Patent Publication Number: US-7896018-B2

Title: Dosage control apparatus

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/065,726, filed Feb. 25, 2005, now U.S. Pat. No. 7,588,046, which was a continuation of U.S. application Ser. No. 10/331,425, filed Dec. 30, 2002, now U.S. Pat. No. 6,880,564, which claims the benefit of U.S. Provisional Application No. 60/412,365, filed Sep. 20, 2002, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention, in general, relates to an implantable drug delivery system. More specifically, this invention relates to a dose control system and valves used to manipulate the delivery rate of a pharmaceutical solution. 
     BACKGROUND OF THE INVENTION 
     Implantable drug infusion therapy has been used to treat various ailments including pain management and diabetes. These drug pumps and delivery systems have been used to deliver pain medication, hormones such as insulin, and other pharmaceutical agents. For example, intraspinal drug delivery may be used to treat chronic pain. By utilizing these systems, pharmaceutical agents are delivered in relatively lower doses to a specific region of treatment. In this manner, full body dilution and membrane barriers are avoided. Similarly, insulin may be delivered without the inconvenience of injections. 
     Infusion pumps come in several varieties. Some infusion pumps are constant rate such as those driven by gas pressures or springs. Others are variable rate pumps driven by hydration of an expandable substance or a variable rate pumping mechanism. 
     Implantable drug delivery systems have several advantages over external drug pumps, oral medications, suppositories, and injections. These implantable systems are unobtrusive, unencumbering, and typically deliver smaller doses to targeted regions. Pills, suppositories, and injections deliver large doses of pharmaceutical agents that pass through a large portion of the body to reach the treatment area. The large dilution ratio caused by this passing requires a large dose to achieve an effective concentration in the treatment area. In addition, patients must remember to administer the correct dose at the appropriate time to achieve the desired therapeutic levels of the pharmaceutical agent in the treatment area. 
     While external infusion pumps overcome some of the limitations of pills, injections, and suppositories, they are often cumbersome and inconvenient. These devices must typically be worn or strapped to the patient, encumbering clothing selection and presenting a risk of damage to the external pump. In addition, catheter incision points are subject to infection. 
     However, current versions of implantable infusion pump systems also have disadvantages. Typically, implantable infusion pump systems provide limited programmability and patient control. In addition, access to the pump system is limited. Some pump systems have a constant rate while others attempt to control flow rates by varying pump speeds or hydration rates. In the case of constant rate pumps, prescription rates are set by the selected flow restrictor and pump pressure. In the case of variable rate pumps, prescriptions are limited by the available rate settings associated with the pump. 
     Patients generally have no control over the prescription. In pain management cases, this can lead to periods of under dosing and periods of unnecessary over treatment. Doctors are also limited in the selection of prescriptions and often must have an office visit with patients to adjust prescriptions. These adjustments are expensive to insurance companies, unprofitable for doctors, and inconvenient for patients. 
     In the case of other treatments such as insulin treatment, the required prescription varies with the behavior and environment of the patient. Insulin requirements increase with carbohydrate laden meals and decrease with activity. Excess insulin can lead to shock and low insulin can lead to excess blood sugar levels and many long-term health problems. 
     Another problem with implantable infusion pumps is determining actual dosage rates and predicting reservoir levels. Limited access to the pump means expensive preemptory refilling. Typical implantable infusion pumps do not maintain rate data useful in determining actual dosage schedules and reservoir levels. Therefore, doctors have difficulty predicting reservoir levels. This often leads to wasted pharmaceutical solution. Worse, the reservoir may empty and patents may suffer from a lack of treatment. 
     A further problem with current dose control systems lies in their method for controlling dose rates. These methods often use many mechanical parts that may wear. Further, these systems use parts that may malfunction under externally applied magnetic fields such as those of an MRI. 
     As such, typical infusion pumps suffer from deficiencies in providing prescription options, actual prescription rate data, and control of dosage. Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein. 
     SUMMARY OF THE INVENTION 
     Aspects of the invention may be found in an apparatus for controlling the flow of a treatment solution. The apparatus includes a housing surrounding an enclosure and having two ports in communication with the enclosure. Each port has a valve seat surrounding the port opening. Further, each port has an associated armature with head pressed against the valve seat by a spring. At least one coil is used to create a magnetic field, which generates a force opposing the spring force, thereby opening the valve. In one case, the spring is the same spring pressing both armature heads against the valve seats. The armatures may have a common central axis and move along this axis in opposite directions. A core or spring stop assembly may be placed between the armatures. A covering of magnetically permeable material may be placed about the coil. The core and covering may be used to direct the magnetic field. 
     The coil may also be used to measure a signal response indicative of an external magnetic field. A flow control module may implement in the coil a signal that induces a magnetic field to oppose the external magnetic field or a degaussing field. 
     Additional aspects of the invention are found in a method for controlling the flow rate of a treatment solution. A valve is provided with two armatures pressed against valve seats by at least one spring. A coil is activated to induce a magnetic field that motivates the armatures to move against the force of the spring and open the valve. The method may further include interpreting a signal from the coil to ascertain the presence or strength of an externally applied magnetic field. A signal may be sent to the coil to induce an opposing field or a degaussing field. 
     As such, a dose control apparatus is described. Other aspects, advantages and novel features of the present invention will become apparent from the detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein: 
         FIGS. 1A and 1B  are schematic diagrams of the system, according to one embodiment of the present invention; 
         FIG. 2  is a schematic block diagram depicting a dose control module for use by the system as seen in  FIG. 1A ; 
         FIGS. 3 and 4  are schematic block diagrams depicting exemplary embodiments of a dose control module as seen in  FIG. 2 ; 
         FIGS. 5 ,  6 ,  7 , and  8  are block flow diagrams depicting exemplary methods for use by the dose control module of  FIG. 2 ; 
         FIGS. 9A ,  9 B,  9 C and  9 D are schematic diagrams depicting an exemplary embodiment of a valve for use in the system as seen in  FIG. 1A ; 
         FIGS. 10A ,  10 B,  10 C and  10 D are schematic block diagrams showing another exemplary embodiment of a valve for use in the system as seen in  FIG. 1A ; 
         FIG. 11  is a schematic diagram depicting a further exemplary embodiment of a valve for use by the system as seen in  FIG. 1A ; 
         FIG. 12  is a block flow diagram depicting an exemplary method for use by the system as seen in  FIG. 1A ; 
         FIGS. 13 ,  14 , and  15  are schematic diagrams depicting an exemplary embodiment of a valve for use by the system as seen in  FIG. 1A ; 
         FIG. 16  is a graph depicting an inductance field resulting from a pulse signal for use by the valve as seen in  FIGS. 13 ,  14 , and  15 ; 
         FIG. 17  is a schematic diagram of a circuit for producing the inductance field of  FIG. 16 ; 
         FIG. 18  is a block flow diagram depicting an exemplary method for use by the system as seen in  FIGS. 13 ,  14 , and  15 ; 
         FIG. 19  is a schematic diagram of a circuit for use by the system as seen in  FIG. 1A ; and 
         FIG. 20  is a block flow diagram of an exemplary method for use by the system as seen in  FIG. 1A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Implantable drug treatment therapy is useful in treating a variety of ailments such as chronic pain management, insulin-dependent diabetes, chemotherapy (systematic and targeted), Myelin treatment, and neurotransmitter treatment, among others. In each of these examples, patients could benefit from greater variety of prescriptions, more control, and accurate monitoring of reservoir levels. 
     For example, in the case of pain management, patients may benefit from selectively applying various doses based on need. A preset array of prescription levels would permit the patient to adjust treatment based on pain, increasing as needed and decreasing otherwise. Limits and other conditions may be established to prevent over dosing. Such a system would permit a patient to compensate for developing tolerances or advancing pain. 
     Patients can also benefit from having more than one pharmaceutical agent or treatment solution delivered to the treatment area. Differing rate of drug delivery for different drugs can be effective for pain management. For example, one pharmaceutical agent may be infused for low-level pain while another is introduced only during extreme pain. In this manner, tolerance development may be moderated for the stronger drugs, or rates may be varied for those that are more expensive. 
     Similarly, treatments such as insulin treatments may be managed more effectively with more patient control and multiple treatment solutions. For example, a patient may modify dose with activity and consumption. Further, agents with varying time-release patterns, co-factors, and supplements may be introduced with varying rates. 
     Such a delivery pattern is realized with a separate dose control system.  FIG. 1A  depicts an embodiment 1 of the present invention. A pressurized drug cavity  2  delivers a treatment solution through a filter  3  and flow restriction  4  to valves  5  and  6 . However, various motivating systems may be envisaged for supplying valves  5  and  6  with treatment solutions. The circuitry  7  using energy from battery  8  manipulates the valves  5  and  6  to produce a flow rate in accordance with a prescription. However, one, two, or more valves may be used. The treatment solution may then travel through a catheter  11  to a treatment region in a patient. A bolus cavity  9  may be located inline to provide for the administering of bolus dosages. 
     The circuitry  7  and battery  8  comprise a dose control module and may be located separate from other elements as denoted by the enclosure  13 . However, other elements such as the valves  5  and  6  may be included with the circuitry  7  and battery  8  as indicated by the enclosure  15 . The bolus cavity  9  may also be enclosed with the circuitry  7  and battery  8 . The drug cavity  2 , filter  3 , and flow restriction  4  may be located in a separate housing. 
     Moreover, various valve configurations may be envisioned. Valves  5  and  6  may be placed in series, parallel, or other arrangements. One, two, or more valves may be included in addition to restrictions to formulate various configurations. 
       FIG. 1B  shows another embodiment 10 of the present invention.  FIG. 1B  has an infusion pump  14  implanted in a patient  12 . From the infusion pump, a catheter  20  leads through a dose control module  18  to a treatment area  22 . The dose control module  18  may have a valve set  16  or other means of directing dosage. Alternately, the dose control module  18  may have a communication link  26  with the infusion pump  14  or valve set that aids in controlling dose. The system may also include an external patient control unit  24 . The external patient control unit may direct the dose control module  18  to change dose rates or prescription configurations. In addition, other infusion pumps  28  may be connected with the dose control module  18  or valve set  16  such that multiple pharmaceutical solutions are delivered through the catheter  20  to the treatment area  22 . 
     The system may be useful in treating various ailments. For example, the treatment area  22  may be intraspinal. The infusion pump  14  may deliver a morphate or other pain modifying pharmaceutical solutions through the dose control module  18 , valve configuration  16 , and catheter  20 . In another case, the infusion pump  14  may deliver insulin through a dose control module  18  and catheter  20  to be absorbed by the bloodstream. 
     The patient control unit  24  may be used to modify dosage to either control pain in the case of a pain medication or control blood sugar in the case of insulin delivery. For example, the patient control unit  24  may permit the patient to select a prescription from a preset array of prescriptions which is then transmitted the dose control module  18 . 
     A separate dose control module  18 , as shown, provides an interchangeable, flexible, dose control solution for implantable drug infusion therapy. Doctors may select a dose control module based on the prescription range, while using a pump with a constant flow rate. Surgeons may also implant multiple infusion pumps and connect them to a single dose control module. In addition, doctors may establish a set of prescriptions selectable by a patient and observe actual dosage rates. 
     To manipulate dosage rate, the dose control module  18  sends time dependent signals to dose or flow manipulating devices such as valves and pumps, among others. A desired dosage rate may be achieved by opening a valve for a specific period of time. Alternately, the signal may open and close the valve such that a time averaged dose rate is achieved. 
       FIG. 2  depicts an exemplary dose control module  30 . Within a hermetically sealed housing, the dose control module  30  may have a processor  32 , instructions  34 , prescription settings  36 , a flow meter  38 , a clock  40 , a control circuitry  42 , a communications interface  44 , a data storage  46 , security instructions  48 , a power supply  50 , dose manipulators  52 , and dose manipulator state sensors  54 , among others. However, these elements may or may not be included. Further, they may be housed together, separate or in various combinations, among others. 
     Processor  32  functions to interpret instructions  34  in view of prescription settings  36  and other data  46 . The processor  32  interacts with control circuitry  42  to establish dosage rates and dose paths through the valves and restrictors  52 . The instructions  34  are software instructions for implementing the various methods used by the dose control module  30  and may include instructions for establishing valve configurations, determining the dose rate, calculating effective strength, determining dosage, comparing dosage to predetermined limits, determining valve position, and communicating with other devices, among others. 
     The prescription settings  36  take the form of parameters associated with a prescription. These parameters may include dose rates, degradation rates, model parameters, limits, and conditions, among others. For example, a prescription setting  36  may be a dose rate of 0.8 milliliters per day, with further limits of three hours at that rate for a limit of 0.3 milliliters over any given 12 hours. In another example, the prescription rate may be expressed in .mu.g/day with a degradation model to determine a corresponding dose rate. However, various dose rates, limits, and conditions may be associated with various therapies. 
     The dose control module  30  may include a flow meter  38 . The flow meter  38  may take various forms including a pressure drop sensor, a rotary meter, a switch, and a force meter, among others. Alternately, the flow meter may calculate flow rates from known pump rates and valve positions. 
     The system may also include a clock  40 . The clock  40  may be used in creating timed signals for manipulating dosage rates. The clock  40  may also be used for determining whether dosage has exceeded the predetermined limitations. Further, the clock  40  may be used to record time stamped data. The clock  40  may be used to determine time of day, time differences, and total time implanted, among others. With the clock  40  and the flow meter  38 , actual dosage data may be recorded, limits and conditions tested, and reservoir levels calculated. The benefits include an understanding of dosage rates, better prediction of reservoir levels, and more accurate adherence to overdose safety limits. Additional counters may be used to count fills and other parameters. 
     The control circuitry  42  is used to establish valve position or dose rates. This is accomplished by selectively sending signals to dose manipulators such as valves and pumps. The processor in accordance with the instructions  34  and the prescription settings  36  directs the control circuitry to create signals, manipulating valve position to control dose rates. 
     The communications interface  44  may take various forms including an interface with an external computer prior to implanting, or a radiofrequency interface to external devices. With a connection to a computer, the dose control module  30  may be programmed and configured prior to implanting. Once implanted, a doctor may interface with the device to establish prescription settings  36 , download or upload other data from the data storage  46 , and determine reservoir levels, among other data. With a patient control unit, a patient may choose a prescription selected from a set of prescriptions preset by the patient&#39;s doctor. 
     The dose control module  30  includes a data storage  46 . The data storage  46  may store time-stamped dose data, dosage data, other parameters associated with valves, restrictors and device configuration, calculated reservoir levels, and other data. The data storage may take the form of various RAM or flash memories, among others. The data may also be transmitted and stored on a patient control unit. 
     The dose control module  30  may also include security instructions  48 . These security instructions can include encryption algorithms or authentication methods such as device identification numbers to limit access to the functionality of the dose control module  30 . Communications with unauthorized devices may be ignored or limited in their access to alter prescriptions. 
     The power supply  50  may take the form of a battery. The power supply may also include a means of recharging from an externally applied RF signal. The system may also monitor the power supply  50 . If the power supply  50  reaches a low level or power is lost, the system may include fail-safe electronic circuitry that could place the valves in a safe position or the valve design can default to a safe configuration prior to the loss of power. For example, a reserve power supply or capacitor may direct the closing of all valves. 
     The dose control module may also include dose manipulators such as valves and restrictions. These dose manipulators may be arranged in various configurations to provide a variety of dosage rates and prescription configurations. Using various valve configurations, the dose control module may also deliver more than one drug, implement bolus infusions, and permit a variety of pharmaceutical delivery rates to one or more catheters. However, the valves may also be located external to the dose control module  30 . 
     The dose control module  30  may also include position sensors  54  for determining the position of valves or state of dose manipulators  52 . Alternately, the dose control module may use signals produced by the control circuitry  42  and processed by the processor  32  to determine the valve position. For example, signal response from an inductance coil may be used to determine the position of a valve core. 
       FIG. 3  depicts another embodiment of a dose control module  76 . The dose control module  70  includes a microprocessor  72 . The dose control module  70  may be programmed using a programming module  74 . Instructions for the microprocessor may be stored in the programming memory  76  and prescription parameters may be stored in the memory  78 . Alternately, instructions may be received through the receiver/transmitter  82 . 
     The program memory  76  may take the form of ROM, RAM, or flash memory, among others. Similarly, the memory  78  may take the form of ROM, RAM or flash memory, among others. 
     The system may also include a clock  80  for time stamping data, determining whether dosage limit conditions have been met, and producing time sensitive signals, among others. For example, the clock may be used in creating an electromagnetic pulse signal for maintaining a minimum magnetic field about an inductance coil. The clock can also be used in determining a dosage ratio or total dosage for comparison with limits and conditions. 
     The power supply module  84  may provide power to the microprocessor. Further, it may be used on conjunction with a voltage multiplier  86  to control valve position. In accordance with the prescription parameters and the instructions stored in the program memory, the microprocessor  72  may provide electromagnetic signals to valves, directing the opening and closing of those valves using a pulse amplitude and width controller  88  and switch matrix  90 . 
     The dose control module may be housed in a module, separate from a pump and reservoir. Valves, restrictions, and other dose manipulators may be included in the module or housed separately. In this manner, a single dose control module may manipulate dose rates associated with more than one pharmaceutical solution and/or multiple valves to achieve a selected prescription. 
     The patient control unit may have a circuitry similar to that shown in  FIG. 3 . The patient control unit may have a processor, various memories, a clock, a receiver/transmitter, a power supply, and a programming modulator interface. With these elements the patient control unit may communicate prescription selection and other data with the dose control module. 
       FIG. 4  depicts an exemplary valve array  110 . The electronics  112  and the dose control module communicate through one or more control lines  114  to a set of valves  118 ,  120 ,  122  and  124 . The system may also include various restrictors  116  and  126 . 
     In this exemplary embodiment, a therapeutic solution enters the inlet and may pass through a restriction  116  if one is in place. The valves are configured to deliver the desired dose rate through the outlet catheter  128 . The valves may be configured in parallel using valves  118  and  122 . Alternately, the valves may be configured in series using valves  118  and  120 . Further, the valves may be configured in various complicated arrangements. 
     For example, if two 0.4 ml/day valves or restrictors separated by valves are placed in parallel, the resulting flow would have a maximum of 0.8 ml/day depending on the pump&#39;s capacity. On the other hand, the two valves or restrictors, in series would yield a lower flow rate. 
     Various configurations of valves and restrictors may be envisioned. Configurations may be envisioned that permit multiple therapeutic solution inlet points delivered to a single outlet, a single inlet to multiple outlets, and various combinations. Further configurations may be envisioned that permit a variety of dose options. 
       FIG. 5  depicts an exemplary method for use by the dose control module. The method  130  begins with the establishment of a prescription or a set of prescriptions as seen in block  132 . A surgeon may establish the prescriptions before or during the surgery using a computer. Alternately, the prescriptions may be established using an RF signal device after implanting. Access to the prescriptions may be varied by time of day, reservoir levels, bolus limitations, time-out periods, and average dose limits, among others. 
     Once implanted, the dose control module may permit the patient to select a prescription as seen in block  134 . The selection of a prescription may, for example, be to initiate a bolus injection or select from a preset set of dosage rates. The patient may activate an external control unit and transmit the desired prescription parameters to the dose control module. The prescription parameters may include dose type, dose rate, drug type, limits, and duration, among other data. 
     The dose control module then determines whether the selected prescription is permissible as seen in block  136 . Permissibility of a prescription may be a function of dosage limits, reservoir availability, and other limits and conditions included as part of the prescription set by a doctor. If the selected prescription provides dosage rates above the prescribed limit, the system ignores the selection as seen in block  139 . Alternately, if the selection is permissible, the dose control module may implement the prescription as seen in block  138 . To implement the prescription, the dose control module configures the valves in accordance with the prescription settings and other parameters. 
       FIG. 6  depicts another exemplary method  140 . The dose control module receives a request for a new dosage as seen in block  141 . The request may be received from a patient control unit or may be preprogrammed in the dose control module. The dose control module may test the request to determine whether it complies with dosage rules as seen in block  142 . These dosage rules may include limits on average dose, periods between bolus treatment, and time of day restrictions, among others. If the request does not comply, the control unit may apply a default dosage as seen in block  148 . 
     However, if the request does comply, the system may determine how to implement the dose. This determination may include determining the strength of the treatment solution in the reservoir as seen in block  143 . The strength of solution may be affected by degradation, initial concentration, time in place, and other factors. For example, the dose control unit may determine the effective concentration of a treatment solution using a degradation model and then implement a flow rate that provides the requested dose as seen in block  144 . However, the determination may be made before the compliance test or at other steps in the method. 
     Once the dose is implemented, the dose control module monitors the length of time the dose has been implemented. This may include storing a start time and comparing a clock value to the start time. Alternately, a timer may be started as seen in block  145 . 
     Periodically, the system may confirm the request with an external patient control unit as seen in block  146 . If the patient control unit confirms the request, the timer may be restarted or a new initial time recorded. 
     However, if the patient control unit does not respond or the unit does not confirm the dose, the dose control module may determine whether time has expired on the does as seen in block  147 . If time has not expired, the dose control module may again seek to confirm the dose. If the time expires, the module may return to a default dose as seen in block  148 . 
       FIG. 7  is another exemplary method  156  for use by the system. Data is received as seen in block  157 . The clock is then accessed in block  158 . The clock may provide a time and date for comparison with stored times or may provide a period since refilling. These times are then applied in a degradation model as seen in block  159 . However, various parameters may be used in a degradation model including model constants, stored values, and reservoir condition data, among others. From the degradation model, the system may determine a strength of the treatment solution and implement a dosage as seen in block  160 . For example, application of the degradation model may provide an effective strength of the treatment solution. A flow rate may be implemented that complies with the dose. 
       FIG. 8  depicts a further method  150  for use by the system. A patient control unit receives data from a dosage control module as seen in block  151 . The data may include flow rate or dosage data, parameters, and prescription options, among others. The data is stored in the patient control unit as seen in block  152 . Operations may then be performed on the data. With flow rate data, the patient control unit may determine a level in a treatment solution reservoir as seen in a block  153 . If the level is below a threshold as determined in block  154 , the patient control unit may alert a patient or medical professional as seen in block  155 . However, various operations may be envisaged and the result of these operations may be transmitted and/or stored in the dosage control module. 
       FIGS. 9A ,  9 B,  9 C and  9 D depict an exemplary embodiment of a valve for use by the system. The valve is enclosed in a hermetically sealed exterior housing  180 . An interior housing  170  surrounds an interior enclosure or chamber  167 . The valve has an inlet port  163  and an outlet port  165 . The inlet port  163  and outlet port  165  connect to the interior chamber  167 . Inside the interior chamber  167  is a core, armature, or plunger  169 , which may include magnetic material. The core  169  may include channels  162  that permit fluid to pass by the core  169  when the core is in the open position. The core  169  also includes heads  171  and  166 .  FIGS. 9A and 9B  depict the valve in a closed position. In the closed position, head  166  rests on seat  168 , effectively blocking the outlet  165 . 
     Outside of the interior chamber  167  and interior housing  170  reside magnets  178  and  172  and coils  174  and  176 . When an electromagnetic signal is directed through connectors  182  and  184  and wires (not shown) to the coils  174  or  176 , one of the coils  174  or  176  induces a magnetic field causing movement of the core  169 . For example, if the core  169  is in the closed position as shown in  FIGS. 9A and 9B , the coil  176  may be activated, inducing a magnetic field which draws the core  169  away from magnet  172  and into the open position. The core  169  may be held in the open position by magnet  178  once the coil  176  is deactivated 
     The hermetically sealed exterior housing  180  and the interior housing  170  may be made of non-magnetic material. The exterior housing  180  and interior housing  170  may be formed of mu-metal, non-magnetic titanium, ceramic, polymer, and other compounds. Mu-metal provides protection against external electromagnetic fields such as those produced by MRIs. The system may also counteract the electromagnetic fields by producing an opposing field using the coils  174  and  176 . 
       FIGS. 9C and 9D  depict the valve in the open position. To move from the closed position to the open position, coil  176  may be activated creating a greater magnetic attraction near the inlet  163 . The core  169  then moves towards the inlet  163 . The coil  176  may then be deactivated and the magnet  178  holds the core in place. Fluid then travels through channels  162  and  164  into the chamber  169  and through the outlet  165 . To close the valve, the coil  174  may be activated, creating a greater magnetic field closer to the outlet, drawing the core  169  back to the closed position. Magnet  172  holds the core in position. In this manner, the position of the core may be cycled to produce the desired dosage rate with minimum energy usage. 
     The permanent magnets  172  and  178  hold the core  169  in position. These permanent magnets  172  and  178  also provide a redundancy protection in the case of mechanical shock to the system. In the event of shock or change in gravitational forces, the magnets  172  and  178  hold the core in the set position. The magnets  172  and  178  also resist fluid pressures from altering the position of the valve core  169 . 
     The seat size of the valve may also be important for reducing unwanted movement of the core. If the seat size is small enough, the pump pressure experienced by the core when proximate to the inlet port will exert a force less than that exerted by the magnet holding the core in place. 
     However, various configurations of seats may be envisioned. Seats may be positioned about both inlets such that fluid only flows while the core is in a transient position. In another example, the inlet and outlet may be reversed. 
     For the configuration shown, the pump pressure will influence the valve to stay in a closed position in the event that power is unavailable or either of the magnets is damaged. Alternately, if a fail open valve is preferred, a valve seat may be placed on the inlet and the dose channels placed about the outlet. The pump pressure would then influence the core to remain in the open position if power is unavailable. 
     An alternate embodiment may be seen in  FIGS. 10A ,  10 B,  10 C and  10 D. In the embodiment shown in  FIG. 10A , the magnet  203  is positioned about a port  192 . Coils  208  and  210  may be alternately activated to move the core  198  into the open position near port  192  or into the closed position near port  194 . In the closed position, a head  200  may rest on the valve seat  206 , effectively closing off flow. 
     The core  198  may take various forms. The core  198  may be made from magnetic material. This material may include paramagnetic material. In which case, the coils and magnets would pull the core  198  into position. Alternately, the core  198  could be composed of diamagnetic material. In which case, the core  198  would be pushed into position by the magnets and coils. The core  198  may also be made from composite materials that include magnetic material such as Teflon-coated ferromagnetic materials, among others. Alternately, the core  198  may be made of a non-magnetic material with magnetic rods or a secondary core inside. 
     The head may take various forms. These forms may include silicone and other biocompatible materials suitable for fitting snug against a valve seat. 
     As seen in  FIG. 10B , the core  198  may have channels  202  and a head  200 . In the closed position the head  200  may rest against a valve seat. However, in the open position, the channels  202  may permit fluid to flow around the core  198  and through the outlet.  FIG. 10C  shows an alternate embodiment in which the channels  216  may be drilled through the core  214 . In this case, the core  214  has a head  212  that rests on the valve seat in the closed position. 
     However, various seats and core styles may be envisaged. For example,  FIG. 10D  shows a triangular core  222  that may be positioned in a cylindrical chamber. The triangular core may have a head  220  that rests on a valve seat effectively closing the valve. However, when open, fluid may pass around the edges of the triangle with little restriction. Alternate embodiments may include a spherical core in an enclosure with a square cross-section. In this example, the sphere may be a silicone coated ferromagnetic sphere. However, many embodiments may be envisioned. 
       FIG. 11  depicts a further embodiment of the valve  230  as a core  238  in a chamber  236 . The valve has a bellows  252 . Coils  248  and  250  may be cycled on and off to move the core  238  through the chamber  236 . When the core  238  rests on valve seat  246 , the bellows  252  may fill with the pharmaceutical solution. Alternately, when the core  238  and the core head  242  rest against valve seat  244 , the bellows  252  may drain through the outlet  232 . One advantage to this system is that the maximum dose a patient can receive in the event of valve failure is equal to the volume of the bellows  252 . 
     In a similar embodiment, one end of the chamber may have channels instead of a valve seat. The core  238  may be positioned at that end and permit fluid flow. In this case, the bellows will act to control pressure fluctuations or spread out the drug delivery. 
     Dosage control systems including the valves of  FIGS. 9 ,  10 , and  11  have another advantage in that the valve position may be determined through the response of the coils to signals. If the core is positioned near the coil, the signal will represent a different inductance than if the core is further from the coil. In this manner, the system may determine valve position and in the event of error, attempt to reposition the valve, stop flow from the pump, or alert the patient, among others. 
       FIG. 12  depicts an exemplary method for operating the valve. The method  270  involves energizing the coil  272  to move the valve position into the desired position. The dose control module may then test to determine whether the core is in the correct position by sending a signal through one or the other coils as seen in block  174 . The returning signal will vary in accordance with the inductance caused by the presence of the core. The dose control module may then analyze the signal as seen in block  276  to determine the position of the core. Alternately, the system may test and analyze the signal prior to energizing the coils. Further, the system may periodically test the position of the core to ensure that the valve is in the appropriate position and is functioning properly. 
     The coils may also be used to counteract external magnetic fields such as those produced by an MRI. The MRI may induce a current in the coils. This signal may be interpreted by a dose control module to ascertain the direction and strength of the magnetic field. A signal may then be sent to the coils to counteract or oppose the external magnetic field. In this manner, valve position may be ensured and damage to the magnets or the core prevented. 
     Another valve for use by the system may be seen in  FIG. 13 .  FIG. 13  represents a solenoid valve with dual armatures, wherein each armature may be opened by one or more coils. Valve  290  has two ports  292  and  294 . These ports connect to a housing forming an interior chamber. Each port has an associated valve seat,  302  and  314 . Against these valve seats may be valve heads and armatures  304  and  312 , respectively. Each of these armatures is held in place by an associated spring  306  and  310 , respectively. These springs,  306  and  310 , may press against a spring stop  308 . Alternately, they may press against separate spring stops. A spool  298  surrounds the enclosure. Coils  300  are wrapped around the spool  298 . Activation of the coils  300  induces a magnetic field that draws the valve heads  304  and  312  away from their respective seats  302  and  314  and towards spring stop  308 . The armatures  304  and  312  may have a common axis of movement but move in opposite directions, toward the center of valve  290 . 
     Fluid flow occurs from one port, i.e. inlet port  292 , through the interior chamber  316  and connecting chamber  320 , and exists through chamber  318  and outlet port  294 . 
     The armatures  304  and  312  may be made of magnetic material. Heads on the armatures may be made of silicone or a material capable of sealing against the valve seats. The armatures may also have channels, grooves, or holes to permit fluid flow when the head is away from the valve seat. The springs may be made of magnetic or non-magnetic material. 
     The hermetically sealed exterior housing  296  may be made of non-magnetic material. The exterior housing  296  may be formed of non-magnetic titanium, ceramic, polymer, and other compounds. 
     The valve system of  FIG. 13  provides several redundancies. Having two springs and valve assemblies ensures that if one valve assembly sticks open, fluid will still be prevented from flowing by the second operational valve assembly. If the valve experiences a directional magnetic field, one valve assembly might open, however, the other would remain closed. Further, if a leak across a seat causes pressure to build in the interior of the valve, the pressure will force the valve assemblies against their seats, preventing unwanted leakage. 
     The design of the inlet size is also important. Smaller inlet diameters prevent leaks from the inlet port by reducing the total force against the head. This smaller force may also permit smaller spring constants to be used, reducing the opening force requirements and thus the power requirements of the coil. 
     An alternate embodiment may be seen in  FIG. 14  in which a common spring  344  presses the valve heads  342  and  346  against their respective seats. During the closed position, the coils  340  wrapped around spool  338  may be activated to draw the valve heads  342  and  346  inward along the axis of flow, compressing spring  344 . The single spring assembly removes the double spring redundancy and hence, the valve may be advantaged by few parts for wear and tear. 
       FIG. 15  depicts a further exemplary embodiment of the valve as seen in  FIGS. 13 and 14 . Armatures  362  and  366  are pressed against valve seat associated with ports  352  and  354  with at least one spring  364 . A coil  360  may induce a magnetic force in the armatures  362  and  366  that opposes the spring  364 . A core  368  is located between the armatures allowing for enough space to permit movement of the armatures sufficient for permitting fluid flow, In addition, a cover  369  is located about the coil. The cover  369  and the core  368  are made from materials that act to guide the magnetic field and in turn strengthen the effect of the coil-induced magnetic field on the armatures  362  and  366 . 
     These valves, shown in  FIGS. 13 ,  14 , and  15 , have the advantage of being redundantly in a closed position. The valves also have the advantage of alternately being in a closed position given a strong magnetic field in one direction along the axis of the valve. Such a strong magnetic field may be experienced during testing, such as an MRI. 
     Moving the valves into an open position may require more energy than keeping the valves open. This is a product of the inductance-produced electromagnetic field. To open the valves, a larger amount of energy must be applied to the coil to produce. a magnetic field strong enough to open the valves. However, once the valves are open, the magnetic field may be maintained using less energy. As such, energy may be conserved by reducing the current applied to the coils or providing a timed signal to the coils, among others. 
       FIG. 16  depicts an exemplary embodiment of a timed signal. The induced magnetic field is represented by the line  0 . To produce this magnetic field, a signal A is directed to the coils. To open the valve, a longer duration pulse is provided to the coils causing the magnetic field to increase. Once the valve is open, the pulse stops, causing the magnetic field to gradually decrease. During this gradual decrease, a current signal B is produced in the coil. This signal may be used for regenerating power sources or recovering energy. In this manner, power may be conserved. Once the magnetic field reaches a minimum, the signal A may produce another pulse, increasing the magnetic field. In this manner, the valve may be kept open using a minimal amount of energy. Alternately, a larger powered pulse may be used to open the valve and a constant low power signal to keep the valve open. 
       FIG. 17  depicts an exemplary circuitry  375  for producing the signals of  FIG. 16 . An induction coil  377  is associated with a valve. A power source  376  is coupled with the coil  377  through switches  378 ,  379  and  380 , and diode  381 . The switches may take various forms including various transistors, four-level diodes, relays, and thyristors, among others. The circuitry may also include an energy collection circuitry  382 . A controlling circuitry may be coupled to the switches. However, various modifications to this circuitry  375  may be envisaged. 
     If switches  378  and  379  are closed or activated, current flows through the coil  377 , inducing a magnetic field. Once the field is strong enough, the valve opens. In one embodiment, the magnetic forces on the armatures in the valve overcome a spring force and open the valve. After initially opening the valve, the switches  378  and  379  are used to produce electric pulses through the coil  377  to maintain the magnetic field above a threshold value below which the valve would close or reseat. 
     Between pulses, the magnetic field motivates a current to flow in the same direction as that used to induce the field. If switch  380  is closed or activated, current is directed through the diode  381  toward the positive end of the power source. Alternately, energy may be collected by an energy collection circuitry  382 . This circuitry  382  is depicted as a capacitor. However, it may take various forms. 
     Various additional switches, diodes and connections may be made to permit periodic reversal of current for producing a degaussing field with the coil  377 . The system may also be grounded as seen in ground  383 . However, various modifications to the circuitry may be envisaged. 
       FIG. 18  is an exemplary method for use by the system. The method  370  calls for energizing the coils as seen in block  372 . This may be accomplished by providing a higher amplitude pulse or a longer pulse to produce the induced electromagnetic field. The coil may then be pulsed as seen in a block  374  to maintain the valve in an open position. The pulsing may be used to reduce the energy requirement of the system. Further, between pulses, the induced voltage and current in the coil may be used to recover energy. 
     The system may be subject to various strong external electromagnetic fields, as in the case of MRI testing. The valves of  FIGS. 9 ,  10  and  11  and those of  FIGS. 13 ,  14 , and  15  may undergo these strong magnetic fields when placed in a patient. It is therefore important to counteract these strong electromagnetic fields to ensure functionality of the valve. 
       FIG. 19  depicts a circuit that may be used to counteract the effects of a strong unidirectional electromagnetic field or produce a degaussing field. The system may test the coil  402  to determine the direction of the electromagnetic field. Then, an opposing electromagnetic field may be produced in the coil by applying the correct voltage or current. To produce current in one direction, the switches  394  and  398  may be closed and the signal generator  392  activated. To produce current in the opposite direction, and thus an opposite electromagnetic field, switches  396  and  400  may be closed while switches  394  and  398  remain open. 
     This circuitry may also be used to periodically change the direction of current across a coil, effectively providing a degaussing field. The circuitry of  FIG. 17  may also be modified to recover power. The circuitry of  FIG. 17  may be incorporated as part of signal generator  392 . Alternately, a modified circuitry may be placed about the coil  402 . 
       FIG. 20  depicts an exemplary method  410 . In this method, the system tests for the electromagnetic field induced by the external, directional electromagnetic field. The system then applies an opposing field by sending a current in the appropriate direction through the coils as seen in a block  414 . 
     In this manner, an external electromagnetic field may be counteracted. For the dual-head solenoid type valve, a strong unidirectional field would attempt to open one side while exerting excess pressure on the other side. Neutralization of the field would ensure valve closure, reduce wear on valve parts, and prevent magnetizing the armatures. For the movable core valve, a strong unidirectional magnet field may place the core in an undesired position, damage the permanent magnets and magnetize the core, Here too, the coils may be used to neutralize the field, Simultaneously, some of an induced current in the coils could be used to regenerate power. 
     Both valve types may also benefit from a reverse current periodically applied to the coils. The reverse current would cause a degaussing of magnetism and prevent residual buildup of magnetism in either the core or the armatures. Such a reverse current may be produced by the circuit of  FIG. 19 . 
     As such, a dose control module and valves are described. In view of the above detailed description of the present invention and associated drawings, other modifications and variations will now become apparent to those skilled in the art. It should also be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the present invention as set forth in the claims which follow.