transitory computer readable medium comprising instructions configured to, when executed by one or more processors, perform the method of any one of claims 1 to 28.

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