Abstract:
A system and method for detecting a surgical implement retained within a surgically exposed human body cavity, includes a tag adapted to be attached to a surgical implement insertable within a human body cavity, including a receiver for receiving an electromagnetic signal and converting it into electric signal; and a circuit to impress said electric signal on the internal human (or an animal) body where the medical product is used; and a transmitter to transmit the electromagnetic signal; and a detector including a receptor for receiving the electric signal from the body and a detector connected to the receptor for detecting the electric signal. The envelope of the induced RF wave is demodulated, thus allowing the voltage at the output to vary at a significantly lower frequency. In the event such pulses are sensed, a sensory alert is actuated.

Description:
This application is continuation-in-part of application Ser. No. 11/438,504 filed on May 22, 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to detection of tagged objects and devices and particularly objects and devices utilized in body cavities during surgery and most particularly to surgical sponges which are frequently “lost” in such body cavities. 
     During a surgical procedure, and especially in procedures where the chest or abdomen is open, foreign objects such as surgical sponges, needles and instruments are sometimes misplaced within the patient&#39;s body cavity. In general any foreign object left within the body can cause complications, (i.e. infection, pain, mental stress) even death, excepting objects such as clips and sutures that are purposely left as part of a surgical procedure. 
     Presently there are two surgically acceptable procedures for detection and removal of the foreign objects. Firstly, a count of all objects used in the operation is kept by surgical support staff. Secondly, x-ray detection is used to locate foreign objects. 
     It is not uncommon however, for object counts to be incorrect, but reported erroneously as correct, because of human error. Furthermore, even x-ray detection is not flawless. Furthermore, and most detrimentally, an x-ray is a time delayed detection method because of the requirement for film development (even with quick developing films). A patient will often be completely sutured closed before x-ray results are obtained, which may indicate the location of a foreign object within the patient. The detection delay may therefore result in the necessity for the surgical team to re-open the patient, thereby increasing the morbidity of the operation. 
     The prior art is replete with means for the detection of foreign objects (aside from x-ray analysis) which may remain in body cavities following surgery. However, such means have either been prohibitively costly, involve detection devices which are too large to be meaningfully useful (i.e., they often impede utilization of the objects they are intended to locate) or simply do not provide effective detection. 
     There have been a number of devices described in numerous patents for detection of surgical objects such as surgical sponges, which operate by means of marker or tag systems using electromagnetic, magnetomechanical, electromechanical detection techniques. For example, U.S. Pat. No. 2,740,405, issued to Riordian, describes the use of a radioactive tracer for detection of the foreign objects. This method is however, among other things, subject to problems involving the hazards of storage and disposal of radioactive materials. 
     In another example of detection devices and methods, U.S. Pat. No. 3,422,816, issued to Robinson et al., teaches a technique wherein sponges are marked with a flexible plastic impregnated with paramagnetic or ferromagnetic powders which are detected by a metal detector. However, this method is limited by the small signals obtainable (making detection unreliable), and the lack of discrimination from other magnetically susceptible metal objects, such as surgical staples, which are intended to remain in the body. 
     In an improvement over the preceding patent, in U.S. Pat. No. 3,587,583, issued to Greenberg, sponges were marked with magnetized particles whose presence is detectable with magnetodiodes. Nevertheless, such method has also not proven to be practical or reliable. 
     A spate of patents disclose electronically based signal devices, such as disclosed in U.S. Pat. No. 4,114,601, issued to Ables, which discloses use of a gyromagnetic transponder for marking a sponge. Detection is accomplished by a mixing of two frequencies beating the tag. The method however appears impractical because of transmission loss at its operating frequency of 5 Ghz. 
     In theory, electronic locators should be ideal for the detection of surgical sponges. However, as a practical matter, it is difficult to make a small tag element with sufficient signal strength for reliable detection and at an economic cost. More importantly, the increased size of a tag element often results in a detrimental effect on the utilization of the object it is intended to locate. Thus, surgical sponges, the most common item for which detection is most important, are useful only if they can be deformed for use. However, deformation often distorts large tag elements and small tag elements do not provide sufficient signal strength for detection. A non-deformable large tag is totally counterproductive since it would effectively eliminate the usefulness of a sponge which must be deformed for use. 
     In U.S. Pat. No. 5,456,718, issued to Szymaitis, a marker is made of non-magnetostrictive or soft magnetic material which will emit known selected harmonic frequencies when exposed to alternating electromagnetic field. However, in practice, this creates a large non-deformable region within the sponge thereby interfering with its function. 
     In U.S. Pat. No. 5,105,829, issued to Fabian et al, a battery powered marker is disclosed which uses capacitive coupling of radio signal to tissue. In U.S. Pat. No. 5,190,059, Fabian et al teach a battery powered tag used in conjunction with a zone marker housing or field generator. Batteries decreasing reliability of the tags while increasing their cost. 
     In U.S. Pat. No. 5,057,095, Fabian et al teach marking surgical instruments with three types of resonant markers which produce identifying characteristics when exposed to an alternating magnetic field. First, there is a mangnetomechanical marker. Second, there is a magnetostrictive marker. (Both these devices are however susceptible to pressure and stress making them impractical in an environment, e.g., sponge, requiring compression, with pressure and stress as a function thereof.) 
     In U.S. Pat. No. 6,366,206 issued to Ishikawa et al., one or more transponders each include a memory containing the corresponding identifying data which is emitted by the respective transponder in response to an electromagnetic signal emitted externally of the transponder. 
     In U.S. Pat. No. 6,026,818 issued to Blair et al., the system includes a ferrite rod, coil and capacitor. The tag resonates with a radiated signal, in response to the wide band transmission, at its own single non-predetermined frequency. 
     A very important characteristic absent from many of the prior art expedients is, besides being effective in use, the economics involved. Thus, many of the tags described in the prior art cost well in excess of $0.30 per tag. While this is usually dwarfed by actual surgical costs, it is nevertheless a sufficiently significant amount to cause concern among potential users of sponges with cost of $0.10 per sponge. 
     As an example of miniature electronic tags, U.S. Pat. No. 4,658,818, issued to Miller et al, discloses the use of a miniature electrical oscillator which is attached to each surgical implement and actuated at the time of surgery. Detection occurs by coupling the oscillation with the patient&#39;s tissue. However, the active tagging system has to have a battery lasting the whole duration of the surgery which increasing the complexity, size and cost of the tagging system and decreasing its reliability. 
     SUMMARY OF THE INVENTION 
     It is therefore an objective of the present invention to provide a method and device suitable for detection of the presence of objects and particularly suitable for use in detection of objects such as surgical sponges and instruments forgotten within the patient&#39;s body cavity during surgery, wherein the device comprises detection tags which are sufficiently small, whereby they do not impede use of an object such a surgical sponge, or are larger but flexible, and are reliable in discriminating detection, and yet are economical for widespread use in objects such as sponges. 
    
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
         FIG. 1  is an example of an electric circuit of the tag and external means to transmit electromagnetic signal. 
         FIG. 2  depicts demodulation of the envelope of the induced RF wave. 
         FIG. 3 . is an example of a circuit that detects the electric signal (pulses) that has been applied to biological tissue at the output  20  of  FIG. 1 . 
         FIG. 4  is a block diagram of a means for blocking an electric signal. 
         FIG. 5  is a block diagram of an electric signal blocking means including RF signal extension timer. 
     
    
    
     The system for detecting a surgical implement (not shown) retained within a human body cavity includes the tag  8  attached to the surgical implement. The tag  8  is inductively coupled from external means for transmission  9 . The tag  8  converts received electromagnetic signal into an electric signal. The electric signal is received by receiving means  10  due to electric conductivity of biological tissue and detected by detector means. The electric signal is blocked from detecting means  10  by blocking means shown on  FIG. 4  and  FIG. 5 . 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     By reference from Communications Electronics Circuits second edition by J. J. DeFrance Rinehart Press, 1972, page 242 to  FIG. 1 , an exemplary description is made of a diode detector for the demodulation of electromagnetic waves. Means  9  for transmitting an electromagnetic signal includes an oscillator  11  and a loop antenna, depicted as an inductor  12 . While the oscillator in this embodiment operates preferentially at 13.56 MHz, other frequencies may also be used. The tag  8  is attached to a surgical implement (not shown) and adapted to be inserted into a surgically exposed human body cavity includes means for receiving the transmitted electromagnetic signal and converting this electromagnetic signal into an electric signal. The means for receiving the electromagnetic signal is depicted as an inductor  13  which is also preferentially a wire loop antenna that is part of the body resonance detector circuit. The values of this inductor and its corresponding capacitor  14  are selected to resonate at the aforementioned oscillator frequency. The diode  15  conducts only on the positive half-cycle of the resonant circuit, tending to charge capacitor  17  of the resonant tank circuit comprised of capacitor  17  and resistor  16 . Values of elements  16  and  17  are chosen so that the discharge time constant is long compared to the period of the RF cycles. The result, as illustrated in  FIG. 2 , is to demodulate the envelope of the induced RF wave, thus allowing the voltage at output  20  to vary at a significantly lower frequency. In this embodiment, the frequency of modulation or intelligence signal will be preferably, but not limited to, 10 KHz. This intelligence frequency should be chosen so as to optimize the physical size of the components in the body resonance detector circuit. Elements  18  and  19  are respectively the output coupling capacitor and resistor whose values are judiciously selected to remove the alternating current from the envelope, thus leaving only the 10 KHz intelligence electric signal. 
     Air core inductors values [element  13  in  FIG. 1 ] 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Number 
                   
                   
                 Inductance 
               
               
                   
                 of turns 
                 Diameter (inch) 
                 Length (inch) 
                 (microHenry) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1 
                 4 
                 0.04 
                 0.22 
               
               
                   
                 1 
                 3 
                 0.04 
                 0.16 
               
               
                   
                 1 
                 1 
                 0.04 
                 0.05 
               
               
                   
                 3 
                 1 
                 0.1 
                 0.49 
               
               
                   
                   
               
             
          
         
       
     
     The first assumption of one turn is based on a nominal, unfolded sponge.
         The third assumption is a worst case of a triple folded sponge with an original 4 inch single-turn coil becoming effectively a three-turn coil.
 
Conclusion: We can assume the inductance, L 2  will be between 0.16 and 0.49 microHenries.
       

     Calculation of element  19   FIG. 1  value based on human tissue conductivity. In the following calculation the value of the element  19  equals to the resistance of human tissue across the output electrodes. 
     Assume electrodes measure 3 mm×3 mm=9 mm ^2 
     The conductivity of human tissue is nominally 0.3 Siemens/meter. Since resistivity is the reciprocal of the conductivitiy, the rho or resistivity of human tissue is 3.33 ohms/meter. Therefore, if we assume 2 mm spacing of the electrodes with this resistivity, then:
 
Resistance=Resistivity×Length/Surface area=Ohms Meters×Meters/Meters ^2 =Ohms
 
Element  19  FIG.  1 =3.3 ohm meters×(2×10^−3 meters)/(9×10^−3 meters)^2=81.5 Ohms.
 
     To determine the value for Element  18  FIG.  1 =t/Element  19  value, where t is the reciprocal of the modulation frequency expressed in hertz. 
     Summary table of element values for exemplary modulation frequencies:
     Element  13  FIG.  1 =between 0.16 microH and 0.49 microH   Element  14  FIG.  1 =between 1.3 microF and 0.44 microF   Element  16  FIG.  1 =50 Ohms (for element  19  value of 82 Ohms)   Element  17   FIG. 1  values:   

     
       
         
               
               
               
               
             
           
               
                   
               
               
                 10 Hz 
                 280 Hz 
                 1 kHz 
                 10 kHz 
               
               
                   
               
             
             
               
                 &lt;=400 microF 
                 &lt;=14.4 microF 
                 &lt;=4 microF 
                 &lt;=0.4 microF 
               
               
                   
               
             
          
         
       
         
         Element  18   FIG. 1  values: 
       
    
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 10 Hz 
                 280 Hz 
                 1 kHz 
                 10 kHz 
               
               
                   
                   
               
             
             
               
                   
                 1200 microF 
                 44 microF 
                 12.2 microF 
                 1.2 microF 
               
               
                   
                   
               
             
          
         
       
     
     Element  19   FIG. 1  depends on the resistivity of human tissue (3.3 Ohm Meters)=81.5 Ohms. 
     The tag  8  includes output conducting means to impress an electric signal on the body depicted as output  20  which can be made as electro-conductive pads. 
       FIG. 1  depicts that inductor  12  (antenna) is electrically connected with the output conducting means. 
       FIG. 3  serves to illustrate an example of a circuit that receives through conduction the low frequency intelligence signal that has been impressed on biological tissue at the output electrodes  20  of  FIG. 1 . The receiving means  10  includes means for receiving the intelligence electric signal from the biological tissue depicted as two conductive pads  31  placed on the biological tissue to receive the input from output  20  of  FIG. 1 . 
     In another embodiment, the lower pad of output  20  may be the antenna itself as it is seen as connected in common to the loop. 
     The values of elements  32 ,  34 ,  35  and  36  of detector means are chosen so as to pass the modulation frequency from the body resonance circuit described earlier as illustrated in  FIG. 1 . Exemplary values depending on frequency are: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 10 Hz 
                 280 Hz 
                 1 kHz 
                 10 kHz 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Element 32 (microHenries) 
                 330 
                 330 
                 330 
                 330 
               
               
                 Element 34 (Ohms) 
                 10 
                 10 
                 10 
                 10 
               
               
                 Element 35 (micro Farad) 
                 767,585 
                 980 
                 77 
                 0.77 
               
               
                   
               
             
          
         
       
     
     Other combinations of frequencies and component values may be calculated by anyone of ordinary skill in the art. Values of anticipated output voltage at 36 for input into an instrument such as a voltmeter given a voltage at 31 of 1 millivolt would be: 
                                                                               10 Hz   280 Hz   1 kHz   10 kHz                                        Output 36   0.002   0.058   0.2   2           (milliVolts)                        
By examination of the component values shown above, the preferred embodiment of 10 kHz modulation frequency allows the selection of more abundant, less expensive and smaller sized elements.
 
     Electric signal blocking means  37  shown on  FIG. 4  includes an antenna  38  for receiving said modulated radio frequency (RF) electromagnetic signal and converting it into an electric signal, and a logical NAND element  39  coupled with the said antenna and the positive lead of the output means  36  of the reception means  10 . The logical NAND element  39  blocks electric signal impressed on the tissue until transmission of RF is stopped. The blockage of an electric signal impressed on the tissue during transmission of RF improves accuracy of the detection in cases if body tissues including skin develop an electric signal similar to signal impressed on the tissue by electrodes  20 . Due to capacitance of the tag  8 , the electrodes  20  continue impressing an electric signal on body tissue some period of time after RF transmission is stopped. After transmission of RF is stopped, logical NAND element  39  does not block any longer an electric signal impressed on the tissue by electrodes  20 . At that time the electric signal impressed on the tissue is detected by detector means by output  40 . As a logical NAND element  39  can be used, for example, Texas Instruments SN7400N integrated NAND circuit. 
     In another embodiment as shown on  FIG. 5 , electric signal blocking means  41  includes an RF signal extension timer  42 , coupled with the antenna  38  and the logical NAND element  39 . In this embodiment, an RF signal extension timer  42  is used for extension of blocking of said electric signal impressed on the tissue for a predetermined duration of time after transmission of said RF is stopped. As an RF signal extension timer  42  can be used, for example, integrated circuit retriggerable timer, NE555. Capacitance of the tag  8  is greater than capacitance of skin and reception pads  31 . In this embodiment, the accuracy of detection is increased due to elimination of influence of capacitance of the skin and reception pads  31 . This duration of extension of blocking the electric signal after RF transmission is stopped can be adjustable from 0 to 250 microseconds by appropriate selection of resistor and capacitor values added to the NE555. 
     An electrocardiographic device can be used as detector means. An electrocardiographic device is available in the operating room and it is electrically connected to the human body where surgical implements are placed. 
     Detecting means can be connected (including wireless connection) to a computer located in the operation room. 
     In another embodiment, conductive pads  31  are adapted for electric contact with the human body inside the human body cavity into which is a surgical implement provided with a tag is inserted. 
     In another embodiment, conductive pads  31  are adapted for electric contact with the human body externally of a human body into which a surgical implement provided with a tag is inserted. 
     In another embodiment, the means  9  to transmit electromagnetic signal is adapted to be located inside the human body cavity into which a surgical implement provided with a tag is inserted. 
     In another embodiment, the means  9  to transmit electromagnetic signal is adapted to be located externally of a human body into which a surgical implement provided with a tag is inserted. 
     A tag could be used as X-ray detectable means. 
     A tag can be attached to X-ray detectable thread to be woven into sponges during their manufacturing. 
     
         
         A tag can be attached to a sponge during or after its manufacturing. 
         A tag can be woven into sponge, sewn, stapled, glued, etc. 
         A tag can be attached to a sponge during or after its manufacturing. 
         A tag can be inserted into a sponge between its layers. 
       
    
     A method for detection of a foreign object used during surgery but not intended to remain in a human body after surgery comprises the steps of:
     (a) providing a foreign object used during surgery with at least one tag,   (b) transmitting an electromagnetic signal of frequency  1  (preferably, but not limited to, 13.56 MHz.) modulated with frequency  2 ,   (c) converting said electromagnetic signal into electric signal, using the tag, into an electric signal with frequency  2 , (preferably, but not limited to, 10 KHz.),   (d) impressing said electric signal with frequency  2  on the tissue of the said body,   (e) electrically connecting detecting means to said body,   (f) blocking said electric signal with frequency  2  from detecting means when said electromagnetic signal of frequency  1  is transmitted,   (g) conducting said electric signal with frequency  2  to detecting means after said electromagnetic signal of frequency  1  is stopped,   (h) detecting said electric signal with frequency  2  conducted by the tissue of the said body using said detecting means when said electric signal with frequency  2  from detecting means after said electromagnetic signal of frequency  1  is stopped.   

     A method for detection of a foreign object used during surgery but not intended to remain in a human body after surgery comprises the steps of:
     (a) providing a foreign object used during surgery with at least one tag,   (b) transmitting an electromagnetic signal of frequency  1  modulated with frequency  2 ,   (c) converting said electromagnetic signal into electric signal, using the tag, into an electric signal with frequency  2 ,   (d) impressing said electric signal with frequency  2  on the tissue of the said body,   (e) electrically connecting detecting means to said body,   (f) blocking said electric signal with frequency  2  from detecting means when said electromagnetic signal of frequency  1  is transmitted,   (g) blocking said electric signal with frequency  2  from detecting means during a predetermined time by a timer duration after transmission of said electromagnetic signal of frequency  1  is stopped,   (h) conducting said electric signal with frequency  2  to detecting means after a predetermined time by a timer duration of said electromagnetic signal of frequency  1  is off,   (i) detecting said electric signal with frequency  2  conducted by the tissue of the said body using said detecting means when said electric signal with frequency  2  from detecting means when said electromagnetic signal of frequency  1  is off.