Abstract:
A cryogenic system having a base unit tethered to a handpiece connectable to a needle probe. The handpiece holds a replaceable cryogen canister assembly. The base unit connects to mains to provide power to the handpiece. The base unit includes a back-up power source in the event of interruptions of power via mains.

Description:
This application claims the benefit of U.S. Provisional Application No. 61/589,263, filed on Jan. 20, 2012, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is generally directed to medical devices, systems, and methods, particularly for cooling-induced remodeling of tissues. Embodiments of the invention include devices, systems, and methods for applying cryogenic cooling to dermatological tissues so as to selectively remodel one or more target tissues along and/or below an exposed surface of the skin. Embodiments may be employed for a variety of cosmetic conditions, optionally by inhibiting undesirable and/or unsightly effects on the skin (such as lines, wrinkles, or cellulite dimples) or on other surrounding tissue. Other embodiments may find use for a wide range of medical indications. The remodeling of the target tissue may achieve a desired change in its behavior or composition. 
     The desire to reshape various features of the human body to either correct a deformity or merely to enhance one&#39;s appearance is common. This is evidenced by the growing volume of cosmetic surgery procedures that are performed annually. 
     Many procedures are intended to change the surface appearance of the skin by reducing lines and wrinkles. Some of these procedures involve injecting fillers or stimulating collagen production. More recently, pharmacologically based therapies for wrinkle alleviation and other cosmetic applications have gained in popularity. 
     Botulinum toxin type A (BOTOX®) is an example of a pharmacologically based therapy used for cosmetic applications. It is typically injected into the facial muscles to block muscle contraction, resulting in temporary enervation or paralysis of the muscle. Once the muscle is disabled, the movement contributing to the formation of the undesirable wrinkle is temporarily eliminated. Another example of pharmaceutical cosmetic treatment is mesotherapy, where a cocktail of homeopathic medication, vitamins, and/or drugs approved for other indications is injected into the skin to deliver healing or corrective treatment to a specific area of the body. Various cocktails are intended to effect body sculpting and cellulite reduction by dissolving adipose tissue, or skin resurfacing via collagen enhancement. Development of non-pharmacologically based cosmetic treatments also continues. For example, endermology is a mechanical based therapy that utilizes vacuum suction to stretch or loosen fibrous connective tissues which are implicated in the dimpled appearance of cellulite. 
     While BOTOX® and/or mesotherapies may temporarily reduce lines and wrinkles, reduce fat, or provide other cosmetic benefits they are not without their drawbacks, particularly the dangers associated with injection of a known toxic substance into a patient, the potential dangers of injecting unknown and/or untested cocktails, and the like. Additionally, while the effects of endermology are not known to be potentially dangerous, they are brief and only mildly effective. 
     In light of the above, improved medical devices, systems, and methods utilizing a cryogenic approach to treating the tissue have been proposed, particularly for treatment of wrinkles, fat, cellulite, and other cosmetic defects. These new techniques can provide an alternative visual appearance improvement mechanism which may replace and/or compliment known bioactive and other cosmetic therapies, ideally allowing patients to decrease or eliminate the injection of toxins and harmful cocktails while providing similar or improved cosmetic results. These new techniques are also promising because they may be performed percutaneously using only local or no anesthetic with minimal or no cutting of the skin, no need for suturing or other closure methods, no extensive bandaging, and limited or no bruising or other factors contributing to extended recovery or patient “down time.” Additionally, cryogenic treatments are also desirable since they may be used in the treatment of other cosmetic and/or dermatological conditions (and potentially other target tissues), particularly where the treatments may be provided with greater accuracy and control, less collateral tissue injury and/or pain, and greater ease of use. 
     While these new cryogenic treatments are promising, careful control of temperature along the cryogenic probe is necessary in order to obtain desired results in the target treatment area as well as to avoid unwanted tissue injury in adjacent areas. Once the probe is introduced into a target treatment area, cooling fluid flows through the probe and probe temperature decreases proximally along the length of the probe toward the probe hub. There can be safety issues with handling removal of sub-portions of the probe and with providing the electrical power. Accordingly, it is desirable to account for these issues in use of the cryogenic probe. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the invention provide improved medical devices, systems, and methods. Many of the devices and systems described herein will be beneficial for monitoring operational parameters when cryogenically remodeling target tissue. 
     Some embodiments of the invention relate a system that can create and regulate a freeze zone in tissue. The system can include a probe, handpiece, cryogen cartridge assembly, and control unit. The cryogen cartridge and probe may attach (and detach) to the handpiece. The cryogen cartridge assembly provides a source of cryogen fluid for delivery to the probe. The probe delivers refrigeration power to cool tissue. The handpiece regulates the delivery of cryogen to the probe from the cartridge. Actuation of a switch on the handpiece initiates an automated refrigeration cycle. 
     The handpiece attaches (and detaches) via a tethered cable to the control unit, also referred to as a base unit or base device. Monitoring and controlling of the handpiece can be performed by the control unit. The control unit can connect to mains and provide operational power to the handpiece. The control unit also can include a back-up power source to provide operational power to the handpiece in case of a mains failure (e.g., blackout, mains cord detachment). In some embodiments, the back-up power source includes enough power to only safely shut down the handpiece. In some embodiments, a mains failure causes the control unit to interrupt or override a treatment algorithm with a safe shut-down algorithm. 
     One embodiment of the invention relates to a system having a base unit electrically tethered to a handpiece. The cryogenic system can include a back-up power source. The handpiece is configured to hold a cryogenic fluid source. 
     Another embodiment of the invention relates to method that provides a cryogenic system. The system can include a base unit and a handpiece having at least one cryogenic needle. The cryogenic system is used to remodel tissue. A cryogenic fluid supply is disposed in the handpiece. A valve within the handpiece is electrically powered by the base unit to actuate for providing cryogenic fluid to the at least one needle. The base unit has a primary power source connectable to mains and a back-up power source. 
     In one aspect of the method, the base unit is configured to provide power from the back-up battery source when the primary power source fails during use of the cryogenic system. 
     In another aspect of the method, the valve comprises a stepper motor coupled to a plunger. 
     In another aspect of the method, the handpiece includes a slave microcontroller for controlling the valve, where the slave controller is controlled by a master microcontroller of the base unit. 
     In another aspect of the method, the back-up power source is a supercapacitor. 
     Another embodiment of the invention relates to a cryogenic system having a base unit. The system includes a handpiece that is connectable to at least one cryogenic needle. A cryogenic fluid supply is disposed in the handpiece. A valve within the handpiece is electrically powered by the base unit to actuate for providing cryogenic fluid to the at least one needle. The base unit has a primary power source connectable to mains and a back-up power source. 
     In one aspect of the system, the base unit is configured to provide power from the back-up battery source when the primary power source fails during use of the cryogenic system. 
     In another aspect of the system, the valve comprises a stepper motor coupled to a plunger. 
     In another aspect of the system, the handpiece includes a slave microcontroller for controlling the valve, where the slave controller is controlled by a master microcontroller of the base unit. 
     In another aspect of the system, the back-up power source is a supercapacitor. 
     Another embodiment of the invention relates to a cryogenic system having a cryogenic handpiece configured to sequentially couple with a plurality of cryogenic canister assemblies, where each canister assembly can include a filter. 
     Another embodiment of the invention relates a cryogenic cartridge assembly for use with a cryogenic handpiece. The cryogenic handpiece can have a cartridge assembly interface. The cartridge assembly can includes a body having an interface configured for detachably coupling with the interface of the handpiece. A cryogenic canister can be supported by the body. The canister may contain cryogenic fluid and a fluid path configured to be in fluid communication with the handpiece when the interface of the body is coupled with the interface of the handpiece. A filter can be disposed along the fluid path between the canister and the interface of the body. 
     Another embodiment of the invention relates to a method that provides plurality of cryogenic canister assemblies configured for sequential use with a cryogenic handpiece. Each canister assembly has an associated canister with a frangible seal, a housing supporting the canister, a pin supported by the housing and movable relative to the seal so as to penetrate the seal when the assembly is mounted to the handpiece, and a desiccant/molecular sieve downstream of the pin and upstream of a port from which the fluid flows into the handpiece. 
     A first canister assembly of the plurality cryogenic canister assemblies is mounted to the handpiece. The cryogenic handpiece mounted with the first canister assembly is used to remodel tissue. The first canister assembly is removed thereby halting use of the cryogenic handpiece to remodel tissue. A second canister assembly of the plurality cryogenic canister assemblies is mounted to the handpiece. The cryogenic handpiece mounted with the second canister assembly is then used to remodel the tissue. 
     Another embodiment of the invention relates to a cryogenic system including a cryogenic handpiece. A plurality of cryogenic canister assemblies can be configured for sequential use with a cryogenic handpiece. Each canister assembly has an associated canister with a frangible seal, a housing supporting the canister, a pin supported by the housing and movable relative to the seal so as to penetrate the seal when the assembly is mounted to the handpiece, and a molecular sieve downstream of the pin and upstream of a port from which the fluid flows into the handpiece. 
     Another embodiment of the invention relates to a system having a cryogenic handpiece configured to engage with a probe assembly. The handpiece can be configured to vent and halt use of the probe assembly via partial disengagement of the probe assembly. 
     Another embodiment of the invention relates to a method, in which a probe assembly with a needle supported by a probe housing and a handpiece attachable with the probe housing is provided. The probe assembly includes an interface with a mechanical attachment and inner and outer seals for mounting to a handpiece. The handpiece includes circuitry identifying a type of needle when coupled to the probe housing, the circuitry disengaging from the housing during removal of the probe so as to shut down cooling when the outer seal still sealingly engages the handpiece sufficiently to vent cryogen fluid therethrough when the mechanical attachment is partially disengaged from the handpiece. The handpiece attached with the probe assembly by providing cryogen fluid from the handpiece to the probe assembly is used to treat tissue. Use of the handpiece attached with the probe assembly is then halted by stopping flow of the cryogen fluid from the handpiece to the probe assembly. The probe assembly is partially detached after halting use to vent residual cryogen fluid remaining within the handpiece and/or probe assembly. 
     In one aspect of the method, the type of needle relates to a number of needles of the probe assembly. 
     Another embodiment of the invention relates to a probe assembly for use with a cryogenic handpiece having an interface coupled with circuitry configured to shut down cooling flow to the interface in response to partial probe disengagement from the handpiece. The probe assembly can include a probe body having an interface configured for coupling with the interface of the probe assembly. A needle may be supported by a probe body. The interface may include a mechanical attachment and a cryogenic fluid seal for engagement with the interface of the handpiece. The mechanical attachment can be configured to restrain the probe assembly relative to the handpiece and the seal to sealingly engage the interface of the handpiece when the probe assembly moves from full engagement with the handpiece interface to partially disengaged from the handpiece. 
     Another embodiment of the invention relates to a system including a probe assembly with a needle supported by a probe housing. The system further includes a handpiece attachable with the probe housing. The probe assembly includes an interface with a mechanical attachment and inner and outer seals for mounting to a handpiece. The handpiece includes circuitry identifying a type of needle when coupled to the probe housing. During removal of the probe assembly, circuitry is disengaged so as to shut down cooling. This occurs while the outer seal still sealingly engages the handpiece sufficiently to vent fluid therethrough when the mechanical attachment is partially disengaged from the handpiece. 
     In one aspect of the system, the type of needle relates to a number of needles of the probe assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a self-contained subdermal cryogenic remodeling probe and system, according to an embodiment of the invention. 
         FIG. 1B  is a partially transparent perspective view of the self-contained probe of  FIG. 1A , showing internal components of the cryogenic remodeling system and schematically illustrating replacement treatment needles for use with the disposable probe. 
         FIG. 2A  schematically illustrates components that may be included in the treatment system. 
         FIG. 2B  is a cross-sectional view of the system of  FIG. 1A , according to an embodiment of the invention. 
         FIGS. 2C and 2D  are cross-sectional views showing operational modes of the system of  FIG. 2B . 
         FIGS. 3A-3B  illustrate an exemplary embodiment of a clad needle probe, according to an embodiment of the invention. 
         FIG. 4  is a flow chart illustrating an exemplary algorithm for heating the needle probe of  FIG. 3A , according to an embodiment of the invention. 
         FIG. 5  is a flow chart schematically illustrating a method for treatment using the disposable cryogenic probe and system of  FIGS. 1A and 1B , according to an embodiment of the invention. 
         FIG. 6A  is a flow chart schematically illustrating a method for treatment using the disposable cryogenic probe and system of  FIGS. 1A and 1B , according to an embodiment of the invention. 
         FIG. 6B  is a flow chart schematically illustrating a method for treatment using the disposable cryogenic probe and system of  FIGS. 1A and 1B , according to an embodiment of the invention. 
         FIG. 6C  is a simplified depiction of the method of treatment of  FIG. 6B . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides improved medical devices, systems, and methods. Embodiments of the invention will facilitate remodeling of target tissues disposed at and below the skin, optionally to treat a cosmetic defect, a lesion, a disease state, and/or so as to alter a shape of the overlying skin surface, while providing protection to portions of non-target tissues, including the skin, which are directly above the target tissues. 
     At least some embodiments of the present invention may improve upon at least some aspects of previous systems. At least some previous systems relied upon the user to mechanically open and close a valve. Some of the present embodiments may improve upon these previous systems by performing this function via electronic control of an electromechanical valve. The improvement enables the system to perform repeatable, automated refrigeration cycles. It also enables monitoring and control for safe, reliable performance. 
     At least some embodiments enable what previously required separate mechanical and electrical connection of the probe to be performed with one assembly step and may be safer to use during installation and removal. Some embodiments also or alternatively enable power and control through a mains operated, external control unit; or fully integrating control and power through component selection in particular the electro-mechanical valve. Some embodiments also or alternatively enable the full integration of the refrigerant into the handpiece by adapting refrigerant cartridges to provide cryogen fluid to an attached needle probe. 
     Embodiments of the disclosed system may be hand held providing ease of use. The system may also enable untethered or disassembled configurations that allow the system to be easily transportable. The system may include sensors and automation for added safety and reliability. The probe and cartridge are designed for safe and reliable use even in instances where they are not handled following normal operating instructions. A user interface may provide key information to the user regarding the system status. 
     Among the most immediate applications, although not the only applications, of the present invention may be the amelioration of lines and wrinkles, particularly by inhibiting muscular contractions which are associated with these cosmetic defects so as so improve an appearance of the patient. Rather than relying entirely on a pharmacological toxin or the like to disable muscles so as to induce temporary paralysis, many embodiments of the invention will at least in part employ cold to immobilize muscles. Advantageously, nerves, muscles, and associated tissues may be temporarily immobilized using moderately cold temperatures of 10° C. to −5° C. without permanently disabling the tissue structures. Using an approach similar to that employed for identifying structures associated with atrial fibrillation, a needle probe or other treatment device can be used to identify a target tissue structure in a diagnostic mode with these moderate temperatures, and the same probe (or a different probe) can also be used to provide a longer term or permanent treatment, optionally by ablating the target tissue zone and/or inducing apoptosis at temperatures from about −5° C. to about −50° C. In some embodiments, apoptosis may be induced using treatment temperatures from about −1° C. to about −15° C., or from about −1° C. to about −19° C., optionally so as to provide a permanent treatment that limits or avoids inflammation and mobilization of skeletal muscle satellite repair cells. In some embodiments, temporary axonotmesis or neurotmesis degeneration of a motor nerve is desired, which may be induced using treatment temperatures from about −25° C. to about −90° C. Hence, the duration of the treatment efficacy of such subdermal cryogenic treatments may be selected and controlled, with colder temperatures, longer treatment times, and/or larger volumes or selected patterns of target tissue determining the longevity of the treatment. Additional description of cryogenic cooling for treatment of cosmetic and other defects may be found in commonly assigned U.S. Pat. No. 7,713,266 entitled “Subdermal Cryogenic Remodeling of Muscle, Nerves, Connective Tissue, and/or Adipose Tissue (Fat)”, U.S. Pat. No. 7,850,683 entitled “Subdermal Cryogenic Remodeling of Muscles, Nerves, Connective Tissue, and/or Adipose Tissue (Fat)”, and U.S. patent application Ser. No. 13/325,004, entitled “Method for Reducing Hyperdynamic Facial Wrinkles” and attached hereto as Appendix A, the full disclosures of which are each incorporated by reference herein. 
     In addition to cosmetic treatments of lines, wrinkles, and the like, embodiments of the invention may also find applications for treatments of subdermal adipose tissues, benign, pre-malignant lesions, malignant lesions, acne and a wide range of other dermatological conditions (including dermatological conditions for which cryogenic treatments have been proposed and additional dermatological conditions), and the like. Embodiments of the invention may also find applications for alleviation of pain, including those associated with muscle spasms as disclosed in commonly assigned U.S. Pub. No. 2009/0248001 entitled “Pain Management Using Cryogenic Remodeling” the full disclosure of which is incorporated herein by reference. 
     Referring now to  FIGS. 1A and 1B , one example of a system for cryogenic remodeling includes a self-contained probe handpiece generally having a proximal end  12  and a distal end  14 . A handpiece body or housing  16  has a size and ergonomic shape suitable for being grasped and supported in a surgeon&#39;s hand or other system operator. As can be seen most clearly in  FIG. 1B , a cryogenic cooling fluid supply  18  (also referred to as cryogen cartridge), a supply valve  32  and an optional electrical power source  20  are found within housing  16 , along with a circuit  22 S having a processor for controlling cooling applied by self-contained system  10  in response to actuation of an input  24 . Alternatively, electrical power can be applied through a cord from a remote power source. Accordingly, functional references to the electrical power source  20  are meant to include external and internal power source embodiments. Alternatively, electrical power source  20  can be an emergency back-up power source in the advent of a power delivery failure from the remote power source. Power source  20  also supplies power to heater element  44  in order to heat the proximal region of probe  26  thereby helping to prevent unwanted skin damage, and a temperature sensor  48  adjacent the proximal region of probe  26  helps monitor probe temperature. Additional details on the heater  44  and temperature sensor  48  are described in greater detail below. When actuated, supply valve  32  controls the flow of cryogenic cooling fluid from fluid supply  18 . Some embodiments may, at least in part, be manually activated, such as through the use of a manual supply valve and/or the like, so that processors, electrical power supplies, and the like may not be required. 
     Extending distally from distal end  14  of housing  16  is a tissue-penetrating cryogenic cooling probe  26 . Probe  26  is thermally coupled to a cooling fluid path extending from cooling fluid source  18 , with the exemplary probe comprising a tubular body receiving at least a portion of the cooling fluid from the cooling fluid source therein. The exemplary probe  26  comprises a 27 g needle having a sharpened distal end that is axially sealed. Probe  26  may have an axial length between distal end  14  of housing  16  and the distal end of the needle of between about 0.5 mm and 5 cm, preferably having a length from about 3 mm to about 10 mm. Such needles may comprise a stainless steel tube with an inner diameter of about 0.006 inches and an outer diameter of about 0.012 inches, while alternative probes may comprise structures having outer diameters (or other lateral cross-sectional dimensions) from about 0.006 inches to about 0.100 inches. Generally, needle probe  26  will comprise a 16 g or smaller size needle, often comprising a 20 g needle or smaller, typically comprising a 25, 26, 27, 28, 29, or 30 g or smaller needle. 
     In some embodiments, probe  26  may comprise two or more needles arranged in a linear array, such as those disclosed in previously incorporated U.S. Pat. No. 7,850,683. Another exemplary embodiment of a probe having multiple needle probe configurations allow the cryogenic treatment to be applied to a larger or more specific treatment area. Other needle configurations that facilitate controlling the depth of needle penetration and insulated needle embodiments are disclosed in commonly assigned U.S. Patent Publication No. 2008/0200910 entitled “Replaceable and/or Easily Removable Needle Systems for Dermal and Transdermal Cryogenic Remodeling,” the entire content of which is incorporated herein by reference. Multiple needle arrays may also be arrayed in alternative configurations such as a triangular or square array. 
     Arrays may be designed to treat a particular region of tissue, or to provide a uniform treatment within a particular region, or both. In some embodiments needle  26  is releasably coupled with body  16  so that it may be replaced after use with a sharper needle (as indicated by the dotted line) or with a needle having a different configuration. In exemplary embodiments, the needle may be threaded into the body, it may be press fit into an aperture in the body or it may have a quick disconnect such as a detent mechanism for engaging the needle with the body. A quick disconnect with a check valve is advantageous since it permits decoupling of the needle from the body at any time without excessive coolant discharge. This can be a useful safety feature in the event that the device fails in operation (e.g. valve failure), allowing an operator to disengage the needle and device from a patient&#39;s tissue without exposing the patient to coolant as the system depressurizes. This feature is also advantageous because it allows an operator to easily exchange a dull needle with a sharp needle in the middle of a treatment. One of skill in the art will appreciate that other coupling mechanisms may be used. 
     Addressing some of the components within housing  16 , the exemplary cooling fluid supply  18  comprises a canister, sometimes referred to herein as a cartridge, containing a liquid under pressure, with the liquid preferably having a boiling temperature of less than 37° C. When the fluid is thermally coupled to the tissue-penetrating probe  26 , and the probe is positioned within the patient so that an outer surface of the probe is adjacent to a target tissue, the heat from the target tissue evaporates at least a portion of the liquid and the enthalpy of vaporization cools the target tissue. A supply valve  32  may be disposed along the cooling fluid flow path between canister  18  and probe  26 , or along the cooling fluid path after the probe so as to limit coolant flow thereby regulating the temperature, treatment time, rate of temperature change, or other cooling characteristics. The valve will often be powered electrically, per the direction of processor  22 S, but may at least in part be manually powered. The exemplary power source  20  comprises a rechargeable or single-use battery. Additional details about valve  32  are disclosed below and further disclosure on the power source  20  may be found in commonly assigned Int&#39;l Pub. No. WO 2010/075438 entitled “Integrated Cryosurgical Probe Package with Fluid Reservoir and Limited Electrical Power Source,” the entire contents of which is incorporated herein by reference. 
     The exemplary cooling fluid supply  18  comprises a single-use canister. Advantageously, the canister and cooling fluid therein may be stored and/or used at (or even above) room temperature. The canister may have a frangible seal or may be refillable, with the exemplary canister containing liquid nitrous oxide, N 2 O. A variety of alternative cooling fluids might also be used, with exemplary cooling fluids including fluorocarbon refrigerants and/or carbon dioxide. The quantity of cooling fluid contained by canister  18  will typically be sufficient to treat at least a significant region of a patient, but will often be less than sufficient to treat two or more patients. An exemplary liquid N 2 O canister might contain, for example, a quantity in a range from about 1 gram to about 40 grams of liquid, more preferably from about 1 gram to about 35 grams of liquid, and even more preferably from about 7 grams to about 30 grams of liquid. 
     Processor  22  will typically comprise a programmable electronic microprocessor embodying machine readable computer code or programming instructions for implementing one or more of the treatment methods described herein. The microprocessor will typically include or be coupled to a memory (such as a non-volatile memory, a flash memory, a read-only memory (“ROM”), a random access memory (“RAM”), or the like) storing the computer code and data to be used thereby, and/or a recording media (including a magnetic recording media such as a hard disk, a floppy disk, or the like; or an optical recording media such as a CD or DVD) may be provided. Suitable interface devices (such as digital-to-analog or analog-to-digital converters, or the like) and input/output devices (such as USB or serial I/O ports, wireless communication cards, graphical display cards, and the like) may also be provided. A wide variety of commercially available or specialized processor structures may be used in different embodiments, and suitable processors may make use of a wide variety of combinations of hardware and/or hardware/software combinations. For example, processor  22  may be integrated on a single processor board and may run a single program or may make use of a plurality of boards running a number of different program modules in a wide variety of alternative distributed data processing or code architectures. 
     Referring now to  FIG. 2 , the flow of cryogenic cooling fluid from fluid supply  18  is controlled by a supply valve  32 . Supply valve  32  may comprise an electrically actuated solenoid valve, a motor actuated valve or the like operating in response to control signals from controller  22 , and/or may comprise a manual valve. Exemplary supply valves may comprise structures suitable for on/off valve operation, and may provide venting of the fluid source and/or the cooling fluid path downstream of the valve when cooling flow is halted so as to limit residual cryogenic fluid vaporization and cooling. Additionally, the valve may be actuated by the controller in order to modulate coolant flow to provide high rates of cooling in some instances where it is desirable to promote necrosis of tissue such as in malignant lesions and the like or slow cooling which promotes ice formation between cells rather than within cells when necrosis is not desired. More complex flow modulating valve structures might also be used in other embodiments. For example, other applicable valve embodiments are disclosed in previously incorporated U.S. Pub. No. 2008/0200910. 
     Still referring to  FIG. 2 , an optional heater (not illustrated) may be used to heat cooling fluid supply  18  so that heated cooling fluid flows through valve  32  and through a lumen  34  of a cooling fluid supply tube  36 . Supply tube  36  is, at least in part, disposed within a lumen  38  of needle  26 , with the supply tube extending distally from a proximal end  40  of the needle toward a distal end  42 . The exemplary supply tube  36  comprises a fused silica tubular structure (not illustrated) having a polymer coating and extending in cantilever into the needle lumen  38 . Supply tube  36  may have an inner lumen with an effective inner diameter of less than about 200 μm, the inner diameter often being less than about 100 μm, and typically being less than about 40 μm. Exemplary embodiments of supply tube  36  have inner lumens of between about 15 and 50 μm, such as about 30 μm. An outer diameter or size of supply tube  36  will typically be less than about 1000 μm, often being less than about 800 μm, with exemplary embodiments being between about 60 and 150 μm, such as about 90 μm or 105 μm. The tolerance of the inner lumen diameter of supply tubing  36  will preferably be relatively tight, typically being about +/−10 μm or tighter, often being +/−5 μm or tighter, and ideally being +/−3 μm or tighter, as the small diameter supply tube may provide the majority of (or even substantially all of) the metering of the cooling fluid flow into needle  26 . Previously incorporated U.S. Patent Publication No. 2008/0200910 discloses additional details on the needle  26  along with various alternative embodiments and principles of operation. 
     The cooling fluid injected into lumen  38  of needle  26  will typically comprise liquid, though some gas may also be injected. At least some of the liquid vaporizes within needle  26 , and the enthalpy of vaporization cools the needle and also the surrounding tissue engaged by the needle. An optional heater  44  (illustrated in  FIG. 1B ) may be used to heat the proximal region of the needle  26  in order to prevent unwanted skin damage in this area, as discussed in greater detail below. Controlling a pressure of the gas/liquid mixture within needle  26  substantially controls the temperature within lumen  38 , and hence the treatment temperature range of the tissue. A relatively simple mechanical pressure relief valve  46  may be used to control the pressure within the lumen of the needle, with the exemplary valve comprising a valve body such as a ball bearing, urged against a valve seat by a biasing spring. An exemplary relief valve is disclosed in U.S. Provisional Patent Application No. 61/116,050 previously incorporated herein by reference. Thus, the relief valve allows better temperature control in the needle, minimizing transient temperatures. Further details on exhaust volume are disclosed in previously incorporated U.S. Pat. Pub. No. 2008/0200910. 
     The heater  44  may be thermally coupled to a thermally responsive element  50 , which is supplied with power by the controller  22  and thermally coupled to a proximal portion of the needle  26 . The thermally responsive element  50  can be a block constructed from a material of high thermal conductivity and low heat capacity, such as aluminum. A temperature sensor  52  (e.g., thermistor, thermocouple) can also be thermally coupled the thermally responsive element  50  and communicatively coupled to the controller  22 . The controller  22  can be configured to receive temperature information of the thermally responsive element  50  via the temperature sensor  52  in order to provide the heater  44  with enough power to maintain the thermally responsive element  50  at a particular temperature. 
     The controller  22  can be further configured to monitor power draw from the heater  44  in order to characterize tissue type, perform device diagnostics, and/or provide feedback for a tissue treatment algorithm. This can be advantageous over monitoring temperature alone, since power draw from the heater  44  can vary greatly while temperature of the thermally responsive element  50  remains relatively stable. For example, during treatment of target tissue, maintaining the thermally responsive element  50  at 40° C. during a cooling cycle may take 1.0 W initially and is normally expected to climb to 1.5 W after 20 seconds, due to the needle  26  drawing in surrounding heat. An indication that the heater is drawing 2.0 W after 20 seconds to maintain 40° C. can indicate that an aspect of the system  10  is malfunctioning and/or that the needle  26  is incorrectly positioned. Correlations with power draw and correlated device and/or tissue conditions can be determined experimentally to determine acceptable treatment power ranges. 
     In some embodiments, it may be preferable to limit frozen tissue that is not at the treatment temperature, i.e., to limit the size of a formed cooling zone within tissue. To achieve this, metering coolant flow could maintain a large thermal gradient at its outside edges. This may be particularly advantageous in applications for creating an array of connected cooling zones (i.e, fence) in a treatment zone, as time would be provided for the treatment zone to fully develop within the fenced in portion of the tissue, while the outer boundaries maintained a relatively large thermal gradient due to the repeated application and removal of refrigeration power. This could provide a mechanism within the body of tissue to thermally regulate the treatment zone and could provide increased ability to modulate the treatment zone at a prescribed distance from the surface of the skin. A related treatment algorithm could be predefined, or it could be in response to feedback from the tissue. 
     Such feedback could be temperature measurements from the needle  26 , or the temperature of the surface of the skin could be measured. However, in many cases monitoring temperature at the needle  26  is impractical due to size constraints. To overcome this, operating performance of the sensorless needle  26  can be interpolated by measuring characteristics of thermally coupled elements, such as the thermally responsive element  50 . 
     One such measured characteristic could be the power required to heat the thermally responsive element  50 , therefore the medium which the thermally responsive element  50 , or the thermally coupled needle  26 , is coupled to. For example, very little power would be required to warm and maintain the temperature of the thermally conductive block in air. Various materials could be characterized. For example, the thermally responsive element  50  could be used to determine whether the thermally responsive element  50 , or the thermally coupled needle  26 , has sufficient contact with skin due to the thermal load of the skin. This would be useful for ensuring that the needle  26  was correctly placed prior to treatment. This could be done without flowing coolant to the needle  26 , or alternatively, by metering very little coolant to the needle  26 , i.e., less than what is required to treat tissue. 
     Once the treatment has started, there may be more or less residual refrigerant that affected the thermally conductive element  50  depending upon how much thermal load was applied to the needle  26 . This could be used to characterize the tissue(s) the probes was placed into. For example, there would be relatively more heat drawn from the thermally conductive element  50  in insulative tissue such as adipose tissue. Since thermal load on the distal end of the needle  26  would be affected by the development of an cooling zone around the needle  26 , the thermally conductive element  50  could be used to determine the state of the needle  26  as ice forms. 
     Power feedback could provide feedback to regulate the delivery of refrigerant based upon the tissue, formation of ice, contact with the skin, or other useful information. The feedback could be used to control the treatment zone to the desired configuration. In addition, the feedback could be used to diagnose a treatment failure. For instance if the probe had three needles delivering refrigerant, but only two were working, the thermally conductive element could detect the failure and inform the user. 
     Temperature feedback could also used in conjunction with power feedback. Temperature sensing could occur on the needle  26  if possible, on the thermally conductive element  50 , and/or remote to the thermally conductive element. For example, the thermally conductive element  50  could reside on a detachable cooling probe and be thermally coupled to a handpiece, with feedback and control circuits located within the handpiece (e.g., housing  16 ). This could be advantageous to provide a low cost detachable cooling probe and for system reliability, since the probe could be coupled to a controller in the reusable handpiece. Thus, practically offering higher capability due to the ability to afford more precise controls. 
     The thermally conductive element  50  could be thermally coupled to the needle  26  at a proximal tissue interface. When refrigerant was delivered, excess refrigerant would return through the needle. The excess refrigerant could be in the form of cool gas or liquid that had not yet converted to gas through the latent heat of vaporization. The excess refrigerant could change dependent upon the tissue(s) the probe was in, variations in tissue temperature, presence of local heat sources (arteries and veins), and metabolic effects. The excess refrigerant could also be affected by the effect of the treatment over time. In particular, changes in thermal loading as a function of the cooling of adjacent tissue and the formation of ice. The thermally conductive element could be tailored to deliver comparable, or more heat than the available refrigeration power. However, the transfer of heat into the tissue would be constrained by the material and dimensions of the needle. For example, a relatively long needle might receive enough heat from the adjacent tissue along its length to prevent the freeze zone from extending more proximally than desired. Alternatively the ability to transfer more heat into the tissue could be achieved by providing improved thermal coupling from the thermally conductive block into the tissue. This could be achieved by increasing the diameter and or wall thickness of the needle, or through the addition of thermally conductive cladding to the proximal portion of the needle. This coupling could also be optimized to extend the length of the protection desired. For instance, the cladding or portion of increased wall thickness and diameter could extend through the dermis and subdermal fat layer, then end. Further the cooling of the tip and the heating of more proximal tissue could be uncoupled. This could be achieved by applying an insulative material between the cladding and the underlying needle. Therefore, the heat through the protected portion of tissue could be controlled independent of the refrigeration of the tip. This would be advantageous in that the heat added would not compromise the refrigerant delivered to the tip and the refrigerant would not comprise the heat added to the tissue. 
     Additional methods of monitoring cooling and maintaining an unfrozen portion of the needle include the addition of a heating element and/or monitoring element into the needle itself. This could consist of a small thermistor or thermocouple, and a wire that could provide resistive heat. Other power sources could also be applied such as infrared light, radiofrequency heat, and ultrasound. These systems could also be applied together dependent upon the control of the treatment zone desired. 
     Alternative methods to inhibit excessively low transient temperatures at the beginning of a refrigeration cycle might be employed instead of or together with the limiting of the exhaust volume. For example, the supply valve might be cycled on and off, typically by controller  22 , with a timing sequence that would limit the cooling fluid flowing so that only vaporized gas reached the needle lumen (or a sufficiently limited amount of liquid to avoid excessive dropping of the needle lumen temperature). This cycling might be ended once the exhaust volume pressure was sufficient so that the refrigeration temperature would be within desired limits during steady state flow. Analytical models that may be used to estimate cooling flows are described in greater detail in previously incorporated U.S. Patent Pub. No. 2008/0154,254. 
     Referring now to  FIG. 2A , the flow of cryogenic cooling fluid from fluid supply  18  is controlled by a supply valve  32 . Supply valve  32  may comprise an electrically actuated solenoid valve, a motor actuated valve or the like operating in response to control signals from controller  22 , and/or may comprise a manual valve. Exemplary supply valves may comprise structures suitable for on/off valve operation, and may provide venting of the fluid source and/or the cooling fluid path downstream of the valve when cooling flow is halted so as to limit residual cryogenic fluid vaporization and cooling. Additionally, the valve may be actuated by the controller in order to modulate coolant flow to provide high rates of cooling in some instances where it is desirable to promote necrosis of tissue such as in malignant lesions and the like or slow cooling which promotes ice formation between cells rather than within cells when necrosis is not desired. More complex flow modulating valve structures might also be used in other embodiments. For example, other applicable valve embodiments are disclosed in previously incorporated U.S. Pub. No. 2008/0200910. 
     Still referring to  FIG. 2A , an optional cooling supply heater (not illustrated) may be used to heat cooling fluid supply  18  so that heated cooling fluid flows through valve  32  and through a lumen  34  of a cooling fluid supply tube  36 . In some embodiments safety mechanism can be included so that the cooling supply is not overheated. Examples of such embodiments are disclosed in commonly assigned Int&#39;l. Pub. No. WO 2010075438, the entirety of which is incorporated by reference herein. 
     Supply tube  36  is, at least in part, disposed within a lumen  38  of needle  26 , with the supply tube extending distally from a proximal end  40  of the needle toward a distal end  42 . The exemplary supply tube  36  comprises a fused silica tubular structure (not illustrated) having a polymer coating and extending in cantilever into the needle lumen  38 . Supply tube  36  may have an inner lumen with an effective inner diameter of less than about 200 μm, the inner diameter often being less than about 100 μm, and typically being less than about 40 μm. Exemplary embodiments of supply tube  36  have inner lumens of between about 15 and 50 μm, such as about 30 μm. An outer diameter or size of supply tube  36  will typically be less than about 1000 μm, often being less than about 800 μm, with exemplary embodiments being between about 60 and 150 μm, such as about 90 μm or 105 μm. The tolerance of the inner lumen diameter of supply tubing  36  will preferably be relatively tight, typically being about +/−10 μm or tighter, often being +/−5 μm or tighter, and ideally being +/−3 μm or tighter, as the small diameter supply tube may provide the majority of (or even substantially all of) the metering of the cooling fluid flow into needle  26 . Additional details on various aspects of needle  26  along with alternative embodiments and principles of operation are disclosed in greater detail in U.S. Patent Publication No. 2008/0154254 entitled “Dermal and Transdermal Cryogenic Microprobe Systems and Methods,” the entire contents of which are incorporated herein by reference. U.S. Patent Pub. No. 2008/0200910, previously incorporated herein by reference, also discloses additional details on the needle  26  along with various alternative embodiments and principles of operation. 
     The cooling fluid injected into lumen  38  of needle  26  will typically comprise liquid, though some gas may also be injected. At least some of the liquid vaporizes within needle  26 , and the enthalpy of vaporization cools the needle and also the surrounding tissue engaged by the needle. An optional heater  44  (illustrated in  FIG. 1B ) may be used to heat the proximal region of the needle in order to prevent unwanted skin damage in this area, as discussed in greater detail below. Controlling a pressure of the gas/liquid mixture within needle  26  substantially controls the temperature within lumen  38 , and hence the treatment temperature range of the tissue. A relatively simple mechanical pressure relief valve  46  may be used to control the pressure within the lumen of the needle, with the exemplary valve comprising a valve body such as a ball bearing, urged against a valve seat by a biasing spring. Thus, the relief valve allows better temperature control in the needle, minimizing transient temperatures. Further details on exhaust volume are disclosed in U.S. Patent Publication No. 2008/0200910, previously incorporated herein by reference. 
     Alternative methods to inhibit excessively low transient temperatures at the beginning of a refrigeration cycle might be employed instead of or together with the limiting of the exhaust volume. For example, the supply valve might be cycled on and off, typically by controller  22 , with a timing sequence that would limit the cooling fluid flowing so that only vaporized gas reached the needle lumen (or a sufficiently limited amount of liquid to avoid excessive dropping of the needle lumen temperature). This cycling might be ended once the exhaust volume pressure was sufficient so that the refrigeration temperature would be within desired limits during steady state flow. Analytical models that may be used to estimate cooling flows are described in greater detail in U.S. Pub. No. 2008/0154254, previously incorporated herein by reference. 
       FIG. 2B  shows a cross-section of the housing  16 . This embodiment of the housing  16  is powered by an external source, hence the attached cable, but could alternatively include a portable power source. As shown, the housing includes a cartridge assembly  50 . The cartridge assembly  50  is connectable with a cartridge receiver  52  of the handpiece  16 , which is configured to hold a pressured refrigerant cartridge. The cartridge receiver  52  includes an elongated cylindrical passage  54 , which is dimensioned to hold a commercially available cooling fluid cartridge. A distal portion of the cartridge receiver  52  includes a filter device  56 , which has an elongated conical shape. In some embodiments, the cartridge assembly  50  is largely integrated into the housing  10 , however, in alternative embodiments, the cartridge assembly  50  is a wholly separate assembly, which may be pre-provided with a coolant fluid source  18 . 
     The filter device  56  fluidly couples the coolant fluid source (cartridge)  18  at a proximal end to the valve  32  at a distal end. The filter device  56  includes at least one particulate filter  58 . In the shown embodiment, a particulate filter  58  at each proximal and distal end of the filter device  56  is included. The particulate filter  58  can be configured to prevent particles of a certain size from passing through. For example, the particulate filter  58  can be constructed as a microscreen having a plurality of passages less than 2 microns in width, and thus particles greater than 2 microns would not be able to pass. 
     The filter device  56  also includes a molecular filter  60  that is configured to capture fluid impurities. In some embodiments, the molecular filter  60  is a plurality of filter media (e.g., pellets, powder, particles) configured to trap molecules of a certain size. For example, the filter media can comprise molecular sieves having pores ranging from 1-20 Å. In another example, the pores have an average size of 5 Å. The molecular filter  60  can have two modalities. In a first mode, the molecular filter  60  will filter fluid impurities received from the cartridge  18 . However, in another mode, the molecular filter  60  can capture impurities within the valve  32  and fluid supply tube  36  when the system  10  is not in use, i.e., when the cartridge  18  is not fluidly connected to the valve  32 . 
     It has been found that in some instances fluid impurities may leach out from various aspects of the system  10 . These impurities can include trapped moisture in the form of water molecules and chemical gasses. The presence of these impurities is believed to hamper cooling performance of the system  10 . When the system  10  is not in use, the filter device  56  can act as a desiccant that attracts and traps moisture within the system  10 , as well as chemicals out gassed from various aspects of the system  10 . 
     As shown in  FIG. 2C , the cartridge  18  can be held by the cartridge receiver  52  such that the cartridge  18  remains intact and unpunctured. In this inactive mode, the cartridge is not fluidly connected to the valve  32 . A removable cartridge cover  62  can be attached to the cartridge receiver  52  such that the inactive mode is maintained while the cartridge is held by the system  10 . 
     In use, the cartridge cover  62  can be removed and supplied with a new cartridge  18  containing a cooling fluid, or an entire new cartridge assembly  50 . In some cases, a procedure may require a plurality of cartridge assemblies  50 . The cartridge cover  62  can then be reattached to the cartridge receiver  52  by turning the cartridge cover  62  until female threads  64  of the cartridge cover  62  engage with male threads of the cartridge receiver  52 . The cartridge cover  62  can be turned until resilient force is felt from an elastic seal  66 , as shown in  FIG. 2C . To place the system  10  into use, the cartridge cover  62  can be further turned until the distal tip of the cartridge  18  is punctured by a puncture pin  68 , as shown in  FIG. 2D . Once the cartridge  18  is punctured, cooling fluid escapes the cartridge by flowing through the filter device  56 , where the impurities within the cooling fluid are captured. The purified cooling fluid then passes to the valve  32 , and onto the coolant supply tube  36  to cool the probe  26 . In some embodiments the filter device, or portions thereof, is replaceable. In other embodiments, the entire handpiece may be single use and/or disposable. 
     The cryogen cartridge  18  is removeably connected at its proximal end to a cartridge cover  62  by a spring device  70 . The cryogen cartridge  18  is removeably connected at its distal end to the filter assembly  66  via an interference fit with the elastic seal  66 . The body of the filter assembly  56  is a nose cone  72  that contains the molecular filter  60 , particulate filters  58 , and the puncture pin  68 . A proximal portion of the nose cone  72  has an internal diameter that engages with the elastic seal  66  via spring device  74 . The nose cone  72  is installed on the tip of the cryogen cartridge  18 . The handpiece  16  has a mating element that the nose cone  72  engages with. A distal portion of the nose cone  72  has a flanged or stepped portion  76 . A switch  78  of the handpiece  16  engages with the stepped portion  76  to provide an indication of positive engagement. 
     The cartridge assembly  50  is attachable to into the handpiece  16 . The threaded cap is then rotated within the mating threads of the handpiece  16 . The rotation of the cartridge cover  62  advances the cryogen cartridge  18  within the handpiece  16 . The nose cone  72  extending from the end of the cartridge  18  engages a port  80  within the handpiece  16  and advances until an o-ring seal on the nose cone  72  is fully seated within the bore of the handpiece  16  mating port. The seated distance is controlled by a separate step on the cartridge nose cone  72  engaging the cartridge housing of the handpiece  16 . Therefore once the o-ring is seated within the handpiece port  80 , no additional loading is placed on the mated port  80 . The cartridge receiver  52  of the handpiece  16  can be constructed as one rigid element, preferably from hard anodized aluminum for its rigidity, heat transfer and electrical isolation characteristics. 
     As the cartridge assembly  50  continues to be threaded onto the cartridge receiver  52 , the cryogen cartridge  18  advances into the now seated nose cone  72 . Further advancement engages a frangible seal at the end of the cryogen cartridge  18  with the puncture pin  68  seated in the nose cone. Puncturing the seal releases cryogen through the bore of the puncture pin  68 . To prevent leakage, the frangible seal on the cryogen cylinder secures to the puncture pin  68 . In addition a secondary elastomeric seal seals against the distal end of the cryogen cartridge  18 . One or both of these may be used to prevent cryogen leakage. 
     In use, the cryogen flows through a  2  micron mesh screen, followed by the molecular filter  60 , and by the particulate filter  58 . The mesh screens  58  serve to remove particulate from the refrigerant stream. The molecular sieves column serves to remove moisture, oils and other contaminants from the refrigerant. The refrigerant exits the cryogen cartridge  18  in a pure form that enables reliable refrigeration performance. 
     The nose cone engages the switch  78  during installation enabling the handpiece to recognize the presence of the cartridge. The cryogen pressure is regulated by heating the cryogen cylinder using a temperature regulated kapton heater  82  that engages the cryogen cartridge  18  along its length and around its diameter. 
     The cartridge assembly  50  is removed by unthreading the cartridge cover  62  and removing the cartridge. The engagement mechanism of the cartridge cover  62  to the cryogen cartridge  18  ensures a pressurized cartridge  18  cannot be fluidly connected with the handpiece  16  without the cartridge cover  62  securing it in place. The nose cone  72  is removed with the cartridge by having secure attachment to the elastic seal  66  at the end of the refrigerant cartridge. Secure attachment can be in the form of an interference fit between the parts or physical latching of the parts together. 
     The probe  26  has sealed tip, 20 g or smaller needles. The needles have sharpened tips for percutaneous insertion. The needles are fully sealed. Cryogen fluid is delivered into the needles through an internal tube. The cryogen expands and evaporates within the tips of the needles cooling the surrounding tissue. The cryogen exhaust passes up the needle and exhausts the system outside of the patient and into the treatment room. 
     The probe  26  threads into a mating manifold in the handpiece  16 . The probe has a sealing o-ring that mates with the handpiece and isolates the refrigerant entering the probe from the cryogen exhaust. The probe  26  has a circuit board with pads that engage pogo pin electrical connectors on the handpiece. As the probe  26  is threaded into the handpiece  16 , the threads first ensure secure mechanical engagement. Further threading passes the inlet o-ring seal past the exhaust port on the handpiece  16 . Then electrical engagement occurs enabling the system to recognize the probe presence and enabling system functionality. Finally, there is an index mark and a feature that provides an audible and tactile click at the rotation stop indicating full probe engagement. Similarly, removal of the probe first results in electrical disengagement. Electrical disengagement triggers the system to close the delivery valve shutting off the flow of refrigerant. Further unthreading results in the proximal, high-pressure sealing o-ring passing the exhaust port on the handpiece. Therefore, any residual refrigerant upstream of the probe  300  is safely vented while the probe is still securely attached to the handpiece. The probe is then fully unthreaded from the handpiece and removed. 
     The internal fluid path passes first through a 2 micron particle filter, then enters a tube within the probe. The fluid path then separates into multiple smaller tubes for each needle that extend into the needle tips. The exhausted gas passes through the annular space between the delivery tube and internal bore of the needles, then exits through the handpiece. In one embodiment, a second o-ring isolates the exhausting refrigerant. This forces the exhaust to pass a sensor in the handpiece. The sensor could be a temperature sensor used to detect proper performance of the system by measuring the temperature of the exhaust stream. 
     The needles on the probe  26  are attached with thermally-conductive epoxy to a temperature-regulated, hard-anodized aluminum block. The attachment provides thermal coupling and electrical isolation. The aluminum block temperature is regulated with a temperature sensor and resistive heating element. The electrical elements are attached to the block using thermal epoxy that provides thermal coupling and electrical isolation. Power is supplied to the electrical elements to regulate the temperature. The heating element and sensor are electrically coupled to the circuit board that mates with the handpiece pogo pins. Therefore, engagement of the probe  26  enables the system to provide temperature regulation of the block and therefore the needles. In addition, the electrical circuit could contain an element such as a fuse that can be disabled once the probe has been used preventing reuse of the probe. Further, the probe  26  could have an identifier such as a resistor or other identification chip that could identify and even provide instructions to the handpiece on the proper functional use of the system. Such an identifier can include information about the gage of needles of the probe  26 , the length of needles of the probe  26 , and/or the type of needle of the probe  26 . In particular a particular treatment algorithm could be enabled. 
     The handpiece  16  mates with the probe  26  and cryogen cartridge  18 , and also with the control unit. The handpiece is plumbed from the cartridge to the probe. An electromechanical valve is present that isolates refrigerant from the probe. A second manual mechanical valve is present in the event the electromechanical valve errors and does not stop flow. Engagement of the mechanical valve vents the downstream refrigerant, preventing further flow of refrigerant to the electromechanical valve and probe. The electromechanical valve is a stepper motor with a plunger that compresses an elastomeric ring. Actuation of the valve opens or closes the fluid path through the elastomeric ring. The selection of a stepper motor enables the use of the system with mains power or self-contained battery power. Treatment operation, including opening and closing the valve is programmed into the system and controlled through the control unit. The treatment cycle is initiated through pressing an electromechanical switch on the handpiece  16 . The treatment can be stopped by pressing the same switch. 
     The fluid path is constructed to have a minimal amount of volume enabling the system to be responsive and enabling the use of small refrigerant cartridges that keep the system small, light and easy to handle. The fluid path is constructed primarily from thermally insulative components. This enables the refrigeration power to be available for cooling the probe needles rather than cooling elements of the system. In addition this makes the system robust to environmental conditions that could heat or cool the refrigerant therefore preventing inconsistent refrigeration cycle performance. 
     Sensors are present in the handpiece to determine the state of the system. Selection of sensors that require low power, such as thermistors, enables the system to be mains powered or alternatively battery powered and ensure the system remains small and light for ease of handling. Sensors are used to ensure proper function such as: opening and closing of the valve during treatment, ensuring proper performance of the probe, and maintaining cartridge pressure. Sensors also detect the state of the system ensuring safe and reliable performance of the system including: monitoring the system for leaks, ensuring the probe and cartridge are engaged and ready for use prior to enabling initiating the treatment cycle, and ensuring the heaters on the probe and cartridge assembly  50  are performing normally. 
     A microcontroller  22 S on the handpiece acts as a slave to a microcontroller in the control unit  22 . The handpiece  16  microcontroller  22 S reads sensors on the handpiece and issues commands based upon the control unit commands. Communication between the handpiece and control unit and power supply to the handpiece are provide through a tether between the handpiece and control unit. 
     The control unit  22  contains a microcontroller that commands the handpiece  16  to perform functions. Feedback is provided to the control unit from the microcontroller  22 S on the handpiece. The control unit  22  provides feedback to the user audibly and visually as to the system state. The control unit is mains powered and has backup power provided from a super cap. The backup power enables the system to notify the user and safely shut the system down in the event of power disruption. 
     In the exemplary embodiment of  FIG. 3A , resistive heater element  314  is disposed near the needle hub  318  and near a proximal region of needle shaft  302 . The resistance of the heater element is preferably 1Ω to 1K Ω, and more preferably from 5Ω to 50Ω. Additionally, a temperature sensor  312  such as a thermistor or thermocouple is also disposed in the same vicinity. Thus, during a treatment as the needles cool down, the heater  314  may be turned on in order to heat the hub  318  and proximal region of needle shaft  302 , thereby preventing this portion of the device from cooling down as much as the remainder of the needle shaft  302 . The temperature sensor  312  may provide feedback to controller  22  and a feedback loop can be used to control the heater  314 . The cooling power of the nitrous oxide will eventually overcome the effects of the heater, therefore the microprocessor may also be programmed with a warning light and/or an automatic shutoff time to stop the cooling treatment before skin damage occurs. An added benefit of using such a heater element is the fact that the heat helps to moderate the flow of cooling fluid into the needle shaft  302  helping to provide more uniform coolant mass flow to the needles shaft  302  with more uniform cooling resulting. 
     The embodiment of  FIG. 3A  illustrates a heater fixed to the probe hub. In other embodiments, the heater may float, thereby ensuring proper skin contact and proper heat transfer to the skin. Examples of floating heaters are disclosed in commonly assigned Int&#39;l Pub. No. WO 2010/075448 entitled “Skin Protection for Subdermal Cyrogenic Remodelling for Cosmetic and Other Treatments”, the entirety of which is incorporated by reference herein. 
     In this exemplary embodiment, three needles are illustrated. One of skill in the art will appreciate that a single needle may be used, as well as two, four, five, six, or more needles may be used. When a plurality of needles are used, they may be arranged in any number of patterns. For example, a single linear array may be used, or a two dimensional or three dimensional array may be used. Examples of two dimensional arrays include any number of rows and columns of needles (e.g. a rectangular array, a square array, elliptical, circular, triangular, etc.), and examples of three dimensional arrays include those where the needle tips are at different distances from the probe hub, such as in an inverted pyramid shape. 
       FIG. 3B  illustrates a cross-section of the needle shaft  302  of needle probe  300 . The needle shaft can be conductively coupled (e.g., welded, conductively bonded, press fit) to a conductive heater  314  to enable heat transfer therebetween. The needle shaft  302  is generally a small (e.g., 20-30 gauge) closed tip hollow needle, which can be between about 0.2 mm and 5 cm, preferably having a length from about 0.3 cm to about 0.6 cm. The conductive heater element  314  can be housed within a conductive block  315  of high thermally conductive material, such as aluminum and include an electrically insulated coating, such as Type III anodized coating to electrically insulate it without diminishing its heat transfer properties. The conductive block  315  can be heated by a resister or other heating element (e.g. cartridge heater, nichrome wire, etc.) bonded thereto with a heat conductive adhesive, such as epoxy. A thermistor can be coupled to the conductive block  315  with heat conductive epoxy allows temperature monitoring. Other temperature sensors may also be used, such as a thermocouple. 
     A cladding  320  of conductive material is directly conductively coupled to the proximal portion of the shaft of needle shaft  302 , which can be stainless steel. In some embodiments, the cladding  320  is a layer of gold, or alloys thereof, coated on the exterior of the proximal portion of the needle shaft  302 . In some embodiments, the exposed length of cladding  320  on the proximal portion of the needle is 2 mm. In some embodiments, the cladding  320  be of a thickness such that the clad portion has a diameter ranging from 0.017-0.020 in., and in some embodiments 0.0182 in. Accordingly, the cladding  320  can be conductively coupled to the material of the needle  302 , which can be less conductive, than the cladding  320 . 
     In some embodiments, the cladding  320  can include sub-coatings (e.g., nickel) that promote adhesion of an outer coating that would otherwise not bond well to the needle shaft  302 . Other highly conductive materials can be used as well, such as copper, silver, aluminum, and alloys thereof. In some embodiments, a protective polymer or metal coating can cover the cladding to promote biocompatibility of an otherwise non-biocompatible but highly conductive cladding material. Such a biocompatible coating however, would be applied to not disrupt conductivity between the conductive block  315 . In some embodiments, an insulating layer, such as a ceramic material, is coated over the cladding  320 , which remains conductively coupled to the needle shaft  302 . 
     In use, the cladding  320  can transfer heat to the proximal portion of the needle  302  to prevent directly surrounding tissue from dropping to cryogenic temperatures. Protection can be derived from heating the non-targeting tissue during a cooling procedure, and in some embodiments before the procedure as well. The mechanism of protection may be providing latent heat to pressurized cryogenic cooling fluid passing within the proximal portion of the needle to affect complete vaporization of the fluid. Thus, the non-target tissue in contact with the proximal portion of the needle shaft  302  does not need to supply latent heat, as opposed to target tissue in contact with the distal region of the needle shaft  302 . To help further this effect, in some embodiments the cladding  320  is coating within the interior of the distal portion of the needle, with or without an exterior cladding. To additionally help further this effect, in some embodiments, the distal portion of the needle can be thermally isolated from the proximal portion by a junction, such as a ceramic junction. While in some further embodiments, the entirety of the proximal portion is constructed from a more conductive material than the distal portion. 
     In use, it has been determined experimentally that the cladding  320  can help limit formation of an cooling zone to the distal portion of the needle shaft  302 , which tends to demarcate at a distal end of the cladding  320 . This effect is shown depicted in later described  FIG. 6C  where non-target tissue, directly above target tissue, including skin and at least a portion of subcutaneous tissue are not made part of the ice-ball. Rather, cooling zones are formed only about the distal portions of the needles—in this case to target a temporal nerve branch. Thus, while non-target tissue in direct contact with proximal needle shafts remain protected from effects of cryogenic temperatures. Such effects can include discoloration and blistering of the skin. Such cooling zones may be associated with a particular physical reaction, such as the formation of an ice-ball, or with a particular temperature required to therapeutically affect the tissue therein. 
     An exemplary algorithm  400  for controlling the heater element  314 , and thus for transferring heat to the cladding  320 , is illustrated in  FIG. 4 . In  FIG. 4 , the start of the interrupt service routine (ISR)  402  begins with reading the current needle hub temperature  404  using a temperature sensor such as a thermistor or thermocouple disposed near the needle hub. The time of the measurement is also recorded. This data is fed back to controller  22  where the slope of a line connecting two points is calculated. The first point in the line is defined by the current needle hub temperature and time of its measurement and the second point consists of a previous needle hub temperature measurement and its time of measurement. Once the slope of the needle hub temperature curve has been calculated  406 , it is also stored  408  along with the time and temperature data. The needle hub temperature slope is then compared with a slope threshold value  410 . If the needle hub temperature slope is less than the threshold value then a treating flag is activated  412  and the treatment start time is noted and stored  414 . If the needle hub slope is greater than or equal to the slope threshold value  410 , an optional secondary check  416  may be used to verify that cooling has not been initiated. In step  416 , absolute needle hub temperature is compared to a temperature threshold. If the hub temperature is less than the temperature threshold, then the treating flag is activated  412  and the treatment start time is recorded  414  as previously described. As an alternative, the shape of the slope could be compared to a norm, and an error flag could be activated for an out of norm condition. Such a condition could indicate the system was not heating or cooling sufficiently. The error flag could trigger an automatic stop to the treatment with an error indicator light. Identifying the potential error condition and possibly stopping the treatment, may prevent damage to the proximal tissue in the form of too much heat, or too much cooling to the tissue. The algorithm preferably uses the slope comparison as the trigger to activate the treatment flag because it is more sensitive to cooling conditions when the cryogenic device is being used rather than simply measuring absolute temperature. For example, a needle probe exposed to a cold environment would gradually cool the needle down and this could trigger the heater to turn on even though no cryogenic cooling treatment was being conducted. The slope more accurately captures rapid decreases in needle temperature as are typically seen during cryogenic treatments. 
     When the treatment flag is activated  418  the needle heater is enabled  420  and heater power may be adjusted based on the elapsed treatment time and current needle hub temperature  422 . Thus, if more heat is required, power is increased and if less heat is required, power is decreased. Whether the treatment flag is activated or not, as an additional safety mechanism, treatment duration may be used to control the heater element  424 . As mentioned above, eventually, cryogenic cooling of the needle will overcome the effects of the heater element. In that case, it would be desirable to discontinue the cooling treatment so that the proximal region of the probe does not become too cold and cause skin damage. Therefore, treatment duration is compared to a duration threshold value in step  424 . If treatment duration exceeds the duration threshold then the treatment flag is cleared or deactivated  426  and the needle heater is deactivated  428 . If the duration has not exceeded the duration threshold  424  then the interrupt service routine ends  430 . The algorithm then begins again from the start step  402 . This process continues as long as the cryogenic device is turned on. 
     Preferred ranges for the slope threshold value may range from about −5° C. per second to about −90° C. per second and more preferably range from about −30° C. per second to about 57° C. per second. Preferred ranges for the temperature threshold value may range from about −15° C. to about 0° C., and more preferably may range from about 0° C. to about 10° C. Treatment duration threshold may range from about 15 seconds to about 75 seconds and more preferably may range from about 15 seconds to about 60 seconds. 
     It should be appreciated that the specific steps illustrated in  FIG. 4  provide a particular method of heating a cryogenic probe, according to an embodiment of the present invention. Other sequences of steps may also be performed according to alternative embodiments. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. Moreover, the individual steps illustrated in  FIG. 4  may include multiple sub-steps that may be performed in various sequences as appropriate to the individual step. Furthermore, additional steps may be added or removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. 
     The heating algorithm may be combined with a method for treating a patient. Referring now to  FIG. 5 , a method  100  facilitates treating a patient using a cryogenic cooling system having a reusable or disposable handpiece either of which that can be self-contained or externally powered with replaceable needles such as those of  FIG. 1B  and a limited capacity battery or metered electrical supply. Method  100  generally begins with a determination  110  of the desired tissue therapy and results, such as the alleviation of specific cosmetic wrinkles of the face, the inhibition of pain from a particular site, the alleviation of unsightly skin lesions or cosmetic defects from a region of the face, or the like. Appropriate target tissues for treatment are identified  112  (such as the subdermal muscles that induce the wrinkles, a tissue that transmits the pain signal, or the lesion-inducing infected tissues), allowing a target treatment depth, target treatment temperature profile, or the like to be determined. Step  112  may include performing a tissue characterization and/or device diagnostic algorithm, based on power draw of system  10 , for example. 
     The application of the treatment algorithm  114  may include the control of multiple parameters such as temperature, time, cycling, pulsing, and ramp rates for cooling or thawing of treatment areas. In parallel with the treatment algorithm  114 , one or more power monitoring algorithms  115  can be implemented. An appropriate needle assembly can then be mounted  116  to the handpiece, with the needle assembly optionally having a needle length, skin surface cooling chamber, needle array, and/or other components suitable for treatment of the target tissues. Simpler systems may include only a single needle type, and/or a first needle assembly mounted to the handpiece. 
     Pressure, heating, cooling, or combinations thereof may be applied  118  to the skin surface adjacent the needle insertion site before, during, and/or after insertion  120  and cryogenic cooling  122  of the needle and associated target tissue. Non-target tissue directly above the target tissue can be protected by directly conducting energy in the form of heat to the cladding on a proximal portion of the needle shaft during cooling. Upon completion of the cryogenic cooling cycle the needles will need additional “thaw” time  123  to thaw from the internally created cooling zone to allow for safe removal of the probe without physical disruption of the target tissues, which may include, but not be limited to nerves, muscles, blood vessels, or connective tissues. This thaw time can either be timed with the refrigerant valve shut-off for as short a time as possible, preferably under 15 seconds, more preferably under 5 seconds, manually or programmed into the controller to automatically shut-off the valve and then pause for a chosen time interval until there is an audible or visual notification of treatment completion. 
     Heating of the needle may be used to prevent unwanted skin damage using the apparatus and methods previously described. The needle can then be retracted  124  from the target tissue. If the treatment is not complete  126  and the needle is not yet dull  128 , pressure and/or cooling can be applied to the next needle insertion location site  118 , and the additional target tissue treated. However, as small gauge needles may dull after being inserted only a few times into the skin, any needles that are dulled (or otherwise determined to be sufficiently used to warrant replacement, regardless of whether it is after a single insertion, 5 insertions, or the like) during the treatment may be replaced with a new needle  116  before the next application of pressure/cooling  118 , needle insertion  120 , and/or the like. Once the target tissues have been completely treated, or once the cooling supply canister included in the self-contained handpiece is depleted, the used canister and/or needles can be disposed of  130 . The handpiece may optionally be discarded. 
     As discussed with reference to  FIG. 5 , a power monitoring algorithm  115  can be applied prior to, during, after, and in some cases in lieu of, the treatment algorithm  114 , such as the one shown in  FIG. 4 . One example of a power monitoring algorithm  600  is shown in  FIG. 6A , which illustrates a method for monitoring power demand from a heater when cooling fluid is passed through at least one needle. The power monitoring algorithm  600  can be performed during an actual treatment of tissue. At operation  602 , the controller (e.g., controller  22 ) monitors power consumption of a heater (e.g., heater  44 ), which is thermally coupled to a needle (e.g., needle  26 ), directly or via a thermally responsive element (e.g., element  50 ). Monitoring can take place during a tissue treatment procedure, for example, as discussed with reference to  FIG. 5 , performed in parallel to a treatment algorithm. Alternatively, power monitoring can take place during a diagnostic routine. 
     At operation  604 , the controller correlates a sampled power measurement with an acceptable power range corresponding to a tissue characteristic and/or operating parameter. This measurement may further be correlated according to the time of measurement and temperature of the thermally responsive element  50 . For example, during treatment of target tissue, maintaining the thermally responsive element  50  at 40° C. during a cooling cycle may be expected to require 1.0 W initially and is expected to climb to 1.5 W after 20 seconds, due to the needle  26  drawing in surrounding heat. An indication that the heater is drawing 2.0 W after 20 seconds to maintain 40° C. can indicate that an aspect of the system  10  is malfunctioning and/or that the needle  26  is incorrectly positioned within target tissue or primarily positioned in non-target tissue. Correlations with power draw and correlated device and/or tissue conditions can be determined experimentally to determine acceptable power ranges. 
     At operation  606 , the controller determines whether the power measurement is correlated within acceptable limits of an expected power draw, or to a power draw indicating a tissue or device problem. If the correlation is unacceptable, then the controller may in operation  608  initiate an alarm to the user and/or halt or modify the treatment algorithm. In some cases, the error is minor, for example, the controller may signal a user indication to modify operator technique, e.g., apply greater or lesser pressure to the skin. In other cases, the error can indicate a major valve malfunction, and signal an alert to abort the process and/or cause a secondary or purge valve to operate. If the correlation is acceptable, then in operation  610  it is determined whether the treatment algorithm is still in process, which will cause the power monitoring algorithm to end or continue to loop. Alternatively, the power monitoring algorithm  600  can simply loop until interrupted by the controller, for example, when treatment algorithm has ended or by some other trigger. 
     In some embodiments, the power monitoring algorithm  600  can be performed exclusively for tissue characterization purposes, e.g., to determine proper operating parameters for a later treatment, by only looping between operations  602  and  604  for a predetermined amount of time to collect data. Data can be collected and correlated by the controller to a particular tissue type and further correlated to optimal treatment parameters. For example, the characterized tissue may have a greater or lesser average amount of adjacent adipose tissue, which could require longer or shorter treatment times. This process could be performed, for example, by inserting the needle into the target tissue and providing only enough coolant to characterize the tissue, rather than remodel. 
       FIGS. 6B and 6C  show another power monitoring algorithm  612  for regulating a freeze zone, that can be implemented parallel to or in lieu of a treatment algorithm, such as the one shown in  FIG. 4 , as well as parallel to another power monitoring algorithm, such as the one shown in  FIG. 6A . At operation  614 , a valve is or has been previously regulated to provide at least one needle with coolant, with the needle being in contact with tissue, as illustrated in  FIG. 6C . After some time, a cooling zone forms within the tissue, and will continue to grow in size as long as the needle is supplied with coolant. Ideally, the ice ball is limited in size to the area of target tissue, to prevent unintentional treatment of the non-target tissue. While coolant is flowing, power demand from the heater is monitored, which can occur immediately or alternatively after a predetermined amount of time has passed since opening of the valve. 
     At operation  618 , the controller determines whether a sampled power measurement correlates to a maximum ice-ball size desired for a particular therapeutic effect, such as tissue remodeling. Correlations with power draw and ice ball size can be determined experimentally to determine acceptable power ranges, and the tissue can be pre-characterized according to a tissue characterization algorithm, such as shown in  FIG. 6A  This measurement may further be correlated according to the time of measurement and temperature of the thermally responsive element  50 . If the power draw does not correlate with the maximum allowable ice-ball size, then the monitoring is continued. 
     After a determination that the power demand correlates with the maximum ice ball size, the valve is regulated to provide the needle with less or no coolant at operation  620 . After some time the ice ball will decrease in size as heat is drawn in from surrounding tissue. During that time, power supplied to the heater is monitored at operation  622 . At operation  624 , the controller determines whether a sampled power measurement correlates to a minimum ice-ball size required to maintain the desired therapeutic effect. If the power draw does not correlate with the maximum allowable ice-ball size, then the monitoring is continued while the ice ball continues to decrease in size. 
     Eventually, at operation  624 , the power measurement will correspond with the minimum ice ball size. This causes the controller to loop the process and provide more coolant, which causes the ice ball to grow in size. The valve can be metered in this manner to maintain the ice ball within acceptable ice ball size tolerances, until the procedure is complete. 
     A variety of target treatment temperatures, times, and cycles may be applied to differing target tissues so as to achieve the desired remodeling. For example, as more fully described in U.S. Patent Publication Nos. 2007/0129714 and 2008/0183164, both previously incorporated herein by reference. 
     There is a window of temperatures where apoptosis can be induced. An apoptotic effect may be temporary, long-term (lasting at least weeks, months, or years) or even permanent. While necrotic effects may be long term or even permanent, apoptosis may actually provide more long-lasting cosmetic benefits than necrosis. Apoptosis may exhibit a non-inflammatory cell death. Without inflammation, normal muscular healing processes may be inhibited. Following many muscular injuries (including many injuries involving necrosis), skeletal muscle satellite cells may be mobilized by inflammation. Without inflammation, such mobilization may be limited or avoided. Apoptotic cell death may reduce muscle mass and/or may interrupt the collagen and elastin connective chain. Temperature ranges that generate a mixture of apoptosis and necrosis may also provide long-lasting or permanent benefits. For the reduction of adipose tissue, a permanent effect may be advantageous. Surprisingly, both apoptosis and necrosis may produce long-term or even permanent results in adipose tissues, since fat cells regenerate differently than muscle cells. 
     While the exemplary embodiments have been described in some detail for clarity of understanding and by way of example, a number of modifications, changes, and adaptations may be implemented and/or will be obvious to those as skilled in the art. Hence, the scope of the present invention is limited solely by the claims as follows.